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Tire width and rolling resistance - wider not always better.
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I have learned much from the folks on ST about tire width, aero, pressures and crr... and look at this...

https://www.bicyclerollingresistance.com/...prix-5000-comparison
Last edited by: Rocket_racing: Feb 19, 19 14:49
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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I saw that earlier today. Nothing surprised me - in fact the conclusions are what I expected. I’m curious what surprised you (assuming I’m interpreting you correctly)?

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Re: Tire width and rolling resistance - wider not always better. [Bonesbrigade] [ In reply to ]
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I was not surprised. It also confirmed my views.
Last edited by: Rocket_racing: Feb 19, 19 15:12
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Re: Tire width and rolling resistance - wider not always better. [Bonesbrigade] [ In reply to ]
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I think what's new in the brr.com write-up is the notion of equalizing pressures for different widths based on casing tension/comfort rather than psi. That has been discussed extensively on ST, but hasn't really made it into the mainstream yet.

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Re: Tire width and rolling resistance - wider not always better. [jens] [ In reply to ]
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jens wrote:
I think what's new in the brr.com write-up is the notion of equalizing pressures for different widths based on casing tension/comfort rather than psi. That has been discussed extensively on ST, but hasn't really made it into the mainstream yet.

Oh right, I thought everyone knew that!? Kidding, we do live in strange world on here with so much valuable info.

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Re: Tire width and rolling resistance - wider not always better. [Bonesbrigade] [ In reply to ]
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There certinally is a lag between what is known, what the general public knows, and what we have data to show.

It is another “hockey stick” relationship with no one right answer.

It is also interesting to see dogma change. Narrow is faster. Wider is faster. Actually, the answer is in the middle, and it depends on many variables. The truth is often in between, and not a simple answer as marketing may push. Medicine is the same way.
Last edited by: Rocket_racing: Feb 19, 19 15:26
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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Confirmed my views (which I adopted from TomA) that tire construction (compound, casing, breaker, etc) is what matters, not width. This is true for surfaces that don't really deform under the rider (e.g. asphalt). Once you go off road, the story changes considerably. In that realm, wider really is faster more often than not.
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Re: Tire width and rolling resistance - wider not always better. [GreenPlease] [ In reply to ]
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Yes and no. My skinny xc bike crushes my fat bike... until it snows, or i hit sand. It is always about finding the happy medium for the situation at hand. Otherwise nino schurter would be on a fat bike. It is rarely a maximize/minimize scenario.
Last edited by: Rocket_racing: Feb 19, 19 15:31
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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Rocket_racing wrote:
I have learned much from the folks on ST about tire width, aero, pressures and crr... and look at this...

https://www.bicyclerollingresistance.com/...prix-5000-comparison

I'm skeptical of Bierman's adoption of absolute drop as "comfort." According to Silca's deflection data, the compliance provided by a given pressure depends on the shape of the irregularities that the tire is suspended against. In particular, the behavior with sharper irregularities tends to be more purely related to PSI, with tire width becoming a less significant factor. So, for most irregularities (i.e. anything that isn't a speed bump), equalizing to 4.5mm of absolute drop is likely underestimating the compliance of the wider tires relative to the skinnier ones. So it might still be true that a wider tire achieves better rolling resistance for a given ride smoothness. (It would also be interesting to characterize this across different amounts of absolute tire drop.)
In practice, where the deflections happen dynamically, this might get considerably more complicated.
Last edited by: HTupolev: Feb 19, 19 15:59
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Re: Tire width and rolling resistance - wider not always better. [HTupolev] [ In reply to ]
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I agree and disagree with you at the same time. You bring up valid points but if you look at the white paper Specialized did on their Roubaix (with the “future shock”) compliance is worth, at most, 2watts... and that’s on cobbles. So there’s a bit of a “ceiling” on what compliance can do to make you faster on the road.
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Re: Tire width and rolling resistance - wider not always better. [GreenPlease] [ In reply to ]
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GreenPlease wrote:
I agree and disagree with you at the same time. You bring up valid points but if you look at the white paper Specialized did on their Roubaix (with the “future shock”) compliance is worth, at most, 2watts... and that’s on cobbles. So there’s a bit of a “ceiling” on what compliance can do to make you faster on the road.

I'm not sure what you mean. My post wasn't addressing the amount of power saved by compliance.

As far as that goes, though, your 2W figure is definitely not generalizable to everything. Suspension effects in tires have been measured as having far greater impact than 2W even on asphalt road (look at post 4b in the Silca series I referenced in my previous post). Edit:
https://silca.cc/...stance-and-impedance
Last edited by: HTupolev: Feb 19, 19 16:20
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Re: Tire width and rolling resistance - wider not always better. [HTupolev] [ In reply to ]
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HTupolev wrote:
I'm skeptical of Bierman's adoption of absolute drop as "comfort."

Yeah, I'm having a hard time believing a 23c tire at 92psi and a 32c version of the same tire at 75 psi have the same comfort level. I'd really want to ride those back-to-back

"They're made of latex, not nitroglycerin"
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Re: Tire width and rolling resistance - wider not always better. [gary p] [ In reply to ]
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gary p wrote:
HTupolev wrote:

I'm skeptical of Bierman's adoption of absolute drop as "comfort."


Yeah, I'm having a hard time believing a 23c tire at 92psi and a 32c version of the same tire at 75 psi have the same comfort level. I'd really want to ride those back-to-back

Which has more compliance: a 23mm tire at 92psi or a 2.2" tire at 46psi?
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Re: Tire width and rolling resistance - wider not always better. [GreenPlease] [ In reply to ]
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GreenPlease wrote:
gary p wrote:
HTupolev wrote:

I'm skeptical of Bierman's adoption of absolute drop as "comfort."


Yeah, I'm having a hard time believing a 23c tire at 92psi and a 32c version of the same tire at 75 psi have the same comfort level. I'd really want to ride those back-to-back


Which has more compliance: a 23mm tire at 92psi or a 2.2" tire at 46psi?

I have no clue, I don't mountain bike. Besides, I'm not sure there's a single tire model that ranges from a 23c to a 2.2".

"They're made of latex, not nitroglycerin"
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Re: Tire width and rolling resistance - wider not always better. [gary p] [ In reply to ]
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gary p wrote:
Besides, I'm not sure there's a single tire model that ranges from a 23c to a 2.2".
Compass Rene Herse gets close. Tire construction is similar across the range, which varies from 26mm to 55mm nominal in 700c.
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Re: Tire width and rolling resistance - wider not always better. [gary p] [ In reply to ]
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gary p wrote:
GreenPlease wrote:
gary p wrote:
HTupolev wrote:

I'm skeptical of Bierman's adoption of absolute drop as "comfort."


Yeah, I'm having a hard time believing a 23c tire at 92psi and a 32c version of the same tire at 75 psi have the same comfort level. I'd really want to ride those back-to-back


Which has more compliance: a 23mm tire at 92psi or a 2.2" tire at 46psi?


I have no clue, I don't mountain bike. Besides, I'm not sure there's a single tire model that ranges from a 23c to a 2.2".

Continental used the same compound to make the Speed King 2.2" mtb tire as it did in the GP4000 SII
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Re: Tire width and rolling resistance - wider not always better. [GreenPlease] [ In reply to ]
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GreenPlease wrote:
Continental used the same compound to make the Speed King 2.2" mtb tire as it did in the GP4000 SII

They're otherwise totally different tires, though. The casing fabric is different, the tread profile is different, the GP4000 has a sub-tread protection belt.
Last edited by: HTupolev: Feb 19, 19 18:23
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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Thanks for this post and for the analysis... this is why we don't yet have 'an app' that does all this for people.. We discuss this exact topic in the marginalgainspodcast episode on asymmetry and have more to come in the next one, but you are spot on that these blanket statements, 'wider is faster', 'narrower is faster' etc, are such gross oversimplifications that they just aren't that useful for any of our purposes anymore, and this data shows how convoluted this can get when you try to look deeper!

This is why doing the testing and keeping a log can create a substantial advantage in the real world... consider that 80% of the people don't know the general rule of thumb and then maybe 5% of people are really willing to do the reading of the current data, and that less than 0.5% of people are willing to actually do the testing.. you can create some pretty asymmetric advantages for yourself if you just dig a little deeper and do some testing. This is why I still keep a full spring schedule of traveling all over Europe working with teams on this stuff over and over again... each year we know more, but if has yet to come anywhere close to 'automatic'..

My couple of thoughts to add here... using tire drop percentage was ground breaking and relevant when Berto did it originally and it has served us well for a long time, but for this purpose it is neither accurate nor really useful when comparing tires at a range of widths. There are nonlinearities at play which make this method unreliable for the purposes of Crr and it tends to under inflate larger tires from my experience.

Second, the bicycle rolling resistance site does awesome work, but doesn't have nearly enough roughness to approximate even good pavement, nor does it have the capabilities to measure impedance, much less the ability to look at impedance at a range of roughnesses. I really like what he did adding Crr at same initial drop of 4.5mm but even this isn't quite accurate from my experience and data as wider tires recruit casing adjacent to the contact patch much more readily than narrower ones, so this model also probably under inflates the larger tires by a few % though is better than the 15% drop method.

Third, much of what is generally missed in the 'wider is lower Crr' is that historically for most tires that had a range of widths for 'same model' of tire, the tread was made separate from the casing and then glued together. Much of the benefit of the wider casings was that for manufacturing purposes the constructor only has a few widths of tread, so the percentage of tread, which is a thicker, higher rolling resistance zone of the tire, tends to get smaller at higher widths as the tread remains the same.. so for Vittoria tires, the 21, 23 and 25 tires of old all used the same tread width.. so the 25 had that much more casing, similar for the Dugast and FMB so beloved by the pros. This is true with any number of brands, but will not exactly be true with the new Vittoria TLR or GP5000 as each tire is produced from it's own casing and rubber layup in it's own specific mold.. now from the data I'd imagine that the 23 and 25mm probably share the tread strip or puncture strip pieces during the layup and similarly the 28 and 32 likely share one or both of these parts as you can see the grouping in the data that they are very similar to each other but different from the other group... and of course this is before we even begin considering the differences between individual layups and the molds used to make each tire. I can tell you from experience that one of the GP4000 molds was considerably more aero than the others and another one of them was consistently lower Crr than the others and I'm sure that the same effects are at play here as well as relatively small manufacturing differences such as how much excess rubber squeezes out of the tool and pressure differentials within a given tool can have measurable effects in the finished product despite the tools all being 'the same' from a production point of view.

Finally, there are also very real aero penalties to larger tires, so the key is to be using them at the right pressures on the right surfaces, this is why we are still running 20mm tires on indoor velodromes, 21 and 23mm tires in TT's on good surfaces and 24-26 for most road racing surfaces with 27-30mm for rougher/harsher conditions and cobbles. Much of the real benefit of the wider tires on rough surfaces is that they widen the target pressure zone, sort of flattening out the hockey stick that we talk about in the podcast.. you just have a little larger margin for error, while also having a bit more safety from an impact damage perspective.. and of course that is also remembering that most of the tires we are using at the ProTour level are using the same tread strip between 27 and 30mm... so there is a bit more of a natural Crr benefit than you see with a molded tire like the GP5000

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Re: Tire width and rolling resistance - wider not always better. [HTupolev] [ In reply to ]
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HTupolev wrote:
I'm skeptical of Bierman's adoption of absolute drop as "comfort." According to Silca's deflection data, the compliance provided by a given pressure depends on the shape of the irregularities that the tire is suspended against. In particular, the behavior with sharper irregularities tends to be more purely related to PSI, with tire width becoming a less significant factor.


I'd just modify that to be smaller irregularities, not necessarily sharp ones. Small as in all the ones we care about; chipseal and pavement cracks for instance. If you hit a big pothole the smaller tire will have more cushion... until you bottom out and blow your tire and rim.

For comfort, tire pressure needs to be normalized, not casing tension or drop.
Last edited by: rruff: Feb 19, 19 19:47
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Re: Tire width and rolling resistance - wider not always better. [rruff] [ In reply to ]
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rruff wrote:
I'd just modify that to be smaller irregularities, not necessarily sharp ones. Small as in all the ones we care about; chipseal and pavement cracks for instance. If you hit a big pothole the smaller tire will have more cushion... until you bottom out and blow your tire and rim.

For comfort, tire pressure needs to be normalized, not casing tension or drop.

I used the word "sharp" because, even for the smallest irregularity category, Silca's test was trying to simulate things like pavement lips. The edge of a "big pothole" is actually a pretty small pointy thing at the tire contact.

"Small" is probably more accurate, though.
Last edited by: HTupolev: Feb 19, 19 20:17
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Re: Tire width and rolling resistance - wider not always better. [HTupolev] [ In reply to ]
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Ya, the pothole isn't a good example since they tend to have a sharp edge. The flat surface test is what BRR is trying to emulate, but I don't think that applies to road riding at all, except maybe when you land after a bunny hop. The 8cm cobble is certainly bigger than what we normally experience, too. The 8mm radius is what I think is most representative of what we see on road bikes. There are some cracks and pavement irregularities that are bigger, but not a lot.

The bottom line is that at the same pressure, all the tire sizes have about the same spring rate for road sized bumps.


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Re: Tire width and rolling resistance - wider not always better. [rruff] [ In reply to ]
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rruff wrote:
Ya, the pothole isn't a good example since they tend to have a sharp edge. The flat surface test is what BRR is trying to emulate, but I don't think that applies to road riding at all, except maybe when you land after a bunny hop. The 8cm cobble is certainly bigger than what we normally experience, too. The 8mm radius is what I think is most representative of what we see on road bikes. There are some cracks and pavement irregularities that are bigger, but not a lot.

The bottom line is that at the same pressure, all the tire sizes have about the same spring rate for road sized bumps.



Am I right in thinking that, on larger impacts, the pressure, and therefore spring rate, increases as the tire deforms over the obstruction, momentarily displacing some of the interior volume of the tire? And that the escalation slope of a larger tire would be more gradual, as the displaced volume represents a smaller proportion of the total static inflated volume?

"They're made of latex, not nitroglycerin"
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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What is kind of interesting is combining this info about rolling resistance with well known info about aero drag.

As you go from wider to narrower or narrower to wider, even if rolling resistance is essentially a wash when using appropriate tire pressures, aero drag is most definitely not a wash.

Because, all other things being equal, narrower is nearly always faster aerodynamically.

So for training or comfort or gravel, sure, there are many reasons to go wider. But if pure speed is the goal, on smooth roads, a narrower tire/rim system is nearly always faster.

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Re: Tire width and rolling resistance - wider not always better. [gary p] [ In reply to ]
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It sounds like you are making a case for the larger tire riding better, but you might be forgetting that these wheels are essentially the same diameter, so the bigger tire doesn't have significantly better "rollover".

The way I'd look at it is, pressure is the dominant factor determining the area of the contact patch. Let's say all the tires are at the same pressure. On a flat surface the bigger tire will have a shorter and wider contact patch, and the smaller tire's will be narrower and longer, but about the same area. In order to achieve this, the smaller tire will experience more vertical displacement... which means it is vertically less stiff. When you are riding on bumps rather than a flat surface, the shape and size of the *bump* has more influence over the shape of the contact patch. When they are small enough relative to the tire size, the tire size becomes irrelevant.
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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Ignoring the discussion of .crr for a moment, I found the following dimensional data on BRR.com interesting:


5000GP 28c 28.5mm wide, 26mm height
4000GPSii 28c 31mm wide, 29mm height
5000GP 32c 31.8mm wide, 30mm height

i.e., the 28c 4000GPSii is closer in size to the 32c than 28c 5000GP.

"They're made of latex, not nitroglycerin"
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Re: Tire width and rolling resistance - wider not always better. [rruff] [ In reply to ]
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rruff wrote:
It sounds like you are making a case for the larger tire riding better, but you might be forgetting that these wheels are essentially the same diameter, so the bigger tire doesn't have significantly better "rollover".

The way I'd look at it is, pressure is the dominant factor determining the area of the contact patch. Let's say all the tires are at the same pressure. On a flat surface the bigger tire will have a shorter and wider contact patch, and the smaller tire's will be narrower and longer, but about the same area. In order to achieve this, the smaller tire will experience more vertical displacement... which means it is vertically less stiff. When you are riding on bumps rather than a flat surface, the shape and size of the *bump* has more influence over the shape of the contact patch. When they are small enough relative to the tire size, the tire size becomes irrelevant.

I'm not sure it's as simple as just looking at the smallest "obstacle" range in that chart and saying tire size is irrelevant to "compliance"...if so, that would imply that tires of varying sizes would have equivalent "breakpoint" pressures for the same load, road surface, and speed.

I don't have any data on that...Josh, do you?

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Re: Tire width and rolling resistance - wider not always better. [DarkSpeedWorks] [ In reply to ]
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DarkSpeedWorks wrote:
So for training or comfort or gravel, sure, there are many reasons to go wider. But if pure speed is the goal, on smooth roads, a narrower tire/rim system is nearly always faster.

Comfort does have some impact on performance.

I've switched from 23's to 25's & it made the world of difference in terms of vibration & cornering confidence.

On a velodrome sure, but I can only think of one bit of tarmac I've raced on where I'd still pick 23's.
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Re: Tire width and rolling resistance - wider not always better. [Tom A.] [ In reply to ]
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Tom A. wrote:
I'm not sure it's as simple as just looking at the smallest "obstacle" range in that chart and saying tire size is irrelevant to "compliance"...if so, that would imply that tires of varying sizes would have equivalent "breakpoint" pressures for the same load, road surface, and speed.

Yes, it seems like that would be true if the roughness was sufficiently small. The vibration response would be close.
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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Don’t mean to hijack/derail the thread, or reply to anyone specifically, but I had a question regarding the article for anyone who might be able to answer.

All of the tire sizes are tested at four different PSI levels, and for each tire, a higher PSI produces lower rolling resistance and a larger tire had lower rolling resistance at a given pressure. What if you owned a wheelset such as the HED Jet+ where the max recommended PSI is 90? At that point are you limited by the wheel manufacturer recommendation? From other threads I’ve read, it doesn’t seem like people who own the Jet+ run near the maximum anyways. I also realize rolling resistance isn’t the end all and drag plays an important role in speed too so you wouldn’t want a huge tire that balloons off the rim.

What I’m trying to ask, in a roundabout way, is what tire size would be faster for a wider wheelset such as Jet+ where there is a limit to how much you can inflate the tires? Generally most people run either a 23mm or 25mm so what does the smaller tire give you that the larger one doesn’t and vice versa? Comfort? Am I trying to oversimplify a more complex subject? Thanks in advance.
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Re: Tire width and rolling resistance - wider not always better. [ballisticpb] [ In reply to ]
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Due to the way larger tires bulge out, a 25mm tire on a rim like that will have a massive aero penalty that offsets any minor crr benefit. Unless you're riding enve wheels, 23 or smaller is better for tt purposes
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Re: Tire width and rolling resistance - wider not always better. [imswimmer328] [ In reply to ]
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imswimmer328 wrote:
Due to the way larger tires bulge out, a 25mm tire on a rim like that will have a massive aero penalty that offsets any minor crr benefit. Unless you're riding enve wheels, 23 or smaller is better for tt purposes


I think you're dramatically overestimating the aero difference between a 23 and 25mm tire on a wide wheel. FLO studied this pretty comprehensively. Their estimation for the time difference over an Ironman distance bike leg between a 23c and 25c GP4000Sii on one of their wheels was 9.17 seconds....with the 25 being faster.

The Goldilox tire was actually the 24c GP Force, which is pretty close, dimensionally, to the new 25c GP5000.

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Last edited by: gary p: Feb 20, 19 16:55
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Re: Tire width and rolling resistance - wider not always better. [gary p] [ In reply to ]
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gary p wrote:
I think you're dramatically overestimating the aero difference between a 23 and 25mm tire on a wide wheel. FLO studied this pretty comprehensively. Their estimation for the time difference over an Ironman distance bike leg between a 23c and 25c GP4000Sii on one of their wheels was 9.17 seconds....with the 25 being faster.

The Goldilox tire was actually the 24c GP Force, which is pretty close, dimensionally, to the new 25c GP5000.

Thanks for the link. Out of curiosity though, is it a true apples to apples comparison to the Jet+? They say in the article that they “found that the Crr on the (smooth) rollers of a tire the Mavic Open Pro wheel at 120psi, is approximately equivalent to the Crr on a 21mm internal width wheel at 100psi." The Jet+ has a 21mm internal width but is recommended not to be inflated above 90psi. Would that 10psi difference make that much of a difference to change the results?
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Re: Tire width and rolling resistance - wider not always better. [gary p] [ In reply to ]
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The gp5000 is far closer to labeled size. A good thing in my books.
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Re: Tire width and rolling resistance - wider not always better. [ballisticpb] [ In reply to ]
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Fairly certain all tires were tested at the same pressure though. At reasonable pressures, the rolling resistance will be similar, resulting in a win for the 23
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Re: Tire width and rolling resistance - wider not always better. [ballisticpb] [ In reply to ]
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ballisticpb wrote:
Don’t mean to hijack/derail the thread, or reply to anyone specifically, but I had a question regarding the article for anyone who might be able to answer.

All of the tire sizes are tested at four different PSI levels, and for each tire, a higher PSI produces lower rolling resistance and a larger tire had lower rolling resistance at a given pressure. What if you owned a wheelset such as the HED Jet+ where the max recommended PSI is 90? At that point are you limited by the wheel manufacturer recommendation? From other threads I’ve read, it doesn’t seem like people who own the Jet+ run near the maximum anyways. I also realize rolling resistance isn’t the end all and drag plays an important role in speed too so you wouldn’t want a huge tire that balloons off the rim.

What I’m trying to ask, in a roundabout way, is what tire size would be faster for a wider wheelset such as Jet+ where there is a limit to how much you can inflate the tires? Generally most people run either a 23mm or 25mm so what does the smaller tire give you that the larger one doesn’t and vice versa? Comfort? Am I trying to oversimplify a more complex subject? Thanks in advance.

Th silca blog section has some great articles on the topic. Essential reading (5 part series)

In short, on a perfect surface, higher pressures give lower rolling resistance. This is the fallacy of higher pressure= faster.

But in real life data shows that even paved roads are rougher than we think, and as pressure increases, suspension or impedance losses start to dominate after a point. That vibration you feel for too high a pressure tire is slowing you down with wasted energy.

So the trick for ultimate speed is to find the happy medium pressure for the ride conditions (lower pressure more essential as the surface becomes more rough), balancing crr and impedance/suspension losses. As a rule of thumb, comfort is faster because less energy is wasted bouncing you around. You just don’t want it too low that things get sloppy, draggy.

The lighter you are, the lower that ideal pressure is. For the average road, for all but the heaviest riders on the thinnest tires, 90psi is probably as high as you need/want to go. Likley it is too high for most.

For aero gains, a rough rule of thumb is that you don’t want a tire that is wider than your rim. Ideally you want narrower. So fit the narrowest tire that can still make you comfortable without rim strikes/pinch flats, and you are probably in the ballpark for the ideal for you for max performance. Closing my eyes and speaking in generalizations, most data i have seen puts 23c above wider tires on aero rims for performance, even when a rim is optimized for the wider tire. But for a big moose of a rider, 23c may be pusing it on the comfort/pressures end. It all depends.
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Re: Tire width and rolling resistance - wider not always better. [Tom A.] [ In reply to ]
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Tom A. wrote:
rruff wrote:
It sounds like you are making a case for the larger tire riding better, but you might be forgetting that these wheels are essentially the same diameter, so the bigger tire doesn't have significantly better "rollover".

The way I'd look at it is, pressure is the dominant factor determining the area of the contact patch. Let's say all the tires are at the same pressure. On a flat surface the bigger tire will have a shorter and wider contact patch, and the smaller tire's will be narrower and longer, but about the same area. In order to achieve this, the smaller tire will experience more vertical displacement... which means it is vertically less stiff. When you are riding on bumps rather than a flat surface, the shape and size of the *bump* has more influence over the shape of the contact patch. When they are small enough relative to the tire size, the tire size becomes irrelevant.


I'm not sure it's as simple as just looking at the smallest "obstacle" range in that chart and saying tire size is irrelevant to "compliance"...if so, that would imply that tires of varying sizes would have equivalent "breakpoint" pressures for the same load, road surface, and speed.

I don't have any data on that...Josh, do you?

No, we have nothing published on this as our awesome outdoor test track was lost a few years back once they finished the road project!! What I can say from doing testing with the teams, where we are typically choosing the tire size based on road roughness and then dialing pressures from there. Even had we done this type of testing in our original data sets I don't think we would have found anything of note as we were using 10psi increments to build out the data set and when considering equivalent radial stiffness of the tires you are looking at something like 1.5-2% pressure change per mm of tire width so our test matrix was way too coarse to capture any effect that may be present here.

What I can say from really granular testing done with Bora, EF and others is that the wider tires consistently have shallower curves both before and after the breakpoint.. so they seem to be a little more forgiving to over/under pressure.. but again, that's looking at different data from different surfaces and tests and not a test designed to evaluate it specifically.

This is a great question as it really gets to the complexity of the problem and how much there is left to learn. the other side of this that is quite interesting is that all of our lab work and Jarno's testing, and every other test machine I've ever seen is using positive bumps, yet when you really get down and look at 90% of tarmac surfaces, they are relatively flat yet full of negative spaces, and the size of the aggregate used in the paving process varies greatly. We have a photo of our 'test track' from a few years back and you can see the if you lay a straight edge on it, the surface is very flat, yet if you look at any particular area you see that it has probably 15 maybe 20% negative space.. so the tires have to squirm and conform at the road level to make the contact patch necessary as the contact patch will be reduced by these porosities and needs to be made up elsewhere. I think this is another area where the larger tires do well as they have relatively easier access to additional tread surface both laterally and longitudinally, but again, we don't have solid lab surfaces to really evaluate this.

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Re: Tire width and rolling resistance - wider not always better. [joshatsilca] [ In reply to ]
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Josh, have you tried using accelerometers to derive a frequency spectrum and seen any correlation to performance? You can definitely feel higher frequencies being damped as pressure is decreased, the question is if the optimal pressure correlates to, for example, some peaks disappearing from the spectrum...
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Re: Tire width and rolling resistance - wider not always better. [marcofoils] [ In reply to ]
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I've only been aggressively riding a bike for 2 1/2 years now. Very early on I saw advantages to optimizing your body weight. Not to be a climber, but just becoming optimal.

IMHO, this is another good example. We keep having this conversation over and over, and within lower level bike racing and AG triathlon there's going to be at least a 30 lb difference from "light" to "heavier" that are still in the same competitive group.

Maybe even 40 lbs.

If we don't think that even half that probably makes a big difference here, we don't even need to be having the conversation to start with.

We talk about needing only the smoothest road or velodrome for 23's. Uhm, I ride 23's all the time just fine. Chip seal bumpy country roads. In town streets. No issues.

I think a lot of people are a bit bigger on the bike than they think they are combined with possibly having fits or setups that make bumps seem unbearable or lose more stability.

Leading to bigger tires and lower pressures.
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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Rocket_racing wrote:
The silca blog section has some great articles on the topic. Essential reading (5 part series).

Thanks for the recommendation and the rest of your detailed answer!
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Re: Tire width and rolling resistance - wider not always better. [marcofoils] [ In reply to ]
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marcofoils wrote:
Josh, have you tried using accelerometers to derive a frequency spectrum and seen any correlation to performance? You can definitely feel higher frequencies being damped as pressure is decreased, the question is if the optimal pressure correlates to, for example, some peaks disappearing from the spectrum...

I've wondered about that as well. Seems like a good approach to the problem.

I'd also mention that bench testing methods (even with a rough roller) do not include the energy lost due to damping, which will mostly be dissipated in the rider's body. That's why they never see a point where higher pressures have higher Crr.
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Re: Tire width and rolling resistance - wider not always better. [burnthesheep] [ In reply to ]
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I think 23c is too wide for a velodrome (for some). And how narrow a tire you can get away with comfort/safety increases as you get lighter. I can do 23c all day.
Last edited by: Rocket_racing: Feb 21, 19 18:48
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Re: Tire width and rolling resistance - wider not always better. [DarkSpeedWorks] [ In reply to ]
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DarkSpeedWorks wrote:
What is kind of interesting is combining this info about rolling resistance with well known info about aero drag.

As you go from wider to narrower or narrower to wider, even if rolling resistance is essentially a wash when using appropriate tire pressures, aero drag is most definitely not a wash.

Because, all other things being equal, narrower is nearly always faster aerodynamically.

So for training or comfort or gravel, sure, there are many reasons to go wider. But if pure speed is the goal, on smooth roads, a narrower tire/rim system is nearly always faster.

Are narrow rims faster now? What is a narrow aero rim and where can we buy them? Seems like they might even be lighter (hopefully).

Indoor Triathlete - I thought I was right, until I realized I was wrong.
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Re: Tire width and rolling resistance - wider not always better. [Rocket_racing] [ In reply to ]
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Rocket_racing wrote:
ballisticpb wrote:
Don’t mean to hijack/derail the thread, or reply to anyone specifically, but I had a question regarding the article for anyone who might be able to answer.

All of the tire sizes are tested at four different PSI levels, and for each tire, a higher PSI produces lower rolling resistance and a larger tire had lower rolling resistance at a given pressure. What if you owned a wheelset such as the HED Jet+ where the max recommended PSI is 90? At that point are you limited by the wheel manufacturer recommendation? From other threads I’ve read, it doesn’t seem like people who own the Jet+ run near the maximum anyways. I also realize rolling resistance isn’t the end all and drag plays an important role in speed too so you wouldn’t want a huge tire that balloons off the rim.

What I’m trying to ask, in a roundabout way, is what tire size would be faster for a wider wheelset such as Jet+ where there is a limit to how much you can inflate the tires? Generally most people run either a 23mm or 25mm so what does the smaller tire give you that the larger one doesn’t and vice versa? Comfort? Am I trying to oversimplify a more complex subject? Thanks in advance.


Th silca blog section has some great articles on the topic. Essential reading (5 part series)

In short, on a perfect surface, higher pressures give lower rolling resistance. This is the fallacy of higher pressure= faster.

But in real life data shows that even paved roads are rougher than we think, and as pressure increases, suspension or impedance losses start to dominate after a point. That vibration you feel for too high a pressure tire is slowing you down with wasted energy.

So the trick for ultimate speed is to find the happy medium pressure for the ride conditions (lower pressure more essential as the surface becomes more rough), balancing crr and impedance/suspension losses. As a rule of thumb, comfort is faster because less energy is wasted bouncing you around. You just don’t want it too low that things get sloppy, draggy.

The lighter you are, the lower that ideal pressure is. For the average road, for all but the heaviest riders on the thinnest tires, 90psi is probably as high as you need/want to go. Likley it is too high for most.

For aero gains, a rough rule of thumb is that you don’t want a tire that is wider than your rim. Ideally you want narrower. So fit the narrowest tire that can still make you comfortable without rim strikes/pinch flats, and you are probably in the ballpark for the ideal for you for max performance. Closing my eyes and speaking in generalizations, most data i have seen puts 23c above wider tires on aero rims for performance, even when a rim is optimized for the wider tire. But for a big moose of a rider, 23c may be pusing it on the comfort/pressures end. It all depends.

You describe suspension losses and aero losses.

As a road cyclist, I don't think that's been sorted out yet - how much credit to give to the one or the other before adding up the benefit. Having moved to an area where road roughness varies a great deal, the importance of suspension has gone up a great deal. In other words, when I'm on a rough road, I care very little about aero.

When I lived in an area where the roads were rather good with less differentiation in road surface, I wanted to maximize aero.

Given TTs and races, it's been my experience that most road surfaces are good to excellent which throws the advantage to aero over suspension (except longer distances might keep me from going overboard on aero).

Indoor Triathlete - I thought I was right, until I realized I was wrong.
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Re: Tire width and rolling resistance - wider not always better. [IT] [ In reply to ]
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Exactly. Different rider weights, different road conditions, all shift the “ideal”.

In short, lighter riders will be able to more easily find a narrower wheel/tire combo that is ideal for both aero and crr/suspension loss.

For the average rider, on the average road, at human speeds, from the data i have seen, i estimate that gains in crr are about equal aero losses. I.e. gains i estimate in aero due to a narrower tire are about offset by losses in crr, and vice versa.

Now, start pushing extremes like speeds 40km/hr plus, or cobbles, or tires far too wide for their aero rims, and things can start to really favor one over the other.

The fun if figuring out the best for your wheels/weight/road conditions.
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Re: Tire width and rolling resistance - wider not always better. [rruff] [ In reply to ]
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rruff wrote:
marcofoils wrote:
Josh, have you tried using accelerometers to derive a frequency spectrum and seen any correlation to performance? You can definitely feel higher frequencies being damped as pressure is decreased, the question is if the optimal pressure correlates to, for example, some peaks disappearing from the spectrum...


I've wondered about that as well. Seems like a good approach to the problem.

I guess no answer is also an answer. I need to finish a few other projects, then I am planning to give this a shot.
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Re: Tire width and rolling resistance - wider not always better. [gary p] [ In reply to ]
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I have issues with the wider tires fitting well on my narrower AC 420 rims. I had some GP4000 25 on there for a while which I preferred were just too tight a fit. The mechanic recommended going back to 23. So according to to this looks like the 5000 might work well.
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