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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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