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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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.

Yes, it seems like that would be true if the roughness was sufficiently small. The vibration response would be close.

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.

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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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?

The gp5000 is far closer to labeled size. A good thing in my books.

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

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.

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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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 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.

Thanks for the recommendation and the rest of your detailed answer!

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.

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.

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).

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

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).

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Indoor Triathlete - I thought I was right, until I realized I was wrong.

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.

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.

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.