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25mm vs 32mm tires, unscientific testing

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25mm vs 32mm tires, unscientific testing

Old 06-03-20, 07:54 AM
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Rides4Beer
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25mm vs 32mm tires, unscientific testing

I've been experimenting with tire widths, from 25mm to 32mm. I've found that comfort and grip with 32mm is great, and doesn't give up as much speed as you might think. Obviously you need to have room to fit 32's, something to keep in mind, at least with the GP5000s I'm running is that they are not only wider, but also significantly taller than 28's.

I recently did two rides on our local 7 mile TT loop. Six laps, going hard, averaged 22.5mph on 32mm, and 22.8mph on 25mm, both GP5000s.

Same wheels/kit/position. On my wheels the 32's measure almost 34mm, and the 25's measure right at 27mm. Wheels are 50mm deep, 19 internal, 27.5 external. So not perfect 105% with the 25's, but close. 23mm might be a hair faster, not sure I want to buy another set of tires to test tho (if someone would like to donate a set, I'd be happy to try them out lol). Over a 43 mile, almost 2 hour ride, I saved about 1 minute with the 25's. Temp/wind/effort felt similar.

Not exactly scientific, but I don't think it's as big of a deal as people make it out to be, at least for average riders. Obviously, if you're chasing seconds and podiums, then optimize everything. I'll keep the 25's on the 50mm wheels for races and TTs, and keep the 32s on the stock wheels for training rides. If your roads are bad, like some are around here, I've found that you'll actually be able to go faster with the larger tires because they're more comfortable, and you're less fatigued from not getting beat up as much. The TT loop I used is pretty smooth, so that didnt' come into play.

Not trying to convince anyone, ride what you want and works for you, just adding some info for anyone who has been hesitant to try larger tires.


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Old 06-03-20, 08:15 AM
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rubiksoval
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Without power, it's difficult to tell what actually happened.
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Old 06-03-20, 08:21 AM
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Originally Posted by rubiksoval View Post
Without power, it's difficult to tell what actually happened.
Upper left. Yup, it is estimated, but the important thing is the number is, within experimental error, the same in both cases.

It comes pretty close to an ideal experiment in many ways. Presumably 10 repeats of each might give more robust statistics, but the basic gist of this is there.

I wouldn't call it "unscientific."

It corroborates what Jan Heine reported.
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Old 06-03-20, 08:25 AM
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Originally Posted by rubiksoval View Post
Without power, it's difficult to tell what actually happened.
True, would be nice to see it with precise power instead of the estimate. Skinnier tires are def faster, I've just always wondered how much faster in real world scenarios.
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Old 06-03-20, 08:26 AM
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Kudos for your work.

Yet.. you introduced the human element into the testing.. your own physical metric. I do tire testing also that confirms your conclusions... done
in 'roll out mode'-- ie: off an incline w all variables SAME.. bike, wheels, rider position et al. No wind.. no car traffic-- to get a 'good run'. My tests almost all done in tubeless mode.. finding non tubeless rubber rolls nearly the same as those designated tubeless.. for one Conti brand. Of course Mr/Mrs Conti dont recommend such.. I own that choice.

Tires are the largest variable.. by far in pedaling/rolling resistance. Even some of the priceier rubber rolls like a tank.
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Old 06-03-20, 09:06 AM
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Originally Posted by Rides4Beer View Post
I recently did two rides on our local 7 mile TT loop. Six laps, going hard, averaged 22.5mph on 32mm, and 22.8mph on 25mm, both GP5000s.
84 miles of riding. Well, thanks for that. I agree that it's hard to know exactly what's happening, but it's nice that you're trying.

Originally Posted by wgscott View Post
Upper left. Yup, it is estimated, but the important thing is the number is, within experimental error, the same in both cases.
The power estimates come from the speed. The estimates are close to the same because the time was close to the same.

It comes pretty close to an ideal experiment in many ways. Presumably 10 repeats of each might give more robust statistics
I'm not sure it's "pretty close to an ideal experiment in many ways" at all. Nonetheless, Rides4Beer did 84 miles of riding. You're thinking 840 miles of riding will turn an unscientific comparison into a robust experiment? Hmmm. I'm not sure about that, either.
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Old 06-03-20, 09:25 AM
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Originally Posted by wgscott View Post
Upper left. Yup, it is estimated, but the important thing is the number is, within experimental error, the same in both cases.

It comes pretty close to an ideal experiment in many ways. Presumably 10 repeats of each might give more robust statistics, but the basic gist of this is there.

I wouldn't call it "unscientific."

It corroborates what Jan Heine reported.
It's estimated. So like I said, without power, it's difficult to tell what actually happened.
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Old 06-03-20, 09:32 AM
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Originally Posted by RChung View Post
84 miles of riding. Well, thanks for that. I agree that it's hard to know exactly what's happening, but it's nice that you're trying.
That's why I admitted that it wasn't very scientific. lol I was going to do the rides anyway, and was curious to see what difference tire size would make. There's also variables that are harder to account for, how much sleep did I get, did I eat enough, etc.

But I can def see where it makes a difference in a race scenario or solo TT, prob less so for group rides, training rides, etc. One thing that stuck out in my mind was from Hambini's test where it was almost a 30w difference in a larger tire for what amounts to a sprint scenario for me, that is huge.
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Old 06-03-20, 09:39 AM
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Originally Posted by rubiksoval View Post
Without power, it's difficult to tell what actually happened.
thats crazy..
😄
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Old 06-03-20, 09:58 AM
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Originally Posted by Rides4Beer View Post
There's also variables that are harder to account for, how much sleep did I get, did I eat enough, etc.
Thus the need for power; it eliminates those variables as it pertains to whether or not you're putting out more power to go the same speed with a particular tire.
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Old 06-03-20, 10:30 AM
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I doubt that the difference is large enough to be measured "unscientifically". I would think that the error bars (differences in rider, environmental conditions, etc.) would swamp any actual difference in performance.

The difference in the measured distance alone is about 0.5%. Then there is the error in the speed/distance measurement itself - how did you calibrate your computer (roll out method? other? there's error inherent in this measurement)? Did you recalibrate when you switched tires (different diameter/pressure may change the functional circumference)? Once you stack all of those errors, I doubt that the comparison would result in any definite conclusions.

Even if you did find a statistically significant difference, how would that apply to different conditions? Bumpy road vs smooth, low traffic vs high traffic (less/more stop and go), different wind angles, speeds, etc.
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Old 06-03-20, 10:37 AM
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I think the obvious takeaway from this thread is someone needs to donate a power meter to aid @Rides4Beer's testing.
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Old 06-03-20, 10:41 AM
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Originally Posted by Seattle Forrest View Post
I think the obvious takeaway from this thread is someone needs to donate a power meter to aid @Rides4Beer's testing.
But then he'd have to change his user name.
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Old 06-03-20, 10:44 AM
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Most of the roads around me have never been that great, and unfortunately some of the ones that are part of almost every route I ride haven't been maintained in years and years, and in the AZ heat that means they're crumbling. On section that's about 3/4" mile long was bad several years ago, now it's absolutely horrible, tons of cracks, tons of large aggregate showing on the surface, some cracks are 2-3" wide, most are just crumbly sections that aren't like the Grand Canyon but still in for a bumpy ride. Here's my unscientific addition to this unscientific testing thread: on my old bike, running a 28" rear tire and a 25" front tire (both Conti GP4KII tires) I had to slow down while riding along much of that section of road, but with my 32" tires on my new bike I can ride through there at full speed. Yeah it's still jarring, but I can do it. On the old bike with the narrower tires the bumpiness and jarring were just too much.

My riding is a few shorter sections of new pavement, lots of average pavement (not super smooth, not all broken up and crack-ridden everywhere), and some sections of truly awful pavement. The experience is way better on the 32" tires than it ever was on the old bike with the narrower tires, and on that old bike just going to the 28" rear (fork was too narrow for 28" up front) was already a huge improvement. I just ordered a 35" Rene Herse Bon Jon Pass tire to put in on my rear wheel to replace the 32" Stampede Pass tire that's now finally close to worn out. I'll stay with 32" up front because the front is running at lower pressure already and is fine and a better match for the width of my rims, but the rear is getting another bump up in size and I can hardly wait to see what it's like.
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Old 06-03-20, 11:01 AM
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Also, to get a good idea of what is what you need to do these a rides using the same tire at various tire pressures. 10 psi apart probably will do from min to max. As well, it'd be nice to know the surface you ride on.

I frequently ride a MUP that is paved with asphalt that uses a very fine aggregate. It's very smooth except for parts that have a tree root expanding under it or areas that crack from movement of the road bed. If you are riding an asphalt or chip seal road with large aggregate, that'll be nice to know as your results may not extrapolate directly to what I am experiencing.
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Old 06-03-20, 11:31 AM
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Originally Posted by Rides4Beer View Post
True, would be nice to see it with precise power instead of the estimate. Skinnier tires are def faster, I've just always wondered how much faster in real world scenarios.
There might be a bit more ability to analyze if you had the metrics for each of the laps for both setups, potentially then also throwing away each setup's best and worst lap times.

Of course other variable is tire pressure and how optimized each was chosen for the surface and your weight, etc
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Old 06-03-20, 02:57 PM
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Originally Posted by SethAZ View Post
Most of the roads around me have never been that great, and unfortunately some of the ones that are part of almost every route I ride haven't been maintained in years and years, and in the AZ heat that means they're crumbling.
When I was a young lad, the main streets in town were paved, but the side streets were gravel. The U.S. and state highways were paved, but most of the county routes, National Forest roads and the roads on the Bad River Reservation were gravel. Every summer, in town they would spray the gravel streets with waste oil (petroleum, not cooking oil) to keep the dust down. I bet they don't do that anymore.

In the winter, the state road (along the south shore of Lake Superior) was often closed (snow), so to get to our friend's house in Cornucopia, we would have to drive through the National Forest (inland, less snow/drifting, easier to keep plowed).

After the McDonald's in town closed, the closest McDonald's to us was in Superior, 65+ miles away, a 1.5 hour drive in good (summer) weather. (We didn't go during the winter.)

It's a different world now.
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Old 06-03-20, 03:57 PM
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Originally Posted by rubiksoval View Post
It's estimated. So like I said, without power, it's difficult to tell what actually happened.
Might be difficult, but hardly impossible.

Power = work/time

The time is nearly identical in both cases, so let's focus on work. Much of the work will be in the form of hill climbing W= mgh. The amount of climbing (h) is almost identical. All of the work is integrated force over distance, and the distances are almost identical. The estimated values for power are coming out as almost identical, even if their numerical values are systematically skewed by 20%. So the differences in frictional forces, wind drag, etc, have to be quite small. Again, this is consistent with Jan Heine's previous experimental results.

An independent control is to look at the cadence in both cases. It, too, is essentially the same.

It is a completely reasonable first experiment.

My point isn't that it is ready for publication. I am just saying the OP is being too modest suggesting it is unscientific.

I have to admit I don't understand why he concludes narrow tires are definitely faster.

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Old 06-03-20, 04:29 PM
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I think it's great that you did this. Thanks for taking the time, expense and then sharing your results.
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Old 06-03-20, 04:32 PM
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Originally Posted by rubiksoval View Post
And to wgscott
OK, let's try it this way:

What evidence do you have that the power for the first ride differs significantly from that of the second ride?

Everything else is the same, so why would you expect (a) the power to be different and (b) the estimates all conspire to hide this?
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Old 06-03-20, 04:34 PM
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Originally Posted by wgscott View Post
OK, let's try it this way:

What evidence do you have that the power for the first ride differs significantly from that of the second ride?

Everything else is the same, so why would you expect (a) the power to be different and (b) the estimates all conspire to hide this?
You don't have the slightest semblance of any idea of what else was the same.

You don't know about wind, tire pressure and rolling resistance, temperature and humidity, position, clothing, etc.

Most importantly, you don't know about his power output. I can ride the same course and have similar power outputs and have vastly different speeds if I crush the uphills and cruise the downhills. Conversely, I can have very different power outputs and have very similar speeds if I put out effort in different ways.

Again, power.

If you don't understand what a power meter is and how it's used, there's really no need to continue derailing the thread.
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Old 06-03-20, 04:40 PM
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Yet all of those things magically conspired to move him the same distance in the same period of time, despite tire differences.

I'm not derailing the thread. I am disagreeing with your dismissal of his results by invoking unmeasured differences that you yourself state are unknowns. His results are better and more robust than what you claim.
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Old 06-03-20, 04:43 PM
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Originally Posted by wgscott View Post
Yet all of those things magically conspired to move him the same distance in the same period of time, despite tire differences.

I'm not derailing the thread. I am disagreeing with your dismissal of his results by invoking unmeasured differences that you yourself state are unknowns. His results are better and more robust than what you claim.
No they're not.

Those tires could be 30 watts slower and he simply put out 30 watts more to make up for the difference. You have no idea. Neither does he.

"Unmeasured differences that are unknown." Yeah. That's the point.

Again, if you don't understand what a power meter does, this is a pointless tangent.
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Old 06-03-20, 04:43 PM
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Originally Posted by rubiksoval View Post
No they're not.
I have no doubt you are a better cyclist than I am. I am not as sure you are a better scientist.
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Old 06-03-20, 04:47 PM
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Originally Posted by wgscott View Post
I have no doubt you are a better cyclist than I am. I am not as sure you are a better scientist.
So is that a snide remark to detract from the apparent issue of you never using a power meter and failing to understand its significance in a matter like this?
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