25mm vs 32mm tires, unscientific testing
06-03-20, 08:10 PM
#51
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It allows you to put in the wheel size and tire width as well.
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06-03-20, 08:35 PM
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This is correct. The Strava estimated power is meaningless, being based solely on speed, as you said earlier. He could have had a brake dragging on one test, Strava would say power was the same. That said, a quick trip over to BRR says that at the same comfort level, i.e. 4.5mm drop for both tires, RR is .1 w less for the 32 per tire. At recommended pressures, 15% drop, it's .7w higher for the 32, per tire. There's also the aero component. If someone wants to do the calculation we could see the theoretical time difference. The OP doesn't mention tire pressures, a significant omission. And all that said, these are pretty neat tires. I haven't gotten cut #1 yet on our tandem.
Someone mentioned traffic, which sometimes can be an issue, but when you run the loop clockwise, you can generally hold speed without traffic interfering as you have the right of way the entire way around the loop, save for one right hand turn at a four way stop. I was lucky enough on both rides to be able to not encounter any traffic at that intersection and was able to take that turn as a high speed sweeper.
06-03-20, 09:26 PM
#53
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Yup, same kit, shoes and helmet, same position, in the drops the entire time (I know that arms horizontal on the hoods is technically more aero, but in the drops is easier to hold for two hours). I felt wind conditions were similar, which is to say a low wind day, this loop is notorious for wind, there's a particular spot where an all out effort can net me 25mph or 18mph, depending on the wind. But I do think conditions were fairly similar both days.
I ran 80/85 on the 32s and 90/95 on the 25s. The surface there is as smooth as it gets around here, good for going fast, with some rolling hills. My club does a TT series there, first race is coming up on the 25th, they do a 10 mile out and back. I'm looking forward to seeing how I do over my performance last year, altho it won't be an even comparison since last year I was on an aero bike with clip on aero bars and 88mm wheels, this year I'll be running Merckx class with my Defy and no aero equipment (same setup I used for these rides).
Someone mentioned traffic, which sometimes can be an issue, but when you run the loop clockwise, you can generally hold speed without traffic interfering as you have the right of way the entire way around the loop, save for one right hand turn at a four way stop. I was lucky enough on both rides to be able to not encounter any traffic at that intersection and was able to take that turn as a high speed sweeper.
I ran 80/85 on the 32s and 90/95 on the 25s. The surface there is as smooth as it gets around here, good for going fast, with some rolling hills. My club does a TT series there, first race is coming up on the 25th, they do a 10 mile out and back. I'm looking forward to seeing how I do over my performance last year, altho it won't be an even comparison since last year I was on an aero bike with clip on aero bars and 88mm wheels, this year I'll be running Merckx class with my Defy and no aero equipment (same setup I used for these rides).
Someone mentioned traffic, which sometimes can be an issue, but when you run the loop clockwise, you can generally hold speed without traffic interfering as you have the right of way the entire way around the loop, save for one right hand turn at a four way stop. I was lucky enough on both rides to be able to not encounter any traffic at that intersection and was able to take that turn as a high speed sweeper.
IME narrower tires at higher pressure are faster on smooth pavement simply because there's less elastic hysteresis. Might as well run Merckx if one doesn't have a full TT bike.
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06-03-20, 10:22 PM
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06-03-20, 10:56 PM
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Pretty cool experiment. I’m impressed you were able to repeat the key variables so accurately. Thanks for sharing!
I have to ask. Was this ride capped off with beer?
I have to ask. Was this ride capped off with beer?
06-03-20, 11:16 PM
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No. Again, speed and cadence being the same doesn't mean that effort is the same. If you're in your 50/17 combo, spinning at 90 rpm, you're going to be going the same speed regardless of whether you're on billiard table flat road or if you're going up a 3% grade. The efforts will be wildly different, but the speed will still be the same for the same gearing and the same cadence. So the fact that the speed and cadence is similar strongly suggests that the gearing is similar, but it still doesn't give us anything that we really want to know. What we want to know is whether one is faster. Faster = less resistance, be it rolling resistance, drag or suspension losses. There could easily be a 20w difference between these efforts and a power meter would show that.
You guys know I don't use Strava so I haven't looked into this personally, but I've been told several times that while their power estimates aren't reliable at any point in time, they're generally pretty close over longer time periods like a couple hours.
06-03-20, 11:24 PM
#58
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The issue is that Strava's power estimate has no idea how to account for rolling and aerodynamic performance of tire changes. If you ride the same route at the same pace on two different tires, it'll calculate exactly the same power estimates because it has no idea that anything changed. Even if you adjust your bike weight in the settings to account for the tire change, that'll do almost nothing, because the weight difference between two road tires represents an incredibly small portion of the resistances that a bike+rider deals with.
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06-03-20, 11:50 PM
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I've no idea if it's significant, but this is two rides over the exact same route in virtually identical conditions, with no changes to setup or equipment.
I was testing riding strictly by RPE, and the side on the right felt easier, but I actually worked harder to go slower.
The differences between the two rides are similar to what the OP had shown in his two rides-- which is enough for me to agree that without power, we can
never know if the two efforts came down to tires-- just as I can't say for certain what accounted for my 69 seconds.
I was testing riding strictly by RPE, and the side on the right felt easier, but I actually worked harder to go slower.
The differences between the two rides are similar to what the OP had shown in his two rides-- which is enough for me to agree that without power, we can
never know if the two efforts came down to tires-- just as I can't say for certain what accounted for my 69 seconds.
1w wouldn't explain 69 seconds. The faster ride was 6*F warmer, which means the air was less dense and put up somewhat less resistance at a given speed. I don't know how to calculate the effect of that.
06-04-20, 12:48 AM
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I don't own a power meter. I do understand the significance. What I don't buy is your implicit argument that the power outputs differ enough from each other and the estimates to exactly compensate for the differences in the tires so that, by magical coincidence, everything that is measured is nearly the same.
By far the simplest explanation for why all the reported numbers are the same is that the width of the tires doesn't make a significant difference.
By far the simplest explanation for why all the reported numbers are the same is that the width of the tires doesn't make a significant difference.
Look, OP did a great job, but to deny that a powermeter would have made this a lot more insightful is just, at this point, ego. You just don't want to admit to it anymore at this stage because you are too invested in standing your ground.
06-04-20, 03:34 AM
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Quite simply, there is enough variability in power on a ride to ride basis that you cant just assume it is the same merely because the speed is the same. On my local loop. I can have 20-30W difference in power for the ride and still have the same average speed.
We are trying to measure relative rolling resistance between 2 tires - in a scientific test, ignoring the effect of power on that calculation is just silly. Without that, the only thing we know is that it is possible to ride these 2 tires at speeds that are close enough, but we dont know the difference in power required to achieve these results. So you are not controlling atleast one of the key variables, thereby making this decidedly unscientific.
And to be clear, that last sentence is not a dig. There is a lot of value in field tests, and while this may not have been a precise scientific test, it does provide useful and practical data. I am guessing the OP is fairly experienced cyclist and so his power efforts for the two loops would be fairly close. So the main point that he was trying to make - that a 25c vs a 32c are not that far apart - is supported by this experiment. I think we can also safely (and non-scientifically) assume that the difference in wattage wouldnt be huge.
(Yes, you can improve the confidence/accuracy of the test results by doing this a few more time, but given that the OP was just doing some field testing and has been kind enough to share that info here, it would be churlish to complain about that).
For my part, I did find the test useful - thanks for taking the time to do it and share it here.
Last edited by guadzilla; 06-04-20 at 07:10 AM.
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06-04-20, 04:14 AM
#62
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keep your expeditious, sleek, fatty tires...i'll stick with my lean and hungry, skinny, uncomfy, placebo, cassius '23's. please wave as you blow past...
06-04-20, 05:38 AM
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50 x 17 & 25mm tires x 90rpm = 20.7mph
50 x 17 & 32mm tires x 90rpm = 21.3mph
So, according to that the 32mm tires will be faster than the 25mm tires. Power used is the unknown but I too have used 32mm tires instead of 25mm and didn't notice much difference in perceived energy use or average spped. the comfort level with the 32mm tires was much greater though.
Cheers
06-04-20, 06:39 AM
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But Strava knows whether you're riding on the flat or up (or down) a hill because they have a digital elevation model. And they take terrain into account when they estimate power. And anyway wasn't this the same route, several laps around the same course? Because that would rule out differences in elevation and surface.
You guys know I don't use Strava so I haven't looked into this personally, but I've been told several times that while their power estimates aren't reliable at any point in time, they're generally pretty close over longer time periods like a couple hours.
You guys know I don't use Strava so I haven't looked into this personally, but I've been told several times that while their power estimates aren't reliable at any point in time, they're generally pretty close over longer time periods like a couple hours.
Ever thought that he was looking at his (average) speed and might have been pushing more to keep it where (subconsciously) intended? Ever gone up a false flat? I have one near me that gets me every time. It looks flat and I always find myself pushing more. Why? Because I don't switch gear and want to pedal at the same cadence. Same gear, same cadence, higher incline = more watts needed. The cadence was indeed very similar across his rides -> for all we know he had to push more to achieve it with the fatter tyres.
Look, OP did a great job, but to deny that a powermeter would have made this a lot more insightful is just, at this point, ego. You just don't want to admit to it anymore at this stage because you are too invested in standing your ground.
Look, OP did a great job, but to deny that a powermeter would have made this a lot more insightful is just, at this point, ego. You just don't want to admit to it anymore at this stage because you are too invested in standing your ground.
That's a curious point, I did the 32mm ride first, so maybe because I was expecting the 25mm tires to be faster I pushed a lil harder to maker sure I went faster, subconsciously of course. In my head, I was trying to keep the effort even, which is to say, as hard as I could go for six laps, felt pretty well spent at the end of both rides.
Last edited by Rides4Beer; 06-04-20 at 11:45 AM.
06-04-20, 06:40 AM
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https://www.bikecalc.com/speed_at_cadence
It allows you to put in the wheel size and tire width as well.
It allows you to put in the wheel size and tire width as well.
06-04-20, 07:10 AM
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That's a curious point, I did the 32mm ride first, so maybe because I was expecting the 25mm tires to be faster I pushed a lil harder to maker sure I went faster, subconsciously of course. In my head, I was trying to keep the effort even, which is to say, as hard as I could go for six laps, felt pretty well spent at the end of both rides.
GCN did this in their video comparing the new Shimano 105 to Dura Ace... but they did the test on a trainer so I suppose that's not relevant here. 
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06-04-20, 07:36 AM
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What's funny is that you probably had a bike that could ride on gravel, but you didn't know it because "gravel bikes" hadn't been invented yet, amiright?
I was born in AZ but actually grew up in Massachusetts in one of these smaller bedroom communities. My street was narrow enough that it didn't have lines marking lanes. They painted lines on it once but it just wasn't wide enough so the next time they "re-paved" it the lines were gone and never replaced. Repaving consisted of spraying down some oil on the street and then covering it with sand and very fine gravel. Whatever stuck was the new road surface.
The problem with the road surfaces where I'm at now is just that I live at the edge of civilization here in the valley. I can ride just 3-5 miles in one direction and be in the middle of town with decent roads and whatnot, or 3-5 miles in the other direction and be in the middle of the desert. Some of the little side roads like the one leading from the back of my housing community out to a more main road haven't been repaved in many years and are just absolutely horrible for a bike. If all the roads were like that I'd just stick to mountain biking, because it's annoying as hell when my routes take me on roads like this. I could get where I'm going and avoid some of these roads but the alternative is some 4- or 5-lane north/south or east/west artery road with craploads of cars doing 60mph in a 45mph zone and all I have is a little 18-20" margin to the right of the white line. So my main routes are mostly crafted with getting the mileage I want without getting annihilated on some of the main drags, though to get longer mileage eventually I've got to do some time on some of the larger roads too. For me, riding with the fatter tires (fat only compared to traditional road cycling) is a no-brainer. The 32mm tires I've been riding have been way nicer on these crappy stretches of road than 25mm or even 28mm were. I've been thinking for a while that I wanted to try out the 35mm version of the Rene Herse tires in the rear on my bike, and it arrives on Friday. First thing I do once I mount it will be to ride out the back of my housing area onto this awful stretch of road and test it out. I'll probably start with a pressure of 5psi less than I've been using in the 32mm version and see how it goes.
I was born in AZ but actually grew up in Massachusetts in one of these smaller bedroom communities. My street was narrow enough that it didn't have lines marking lanes. They painted lines on it once but it just wasn't wide enough so the next time they "re-paved" it the lines were gone and never replaced. Repaving consisted of spraying down some oil on the street and then covering it with sand and very fine gravel. Whatever stuck was the new road surface.
The problem with the road surfaces where I'm at now is just that I live at the edge of civilization here in the valley. I can ride just 3-5 miles in one direction and be in the middle of town with decent roads and whatnot, or 3-5 miles in the other direction and be in the middle of the desert. Some of the little side roads like the one leading from the back of my housing community out to a more main road haven't been repaved in many years and are just absolutely horrible for a bike. If all the roads were like that I'd just stick to mountain biking, because it's annoying as hell when my routes take me on roads like this. I could get where I'm going and avoid some of these roads but the alternative is some 4- or 5-lane north/south or east/west artery road with craploads of cars doing 60mph in a 45mph zone and all I have is a little 18-20" margin to the right of the white line. So my main routes are mostly crafted with getting the mileage I want without getting annihilated on some of the main drags, though to get longer mileage eventually I've got to do some time on some of the larger roads too. For me, riding with the fatter tires (fat only compared to traditional road cycling) is a no-brainer. The 32mm tires I've been riding have been way nicer on these crappy stretches of road than 25mm or even 28mm were. I've been thinking for a while that I wanted to try out the 35mm version of the Rene Herse tires in the rear on my bike, and it arrives on Friday. First thing I do once I mount it will be to ride out the back of my housing area onto this awful stretch of road and test it out. I'll probably start with a pressure of 5psi less than I've been using in the 32mm version and see how it goes.
I agree that bad pavement can be worse to ride on than bad gravel. Potholes in pavement can dent a rim and buck you off the bike, you do a lot of dodging around, whereas potholes in a gravel street are much easier to deal with, you just ride through them. Gravel can be tough to handle when you're riding high pressure/low volume tires. There's a gravel road (somewhat) near me with lots of hills and blind curves with driveways, and even riding on my 35 mm tires it takes a lot of attention to stay upright and in my lane.
06-04-20, 08:25 AM
#68
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It is completely disingenuous to attribute to me something I never said or even implied, and then get whiny about me being too invested.
06-04-20, 09:30 AM
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Well, thank you at least for quoting me correctly. I stand by my original characterization. "in many ways" is the critical qualification.
06-04-20, 10:00 AM
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All this arguing and none wanting to go out and do further more controlled testing to show their results. I really don't care about the arguments one way or the other. Since I'm not competing with anyone to get to the line fist, I really only care about perceived effort. And my perceived efforts on the very smooth asphalt I ride have me feeling much better with my 25 mm tire on the back filled to max 125 psi and the front at 100 psi. I'm only 172 pounds currently.
My legs feel worse after a ride every time I try the lower pressures others tout. If I am riding a road with coarse aggregate, then I do lower the tire pressures. But it's all for perceived effort and comfort. Not that I have to be first across the line.
If I ran a much wider tire, from every thing I've read, it won't be a significant difference. 25 mm tires aren't the 18 mm tires that the articles were aimed at.
My legs feel worse after a ride every time I try the lower pressures others tout. If I am riding a road with coarse aggregate, then I do lower the tire pressures. But it's all for perceived effort and comfort. Not that I have to be first across the line.
If I ran a much wider tire, from every thing I've read, it won't be a significant difference. 25 mm tires aren't the 18 mm tires that the articles were aimed at.
06-04-20, 10:08 AM
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Ummmm ... I think there is a very knowledgeable person already posting in this thread that has done plenty of testing of this type, and has developed a very powerful analysis method to aid in the endeavor.
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06-04-20, 10:10 AM
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06-04-20, 10:12 AM
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......
Also, I am saying what the OP observed is consistent with
previously-reported, well-controlled experiments,
so taking the numbers you actually see at face value isn't quite as idiotic as some here have suggested.
previously-reported, well-controlled experiments,
so taking the numbers you actually see at face value isn't quite as idiotic as some here have suggested.
06-04-20, 10:20 AM
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