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Tire Width Myths

Old 04-12-21, 12:48 PM
  #51  
gofish44
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And for a deep dive. . .

Visit bicyclerollingresistance.com for a deep dive into tires. I particularly appreciate that his testing of road tires is done at 29 kpm, a speed that most of us can achieve, some of the time. Many other sources test tires at 45 kpm which is relevant for pros and those Cat 1 and 2 amateurs out there, but not for most of us. The bottom line on those GP5000's? . . . They are probably the best all rounders going for most of us, most of the time.

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Old 04-12-21, 01:29 PM
  #52  
Bill in VA
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Originally Posted by Pratt View Post
Not that will in any way settle this debate, in fact, probably the reverse, but you can find out if more or less pressure is faster in your tires by "brushing" with a friend.
Start out coasting eat the same speed, next to each other on a nice down hill. Then repeat with more or less pressure in your tires, and no change to your friend's. Similarly, keep the weights, positions, etc. unchanged from trial to trial. You should be able to see the effect easily. You can call sprinting back up the hill for another run "intervals."
This is wisdom!

Actually, I bought my first Compass (now Rene Herse) 28mm tires for two features, lightweight and had tan sidewalls in a world of black sidewalls, in hopes of duplicating (or what I remembered) from an old set of Clement (original) hand made cotton clinchers that were truly great. I had been using Continental GP4000SII tires in 28mm. I had not read any of the Rene Herse or other testing articles.

At the first ride of our small vacation group, I received comments on the 'old school' tires. However, as we rode, I found that in a coasting downhill, I would always end up passing the other riders and coast longer on the flats. So we did some deliberate comparisons, with similar results. Another rider with a similar sized bike, who was running 25mm tires, switched bike with me and we still had the same outcomes. While I like to think I am good at adjusting cup and cone bearings for smooth performance, I fully doubt that was an issue. We later in the week did the same, admittedly non-scientific, tests using my alternate wheelset that had the Continentals 28s, with similar results, but not as much difference.

I use the Rene Herse for most of my riding, but if it is damp or misty, I use the Continentals as they feel more grippy in corners in damp or wet.

When we got home, that rider bought a set of 25mm Continentals GP4000SII since they were more readily available locally and were in black.

Now there are more tan-walled tires, and more supple casings, but my experiences with Rene Herse keep me going back. I feel the same about the Continentals, and will probably replace the 28mm GP4000SII with 32mm GP5000s.

As always, my opinions and non-scientific observations. so in this case, truly a YMMV.
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Old 04-12-21, 01:58 PM
  #53  
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Originally Posted by gofish44 View Post
Visit bicyclerollingresistance.com for a deep dive into tires.
While that site has lots of data, you need to take it with a big grain of salt. They are all drum tests and it is well-known that drum and road while related are not perfectly correlated. Roads are flat, drums are not. Road surfaces are also different than drum surfaces. Bumpy roads lead to vibration which leads to less efficient cyclist energy transfer and there is no cyclist in the equation at that website.

For example here is their comparison of the GP5000 at all different tire sizes. Their conclusion is there is not much overall difference if you use recommended pressures.

But, in actual on-road studies the wider tires do better. For example, FLO Cycling has the below graph buried in one of their blog posts.



The 32mm tires are clear winners in a test on a road with a bike. Read the post for more details on the test. Note that FLO is a wheel company, not a tire company, they have no skin in this game.

What I would like to see is this kind of data extended out to 35 and 40mm tires, e.g. for the GK slick series.
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Old 04-12-21, 02:01 PM
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Continental Ultra Sport II/III

Originally Posted by wphamilton View Post
I clued into this around 10 or 12 years ago. While it was absolutely true that my wider tires were slower, at any pressure, it was because I'd buy the most inexpensive durable wide tires that I could find. By wide I mean 32's. Even when I wanted more supple 32's they couldn't be found, unless you were willing to pay 5-10 times the price for them.

I came to realize that if width and pressure make a difference - and I still don't doubt that they do- it's much less difference than the makeup up tire makes.
@wphamilton;22005925, Strongly suggest you give these a try for a reasonably priced wide and supple tire. I ride these in 32mm and love the ride! Probably have 85-90% of the benefits of their premium tires (GP400, GP500, etc.) for less than half the price, try $20.00! Pretty low rolling resistance to boot, if that concerns you.
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Old 04-12-21, 02:14 PM
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Originally Posted by cannonride15 View Post
@wphamiltonStrongly suggest you give these a try for a reasonably priced wide and supple tire. I ride these in 32mm and love the ride! .
I've got nice 28's all around - we've got more choices nowadays. Appreciate the consideration though. Most of my best cycling deals came from someone giving a heads up on Bike Forums.

*ps Ultra Sports are on my best bike now, I really like them.

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Old 04-12-21, 03:16 PM
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Originally Posted by scottfsmith View Post

But, in actual on-road studies the wider tires do better. For example, FLO Cycling has the below graph buried in one of their blog posts.



The 32mm tires are clear winners in a test on a road with a bike. Read the post for more details on the test. Note that FLO is a wheel company, not a tire company, they have no skin in this game.
.
Another real interesting "real world" test. So they found optimal rolling resistance in the real world to be 95psi for 32mm GP5Ks, huh?
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Old 04-12-21, 03:22 PM
  #57  
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Originally Posted by Sy Reene View Post
Another real interesting "real world" test. So they found optimal rolling resistance in the real world to be 95psi for 32mm GP5Ks, huh?
What about it? Without being familiar with the road surface or knowing the rider's weight, it could be just about anything.
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Old 04-12-21, 03:23 PM
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How to get past 100 replies

Let's mix in some helmet safety data, some odd Grant Petersen views, electronic shifting opinions, and we'll crash the server.
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Old 04-12-21, 03:28 PM
  #59  
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Originally Posted by walnutz View Post
Everything ok over there?
It was until I hit that hill.

What tire do you recommend?
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Old 04-12-21, 03:32 PM
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Originally Posted by HTupolev View Post
What about it? Without being familiar with the road surface or knowing the rider's weight, it could be just about anything.
Exactly. It's fairly meaningless. Just didn't want anyone getting the idea that 95psi is a good starting point for their 32mm tires IRL. I'm going to go out on a limb thinking that Flo conduct their testing with a <250+ lb rider.

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Old 04-12-21, 03:47 PM
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Originally Posted by Sy Reene View Post
So they found optimal rolling resistance in the real world to be 95psi for 32mm GP5Ks, huh?
I would interpret it that they found there is relatively little difference from 65 to 95psi: the curve is pretty flat there. They didn't talk about it much but if you are too close to the 95psi, when you hit a rougher patch of pavement the resistance curve will head up sharply. So unless you are riding on great asphalt all day you need to be more on the 65 side to not greatly slow down on the rougher stretches.. pay a very small penalty on the good stuff and win big time on the rougher stuff. Some of their other blog posts go into this. All in all a good read.
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Old 04-12-21, 05:32 PM
  #62  
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Originally Posted by scottfsmith View Post
While that site has lots of data, you need to take it with a big grain of salt. They are all drum tests and it is well-known that drum and road while related are not perfectly correlated. Roads are flat, drums are not.
Whitt & Wilson give a couple of formulas to find the equivalent drag on drums of different diameters. Both bicyclerollingresistance.com and Tom Anhalt's tests make this adjustment to convert from drums to "flat" roads. In addition, below the impedance breakpoint, the correlation of real road tests and (adjusted for drum diameter using the Whitt & Wilson equation) drum tests are quite high. For two tires A and B, if Crr(A) > Crr(B) on drums then *almost always* Crr(A) > Crr(B) on the road (below the impedance breakpoint). The only times I've seen the ordering switch is when the tires were very close to begin with. That's why as long as you stay below the impedance breakpoint, we still do roller testing. On road field testing is much more time-consuming.

That said, we likely would not have observed the impedance breakpoint without careful field testing, so it's good to be able to do them (even thought they're time-consuming and kind of a pain in the butt).
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Old 04-12-21, 06:00 PM
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Originally Posted by RChung View Post
Whitt & Wilson give a couple of formulas to find the equivalent drag on drums of different diameters. Both bicyclerollingresistance.com and Tom Anhalt's tests make this adjustment to convert from drums to "flat" roads. In addition, below the impedance breakpoint, the correlation of real road tests and (adjusted for drum diameter using the Whitt & Wilson equation) drum tests are quite high. For two tires A and B, if Crr(A) > Crr(B) on drums then *almost always* Crr(A) > Crr(B) on the road (below the impedance breakpoint). The only times I've seen the ordering switch is when the tires were very close to begin with. That's why as long as you stay below the impedance breakpoint, we still do roller testing. On road field testing is much more time-consuming.

That said, we likely would not have observed the impedance breakpoint without careful field testing, so it's good to be able to do them (even thought they're time-consuming and kind of a pain in the butt).
What's your take on the Flo testing, that evidently puts 2 disparate tire widths (25 and 32mm) both with optimal rolling resistance at about the 95psi mark?
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Old 04-12-21, 06:25 PM
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Thanks for the clarification RChung.

Originally Posted by RChung View Post
For two tires A and B, if Crr(A) > Crr(B) on drums then *almost always* Crr(A) > Crr(B) on the road (below the impedance breakpoint).
Yes, and this also holds for the two sets of data I referenced. But, at recommended pressures the rollingresistance.com site has the 32c tires as 7% worse than the 25c (11.4 vs 10.7 watts) whereas eyeballing the FLO data it looks like it is ~7% in the opposite direction so a 14% discrepancy between the two data sets (note the recommended pressures from the rolling resistance site are 100psi for the 25s which in fact is just into the impedance breakpoint, if we did 95psi instead it would be before it; it is 75psi for the 32c). So, even below the breakpoint there is a discrepancy. There still are impedance effects below the breakpoint, that is just the point where impedance dominates. So maybe that is why the drum and road data are not agreeing here.
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Old 04-12-21, 06:54 PM
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Originally Posted by RChung View Post
That said, we likely would not have observed the impedance breakpoint without careful field testing, so it's good to be able to do them (even thought they're time-consuming and kind of a pain in the butt).
I appreciate field tests are difficult and time consuming, but enough is enough. We’re well past the preliminary quick and dirty stage for these tests, and it’s time we start including some estimate of error in the results. For example, does the data from Flo represent an average over a series of runs, in which case seeing the spread would tell us a lot about their precision; or was there only a single run with each tire in which case I wonder how identical the position was for the two tests.

I realize these questions might be answered in the later article I couldn’t find, but the picture they paint in this one raises more questions than it answers.*

* like what were the widths as measured?

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Old 04-12-21, 07:25 PM
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Originally Posted by Sy Reene View Post
What's your take on the Flo testing, that evidently puts 2 disparate tire widths (25 and 32mm) both with optimal rolling resistance at about the 95psi mark?
I talked with Chris and Jon about their test protocols a while back but I don't know exactly what the road surface looked like -- they were using a not very trafficked dead end road near their offices that had a little slope up to a turnaround point and I got the impression that the surface was not silky smooth because it led up to some industrial site. They're using the Aerolab Tech sensor now and although I haven't seen the sensor itself yet, I've been told that the data quality others have been getting out of it is good. I'll have to reserve judgement until I see the data myself but Chris and Jon sell wheels, not tires, so the rolling resistance component was sort of a side issue, not their main goal. They're trying to figure out how to design a wheel that will go with a fast tire so they want to know what a fast tire is. This is a long way of saying that until I see the data (or get a sensor myself) I would look at general trends but not exact differences between tires.

Originally Posted by scottfsmith View Post
So, even below the breakpoint there is a discrepancy. There still are impedance effects below the breakpoint, that is just the point where impedance dominates. So maybe that is why the drum and road data are not agreeing here.
Yes, good point. Lots of people seem to think of these effects are like a light switch that's either on or off. Currently, our working hypothesis is that they're more like sliders, and the impedance slider ramps up nonlinearly and fast, while the hysteresis slider ramps down kinda more gently. The surface will influence the rate of increase of the impedance slider, which is why we see both a V shape and asymmetric legs. But that's just our current working hypothesis.

Originally Posted by asgelle View Post
I appreciate field tests are difficult and time consuming, but enough is enough. We’re well pest the preliminary quick and dirty stage for these tests, and it’s time we start including some estimate of error in the results. For example, does the data from Flo represent an average over a series of runs, in which case seeing the spread would tell us a lot about their precision; or was there only a single run with each tire in which case I wonder how identical the position was for the two tests.
I agree, and wish they shared more detail about the tests and about the errors. I tried to give Chris and Jon a little tutorial on one of the ways I assess variablity but I'm sure Chris Morton of Aerolab Tech has ways to do that, too. (As an aside, The Thortons, and Chris Morton, and Andy Froncioni from Alphamantis, and the guys from Notio are all Canadians. What's with that?).

To be fair, doing good and careful field tests is a pain and I'm reticent to tell people (other than Jan) that they need to do more tests.
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Old 04-12-21, 09:31 PM
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Originally Posted by RChung View Post
To be fair, doing good and careful field tests is a pain and I'm reticent to tell people (other than Jan) that they need to do more tests.
I agree completely. I don't believe I'm in any position to say Flo or anyone else should do more or better tests. What I can say is that as consumers of the data, we should be more critical what data is presented and especially skeptical about drawing any conclusions from them. Using this case as an example, I'm not sure it's safe to say there's any difference between these two tires. The measurement uncertainty could quite conceivably make it so there is no statistical difference between the two data sets. Therefore, we should hesitate before drawing any conclusions from these results.
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Old 04-12-21, 11:19 PM
  #68  
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A larger contact patch will create more rolling resistance. Increasing tire pressure reduces contact patch size, decreasing pressure increases contact patch size. Tires with softer rubber have larger contact patches than tires with harder rubber. Wider tires have a wider contact patch, and therefore more rolling resistance. But there are people here who think that bigger tires have less resistance because they can absorb road irregularities, small debris, and gravel, this is opposite to reality. But then for centuries people insisted the world was flat, and sometimes killed or died to support their belief in this "fact."

At one time I was a distributor for Pirelli tires, the company had been conducting studies on new features to increase fuel efficiency through tire design, and marketing these tires to auto manufacturers in order to help them meet mandatory fuel mileage standards. Wider and softer tires must always come at the cost of increased rolling resistance.
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Old 04-12-21, 11:22 PM
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The size of the contact area does not itself change the rolling resistance. It's derivative of other factors, such as pressure in the tire and the weight on the tire, which do impact rolling resistance.
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Old 04-13-21, 05:07 AM
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Originally Posted by RChung View Post
I talked with Chris and Jon about their test protocols a while back but I don't know exactly what the road surface looked like -- they were using a not very trafficked dead end road near their offices that had a little slope up to a turnaround point and I got the impression that the surface was not silky smooth because it led up to some industrial site. They're using the Aerolab Tech sensor now and although I haven't seen the sensor itself yet, I've been told that the data quality others have been getting out of it is good. I'll have to reserve judgement until I see the data myself but Chris and Jon sell wheels, not tires, so the rolling resistance component was sort of a side issue, not their main goal. They're trying to figure out how to design a wheel that will go with a fast tire so they want to know what a fast tire is. This is a long way of saying that until I see the data (or get a sensor myself) I would look at general trends but not exact differences between tires.
.
The problem is that for the wheels they're selling, their actual product webpages recommend air pressures quite a bit lower than 95psi.
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Old 04-13-21, 05:34 AM
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Originally Posted by scottfsmith View Post
I would interpret it that they found there is relatively little difference from 65 to 95psi: the curve is pretty flat there. They didn't talk about it much but if you are too close to the 95psi, when you hit a rougher patch of pavement the resistance curve will head up sharply. So unless you are riding on great asphalt all day you need to be more on the 65 side to not greatly slow down on the rougher stretches.. pay a very small penalty on the good stuff and win big time on the rougher stuff. Some of their other blog posts go into this. All in all a good read.
It looks like they also posted a follow-up article here: https://flocycling.com/blogs/blog/fl...stance-results

This chart, taken from the above, appears at first glance to replicate the trend seen in their first article. However, the outlier is the middle-sized 28mm tire is added, where its lowest RR is record at 80psi, while the 25 and 32mm tires are still at 95psi. All in all, at a ballpark level for average road condition (whatever that is), a 95psi optimal inflation for 25mm tire, and a 80psi optimal for 28mm tire, could make sense for some (eg. myself perhaps). OTOH, the 32mm tire testing just seems off. I think around BF, most modern opinions would be advising to inflate at the approx. 65psi level. Maybe most surprising is nobody asked Flo in the article Q&As how they reconcile these findings vs. the recommended tire pressure inflation charts they publish.



Edit to add: FWIW, this is presumably the road surface they were testing on:

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Old 04-13-21, 06:18 AM
  #72  
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Originally Posted by 50PlusCycling View Post
Wider tires have a wider contact patch, and therefore more rolling resistance.
I think you need a lesson in geometry (and probably the model for rolling resistance in a bicycle tire). A wider contact patch all else being equal will produce lower rolling resistance.
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Old 04-13-21, 09:07 AM
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Originally Posted by Sy Reene View Post
It looks like they also posted a follow-up article here: https://flocycling.com/blogs/blog/fl...stance-results
Thanks Sy Reene I missed that page somehow.

Here is a graph of their data for 21mm rims that I did which like the earlier graph puts all the tires on one graph:



Indeed the 28mm is odd. The fact that both 17mm and 21mm rims had a similar curve for the 28mm tire tends to make me think this is not just noise in the data. Note that these numbers are different than the previous ones, they are all lower.

The pavement looks a lot like average pavement around here, 5-year or so years old and plenty of tar missing.
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Old 04-13-21, 09:13 AM
  #74  
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Originally Posted by scottfsmith View Post
Indeed the 28mm is odd. The fact that both 17mm and 21mm rims had a similar curve for the 28mm tire tends to make me think this is not just noise in the data.
My only takeaway from this is that since a nominal 25 and 28* mm tire show effectively identical results up to ~95 psi, their data is crap.

It also tells me that they're willing to draw conclusions from unreliable data, so their credibility has to be questioned as well.

*sorry, I meant 28 and 32.

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Old 04-13-21, 09:16 AM
  #75  
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Originally Posted by asgelle View Post
My only takeaway from this is that since a nominal 25 and 28 mm tire she effectively identical results up to ~95 psi, their data is crap.
Do you mean 28 and 32? The 25 is higher resistance uniformly.
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