Who rides 28mm + tires on tarmac?

[Mr.Gib]

Isn't that "simple vibration" actually the bicycle bouncing up and down? Albeit the amplitude is very small. At some point, whether going narrower and harder or wider and softer, there is an actual point of diminishing returns that is surface dependent. The search continues.

[Hexsense]

At first i'm not sure if zefs's comment is legit or placebo.
But when he said "Simple road vibration does not make you loose speed" then there are some wrong impression there.

Vibration/change in height, no matter how small it is, have to be absorbed somewhere. Either it's absorbed by tire deforming which lose a bit of energy or transmitted through and be absorbed by the rider (or bike, which you also wouldn't feel it).
Deforming butyl tube or thick slow tire waste more energy than latex tube and thin race cotton tires etc, but any tire and tube deformation is still way more efficient than human body. That's why pneumatic tire (for small bumps) and suspension system (for bigger ones) were invented in the first place, to reduce amount of energy wasted by moving up and down vertically on not-completely-smooth surface.

However, on very smooth tarmac (as shown in Silca test on newly built tarmac), the bump is so small that the cut off where it is slower to go for too high pressure is around 110psi. So 100psi-ish are still fast on that kind of smooth surface. And wide tire on not wide enough rim is slower aerodynamically, so he is right for that kind of smooth road. But not everywhere is a newly built tarmac.

[2old4this]

... I found 28mm tires (which measure 31mm on modern rims) to be slower in every way (uphill even more so). The only benefit was comfort and handling which is great if you are after that, but I belive most people want them to be faster too since they care about numbers/avg speed. ...

The topic starter asked about how they feel on tarmac and how aero they are.

This has been my experience as well. Especially on the climbs, I am definitely slower with wider tires with less pressure. There is no doubt, they are more comfortable to ride, especially on the gravel. But on good tarmac, 23mm tires are good (excluding potholes) and I am faster with them at 110psi+ (tubular...)

[Mr.Gib]

... I found 28mm tires (which measure 31mm on modern rims) to be slower in every way (uphill even more so). The only benefit was comfort and handling which is great if you are after that, but I belive most people want them to be faster too since they care about numbers/avg speed. ...

This has been my experience as well. Especially on the climbs, I am definitely slower with wider tires with less pressure. There is no doubt, they are more comfortable to ride, especially on the gravel. But on good tarmac, 23mm tires are good (excluding potholes) and I am faster with them at 110psi+ (tubular...)

But this is just the riders impression. Again, without data we really have no idea. I can ask a question which illustrates my point: why would the increase in rolling resistance due to wider tires at lower pressures have even more impact when climbing as opposed to level riding or descending? In fact wouldn't losses at higher speeds be greater as the soft tire must flex and unflex more rapidly thereby increasing hysteresis losses? (I am not a physisist so those that are should correct me if I have this wrong).

[cunn1n9]

... I found 28mm tires (which measure 31mm on modern rims) to be slower in every way (uphill even more so). The only benefit was comfort and handling which is great if you are after that, but I belive most people want them to be faster too since they care about numbers/avg speed. ...

This has been my experience as well. Especially on the climbs, I am definitely slower with wider tires with less pressure. There is no doubt, they are more comfortable to ride, especially on the gravel. But on good tarmac, 23mm tires are good (excluding potholes) and I am faster with them at 110psi+ (tubular...)

But this is just the riders impression. Again, without data we really have no idea. I can ask a question which illustrates my point: why would the increase in rolling resistance due to wider tires at lower pressures have even more impact when climbing as opposed to level riding or descending? In fact wouldn't losses at higher speeds be greater as the soft tire must flex and unflex more rapidly thereby increasing hysteresis losses? (I am not a physisist so those that are should correct me if I have this wrong).

I believe that RR is constant and independent of speed. If so then proportionally the impact of RR is more notiaceble at climbing speeds than 40kmh so you would feel it more. I agree that the bigger tyres do feel sluggish.


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[jlok]

They don't feel sluggish when you have the appropriate rims to support the tyres (clincher).

[zefs]

Rolling resistance increases as you go uphill and they are heavier too which would add more.

They don't feel sluggish when you have the appropriate rims to support the tyres (clincher).

You are confusing something, the optimal setup of wide tire and rim makes them faster compared to a non-optimal setup aero wise.
That doesn't mean a wide rim and tire combo is faster and more aero than a narrower one, I think that is obvious.

e.g a 25mm tire measured 28mm on 19c wheels would be faster than 28mm tire which measures 31mm on 19c wheel and makes the tire bulge outside the rim profile.

But it's not aero/weight losses only, people tend to go wider for comfort, to gain that comfort you put less air = more rolling resistance. Yes, based on tests putting about 20psi less on the wider tire will give the same air volume and not increase rolling resistance but still you are using less air total, which is slower 3w per wheel than using maximum air pressure (https://www.bicyclerollingresistance.co ... i-23-25-28)
None runs wide tires at max psi.

So if you take the rolling resistance test along with silca you get an idea of the difference, without adding aero/weight losses.
If you have an optimized wide wheel/tire combo you could run at max psi for racing and reduce it for comfort/handling for anything else.

[mpulsiv]

Real world example here. My race bikes with latex tube and cotton Veloflex 25mm (25mm wide) at 90 psi is slower than my 19 lbs. steel bike with 28mm (30mm wide) GP4000S at 60 psi. I was just looking at PR’s to verify this. My favorite playground is 44 miles long with ~3000 ft. of elevation. When I say slower, it’s not by seconds, we are talking 3-4 minutes. Due to footprint of the tire, I was working way less to maintain speed. GP4000S are far for supple but they roll damn well with latex tube. Prior to 28mm, I trained and raced on 25mm GP4000S and they didn’t impress me like 28mm GP4000S.
I don’t see myself ever going back to 25mm tire, even for racing. Waiting on availability of 28mm Veloflex to race in 2019.

[zefs]

Yeah everyone loves tailwinds...

[Matt28NJ]

I don’t see myself ever going back to 25mm tire, even for racing. Waiting on availability of 28mm Veloflex to race in 2019.

I feel the same way; I want to race on 28's for grip and stability.

Problem is, not many frames out there, including mine, can accommodate a tire measuring out at 31mm wide!

The Allez Sprint Disc seems to be a good fit for a relatively inexpensive race machine (i.e. something that you can write off) that can take big 28mm tires.

[Mr.Gib]

Real world example here. My race bikes with latex tube and cotton Veloflex 25mm (25mm wide) at 90 psi is slower than my 19 lbs. steel bike with 28mm (30mm wide) GP4000S at 60 psi. I was just looking at PR’s to verify this. My favorite playground is 44 miles long with ~3000 ft. of elevation. When I say slower, it’s not by seconds, we are talking 3-4 minutes. Due to footprint of the tire, I was working way less to maintain speed. GP4000S are far for supple but they roll damn well with latex tube. Prior to 28mm, I trained and raced on 25mm GP4000S and they didn’t impress me like 28mm GP4000S.
I don’t see myself ever going back to 25mm tire, even for racing. Waiting on availability of 28mm Veloflex to race in 2019.

Perhaps, but this experiment lacks proper control. How big is the sample size? Corrected for temperature? A loop I assume? And yes (zefs) indeed wind? I have loops where I can get a tail wind both ways or the opposite if I wish.

Now with 50 rides on each bike, and good power data, I think you would have something meaninful if not definitive. Because you can't ever properly account for wind and atmospheric effects, the sample size may have to be even bigger to fully average out those uncontrollable factors.

[Hexsense]

I believe that RR is constant and independent of speed. If so then proportionally the impact of RR is more notiaceble at climbing speeds than 40kmh so you would feel it more. I agree that the bigger tyres do feel sluggish.


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Another misconception, Rolling resistance depend on speed. But it grow linearly, hence less important than Wind resistance which grow as cube when the speed rises.

Rolling resistance increases as you go uphill and they are heavier too which would add more.

Heavier, yes. But more rolling resistance too? Do you have any evidence or explanation?

You'd feel more of the rolling resistance difference when you climb, because the speed decreases and wind resistance is shrinked to a point it can no longer overshadow difference in rolling resistance in the total drag. You'd feel more of the difference, yes. But i don't see rolling resistance increases when you go up hill, more like it'll decrease as you also decrease the speed.

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[fa63]

I have been running 30+ mm tires on my road bike for about a year now. I have tried a couple different tires; went as big as 35mm but didn't care for those much. Felt sluggish to me. I have since settled on 28mm Conti GP4K SII; still comfortable (they are about 31mm on my HED Belgium+ rims) but also seems to roll very well.

[Marin]

Generally, wider tires will have less rolling resistance compared to a narrower tire of the same construction. This has been proven often enough now.

You will have aero disadvantages - especially at higher speeds - because of the wider frontal area and because a tire wider than the rim negatively influencing the airflow.

The bike will also feel different, but that's a matter of taste.

[jlok]

Yes, I think only the Enve 4.5AR is aero optimized for 28c tyres. The tire/rim transition is very smooth.