Who rides 28mm + tires on tarmac?

Discuss light weight issues concerning road bikes & parts.
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Calnago
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by Calnago

Hexsense wrote:
Tue Oct 02, 2018 4:06 pm
zefs wrote:
Tue Oct 02, 2018 8:53 am
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.
I'll add my thoughts here... as I'm of the belief that a fat tire at low pressure will indeed be harder to push up a hill, just based on my own experience, no data to support it, although I also believe that real life experience is a pretty good "data point" in itself. So, what is "rolling resistance" besides friction between the tire and road. Let's assume a constant contact patch for a moment, but a 100lb rider vs a 200lb rider. Is there more rolling resistance with the 200lb rider? I think so. Suppose you're sanding a board for example. You can apply light pressure (less weight), or really get into it and apply a lot of pressure (more weight). Which one produces more friction... I'd say the one where you're applying more pressure. Ok, so if you agree with that, assume there's also this thing called gravity... I know it exists and being a big guy it affects me more than the little guy, at least that would explain why most "climbers" are "little". Going up hill is simply harder as the weight increases for sure, but also due to gravity. It doesn't take much more effort to keep the 200lb guy rolling on flat ground than it does to keep the 100lb guy rolling (on flat ground). But that all changes dramatically as soon as a hill looms ahead, thanks to gravity. Aero factors at uphill speeds are pretty negligible (you can argue this if you want). So, even with tires with the exact same contact patch.... wouldn't the heavier rider be creating more friction between the tire and the road, due not only to the extra weight, but also by the evil forces of gravity as he ascends trying to catch his li'l fuker of a friend bouncing on ahead.

So, yeah... I think rolling resistance is indeed greater going uphill than it is on level ground because of two things... absolute weight, and the effect of gravity on that weight.

Just a thought.
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by Weenie


zefs
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by zefs

Hexsense wrote:
Tue Oct 02, 2018 4:06 pm
cunn1n9 wrote:
Tue Oct 02, 2018 7:41 am
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.
zefs wrote:
Tue Oct 02, 2018 8:53 am
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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My point was that if you are using a tire that creates more rolling resistance on the flat (because you use less air pressure to gain comfort) it will be even slower uphill both because of the RR and weight difference.

ducman
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by ducman

Just putt some GP4000 28's on my bike for the winter. Gonna ride them tomorrow morning. 😁

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pdlpsher1
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by pdlpsher1

Can someone confirm the weight of a new Conti GP4K II 28mm tire? I had one a while back if I recall the weight was around 275g. Bicyclerollingresistance.com has listed the actual weight at 267g. FWIW my new Conti GP4K II 25mm weighs 213g.

A wider tire is faster than a narrower tire at the same pressure. This is true. But there's a point when you start dropping the pressure on the wider tire and it becomes slower than the narrower tire at a higher pressure. Bicyclerollingresistance.com has tested the three sizes of the Conti GP4K IIs. At 60psi, the 28mm is slower than the 25mm at 80psi. My point is that if you start dropping the pressure on a wider tire, you are also losing the RR advantage of the wider tire. You simply don't get the best of both worlds- lower RR and more comfort. Plus you have the weight penalty of the wider tire to take into account. RR test link here: https://www.bicyclerollingresistance.co ... i-23-25-28

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fa63
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by fa63

Yes, by about 0.5 W :-) Plus whatever aero penalty comes with it; maybe another 4-5 W? I can live with that.
pdlpsher1 wrote:At 60psi, the 28mm is slower than the 25mm at 80psi.

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pdlpsher1
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by pdlpsher1

fa63 wrote:
Tue Oct 02, 2018 5:47 pm
Yes, by about 0.5 W :-) Plus whatever aero penalty comes with it; maybe another 4-5 W? I can live with that.
pdlpsher1 wrote:At 60psi, the 28mm is slower than the 25mm at 80psi.
Don't forget the weight penalty of 54g. per tire. I hope your rides don't have a lot of acceleration/deceleration :D

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Calnago
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by Calnago

The thing is, you don’t ride a high volume tire at the same pressure as a low volume tire. You could, but you’re defeating the purpose. For instance, at 200+ lbs I ride my Veloflex Arrenberg tubulars (25mm) at ~100psi rear and 90psi front. Using 27mm Veloflex Vlanderen tires I’d run closer to 80psi. Running the Vlanderens at 100psi would be akin to bouncing around like a pinball. But yes, they would roll fast I’m sure.
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bremerradkurier
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by bremerradkurier

pdlpsher1 wrote:
Tue Oct 02, 2018 5:54 pm
fa63 wrote:
Tue Oct 02, 2018 5:47 pm
Yes, by about 0.5 W :-) Plus whatever aero penalty comes with it; maybe another 4-5 W? I can live with that.
pdlpsher1 wrote:At 60psi, the 28mm is slower than the 25mm at 80psi.
Don't forget the weight penalty of 54g. per tire. I hope your rides don't have a lot of acceleration/deceleration :D
the 28mm tire at 60psi will allow you to carry more speed through turns, saving you from having to accelerate and possibly putting you a few bike lengths ahead of your fellow riders on narrower tires.

emotive
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by emotive

DT Swiss did some great data collection when they developed their ERC1100 DICUT wheels. They tested the wheels with both GP4K 25mm and GP4K 28mm. The 25s are more aero, and the 28's roll faster. Where is the break even? Their conclusion is that the 28 is faster for riders averaging less than 35km/h. Above that pace, the aero penalty outweighs the lower rolling resistance.

They also highlight that 75% of aero comes from the rider, and only 8% from wheels, and being comfortable is important for sustaining an aero position on the bike, so wider tyres contribute to rider aerodynamics.

Dig into their data at https://www.roadrevolution18.dtswiss.com/endurance/

jlok
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by jlok

emotive wrote:
Wed Oct 03, 2018 1:27 am
DT Swiss did some great data collection when they developed their ERC1100 DICUT wheels. They tested the wheels with both GP4K 25mm and GP4K 28mm. The 25s are more aero, and the 28's roll faster. Where is the break even? Their conclusion is that the 28 is faster for riders averaging less than 35km/h. Above that pace, the aero penalty outweighs the lower rolling resistance.

They also highlight that 75% of aero comes from the rider, and only 8% from wheels, and being comfortable is important for sustaining an aero position on the bike, so wider tyres contribute to rider aerodynamics.

Dig into their data at https://www.roadrevolution18.dtswiss.com/endurance/
This is the rim profile that their tests are based on.
Image
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pdlpsher1
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by pdlpsher1

The DT Swiss article talked about aerodynamics, rolling resistence, and comfort. Nowhere do they mention anything about weight of the tire. We are talking about 110g. of additional rotational weight. How can DT Swiss make a conclusion on the optimal tire width without taking rotational weight into account?

jlok
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by jlok

Hutchinson 28c TLR tire is 270g; sealant 30g; tubeless valve maybe 5g so 110g difference maybe a bit overestimated.
Litespeed T1sl Disc / BMC TM02 < Giant Propel Advanced SL Disc 1 < Propel Adv < TCR Adv SL Disc < KTM Revelator Sky < CAAD 12 Disc < Domane S Disc < Alize < CAAD 10

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pdlpsher1
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by pdlpsher1

The 110g diff is for the Conti GP4K II, and two tires not just one. Each tire = 55g heavier. My GP4K II 25mm weighs only 213g new. On my 17C rims they measure 27mm wide. On my 21C Hed rims they measure 29mm wide. My bike can take up to 32mm measured but I don’t see the need for that wide of a tire unless I’m riding cobbles or gravel.


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pdlpsher1
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by pdlpsher1

By the way I use 23mm on the front and 25mm on the rear. The 23mm GP4K II measures 25mm on the 17C rim. My 21C Hed rims are only used on the tandem. At 95psi front and rear the 25mm (29mm measured) feels fast and nimble.

JoO
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by JoO

I suggest reading this
https://janheine.wordpress.com/2018/01/ ... re-slower/

A few days ago I mounted challenge Strada 36 tires on my winterbike (cyclocross bike).
I thought there were very slow until I looked at my garmin.
The lack of vibration makes our minds think we go slower because we associate higher speed with more vibration.

by Weenie


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