Gravel tire rolling resistance tested

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FlatlandClimber
Posts: 2491
Joined: Tue Mar 31, 2020 3:37 pm

by FlatlandClimber

Singular wrote:
Thu Jan 06, 2022 9:09 pm
FlatlandClimber wrote:
Thu Jan 06, 2022 7:53 pm
Singular wrote:
Thu Jan 06, 2022 5:19 pm
What often contributes to gravel bikes being slower is that power gets lost in the drivetrain (due to single/smaller chainrings).
Like how many watts do you think the smaller chainrings make up? 3W at 300W? Hard to imagine it's more than that.
It's not like Gravel bike chainrings are that tiny compared to a climbing set up on an RB (46/30 or 48/31 vs 50/34 or in SRAM 43/30 vs 46/33).

For 1X the difference is probably even less. You have smaller Chainrings, but larger sprockets.

There are many reasons why a gravel bike is slower (geometry, tires, weight, usually no focus on aero), but I don't think chainring size is a noticeable factor really.
Like mentioned, it is one of the marginal drains;

Image

The crux of smaller/single chainrings is that you have to use smaller sprockets too for the same gearing.
I think this graph has been referenced a little too frequently here.
In the middle section, the gears are seperated by a watt or so. The far ends of the gearing (48/10) is not a gearing you use frequently in gravel (maybe never?).
I don't think it makes a ton of sense to compare gravel gearing to 53/39, but rather to 50/34 (at least for me).
So what do you thing would be the difference in friction between 50/34 road or 48/31 gravel?

Also, in gravel you usually don't want the "same gear".
I don't know how people use their gravel bikes (Ronald Kuba uses his as a Winter road bike, and goes 20% hard pack, 80% Road... Fine).
But if you really go rougher gravel, steeper forest paths, mud etc, road gearing just doesn't cut it. You need small gears and don't need tiny gear jumps or a 4.8:1 top end gear.

So my thesis would be:
Gravel gearing is smaller because you go slower (higher friction tires, slower rolling surface, more technical riding, steeper roads, less traction in corners and on climbs), not the other way around.
Cervelo P5 Disc (2021) 9.1kg
Factor Ostro Gravel (2023) 8.0kg
S-Works SL8 (2023) 6.3kg

*weights are race ready, size 58/L.
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Singular
Posts: 537
Joined: Mon Jul 27, 2020 8:59 am

by Singular

FlatlandClimber wrote:
Fri Jan 07, 2022 4:29 pm

I think this graph has been referenced a little too frequently here.
In the middle section, the gears are seperated by a watt or so. The far ends of the gearing (48/10) is not a gearing you use frequently in gravel (maybe never?).
I don't think it makes a ton of sense to compare gravel gearing to 53/39, but rather to 50/34 (at least for me).
So what do you thing would be the difference in friction between 50/34 road or 48/31 gravel?

Also, in gravel you usually don't want the "same gear".
I don't know how people use their gravel bikes (Ronald Kuba uses his as a Winter road bike, and goes 20% hard pack, 80% Road... Fine).
But if you really go rougher gravel, steeper forest paths, mud etc, road gearing just doesn't cut it. You need small gears and don't need tiny gear jumps or a 4.8:1 top end gear.

So my thesis would be:
Gravel gearing is smaller because you go slower (higher friction tires, slower rolling surface, more technical riding, steeper roads, less traction in corners and on climbs), not the other way around.
Well, it is thrown around quite liberally and that's for a reason - it is one of the better (graphic) comparisons. What takes it away from this subject is that it is road focused and that it is more showing the flaws of tiny sprockets than small chainrings.

With that said; the challenge is the breadth of gravel as a concept, going all the way from all-out racing (the elephants' graveyard...) on rock hard roads to rowdy and rugged. When talking about efficiency and speed, my viewpoint is from the racing side of things but I do most certainly enjoy the adventure side of things too (but not with an emphasis on performance). The last time I pinned on a number for a gravel race we covered 37km and 500m of climbing in the first hour and I spent most of that time wearing on my top gear (48x13). That is a stark contrast from the week after, when trying to maneuvre through fist-sized rocks at (less than) walking pace with no other goal in mind than getting to quite a few tempting cold ones before sunset...

In general, I think we are on the same track - gravel bikes have lower (and wider) gearing because of the intented use, but the gearing (and other design elements/compromises) needed for that use case does also come into play when taking it into comparison with a road bike.

FlatlandClimber
Posts: 2491
Joined: Tue Mar 31, 2020 3:37 pm

by FlatlandClimber

I certainly wasn't referring to adventure biking (as in bike packing and exploring) either.
In Central Europe "gravel" is a term frequently used for going "cross-country" (literally, not the MTB discipline). So that involves road, beaten paths, hard pack, forest paths, mud, Gras, everything.

Especially when riding in forests, the pitches can be mega steep and traction can be very low. That's where knobby tires, low gears and large gear jumps are a must, and a "Ultegra for Gravel?" Would not work too well.

That's why I think having the "right" tires and gearing is a lot more important, even in high performance applications, than just having the stuff that performs best in a lab.
Cervelo P5 Disc (2021) 9.1kg
Factor Ostro Gravel (2023) 8.0kg
S-Works SL8 (2023) 6.3kg

*weights are race ready, size 58/L.
Sold: Venge, S5 Disc, Roubaix Team, Open WI.DE, Émonda, Shiv TT, Crux, Aethos, SL7

Singular
Posts: 537
Joined: Mon Jul 27, 2020 8:59 am

by Singular

FlatlandClimber wrote:
Sat Jan 08, 2022 6:05 pm
I certainly wasn't referring to adventure biking (as in bike packing and exploring) either.
In Central Europe "gravel" is a term frequently used for going "cross-country" (literally, not the MTB discipline). So that involves road, beaten paths, hard pack, forest paths, mud, Gras, everything.

Especially when riding in forests, the pitches can be mega steep and traction can be very low. That's where knobby tires, low gears and large gear jumps are a must, and a "Ultegra for Gravel?" Would not work too well.

That's why I think having the "right" tires and gearing is a lot more important, even in high performance applications, than just having the stuff that performs best in a lab.
We do very much understand eachother, obviously - once again, I think that the thing that makes the subject complicated is the enormous breadth. That will surely be broken down eventually (like on the MTB side), but for now were all one happy gravel family. Cheers!

FlatlandClimber
Posts: 2491
Joined: Tue Mar 31, 2020 3:37 pm

by FlatlandClimber

🤙🏻👍🏻
Cervelo P5 Disc (2021) 9.1kg
Factor Ostro Gravel (2023) 8.0kg
S-Works SL8 (2023) 6.3kg

*weights are race ready, size 58/L.
Sold: Venge, S5 Disc, Roubaix Team, Open WI.DE, Émonda, Shiv TT, Crux, Aethos, SL7

warthog101
Posts: 872
Joined: Wed Sep 25, 2013 10:05 am

by warthog101

I am riding gravel roads here.
New routes, no traffic. Win win.
48/31 chainset.
36-11 11s cassette.
Ample range for what I am doing.
Most of the time in the big ring.
Any loss in gearing efficiency is marginal at worst.
Tyres are a much bigger loss imo.
They roll significantly slower than road tyres

https://www.bicyclerollingresistance.co ... el-reviews

https://www.bicyclerollingresistance.co ... ke-reviews

I am using GP5k TL on the roadie
So according to BRR 16.6 watts of rolling resistance.

Gravel king sk on the front and tufo Speedero on the back on the gravelly.
2x GK sk = 49.4 watts of rolling resistance.
(Speedero not tested)

Over 30watts more resistance. Tbh it feels more than that.

yinzerniner
Posts: 206
Joined: Tue Jun 13, 2017 8:54 pm

by yinzerniner

warthog101 wrote:
Sun Jan 09, 2022 6:31 am
I am riding gravel roads here.
New routes, no traffic. Win win.
48/31 chainset.
36-11 11s cassette.
Ample range for what I am doing.
Most of the time in the big ring.
Any loss in gearing efficiency is marginal at worst.
Tyres are a much bigger loss imo.
They roll significantly slower than road tyres

https://www.bicyclerollingresistance.co ... el-reviews

https://www.bicyclerollingresistance.co ... ke-reviews

I am using GP5k TL on the roadie
So according to BRR 16.6 watts of rolling resistance.

Gravel king sk on the front and tufo Speedero on the back on the gravelly.
2x GK sk = 49.4 watts of rolling resistance.
(Speedero not tested)

Over 30watts more resistance. Tbh it feels more than that.
Your numbers don't really mean anything without tire sizes and pressures. 16.6w total is at crazy high pressures with tubes, and similar with the 49.4w earring. Also while BRR has been the go to for comparative testing the methodology is not ideal for rating tubeless tires.

That being said, if you're normalizing for casing tension / tire drop / comfort level then you're probably looking at a 5-10% difference in rolling and wind resistance at typical long distance flat speeds (20mph/32kph) between 28mm gp3k TL and ~40mm GK SK. So they'll be noticeably slower on paved roads, but on rougher terrain the increased grip, sturdiness and control will likely make the GK come out ahead.

But as others have said numerous times if you want best bang for buck to increase speed bike position is king.

warthog101
Posts: 872
Joined: Wed Sep 25, 2013 10:05 am

by warthog101

Yeah they are all tubeless. I am aware BRR uses tubes. There is nothing else I have seen that measures the resistance of both using the same protocol to compare
80psi in the GP5K TL. 25 f &28r.
The gravel tyres are 40c at ~ 35psi.
The gravel kings are measured at 36psi for 24.7watts of drag per tyre.
GP5K is 9.9 watts at 80 psi.
Still very close to 30watts of extra drag.

Yeah I agree aero is king, wide tyres lose out there too.
If you can sit on 40kmh with those gravel boots on, there will be significant aero penalty from them also.
Gravel tyres, in comparison are slow.
Just how much slower they do roll I found surprising.

For the dry hardpack stuff I ride, I dont need an aggressive tread.
Got some Terra Speeds on the way. I'll see how they go.

yinzerniner
Posts: 206
Joined: Tue Jun 13, 2017 8:54 pm

by yinzerniner

warthog101 wrote:
Sun Jan 09, 2022 10:04 pm
Yeah they are all tubeless. I am aware BRR uses tubes. There is nothing else I have seen that measures the resistance of both using the same protocol to compare
80psi in the GP5K TL. 25 f &28r.
The gravel tyres are 40c at ~ 35psi.
The gravel kings are measured at 36psi for 24.7watts of drag per tyre.
GP5K is 9.9 watts at 80 psi.
Still very close to 30watts of extra drag.

Yeah I agree aero is king, wide tyres lose out there too.
If you can sit on 40kmh with those gravel boots on, there will be significant aero penalty from them also.
Gravel tyres, in comparison are slow.
Just how much slower they do roll I found surprising.

For the dry hardpack stuff I ride, I dont need an aggressive tread.
Got some Terra Speeds on the way. I'll see how they go.
I just mounted some terra speed 40 and they're noticeably faster feeling than the GK sk 40 I previously had on. Not sure if it's because of the rubber or casing but it's more supple / soft while not having as sluggish a feel when accelerating or putting down power.

Will have to ride a lot more to see if they're measurably faster, or how well they last on my regular gravel loop which is roughly 60/40 pavement / dirt. But overall if you like the go5k you'll like the terra speeds.

req110
Posts: 867
Joined: Thu Nov 22, 2018 10:23 am

by req110

I am now on tufo gravel thundero but considering some thing faster again.

A) challenge Strada Bianca htlr
B) terra speeds again, those were really fast!
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warthog101
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by warthog101

Thanks. Looking forward to the Terras.
I have had a great run out of Conti road tyres.

Singular
Posts: 537
Joined: Mon Jul 27, 2020 8:59 am

by Singular

There's a bit apples-to-oranges comparison going on there - using the GP5000, arguably the fastest (and best...?) real-world racing tyre, as a baseline makes everything else look shite. The delta between a GP5000 and a leading gravel tyre (like a Terra Speed or a slick Gravel King) is according to the measurement of Jarno Bierman about 10W per wheel (and with some finger-counting my own darling, the Vittoria Voyager Hyper, ends up at a similar value).

Wheel specifics (width and height/depth) does play into CRR a tiny bit, but makes a huge impact on the Cd part of CdA (and the A part is, well, also not benificial for gravel tyres...). If not venturing into the 3T style super-wide deep sections, I think that an additional 10W is easily eaten by just wheel/tyre aerodynamics.

...but as I've touched on with FlatlandClimber earlier; these are all applicable only in a gravel racing or gravel-bike-trying-to-keep-up-with-road-bikes scenario. In other use cases, other things are more important (such as grip, puncture protection and plain ol' fun).

And to revisit my hobby horse; sensations are really, really bad at predicting performance.

warthog101
Posts: 872
Joined: Wed Sep 25, 2013 10:05 am

by warthog101

Jarno Bierman

What's even better, rolling resistance at lower air pressures is extremely low as well with a rolling resistance of just 9.9 watts at 80 psi / 5.5 bars.

25c 5000TL

Rolling Resistance
Low Air Pressure
(36 psi / 2.6 bar)21.6 Watts


40c Terra Speed

Pretty close to the pressures I run.
The Terra Speeds are 3.1watts better per tyre than the GK sk.
I'll see how they go.


Point is I read the argument drive train friction losses are a contributing factor to the slower speed a gravel bike travels at.
Mine is significantly slower on road sections as per strava segments, ridden multiple times on each bike.
I see rolling resistance and aero losses as the more significant reasons why.



jromano89
Posts: 22
Joined: Sat Oct 02, 2021 6:48 pm

by jromano89

I installed 32mm GP5000 S TR tires (with 25/28 latex tubes) on my gravel bike and went for a ride today. These results are unscientific but I easily set a new PR on my most traveled Strava segment.

Every run to-date has been between 1:56 and 2:06 in summer gear with various tires -- Terra Speed, Pathfinder, and Race Kings mostly. In winter gear, every run has been between 2:11 and 2:19 due to being way less aero.

Today's run was 1:54 in winter gear.

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yinzerniner
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by yinzerniner

jromano89 wrote:
Sat Jan 15, 2022 10:38 pm
I installed 32mm GP5000 S TR tires (with 25/28 latex tubes) on my gravel bike and went for a ride today. These results are unscientific but I easily set a new PR on my most traveled Strava segment.

Every run to-date has been between 1:56 and 2:06 in summer gear with various tires -- Terra Speed, Pathfinder, and Race Kings mostly. In winter gear, every run has been between 2:11 and 2:19 due to being way less aero.

Today's run was 1:54 in winter gear.
I'm guessing your route is mostly tarmac or somewhat smooth roads vs a long gravel or off-road segment?

But a ~15% improvement is pretty sizable. Using the Silca pressure calculator for switching between 28mm GP5k TL and 40mm terra speed i saw a royghly 10% overall speed loss on tarmac sections, but on a decently long rail trail saw 15% speed gain, mostly due to confidence in not having to avoid every obstacle. So similar results as it pertains to optimizing tires for ride conditions ie horses for courses.

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