Gravel tire rolling resistance tested

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Marin
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Location: Vienna Austria

by Marin

It's always a compromise, and that makes it interesting. Even if the off-road sections are really gnarly, a narrower/faster tire may be the better overall choice if there's a long road section.

My typical "special event" rides are out of Vienna and up the nearest mountain that's over 1000m high, so I'll have 50k on tarmac, 50k on gravel/hiking path and 50k tarmac back.

For the non-tarmac part I'd like to be on my 27.5"x2,2 Conti Race Kings, but overall Vredestein Aventura 44m are the better choice.

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themidge
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by themidge

^ This is the kind of thing that makes me confused about gravel tyre choice :')

About half of a normal gravel route for me is tarmac, a quarter of actual gravel (farm/forestry tracks), and then the rest is the muddiest rockiest most chewed up paths you've ever encountered. The fastest tyre would almost certainly be a ~38-42mm semi slick, but to be honest the only time I think about my tyres is on the most technical sections when I'm sliding around over muddy rocks and roots. Despite my routes being largely road, I care more about my tyres on the off road section. Low rolling resistance is once thing but if I have no grip what's the point?

Currently on Schwalbe G-one Bite in 27.5x2.1", starting to think I should just ride an XC bike :noidea:.

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CarlosFerreiro
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Location: Shetland, Scotland

by CarlosFerreiro

I've dropped down to just my gravel bike for all road and gravel use, but have also taken it up to 3 or 4 wheelsets and more like 6 tyre choices! Tyres, wheels and pressures depending on route type and length, weather and time of year. :)

Marin
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by Marin

themidge wrote:
Thu Jan 20, 2022 1:22 am
Currently on Schwalbe G-one Bite in 27.5x2.1", starting to think I should just ride an XC bike :noidea:.
Just experiment and use whatever is the most fun overall. For me part of the fun is being able to ride really fast on the road while knowing I can still survive rocky singletrack :)

JMeinholdt
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Location: Topeka, KS

by JMeinholdt

themidge wrote:
Thu Jan 20, 2022 1:22 am
^ This is the kind of thing that makes me confused about gravel tyre choice :')

About half of a normal gravel route for me is tarmac, a quarter of actual gravel (farm/forestry tracks), and then the rest is the muddiest rockiest most chewed up paths you've ever encountered. The fastest tyre would almost certainly be a ~38-42mm semi slick, but to be honest the only time I think about my tyres is on the most technical sections when I'm sliding around over muddy rocks and roots. Despite my routes being largely road, I care more about my tyres on the off road section. Low rolling resistance is once thing but if I have no grip what's the point?

Currently on Schwalbe G-one Bite in 27.5x2.1", starting to think I should just ride an XC bike :noidea:.
I did a comparison between a semi-slick 40c gravel tire (Vittoria Terreno Zero) and a 27c road tire (Challenge Paris-Roubaix) and there was only a small difference in on-road speed. Yes, you give up some speed on the tarmac sections, but with as delicate as you'd have to be in the rough stuff, you'd more than make up for it with a tough gravel tire. Again, it's all about knowing the route though.
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TobinHatesYou
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by TobinHatesYou

Absolutely depends on the route. If it’s mixed 50/50, but front-loaded with tarmac, then you’d be at risk of missing an early break/split on more aggressively treaded tires.

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fa63
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Location: Atlanta, GA, US

by fa63

Swiss Side just dropped this:

www.swissside.com/blogs/news/gravel-report

jfranci3
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by jfranci3

fa63 wrote:
Thu Jan 20, 2022 8:34 pm
Swiss Side just dropped this:

www.swissside.com/blogs/news/gravel-report
I've got two criticisms of this
1) (minor) They used the most aero of aero of aero setups rather than a more common one. There's never a day you're ever going to be flipping a coin there. A semi-aero bike would have been a better data point (Tarmac or something). It's a nice measure for OVERALL penality for best to realistic....except for the complete lack of water bottles (major).

2) (major) Looks like they used the tire rolling resistance #s off BRR. This makes sense, except the tests are different. As shown in the GP5K (tubed) tests, the CX tube yields a number about 4-5w higher. You're going to running that gravel tire TL, so consistent with BRR's own data you can subtract about 4w from their number per end - so 8w with their math (which is again flawed because of weight dist). They used a TL w/ 20ml sealant v thick tubed tire; in BRR's own test that's worth 2w there too (tubed v tubed, then road tubed v TL - or basically the GP5k TL road test v the GP5k TL 32c gravel test (the 25 v 32 were only 1.5w differece)).

The difference is about 7w rolling at 30kph. This is consistent with BRRs test between the GP5k TL 32 (tubed), GP5k TL TL, and the Terra Speed 38. That puts you at 24W (for both) @ 30kph. This seems about right, because a Terraspeed is basically a GP5K with mini knobs.

You're not going to be choosing between a 25c tire and 40c tire. I like to think it's about 1.5w per tire increment (roughly in agreement with SS), 1.5w for mini knobs (same agreement), so they've got 15w aero difference between the 25c and 40c tire/bike - I can find about a 6w aero penalty for the tire, leaving 13w for the frame/wheel/bars, which is about right... and you can put aero bars on a gravel bike so you can recover about 4w there.

Anyway, the penalty for slapping 38c tires on your Aspero is about 3-4w(aero) & ~5w(rolling) ; the penalty for taking your 32c tire Aspero on a road ride is about 17w at 30kph (1.5w rolling; 3w aero + 13w for the rest of the setup) - as long as youre not on the bike and you dont have water bottles. This about the same difference any light-road bike would have .
Last edited by jfranci3 on Fri Jan 21, 2022 5:12 am, edited 2 times in total.

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fa63
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by fa63

I agree with your points. I still found it interesting, as I actually frequently ride a gravel bike with 40c slick tires on the road and had often wondered what the wattage penalty is compared to my road bike (which admittely is not aero optimized). At some point, I had back-calculated my disadvantage to be about 20W at 30 kph (which is typically what my rides end up at) but that was a rough calculation as I don't ride with power anymore.

jfranci3
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by jfranci3

fa63 wrote:
Fri Jan 21, 2022 1:24 am
I agree with your points. I still found it interesting, as I actually frequently ride a gravel bike with 40c slick tires on the road and had often wondered what the wattage penalty is compared to my road bike (which admittely is not aero optimized). At some point, I had back-calculated my disadvantage to be about 20W at 30 kph (which is typically what my rides end up at) but that was a rough calculation as I don't ride with power anymore.
I think the lesson here is that the gravel frame isn't any less aero than a TCR/Emonda/Aethos or AL road bike. The tire aero / wheel differences seem plausible. The road bike setup as a reference is a data point from "full optimized". Good to know what the cost of knobs are. Good to see what the difference in wheels are.

warthog101
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by warthog101

fa63 wrote:Swiss Side just dropped this:

www.swissside.com/blogs/news/gravel-report
If you have every ridden your gravel bike out on the road, you may have noticed that you seem to have to work harder to achieve the same speeds. If you have a power meter, you will see a higher power for the same speed. Even though the gravel bike might ‘feel’ smooth and easy to ride, there are two key invisible players working against you. Aerodynamic drag and rolling resistance. 

A typical gravel bike setup has around 40W higher overall resistance at 30km/h than road bike, with this penalty split equally between aero drag and rolling resistance.


Sounds about right. My gravelly is significantly slower than the roadie.

Singular
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by Singular

warthog101 wrote:
Fri Jan 21, 2022 11:20 am
fa63 wrote:Swiss Side just dropped this:

www.swissside.com/blogs/news/gravel-report
If you have every ridden your gravel bike out on the road, you may have noticed that you seem to have to work harder to achieve the same speeds. If you have a power meter, you will see a higher power for the same speed. Even though the gravel bike might ‘feel’ smooth and easy to ride, there are two key invisible players working against you. Aerodynamic drag and rolling resistance. 

A typical gravel bike setup has around 40W higher overall resistance at 30km/h than road bike, with this penalty split equally between aero drag and rolling resistance.


Sounds about right. My gravelly is significantly slower than the roadie.
jfranci3 right above presents a few very valid points in regard to the methodology of their report. I can't complain about the aero testing (but as mentioned, it is not really a fair comparison...) as it is SwissSide's main game but I think that they read too much into the RR testing.

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

by warthog101

Singular wrote:
warthog101 wrote:
Fri Jan 21, 2022 11:20 am
fa63 wrote:Swiss Side just dropped this:

www.swissside.com/blogs/news/gravel-report
If you have every ridden your gravel bike out on the road, you may have noticed that you seem to have to work harder to achieve the same speeds. If you have a power meter, you will see a higher power for the same speed. Even though the gravel bike might ‘feel’ smooth and easy to ride, there are two key invisible players working against you. Aerodynamic drag and rolling resistance. 

A typical gravel bike setup has around 40W higher overall resistance at 30km/h than road bike, with this penalty split equally between aero drag and rolling resistance.


Sounds about right. My gravelly is significantly slower than the roadie.
jfranci3 right above presents a few very valid points in regard to the methodology of their report. I can't complain about the aero testing (but as mentioned, it is not really a fair comparison...) as it is SwissSide's main game but I think that they read too much into the RR testing.
It agrees with my speed differential between gravelly and roadie.
The same segments ridden multiple times on each are greater than 3kmh slower on the gravelly.
I have them set up relatively similarly.
Tubeless on both.
I put a fair bit down to rolling resistance.
Several mates I also follow on Strava.
Yep, 3kmh or more slower than their roadies.

I cant fit greater than 28c on my roadie to confirm it.
However I am going to get some light bicycle WR50 for the Revolt.
I will try them with some road tyres.

tanhalt
Posts: 410
Joined: Wed Dec 27, 2006 6:36 pm

by tanhalt

jfranci3 wrote:
Fri Jan 21, 2022 12:08 am
fa63 wrote:
Thu Jan 20, 2022 8:34 pm
Swiss Side just dropped this:

www.swissside.com/blogs/news/gravel-report
I've got two criticisms of this
1) (minor) They used the most aero of aero of aero setups rather than a more common one. There's never a day you're ever going to be flipping a coin there. A semi-aero bike would have been a better data point (Tarmac or something). It's a nice measure for OVERALL penality for best to realistic....except for the complete lack of water bottles (major).

2) (major) Looks like they used the tire rolling resistance #s off BRR. This makes sense, except the tests are different. As shown in the GP5K (tubed) tests, the CX tube yields a number about 4-5w higher. You're going to running that gravel tire TL, so consistent with BRR's own data you can subtract about 4w from their number per end - so 8w with their math (which is again flawed because of weight dist). They used a TL w/ 20ml sealant v thick tubed tire; in BRR's own test that's worth 2w there too (tubed v tubed, then road tubed v TL - or basically the GP5k TL road test v the GP5k TL 32c gravel test (the 25 v 32 were only 1.5w differece)).

The difference is about 7w rolling at 30kph. This is consistent with BRRs test between the GP5k TL 32 (tubed), GP5k TL TL, and the Terra Speed 38. That puts you at 24W (for both) @ 30kph. This seems about right, because a Terraspeed is basically a GP5K with mini knobs.

You're not going to be choosing between a 25c tire and 40c tire. I like to think it's about 1.5w per tire increment (roughly in agreement with SS), 1.5w for mini knobs (same agreement), so they've got 15w aero difference between the 25c and 40c tire/bike - I can find about a 6w aero penalty for the tire, leaving 13w for the frame/wheel/bars, which is about right... and you can put aero bars on a gravel bike so you can recover about 4w there.

Anyway, the penalty for slapping 38c tires on your Aspero is about 3-4w(aero) & ~5w(rolling) ; the penalty for taking your 32c tire Aspero on a road ride is about 17w at 30kph (1.5w rolling; 3w aero + 13w for the rest of the setup) - as long as youre not on the bike and you dont have water bottles. This about the same difference any light-road bike would have .
If they DID use BRR's values for the rolling resistance power, then it has another issue...namely that there's no correlation (at least AFAIK) between the power values reported by BRR and actual field test values for "real world" Crr.

In my own roller testing (which DOES make an attempt to compensate the roller values to reflect the expected Crr on a flat surface) I'm seeing ~half the rolling resistance power required between a GP5K and a Terra Speed.

JWTS
Posts: 98
Joined: Tue Jun 26, 2007 10:44 pm

by JWTS

warthog101 wrote:
Fri Jan 21, 2022 11:20 am

Sounds about right. My gravelly is significantly slower than the roadie.
I'm riding a Caledonia 5 as my gravel and road rig. I'm running a Terra Speed 35 back (measures 36.5) and a Terra Speed 40 up front. While not a true "travel" bike, it's prett capable. When I switch it to road wheels, it measures within the noise of my past aero road bikes (Reacto Disc and Giant Propel rim brake).

Based on these numbers, I imagine an Aspero 5 (better cable routing) with a more aero handlebar/stem set-up and road wheels would be pretty close to best road aero set-up, probably within 5-7W of an S5 with bottle cages. Not bad.

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