How much slower are Gravel tires?

51 replies · 16,239 views

davist
38 posts
#41Dec 6, 2019, 6:06 AM
Koyote wrote:Boy, this thread really has legs. And I wonder why? I mean, "horses for courses," as the Brits say. If you're using gravel tires for their intended purpose (umm, riding on dirt and gravel roads), they'll be faster than skinny road tires; and if you're using those road tires for their intended purpose (on smooth paved roads), they'll be faster than gravel tires.

It's kind of like wondering whether a Jeep is slower than a Porsche 911: either will be superior if used for its intended purpose.

Yup.. my 650b x 47 WTB Horizon slick tires take more effort to push on the road than my 700c x 28 Conti 4ks. Probably somewhere between 1-2 mph but not relevant. I was surprised how "fast" my new 2.1 thunder burt Schwalbe's feel vs the Horizons, basically the same.
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ljsmith
762 posts
#42Dec 6, 2019, 7:05 AMedited
Koyote wrote:Boy, this thread really has legs. And I wonder why? I mean, "horses for courses," as the Brits say. If you're using gravel tires for their intended purpose (umm, riding on dirt and gravel roads), they'll be faster than skinny road tires; and if you're using those road tires for their intended purpose (on smooth paved roads), they'll be faster than gravel tires.

It's kind of like wondering whether a Jeep is slower than a Porsche 911: either will be superior if used for its intended purpose.

It all depends how you use your bike. I have a gravel bike and a road bike, so I tend to agree with you. But I get the feeling that a lot of people on this forum use their bikes as all around bikes (they only have 1 horse). They ride a mix of pavement and gravel and not everyone can afford two wheel sets and sets of tires. So finding tires that roll well on and off-road is important to them.
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Koyote
288 posts
#43Dec 6, 2019, 7:18 AM
ljsmith wrote:

It all depends how you use your bike. I have a gravel bike and a road bike, so I tend to agree with you. But I get the feeling that a lot of people on this forum use their bikes as all around bikes (they only have 1 horse). They ride a mix of pavement and gravel and not everyone can afford two wheel sets and sets of tires. So finding tires that roll well on and off-road is important to them.

But that was not really the point of the original post, at least as I perceived it.

And regardless, if you are riding a bike on both pavement and gravel/dirt, you are probably not looking at road tires...Rather, you're looking at a narrow slice of the gravel tire options. Of course road tires will offer less rolling resistance, but that is beside the point.

When choosing tires, my first criteria are width/volume, tread/traction, and durability, since those variables determine whether I'll be able to ride on the intended terrain. Trying to minimize the rolling resistance seems like a good way to ensure that I'll run out of traction, slice up the tire, or both.
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jockstick
47 posts
#44Feb 10, 2021, 1:37 PM
ccand51997 wrote:I'll share some numbers that I've shared on another site and was ignored or people said my methodology was not good compared to some other methods. Frankly, I've done power meter testing over the past 15 years often enough that I am pretty confident in the results.
So here were the tires:

Conti GP4000S2 25mm at 80 psi (This was my control tire)
Conti Raceking Protection at 25psi old (center tread worn down, plus I ground it down some more)
Conti Raceking Protection new
Schwalbe G-One Speed 2.0 at 25 psi

I made multiple runs each lasting circa 5 minutes on a very consistently steep road (in excess of 10 percent) that was paved but not at all smooth.
I averaged the same 200 watts on each run. If you were to throw out the top run and the bottom run, all of them fell between 5:13 and 5:17.

Without listing out all the individual times, the result was that the GP 4000 had the fastest averaged time at 5:12
The two Race Kings and the G-One Speed averaged 5:15 to 5:17. Now, in order to swap out tires on the bigger tires I was not running them tubeless so they were tested with a butyl tube where my GP4000 had a latex tube. Thus my conclusion was that quality big tires lose almost nothing to a quality road tire. Now, obviously the new GP5000 is going to be a bit faster.

I've done similar tests with G-One Allround and WTB Resolute and found them just slightly slower than a G-One Speed, but it was close enough I would not sweat the difference there either.
Frankly, I was surprised how close they all were to each other. Part of it is that I don't buy cheap tires, so I expected them all to be decent.

Last comment. This was aimed at testing rolling resistence, thus the steep hill. Obviously the aerodymanics is going to play a part when you are out solo riding and matter less when you are with a group ride.

Just stumbled across this post. Really interesting test! Would be really curious for you to repeat this on a flat section so we can see the impact of aerodynamics. I've read a lot that thicker tires make a big aero difference, but have never seen this quantified.
I'm switching from 700x42 WTB Resolutes to 650x2.2 Conti Race Kings to better handle chunky gravel. Really curious how much aero l'm giving up!
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chas
1,305 posts
#45Feb 10, 2021, 3:16 PM
When I'm riding solo, I'm doing 15mph or so (maybe less, lol). So I don't care about Aero. Yeah, maybe I'll do 20mph commuting on road tires and it starts to make a difference there.

But when I'm doing 25-30mph, I'm in a group ride (gotta get the adrenaline going), and more often than not I'm drafting (yeah, I pull too, but not for 5 minutes). In those conditions, aero doesn't mean anything. But rolling resistance is huge.

Aero goes up exponentially, Rolling resistance linearly. This makes Aero huge when doing a solo ride time trial, but it seems to flip when doing a group ride.

When I'm doing a 20-25mph gravel ride (i.e. race conditions), I have a lot bigger concerns than being aero. That isn't my priority.
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nellborg
142 posts
#46Feb 10, 2021, 3:30 PM
A 10% grade for 5+ minutes! That's like 99% aero resistance and 1% misc resistance, so I don't think that's a good test of rolling resistance at all.

But, that's the big question for me, too. Do I run 42-44's or 35-40's? At 195 lbs, I think that I should be on 42-44's at lower psi than on 38's at higher psi on most gravel, just to lower the impedance.

I've listened to all the Marginal Gains podcasts, and I thought that Josh said that there's very little penalty for going wider, but I might have mis-heard that. I would think, though, that at 15-20 mph avg, over surfaces with high rolling resistance and higher impedance, and knowing that nothing in the 35-44 mm range will work in combination with the rim to be aero, I just don't feel that width is all that important for gravel.

Casing quality / suppleness, and slick / semi-slick, aero spokes are important, but tire width on too-narrow-to-be-aero rims? I'm a skeptic re tire width.
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jockstick
47 posts
#47Feb 10, 2021, 5:21 PM
nellborg wrote:A 10% grade for 5+ minutes! That's like 99% aero resistance and 1% misc resistance, so I don't think that's a good test of rolling resistance at all.

Going up a steep grade at a slow speed, it minimizes aero impact, so it's more rolling / misc resistance.
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ccand51997
265 posts
#48Feb 10, 2021, 5:28 PM
jockstick wrote:
I'm switching from 700x42 WTB Resolutes to 650x2.2 Conti Race Kings to better handle chunky gravel. Really curious how much aero l'm giving up!

Without actually doing the test I would speculate that is going to be a wash. The 700c wheel is taller and narrower; the 650b shorter and wider. And the RaceKing is just a better all-around tire in terms of rolling resistance, durability, float, traction and puncture resistance.
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ccand51997
265 posts
#49Feb 10, 2021, 5:48 PM
jockstick wrote:

Going up a steep grade at a slow speed, it minimizes aero impact, so it's more rolling / misc resistance.

You know, it is funny; I went back and looked and I never specifically said I was going uphill (I was) so yah, downhill would not be a great test of RR, but those were uphill on about an 8-12 percent grade.
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ccand51997
265 posts
#50Feb 10, 2021, 6:02 PM
chas wrote:When I'm riding solo, I'm doing 15mph or so (maybe less, lol). So I don't care about Aero. Yeah, maybe I'll do 20mph commuting on road tires and it starts to make a difference there.
Re: Lower speeds. I agree that off-road I'm not going to worry about it much. Where I ride, I want more float and traction. For this I love the Conti Raceking.

But when I'm doing 25-30mph, aero doesn't mean anything. But rolling resistance is huge.
Re: Wind Resistance in a group. I don't think that people understand how much dirty air their is in a group. Drafting one person reduces wind resistance by like 30 percent, but riding with someone perfectly positioned in front back and sides only drops it down to 45 percent or so. So aero in a pack is almost half as important but at 25-35 mph that half is probably still a lot bigger than the difference in crr of most of the good tires right now.

When I'm doing a 20-25mph gravel ride (i.e. race conditions), I have a lot bigger concerns than being aero. That isn't my priority.

My two main gravel rides each year have about 7,000 feet of climbing. One is 20/80 pavement/dirt with most of the pavement at the very beginning and end and two huge, rough often sandy descents so I ride 2.2 inch tires. Both races have a frenetic start before about an hour of steep climbing on dirt so there is not much pack riding at all. I average like 13 mph.
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nellborg
142 posts
#51Feb 10, 2021, 7:15 PM
Funny. I just assumed downhill - maybe because the various RR tests online (like GCN, Bike Radar) do downhill roll tests.
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stu
646 posts
#52Feb 11, 2021, 1:15 AM
If you're climbing a 10% grade I think most of your power will go into working against gravity so tire differences will be hard to notice.

A quick calculation: If the rider, bike, and gear add up to 200 lbs, the grade is 10%, and the speed is 5 mph then about 200 W will be required just to overcome gravity. I'd expect differences in rolling resistance at just 5 mph to be very much smaller than 200 W.
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