Gravel tire rolling resistance tested

[FlatlandClimber]

Is there any explanation as to why BRR prodtocls consistently have lower Crr for MTB tires vs Gravel tires?
I am seriously considering MTB tires (RaceKing ProTection) instead of Gravel tires (Pirelli Cinturato Gravel H).

[pdlpsher1]

Comparing two tires with different widths is difficult. A tire's deformation (hence rolling resistance) is determined by the tire's casing tension. The casing tension is determined by the tire casing's size and air pressure. As a tire gets wider the air pressure must be reduced to keep the casing tension the same. BRR does reduce/increase the air pressure to make tires with different widths in the CX/Gravel category comparable. They do so by adjusting the air pressure to the measured casing width. By doing this they make the CX/gravel tires somewhat comparable. As for the MTB category they don't do this adjustment. Most of the MTB tires they test are between 2.20-2.25" wide, thus making the results comparable without air pressure adjustments. However one cannot compare a gravel tire's result to a MTB's tire result. They are apples and oranges.

[FlatlandClimber]

I didn't really get how these are not comparable. They are loaded by the same amount of weight, roll at the same speed, on the same surface and power required is measured the same way by the same person.

Although these are not exact to the third decimal, it should still be somehow be reflective of what to expect when riding these two tires.
I at least wouldn't know why not.

Tire pressure on the metal drum is always questionable. The gravel and MTB always perform the best at the highest pressure, which obviously isn't the same on the road and especially not on the trail.

[petromyzon]

Is it consistent though? Only the top two MTB tyres are faster than the gravel tyres and the overall spread is quite similar.

You can't directly compare because the effect of pressure on CRR is large (>10% over typical pressure ranges). Testing MTB tyres at 25 psi and gravel at 30-45 psi or whatever he (Jarno/BRR) does sounds more than reasonable to me but to be confident that a tyre from his MTB section is definitely faster than a tyre from his gravel section you would at least have to adjust the pressure based upon casing tension as described above.

Even then the tyres could perform quite differently in real life on your roads. I would suggest that if your bike can fit a range of sizes you should base selection on how rough the terrain is, how rowdy you like to get and whether you like to ride it "underbiked" or "overbiked".

[pdlpsher1]

Tires from different categories are NOT comparable. If you really believe they are, then you should get this tire, which has been tested to be the fastest 40mm tire tested on BRR if you go by their chart on the right

Trust me. Don't get the Speed King. If you want something faster than the Gravel H get the Conti Terra Speed 40mm. It uses the same fast compound as the Speed King.

https://www.bicyclerollingresistance.co ... otion-2016

[zmjones]

Tires from different categories are NOT comparable. If you really believe they are, then you should get this tire, which has been tested to be the fastest 40mm tire tested on BRR if you go by their chart on the right

Trust me. Don't get the Speed King. If you want something faster than the Gravel H get the Conti Terra Speed 40mm. It uses the same fast compound as the Speed King.

https://www.bicyclerollingresistance.co ... otion-2016

that isn't true. he uses the same drum for each category. if the casing tension is comparable the results are comparable.

and what is wrong with the speed king? i run race/speed kings on my gravel bike and think they are pretty fast. terra speed is not a bad recommendation but the casing on the racesport version of the speed/race kings is a nice balance between supple/durable imo.

the best tires in the mtb category are race day tires which in some cases (big one) aren't made anymore. for whatever reason there aren't many race day type tires in the gravel category. specifically not from schwalbe and continental (maybe the terra speed sorta qualifies).

[pdlpsher1]

Casing tension has nothing to do with the drum or how much force the drum is applied to the tire. It's a function of the tire's cross section area and air pressure. Jarno at BRR attempts to adjust for differences in casing tension for those tires tested under the CX/Gravel category. But his method is not perfect and it's only an estimation. So even the tires tested within the CX/Gravel category are not 100% comparable.

[zmjones]

Casing tension has nothing to do with the drum or how much force the drum is applied to the tire. It's a function of the tire's cross section area and air pressure. Jarno at BRR attempts to adjust for differences in casing tension for those tires tested under the CX/Gravel category. But his method is not perfect and it's only an estimation. So even the tires tested within the CX/Gravel category are not 100% comparable.

aren't those two factors the only reason different tires tested on the same drum would be incomparable? if not what am i missing?

[pdlpsher1]

Casing tension has nothing to do with the drum or how much force the drum is applied to the tire. It's a function of the tire's cross section area and air pressure. Jarno at BRR attempts to adjust for differences in casing tension for those tires tested under the CX/Gravel category. But his method is not perfect and it's only an estimation. So even the tires tested within the CX/Gravel category are not 100% comparable.

aren't those two factors the only reason different tires tested on the same drum would be incomparable? if not what am i missing?

This in-depth article will answer all of your questions. Jarno uses the term 'spring'. 'Spring' rate is directly correlated to a tire's casing tension. In a nutshell, to make a narrow tire's Crr comparable to a wide tire's Crr, one has to adjust the air pressure (hence casing tension). Jarno only adjust the tire pressure for tires tested WITHIN the CX/Gravel tire category. He doesn't adjust the Crr results for tires tested ACROSS different tire categories. I hope this helps.

https://www.bicyclerollingresistance.co ... comparison

[FlatlandClimber]

Tires from different categories are NOT comparable. If you really believe they are, then you should get this tire, which has been tested to be the fastest 40mm tire tested on BRR if you go by their chart on the right

Trust me. Don't get the Speed King. If you want something faster than the Gravel H get the Conti Terra Speed 40mm. It uses the same fast compound as the Speed King.

https://www.bicyclerollingresistance.co ... otion-2016

According to BRR, different categories are comparable. To quote: "My (educated) guess for a tubeless Marathon Almotion TL-Easy is 15.0 watts at an air pressure of 60 psi / 4 bars which makes this tire competitive with some of the fastest road bike tires while offering a much higher puncture resistance."

I don't want the outright fastest tire, but a fat Mountainbike tire with more knobs that's just about as fast as The Pirelli would have been amazing. More grip, more comfort, better cornering, not notably slower.

If course he has to run lower air pressure on the wider tires. I would definitely run lower air pressure. If I had to critique one thing about BRR it would definitely be that his results are consistently too good for high pressure.

[Marin]

Pure rolling resistance will always decease with increasing pressure.

Lower pressure means the rider's mass is better isolated from road shock, so less energy is lost in shaking your body.

My own rolldown tests are in our undeground car park which has a quite bad surface with lots of cracks an irregularities, and even with my fat ass on the bike, lower pressure is NEVER faster.

This might be different for very rough roads a higher speeds, and especially for gravel - plus there's fatigue too that might be lower with more cushioning. But you're not measuring pure rolling resistance anymore when you're looking at these things!

[FlatlandClimber]

I am absolutely surprised myself and my experience so far has been, that 27.5 usually feel very sluggish. However, I have only made experience with 650b that are heavily treaded and heavy in weight.
I have no experience (yet) with supposedly fast MTB tires like the race king.
On the other hand, I must say that I have never experienced any gravel tire that is nearly as nimble and rolls as well as the Pirelli Gravel H (45c).Schwalbe Pro One Allround (40c) and Maxxis Re-Fuse (40c) feel loads slower (whereby the latter is hardly surprising).

[Steve Curtis]

If it bothers you guys so much, why not invite the CRR guy to the forum for a q&a ?
Settle it once and for all.

[tritiltheend]

Pure rolling resistance will always decease with increasing pressure.

Lower pressure means the rider's mass is better isolated from road shock, so less energy is lost in shaking your body.

My own rolldown tests are in our undeground car park which has a quite bad surface with lots of cracks an irregularities, and even with my fat ass on the bike, lower pressure is NEVER faster.

This might be different for very rough roads a higher speeds, and especially for gravel - plus there's fatigue too that might be lower with more cushioning. But you're not measuring pure rolling resistance anymore when you're looking at these things!

It seems you're defining rolling resistance as "resistance as measured on a perfectly smooth drum". In that case, then yes, higher pressure means lower rolling resistance. Such tests are useful in terms of comparing how much is lost from just the deformation of the casing and tread. In the real world, though, it's a lot more complicated. If you think of rolling resistance as resistance to forward movement from rolling on the riding surface (i.ei., excluding aerodynamics of the tire), things look a lot different. Tom Ahnalt and Josh Poertner have done a lot of real world testing that clearly shows that on even relatively smooth pavement excessive pressure can cause a significant increase in rolling resistance due to the inability of the tire to absorb small irregularities. There's also a lot of data indicating that the rougher the surface, that wider tires at lower pressure have an increasing advantage, which is also pretty obvious out in the real world.

I've recently run both Conti Terra speed 40c tires that measure 40mm wide, and WTB Resolute 42c tires that actually measure 45mm wide on my rims. It's clear on pavement that the Conti has lower rolling resistance, but once I'm off road the WTB tire is clearly faster as it better absorbs rough surfaces. If I was going to ride mostly pavement, the Conti would be faster, but it doesn't take much additional offroad before the significant advantage the WTB tire has will overwhelm the losses on pavement. I'd also note that the increased rolling resistance is primarily noticeable on paved hills, when aerodynamics are no longer the main source of resistance. A slower tire will feel heavier on paved hills, but most of what you are feeling is usually the additional rolling resistance. In the case of the WTB vs. the Conti, the WTB feels heavy on the paved hills but the half pound of extra weight they add is really trivial in terms of the total mass being pushed up the hill.

I think BRR is a good resource but you have to use a good amount of judgement in interpreting the results. Even the road tires require interpretation as they use butyl tubes for testing tubed clincher tires, which puts them at a disadvantage to tubeless. If you run latex tubes in your clinchers then the ranking order changes significantly vs. tubeless.

It gets very complex when you start comparing gravel tires of widely varying width and tread pattern. It's a challenge to fairly normalize different widths and the different optimal pressure, and of course tread pattern for unpaved surfaces adds a huge additional element. I think they try the best they can but I think there's still a lot to learn about how to properly quantify this stuff. I'd use their tests as just one useful data point and not as a definitive test as to how the tires will perform in the real world.

[Marin]

It's clear on pavement that the Conti has lower rolling resistance, but once I'm off road the WTB tire is clearly faster

How do you know this?