Can anyone point me to a controlled study on gravel tires and optimal pressure from a watts expended perspective? I presume the gravel causes a lot of deflection so it’s likely very different calculus compared to road. Does one reach a point of diminishing returns going very low (<30 psi on a 35mm)?
I know there’s a lot of variables in play, but curious if perhaps anyone on this forum has a powermeter hooked up to their gravel rig and done tests on their own??
I’m not aware of a study, but the limiting thing for pressure on gravel will be the likelihood of pinch flats.
I generally ride 40/45psi on 35mm gravel tires. Wouldn’t go lower.
I’ve pinch flatted a 2.4” rear MTB tire running at 25 psi … so no way I’d run below 30psi on a 35mm gravel tire (of course it depends on the quality of the gravel road, but where I ride, the gravel can get pretty gnarly in spots).
Note: I run tubeless in both MTB and gravel, and weigh 155lbs
Keep in mind that rider weight is a huge factor to consider for tire pressure. So, along with the tire size, knowing the rider weight is a critical detail in evaluating their settings vs your own.
Just anecdotal experience…but I recently did the 62 mile Barry Roubaix race. I’m 190lbs, had 40mm tires, ran 40psi in them, tubes. My impression was it was WAY too high. If I did it over again, I would have tried something 30-35 psi. It was fairly tame gravel. I really don’t think pinch flats are all that great a concern unless the gravel is pretty chopped up with potholes. And even then…you’re not going to have sharp edges like you do with asphalt. For what it’s worth, I race cyclocross on 35mm tires at under 35psi, and have never had a flat.
It was a pretty jittery ride the whole time in the gravel race. Back ended up being pretty sore the last 20 miles. With the amount of vibration and bouncing I felt the whole time, I’m pretty confident lower pressure would have been faster too. I ran the higher pressure because a decent portion of the race was on asphalt…but realistically, lower pressure would not have harmed me. Being a bit on the bigger side, I was passing people on downhill asphalt sections without pedaling anyway…I could have given up a few watts and just tucked in behind people on the pavement.
I’m 175 Pounds.
I’m running Panaracer Gravel King SK 35mm at 35psi front, 38 psi back.
Interesting. I run same size SKs. Given I’m about 7% lighter with rig I guess 32/35 would be my equivalent. That’s way less than the 40ish I run now on Tubeless. I’m all for additional comfort as a side benefit.
Thanks for the tips!
Pinch flats on tubeless? I Didn’t know that can happen. I think the difference between you and the others mentioned here is quality of gravel. Mine is really tame and smooth. Even asphalt like. I’ve heard more mountainous areas are a very different story.
Yup, you can pinch a tubeless. It’s tougher to do, compared to tubed, but very possible.
It’s one reason we see tire inserts becoming “a thing” for MTB tubeless setups.
I was running 40psi as well. Panaracer suggested 35/38 setup for the SK. Much more comfy and the rolling resistance is quite good.
I’ve only pinch flatted a tire once, but it was a pain to fix on the trail, so don’t want that to happen again!
I could get away with a lower pressure for gravel 99.x% of the time - but there are some short stretches on roads I ride on that are closer to jeep trail than to gravel… so I add a few psi just to on the safe side.
I’ve also had burping on gravel washboards. Like you say, not ride ending. Just lose some sealant.
I run low 20s on my cx tires, but they’re tubulars and I weigh around 145-147 in race season. For gravel, mid 30s have been pretty good for me on my cx wheels/setup tubeless.
It’s an interesting thought experiment, since rider weight is such a huge factor (take if from a Clydesdale). It seems to me that the way to formulate the experiment would be (rather than a specific tire pressure) to measure static tire deflection. That should put folks on an even playing field. For reference, on gravel, I run in the low 30’s with 2.3 front and 2.1 rear tires tubeless. anything less and I feel like I’m going to roll the tire off the rim cornering.
I have read a couple of articles that look at tire pressure based on tire deflection. Essentially they look at rim/axle drop (compression when loaded with the rider) to get the optimum pressure. It makes more sense overall, but is a hassle to evaluate and measure without special tools or help from another person.
The TR podcast with the Flo Cycling wheel guys was talking about attempts to measure casing tension inside the actual tire (it was Silca testing IIRC). This also could be a better way to setup a tire but it is even more complex to achieve.
For now, the pressure charts and experimentation are about the best we have.
It’s not a study per se, but it is some very detailed guidelines from a big name source, Enve, with variables for rider weight and rim and tire size:
https://gravelcyclist.com/bicycle-tech/gravel-bike-tyre-tire-pressure-guidelines-by-enve-composites/
It’s based on their rims, but if you have similar internal rim and tire widths it should be easy to extrapolate.
That chart makes sense to me. I actually had pressure almost exactly in line with it for Barry Roubaix before I chickened out and put about 8 psi back in haha.
https://blog.silca.cc/road-to-roubaix-the-complete-story-1-0
https://blog.silca.cc/asymmetric-effects-of-tire-pressure-optimization
and more articles on this on their web site