Tires: Should we ride a width, or a pressure?

[Kontact]

The recent trend has been toward 25c tires for racers, because that smooths da bumps better than 23c. And I'm sure they do - for your average size racer.

I think we all are familiar with this:



What if the reason to ride 25s has nothing to do with their shape, and everything to do with their pressure? In other words, maybe your average 170 lbs pro (just grabbing a random number), has the best rolling resistance at 99 psi, and 99 psi dictates that you need the volume of a 25c tire when you weigh 170. But what about a 140 lbs rider? Should they also be riding 25s, but at 86 psi, or would it be better to stick to something closer to 99 psi and go down to a 23c tire?


If you think about tire psi being like the durometer of solid rubber or the preload on suspension a spring, it makes more sense to think that efficient shock absorbency comes at a particular psi.

Or maybe, it comes at a particular psi for each rider weight. Which may or may not follow the curves plotted in the graph for tire size vs. psi.

I think it is quite possible the fastest tire for someone who weighs 110 lbs might be a 20c tire run at 95 psi, rather than lugging around a bigger tire at pretty low pressure.

Or that a 200 lbs rider gets the best rolling resistance on 28s at 100 psi rather than 25c tires at 112 psi.


I have no data on this, just thinking about it and what tires actually do to conform to the road surface. And I'm also assuming something like road race use, where the goal is efficiency through rolling resistance, rather than all the other reasons there are to vary tire size and pressure.

[Bonesbrigade]

I always start the pressure I want to run and then that determines the width for my bikes.

I’m 140 pounds and I like my road pressure to be around 80psi, so I use 23mm tires. Unless I hit something square, I won’t pinch flat using this width and pressure and it’s quite comfortable. Keep in mind this is for smooth roads. 25mm tires and larger are slower for me on smooth surfaces.

The rougher the surface the lower the pressure and hence the wider the tire to prevent flatting. On my gravel bike I like 650x48 because I like to hit rough double track fast. This requires pressures around 25psi, so I need large enough volume to prevent flatting.

[shovelhd]

Both.

[Pastashop]

Because of the characteristic response time of the tire being much shorter than any other component providing suspension, the tire cross section (aka “width”) should be selected first, based on how large of a bump you want to be able to roll over at speed, without getting a flat (“puncture”) or a dent in the rim. Basically, prevent bottoming out.

Then, go with a pressure that’s high enough to keep the tire from wallowing, but low enough that it doesn’t blow off the rim, break the sidewall, or cause too harsh of a ride.

Then comes the overall, outer circumference...

[Kontact]

Originally Posted by Pastashop

Because of the characteristic response time of the tire being much shorter than any other component providing suspension, the tire cross section (aka “width”) should be selected first, based on how large of a bump you want to be able to roll over at speed, without getting a flat (“puncture”) or a dent in the rim. Basically, prevent bottoming out.

Then, go with a pressure that’s high enough to keep the tire from wallowing, but low enough that it doesn’t blow off the rim, break the sidewall, or cause too harsh of a ride.

Then comes the overall, outer circumference...

And what width is correct for road chatter, and how was that derived?

[ultraman6970]

Not a rant but all the time somebody had way too much time to do the calculation to built stuff like this and at the end, in racing world, pretty much everybody will run their tubulars between 85 and 120 psi w/o caring that much about how wide the tubulars are.

Looks like the table is talking about clinchers? I wouldnt run a clincher at 58 psi if i was 120 pounds less a tubular no matter how wide it is. One pot hole and the rim is gonzo.

[cribbit]

Been reading more about this wider tire lower pressure idea a bunch, interesting to learn about after always being beaten with the "21c or 23c at max pressure" ideology.

How do tubulars fit into this? I was once told the benefit of tubulars is being able to run higher pressures, and now we're supposed to run lower pressures?

[thwart]

I assume everyone is familiar with this chart.

Note the weights referred to here are on each wheel, not total bike weight.

[oldpotatoe]

Should 'we' ride a width or a pressure...that chart is dopey. >180 pounds, max pressure on sidewall? Balderdash..for 25mm Vottora Corsa Elite-85 psi and I'm .1 offa ton..When I rode Conti sprinters, same and their max is like a zillion psi or something(175??)..

[Kontact]

Originally Posted by oldpotatoe

Should 'we' ride a width or a pressure...that chart is dopey. >180 pounds, max pressure on sidewall? Balderdash..for 25mm Vottora Corsa Elite-85 psi and I'm .1 offa ton..When I rode Conti sprinters, same and their max is like a zillion psi or something(175??)..

I was about to post the table Thwart did, which is a more sensible approach.

[Dave B]

I am a huge fatty. I don't ride above 100psi on any size tire. Typically between 80 and 90.

I likes it comfy.


but I will say on cross tires I get a bit weird and probably pump them up too high.

[pjbaz]

Originally Posted by Dave B

I am a huge fatty. I don't ride above 100psi on any size tire. Typically between 80 and 90.

I likes it comfy.

but I will say on cross tires I get a bit weird and probably pump them up too high.

I totally understand ... I'm not a fatty - only 165 or so - and I run my road tires usually 100-105 in the front and 110 in the rear on 23mm Conti GP4000s. BUT on my CX bike I run them around 40 which is higher than I probably "should" lol

[Dave B]

Originally Posted by pjbaz

I totally understand ... I'm not a fatty - only 165 or so - and I run my road tires usually 100-105 in the front and 110 in the rear on 23mm Conti GP4000s. BUT on my CX bike I run them around 40 which is higher than I probably "should" lol

Yeah about that on cross tires, but why run the road tires so high? I would think you would feel everything on the road. Unless that is the purpose.

[pjbaz]

Originally Posted by Dave B

Yeah about that on cross tires, but why run the road tires so high? I would think you would feel everything on the road. Unless that is the purpose.

Habit more than anything. I've always run them that way and I've had very few issues. I don't need to monkey with things and create gremlins.

Mostly, I'm a curmudgeon

[pncguy]

Originally Posted by pjbaz

Mostly, I'm a curmudgeon

Let's be honest: how many of us aren't?