How W I D E are you?

[Clean39T]

Originally Posted by benb

Actually I wonder how many of us use his tire pressure calculations/guidelines? I think some of his observations might make more sense if you're setting up the tires the same way he is.

I think that has a big effect with these wide tires.

I am a very strict adherent to hist tire pressure ideas.

I set up for 41% weight on the front and 59% weight on the back. That is a pretty big variation in pressure.

E.x. I said I have 26s and 32s on my two bikes respectively. Based on 41/59 I run these pressures, and I'm about 175lbs.

26c: 62psi front, 88psi rear
32c: 45psi front, 65psi rear

It works really well. Get the weight distribution right and you're running lower pressures without anything getting squishy or sloppy. It's seem absolutely nuts to me at this point to think I used to run equal pressure front & rear. That almost always leads to a really harsh ride on the front of the bike and a squishy rear tire.

Weight distribution is dynamic though - so you're only getting it "right" when riding in a straight line on flat ground and not braking or accelerating....no?

[prototoast]

Originally Posted by Clean39T

Weight distribution is dynamic though - so you're only getting it "right" when riding in a straight line on flat ground and not braking or accelerating....no?

Any tire pressure scheme would be generally subject to this critique.

[veggieburger]

700x23 on the road, same width for the last 15 years.

[benb]

Originally Posted by Clean39T

Weight distribution is dynamic though - so you're only getting it "right" when riding in a straight line on flat ground and not braking or accelerating....no?

It's pretty much wrong all the time if you stick with the time honored 50/50 distribution.

Once you get your particular distribution right IME you don't notice a squishy front tire when riding uphill, etc..

I think a lot of the time weight distribution shifting is probably overplayed. Pretty much no one can pull a wheelie at full speed on a road bike or even really shift the weight back. We spend an extremely small amount of time under really hard braking forces. The tires don't have much room to squish down to shift weight and we don't have suspension. Maybe under a full spring you put out enough power to shift weight back.. but we all get out of the saddle and transfer weight forward. I bet a lot of time we move our bodies around in ways that keep the distribution pretty even.

It's nothing like a motorcycle where the front suspension will squat down multiple inches under hard braking very frequently and the motor has enough power to lift the front wheel under hard acceleration up to really high speeds. (And motorcycles have really wildly different weight distribution compared to bicycles anyway cause the motor shifts the weight forward greatly.)

[Clean39T]

Originally Posted by benb

It's pretty much wrong all the time if you stick with the time honored 50/50 distribution.

Once you get your particular distribution right IME you don't notice a squishy front tire when riding uphill, etc..

I think a lot of the time weight distribution shifting is probably overplayed. Pretty much no one can pull a wheelie at full speed on a road bike or even really shift the weight back. We spend an extremely small amount of time under really hard braking forces. The tires don't have much room to squish down to shift weight and we don't have suspension. Maybe under a full spring you put out enough power to shift weight back.. but we all get out of the saddle and transfer weight forward. I bet a lot of time we move our bodies around in ways that keep the distribution pretty even.

It's nothing like a motorcycle where the front suspension will squat down multiple inches under hard braking very frequently and the motor has enough power to lift the front wheel under hard acceleration up to really high speeds. (And motorcycles have really wildly different weight distribution compared to bicycles anyway cause the motor shifts the weight forward greatly.)

True. Sorry for the red herring.

When I most notice the squish of too-soft tires is downhill cornering and hoofing up steep hills out of the saddle --- and when I most notice too-hard tires is riding in a straight line over rougher surfaces.

Gotta a pick a middle-ground I guess and live with it

[Duende]

38’s gravel - my frame won’t fit any bigger tires, but I’ve no complaints. Gets me through the rocky stuff... have yet to encounter any issues. Traction is solid.

25’s road - remarkably better than 23’s for my weight. Trying out some 28’s soon here though. We shall see.

[brewsmith]

Originally Posted by AngryScientist

i completely disagree with Jan on this one.

for my perception, 38mm is WAY too big for the road. i tried a set of the 38c compass tires for a while, and didnt like them at all. felt too sluggish to me, and worse, turning and handling felt imprecise and almost dangerous.

25c on the road is perfect for me.

Totally agree. I had some 38c Compass tires on the Hampsten for one ride and it was miserable, they felt heavy and sluggish even at higher pressures. To 30c Stada Biancas changed the ride 100% for the better

[DarkStar]

Originally Posted by simonov

On 700c wheels, I find anything over 32 to be sluggish and tractor like. For fast road riding, I still think 25 is the sweet spot and 28-30 for crappy roads without losing too much of that nimble feeling. When I wear out my last set of 38s, I'll never go that big on 700c wheels again.

Totally agree.

[benb]

Originally Posted by Clean39T

True. Sorry for the red herring.

When I most notice the squish of too-soft tires is downhill cornering and hoofing up steep hills out of the saddle --- and when I most notice too-hard tires is riding in a straight line over rougher surfaces.

Gotta a pick a middle-ground I guess and live with it

I went through a period where I started experimenting with lower pressures and if you're working on guesswork I think getting one tire wrong can make you think the other tire is wrong and then you're chasing your tail.

Jan's graph based on 15% drop is a really useful starting point. I think most of us will have a little fudge factor up or down based on preference and tire selection and such but the basic idea of calculating based on load on each tire is really sound.

For me the last step was increasing the rear tire pressure.. I was generally running it too low cause I was reluctant to go all the way to a 60% rear/40% front setup. It does seem really extreme when you start trying his recommendations. But often when the rear was too low for some reason it was tricking me and making me think something was wrong with the front.

[scottcw2]

How does that calculation vary based on rider weight?

[Hellgate]

Corsas in a 23 at 95 & 100 psi. I'm 156 these days. The roads I ride are in very good condition.

[benb]

It's based on this:

https://www.renehersecycles.com/wp-c...BQTireDrop.pdf

I have a spreadsheet I made that adds lines for additional tire sizes & provides a worksheet for you to calculate it based on your inputs. (Put in your weight, weight of bike, weight distribution, etc..)

I have shared the spreadsheet here before. I can try to do so again when I have access to it.

For me most of the fiddling had to do with the issue that it's not that easy to get a real measure of weight distribution. You can supposedly do it with 2 identical scales but I don't have that. I have also been for bike fittings where the high end fit bikes will measure it for you as the fit changes.. that's a good way to get an accurate # but it ignores the weight distribution of your actual bike, your tools, water, etc..

[merckx]

I am also in the 28-30 for road riding camp. I prefer fat tubs like the Vlaanderens and 30mm Corsa Controls. They still feel zippy, but have the cushy of a 35mm supple clincher like a Bon Jon.

[sparky33]

Some bikes&wheels feel zippy with 38s, some don't. It's the whole bike that feels good or not. Tires are one part of system.

[Hilltopperny]

Depends on the bike. My Drifter is running 35mm and they perform well on and off road. I ran 32s on my recently sold MRB and that performed exceptionally well with that setup.
My Great Divide sits on belgium+ with 28s and is my go to road bike. The Ottrott is on 25mm tires and still rides extremely well planted and comfortable and has room for 28s, but I just haven't felt a need for them.




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