Calamari Marionette Ph.D
Join Date: Dec 2013
Location: Coeur d' Alene
Bikes: Gas Pipe Nerdcycles
Mentioned: 2 Post(s)
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Originally Posted by garage sale GT
If you have a large tire and a small tire and they both deform the same percent, then the volume of rubber undergoing hysteresis is larger in the large tire. Same shape change, greater size.
Exactly correct. That's why I said ~15%. That's also why I said extreme variations like 3% vs 30% wouldn't be fair.
This brings us full circle so I'll quote myself.
Originally Posted by SquidPuppet
A 50mm tire at 60psi will have less rolling resistance than a 35mm tire at 60psi due to less deformation.
^ That is an obvious exaggeration, and maybe close to a 3% vs 30% comparison. It's unfair, but it makes the point than an eqaulity can be found somwhere in between.
We both know we are not going to ride the small tire all mushy (massive rolling resistance) at 60psi, and we wouldn't ride the big tire inflated to (unnecessary) granite status. Where does that leave us? If we determined the perfect desired amount of energy required to roll the tire and defined it as "rolling resistance X", we would be able to achieve that with either tire by fine tuning pressure, but ultimately the large tire would require less. The result is the same rolling resistance, but better ride quality with the large tire. That's why I say that for noncompetetive cruising applications, nobody will notice a speed difference, but they will notice a bump absorbing difference.
I can't say I remember the exact number, but 14.83 MPH is stuck in my head for some reason as the threshold over which greater tire width started to suck up energy due to air drag. So folks interested recreational speedy riding would certainly benifit from narrow tires, and that's what I'd recommend.
Last edited by SquidPuppet; 08-18-14 at 04:35 PM.