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Does over inflation of tires slow the speed down?
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I generally train on 80-90psi. But, during an IM I pump them up to 115psi.
I remember several years ago I rode some solid tubeless tires, they were hard as a brick and were slow in regards to speed.
Wondering if there's a point in inflation of tires where you actually become slower.

Michael in Kansas
"Once you learn to quit, it becomes a habit"
"Its not whether you get knocked down, it's whether you get up" Lombardi
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Re: Does over inflation of tires slow the speed down? [jayhawk.] [ In reply to ]
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yes, lots of information on the board if you use search function. or go read the study silca did.
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Re: Does over inflation of tires slow the speed down? [jayhawk.] [ In reply to ]
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jayhawk. wrote:
I generally train on 80-90psi. But, during an IM I pump them up to 115psi.

I remember several years ago I rode some solid tubeless tires, they were hard as a brick and were slow in regards to speed.
Wondering if there's a point in inflation of tires where you actually become slower.


Short answer: yes

Longer answers:
https://silca.cc/...y-and-previous-works
https://silca.cc/...stance-and-impedance

http://bikeblather.blogspot.com/
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Re: Does over inflation of tires slow the speed down? [jayhawk.] [ In reply to ]
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Easy way to visualize this is take a small rock and try to roll a heavy wheel over it that has no pneumatic outer layer (think of the wheels of a train for example). The entire weight of the wheel will have to be lifted over the rock. The pneumatic wheel won't need to be lifted. The energy needed will go into deformation of the rubber around the rock and then back to normal. You'll feel it pushing the wheel, but it won't be that bad. The hard wheel, you have to fight gravity.

This is the extreme case. Obviouly a wheel inflated to 130 psi will still have pneumatic properties, but less so...the rougher the surface the worse the performance given all the irregularities the rubber has to deform/lift itself over. Both the energy going into "lifting" the bike and the energy going into deformation may be more.
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Re: Does over inflation of tires slow the speed down? [jayhawk.] [ In reply to ]
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jayhawk. wrote:
Wondering if there's a point in inflation of tires where you actually become slower.

Yes. If the tires are hard enough that the entire bike is getting vertically deflected by surface irregularities, the energy that becomes that deflection is coming from your forward momentum.

High-performance tires simply don't lose that much energy from being deformed against the ground as they roll, so if you're running fast tires at super-high pressures, the energy wasted buzzing the bike and rider can easily exceed what you're saving by making the tire stiff.
Since pumping a tire softer can also have comfort and handling benefits, erring on the squishy side is not a bad idea,
Last edited by: HTupolev: Aug 6, 18 15:58
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Re: Does over inflation of tires slow the speed down? [Sean H] [ In reply to ]
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Do you have a link for the Silca study?

Michael in Kansas
"Once you learn to quit, it becomes a habit"
"Its not whether you get knocked down, it's whether you get up" Lombardi
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Re: Does over inflation of tires slow the speed down? [jayhawk.] [ In reply to ]
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jayhawk. wrote:
Do you have a link for the Silca study?

Dudebro. Post 3.
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Re: Does over inflation of tires slow the speed down? [devashish_paul] [ In reply to ]
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devashish_paul wrote:
Easy way to visualize this is take a small rock and try to roll a heavy wheel over it that has no pneumatic outer layer (think of the wheels of a train for example). The entire weight of the wheel will have to be lifted over the rock. The pneumatic wheel won't need to be lifted. The energy needed will go into deformation of the rubber around the rock and then back to normal. You'll feel it pushing the wheel, but it won't be that bad. The hard wheel, you have to fight gravity.

This is the extreme case. Obviouly a wheel inflated to 130 psi will still have pneumatic properties, but less so...the rougher the surface the worse the performance given all the irregularities the rubber has to deform/lift itself over. Both the energy going into "lifting" the bike and the energy going into deformation may be more.

That's a good analogy.

There was a thread I created last year about tyre pressure. I was new to tubs and was tinkering around with different tyre pressure. I was training on tubs and was on 120 - 130 psi (Swachlbe Ultremo) and was racing on Vittoria Corsa Speeds on a similar pressure. I did a OD with 140 and they felt OK, they did a sprint at 150 and although they felt fine, I wasn't bouncing around, road surfaces were great, I rode slow. Perhaps it was an off day, not sure. But anyway I posted on here and got told "way too high", so am now down to 110 - 120. I haven't figured what the optimum tyre pressure is as there are lots of variables and lots of different opinions, but for me on perfect roads no higher than 120. I certainly didn't go quicker with higher tyre pressure past 120.
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Re: Does over inflation of tires slow the speed down? [Tom A.] [ In reply to ]
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There are two aspects of this issue that are usually neglected:

1) The psychological (and possible physiological) effects of a bumpier ride on power output. Somewhere, years ago, I saw a study on this. If your teeth are rattling from the bumps, your power output drops.... This bolsters the case for lower pressures.

2) The loss to "torsional resistance" (I'm not sure if that's the right term) on the drive wheel. This is probably not an issue for most triathletes/tters, who are typically riding in fast, high inertia, circumstances. But when you go uphill, things change....
The uneven force of pedaling up a steep hill gets translated more efficiently to forward motion if the tire is less pliant. In the hillclimb Crr tests I did years ago (5-10mph), it seemed like no pressure was too high. I got very good results in Mtb hillclimb races with tires inflated to 70-80 psi (3X what everyone else was using).

My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers
Last edited by: jens: Aug 6, 18 21:01
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