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Author Topic: Tyre Inflation Pressure vs Handling  (Read 342 times)

Harvard

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Tyre Inflation Pressure vs Handling
« on: May 16, 2018, 10:38:00 AM »
Why does reducing tyre pressure improve handling?

This is just a theory:

 When the pressure in a tyre is reduced the contact patch is enlarged. The total dynamics of the rolling tyre start where the “rubber hits the road”. As such one half of the increase in the contact patch length is added to the mechanical trail there by increasing the straight line stability in the same manner as increasing the caster angle.

 (Mechanical Trail is the moment arm between the steering pivot point (fore) and the center of the contact patch (aft))

Ghostman

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Re: Tyre Inflation Pressure vs Handling
« Reply #1 on: May 16, 2018, 11:11:42 AM »
Are you an engineer? My head hurts after reading that.  :)  I have enough to think about already. I think there is a fine line to the right amount. I have experminted over the years and could never tell much difference with the + - 5 psi here or there vs weight. The road and ambient air temp can fluctuate the air pressure more than that. High pressure stiffer ride to low you get sidewall roll. I just stay at the recommendation on the coach anymore and seems to be fine over the years for me.
“Never be afraid to trust an unknown future to a known God.”

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Gary RV_Wizard

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Re: Tyre Inflation Pressure vs Handling
« Reply #2 on: May 16, 2018, 11:26:15 AM »
You can't make a statement like that unequivocally.   Reducing pressure doesn't necessarily improve it at all. It may even make it worse.   What generally improves handling is having the optimal pressure for the load. But even then, "optimal" is somewhat subjective in that it trades ride comfort for better control in cornering or lane tracking. And as ghostman says, that psi value can change from day to day with changes in ambient temperature, road surface temperature, changes in the weight load, etc.

But yes, the difference in the contact patch size is a major part of that change.  Other factors are sidewall stiffness, deforming of the tread pattern,  and probably a dozen other things a tire engineer could cite.  On my own coach, I optimized the front tire psi for highway cruising and found it deficient when I got onto a somewhat twisty road. Experimenting a bit, I found I need about 5 psi more pressure to get more predictable cornering manners, but the range for those better manners was fairly narrow, maybe +/- 3 psi. If I increased 10 psi, both the cornering and the straightaway ride comfort deteriorated.
« Last Edit: May 16, 2018, 11:27:57 AM by Gary RV_Wizard »
Gary
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Gary Brinck
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