Pro Series Tires

[Bam Bam]

Does anyone have the exact diameter of the Hoosier F1600 series tires at pressure? Mine are buried right now in the trailer & can't get to them but want to get the right info into my data system if possible.

[reidhazelton]

Food for thought, and something I wonder about....

I saw a car on a chassis dyno and was surprised how much the fat tire increased in diameter at high speeds due to the centrifugal force on it.

Anyone ever measure that or try to calculate it. Just curious....

[Lotus7]

laser ride height sensor + a bit of math.... :-)

[Dan Pyanowski]

Steve:
If you're looking for basic measurements, I measured mine this past weekend at the Glen, if that helps.
Fronts: 66.5" circ.
Rears: 70.25" circ.

[Neil_Roberts]

Originally Posted by reidhazelton

I saw a car on a chassis dyno and was surprised how much the fat tire increased in diameter at high speeds due to the centrifugal force on it.

Anyone ever measure that or try to calculate it. Just curious....

Of course! These numbers are for the club spec Hoosier C2500 FF rear:

0 mph loaded radius, measured at 18 psi cold = 10.75"
135 mph loaded radius, calculated at ~18 psi hot = 11.03"

That's a 0.56" diameter difference, about what I would expect from bias tires. The calculated radius is based on logged GPS speed and rpm at at point on the track where the vertical acceleration was 1.00 g.

These photos from way back when show that the diameter growth with speed is easily visible, both front and rear: