OT: Tire sizes

[217gsr]

Does anyone know how to calculate the rolling circumference (sp?) of a tire? I'm trying to compare a 195/55/15 (stock Michelin XGTV4) to a 205/40/16 (Kuhmo Ecsta).

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6 psi JRSC GSR: GSS-317, 3" intake -> 217 hp/155 ft-lbs.
New: BTC, MAP controller, and stock timing!
Soon: Endyn stepper?

[NeedToGoFASTER]

Well theoretically your middle number is the aspect ratio of the sidewalls, so 195/55 will give a sidewall height of 195*0.55=107.25mm.. Double this (one sidewall on each side) and add 15"*25.4, and you end up with 59.55cm.

For the other tires, 205 * .40 = 82mm, 16" * 25.4 = 406.4mm. 2 * 82mm + 406.4mm = 57.04 cm. So the Kuhmos should be about 1 inch smaller in overall diameter. All this is sort of approximate though.. Tire diameter changes over speed and wear. And I might not know what I'm talking about

Richard

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98 GSR driven everywhere.
Akimoto intake, MSD 6a, Magnecor 8.5mm, Autometer A/F,Boost,F/P, B&M F/P, NGK BKR7E, JRSC, JR MAP Mod, Walbro GSS-342.
Ex-Squeezer.

[217gsr]

That's exactly what I'm looking for. Doesn't this slightly change the actual mph's that are displayed on the speedometer? If a tire circumference is smaller (as in the case of the Kuhmo's), doesn't that mean for each unit of speed, the tire rotates a little bit LESS? So wouldn't that mean that not only are my MPH readings a little lower than my actual speed, but my odometer reading is also reading a little lower than actual?

Or it could be the other way around.



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6 psi JRSC GSR: GSS-317, 3" intake -> 217 hp/155 ft-lbs.
New: BTC, MAP controller, and stock timing!
Soon: Endyn stepper?

[2kbill]

A handy website with a tire upgrade calculator - mr2.com/FORMS/tire.html


Bill

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[217gsr]

Handy site. . . Thanks!

Now I can finally calculate my ACTUAL mileage.

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6 psi JRSC GSR: GSS-317, 3" intake -> 217 hp/155 ft-lbs.
New: BTC, MAP controller, and stock timing!
Soon: Endyn stepper?

[zip]

Anybody ever thought about using 195-50-15 tires on autocross and road racing events to increase your final drive by 3.2%? This multiplies your torque output!

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Innovator of the JRSC electronic boost controller
Mods

[JRCivic]

Smaller than stock diameter tires make your speedometer/odometer read faster than normal, and larger than stock diameter tires create slower than actual readings.


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'93 Civic Si H/B with B18C1, JRSC @ 8psi
Best 1320: 12.68 at 110 mph