open your door... theres a sticker with tire sizes.... get that size...

will work out better for ya in the long run!!!

215/65-16'* won't screw the speedo up. Little narrower and a little taller, but probably not really noticeable. At least it would fill out the wheel wells....

Why we are here, I went form 225-60-16 to a 225-55-17 that going to jack with my stuff?

And won't the tranny suffer also?

Not really...

Shifting can be fubard though if wheel sizes are way off, IIRC The ol' BADSSEi with the blowzilla couldn't shift out of 2nd because it'* tires were too big, and the Redline/Speedo weren't matching up with the shift programs in the PCM. This obviously isn't the same thing..

Go 245\50\16. Your spedometer should only be off about 2-3 miles at 60.

MMBLF has given you the tools you need to figure this out. For example:

225mm is the tire width

multiply by .60 (the aspect ratio) to get the height of one side of the tire: 225 x .6 = 135mm

multiply the tire height by 2 for both sides of the tire: 135 x 2 =270mm

Convert to inches: 270mm / 25.4mm per inch = 10.63 inches

Add the diameter of the wheel: 16 + 10.63 = 26.63"

So, 26.63 inches is the height (or diameter) of the stock tire on the stock wheel

To determine speedometer error, calculate the distance the stock wheel and tire travels in one revolution = circumference of the tire on the wheel = 3.1416 x diameter = 3.1416 x 26.63 = 83.66 inches. Compare that to the new wheel and tire. For example 245/50/16

245x.5=122.5 122.5 x 2 = 245 245/25.4=9.65 in 9.65 +16 = 25.65" 25.65x3.1416= 80.58"

83.66 - 80.58 = 3.08/83.66=.0368 x100 = 3.7% speedometer error. At 65 mph, that'* equivalent to 65 x .037 = 2.4 mph slower true speed than speedometer indicates, just like nb_ssei said.

Comparing a new tire with 9/32" of tread to a worn out tire with 2/32" of tread, there is a difference in height of 14/32" = .4375" which corresponds to a difference in circumference of 3.1416 x .4375" = 1.37 inches. That would produce a speedometer difference of 1.37/83.66 = 1.65% or 1.1 mph difference at 65 mph.

I don't know if our speedometers are set to the mid-wear range of our stock tires and wheels so that when the tires are new, the speedometer reads a little slow, and when worn out, a little fast? My guess is the speedometer is correct for new tires. But, if you just compare one new tire/wheel to another, you will come close enough to figure out whether you want to live with the difference.

I hope someone will let me know if my arithmetic or logic is faulty.

Try one of the following calculators, it might help if you don't want to do the math yourself, but BB is on the money. Thanks Bill.


http://www.1010tires.com/TireSizeCalculator.asp



http://www.discounttire.com/dtcs/infoTireMath.dos



http://www.miata.net/garage/tirecalc.html

I've messed with countless tires on Bonnevilles and trust me, STOCK wins.

Get yourself some nice Yoko'*, BFG'*, or whatever you find suitable for your handling needs and run with it. I've had ugly wheel well gaps, smaller profiles running my speedo too fast, you name it.

I finally went back to some Yoko Z-rated tires with the stock 225/60/16 size and it ruled...until...you know.