1978 tire question
 

I currently have 225x70x15's mounted on 15x8 ralley wheels. I want to mount 225x60x15's in the front, and 235x60x15's in the rear.

Will this clear without any modifications?

Thanks.

RE: 1978 tire question
 

The first number is the "fatness" of the tire, the bulge between the rim and the tread. Your front bulge is the same, so you should have no issues there. Your rear bulge is going to be 10mm wider than what you currently have. That is less than 1/2 inch. So if you have 1/4" clearance on both sides now, you shouldn't have any problems. The second number is the "tallness" of the tire in relation to the bulge. 60 is 10 less than 70, so 10% of the bulge "shorter" from the rim out to the tread. your tire tread will be about 22/23mm closer to the rim, just under an inch. Closer is usually not an issue. :)

This combination will change your revolutions per mile though, so your speedo and odometer will not be the same.

rim to tread...
(225 * .70 / 25.4 ) == 6.2 inches
(225 * .60 / 25.4 ) == 5.3 inches

radius from center to tread.
6.2 + 15/2 = 13.7" radius from center to tread.
5.3 + 15/2 = 12.8" radius

circumference of tire (distance per rotation)
13.7 * 2 * 3.14 = 86.0 inches
12.8 * 2 * 3.14 = 80.3

So you'll be showing about 7.5% higher on your speedo than you are showing now at the same speed, and your odometer will be counting about 7.5% more miles for the same trip.

bill.

RE: 1978 tire question
 

I'm not so much worried about the speedo issue, as this car is a summertime weekend warrior that doesn't get a whole lot of miles put on it (I work in Metro Detroit, but live about an hour north of it, so driving it down to work doesn't appeal to me).

What I get out of this is that the rubber that I want to put on it, will work.

Thanks.

RE: 1978 tire question
 

I had 255/60-15 on the OEM rallys with no problems.