Switching Tire Sizes

[MOPARJ]

I currently run a .030 over 318 with 8.5:1 compression, Comp XE268 cam, headers, Holley 600 carb, 904, 3.23 gears, and 2300-2500 tc in my 73 Duster. The tires on the rear currently are 235/70/15s, which are about 28" OD and 7.5" wide. I run SS leaf springs, so the rear sits up a tad.

I am looking into dropping the OD down a bit to lower the rolling resistance with the 3.23 gear.I dont want the car to be lower than exactly level. I was thinking of dropping to a 255/60/15, which is 27.1" tall, and 8.2" wide. Will this fit on a 73 Duster? Also, will it do a lot to raise revs on the hwy and result in slightly better performance at low rev acceleration on the street and times at the track? The key is I dont want to lose any width and dont want to have too short of a tire.

 

[abodyjoe]

going to a 27 inch tire will only lower the car a half inch...


here, play around here to see the rpm difference between tire sizes.. http://www.bigblockdart.com/techpages/speedtire.shtml

 

[dgc333]

A 255 tire is 10" wide, a 235 tire is 9.25" wide. The numbers you are stating must be the tread width. It's the actual cross section width that you need to worry about.

I have 255/60-15 on 8" wide rims on the back of my 68 Barracuda and they fit fine. As with any tire you put on the car the back spacing of the rim is going to have a big impact on how they fit. The 8" wide rims I have have 4.5" of back space which leaves more room to the outside of the wheel well and about 1/2" clearance to the spring. A wheel with 4" of back spacing would have allowed me to install a 275/60-15 tire.

 

[MOPARJ]

going to a 27 inch tire will only lower the car a half inch...


here, play around here to see the rpm difference between tire sizes.. http://www.bigblockdart.com/techpages/speedtire.shtml

I dont think it is so much the gain in revs that I am concerned about. I just wonder if it will help the low end launch any. I am running 15x8 Cragar SS wheels on the rear.