Hi guys, first of all, sitting here in Munich Germany, find a tire shop who has some knowledge is quite a challenge when it come to classic US cars I'd like to get new wheels on my ride, as those currently on are too modern, which on top put me at risk of getting pulled aside by the local police as they are not matching the history plate I'm having and some regulations that come along with Now, I know what kind of look and form I'd like to go for and know some basic details like bolt pattern and stuff, but in terms of size, backspacing etc., I'm totally lost. And then there seems to be something like matching the tire size for the speedometer and rear transmission/differential to still work properly (there is so much stuff to read out there which makes things often times more complicated *g) that is what I'm having today that is the type of wheels I'd like to go for that is the type of fitting I'd like to have (getting the car possibly slightly lowered at some point, and also having balloon like rims with white letters) so what I think to know is: - center bore 2 3/4 inch? - bolt pattern 5x 4 3/4 inch? - possibly 15" wheels, but what width? 15x10 or 15x8? possibly smaller in the front? - and what tire size to take? any suggestions or tipps?
Read through this thread first, http://www.v8buick.com/index.php?threads/what-tire-size-and-rim-combo-are-you-running.194022/ It will answer a lot of your questions.
thanks Larry for the link, I actually read the thread almost completely and am quite sure now that it will be 15x7 and 15x8. Regarding the backspacing I have to do some last measurements to make sure they fit, but that is another thing. What I'm left with is the tire size. I'd like to have something like 235/60 in the front and 275/60 in the rear. But what I found out is that the difference between stock and new radius (?) is quite a lot, so the speedometer will be off by quite a lot? Something like 7% ... Original tire size was 185/70R14 as far as I know. Is the speed shown at the speedo taken from the front or from the back axle of the car (or is it even mixture as I found out that there are multiple sensor in the car? And I've read somewhere that it's somewhat important to have the matching tires to the differential in the rear? could someone push me in the right direction for this topic the manual was not helping much ...
No, the original tire size for a 1972 Skylark was a G78-14. The optional tires you could order with a GS were G60-15's. A P245/60R-15 is very close to that G60-15. A 26.6" tire height will give you the correct speedometer reading assuming the transmission hasn't been changed at some point in the vehicle history. In any case, you can swap DRIVEN speedometer gears in the transmission pretty easily in most cases. Speedometer reads off the rear tires via the transmission. A P185/70R-14 is only 24.2" tall. Not only would that look pathetic on your car, but the speedometer would be way off. If you want to go with a P275/60R-15 out back and the 245/60R-15, that should look great. Or, you can just go P245/60R-15 all around.
thanks, Very good information! I think the transmission is not the same anymore. Following the mechanic who did a full rundown when the car arrived 2 years ago, it's a TH400, rather than a TH350 which should have been in the car when it left the factory. (But that I've never investigated my self , or did any proper research on yet ) interesting too. I'm now running on 255/40R18 which is a height of 26". 275/60R15 have a height of 28" and 235/60R15 have 26.1" Since I really want to get some wider tires on the rear, changing the gears might actually be necessary.
