I have 295 50 15 on the back on a 1971 Monte Carlo SS 4.5 BS on the rim 8" wide rims 26.5 over all diameter the front i have 245 60 15 26.4" over all diameter. SEEMS weird to have different profile but once you take into consideration what the profile does to the actual width and tread of the tire you will see this looks correct. Fat tires 11.5 tread 12.5 bubble to bubble I think this is still with my 235 60 15 front tires still. Backs have always been 195 50 15
I got about 1.5" to the frame and 2.25" clearance to the body on the back tires with my current set up of P235/70r14 and 7" wide rims. I believe the 14x7 rims have 4" back spacing typically and I'm measuring that in mine. Of course the spare has 4.5"... Lol. Anyways I have a 9.25" section width of tire for a 235. a 255/60r15 would give me 10.04" of width and the same height of 27". a 255/60r14 still gives me 10.04" of width but the height drops to 26". A 275/60/15 is nearly 11" wide, and with 4.5" BS, that's 1.5" closer to the frame so that won't work. Still need to figure out the front clearance. I don't think I lose a whole lot of economy/cruising pleasure by going from 27" to 26" height. thinking BF Goodrich only has a 245/60/14 or 235/60/14 now. Ugh! Is a 255/60/r14 made for muscle cars?
All Gm Should be 4.25 back spacing.. 4" was for Corvettes Need to measure where the tire bead is. I can tell you, HOW EVER you measure do the same always- so you do not goof yourself up. JUST be careful when ordering RIMS as you will need to know how to measure your back spacing properly the way all wheel makers do. Jim
Thank you. Based on what you said, the first drawing below has the dimension arrows shown incorrectly (yellow rims) while the second drawing has the correct measurements, to the tire bead? It's confusing as jegs shows it to the outside of the rim. http://www.jegs.com/images/wheelmeasureguide.pdf
A 68 or 69 Skylark/GS is not the same as a 71 Monte Carlo. That combination you have will not fit on the 68-69 cars. You would need 5" minimum B.S. to fit that wide a tire.
PLEASE please remember all the measuring in the world will not help unless you know how far over the tire bubble will hang past the rim edge too. A Wider tread tire on a narroer rim will have more bubble past the rim edge on the inner and outer... A skinner or same width tread as the rim width will have much less bubble . Mine have alot of bubble as I put them on 8 or 8.5 inch wide rim with 11.50 inch tread. Ok? Jim
You are talking about section width, which in your 295 tire is 295mm, or 11.6". My point is that might fit on your Monte Carlo, but it definitely will not fit on a 68-69 Skylark/GS, not on a 8" wide rim with 4.5" B.S. It would on a 70-72 skylark /GS, but not on the 68-69.
Monte has the fender skirt like the 68 69 also... Jim Remember all the things that are different from car to car and how you restore your cars suspension. MAke sure your body is on true to the frame and rear springs can also raise and lower the rear suspension ride height etc. Measure your inner to outer fender and that is your max tire width side wall your going to fit. From there you can use a straight edge to from the drum up to the where your closest area would be for tire rubber on the outer fender. Measure how many inch to theouter fender and measure the how many inches to the inner fender and this will help you determine your backspacing needed.. Remember to measure BOTH sides as thery may be different from either body on frame issues OR from body work to the car. Jim JD
Yes, but I'm thinking the wheel wells are not the same Yes, good advice with any car, especially when you get near the limits, like using 10" wide wheels, or the maximum tire sizes.
I will confess I not read the whole thread, but it occurs to me if you have a 3.31 gear now, you just need to add a posi case to it, and your good to go. That's a great street gear for a Buick. JW
Thanks Jim, that's what I'm going to do for now. Then see how it launches and maybe widen the tires and/or tweak the height. I don't think I can get BF Goodrich 27" tires amy more for a 14" rim, so the 15" would help me gain width and keep the height if I want.
Pulled the differential cover off today. 43 ring gear teeth, 13 pinion gear teeth. (43/13) = 3.31 Definitely a 3.31 gear ratio here. 12 bolts on the ring gear. https://vimeo.com/139810400
Excellent driving gear. LEAVE IT. Jim Posi it and be done. NEW bearings should be at the top of the list.
Thanks! Are there any good videos/tutorials on how to do this? Someone whose done a few of these is going to do it and in helping, but I want to really understand what's going on before I get into it. Also, what kit should I be looking at? Could the bearings be good and not need replacing? Do they need to be pressed in? I'm very green on this stuff.
I have a web site that always gets forwarded on this forum. ALWAYS willing to help walk anyone through as long as time is not high priority. Remember your getting FREE set up info that would normally be paid for. Also being a full differential shop can sell you anything you need for the differential. rebuild kits for rears are in the 75-135.00 range for 12 bolt chevy The kits we sell have ALL the parts you need to setup the center section with out any part missing. www.jdrace.com is the link. Take care, Jim JD
