I picked up a 70 GS350 . The car has some old Firestones on it - 22 years old.I am wondering if anyone has any comments as to the size I was going to go back with that is on the car- 255/60 Front 275/60 rear.
I have those same sizes on my car. The optional tires on the 70-72 GS were G60-15 all around. The closest P Metric radial size is P245/60R-15. The 275 tires are 28" tall, about 1.5" taller. That size reduces (numerically) your gear ratio, and you will have a speedometer error if the speedo gears inside the transmission are not changed.
As it is a 350 with small cam, stage one intake, HEI and headers (the mystery motor has about 5000 miles on it )I would rather not put a back tire on it that would kill the gear I have. Im not sure what it is but given the rest on the car it would be whatever the 70 GS came with (3.42). Any thoughts as to if I should go back with. I may spray it later on with a 75hp kit......
245/60 15 is nominally the same height as a 295/50 15 (I run this combination). The 295 requires at least an eight inch rim and sufficient back space (4.5 inches comes to mind) to make it all fit in the hole. What's going on with your suspension? Got F41? The BIG ass rear tires definitely altered my handling (to my liking) pushing it further from neutral to slight understeer in combination with the Trans Am front sway bar. On the throttle at a right turn apex is a squared up holy-sh!t E-ticket ride.
Not familiar with F41....As Larry mentioned the 275 on the rear will work against the gear ; 245 may be a bit to wide- guess its like Goldie locks and the 3 bears...245/60/15 is factory all the way around..... Im understand 255front 275rear is common....why run different tires ?
I also run BadBrad’s combo for the best traction short of drag radials. As noted you’ll need 8 inch wheels on the rear and you won’t be able to rotate the tires. This may be your best choice for a hot 350 especially if you spray it later. But if you want to keep the same diameter as the original Poliglas tires all around on the stock 7 inch wheels the 245:60 x 15 is the way to go. But those 295/50s sure do look bad ass on the back!
F41 - heavy duty springs, front and rear stabilizer bars, boxed rear control arms. F40 heavy duty springs, front and rear stabilizer bars but a question if the stabilizer bars were of smaller diameter but no boxed rear control arms. .
I'd go 245/60R15 all the way around based on your comments/desires. '70 GS 350 would've orig. had 3.23 as std. exc. w/a manual transmission & trailer tow, then 3.64 posi. Otherwise, w/auto or manual, optional "performance axle" was 3.42 which could've been had in either open or posi.
Thank you. I went with the 245/60 , would like to fill the rear wells up a bit more but its okay for now ... It may have a 3.23 in it ( 2000 rpm @ 60mph) ...poor thing can't get out of its own way... any wisdom going to a 3:42 or 3:64 ?
350's like more gear. In my old 350 4-sp, I went from 3.23 to 3.42 to 3.73 and the went quicker (Inwas running it @ the track a lot) w/ea. change. I don't recall exactly how much quicker but a probably a couple to a few tenths. Next one is getting a 3.91.
Read Larry’s ‘supertune’ thread. A lot of seat of the pants improvement can be had with timing and distributor curve. Patrick
Lift rear end. In neutral, turn rear wheel exactly one turn while counting paint pen marked driveshaft revolutions. There's your gear ratio.....
Nope, that's the typical RPM at 60 MPH for the common 2.56. 336/26.6 X 2.56 X 60= 1940 RPM The 1970 cars came with a Buick only 8.2 10 bolt, or some Canadian cars came with a 12 bolt. Count the number of cover bolts. 2.56 was a common ratio. There are NO new gear sets for the 68-70 8.2.
I looked for the superfine thread , what came up where some posts that it had Benn moved...than again I am learning to maneuver around the website. if you know where I can find it let me know. Thanks, J
