vettecor

I have decided to go with 3:70 gears for my '77 TH-350. In fact they are being installed right now. I have also just replaced my rear tires with 255/60/15 SS20 Firestone Firehawks.

What type of errors will this cause for my speedometer and/or tach?


Thanks
Larry :seeya

rrent

Shouldn't change your tach - be it mechaincal or electric - its engine driven.

When I got the "nothing fancy"'77 - had had the 2.something:1 rear changed to a 3.55:1 - my speed showed much faster than I was going - speedo=65MPH car actually moving 50MPH or so. I changed out the gears in the tranny a couple of times - find a good Chevy counter guy and he can (or at least mine was able to) tell you the percentage the different gears will change and you just have to figure the percentage your gauge is off.

good luck
Ronnie

Chuck Harmon

Your tires are the correct diameter, but you didn't say what gears you are changing from. Divide your old gear ratio by 3.70. i.e. 3.08/3.70=83% If your speedometer reads 70mph, you are going 83% of that speed, ~58mph.

Chuck