fattie92

iv got 275/60/r15's in the back, connected to a 3.23 gear on my 84 TA. i was wondering how i can calculate how far off my spedo is.

Ricktpi

This might help:
http://www.chevytalk.com/tech/index.html
Click on Transmissions there & there is an article with links on how to calculate.

fattie92

thanks

SSC

Also, www.700r4.com/ has a calculator. If you use what tire size is supposed to be on the rear of your car and the new size it will tell you how many teeth difference on the driven gear. 1 tooth equals 1.8 to 2 mph difference.

fattie92

what was the normal tire size on a 84 ta???????

alex13507

or you could use the more precise method... do about 75 by a cop... in a 45... then subtract 10 from what he says!!!

sorry... had to say it...

fattie92

i must be a retard, cuase i cant figure this out. there isnt a way to figure out how many MPH your off?

Ricktpi

Here is another one:
http://www.fbody.com/calc.htm
Look at the last one on the page.

fattie92

who can put 275/60/r15 in inches?

SSC

I posted it last night, guess it diddent go through. Your supposed to have 215 65 r15 tires on stock 15in rims. Your new tires require 15 tooth drive gear and 35 tooth driven gear, or an 18 tooth drive and 42 tooth driven to be correct. The correct count for the stock 215 65 15's is an 18 tooth drive and 45 tooth driven. Your about 8MPH slow with your new tires.

fattie92

8mph slow all the time? or at a certian speed? i found out that 215's are 26inches in dia.. but what are 275s?

SSC

Your 8 MPH slow in every gear. The calculator @ the web site I gave you doesent need the metric size so 26 or what ever in doesent matter. What does matter is the fact you need a 42 tooth drive gear to correct the speedometer reading, since you should have the offset speedo housing, assuming your car came stock with those gears you just need an $8 part to get the correct speed.

Der91Z

iTrader: (1)

go on the highway and use the mile markers. Count one mile and see what your odometer saids.

fattie92

is it a pain to change the gear?

Der91Z

iTrader: (1)

it can be if you've never done it before, but theres a first for everything. Ask a near-by thirdgen.org member to give you a hand.

SSC

NO! Its very simple. All you need is a 10mm wrench, pliers, a jack and a jackstand. The housing that the speedometer cable goes into is what you need to remove and it only takes about 10 min to do the job. You need to make sure the speedometer housing is the offset one I mentioned. The standard housing is not offset and the 42 tooth driven gear will not fit but if your car came stock with the 3.23's it "SHOULD BE" an offset housing, GTG.