Final Drive Ratio

I would like to find out the best diff ratio to run in a ZF in a gtd 40,I would like to achieve low rpm cruising. What speeds would a 4.22 diff with .705 5th gear give with 335zr17 pzero's be likely to give per 1000 r.p.m.?

Roy, I'd give that an estimate of about 28km/h or about 17mi/h.
You basically divide your revs by the gear ratio and then by the diff ratio.
Then you work out the circumference of the tyre, multiply it by the rpm of the tyre, multiply it by 60 and you get the km/h.
If anybody else can confirm or correct these figures, please do.
Help I was of assistance,
Adrian

26.3 MPH per 1,000 rpm

Free Virtual Engine Calculator


Jeff

Jeff,
Exactly which figures did you use with the engine simulator?
I got the same result as my initial calculations, but yours seems more realistic.
Regards,
Adrian

Hi all.
A peek at the Pirelli figures (www.thetirerack.com) reveals a revs per mile of 799, assuming you have 35 profile tires.
A little mathematics gets you the following-
1:1 gearing everywhere, 799 revs = a mile per minute, 60 mph!
1000 revs gives you 75.1 mph.
4.22 diff takes this to 17.79 mph
0.705 fifth gear moves this up to 25.23 per 1000 revs (or 40.64 kph)
Being Z rated tires, their rolling circumference barely alters at legal road speeds (the industry standard test is performed at, I believe, 40 mph).
So, a 100 mph cruise at a touch under 4000 rpm, and 60 mph at very close to 2,400 rpm.
Also, your maximum speed would almost certainly be limited by engine revs.



Rob

Jeff Frigo,

Did you ever live in Harvey, Illinois?

John

Thanks guys for your help, all Ive got to do is install it now!

Adrian:

Used 2.97 for gear ratio (4.22x.705) and 26.23" for tire height.

John:

Never lived in Harvey, but how about Glenwood? Graduated from HF in 1981

Jeff

Jeff,

One of my neighbors growing up was Jeff Frigo (from Harvey, Ill). Nice meeting you though and thanks for you GT40 input.

John