Quick tyre size, gear ratio question

[GRPABT1]

Hey guys this is just a quick one for the guys who are good with ratios and tyre sizes etc.

I'm running 235/75 X 15 on standard WT 1.3 gearing (1988 model with metal flairs) and I've had a set of 6.5 transfer gears sitting here in boxes for months waiting for a set of new pedes to suit. Now I was wondering if it would be feasable to run 6.5's on 235/75 tyres until I get the new tyres.

So what revs am I looking at in 5th at 100kph and in 4th and 60kph?

It's a twin cam GTi motor so a little extra revs (say 4000rpm at 100kph) is acceptable I think.

Thanks for your help guys/girls.

[Highway-Star]

Assuming the following:

5th gear = 0.864:1
High R = 1.7:1
Diff = 3.7:1
Tyre diametre = 0.733m


100km/h in 5th = 3967rpm

4th gear at 60km/h = 2754rpm.


Those numbers are assuming your tyres are exact size etc, so its ballpark anyway.

Some Sierra 5 speeds seem to have had a slightly higher 5th gear ratio, if yours is one then it may be better for you.
Some early wide tracks seem to have scored the 3.9 diffs, if thats the case it will rev more.

If you want an Excel spreadsheet that I do this with just PM me, and I can e-mail you the one I made.

[GRPABT1]

Thanks man, I knew one of you math whizzes would figure it out Sounds like I'm gonna put them gears in asap and get low get low get low hahaha