[jimmey]

Hey Guys,

Just wondering if someone could give me a quick run down on the math behind working out revs from gear ratios and tyre sizes and what not?

For example I want to put an M15A (non VVT) motor with an M13A manual box and tranny running standard sierra diffs, pushin 30/31 inch tyres.
(In a 90ish model Wt Sierra)

so to my understanding it goes

M13A Ratios

1st 4.425
2nd 2.304
3rd 1.674
4th 1.190
5th 1.000
Reverse 5.151
Final gear ratio 3.416

Transfer gear ratio
High 1.320
Low 2.643


G13A Ratios

1st 3.652
2nd 1.947
3rd 1.423
4th 1.000
5th 0.864
Reverse 3.466
Final gear ratio 3.727

Transfer gear ratio
High 1.409
Low 2.268



Question 1:
This is really more of a "correct me if I'm wrong", but since the diff ratio is only out by roughly 0.500 on the M13A, everything should really be running in check through the whole drive line? like the M15A would be runnign at the correct revs (with stock tyres)?

Question 2:
Would the revs be higher or lower since the diff ratio is out by 0.005?

Questions 3:
How the hell do I work out all of this and then work out tyre sizes and what not?????


Cheers Guys!

Jimmy

[Marko_SJ]

Jimmy, do any of these calculators help?

http://www.rocky-road.com/calculator.html

On 30 inch tires, in 5th gear m13a box (1:1), Edit: I see you mean sierra transfer (1.4) ( and sierra WT diffs (3.7) I get 3480rpm at 60mph which is a bees dick near 100kmh.

This seems close to where my stock sierra (although spinning faster I think) was at 100 with 30s and no gearing IIRC.

Apologies if this is not what you were looking for.

[madmacca]

http://www.grimmjeeper.com/gears.html

try this one , has most zook boxes in the drop downs and gives revs to kmph

[Gwagensteve]

Do you have excel? Build your own - it's about 10 minutes work.

I use mine all the time.

Steve.

[jimmey]

Marko_SJ wrote:

Jimmy, do any of these calculators help?

http://www.rocky-road.com/calculator.html

On 30 inch tires, in 5th gear m13a box (1:1), Edit: I see you mean sierra transfer (1.4) ( and sierra WT diffs (3.7) I get 3480rpm at 60mph which is a bees dick near 100kmh.

This seems close to where my stock sierra (although spinning faster I think) was at 100 with 30s and no gearing IIRC.

Apologies if this is not what you were looking for.

Thanks so much!! this calculator works amazing!!

[Marko_SJ]

jimmey wrote:

Marko_SJ wrote:

Jimmy, do any of these calculators help?

http://www.rocky-road.com/calculator.html

On 30 inch tires, in 5th gear m13a box (1:1), Edit: I see you mean sierra transfer (1.4) ( and sierra WT diffs (3.7) I get 3480rpm at 60mph which is a bees dick near 100kmh.

This seems close to where my stock sierra (although spinning faster I think) was at 100 with 30s and no gearing IIRC.

Apologies if this is not what you were looking for.

Thanks so much!! this calculator works amazing!!

Glad to help the few times I can...