Any Gearbox mathematicians here ?

[matt brighton]

I struggled to get CSE maths..... so any help gratefully received

What MPH per 1000 rpm should I see if I have a DK gearbox and run my massive balloon 225/80/14 tyres (yes 225/80)

or just what revs will i be seeing at 60/70/80 mph ?

I have a 2.0 subaru na engine

Thanks

Matt

[itchyfeet]

easier maths if you know what gearbox you have currently and what speed you get at say 3000prm in top gear ( assuming you have a rev counter)

then it's just look up the gearbox data and work out the ratio

[itchyfeet]

I passed two maths exams at school, CSE, O level, A/O level and A level

[matt brighton]

Thanks Itchyfeet...

Anyone else ?

Best

Matt

[slowcoach]

There are rpm calculators aren't there? (Using the tyre size, final drive etc)

[937carrera]

I converted my advanced finger counting knowledge into an excel spreadsheet a few years ago which I have deployed over a number of vehicles, and have quite a few T25 boxes pre filled so

DK box on your balloons, 21.5 mph / 1000 rpm in 4th

50 = 2326 rpm
60 = 2791 rpm
70 = 3256 rpm

80 you can do yourself

That's the simple maths done with, tyres are not solid items and they deflect, so the rolling radius is not as calculated. I did a bit of work on this for BigBadBob76 and reckon that in reality the gearing is about 3% lower (so revs are a bit higher for a given speed)

Now waiting for Aidan to come along

[diabolov]

Glad you did that spreadsheet Carrera, I can put my shoes and socks back on now

M

[matt brighton]

Thanks V much Carrera - that looks more relaxing than what I'm getting with my original gearbox

Just have to fit the thing now

[ZsZ]

its german, but can be figured out:
https://t3-infos.de/images/Getriebeauslegung.xls" onclick="window.open(this.href);return false;