14 replies to this topic

[Kaison]

Model: Rover Mini Sprite
Year: 1992
Description of problem (please be as in depth as possible):
I've been thinking about getting a nice set of 10" wheels for a while as they really suit the cars and look STUNNING!!

But I use to car to commute around 50 miles each way to college and most of it is on dual carriage ways so I'm usually going around 70ish most of the way there. - So having a high top-speed is important to me.

I'm know there's a basic calculation to find out the difference. . . but I don't know the actual ratio of 4th or the final drive and my mind isn't working great as I have the flu again.

I want to have the revs as low as possible at 70MPH in 4th.
I don't have a rev gauge so it's more by the sound and feel of the car.
At the moment it's not too bad. . . a little high but makes travelling around towns and the twisties more fun! - So how much will 2" affect the top speed?

[RayBoogs]

i changed from 12" to 10" wheels, and didn't notice that much of a change, it is a slight bit higher but not to make you think your engine is going to blow up

Jack

[Cooperman]

There is hardly any difference. The 10" wheels with 165 tyres are 70% profile and the 12" at 165 section are only 60% profile.
So the tyres are 10% of 16.5 cm larger in section depth with 10", which is about 0.65" against the 1" smaller radius, so the difference, i.e. reduction in rolling radius is about 0.35" when the tyres are new. A new 10" is virtually the same as a worn 12" in fact. With new tyres on 10" and 12", the difference is, from memory, about 3% lower gearing with the 10" wheel and 165/70x10 tyre.

[james962]

I'm on 10's, and with a 3.44 diff it's doing 4000rpm @ 70mph

[jimmyH]

I know there is a chap here with an MPI with 10's
Was wondering what RPM it sits at at 70. With my 12's its 3000 rpm at 70.

[Cooperman]

I'm on 10's, and with a 3.44 diff it's doing 4000rpm @ 70mph

On a 3.44 with 10" wheels it will be doing 16.5 mph/1000 rpm in top. I make that 66 mph. Probably speedo error, which is normal with the Mini.

[Cooperman]

I know there is a chap here with an MPI with 10's
Was wondering what RPM it sits at at 70. With my 12's its 3000 rpm at 70.

It all depends on the final drive ratio. 3000 rpm at 70 mph sounds like a 2.76, which is very high and tends to kill the acceleration a bit.
Personally I don't like diffs lower than 3.1:1 as that gives a good compromise between cruising revs and acceleration.

The revs at 70 between 10" and 12" wheels will not differ by more than about 3%, i.e. 90 rpm on 3000 rpm.

Edited by Cooperman, 31 October 2010 - 09:20 PM.

[MRA]

A simple test is to mark your tyre and the ground in the same place, now roll your Mini for one wheel rev, add a mark at the same place as the mark on your tyre, now measure the distance, change your wheel and tyre combination and do it all again, the difference will be your error, ie 3%

[ado15]

Reading the OP and since nobody else has mentioned it, you should be aware that you can't fit 10" wheels directly to your '92. You would need different front brakes to allow this.

[MinBinPat]

How do you think 10" wheels would work with 3.105 final drive?

[nicklouse]

How do you think 10" wheels would work with 3.105 final drive?

put your info into this and you will see exactly what changes.

 

http://www.guess-wor.../Tech/ratio.htm

[Cooperman]

How do you think 10" wheels would work with 3.105 final drive?

10" wheels are better with any final drive ratio.

[MinBinPat]

That's a great calculator, seems not much difference with 10". 

I'm gonna put 10s on with fiesta brakes, just for the fun of doing it...

[MinBinPat]

What are the thread sizes I need for the flexi hoses...

[MinBinPat]

No worries mini sport make the perfect hose for fiesta brakes....