9 replies to this topic

[28hodge]

So the rover mini 1275 coopers came as std with a 3.105fd on 12" wheels.

I have converted my resto onto 10" what I am trying to figure out is what that effectively does to the fd ratio?

I know it'll accelerate quicker and make more rpm noise on the mway but it's not a daily drive and its planned use will be 12car rallies.

Edited by 28hodge, 30 July 2016 - 01:42 PM.

[mini-geek]

As far as I know the rolling radius is the same.,

You can check on www.willtheyfit.com

[86mayfair]

As above, I don't have the figures but some people have posted them on the forum before. From memory, it's very, very similar

[alex-95]

yep not much difference

The actual rolling radius of 10", 12" and 13" wheels is not much different. The rolling radii are:

10" wheel with 145/80 x 10 = 9.56"
10" wheel with 165/70 x 10 = 9.54"
12" wheel with 165/60 x 12 = 9.89"
13" wheel with 175/50 x 13 = 9.95"

So the gearing on the 13" with 175/50 tyres compared to the 10" with 165/70 tyres is 4.08%. That's not a lot when you consider that tyre wear from new to 2 mm tread depth can alter this gearing by around 2% to 2.5% on the average tyre.
The reason cars with 10" wheels have better performance is because 10" wheels with 165 tyres have better handling and, certainly in the wet, better road holding.
Remember, "Faster into a corner + faster through the corner = faster all the way down the following straight", which equals better performance.

In tuning any car for better performance, the order of priorities has always been:
1. Improve brakes
2. Improve suspension & tyres
3. Up-grade engine.

To improve the brakes on any disc-braked Mini (except, perhaps, the 997 & 998 Coopers), all you need are better brake pads and good quality discs. Unless racing, you don't need 4-pot calipers or rear discs, or anything else the tuning shops would like you to spend your hard-earned cash on.

[28hodge]

That solves that then, might potentially put a bigger final drive in at a future date if I feel the need but hopefully the stock gearing will be ok, as I say it'll never be a daily so a bit of mway/dual carriageway discomfort will be fine.

Willtheyfit.com is a handy little website too, cheers for that.

[carbon]

3.1 final drive with a 1275 on 10 inch wheels works well all round.

 

Would not change for higher diff unless you spend a lot of time on the motorway.

[Magneto]

I had the 2:76 final drive in my Clubby and it cruised beautifully at 75 mph, 3400 rpm. However it was a little doggy in town, I think the 3.01 would be ideal....

[GraemeC]

I think you might find the 3.1 a bit high. It'll work, but a lower ratio will give you more punch through the gears in the lanes.
I use a 3.7 with an SW5 and still sometimes feel over geared.

[Spider]

I've tried a 3.2 and settled back on a 3.4.

 

I found the 3.2 just took that 'nippiness' out of them.

[28hodge]

3.1 final drive with a 1275 on 10 inch wheels works well all round.
 
Would not change for higher diff unless you spend a lot of time on the motorway.

Ah when I said higher diff I meant 3.44 which I know gears it down but is a higher number, sorry for confusing, won't be using anything higher than 3.1 as motorway cruising ability is a pretty low priority