24 replies to this topic

[blacktulip]

a 3.1 crown and pinion will help you achieve your goal. they still pull good. maybe a good service and rolling road will benefit you too.

[Dale_]

a 3.1 crown and pinion will help you achieve your goal. they still pull good. maybe a good service and rolling road will benefit you too.

And with the 3.1 I won't notice a lot of difference in acceleration? :)

[CK's mini]

Any reason why wheel size hasn't been mentioned yet?

[blacktulip]

 

a 3.1 crown and pinion will help you achieve your goal. they still pull good. maybe a good service and rolling road will benefit you too.

And with the 3.1 I won't notice a lot of difference in acceleration? :)

 

i will be technically different but i dont think it will be bad enough to worry about.

[ACDodd]

If you want higher gearing an not loose acceleration its simple physics. If you increase the final drive gearing (in this context lower the number) you must increase average engine torque by the same amount. 5% increase in gear ratio needs 5% more engine torque to compensate.

[Cooperman]

Any reason why wheel size hasn't been mentioned yet?

Because it makes virtually no difference.

Do the maths: 145/80 x 10, 165/70 x 10, 145/70 x 12, 165/60 x 12, 175/50 x 13 are all within a few per cent the same in terms of rolling radius.

[Steve G]

In theory you could build a gearbox with more widely spaced ratios. If you had good spread of power/torque it would work.  I doubt that there are suitable parts available to do it though.

Was there ever a Mini or Metro with a 3 plus economy gearbox ?  I know a few manufacturers did one which was basically like a 5 speed with a missing 4th. 

[Tamworthbay]

In theory you could build a gearbox with more widely spaced ratios. If you had good spread of power/torque it would work.  I doubt that there are suitable parts available to do it though.
Was there ever a Mini or Metro with a 3 plus economy gearbox ?  I know a few manufacturers did one which was basically like a 5 speed with a missing 4th.

they tended to mess about with the FDR more from what I understand. My old City E would cruise at lowish revs at 70mph all day but wasn't the quickest off the mark.

[Dale_]

I have just been flicking through and I see that someone had posted this....


I have a 1330 with twin 1.25s, decent head etc and a Newman Phase 2 cam. It's brilliant but the top end is probably stiffled by the small carbs even though slightly Vizarded. The gearing is just right (3.44 diff) pulling to a genuine 72mph (more on the clock) at 6250rpm in 3rd at which point the torque at the wheels in top is the same.



Is that possible? 72 in 3rd?

[Cooperman]

That looks about right with a 3.44:1 FDR without doing the calculations. 6000 rpm in top is about 100 mph so long as there is the 80+ bhp to push it to that speed against the aerodynamic drag.

With a 3.1:1 FDR around 78 mph in 3rd should be possible.

Minis are old cars. They need to rev in order to go. The other problem with really high geared cars is that they can be faster in 3rd at high revs than in top because the gearing is too high to allow the engine to pull at best power in top. I know this may sound strange, but if peak power is at, say, 5500 rpm and gearing would mean the car would be doing, say, 110 mph at those revs, it will never pull to that speed in top, so the maximum speed might be much lower.

The question is how fast are you intending to cruise? You probably need to be using around 3800 rpm at 70 mph in top which equates nicely with a 3.1:1 FDR which is what many have advised. 

Now my modern car is cruising at 1750 rpm at 75 mph and will do 0 - 60 in about 7.2 seconds, but I would never expect an old and classic car to pull low revs at 75 mph or accelerate like that.

You can cruise a Mini at up to 4500 rpm as that is what used to be done when they were new cars and with a 3.1:1 FDR that will be over 80 mph.