Which final drive ratio should I run in my Classic Mini?

Followed closely by 'which camshaft should I choose?', the question of final drive ratios has become the most popular email request in the MED inbox. So let's dig into the numbers, and give our personal recommendations on what's best for your project. 

What is the final drive ratio, and why does it matter?

The final drive ratio is the number of teeth on the crownwheel divided by the number of teeth on the pinion. Classic Mini final drive ratios vary from 2.76:1 to 4.5:1.

The small pinion gear fits on one end of the gearbox mainshaft, and the large crownwheel gear is bolted directly to the differential. These two gears transmit the final rotational torque from the gearbox to the driveshafts/wheels. 



Transmitting from a small gear to a large gear reduces shaft speed, and therefore increases rotational torque - a process known as gear reduction.

Without gear reduction at the final drive, and the transmission as a whole, the A-Series engine would be placed under an unrealistic strain to try and drive the car. 

Without this reduction, each rotation of the crankshaft would translate to one rotation of the driveshafts, which multiplied by the diameter of the wheels and tyres, would equate to an enormous road speed.

We've done the maths, and with 10-inch wheels and the engine revving to 6000rpm, you'd be travelling at approximately 341mph...



Except that you wouldn't, given that it takes top fuel dragsters some 10,000+bhp to achieve such speeds on the 1/4-mile, and we're usually dealing with less than 100bhp. So this is where gear reduction comes into play, allowing engines with modest power output to drive a car at realistic speeds.    

Returning to the ratios we mentioned above, given the same 6000rpm engine speed and typical 10-inch wheels, road speed in fourth gear with the 2.76:1 final drive equates to around 124mph, while the 4.5:1 will give you just 76mph.

This gives an indication of the range of gearing, but not the full picture, as your brick-shaped Mini (albeit a small brick) will need an abundance of power to try and push through the air at 124mph. 

76mph on the other hand - even a standard 998 Mini should be able to achieve this, eventually, with a tail wind! 

The shorter the final drive gearing, the higher the number, and the less strain that's placed upon the engine to propel the Mini at a given speed. Shorter gearing will accelerate the car more quickly.

Think of using shorter gearing like going for a walk with little legs, and taller gearing having big long legs - you'll need more steps with little legs to cover the same distance, but each stride with your big long legs will take more effort.

Back to Minis, and it's not just a case of fitting the shortest gearing possible for the best performance, as it all depends on the application. Taller gearing will result in a higher top speed potential.

Cruising at very high RPM on the motorway for hours on end will not only test your patience, it won't help fuel economy or engine longevity one bit. There will always be some degree of compromise when choosing the perfect final drive ratio for your Mini.   

Does wheel size make a difference?

Absolutely, yes - the larger the overall wheel and tyre diameter, the further the car will travel per revolution.

A larger wheel and tyre has a larger rolling circumference, so your gearing will become taller, giving a lower engine RPM for a specific road speed. 

Say we change the tyres from 165/70/10 to 175/50/13 - the rolling circumference has increased by 4.16%.

At 6000rpm in fourth gear, with a 3.44:1 final drive on 10-inch wheels, the Mini will be doing 99mph. Swap to 13-inch wheels, and at the same 6000rpm it will now be doing 103mph, potentially. 

To flip this around, 70mph on 10s will see you humming along at 4238rpm, whereas the 13s will lower this to a slightly more comfortable 4067rpm.

But I have a different gearset to standard - does this matter?

Yes, but only when using 1st to 3rd gear, as fourth is always a fixed 1:1 ratio, whereby the pinion gear is driven at the same speed as the input gear.

There were various different gearsets fitted by the factory during the Mini's 41-year production run, to suit the performance characteristics of the particular model. 

This in itself would be worthy of a secondary blog post - we should come back to this in future if there's enough interest in the subject!

For the purpose of this feature on final drives, it's worth just mentioning close-ratio gearsets, as fitted to certain Mini 1275 GT and Cooper S models, plus all aftermarket straight-cut gearsets thereafter.

These sets juggle the ratios between first and third gear by making first gear taller, so there is a smaller drop in engine RPM as you change up a gear. 

This is much better suited to use in a high performance Mini, like a rally car with a narrow power band, as it effectively keeps the engine singing in its optimum RPM window. 

If you back-to-back test a Mini with a standard gearset versus a close-ratio gearset, acceleration up through the gears always feels more brisk with the latter, as the RPM does not drop off by such a large amount on each gear change. 

The downside with a close-ratio gearset is that comparatively tall first gear - you need to be careful not to choose a combination of gearing that will leave you all at sea. See what we've done there?

With a tall final drive, close-ratio gearset and large wheels, acceleration off the line will be a struggle - you may even need to slip the clutch.

What's the perfect final drive ratio for a road Mini? 

Unfortunately, there is no one-size-fits-all, as your idea of the perfect road Mini could range from a factory-standard 850 on 10-inch wheels to an all-out fuel injected 1460 8-porter on 13s. 

For most, the sweet spot is between a 3.21:1 and 3.47:1.  

The key here is to match both the engine performance and the intended use of the Mini. A large-capacity engine with plenty of torque at lower RPM will be able to pull taller gearing much more comfortably than a small-capacity engine with all-or-nothing power delivery at high RPM.

Our general recommendation for a 1275-based B-road blaster with occasional jaunts on a motorway or A-road would be an MED straight-cut 3.47:1.  

Planning on venturing away on a longer road trip? We'd suggest running a 3.21:1. The A-Series is relatively comfortable buzzing along on the motorway at 3500-4000rpm.

We would resist the temptation to go taller than this if performance is important to you, as unless the engine is producing enormous low-down torque, a forced induction setup perhaps, this will severely blunt the car's acceleration. 

Below we've listed the estimated engine RPM in fourth gear at various road speeds, with 165/70/10 and 175/50/13 tyres.

Bear in mind that the Mini speedometer often under reads by some degree, so this is closer to actual road speed.

The table highlights how hard it would be to cruise at 70mph with a competition-orientated final drive ratio, compounded by the use of smaller 10" wheels.

Pulling 5500rpm at 70mph is not our idea of a fun day out!

At the other extreme, the tallest ratios will make the Mini feel sluggish around town, and you will likely need to change down to third gear for the hills. This would be no good for track outings or auto tests.

What's the perfect final drive ratio for a competition Mini? 

As a general rule, this will be a much shorter ratio than the gearing of a road-going Mini, to allow the engine to spend all of its time at a higher RPM level. Cruising comfort, fuel economy and engine longevity are not usually a concern on a race Mini, unless it's some kind of endurance event. 

Over the years we have found that 3.88:1 is best suited to circuit racing cars, while 4.2:1 works especially well in sprint/hillclimb Minis.

For a hardcore trackday Mini, take a look at our 3.75:1 gear set. 

Remember that a full-race A-Series engine typically produces peak power at 5000+ rpm, holding on until just over 8000rpm if the cylinder head modifications, camshaft and rotating assembly allow.

Anything taller than a 3.6:1 final drive ratio is unlikely to result in a competitive car, unless the circuit has exceptionally long straights. 

Even then, you may still achieve a faster lap time by simply backing off at the end of a long straight, making the time back in the corners. 

In the ideal scenario, you would reach maximum RPM in fourth gear at the end of the longest straight. In reality, unless you're only competing at one specific venue, some compromise will be required.

The following table is more useful for competition Mini gearing, giving an idea of the car's speed in fourth gear at 5000rpm and 8000rpm. Again this is assuming 165/70/10 and 175/50/13 size tyres.

We've omitted ratios any taller than the standard 3.44:1, because as you can see, the top speeds on a 3.44 are already unrealistic for any Mini on a race circuit.

For the same reason, we do not manufacture our straight-cut final drive gears in a taller ratio, as there is no demand.

It is worth noting that you can tweak the final drive gear ratios by altering the Mini's drop gears. We manufacture three different ratios - 1:1, 1:1.043 and 1:0.958. Simply multiply the final drive ratio by the drop gear ratio, and that will be your overall gearing.

We'll come back to this later, but in the meantime, we're here to help if you'd like any further help or advice on this, so stay in touch.