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Discussion Starter #1
I think I discovered a possible reason for the electronic governor on the speed. It has to due with the gear ratios.

From the recent Road & Track review (February) of the MINI Cooper.
1st 13.46
2nd 7.67
3rd 5.25
4th 4.15
5th 3.35

Given a 6750 readline, that had max speeds of:
1st 37mph
2nd 65mph
3rd 96mph
4th 121mph
5th 124mph (est at 5550)

From www.miniusa.com, the ratios for the Cooper S are:
1st 11.42
2nd 7.18
3rd 5.4
4th 4.4
5th 3.66
6th 2.97

If we figure that the speed (S) at any gear is equivalent to:

S = (RPM / Ratio) * K

Where K = some constant.

From the Road and Track numbers, it would appear that K is about 0.074.
1st ~43.7mph
2nd ~69.5mph
3rd ~92.5mph
4th ~113.5mph
5th ~136.4mph
6th ~168mph (theoretical, in a vacuum without governor engaged)

The fact that the top speed is limited to 135mph makes sense if you consider, how destructive it could be to the engine if the driver were to suddenly down shift into 5th while above ~137.

The Portland MINI dealership, is on a road (or will be in April) that has a couple of nice curves, while it cuts through a small canyon, on an unobstructed (No lights or merging lanes) uphill run onto the freeway. It should be a fun place to try a rolling start 2nd gear winding acceleration to 60. Demo car only of course. There's no way I would be that disrespectful to what will be someone's pride and joy. I know I want a low millage, right off the truck, car.

Cheers,
Brant
 

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Economy gear

I've always wondered why cars don't have an ultra-economy gear on them, so that if you're doing above about 80mph on the motorway then your revs would be down below 2500rpm. On cars like the S with a lot of torque they would be great at keeping the fuel economy sensible. Is there a legitimate reason why this couldn't happen? (other than the old conspiracy that motor manufacturers and fuel companies work together to keep them both in business!!!)
 

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There *used* to be such a gear - called "overdrive". Popular when cars had three, or occasionally four, gears. Oh, and on tractors, too (now that tells you something important :D )

It's key disadvantages were poor reliability, pushing up maintenance costs, and accelerated wear on the rest of the gearbox. A true fifth or sixth gear is more economical. Besides reliability, there is less drag factor induced in the 'box for reduced fuel consumption. I'm just old enough to remember overdrive-equipped cars - bought second-hand at the buyer's peril!

The six-speed box on the S should ensure comfortable M-way cruising without high revs as it is.

Overdrive - gone and deserves to be forgotten.
 

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My current car has an overdrive, .67 I believe, and have not had any problems with it. The car has a 318 V8 engine that I built up a bit and I get around 32-36 mpg on the freeway.
 

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Discussion Starter #5
I know what you mean. Decades ago, I used to have a car that was very under powered. But every once in a while, when I'd catch a good tail wind, I'd find myself looking for a 6th gear.

However, ever with the extra oomph in the Cooper S, I question it's ability to hold 80mph with such high gearing at only 2500 rpm instead of 3211 rpm.

To reach your suggested pairing, the last gear would have to have a final ration of ~2.3125. Seems about where 7th gear would be, given the spacing.

Although I believe it has been stated by MINI that the goal in designing the MINI wasn't to produce another economy box, but a fun and sporty vehicle.

I like (at least I think I will) the closer gears of the 6 in the S better than the 5 speed in the regular Cooper. Being closer means it will be easier to find a gear that allows you to keep its RPMs where most of the power is.

One thing I will be interested in though, for driving in town, is how strong the engine is at lower RPMs.

Cheers,
Brant

PS. Only 30 Days until USA launch.
 

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Discussion Starter #6
I Believe technically both the Cooper and S have "Overdrive." Basically it's where any gear combination provides a ratio of less than 1:1 to the drive shaft. I don't believe they were ever measured after the differential.

From the same R&T article on the Cooper

Ratios in the transmission:
1st 3.42
2nd 1.95
3rd 1.33
4th 1.05
5th 0.85 (Over Drive)


When you add back in the differential (3.94), the final drive ratios are:
1st 13.46
2nd 7.67
3rd 5.25
4th 4.15
5th 3.35

In my calculations all I had was the final ratios. If we assume the use of the same differential then we get figures similar to these:
1st 2.90
2nd 1.82
3rd 1.37
4th 1.12
5th 0.93 (Over Dirve)
6th 0.75 (Over Dirve)

That's a 12.79% gain in 6th gear speed at the same RPM's compared to a Cooper in 5th. You might also notice, the taller 1st gear in the S compared to the Cooper.

Cheers,
Brant
 

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The key difference between a final drive ratio of less than 1:1 and "overdrive" as fitted to cars in the 60's and 70's is the latter was effectively an extra gearbox fitted on the prop shaft after the main box.

As a result, the main gearbox had to do work it wasn't really designed for, and you had a second box of bits which wore out and went wrong. Plus it's a real problem if the driver dropped down a gear or two without disengaging overdrive first ("Your main shaft bearings have gone, mate. How much will it be to repair? I'm not sure you want to know ...").

A final gear (or gears) with a less than 1:1 ratio isn't particularly unusual, and the driver can drop down into lower gears without worrying about anything more than engine revs (I saw a Ferrari go from sixth to first once. The cylinder head went quite a long way ...)
 

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This is my bit.....

I believe the problem you will find is that if you leave a car pulling at very low revs in a tall gear that it actually can't accelerate in, you stand a very high chance of shredding the piston rings under the load. The Corvette ZR-1 used to have a 6th gear that would leave the motor revving at just over 1,000rpm at 70mph. It was bloomin' useless. If you tried to accelerate in it the load would outweigh the torque capacity of the motor and it would just hopelessly burn more fuel whilst you weren't going anywhere any quicker. A slight diversion.
By the way, the bit about overdrive being a second gearbox is not actually true. You'll find that a couple of manufacturers did that, such as Chevrolet yet again on the Corvette, but typically overdrive is just a gear that is geared exceptionally higher that the other ratios.

MitchyBoy;)
 

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Discussion Starter #9
I guess it's because I'm not as old as my gray hair would indicate. I didn't start legally driving until about 1982. So I missed the 60's and 70's.

Every car I've ever driven that had OD was an automatic, and OD was simply a 4th or 5th gear. Sounds like a part of automotive history worth missing.

As for the decapitated Ferrari engine, LOL, I had a hard time not envisioning Tim Alen and his magical mechanical mischief.
 

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The extra set of gears in a separate box was the way most British car companies did it in the 60's and 70's - certainly Triumph, MG and Austin Morris. Not sure about the UK-built Fords. The overdrive box was often located at the back of the car, after the prop-shaft on the input to the differential on the back axle.
 
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