1. Cruising RPM is higher
2. Gas milage is less
3. More torque applied to the driveline
4. Top speed RPM limited
But - these negatives are very slight
1. The difference in cruising RPM is slight
2. People don't buy M5s for gas milage
3. Standard gears apply just as much torque, but in different gears.
4. With speed limiter, doesn't matter
__________________
-Bart
2002 Bluewater/caramel
Any other car is a compromise
I still cannot understand why anybody would care to spend money on this "upgrade."
1. The engine has a given amount of power (energy that it can put out per second).
2. You throw away about 15% of the power on the way to the ground.
3. The remaining power goes into kinetic energy (making the car go fast) and fighting the atmosphere (drag).
The gears add no power. The only argument on their behalf could be that they let you make better use of your power, i.e., one can have better shift-points on the HP curve, or something along those lines.... but can it be worth the money? Hardly.
Did anybody post zero to 60 and 100mph times with and without it? (Or, better yet, 1/4-mile times?) Is there *any* difference?
I can see spending the money on something cosmetic (19" wheels), useful (xenon HID fog lights, or [perhaps?] stage III), but this makes no sense.
The gears are expensive, but I had mine done last week, and the only issue I have is I wish I had done it sooner! The car feels much quicker - ride in one, and I think you'll feel what we've all been saying. Heard of anyone who has done the gears and NOT been happy?
Drag racers go to lower gears in order to come off the line harder and keep the car in its maximum HP and Torque RPM.
This is needed because of too much traction (drag slicks and suspension rework) or needing to be in a higher RPM off the line. Neither of these seems to be a problem with the M5.
And with a 6-speed, having the right gear is not that hard.
I would say the 1/4 mile speed would be exactly the same (a matter of HP/weight, not gears) and the ET would be very close as stock gears would be able to come off the line faster.
Now once rolling, by definition, you would always have a lower gear for any given speed. But the real acceleration story is torque times overall gear ratio.
So... If anyone wants to provide me with the HP and Torque figures for the RPM range for the M5 engine and the transmission gear ratios, I will calculate the torque "under the curve" and give you an average Torque number available for acceleration for both gearsets in different speed ranges.
__________________
-Bart
2002 Bluewater/caramel
Any other car is a compromise
I don't know if I have more wheelspin off the line with the 3:45s as I do not drag race the car. I have no problems launching the car with the new gears - if they were 4:11s, I think it would be a different story, but 3:45s really are not all that steep. Here's what Dinan has on their web site (http://dinanbmw.com):
"Dinan offers a 3.45 differential for the M5, featuring a shorter final drive ratio. The 3.45 final drive gearing takes advantage of torque multiplication, lowering the stock 3.15 gearing for a 9.5% increase in torque delivered to the ground. The improvement in acceleration comes with only a minor increase in engine speeds at cruise and no effective reduction in top speed."
BTW, I'm sure you know that many other HP cars come from the factory with gears at least as low as the 3:45s.
Those of you who are still pondering this upgrade are coming in at the wrong angle... ie: you are worried about stuff that is not important..
1) Gas consumption - now really? if you/we/I were/are worried about this?, you've obviously bought the wrong car! Prior to my 3.45 gear upgrade I was averaging about 13 mpg in mixed driving. I had been doing this on a consistent basis for over one year since purchasing the BEAST. I am now getting (after a month or two of driving the same way) about 12.2 mpg. I could probably get higher than that if I were to use 6th gear more often, but it is just so much fun in 3rd, 4th, and 5th!!
2) 0-60 times - who gives a crap? those numbers are always suspect anyway and are based on pristine conditions which typically don't exist much in the "real" world.
All I can say ...and those of you who have done the upgrade as I have can back me up... is the car FEELS and IS faster.
I agree that it is expensive... but if you ride in a car which has the new gears (Trust me on this!!!) - you will want the upgrade.
__________________
Andy
'00 Imola Red M5 - sold 4/02
'00 Mustang Cobra R - #155 of 300
'02 F-250 SD Powerstroke Crew Cab 4X4
'00 Honda Accord V6
Dinan 3:45 diff - can it be true?
if you/we/I were/are worried about this?, you've obviously bought the wrong car! Prior to my 3.45 gear upgrade I was averaging about 13 mpg in mixed driving. I had been doing this on a consistent basis for over one year since purchasing the BEAST. I am now getting (after a month or two of driving the same way) about 12.2 mpg. I could probably get higher than that if I were to use 6th gear more often, but it is just so much fun in 3rd, 4th, and 5th!! 
Ka-Ching!
Linear Mode
