# M3 CLS wheels & air box..



## marksmith (Aug 9, 2003)

*RGR lip.....*

Thanks for the photo. I have found different 3 images of the RGR which all have slight variations of the lip inset. (Tirereack, Blekkers and RGR.) The wheels on the CSL and indeed different (and the nicest.) Are there different incarnations of thre RGR?
-Does Bekkers sell BMW OE wheels or knockoffs?


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## Mr. The Edge (Dec 19, 2001)

marksmith said:


> Thanks for the photo. I have found different 3 images of the RGR which all have slight variations of the lip inset. (Tirereack, Blekkers and RGR.) The wheels on the CSL and indeed different (and the nicest.) Are there different incarnations of thre RGR?
> -Does Bekkers sell BMW OE wheels or knockoffs?


it just depends on wheel width and offset--that pic above is how they look on M3's though (E46's)


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## Pinecone (Apr 3, 2002)

JetBlack330i said:


> AFAIK, in the 330, 60mph comes in 2nd gear @6000rpm.
> Red line is @6250rmp. Any appreciable gear change would require an extra shift.They also use fat and sticky tires. They do burn outs to get even more grip.
> They do many other things, not just gears.True, but HP measures how much work you can do with that torque.
> If you want to go fast, you go up in gear (numerically lower). That multiplies HP, but divides torque by the same factor. That's a good point.
> ...


We are talking M3 here, not 330. But yes, if the 330 has to shift an extra time (2 - 3) to reach 60 the overall time will be longer, but the 1/4 mile may be faster, and the acceleration in any gear will be faster. Or you could go to gearing that moves 60 MPH to 6000 RPM in 3rd (not really street practical) and then the increase in accaleration will make up for the extra shift, that is what the serious drag people do. They do all 4 or 5 gears in the 1/4 mile.

As for the lower (higher numerical) drag ratios, see the above. If you put enough rear to top out exactly at redline in top gear at the end of a 1/4 mile, you will be quickest there.

Gearing does NOT change RW HP. It does change RW torque. This is because gearing also changes RPM at the same time it changes torque, in an equal but opposite manner. For example, if you have a 2 to 1 gear set, it doubles the torque, but halves the RPM. Since HP = (torque x rpm)/5252, then by doubling torque and halving the RPM you end up with the same HP ( (T1 x R1)/5252 = ((T1 x 2) x (R1/2))/5252 ).

What really makes the car accelerate is the area under the torque curve. Not HP. Take the S2000 versus an S52 M Roadster. Both come with 240 HP. But the M Roadster makes more torque throughout the range. The S2000 uses high RPM. The S2000 is lighter, but is slower 0-60. Why with the same HP, because of less area under the torque curve. HP can be a very rough guide to the area under the curve, but not always good enough.

This is also what makes the M3 so sneaky quick. The torque curve is almost flat from 2000 RPM to 6500 RPM (242 pound feet to a max of 266, back down to 243 at 6500, and it stil makes 220 at 7900 RPM). You never get a kick in the pants, but the cars just accelerates.

Gearing increaes torque at low speeds for faster acceleration. It doesn't move the power band of the engine as you seem to be saying ("Gearing simply takes from the high end and shifts it to the lower end."). It does trade off speed for greater torque and greater acceleration.


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## JetBlack330i (Feb 8, 2002)

The Dinan 3.15 diff that the original poster mentions was applied to his 330ci.
What I meant to say is exactly what you said.
The easiest to understand analogy I can think of is a bicycle. The person pedaling it (engine) is producing the same torque and power. The driving wheel will see increased torque, but at the expense of slower overall speed. It just converts one form of energy into another. It doesn't produce more. So if you gain energy somewhere, you must lose it somewhere else.
In the case of a bicycle, it's trivial that using a numericaly higher gear is clearly advantageous, because you want more torque at the wheel to help you launch. My point is that in a car when I already can spin the wheels in place at launch, that may not be so obvious. Because you loose speed, will what you gain at launch make up for that loss when you hit the 60 or 100mph marker? I think BMW already optimized the gear ratio for 0-60, a very important marketing number.
I think we both are saying the same thing, but I focus on the engine and you on the wheels. On the engine side, that equation you mention does show increased power (you force the engine to work at higher rpms). Again, gears are not making the engine produce more power, it's making the engine work at a different rpm region (one that originally has more power) for the same speed.


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## Pinecone (Apr 3, 2002)

1) Put stickier rubber on, and you can no longer spin the tires and hook up the extra torque.

2) Can you spin the tires at say 10 MPH once you launch by pushing harder on the throttle? If so, you REALLY need better tires. 

Right at the start is a strange place. Too much torque will spin the tires, however a fraction of a second later, you can use all the torque you can get. But right at the start, you still need enough torque to accelerate from rest, which is a good bit. And there is the the rest of the run. My old Dodge Daytona Turbo Z was the other way, no starting line torque, so a few years later the conteporary Camaros and Mustang would beat it 0 - 60, but 5 - 60 it still ruled.

BMW gears their cars for launch. Every BMW I have looked at a gear-speed chart shows a BIG gap in 1 - 2 shift based on maintaining torque.

Normally the way you find the optimum shift point is to graph the torque delivered to the rear wheels. You shift when the torque in the lower gear falls to the torque delivered at the same road speed in the next gear.

In BMW street cars, the difference between the ratio of 1st and 2nd is MUCH greater than the ability to rev.

If BMW wanted to optimize for 0 - 60, 2nd would be much lower (set to shift near redline with perfect torque carry over), and then tune the rear ratio for to just make 60 at the top of 2nd.

Or they could move 1st higher to get the same result, but with a lower rear.

Or in an extreme case, take the 2 -3 shift, but move the band to just reach 60 in 3rd.

And since you don't always do a 0-60 run, you will feel more acceleration in EVERY gear with a lower rear ratio. That is why the oriingal post stated that the change in rear was the best bang for the buck.


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