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      08-19-2014, 05:23 PM   #1
M3ryder55
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How Do You Feel About Changing the Rear Gears?

Let me start off by saying this section of the forums is not my specialty nor is this topic I'm asking about

I'm sure many of you remember on the E46 and E9X generations, many people would change their gearing on their cars to get better acceleration (shorten their gearing I believe). The diffs would get swapped out for 4.10 or 3.90s I'm not sure, again not my area.

I never considered nor looked into it. I never did mainly because I did not want to overwork the engine being in high revs all the time. This time around it might be different.

Why?

Because the gearing stock on these cars is good, however up top the pull starts to die, 6th and 7th gear is completely useless (For DCT people). Even 5th gear is ehhh. The money gears are 2-4, 3rd gear is incredible. I haven't pushed the car yet, but 4th gear takes you to about 120mph from videos i've seen posted.

That leaves us with another 3 gears.

But my question is, will changing the rear gears improve the pull at higher speeds?

Again I apologize for my lack of understanding. I was just curious and wanted to get some input from what you guys feel.
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      08-20-2014, 01:25 AM   #2
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Quote:
Originally Posted by M3ryder55 View Post
Let me start off by saying this section of the forums is not my specialty nor is this topic I'm asking about

I'm sure many of you remember on the E46 and E9X generations, many people would change their gearing on their cars to get better acceleration (shorten their gearing I believe). The diffs would get swapped out for 4.10 or 3.90s I'm not sure, again not my area.

I never considered nor looked into it. I never did mainly because I did not want to overwork the engine being in high revs all the time. This time around it might be different.

Why?

Because the gearing stock on these cars is good, however up top the pull starts to die, 6th and 7th gear is completely useless (For DCT people). Even 5th gear is ehhh. The money gears are 2-4, 3rd gear is incredible. I haven't pushed the car yet, but 4th gear takes you to about 120mph from videos i've seen posted.

That leaves us with another 3 gears.

But my question is, will changing the rear gears improve the pull at higher speeds?

Again I apologize for my lack of understanding. I was just curious and wanted to get some input from what you guys feel.
Because of the power plateau generated by the S55, changing the final drive has a very low almost negligible impact on performance.

See my thread here where DCT gear ratios are discussed.

IMO it is not the final drive that needs to be altered to improve performance, but rather the individual gear ratios themselves. The improvement would not be huge though, and it certainly would not be worth the cost.
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      08-20-2014, 02:56 PM   #3
bruce.augenstein@comcast.
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Quote:
Originally Posted by M3ryder55 View Post
Let me start off by saying this section of the forums is not my specialty nor is this topic I'm asking about

I'm sure many of you remember on the E46 and E9X generations, many people would change their gearing on their cars to get better acceleration (shorten their gearing I believe). The diffs would get swapped out for 4.10 or 3.90s I'm not sure, again not my area.

I never considered nor looked into it. I never did mainly because I did not want to overwork the engine being in high revs all the time. This time around it might be different.

Why?

Because the gearing stock on these cars is good, however up top the pull starts to die, 6th and 7th gear is completely useless (For DCT people). Even 5th gear is ehhh. The money gears are 2-4, 3rd gear is incredible. I haven't pushed the car yet, but 4th gear takes you to about 120mph from videos i've seen posted.

That leaves us with another 3 gears.

But my question is, will changing the rear gears improve the pull at higher speeds?

Again I apologize for my lack of understanding. I was just curious and wanted to get some input from what you guys feel.
Generally speaking, and also specific to the new M cars, a change in final-drive gearing won't do much for acceleration. What it will do is make the car more lively in high gear out on the highway, since when you tickle the gas, you're starting out with more power due to increased revs. Therefore, your 60-90 MPH times will improve in high gear. There will be little to no advantage in top end acceleration, however. More on that below.

In a drag race, there will be little difference, just as in the E46 and E9X variants. In theory, the geared car will launch harder due to improved initial mechanical advantage and revs, but since these cars are pretty much traction limited even with stock gearing, the geared car will struggle that much harder to hook up. Once hooked up, however, the geared car will pull harder than the stock car - until it has to shift. Once the geared car is in second gear, the stocker will still be pulling hard in first, and will therefore then have an advantage - until it has to shift. Then the geared car has an advantage, until it has to shift. And so on.

The cars will trade advantages as each car shifts, but since the geared car will theoretically have the early advantage in each gear, it will tend to have an ET advantage, even if trap speeds are similar.

Approaching the top end, it will remain a see-saw battle, with one car perhaps having an advantage at 120 MPH, the other at 130, the first car at 140, then the other vehicle at 150, etc.

In short, it's gear spacing (in the transmission) that will most affect the top-end rush, not the final-drive gearing, and both transmissions in the M4 have nice, close gearing up there. In my opinion, forget about a final-drive gearing change.

What will affect the top-end rush is horsepower, pure and simple. Find your local chip shop and have at it.
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      08-20-2014, 05:31 PM   #4
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There weren't "many" to change gear ratios in the e90 M3.. On the f80 platform the turbo is most the reason for the feeling of "lack" of top end or the car running out of breath.. In the end, It all depends on what type of power band the user prefers. I feel with the f80 platform there many more variables for a specific power band, over the e90 platform.
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