[XutvJet]

This is a bit technical so bear with me.

I've always found the M235 6MT gearing to be a bit long. Assuming 7,000 rpm shifts, 1st is good for 41mph, 2nd 72mph, and 3rd 109mph. Using numerous dynos as a basis, the calculated ideal shift points for a stock M235 6MT are 7,000rpms on the 1-2 and 2-3 and 6,700rpms on the 3-4. The M235 comes with a 3.08 gear. The M2 6MT comes with a 3.42 gear, but has 1" taller tires which negate much of the increased gearing. It's top speeds are 39mph, 68mph, and 103mph. If you were to give the M235 a 3.23 gear, it would have the same gearing as the M2.

Anyway, I'm looking into an LSD for my M235 and am debating whether I should build it with a deeper rear gear ratio (3.23 or 3.42). However, I do plan on adding a catted downpipe and some sort of mild piggyback tune. Both these mods will greatly increase torque in the low and mid range and elevates the entire powerband a bit (which greatly improves acceleration). Tunes tend to slightly reshape the powerband with peak power occuring in a lower rpms (~5800rpms vs ~6200rpms) and it appears that the ideal shifts points may shift downwards a few hundred rpms after a tune. Downpipes seems to not have this impact on the powerband.

A deeper gear ratio will also increase torque multiplication, giving the car more punch in the lower rpms. However, I also know that it's possible to over-gear a car to the point that you'll actually make it slower. Also, adding torque enhancing power mods like those noted above may negate the need for extra gearing. For many turbo, the torque spread is so wide that gearing isn't as important as say for a high winding naturally aspirated motor.

Million dollar question: I'm most interested in improved 2nd and 3rd acceleration. So for those of you that have tuned 6MTs, do you find the stock gearing to be better now that you have more low and midrange power?

[Dylan86]

I feel if I had a shorter 2/3 gear, I'd just inherit more wheelspin. With FBO/meth @16psi, I can hookup well in dry conditions, in 2nd gear. I think the only reason I can, is due to the longer gear. That said, If I weren't at this power level, the gear ratio could definitely be shortened.

Decisions , decisions.. lol

[aaaaah]

I'd keep the longer gearing so that I can easily and quietly sit at 75mph on the highway.

[Heitzer]

I have changed the gearing to 3.42 with a Wavetrac LSD. Tried a mild boost for a while (+4 psi) and actually took it out because I didn't help create more fun. If acceleration times are your goal you may feel differently.

The problem with modern cars and turbos in particular is that power comes to easy and there is less sensations of the speed. On the road and for commuting at least, less is more.

[CAMOETO]

A 3.23 gear may not be a bad idea, but I feel the car needs some wider tires even with stock power and gearing.

[amw896]

Coming from Japanese manuals, I absolutely love the long gearing in BMWs especially. Drove a few older models and always felt this way. Also, going FBO helps with the driving experience since you will get even more torque so u always feel like ur in the sweet spot. To touch on your question though, traction is the biggest issue with this car, even with the Mperf LSD. I'm FBO with BM3 tune on pump gas, pushing 370/420/whp/wtq and cannot maintain traction with DSC off in the first 2 gears. The torque is too much for the 245section rears to handle. That said, driving in sport+ is incredible. BM3 tune actually peaks 2psi higher in sport+ vs dsc off but the car is crazy good at putting the power down. You will love the extra power for sure but I would say set yourself up for wider and better tires and an lsd to put it all down.

[Maynard]

Don't know if this factors in, but I hear that many cars launch better from 2nd gear (first being done so fast that it isn't worth the shift time, and also better hook up from less wheelspin). Higher final drive ratio should be better for this, right?

[XutvJet]

Thanks for the responses everyone. It's a great help. After some deep thinking, I'm set on doing the OEM 3.08 geared M-Performance LSD (far far cheaper than building one) and keeping the stock gearing. I'm then going to do the HJS Euro catted DP (it looks completely OEM; I like that and am willing to pay more for that). Then I'll likely do the Dinantronics Sport and set it to 2 or 3 psi. All that should put the car in the ~340whp/360wtq range or similar to a stock M2.

I want to preserve as much driveability as possible all the while improving straight line acceleration a bit. I'm past having a blistering fast street car and have no desire to turn my M235 into a 400whp/500wtq coupe that has trouble keeping it's rear tires planted. I want to improve the balance of the M235 without much compromise and impact to it's use as a daily driver and street car. I want the power usable.

[CAMOETO]

Originally Posted by XutvJet

Thanks for the responses everyone. It's a great help. After some deep thinking, I'm set on doing the OEM 3.08 geared M-Performance LSD (far far cheaper than building one) and keeping the stock gearing. I'm then going to do the HJS Euro catted DP (it looks completely OEM; I like that and am willing to pay more for that). Then I'll likely do the Dinantronics Sport and set it to 2 or 3 psi. All that should put the car in the ~340whp/360wtq range or similar to a stock M2.

I want to preserve as much driveability as possible all the while improving straight line acceleration a bit. I'm past having a blistering fast street car and have no desire to turn my M235 into a 400whp/500wtq coupe that has trouble keeping it's rear tires planted. I want to improve the balance of the M235 without much compromise and impact to it's use as a daily driver and street car. I want the power usable.

I feel the same way. Mine is a RWD m240i with the MP LSD running ~ +4 PSI of boost. Even with the LSD, it's hard to put the power down in 1st without the nannies. This car is begging for at least 275 rear tires.