I came across this 1M for auction on carsandbids today (
https://carsandbids.com/auctions/rG5RyJqw/2011-bmw-1m ) and found this interesting comment from the seller regarding an aftermarket rear differential that he had installed:
"These cars were originally shipped with the M variable differential from the E9x M3 with the DCT transmission. The final drive ratio of 3.154:1 was well suited for Autobahn speeds but quite tall for North American roads and speeds,[although the total 369 ft lbs of torque available in boost/passing made up for this gearing ].
This car has a, new in 2020, M variable differential with a final drive ratio of 3.620:1. This is the same final drive ratio as the E46 M3 6 speed manual. Here are some speeds in various gears as per recent speedo and gps test.
2nd gear. 4000 rpm 39 mph/63 kph
3rd gear. 4000 rpm 58 mph/93 kph
4th gear. 3000 rpm 58 mph/93kph 4000 rpm 74 mph/119kph
5th gear. 3000 rpm 67 mph/108kph 4000 rpm 88mph/142kph
6th gear. 3000 rpm 78 mph/126kph 4000 rpm 102mph/165 kph
I have been thrilled with this upgrade. The driver is now able to enjoy using more of the 6 gears more often while accessing the power band sooner for quicker response and acceleration. It is fantastic!"
Just thought I'd toss this info into our 1addicts 1M forum for the 4 original owners left and the other 5 who regularly visit and post.