BMW 1 Series Coupe Forum / 1 Series Convertible Forum (1M / tii / 135i / 128i / Coupe / Cabrio / Hatchback) (BMW E82 E88 128i 130i 135i)
 





 

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      02-12-2010, 09:18 AM   #1
Evice
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Differential Ratio

Hello fellas.

Does anyone know the differential ratio for 128i ? I wasn't able to find this info.

I appriciate it if you could help

Thanks!
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      02-12-2010, 10:13 AM   #2
wnta135
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The 128A is 3.73 while the 128M is 3.23 from the data I found.
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      02-12-2010, 10:36 PM   #3
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awesome. thanks.
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      02-13-2010, 10:38 AM   #4
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The BMWUSA website has all the gearing info:

http://www.bmwusa.com/Standard/Conte...fications.aspx

(128i Coupe & Cabrio gearing are the same)

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      02-13-2010, 08:05 PM   #5
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Is Final Drive ratio = ratio on the differential ? I didn't know this.
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      02-14-2010, 11:16 AM   #6
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I believe you need to multiply the ratio of the transmission times the rear end to get the final drive ratio - the ratio between engine rotation and wheel rotation.

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      02-14-2010, 03:23 PM   #7
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The "Final Drive" ratios quote by BMW are the differential or "rear end" ratios. Multiplying that by each gearbox ratio will give you the "Overall Gear ratio" for each gear. (To further confuse matters, on most motorcycles, you must also multiply by the "Primary" ratio!).

So if you are comparing ratios between the MT & Steptronic, you need to do the multiplication for each gear to get the Overall Ratios - otherwise its apples to oranges.

Hope that helps.

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      02-15-2010, 12:45 PM   #8
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Thanks for all the explanations. The reason I asked this was, I am trying to calculate the optimum engine rpm for a good launch for a 128i. Basic rule of thumb I follow is that; tyres cannot respond with a forward force much greater than the weight that is on them, so they simply will spin if you stomp on the throttle..Well of then you are adding the weight trasfer to the back wheels, the distance from the ground to the center of wheel etc etc etc.. this calculation goes on )
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Last edited by Evice; 02-15-2010 at 12:55 PM..
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