Final drive/ABS/crown wheel/?

[Hann]

Does anyone know for sure whether the 2.75 33/12 final drive of a 1200/1250 RT has the same number of ABS sensor pulse segments on the back face of the crown wheel as the 2.91 32/11 crown wheel of a 1200/1250 GS?
2013 onwards models, drive on the nearside.

The pickup segments as seen here;

 

[Santa-2512]

Does anyone know for sure whether the 2.75 33/12 final drive of a 1200/1250 RT has the same number of ABS sensor pulse segments on the back face of the crown wheel as the 2.91 32/11 crown wheel of a 1200/1250 GS?
2013 onwards models, drive on the nearside.

The pickup segments as seen here;

You need to be a bit more specific,

2x model revisions per year , so month of manufacture for parts you have and are interested in will help

 

[Bem]

Realoem.com is your friend - spend an hour or two looking up the relevant part and part number, then compare. If its the same part number..............

 

[knutk]

Two crownwheels with different number of teeths (32 vs 33) wiil not have the same part number. Additionally, BMW no longer publish pertnumber for the internal gears for the LC bevel drive.

However, allow me to do a bit of logical guessing.
Since the crown wheel in both cases reflect the rpm of the rear wheel, it seems logical to keep the same number of pulse segments for both crownwheels. as the ABS is interested in rotation of the wheel rather than engine rpm. Also, the RT and GS share the same type of ABS ring on the frontwheel.

 

[Hann]

I have received info to the effect that the RT 2.75 (33T) has 49 segments and the GS 2.91 (32T) has 47....a difference of ~4%.
From looking at images of both types it looks like the sensor is located on the same radii and positioning on the final drive casing on both types so i don`t know why BMW added 2 additional segments for the 33T crown wheel even though i would assume it`s of a slightly larger diameter to account for one more tooth?
Does the sensor read both frequency and count? (how many times the segments that pass the sensor per second, say for ABS & road speed and the count/number of segment passes that calculte one complete rear wheel rotation for the odometer?)
Is a 4% error enough to throw the ABS electronics into a wobbly?
Can i live with a 4% error on top of the already slightly optomistic speedo (2mph when compared to GPS) and additional `fake` miles on the odo?
Is it worth the hassle just to have a few hundred rpm less when cruising, i`m betting this slight niggle of mine would never even occur to most GS LC owners....

 

[Hann]

I have received info to the effect that the RT 2.75 (33T) has 49 segments and the GS 2.91 (32T) has 47....a difference of ~4%.

Having finally got my mitts on an RT final drive i can confirm that both the 2.91 and 2.75 have the same number of pickup segments - 48...
The descrepancy in the numbers i recieved previously was probably down to the parts operative attempting to count the segments through the speed sensor hole in the case which is obscured by the wheel/disc flange so it is very easy to mis-count.

My heart sank on my first count as i counted one more than the 2.91, but subsequent checking resulted in the crown wheel having the same number as the GS, i then proceeded to re-count about half a dozen times just to make sure!
I was really pleased with this news as it meant that the final drive swap on my GSA would be `plug`n`play` with no potential issues with the ABS, speedo or odometer.
I did the swap today and took it for a test ride - as expected from the figures i calculated there is a difference of ~ 6% in both road speed and/or engine speed - quite a subtle change but noticeable and worth doing for someone like me who is ultra engine speed sensitive.

Before: 69mph @ 4000rpm. Or, 4060rpm @ 70mph.
After: 73mph @ 4000rpm. Or, 3835 @ 70mph.

When i first test rode a 1250 last year it was immediately apparent that it was slightly lower geared than the Hexhead i had at the time and i knew it would be a niggle - and it has been, hence my desire to do the swap.
No loss of driveability or throttle response was detected - the 1250 is more flexible than a 15 year-old double-jointed Russian gymnast and the huge glob of torque this motor is blessed with is more than enough to retain all the riding character it had before, after all, i`ve only made the bike have the exact same engine and drivetrain as an RT and BMW thought those were satisfactory...





I expect 99.9% of GSA owners will not even have noticed or be worried about this but for me it was deffo worth doing.
Previous to this swap my speedo was 2mph optimystic compared with the Satnav, the same descrepancy was seen after the RT drive was installed.
The engine speed and road speed corralate exactly on the TFT compared to the calculationss i made (as they did before) but interestingly if the speedo is 2mph optimystic that must also mean that the tacho is too. I`m not concerned about that, it`s just an observation..