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Thread: Final drive swap '06 GS to '05 RT

  1. #1
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    Final drive swap '06 GS to '05 RT

    Anybody done it? I am going to try running the FD from a '06 GS {2.82} gearing on my '05 RT {2.62} gearing. Not a huge difference but I expect to lose a little top end and fuel economy and gain a little more early and mid-range grunt. I am usually two-up and loaded anyways. Thoughts??
    Last edited by deilenberger; 03-03-2013 at 10:22 PM. Reason: added years to thread title

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    Lowering gear ratio on a R1200RT

    Crazy Horse I don't know if it is possable but would really like to do the same
    on my RT. It doesn't need a whole lot but any would sure make life easier starting from a stop.
    I doubt we are the only ones wondering if? I'm not convinced you'd lose economy, I spend lots of time
    on roads where limit is 55mph meaning I cruise in 5th (6th being too high) economy seems same.
    Will Stagg Central Coast of Commiefornia
    2012 R1200RT (most awesome unit)

    Yamaha TW200 adventure bikes (3) waay fun units

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    Lost again Texpaul's Avatar
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    I 'm doing something similar changing an '05 GS (2.82) to a HP 2 rear end (3.00). I know there are some issues with speed/abs ring but not sure on details. Might try www.motohank.com for some advice on what might work and what might need modification.
    Paul Mulhern
    MOA# 56330
    '05 1200GS Big Blue

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    Cam Killer marchyman's Avatar
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    If the bike has ABS you may start getting ABS errors. Don't know if a dealer can tell the ABS system that the drive ratio has been changed or not.

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    Tourmeister gr8ridn2's Avatar
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    Since the ABS and Speedo read wheel speed I don't think there will be any issues.
    2014 R1200 GSA W

    Riding is the art of throwing yourself at the ground and missing

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    A bozo on the bus deilenberger's Avatar
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    Dear Crazy Horse,

    Please look at: http://forums.bmwmoa.org/showthread.php?46055 - you were almost there with the models, so I added the years to the thread title. This might well make a difference in compatibility.. Please put both year/model in thread titles to the tech forums in future posts. Makes it easier for people who may have BTDT to spot your thread, and is useful later for people looking for the same info.

    Best,
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  7. #7
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by gr8ridn2 View Post
    Since the ABS and Speedo read wheel speed I don't think there will be any issues.
    This actually came up on a GS-911 specific mail list I'm on. Someone did this sort of swap and has been getting ABS errors since he did it. While both rear drives DO read rear-wheel speed, the calibration of the speedo cluster has to be matched to the gear-tooth count in the rear drive (since that's what the ABS/Speedo-sensor is sensing.. the big teeth on the crown gear, the number of which changes with a ratio change.) The ABS system determines wheel slippage by comparing the speed of the front and rear wheels relative to each other. With a different tooth count on the rear drive, the speed reading from the rear wheel will not be the same (at any given speed) as with the original drive - causing a likely ABS error condition.

    Since the GS-911 doesn't have the capability of recoding anything on the bike - there wasn't a good answer to the chaps problem. The general thinking was the instrument cluster had to be coded to believe it was installed in the bike the rear drive originally came in. It's unknown if the dealers computer system has the capability to do this coding.

    It will be interesting to see if this problem occurs with this swap.
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  8. #8
    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by Crazy Horse View Post
    Anybody done it? I am going to try running the FD from a '06 GS {2.82} gearing on my '05 RT {2.62} gearing. Not a huge difference but I expect to lose a little top end and fuel economy and gain a little more early and mid-range grunt. I am usually two-up and loaded anyways. Thoughts??
    If you want more low/mid torque, you could replace the stock o2 sensors with widebands. It's been done to good effect on a few 1150s now with more being started. I also know of three 1200 riders who are doing it. I've got a long thread in the Oilhead section on this topic.

    The other thing is there are some advanced-cam sprockets that are supposed to add low/mis range.

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    Is not being done to get more mid-range, rather to replace a trashed drive. Bought it marked as 2006 RT final drive only to find out it's from a GS. Gonna try and run it though cause spring is coming and I have 30 days to return the part to seller. Originally tried a FD from a '08-'09 RT and though the hardware all mounted up the sending unit is generation 2 and not gen. 1 like on the '05 so it would not read at all. No ABS or speedo. Sooo this is the second attempt. Should be mounted in the next day or so and I'll keep you posted if it was successful.

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    ABS trouble

    Quote Originally Posted by marchyman View Post
    If the bike has ABS you may start getting ABS errors. Don't know if a dealer can tell the ABS system that the drive ratio has been changed or not.
    If you are having trouble with the ABS after changing gear ratios in the final drive then you have something wrong with the ABS
    The ABS sensor reads the wheel speed are the lack of to determine if the front is different than the rear.
    It does not give a damn about what the engine rpm is are what the drive shaft speed is.
    You are not changing the wheel diameters and the abs ring should be the same.
    I would suspect that the mileage will increase with the slightly lower gear ratio when running loaded.
    Dave

  11. #11
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    I agree. You are changing the FINAL drive ratio, which affects the engine speed for a given road speed. If the ABS tone wheel and tooth count are the same, tire diameters are the same, the ABS should not sense any difference.

    With the tire sizes the same as stock, at any given speed they are still turning the same rpm front and rear until some slippage is detected. But the engine rpm in any given gear will be different than with the original final drive.

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    No real test yet cause of getting 6 inches of snow yesterday. Has been bench tested on the lift however and no faults up to about 20 MPH. I will update the thread when I get a chance to actually RIDE.

  13. #13
    A bozo on the bus deilenberger's Avatar
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    Andy and Dave...

    The rear drive speed sensor reads the dimples in the rear drive crown gear - they can be seen in the DIY on rebuilding a rear drive:

    http://forums.bmwmoa.org/showthread.php?66095

    I had assumed (like on many BMW cars) they used the actual teeth of the gear as the tone-wheel.. not the case on the R12 drive.

    There is no separate "tone wheel" - that's only used on the front wheel. The tone wheel is cast into the crown gear back. Question is - is the dimple count the same on the two gears? If it is - then there is no problem. Just based on what I've heard on the GS-911 list, this may not be the case. Based on what would make sense manufacturing these gears - the same dimple count would make sense (make a blank, then machine it for different gear ratios - and the dimples appear to be cast as part of the blank.)

    Proof is in the pudding - so I guess we have to wait until the bike is ridden (which probably won't happen this week in NJ..)
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  14. #14
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    dimples

    Quote Originally Posted by deilenberger View Post
    Andy and Dave...

    The rear drive speed sensor reads the dimples in the rear drive crown gear - they can be seen in the DIY on rebuilding a rear drive:

    http://forums.bmwmoa.org/showthread.php?66095

    I had assumed (like on many BMW cars) they used the actual teeth of the gear as the tone-wheel.. not the case on the R12 drive.

    There is no separate "tone wheel" - that's only used on the front wheel. The tone wheel is cast into the crown gear back. Question is - is the dimple count the same on the two gears? If it is - then there is no problem. Just based on what I've heard on the GS-911 list, this may not be the case. Based on what would make sense manufacturing these gears - the same dimple count would make sense (make a blank, then machine it for different gear ratios - and the dimples appear to be cast as part of the blank.)

    Proof is in the pudding - so I guess we have to wait until the bike is ridden (which probably won't happen this week in NJ..)
    I agree with you on the dimples they to my knowledge are the same on what ever ring and pinion you have.
    But with BMW German engineering I have been proven wrong before.
    Did not intend to state there was a ring on the rear only that the speeds are matched front to rear
    Dave

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    Hey ya'll just to update the thread, The RT has been out several times this spring despite really crappy weather and no faults to report in the final drive exchange. I cannot remember what I ran for RPM's before but now at 70 MPH in 5th gear I'm running about 4,500 and it drops to about 4,000 in 6th. All seems well,
    {fingers crossed}. See you on the road....

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