FD interchange

[ggfossen]

Are final drives for RTs and GSs interchangeable? An easy way to gear down the
'07 RT??

Gary

[deilenberger]

Are final drives for RTs and GSs interchangeable? An easy way to gear down the
'07 RT??

GaryYes.

[markgoodrich]

I'm curious, why would you want to do this?

[ggfossen]

Lower low, slower slow. I don't need 146 mph. I do need an absolute crawl, and a little less clutch burn on grades. We have a lot of steep roads. I don't think it would make a lot of difference on MPH, if I cared (and I don't), because I seldom really need 6th gear.

[markgoodrich]

I see, makes sense, thanks.

[ggfossen]

Mark,

In all probability, I will never get to the change. Too cheap. I do, though, scratch and ponder a lot.

I was disappointed that the bike was geared so high. I don't understand why as the top end is almost too much for even the autobahn.

If I'm not mistaken, the PD bikes are geared lower so they can go slower. I guess BMW never considered that many of us may want to crawl along in traffic, and start on steep grades. Lombard street is in the US, and not Germany. Come to think of it, it's one way down hill, but....???

It probably is possible to change just the gears, themselves, and not the entire final. It will take a bit more scratching and pondering.

And I meant MPG, and not MPH in the above

Gary

[Bokrijder]

The 850R final drive is a good choice, though probably difficult to find a used unit.
If buying used, be sure to ask if the unit is ABS or non ABS.
I bought a new 850 drive for my 02 1150GS and have been very pleased with the results.
The MPG numbers did not suffer. Off road - the clutch is much happier. High speed - the oil head loves RPMs.

Motard

[ggfossen]

Motorad,

I've never seen one of these taken down. Is it possible to change just the gears, themselves? Maybe like ring and pinion in autos? It seems that might offer a few more choices.

Gary

[PGlaves]

Motorad,

I've never seen one of these taken down. Is it possible to change just the gears, themselves? Maybe like ring and pinion in autos? It seems that might offer a few more choices.

Gary

Yes but the parts are fairly pricey. The combination of new parts, and the labor to properly set up the drive probably exceeds the cost of a new drive. A drive off a low mileage wreck would be my choice.

[ggfossen]

Paul,

Any idea what happens with the electronics, or speedo and such, if the ratios are changed?

Gary

[Bokrijder]

Paul is on the money. The new drive will run in the $900 range, but I feel that it was worth the cost.
My research revealed the 850R ratio to be the most effective, but it carried the downside of being difficult to find in a used unit. ( opinion based on my experience in searching for a used 850 drive)
Maybe someone can help with a recommendation which will help achieve your goal while being readily available on the used market.

Motard

No problems with speedo or electrics - just make sure that the drive is ABS compatible if required

[deilenberger]

The 850R final drive is a good choice, though probably difficult to find a used unit.
If buying used, be sure to ask if the unit is ABS or non ABS.
I bought a new 850 drive for my 02 1150GS and have been very pleased with the results.
The MPG numbers did not suffer. Off road - the clutch is much happier. High speed - the oil head loves RPMs.

MotardUnfortunately - the 850R drive is an older generation and will not fit a hexhead.. not even close actually.

[Bokrijder]

Unfortunately - the 850R drive is an older generation and will not fit a hexhead.. not even close actually.


That's what happens when one doesn't read the first post !!! -- My mistake, sorry



Motard

[PGlaves]

Paul,

Any idea what happens with the electronics, or speedo and such, if the ratios are changed?

Gary

Nothing happens as long as it is an ABS drive.

[ggfossen]

I was wondering about the interchangeability factor. I suspect one has to stay within the same generation of build. None the less, there seem to be several different ratios between the different bikes.

Perhaps the speed sensor is then incorporated in the anti-lock unit on the wheel, itself? If it is coming off anything in front of the changed FD, the reported speed would be incorrect, no?

I'm sort of stumbling, here, because this is not my field of expertise. Come to think of it, I don't have one. Ah, but I do tinker.

Thanks,

Gary

[deilenberger]

Gary,

Interesting point. The speed/ABS sensor is located in the rear drive, and reads off a "tone-wheel" (which is usually a slotted disk attached to the big gear the wheel bolts up to..) As the wheel turns - the tone disk turns 1:1..

Assuming the same tire diameter - the calibration wouldn't change with different ratios since they are reading the number of rotations of the rear-wheel - not interpolating it from the drive-shaft rotations.

If different size tire diameters are used (OD) on the RT vs GS - then I expect some calibration correction factor is plugged into the software on the computer(s) that run(s) the speedo/odometer/ABS-controller.

EDIT - the only time I could see this NOT being true - is if BMW had the sensor read the crown-gear teeth, and the number of teeth changed with drive ratio changes... dunno if this happens or just the pinion gear tooth count changes.. Unfortunately - the on-line parts catalog doesn't have detail on these parts..

[ggfossen]

Don,

I had not considered the possiblity of different tires, but I doubt that would be more than a couple of percentage points; not enough to really spoil the mix.

The more I delve into this, the curiouser and curiouser it becomes...and more interesting.

Bottom line, it actually is a viable possibility...if I ain't too cheap.

Gary

[AntonLargiader]

It would have to be from an '07 or later. The teeth for the speed sensor are different between IABS and IABS2. Count them on the front wheels some time.

[ggfossen]

Anton,

I will have to keep my eyes, and ears, open. This may be one of those projects that never gets done, but interesting to contemplate.

I have not experience any great difficulties with the higher ratios, but I sincerely believe, it would be more fun if they were a bit lower.

Thanks,

Gary