R1150GS GearingJuly, 2001I've heard that one of our own has modified his R1150GS gearing to be somewhat lower (cRAsH, you listening?). Perhaps we could coax a few words out of him on this subject. I personally would be interested in knowing:
1). How much lower first gear is post modification, I'd be happy to reduce the entire final drive ratio by 10% - 20%, but any change would be welcome. It kills me having to slip the clutch so much getting started on a slippery hill because 1st is so damn tall.
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Ok, here's the skinny.I took the final drive from an 1100GS and mounted it on my 1150. That changed the final to a 33/11 - a 3.0 ratio. The stock 1150 final is a 31/11.That means, in laymans terms, the shaft turns 3 times for the wheel to turn once. My take is that the marketing department told Hans to make a 6 speed because the 1100 needed more top end and they needed to sell the idea so folks would upgrade. Hans made a very nice 6 speed, but the difference in top-end wasn't enough to justify the cost for the bean-counters. Since the tranny mod was probably already in the works when this was discovered, the obvious solution was to change the ring gear for more "top end". On a faired bike, that works to a point. On the GS, you typically run out of ponies before you run out of gear because the GS is streamlined much like a brick. I think it was a last second knee-jerk reaction, because the 1150 RT has a 32/11 final. Why would it be geared lower than the GS???? Anyway, whatever the reason, we all know it's a joke. The gear ratios in the tranny are pretty well spaced to me, but I have a bias towards this bike. If you change 1st, you then have to change 2nd, then 3rd, somewhere the Piper has to be paid. Plus, digging in your trannies guts is not a job for the squemish, and is not an afternoon job. Changing the final drive ratio is, if you buy the drive as a unit. I got mine from the web for $300 - and it had many less miles than mine. Here's the write up I sent to the list: ************************************************ It all started out so well, then I realized I didn't HAVE a 12mm hex OR a 30 mm socket. Off to Sears. They were out. Orchard Supply, nada. 3 autoparts stores and an hour later, I find one. Cool, I head back home. Oh yeah, the thread lock has to be heated to 280 degrees. Crap, back to the store for a torch. Now we're cookin'... Get it put back together, hmmm, sure feels loose. Look at the old drive, I forgot to put the U joint in! DUH! Take it all apart, put the U joint in, now its dark and cold. ... to be continued tomorrow -- I need a beer.
DON'T HIRE THIS MECHANIC!
Wow.
Time to suit up, and see what I lost on the top end.
WAHOO!!! It works! Roll on (in 6th) from 90 - 120 = 10 seconds. Not bad atall. Seems like I didn't lose any top-end. I'm sure in a wind-free environment, or faired, it would be apparent, but not today. Today, I was very happy. My biggest complaint about the 1150 seems to have been fixed. Big sigh of relief. One unexpected treat - it's almost like I added 10 horsepower. It feels like it pulls stronger in every gear, the front wheel was hopping up easily on acceleration (no, I didn't wheelie for a half mile... or did I...?) All in all, an A+ upgrade.
Summary:What I did:Buy a used final drive from an 1100GS to install on my 1150GS (It actually had less miles than mine - go figure).
Why I did it:
Details: The rest, as they say, is history....
************* Lauren's Chart and comments ********
Gear R100GS R100GS R1100GS R1150GSC
1 4.40/4.66 4.25 4.16 3.86 The numbers after a slash are what I calculate to be a 6% overdrive or underdrive. Notice that the Guenther 6 speed with overdrive is fairly close to the R1150GS six speed with the exception of first gear which is probably more appropriately geared than the R1150GS first gear. A 6% percent underdrive would give the Oilhead six speed a first gear ratio of 4.09:1, and a 10% underdrive would be about 4.25:1 - which would probably be better since the R1150GS has a 2.82:1 final drive, which brings me to the next chart. To get the big picture on gearing a person should really know the overall gearing; the combination of transmission gearing and final drive. One of the reasons people notice the tall first gear in the new GS is that is has such a tall final drive (2.82:1 compared to the 3.0:1 of the R1100GS and 3.09:1 of the R100GS).
Gear R100GS R100GS R1100GS R1150GS
1 13.6/14.4 13.13 12.48 10.89 For the Airhead GS owners, you can see that the Guenther six speed without the taller sixth (he calls it an overdrive, but it would have to be less than a 1:1 ratio to be a true overdrive), is about equivalent to the standard five speed with a 6% taller fifth. The advantage would be that the gears are closer together, especially in the lower gears where I find second gear too high off-road. If the Guenther six speed were had with the 6% "overdrive" then the jump from fifth to sixth would be just about the the same as the jump from fourth to fifth on the five speed with the taller 6% "overdrive" - a jump I would not find objectionable as there is very little gap between the standard fourth and fifth now. For the Oilhead GS owners - you can now see why people complain about the tall first gear; the tall final gearing exacerbates the problem. My opinion is that the tall final gearing *is* the problem - not the tall first. This is a good close ratio box; except for the jump from fifth to sixth the ratios are even closer than the Guenther six speed - and I think the larger gap between fifth and sixth is about right, even better than the Guenther as I like my top gears to be tall and I think the 1150 can pull the gearing. I think BMW made a good choice of ratios in the box, but screwed up when they chose such a tall final drive. Notice what happens if they had left the final gearing at 3.0:
Gear R100GS R100GS R1100GS R1150GS
1 13.6/14.4 13.13 12.48 11.58 Now notice that first gear is about 6% lower as are all the other gears since that is the difference between the 2.82:1 and 3.0:1 final drives. You lose a little bit of top end but you still have a top gear that is 9% higher than the five speed on the R1100GS. The difference in the first gears drops from 13% to 7% - still a little taller, but probably manageable and maybe the best compromise that can be had. I guess what I am getting at is that it might be more worth your while to check out whether you can put 3.0:1 final gearing your 1150 than it would to pay someone like Guenther to make a custom gear set (as much as I want to keep Guenther in business - at least until I get my six speed ;-). Some more numbers I ran to see what I could expect for different rations with the Guenther six speed on my bike. All other remain the same and are shown for comparison.
Gear R100GS R100GS R1100GS R1150GS
1 13.6/14.4 12.75 12.48 11.58
Gear R100GS R100GS R1100GS R1150GS
1 13.6/14.4 11.99 12.48 11.58 Given these numbers I think I would choose the 3.0 final drive over the 2.82 final drive for even a well breathed on Airhead. Personally, after looking at the numbers, I think I would have dropped first gear down to nearer to 4.00:1 or left it at the 4.16:1 of the R1100GS and then used the 2.82:1 or 3.00:1 final drive. But that is not what they did, so people who have an R1150GS have three choices as I see it: 1) If they can, go with a 3.00:1 final drive - which I think would be the cheapest and easiest route. 2) Go ask Guenther what he can do - I would only do this if I wanted to keep the 2.82:1 final because I liked the way the bike performed in top gear with regards to RPM (I think dropping down to 3.00:1 may actually improve performance in sixth with regards to acceleration and top speed). 3) Leave it alone and learn to live with it. I have two six speed bikes - both dirt bikes (a DRS350 and a TLR200) - and I think the optimal spread is to have a first gear that is good for off-road, second gear that is spaced fairly close to first, and a third that is not spaced too far from second. Fourth, fifth, and sixth can be spread out more as I almost never ride in those gears off-road. Fifth and sixth should be spread out fairly good as those I use for cruising down the highway. One little note to make sure there is not confusion; as noted in my posts, a lot of bikes have a "primary gear reduction". The R1150GS has this primary reduction gear, as does my DRS350. This means that the transmission has a certain set of gear ratios internally, but the effective reduction ratios *coming out of the transmission* is not the ratio quoted; the ratio is that gear ratio multiplied by the *primary reduction ratio*. This is why you will often see two different sets of ratios quoted for a given bike - as there are for the R1150GS six speed. The difference between the two sets of ratios is the primary reduction - in the case of the R1150GS the primary reduction is approximately 1.9:1, and you must multiply all of the ratios by that that reduction to compare those ratios to the R1100GS ratios (unless you are very good at juggling ratios in your head) or you will be rather confused. To get the "big picture" I usually look at the "overall ratios" which are the *effective* transmission ratios, multiplied by the final drive reduction ratio. You could go even further and factor in tire size if you were comparing bikes/cars that had differenct sized wheels/tires, but for our purposes that is not needed.
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Calculated RPM vs. mphStock R1150GSFinal drive: 2.82
R1150GS
It uses stock BMW parts so it should be just as robust.
FWIW,
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