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Old 03-30-2013, 09:44 PM   #1
Bluethumb OP
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Higher final drive for a G/S - ST Options?

What can I do to lower r.p.m.'s of a ST? At hiway speeds of 70 m.p.h., the engine is spinning about 1,000 more r.p.m.'s then my R100. I know of two ways to change the ratio of the final drive on a G/S - ST. One is with the higher 5th gear and the other is the optional final drive. The higher 5th gear is expensive from what I've read, the cost of the gear plus the time and expense of a rebuild. I thinK I've read it drops r.p.m.'s by 400-500. The optional final drive is NLA I believe, but if it is still available I'm guessing it's unbelievably expensive and I'm not sure how much it drops r.p.m.'s.

Is there another option? Is it possible to use a different FD and re-lace the rear hub to a ST rim?

Any other way to replace the final drive with another to drop engine speeds?
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Old 03-30-2013, 10:43 PM   #2
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Quote:
Originally Posted by Bluethumb View Post
What can I do to lower r.p.m.'s of a ST? At hiway speeds of 70 m.p.h., the engine is spinning about 1,000 more r.p.m.'s then my R100. I know of two ways to change the ratio of the final drive on a G/S - ST. One is with the higher 5th gear and the other is the optional final drive. The higher 5th gear is expensive from what I've read, the cost of the gear plus the time and expense of a rebuild. I thinK I've read it drops r.p.m.'s by 400-500. The optional final drive is NLA I believe, but if it is still available I'm guessing it's unbelievably expensive and I'm not sure how much it drops r.p.m.'s.

Is there another option? Is it possible to use a different FD and re-lace the rear hub to a ST rim?

Any other way to replace the final drive with another to drop engine speeds?
The issue is the three bolt hub. I dont think there is a spoke hub that will fit a four bolt FD with a higher ratio. You can't just change out the crown gear either, cause that's where the bolts fit.

By far, the best option is to add the tall 5th to the tranny. It's actually a very easy job. As I remember, its the low 1st that is a bitch because it goes into the intermediate shaft which requires many tons of force to press.
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Old 03-30-2013, 10:46 PM   #3
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...or the higher 32:10 ratio 3 lug mono final drive is still available new. They're basically non-existent on the used market.
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Old 03-31-2013, 04:44 AM   #4
Beemerboff
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Most of the hi 5 th gears are 5% higher - on a decent running motor you wouldnt know the difference unless someone told you.

Just fork out for a new 32/10 as AW says, and sell the three stud 37/11 - they are hard to find and sell for reasonable money.
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Old 03-31-2013, 08:38 AM   #5
Airhead Wrangler
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Originally Posted by Beemerboff View Post
Most of the hi 5 th gears are 5% higher - on a decent running motor you wouldnt know the difference unless someone told you.

Just fork out for a new 32/10 as AW says, and sell the three stud 37/11 - they are hard to find and sell for reasonable money.
Actually, I think the 32:10 works out to be about a 5% difference. It's 3-4 mph higher at 5000rpm. 78mph instead of 75mph. If you add a 5% taller 5th on top of that you'll get a 5th gear that's nearly identical to a R100GS final drive ratio, but the rest of your gears would be a bit lower.
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Old 03-31-2013, 03:58 PM   #6
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How do I track down Richie Moore? And hat do you mean by + 10?
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Old 03-31-2013, 05:19 PM   #7
Beemerboff
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AW -you are right on at five+ percent - somehow I had it in my head that 37/11 was 3.56 , but I just booted the Cray and you are correct.

BT, there is some tricky engineering in these gears - remember you are only changing one of a pair, so a change in gearing can only be accommodated in the size and profile of the tooth.

This is normal gear cutting practice, of course, as the sum of the number of teeth in the pairs in a normal box is rarely the same for all pairs, but there is a limit to how far you can go with any given gear, and it seems that most folk are happiest at 5% difference from the stock OEM gear.
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Old 03-31-2013, 05:24 PM   #8
AntonLargiader
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moorespeed.uk I think.

However, I would carefully consider your riding style before going to a drastically taller 5th gear. I personally like the "Four and a half speed" Airhead gearbox because it lets me downshift on the highway without changing the RPM all that much.

The ratio that I've seen that's higher than 5% involved all three helicals. I can get that gearset also, but I've only been asked for it one once.
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Old 03-31-2013, 06:44 AM   #9
Clay Spinner
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I concur with airhead wrangler.... I've been trying to find a 32:10 bevel for two years now... Not even a sniff. I've just had a higher 5th installed but if you are planning for only road use, Richie Moore of morespeed does a +10. Check out his site and email him.

Clay Spinner screwed with this post 03-31-2013 at 01:45 PM
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Old 04-02-2013, 04:36 AM   #10
StephenB
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Quote:
Originally Posted by Bluethumb View Post
What can I do to lower r.p.m.'s of a ST? At hiway speeds of 70 m.p.h., the engine is spinning about 1,000 more r.p.m.'s then my R100. I know of two ways to change the ratio of the final drive on a G/S - ST. One is with the higher 5th gear and the other is the optional final drive. The higher 5th gear is expensive from what I've read, the cost of the gear plus the time and expense of a rebuild. I thinK I've read it drops r.p.m.'s by 400-500. The optional final drive is NLA I believe, but if it is still available I'm guessing it's unbelievably expensive and I'm not sure how much it drops r.p.m.'s.

Is there another option? Is it possible to use a different FD and re-lace the rear hub to a ST rim?

Any other way to replace the final drive with another to drop engine speeds?
There is a solution that hasn't been mentioned yet: the adaptation of a 88-95 RxxGS rear wheel to a monolever 4-lug FD. That gives you three FD ratios from factory:37:11 (R80RT Mono), 32:10 (R100RT Mono) or 33:11 (R100RS Mono) . Details are here: http://www.stephenbottcher.net/BMW/rearconv.htm

Hope that helps, Stephen
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Old 04-03-2013, 11:04 AM   #11
bajaburro
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tall 5th

it's the best option for your bike.just lowers the rpm in 5th enough to make freeway riding a bit nicer.
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