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Old 10-30-2012, 06:17 PM   #1
DiabloADV OP
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Final drive Q...

The two airheads I have (R60/5 in parts, and R90/6 "dirtbike" being restored) both came with 37/11 final drives. Am I right in thinking this ratio is not ideal for highway miles (ie, dualsport) on the R90/6 (which is actually 1000cc)?

What ratio drive should I look for for all-round riding (ride the highway to the trails, and then ride on the trails)? I can always keep one of these for a genuine offroad trip.

And...anybody want to trade me a higher ratio drive for one of these low ones?
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Old 10-30-2012, 06:41 PM   #2
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ratioring/pinion teethrpm @55mphrpm @70mphspeed @7200rpmspeedometer ratiousual model
2.9132/11305038811301.078R100
333/11314740051261.112R90S-R100
3.0934/11324141251221.144R90-R100/7
3.232/10335742731181.186R75-R80
3.3637/11352544861121.244R60-R75
3.4431/9360845921101.259
3.5632/9373447521061.318R60-R65
2.6234/13This was for racing, /5 and later
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Old 10-30-2012, 07:28 PM   #3
pommie john
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The normal drive on the 900s is a 33/11 some had a 32/11 but if you find one of them, sell it on ebay they're quite rare.
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Old 10-30-2012, 07:54 PM   #4
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pommie john, Which one are you saying is rare? All the RTs and RSs came with the 32/11, which in the day were called the Autobahn rear end as with it you got the highest top speed. The 33/11 was also very commonly found on a lot of other bikes, including some R90s and R100s. It was also a factory option for the R80s of 1978. I know of at least 3 R80s near by with the 33/11 and a lot more with the 32/10 and 2 that have the 37/11 which was called the Alpine rear end due to it being very popular with those that did a lot of mountain riding. In the mid 70s thru early 80s, you could order different rear ends on the bikes, if you were willing to wait for it to get shipped.

But, you could also pick your bike up at the factory or one of the dealers in Germany, back then as well. You just had to make the arrangements thru you local dealer and pay up front for it. I did just that in 1979 for a brand new R100RT, I got to ride it all over Europe with my wife, then take it back to them and they packed it up and arranged the shipping to Montreal where I picked it up again and road across Canada to home. They don't do that anymore, which is too bad. It was a great arrangement for a minimal extra cost. I think it was an additional $250 back then. Would probably be around $5000 now.
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Old 11-01-2012, 12:17 AM   #5
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Quote:
Originally Posted by DaveBall View Post
pommie john, Which one are you saying is rare? All the RTs and RSs came with the 32/11, which in the day were called the Autobahn rear end as with it you got the highest top speed. The 33/11 was also very commonly found on a lot of other bikes, including some R90s and R100s. It was also a factory option for the R80s of 1978. I know of at least 3 R80s near by with the 33/11 and a lot more with the 32/10 and 2 that have the 37/11 which was called the Alpine rear end due to it being very popular with those that did a lot of mountain riding. In the mid 70s thru early 80s, you could order different rear ends on the bikes, if you were willing to wait for it to get shipped.

But, you could also pick your bike up at the factory or one of the dealers in Germany, back then as well. You just had to make the arrangements thru you local dealer and pay up front for it. I did just that in 1979 for a brand new R100RT, I got to ride it all over Europe with my wife, then take it back to them and they packed it up and arranged the shipping to Montreal where I picked it up again and road across Canada to home. They don't do that anymore, which is too bad. It was a great arrangement for a minimal extra cost. I think it was an additional $250 back then. Would probably be around $5000 now.
Maybe they're more common on your side of the pond, but when I was looking for ratios for my race bike the wreckers were full of 32/10, fewer 33/11 and 32/11 were hard to find in the UK.
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Old 11-01-2012, 04:17 AM   #6
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Quote:
Originally Posted by pommie john View Post
Maybe they're more common on your side of the pond, but when I was looking for ratios for my race bike the wreckers were full of 32/10, fewer 33/11 and 32/11 were hard to find in the UK.
The 32/10 is 5% (or so) taller than the 37/11. I'm going to put that on my dirt bike. That with an 17" wheel is perfect for dirt ... put an 18" wheel on it for road, and you'll cruise at 80 mph all day at 4500rpm.
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Old 11-01-2012, 11:59 AM   #7
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Originally Posted by pommie john View Post
Maybe they're more common on your side of the pond, but when I was looking for ratios for my race bike the wreckers were full of 32/10, fewer 33/11 and 32/11 were hard to find in the UK.
32/11's are the shit here in the states and are the most sought after ratio although I think they are too tall for most airheads. In my experience, 34/11's are the rarest. I have never even looked into the taller than 32/11 situation. I will never have a bike that could use it!
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Old 08-01-2013, 02:15 PM   #8
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Kicking this (great, informative) older thread to the top to get some feedback on low speed technical riding (picking a line through rough stuff, etc). My '79 R100T has its original 32/11 final. With a 120/90-18 rear tire, I feel I have to slip the clutch too much to keep it from stalling on some steeper, rocky hills. And that was with no extra gear (weight) on the bike.

I just replaced the 120/90 rear tire with a 4.00-18, which is narrower, but even taller. Should I look for a 32/10 or a 37/11 final to keep the revs a bit higher at low speed? Or is the difference between the two (only 5%) not worth worrying about?

I am not an 80mph highway kind of rider (no faring). If I have to slab it, I prefer 65-70 max unless I am passing someone. Overall I prefer back roads at 50-60 and dirt roads & trails at a lot less!

Thanks for any more detailed BTDT input.
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Old 08-01-2013, 05:44 PM   #9
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Quote:
Originally Posted by Jim K in PA View Post
Kicking this (great, informative) older thread to the top to get some feedback on low speed technical riding (picking a line through rough stuff, etc). My '79 R100T has its original 32/11 final. With a 120/90-18 rear tire, I feel I have to slip the clutch too much to keep it from stalling on some steeper, rocky hills. And that was with no extra gear (weight) on the bike.

I just replaced the 120/90 rear tire with a 4.00-18, which is narrower, but even taller. Should I look for a 32/10 or a 37/11 final to keep the revs a bit higher at low speed? Or is the difference between the two (only 5%) not worth worrying about?

I am not an 80mph highway kind of rider (no faring). If I have to slab it, I prefer 65-70 max unless I am passing someone. Overall I prefer back roads at 50-60 and dirt roads & trails at a lot less!

Thanks for any more detailed BTDT input.
.

Gearing can be subjective thats for sure - need to suck-it-&-see. Shame that you're on other side of planet, I have a spare 37/11 that I could have loaned you to try. Though I reckon the 37/11 may be going too far the other way - maybe 34/11 or 32/10??

Difference between 32/11 and 34/11 is 7%
Difference beween 32/11 and 32/10 is 10 %
Difference between 32/11 and 37/11 is 15 %

When you look at it in these terms, 5% is a noticeable amount

Don't forget that your speedo will read wrong with a different bevel ratio.
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Old 08-01-2013, 06:07 PM   #10
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If it were me, I'd look for the 32/10, because it sounds like I like to go a bit faster than you . But the 37/11 was the 'most common' final drive made for the dual shock ... you can find one of those really easily. Just make sure you get one with good splines. For the sort of riding you describe, either would be fine. A 37/11 with the R100 engine you would see a HUGE response off the line ... and depending on the balance of your flywheel, should be very smooth all the way to 80 or so.

Play around with this page: http://www.largiader.com/articles/gearing/

This is Anton's gem ... and because all of BMW airhead transmissions are the same, we can compare final drives. I think if you realize that giving up top end will increase your bottom end ... you can figure out what you want.


Quote:
Originally Posted by Jim K in PA View Post
Kicking this (great, informative) older thread to the top to get some feedback on low speed technical riding (picking a line through rough stuff, etc). My '79 R100T has its original 32/11 final. With a 120/90-18 rear tire, I feel I have to slip the clutch too much to keep it from stalling on some steeper, rocky hills. And that was with no extra gear (weight) on the bike.

I just replaced the 120/90 rear tire with a 4.00-18, which is narrower, but even taller. Should I look for a 32/10 or a 37/11 final to keep the revs a bit higher at low speed? Or is the difference between the two (only 5%) not worth worrying about?

I am not an 80mph highway kind of rider (no faring). If I have to slab it, I prefer 65-70 max unless I am passing someone. Overall I prefer back roads at 50-60 and dirt roads & trails at a lot less!

Thanks for any more detailed BTDT input.
__________________
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Old 08-01-2013, 07:08 PM   #11
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Originally Posted by supershaft View Post
32/11's are the shit here in the states and are the most sought after ratio although I think they are too tall for most airheads. In my experience, 34/11's are the rarest. I have never even looked into the taller than 32/11 situation. I will never have a bike that could use it!
I built a 2.75 for a guy who was going to Bonneville with a hot-rodded R75. To no ones surprise (except his, I suppose), it was way too tall.
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Old 08-01-2013, 07:23 PM   #12
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Originally Posted by bmwrench View Post
I built a 2.75 for a guy who was going to Bonneville with a hot-rodded R75. To no ones surprise (except his, I suppose), it was way too tall.
Hey wrench, so you built one with new crown and pinion..
Is there a source for longer than 32/11 gear sets?
(apologies for threadjack Jim)
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Old 10-30-2012, 09:36 PM   #13
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So...sounds like I should be looking for a 33:11 for highway and backroad riding, and keep one of my 37:11 drives for offroad/mountain trips.
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Old 10-30-2012, 09:39 PM   #14
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I have a stock 33/11 on my 88 R100 RS - and although it won't have the top speed on the highway that the 32/11 would, it'll still ride all day at 80 mph plus and hit over 100 without any complaints.

I think the 33/11 is better in real world back-road/country or urban anyway - torquier off the line, better low end usability.
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Old 10-31-2012, 04:01 AM   #15
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Originally Posted by Zodiac View Post
I have a stock 33/11 on my 88 R100 RS - and although it won't have the top speed on the highway that the 32/11 would, it'll still ride all day at 80 mph plus and hit over 100 without any complaints.

I think the 33/11 is better in real world back-road/country or urban anyway - torquier off the line, better low end usability.
Another vote for the 33/11
Road, dirt, trail.
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