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Old 07-15-2012, 04:44 PM   #1
limeymike OP
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Swapping final drive

Is putting a final drive from a R100 onto a R80 easy, ie bolt on? Looking to lowering the cruising rpm. Its an '86 mono.

limeymike screwed with this post 07-15-2012 at 04:53 PM
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Old 07-15-2012, 05:06 PM   #2
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The speedo will be off. Some put tape on the speedo glass to remind them.

Check the splines. They also get greased.
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Old 07-15-2012, 05:38 PM   #3
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Quote:
Originally Posted by disston View Post
The speedo will be off. Some put tape on the speedo glass to remind them.

Check the splines. They also get greased.
No splines on this final to grease
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Old 07-15-2012, 06:31 PM   #4
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And if you can, grab the speedo of the R100 as well, that way it will match up with the final drive and show correct speed, or at least a lot closer to correct.
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Old 07-15-2012, 07:15 PM   #5
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Direct swap between monos. Go ahead!

When swapping a final drive to a different ratio, what combo might work so that the original speedo becomes accurate?

If the oem setup is say, 7% optimistic, which setup might compensate for this and return the display to accuracy?
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Old 07-15-2012, 07:38 PM   #6
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I think he will be going from a 3.37:1 to a 3.0:1? That's a big jump. Over 10%. If it's in the right direction you could get the speedo to a theoretical 3%? My 3.0:1 speedo isn't off nearly as much as many report according to speed sign radar and tickets I get. I would say mine reads about 2 to 4% fast? Maybe 3 to 5% at the most I would guess?
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Old 07-15-2012, 07:43 PM   #7
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easy swap adn one you might very well like. On my 85 I swaped out the final drive off a R100 and the speedo. I noticed near at least a 500 rpm drop at speed
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Old 07-15-2012, 08:13 PM   #8
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Originally Posted by coastranger View Post
easy swap adn one you might very well like. On my 85 I swaped out the final drive off a R100 and the speedo. I noticed near at least a 500 rpm drop at speed
I have heard similar numbers quoted from the swap so I think it is worth it.
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Old 07-15-2012, 08:19 PM   #9
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Originally Posted by supershaft View Post
I think he will be going from a 3.37:1 to a 3.0:1? That's a big jump. Over 10%. If it's in the right direction you could get the speedo to a theoretical 3%? My 3.0:1 speedo isn't off nearly as much as many report according to speed sign radar and tickets I get. I would say mine reads about 2 to 4% fast? Maybe 3 to 5% at the most I would guess?
With the stock final drive my speedo reads 70mph at an actual speed of 65mph, that's taking the actual speed from a TomTom gps that I temporarily rigged up. approx 7% error.
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Old 07-15-2012, 08:44 PM   #10
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Quote:
Originally Posted by limeymike View Post
With the stock final drive my speedo reads 70mph at an actual speed of 65mph, that's taking the actual speed from a TomTom gps that I temporarily rigged up. approx 7% error.
That's pretty typical. You'll find that your odo is pretty much bang on though. There was a thread about speedo error a while back. It's worth a read if you can find it.
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Old 07-15-2012, 09:30 PM   #11
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Easy bolt on. Look for a speedo that says 1.078 on the face.
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Old 07-16-2012, 12:04 AM   #12
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I thought the speedos were all the same and the gearing of the speedo drive needed to match the final drive
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Old 07-16-2012, 06:08 AM   #13
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Originally Posted by Rucksta View Post
I thought the speedos were all the same and the gearing of the speedo drive needed to match the final drive

Nope. The internal gearing of the speedo has to match the final drive. Your speedo will have "W=_____" on the face. This indicates what final drive ratio it is intended for. Annoyingly they use a completely different metric for the speedos rather than just listing the corresponding final drive ratio. W = the number of rotations per mile (or km for 'rest of world' market bikes). At some point (can't remember when exactly) they changed W from thousands of rotations per mile to just rotations per mile. eg: W=1.202 became W=1202.
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Old 07-16-2012, 06:22 AM   #14
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Originally Posted by Airhead Wrangler View Post
W = the number of rotations per mile (or km for 'rest of world' market bikes).
I didn't know that. That IS annoying. Do you know if the 'W' metric takes into account the diameter of the rear wheel?
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Old 07-16-2012, 06:34 AM   #15
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Do you know if the 'W' metric takes into account the diameter of the rear wheel?
I've never really though about it much, but I guess it would have to.
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