front or rear Sprocket
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From: Canada
front or rear Sprocket
Hi all I have a 1989 FXR low rider and at hwy speed my rpm is about 3800 at 110 kph or 68 mph. Should I change my front sprocket or rear sprocket? the bike is belt drive. The other idea is to change my primary drive to clutch? what is the best to get my rpm down to about 3000 at the same speed? I am looking to drop about 20% RPM any thoughts would be nice thanks.
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Joined: Jun 2007
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From: Bedford UK
My International spec 1990 FLHS had the opposite problem! So your bike sounds as if it may have been altered. US spec rear drive is 32/70, primary is 24/37. This gives 67mph at 3,000rpm. Another possibility is that either your speedo drive or tacho is the wrong version!
Before doing anything check what you actually have.
Before doing anything check what you actually have.
Grand HDF Member
Joined: May 2008
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From: Picayune, Ms.
What GR said.
Get a GPS, pick a straight road, preferably North/South orientation and make a couple of runs at different speed vs RPM's in different gears.
But! It sounds like someone was doing traffic light drag racing with the bike.
To answer you question, change the rear sprocket, to replace the front you must totally remove the primary. Fun, but not a simple task.
Get a GPS, pick a straight road, preferably North/South orientation and make a couple of runs at different speed vs RPM's in different gears.
But! It sounds like someone was doing traffic light drag racing with the bike.
To answer you question, change the rear sprocket, to replace the front you must totally remove the primary. Fun, but not a simple task.
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From: Bedford UK
Thinking this through again, there are very few options of pulleys available, especially the rear. However there are several engine sprockets/compensators available. I fit a 21T to my TC88, to really wake it up! Most likely change to your bike is a smaller front primary sprocket IMHO.
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Joined: Sep 2007
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From: Bluffton, South Carolina
That sounds a little high, first check to see if the stock pulleys/compensator sprocket are on the bike. If they are the easiest way to change the ratio is with a larger tranny sprocket. You can change the compensator sprocket, but that will make the engine turn over a bit harder which could become a problem later. Hope this helps.
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From: Canada
My International spec 1990 FLHS had the opposite problem! So your bike sounds as if it may have been altered. US spec rear drive is 32/70, primary is 24/37. This gives 67mph at 3,000rpm. Another possibility is that either your speedo drive or tacho is the wrong version!
Before doing anything check what you actually have.
Before doing anything check what you actually have.
Thank for the info; I tried it beside a buddies bike and use a digital tac and got the same readings. it sounds like it wants to fly apart by about 85 mph. I will count the teeth. I think the last owner changed the rear for more off line pull. Goes like H*LL but you run out of rpm I have hit the rev limiter more time then I should. now I am putting in an ultima 107 and it has a lot more power so a gear change wouldn't be a bad thing.
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From: Niles Canyon Ca.
Hi all I have a 1989 FXR low rider and at hwy speed my rpm is about 3800 at 110 kph or 68 mph. Should I change my front sprocket or rear sprocket? the bike is belt drive. The other idea is to change my primary drive to clutch? what is the best to get my rpm down to about 3000 at the same speed? I am looking to drop about 20% RPM any thoughts would be nice thanks.
http://www.nightrider.com/biketech/calc_speed_rpm.htm
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Joined: Jun 2007
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From: Bedford UK
That is very close to the difference in rpm we mentioned earlier. I guess you will also need a longer, stock length belt, but you should then be back to stock.
Last edited by grbrown; Sep 27, 2011 at 02:55 AM.