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drag racer
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does different ride heights with air ride installed change belt tension?
 

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Blueslover said:
No...regardless of wheel position vertically, distance between the two pulley's never changes.
Actually, that's not right. The only way that would be possible was if the transmission output shaft was concentric with the swingarm pivot. Since the swingarm pivot isn't concentric there is belt tension change with swingarm rotation.

E.g., for a VRSCA model with a 28 T front pulley and a 72 T rear pulley running a 149 T belt the minimum belt tension occurs at full rebound or compression and results in a "center to center" pulley distance of about 26.999" (685.8 mm). The maximum tension occurs when the two pulleys are "inline" with the swingarm pivot (close to static height) and the "center to center" pulley distance is 27.008" (686.0 mm). It's not much change but it will result in reduced tension at compression and rebound positions.
 

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stever975 said:
Actually, that's not right. The only way that would be possible was if the transmission output shaft was concentric with the swingarm pivot. Since the swingarm pivot isn't concentric there is belt tension change with swingarm rotation.

E.g., for a VRSCA model with a 28 T front pulley and a 72 T rear pulley running a 149 T belt the minimum belt tension occurs at full rebound or compression and results in a "center to center" pulley distance of about 26.999" (685.8 mm). The maximum tension occurs when the two pulleys are "inline" with the swingarm pivot (close to static height) and the "center to center" pulley distance is 27.008" (686.0 mm). It's not much change but it will result in reduced tension at compression and rebound positions.
Let me rephrase my earlier statement...the distance does not change enough to make a damn bit of difference. .009 is statistically insignificant in this particular application. We're talking about a belt here, not crank runout.
 

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Blueslover said:
Let me rephrase my earlier statement...the distance does not change enough to make a damn bit of difference. .009 is statistically insignificant in this particular application. We're talking about a belt here, not crank runout.
This isn't a statistical variation. The belt tension is always reduced when the swingarm moves up or down since it's a simple matter of geometry. I'll agree that it's a small amount but I'm not sure that it's insignificant since it takes very little motion to change belt tension and the power transmission rating of the belt is directly proportional to the belt tension.
 

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It changes it just a tad, not enough to worry about though. Set up your belt a smidge on the loose side and you'll be just fine.
 

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Soundhound said:
The original question in this thread was: Do different ride heights using air ride shocks affect belt tension?

I'm saying there is a decrease in belt tension as the swingarm moves up or down from the "in-line" maximum tension position since the swing arm pivots on a different axis than the front pulley. It was pointed out by Blueslover that this was an insignificant change in belt tension. Perhaps this is true, but I wouldn't recommend drag racing with an air ride setup in a "slammed" setting if the belt tension was adjusted according to the Service Manual setup.

I'm not sure what Cheatin is suggesting. I would set the belt tension using the Service Manual procedure. If you set it a "smidge on the loose side" it will just get looser when the wheel moves up or down.
 

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stever975 said:
The original question in this thread was: Do different ride heights using air ride shocks affect belt tension?

I'm saying there is a decrease in belt tension as the swingarm moves up or down from the "in-line" maximum tension position since the swing arm pivots on a different axis than the front pulley. It was pointed out by Blueslover that this was an insignificant change in belt tension. Perhaps this is true, but I wouldn't recommend drag racing with an air ride setup in a "slammed" setting if the belt tension was adjusted according to the Service Manual setup.

I'm not sure what Cheatin is suggesting. I would set the belt tension using the Service Manual procedure. If you set it a "smidge on the loose side" it will just get looser when the wheel moves up or down.
I forgot to add I set my belt up with the suspension all the way down, set the belt a tad loose, and it's fine all the way from top to bottom of the shock stroke. I like my belt just a tad on the loose side anyways.
 

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Geez....we aren't doing machine work here, we're talking about a drive belt.

.009 is so small a number in this application, it is insignificant. You would be unable to effectively adjust belt tension .009 more or less than wherever it starts from. If we talk about tolerances between a bearing and a shaft, then .009 begins to mean something. Ambient temperature also effects belt length, but I'm not going to worry about how much when adjusting my belt, because the effect is insignificant. You'd have to set up a dial indicator to effectively measure .009 variance, like you would do to check crank runout, etc.

I would NEVER ride a bike with air suspension slammed all the way down...that is for when it is parked. Adjust the belt according to the service manual specs, measured with a RULER, and you will be perfectly fine with the air shocks, if you ride with them in a normal suspension travel mode.

Any other discussion on this topic is an intellectual excercise.
 

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Steve
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I ride with my suspension down quite a bit. Doesn't seem to hurt anything and the ride actually isn't that bad. I guess it depends on the road and the rider. I really just wanted to see if posting this would make me intelligent.
 

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PHATVROD said:
I ride with my suspension down quite a bit. Doesn't seem to hurt anything and the ride actually isn't that bad. I guess it depends on the road and the rider. I really just wanted to see if posting this would make me intelligent.
The only thing I would check is to be sure the tire is not rubbing anything when it's hitting irregularities in the road surface...if it's not, then it's fine to ride them slammed down. You're just giving up your suspension travel is all...makes it ride like an old hardtail HD.
 

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PHATVROD said:
I ride with my suspension down quite a bit. Doesn't seem to hurt anything and the ride actually isn't that bad. I guess it depends on the road and the rider. I really just wanted to see if posting this would make me intelligent.
Dunno, but apparently it makes you 'intellectual'.:D You might want to check your air pressure if riding slammed "isn't that bad". My '56 panhead wasn't that bad either at 12 psi.
 
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