Chain tension on lowered rear.

[Shortarse]

Hi XRV,

I've got an XL650V 2006 which I can just about touch the ground on. I've already got the low seat. I dropped the forks through the yoke by about an inch but with my new crash bars (Wemoto) when braking hard the crash bars hit the front mudguard so I put them back to normal and also bought the Touratech springs. Now the front is fixed and the bike feels much better.

I have now taken to the rear, I've adjusted the rear preload by about .75 of an inch and I can now get the the balls of my feet on the ground. This REALLY helps a massive amount!

My question (finally) is about the chain tension/slack. When I'm actually on the bike how loose/tight should the chain be?

As the chain tightens as the bike gets lower I thought I better check it, it's quite tight when I'm on it so I've loosened it a little. there's now about 25mm of slack when I'm sitting on it.

I know I'm supposed to check the slack when the bike is on the side stand but now with the lower preload the rear suspension compresses more when I put my bum on the seat so surely the chain needs to have more slack?

Your views on this would be most appreciated.

Thank you!
Richard
5ft 4"

[djadams]

Not really...

The slack you need in the chain is the amount that will leave just a little slack in the chain at the point in the suspension travel when the chain run is at it's longest.

That point will always be when the centre of the front sprocket, the swingarm pivot and the centre of the rear sprocket all lie on a straight line. (As an aside, if the front sprocket and swingarm pivot were centred on the same point, you could run almost no slack at all and have no problem as the chain run would never change length).

By reducing your preload, all you've done is let the suspension squash down further towards that "longest chain run point" when you sit on it (increased the static sag). At a standstill, the swingarm is now in the same position it would have been in before whilst riding over a small bump or accelerating a little.

The actual maximum length of the chain run hasn't changed at all, as the swingarm is still travelling up and down along the same arc. So - if you're used to setting the chain tension with the bike unladen on the sidestand (i.e. with very little sag in the rear suspension) you can carry on using the same set up.

HTH,
dan.
(5'9")

[FatFergie]

Not really...

The slack you need in the chain is the amount that will leave just a little slack in the chain at the point in the suspension travel when the chain run is at it's longest.

That point will always be when the centre of the front sprocket, the swingarm pivot and the centre of the rear sprocket all lie on a straight line. (As an aside, if the front sprocket and swingarm pivot were centred on the same point, you could run almost no slack at all and have no problem as the chain run would never change length).

By reducing your preload, all you've done is let the suspension squash down further towards that "longest chain run point" when you sit on it (increased the static sag). At a standstill, the swingarm is now in the same position it would have been in before whilst riding over a small bump or accelerating a little.

The actual maximum length of the chain run hasn't changed at all, as the swingarm is still travelling up and down along the same arc. So - if you're used to setting the chain tension with the bike unladen on the sidestand (i.e. with very little sag in the rear suspension) you can carry on using the same set up.

HTH,
dan.
(5'9")

I agree, almost . The geometry hasn't changed that much so the slack recommended by the handbook should be correct. Better to be too loose than too tight though and if your suspension is slightly lower then that will be the case.
If you want to check if it's right put your bike up on its main stand (or blocks/axle stands) and disconnect the shock, move the swingarm 'til the sprocket, swingarm pivot and rear axle are all in line. At this point the chain should be almost tight with just a little play but should still run freely. When you connect the shock again you'll see what freeplay you've got for any particular way you want to check it. Just use the same method each time you do.

[djadams]

Quite - assuming minimal sag unladen on the sidestand with either pre-load setting, the geometry won't have changed at all. However, if there is a little more sag (unladen on the sidestand) with the reduced preload, the chain run will be slightly longer in this condition so you can actually have a little less slack in it than the handbook's setting...

But - point to note - the handbook doesn't know what pre-load you've set within the adjustment range, so gives a value that is going to be OK for all pre-loads - therefore according to Honda there's just no need to change what you're doing!

If you're feeling conscientious, Fergie is absolutely right that to get it spot on you could whip out the rear shock and find that longest chain run point, but don't feel you have to as I agree with Honda that it really doesn't need to be that precise!

[AIRWOLF]

An easier way to get the output shaft, swingarm pivot and rear wheel spindle in line is just get a couple of mates to push the back end down to said position, there should then be just a little slack.
once this is done you can measure the slack when on side stand, and use this measurement as your standard.

Oh, and welcome to the site mate.

[FatFergie]

An easier way to get the output shaft, swingarm pivot and rear wheel spindle in line is just get a couple of mates to push the back end down to said position, there should then be just a little slack.

This works but doesn't allow you to spin the wheel to check that it runs freely or for tight spots.

[Shortarse]

Afternoon Chaps,

Well, what an amazing forum. How many replies in less than a day? Thank you!

I've thought about what has been written above and it all makes perfect sense. I shouldn't have changed the slack at all but I did. Now I'm going to get some mates to sit on it so it all lines up, then I'll adjust until I have about 15mm free, then I'll put it on my sidestand and measure and use that as my standard.

Thanks guys! I was beginning to think of myself as an outcast in these days of racing bikes and BMW GS's, what no Transalps? Then I found your site. Phew!

Richard

[djadams]

Yeah, we're great...

Welcome to the site by the way! Joking aside, it is a very helpful place.