That's where the problem lies! the 3 points never line up! so the swingarm effectively keeps getting longer.

I've just wrecked a chain and bent a swingarm pivot bolt on the race bike got the chain a bit too tight

I can remove the shock and sit the tyre on the end of the rear subframe and they are just about lining up.

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Nige...1125d 9.43@140mph

Followed this thread for some time.
Been playing with belt tension measurement today. Disconnected rear shock and fitted a belt tension meter on the top run. It's primitive and uses 3 simple pulleys and a spring with a dial pointer. The pulleys are in a line and the centre one is sprung to create a degree of tension on the belt by pushing it out of line. Given we have a fixed tensioner, any change in tension does show up, for example if you deflect the bottom run of the belt by an inch or so, it shows a 10 lbs change. it's not perfect because this thing was originally designed to measure weight loading on quarter inch steel rope but it does show up tension changes.
I did not fully remove the rear shock so I could only see what happens over the first 3 inches of travel and the result is no measurable change so Eric may well have got his maths pretty good on the position of the current idler wheel as Maz says.
However, it you tap the top run of the belt with say the handle of a small screwdriver it will play a note just like a guitar string. That note does rise as you compress the suspension which indicates the belt top run is either getting shorter ( triangle geometry shows it isn't) or the belt is getting tighter.
I need to have few more hours so I can remove the rear shock to allow full travel and re test.
I happen to agree with both camps in that I like the idea of a sprung tensioner to (hopefully) allow foreign objects to pass without damage, and reduce the tension influence on the suspension, but the idea that the top run could potentially run loose and then shock load up again on opening the throttle also concerns me. Doesn't seem to be a problem on the tubers etc but they don't have the torque or power of an 1125.
Just a thought here, any tensioner needs to have limits and the WB is no different as can be seen on the milled slot. This will limit how slack the belt can get on the top run and prevent possible tooth jumping. That position is critical and is a balance of how big a foreign object you allow around the pulley, and how much slack you allow the top run on overrun.
You could have a dual spring arrangement. The weaker of the two would provide the day to day tension. Once that became coil bound the second stronger one would move to allow stones ect to pass. We have similar system on one belt of our combine harvester. Selection of those springs would be critical. I do appreciate that those combine systems would not over run but they do suffer violent changes of load ( From 0-220hp almost instantly) and need to have a minimum tension to transmit power being V belts. Idler Tension springs are adjistable to preset lengths to account for belt wear. V belts will also pull down slightly into the pulleys so we must discount them.
Maz says his system reduces static load whilst being bog stock. I read that as meaning he still uses the original fixed tensioner which I like due to reduced weight and moving parts. To reduce belt tension I see 3 options, reduce the pulley diameter in a lathe (not much to play with), alter the support holes where the idler bolt goes through (seen that elsewhere on the forums but not for 1125), or machine offset support spacers for the idler pulley bearings, so come on Maz enlighten us with your wisdom before my brain or wheel bearings seize.

The reality is that we are not dealing with static load but a very dynamic one. I cant quantify this, but the faster you travel or accelerate, the more power is needed, the belt will therefore stretch minutely on the top run albeit by small amount. As the bike squats under power, any increase in length needed from suspension movement, may well be provided by the additional power stretching the belt's top run. There is even a chance that a belt that appears tensioned, could run slack on its bottom run under full power if not quite tight enough. A slack belt will wear more if the teeth are squirming in the sprocket and if really slack, could fail because power is being transmitted through too few teeth on the engine sprocket due to the remainder not being held firmly in the sprocket teeth. That also applies to a chain and my old Yam trials bike had a sprung chain tensioner mainly because the front sprocket had low teeth numbers.

Just my tuppence worth.

Jolt kills Buell belts, the rate of change of acceleration...

http://en.wikipedia.org/wiki/Jerk_%28physics%29

The higher the static load on the belt, the lower the jolt when you shut off the throttle then crack it open again.

Using a free spirits tensioner on an XB reduces the static load and prolongs the life of the gearbox output shaft bearing, which is a known weakpoint. The 1125 does not appear to have a problem with the gearbox output shaft bearing, so, unless you have a longer than normal swinging arm, why bother deviating from the fixed tensioner wheel?

I do think the 1125 belts should have been 50% wider though...

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08 Specialized Langster

So based on that theory the belt's on the XB's that are fitted with the free spirit tensionersshould not last as long as XB's without then fitted...... Is this the case? I thought people were saying they lasted longer

If you are into closing and openning the throttle quickly, I don't reckon they will...

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08 Specialized Langster