Chain !! - Page 2

Luddite · 09-08-2019, 04:44 PM

Quote:

Originally Posted by Uncle Bob

I have a question: Does this mean that chain tension is, to some degree, influenced by static sag?

The reason I ask is that I'm going to be setting up (fiddling with) the suspension shortly, and if the chain is a bit loose plus the sag is too little I may be able to kill two birds with one stone i.e. by adding a little more static sag it will tighten the chain slightly?

It does indeed, Bob. (We're back to trigonometry again here - sorry!)

(Unless you've got an early Bimota, with swinging arm mounted coaxially with the sprocket), the chain slack will vary depending on suspension travel because of the different paths followed by the wheel spindle (R1) and the one needed to keep the distance between the sprocket centres constant (R2). You can see that the swinging arm describes a tighter arc (R1) than the one centred on the front sprocket (R2).

The chain is at it's tightest when the sprockets are in a line. Any movement either side of that line will slacken the chain. (This is where the trigonometry comes in!)

You can see that, when the sprockets and pivot are in line (P1), the distance between sprocket centres is a + R1.

When the rear sprocket is either side of that line (P2), the distance between sprocket centres effectively becomes one side (side b) of the triangle a, b, R1. And you can see that, as side b is shorter than a + R1, the chain will slacken.

What all that means is, the more sag you have when you adjust the chain, the closer it will be to it's tightest position, so the less play will be needed.

Hope that makes sense.

Darren69 · 09-08-2019, 05:29 PM

If the bike has done 13k miles on the same chain and spockets then its probably time to change them all.

Darren69 · 09-08-2019, 05:37 PM

I would also advise you replace the standard rear sprocklet carrier/hub with a 2 part one like Renthal do so you can change the sprocket with the wheel still in. They acan be a swine to get out as the wheel nut is jeezus tight.

Nickj · 10-08-2019, 02:59 PM

The pivot for the swinging arm isn't the same as the rotational centre of the gearbox sprocket so the tension is set so as to be not too tight when the driven sprocket bob's up and down.
I do remember in the dark dim past that someone proposed and made a limited number of gizmo's to remove this effect. Essentially a pair of mounts on the swinging arm fairly close to its pivot point with rollers to carry the chain.
Nice idea that seemed to work but never caught on.

mickj · 10-08-2019, 03:35 PM

Quote:

Originally Posted by Darren69

If the bike has done 13k miles on the same chain and spockets then its probably time to change them all.

I wont be happy if that's all a chain and sprocket set will last, I have sold three bikes with over 30k on them and they were still in reasonable nick.

Uncle Bob · 12-08-2019, 08:05 AM

Quote:

Originally Posted by Luddite

Hope that makes sense.

Yes, thank you!

350TSS · 12-08-2019, 01:59 PM

I used to think that a concentric SA spindle and gearbox sprocket would be a good idea, constant tension etc but the pull on the top run when the 2 are eccentric helps weight transfer towards the rear, which aids traction and steers the bike as the rear wheel is always pointing on a tighter radius than the front. It also means that it makes it difficult to wash out the front wheel when accelerating out of a corner (virtually unknown for a low-side front crash when accelerating, the more painful high-side rear keeps you on your toes though).

09-08-2019, 05:29 PM	#17
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,022	If the bike has done 13k miles on the same chain and spockets then its probably time to change them all. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

09-08-2019, 05:37 PM	#18
Darren69 Transmaniacon MOC Join Date: Sep 2013 Location: Sutton In Ashfield Bike: Multiple Monsters Posts: 6,022	I would also advise you replace the standard rear sprocklet carrier/hub with a 2 part one like Renthal do so you can change the sprocket with the wheel still in. They acan be a swine to get out as the wheel nut is jeezus tight. __________________ Roast Beef Monster! Termignoni and Bucci - Italian for pipe and slippers! S4 Fogarty, S4R 07T, 748, Series 1 Mirage

10-08-2019, 02:59 PM	#19
Nickj Too much time on my hands member Join Date: Jun 2007 Location: Forest Of Dean Bike: S2r Posts: 3,189	The pivot for the swinging arm isn't the same as the rotational centre of the gearbox sprocket so the tension is set so as to be not too tight when the driven sprocket bob's up and down. I do remember in the dark dim past that someone proposed and made a limited number of gizmo's to remove this effect. Essentially a pair of mounts on the swinging arm fairly close to its pivot point with rollers to carry the chain. Nice idea that seemed to work but never caught on. __________________ "The final measure of any rider's skill is the inverse ratio of his preferred Traveling Speed to the number of bad scars on his body." Song of the sausage creature

12-08-2019, 01:59 PM	#22
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,419	I used to think that a concentric SA spindle and gearbox sprocket would be a good idea, constant tension etc but the pull on the top run when the 2 are eccentric helps weight transfer towards the rear, which aids traction and steers the bike as the rear wheel is always pointing on a tighter radius than the front. It also means that it makes it difficult to wash out the front wheel when accelerating out of a corner (virtually unknown for a low-side front crash when accelerating, the more painful high-side rear keeps you on your toes though).