# Sprocket Tensioning

I’ve heard that for #35 chain, if you space the sprockets 3/4 in away from each other, you do not need tensioners? Is this true, and if so, where is the measurement taken from? Furthermore, do most teams prefer using this method, or machining bearing blocks? Thanks in advance.

Do you mean to say that you increase the normally calculated center distance (note that the distance should be center to center for a two sprocket system) by 3/4"? I’ve never heard this myself, but I think that might be too far; the pitch of 35 chain is only 3/8", so doing this would make the chain two links too short - and I don’t think you want to stretch that far.

The problem with chain is that it starts to stretch and sag no matter what you do, so having tensioners allows you to keep a chain longer. You just keep tightening it as slack develops. Your chain life also improves when it’s at the correct tension which is why you should do the center distance calculation. There are simple online tools to handle it, but it’s based on fairly basic geometry and you can do it by hand as well.

Can you clarify the last question?

If you use the correct length of chain and have your sprockets properly spaced you can typically avoid using tensioners, half links, and even master links (with the right chain breaker tool and technique) altogether. However, it is still wise to prepare to have a tensioning method available, as well as Master Links, and Half Links for quick fixes.

How do you find the right length of chain to use? There actually are formulas to help you figure this out.
Ideally you want to use only whole links and the total number of links should be a whole even number, ex… 16, 18, 20, 22…

Chain pitch is either .250 (25) or .375 (#35)

Formula for Center to Center Distance of Sprockets:
(B1/8) * (2B4-B2-B3 + SQRT((2B4-B2-B3)^2-(8/3.14159^2)*((B2-B3)^2)) )
B1 = chain pitch
B2 = Sprocket 1 teeth
B3 = Sprocket 2 teeth

Formula for Number of WHOLE Links:
(2E4/E1+E2/2+E3/2+((E2-E3)/(23.14159))^2/(E4/E1))
E1 = chain pitch
E2 = sprocket 1 teeth
E3 = sprocket 2 teeth
E4 = Center distance

ChainLengthCalculator.xls (33.5 KB)

ChainLengthCalculator.xls (33.5 KB)

Thanks, and sorry for the inaccuracies in my question. I meant that I’ve heard that for #35 chain, sprockets can be spaced in multiples of 3/4. I’m guessing this is correct. Also, would teams still recommend using a bearing block, so that you can account for chain stretching.

We calculated exact distance for a 12 tooth to 60 tooth #35 chain drive for our arm (heavy load) and got it right and had no problems whatsoever with it. #25 does stretch a bit so it’s nice to be able to tension it.

Use this:

Joe Johnson’s Chain Visualizer - One of the best Chain Calculators, its really powerful.

http://www.chiefdelphi.com/media/papers/1598

-RC

This is only true when the sprockets are the same size, and it’s actually pitch multiples, so the multiple should be 3/8". That gives you an integer number of links. (3/4" will work because it is a multiple of 3/8".)

http://www.rbracing-rsr.com/chainlength.html is a very simple calculator. Set the pitch to .375 and try different combinations of sprocket size and different lengths. You’ll see that for a 1:1 sprocket ratio it’s easy to get integer numbers of links (just put a multiple of .375 for your center distance). For any other ratio, you’ll have to use a bit of finagling to get it a center distance that yields an integer number of links.