A forum for owners of Yamaha TTR250 trail and enduro bikes!

ok here it is.

I have listed below most sprocket combinations, grouped according to what I think is the minimum feasible number of chain links which can be used with a properly adjusted new chain. So there is a group for 106 links, 108 links and 110 links. Many combos in each group could also use the next higher number of chain links (ie 108 links, 110 links, 112 links respectively) and vice versa.

To give an idea of where the axle sits, I have listed the approximate number of mm the axle position would be to the rear of the absolute maximum forward position when using a new chain. For situations near the axle limits, you would be best advised to "suck it and see".

Note that the total amount of fore and aft axle movement possible (at least on my TTR) is 23mm, from the very first snail cam indentation, to the very last indentation (any further and the axle would start to want to drop into that recess at the end of the swingarm).

You will need to add an extra allowance of about 8mm or 9mm for chain stretch (1% permitted on modern chains). However, be aware that nearly all this stretch happens mainly at the very end of chain life - you don't save much by waiting for the full stretch before replacing.

By the way, note that every 4 tooth increase on the rear will drop the bottom of the rear sprocket by 10mm (increasing drag on the rear guide) as well as wanting to move the axle forward by 16mm and so requiring an extra 2 links of chain to get it properly positioned again. I suppose that a 13T front sprocket might slightly increase wear on the front swingarm rubber.

If you use a combination which sits with a small axle offset, be conservative in tyre size - there is not much room.

I have included a column named 'ratio' which is the gearing (bigger number means lower geared).

calculated numbers have been rounded.
all care but no responsibility on my part, so no complaints.

feedback welcome, especially on marginal cases, if you have fitted NEW chains and sprockets and adjusted to (say) 40mm slack - the snail cam position would be useful. 

if you own some weird old rally raid model with 428 chain, ignore this table.

1. SOME 106 LINK COMBINATIONS:

ratio teeth axle

3.31 13/43 +16mm
3.07 14/43 +12mm
3.38 13/44 +11mm
3.14 14/44 +8mm
3.46 13/45 +7mm
3.21 14/45 +3mm
3.54 13/46 +3mm

2. SOME 108 LINK COMBINATIONS:

ratio teeth axle

3.29 14/46 +15mm
3.62 13/47 +15mm
3.36 14/47 +11mm
3.69 13/48 +11mm
2.43 14/48 +6mm
3.77 13/49 +5mm
3.50 14/49 +2mm

3. SOME 110 LINK COMBINATIONS:

ratio teeth axle

3.85 13/50 +17mm
3.57 14/50 +13mm
3.92 13/51 +13mm
3.64 14/51 +9mm
4.00 13/52 +9mm
3.71 14/52 +5mm

The snail cam numbers can be roughly related to axle offsets by multiplying them by 1.7, so snail cam position number 7 would correspond to just under +12mm in the tables above.

A reasonable way to calculate incremental changes to your current setup is as follows:

adding 1 tooth to front sprocket moves axle forward about 3.7mm
adding 1 tooth to rear sprocket moves axle forward about 4.4mm
adding 2 links to chain moves axle back about 16mm
chain wear from new to worn out moves axle back about 9mm
increasing snail cam position by one number moves axle back about 1.7mm

btw, increasing snail cam by one number (3 clicks) is roughly all you need to vary the
vertical chain slack between 30mm and 50mm when adjusting chain tension. 
 

Anytime Brian

As you know chain lenght is one of the most complex subjects & it's hard to tell if your right even if your good at maths because the of tire clearance issue ect.

If anyone finds something wrong or is using a different chain length than in this reference please inform of this so it can be changed. All info is welcome aslong as it's solid info. It can be hard to count chain lenght & hence so much confusion throughout the internet. I have looked at many different sources of info & all are conflicting or wrong & why it makes it harder to tell actual chain length rather than just go off a rule of thumb.

Cheers all that help

.....................

Jarrah.

I have put a 14/52 on mine today. I have a 110L O-Ring chain with 40mm of slack.

I am running a 110-100-18 AC10 rear tye.

I have clearance wheel does not rub on the black plastic mudguard and its away from the swing arm.

Snail adjusters on about 4.2