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25-11-2020, 03:36 PM | #1 |
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Join Date: Aug 2011
Location: Southampton
Bike: M1100evo
Posts: 2,465
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+1 for makemdan's gearing suggestion. There are lots of posts/threads on the forum debating the pros and cons of smaller front versus larger rear sprocket. I've got the 14 tooth front but will try 15/42 when I need to replace my chain.
One thing to watch with the larger rear sprocket is setting chain tension. With the Evo, (and, I think, all the single-sided swinging arm models), the suggested 61mm - 63mm is not the amount of up-and-down chain movement, it is the clearance between the chain run and the underside of the swinging arm. Consequently, a larger rear sprocket will have the effect of moving the chain further from the swinging arm so, if you use the original 61mm - 63mm gap, the chain will be overtight so bear that in mind when tensioning. I don't know what the relative diameters of the 39 and 42 tooth sprockets are so I can't work out what the new clearance should be but I'd think another 5mm or so? The best way to determine the new correct clearance, (and something you can do, Ian, if you're changing your shock), is, with the shock removed, pull the swinging arm up until the front and rear sprockets and swinging arm pivot are all in line. (It's at this point that the chain will be at its tightest.) If you set the chain tension in this position, then at any other point in the swinging arm's travel, the chain will be slacker. Then, with the bike back together and on the side stand, you can measure the new clearance and use that as your reference for future chain adjustment. If you do that, Ian, do let us know what the figure is, as it'll be useful for anyone else running the 15/42 combination. |
25-11-2020, 03:42 PM | #2 | |
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Join Date: Jul 2019
Location: grimsby
Bike: M1100evo
Posts: 95
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25-11-2020, 04:02 PM | #3 | |
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Join Date: Aug 2011
Location: Southampton
Bike: M1100evo
Posts: 2,465
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The 42T rear requires a longer chain (+2 links) so is more work and more expensive. In theory, the larger rear will give the chain and swinging arm protector, (the nylon slider), an easier time than the smaller front. In the real world, I've done over 10,000 miles on the 14T and only adjusted the chain probably less than half-a-dozen times and there still appears to be plenty of life left in it. I think, unless you're planning on covering 12,000+ miles a year, it's not a consideration. If you haven't seen it already, all my mods are detailed here http://www.ukmonster.co.uk/monster/s...ad.php?t=55168 pick the ones you want! |
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25-11-2020, 09:02 PM | #4 | |
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Join Date: Jul 2008
Location: West Boldon
Bike: M1100evo
Posts: 55
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26-11-2020, 07:35 PM | #5 |
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Join Date: Jul 2008
Location: West Boldon
Bike: M1100evo
Posts: 55
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Maybe being simplistic here but wouldn't the new range be the original + the difference between the radii of the 2 sprockets?
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26-11-2020, 08:43 PM | #6 | |
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Join Date: Aug 2011
Location: Southampton
Bike: M1100evo
Posts: 2,465
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Because you're only changing the rear sprocket, then, yes, the chain link on the very bottom of the new, larger, rear sprocket will be farther from the swinging arm by R2-R1 (where R1 is the radius of the 39T sprocket and R2 the radius of the 42T). But, by contrast, a chain link at the bottom of the gearbox sprocket will be exactly the same distance from the swinging arm, whichever size rear sprocket you have. Consequently, if you think of the chain as being the base of a triangle between the gearbox sprocket (A), rear axle (B) and bottom of rear sprocket (C), you've increased the length of side BC and increased the angle between sides AB and AC. So the clearance difference will be at its maximum (R2-R1) at point C and zero at point A. As you measure the clearance working from C to A, the difference will gradually reduce until it is zero at point A. As the chain clearance is measured half-way between front and rear sprocket, the increased clearance will also be someway between zero and R2-R1 (but not half-way between!). Last edited by Luddite; 26-11-2020 at 08:50 PM.. |
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