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You'll find this if you search anyway, but...

I feel it's better to go larger on the rear sprocket as it won't diminish the diameter of the front sprocket and possibly increase wear on the plastic chain slider that protects the swing arm or marginally increase wear on the chain from turning around a tighter radius up front.

Two teeth up on the rear will be comparable to one less on the front and is the most popular swap.

Go with steel. I've bought Afam steel sprockets (2 larger on the rear) and DID VM520 for both my Monster and BMW F650 from Chris at ca-cycleworks. Afam is top quality in my book. You can expend the effort and shop around for something cheaper, but Chris only handles good stuff and is fairly competitive price wise. And he is a sponsor here on the DML.

You'll need access to a chain tool to cut the new chain to length and rivet the new master link - DON'T use a clip type masterlink. Being a tool junkie, I sprung the big $$$ for the Motion Pro Jumbo Chain Tool from Chris with the first chain order. It won't break in the middle of a job and will handle up to 530 chain (too bad it doesn't go down to the 430 that's on the XR 80 and YSR 50). I've done 2 chains in less than a year, and an acquaintance has offered to throw me a few bucks for doing a chain for him, so that tool has pretty much paid for the investment.

A rear pit stand or way to support the bike while pulling the rear wheel.

And a torque wrench is really good to have to avoid stripping sprocket fasteners.
 

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When I changed my rear sprocket, I had printed copies of Strati's and Chris' step-by-step instructions with me in the garage. Not ONLY do they have good pictures and helpful hints, but they were also really good places to put greasy stuff so it didn't pick up dust off the floor.

www.ducatitech.com
www.ducatipipemod.com
 

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A 15/43 combination isn't enough of a jump. Either get a 44 or 45 for the rear or go with 14/42.

I had an aluminum AFAM rear sprocket and it would have lasted longer if the chain was "willing". Steel wears better, but aluminum is lighter.

You can swap the sprockets without any special tools, just normal wrenches.

Be sure you put the spacer on the sprocket side with the flat side against the swingarm.
 

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So is it a general opinion that I will need a new new chain just going from 39 to 42 in the rear? My chain is very new and Id hate to have to buy another.
 
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Discussion Starter · #8 ·
So is it a general opinion that I will need a new new chain just going from 39 to 42 in the rear? My chain is very new and Id hate to have to buy another.
that's exactly why i'd say go with a 14 in front instead... if you go with a rear 42, you'd need to buy a new chain anyways, so why not go with a front 14 instead. even if it wears the chain a bit more quickly, at least you'll get SOME miles out of it. then when the chain's toast, get a new chain, a larger rear and put the original 15 back on.
 

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Well, my rear sprocket is toast, Ill post pics when I get home, so I have to replace it. I was hoping I could two up in the process but if I have to get a new chain maybe Ill stick with the stock 39 size.
 

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That would be nice if it worked out that way...thing is, you have to take into account that the front and rear sprockets are much different in diameter....that's why you get a more dramatic change by dropping a tooth in the front compared to adding one to the rear....
 

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To determine how much the axle will move with a different sprocket and the same chain, four more teeth added to the sprocket(s) will move the axle towards the engine exactly the distance between the pins of one link in the chain. Add two teeth at the rear and it moves forward half of that distance. (Okay, it's actually about 2% more because of the angle of the chain coming off of the rear sprocket.)

If you are going up three teeth (39 to 42) and have 3/4 of a link of adjustment space, you won't need a new chain. When I went up two on my M900 (39 to 41), there was plenty of room left, and I did it when I had less than 1000 miles on the bike, so the chain was same as new.

To figure how much you're dropping the gearing, just get out your calculator.

14/15 = 0.9333... or about 6 2/3%

39/40 = 0.975 or 2.5%
39/41 = 0.9512 or about 5%
39/42 = 0.9285 or about 7%

You get the idea. Subtract the result from 1.0 to get the fraction. Multiply that by 100 to get the percentage.
 

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i did -1 in the front AND +2 in the rear, all while keeping the stock chain. they had to move the rear tire as close to the front as humanly possible, and it was still a tight fit. but it works!
 
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