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Mostly Harmless
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Discussion Starter #1
Does anybody know of a rule of thumb regarding how many links you have to add to your chain when you increase the rear sprocket size quite a bit?

The stock rear sprocket is a 37, and I have a 38 on there now. I have a 40 on order, and I'm almost certain I'll have to add at least two links. I'm just wondering if that's a correct assumption, and if I go up to a 42, if I'll have to add more, and if so, can I add 'em now to not worry about it later?

Rob
 

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chain links

I would only add one link, I thought the same thing as you when I replaced the chain and sprockets on my Scrambler. I went from a 38 rear to a 40 and ordered the chain 2 links longer than stock. I didn't need 2 links, one would have been plenty which doesn't make sense. I don't recall if I counted the new chain links or not, maybe I got a longer chain than I was supposed to. Anyway with the new chain/sprocket setup the eccentric is rotated farther than it was with the stock chain.

You will probably have to do something with the swingarm skid plate, I don't think a 40 will clear, I read a 39 will. I may switch to a 39 after some seat time.

I'm thinking in the future of switching the carb to an FCR. I'm not big on the CV style. I have to believe the performance and response will be greatly improved. Also a piston swap to up the comp ratio into the 12:1 range is in the future, lots of potential hiding inside this machine.
 

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Mostly Harmless
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Discussion Starter #3
My thinking is that a 40 is probably going to be either one tooth two much or one or two teeth too little. A 39 should let me climb the big hill at Sand Mountain at the top of third gear, but a 40 will require fourth. The concern is that I may not have enough RPMs to stay in fourth the whole way up.. so therefore a 41 or 42 will be required.

Whatever I end up with (39/41/42), I will probably end up putting the 14 back on the front for regular riding, since with the 13 on there, I will be severely overgeared for normal riding, even on the dunes.

Thanks!

Rob
 

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Maybe you should consider going the other way with your gear ratio for hill shooting. The least number of shifts will be the fastest if you can get it to launch and pull hard on the start without bogging the motor and crest the hill at the rev limit, that's the best you can do. You have to decide which gear to start off in (1st or 2nd) and then gear accordingly....
 

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Mostly Harmless
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Discussion Starter #5
I have to disagree with you on that one. My original gearing (14/37) let me climb the hill at the top of 2nd, but I'm faster up the hill with the 13/37 setup, and faster still with the 13/38, because I can use the upper part of third. This means I'm going faster because of the higher gear that I'm in, even though the gearing itself is getting shorter.

I met a guy out there a few weeks ago with a 2001 Raptor and that's how I learned this. His bike was 100% stock except for a drilled out stock muffler. He was running 11/48 gears (stock is 13/40) and 23" paddles, and he pulled the hill in fourth gear. I personally saw him eat up a piped Banshee that I later ran and only barely took.

Shows how much gearing is worth on the dunes. The key is to keep the motor in the powerband as much as possible.

Rob
 

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I'll have to look at the trans gear ratios, I'll bet from your experience that the higher gears are spaced much closer than 1st and 2nd which will work better with the lower final ratio. Can you now launch in second? My thinking was to make it pull longer in first and only need second but if the gap is too large between the two it would kill the motor when you shifted. It just comes down to optimizing what you have to work with. The Raptor with the 23" paddles makes sense, those big tires will move you in a hurry if you can set it up to pull them....
 

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Discussion Starter #7
I found out that the 40T wouldn't be ready in time for this weekend, so I changed the order to a 39 and a 41. With luck I'll have 'em for NEXT weekend. I hope.

Rob
 

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Mostly Harmless
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Discussion Starter #8
You don't have to add a link to drop to a 13-tooth in the front. You also don't have to add a link to go up to a 38 in the rear.

For dirt riding, I think the 13 is still a good idea... try it (it's only $15 and takes fifteen minutes to install). If you don't like it you can always go back.

If you're racing, the stock gearing is probably better because you will have more hookup problems in 1st and 2nd with the 13 (think of it as similar to putting 3.73 gears into your Camaro that came with 3.42 from the factory), but overall response improves quite a bit.

It also makes climbing over rocks easier since you don't have to use as much gas to keep it from stalling when letting the clutch out.

Rob
 

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If anyone cares, I got a 13 and a 40 tooth sprocket. The 13/40 combo fits without adding any links to the chain, however I did have to slightly modify the chain guide nearest the rear sprocket. This gearing is very short and is not very functional. I was going for the 14/40, but I will have to add a link or two to the chain. The 14/40 is very close to the 13/37 and should transmit less torque to the swingarm due to the larger front sprocket. Hope this helps anyone searching for different gearing. :)
 

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Discussion Starter #10
What exactly did you do to the chain guide?

I haven't put my 40 on yet... I will before my next trip to the dunes.

I'm bummed that links will have to be added to use the 14 with it. My goal was to run the 13/40 for drag racing up the mountain and then switch to 14/40 for regular riding.

Also... if one or two links are added, do you think the chain will tighten enough to go back to 13/37? It'd be worth doing if so.

Rob
 

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Rob, sorry it took so long to reply. On the bottom, left side of the swingarm, there is a chain guide that 2 bolts go through. (These bolts also hold the skid guard on.) The rear of the chain guide must be rounded with a dremel tool (or something) because the original shape contacts the 40 tooth sprocket. It's pretty obvious when you go to put it on. I'll try to get a pic posted tonight to help you out. I'm not positive, but I think adding two links will allow you to use a 13/40 and 14/40. With the 13/40 there is barely enough slack available. My guess is that adding 2 links would work fine. It would be nice to find the magic number of links that would allow us to use all gearing, from 13/36 to 14/40, without changing links.
 

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My internet connection is screwed up at home. I'll post that pic I promised as soon as I can.
 

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Here ya go. Not the best looking mod I've done, but it works.
http://photos.yahoo.com/bc/sportzmann2000/vwp?.dir=/Predator&.src=ph&.dnm=P3060002.jpg&.view=t&.done=http%3a//photos.yahoo.com/bc/sportzmann2000/lst%3f%26.dir=/Predator%26.src=ph%26.view=t
 
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