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Discussion Starter #1
Hi all,
can any of you peep's recomend a sprocket sizes for doing trackdays, i have just done cadwell, had a great day but would like a bit more speed on the straights, at best i can just pull 102mph or is that about the best i can get???
advice appreciated

Pat...
 

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I only lose out down Park straight on my SM. So Gary Gixer flys past you on the straight bit, just cut him up at Mansfield :D

Who gives a crap about the straight bits
 

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In the first part, you've pretty much answered your own question. And in the second part, yes you can definitely get it moving faster than 102 with suitable gearing.

Best move is to count the teeth of both sprockets you have now. divide the rear teeth by the front to get your drive ratio, and reference point.. Then run a few numbers to work out how best to change your drive ratio to suit the track your at. A lower ratio will achieve a higher top speed. But remember it will effect all gears not just 5th. so all your change points will be marginally later, engine braking less sharp, etc.

While your considering that, keep in mind that different tooth combinations require different length chains. And will change where the axle tightens up, effectively changing your wheelbase. So some combinations will cost more than others, and have greater/lesser effect on handling.

If I were to take a wild guess at your current config, I would suggest the cheapest option would be to obtain a rear sprocket 2 teeth smaller than your current one, on the hope that the axle can move back far enough to get propper chain tension. But do keep in mind that chains stretch, and teeth wear, so new and old parts do not play well together, and will cause accelerated wear. Personally, I put aside the full set I had fitted, then bought a new chain and a bunch of cogs in different sizes. Swapped them around over a fortnight and found a couple of sweet spots for different applications. Wound up with two sets that I swap between.

Anyway its easy mechanistry, go forth and play.
 

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Gearing

Living in Qatar I do the full Losail MotoGP circuit on my 640. I think I am correct in saying that the main straight is the longest on the MotoGP calander. I have changed from the standard 16/42 gearing to 17/40. Cant say that i noticed any lack of drive out of even the slowest corners. There are a couple of places that I am now in one gear lower but on the long straight I can now pull and indicated 183 Kmh ( Low 170's before). My lap times have gone from 2:46 ish on 16/42 down to 2:42 on 17/40.

Hope that helps.:scooter:
 

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When I first got my 640 it came with 17/ 38 gearing was good for about 120mph tailing a SAAB on a dual carriage way. could easily pull 115 on its own but it did knock off a lot of acceleration a lot happier with 16/42 will still clear 105 but the way it gets there is something else. With the 'taller original gearing the bike really did struggle into strong head winds and would not pull more than 100.
 
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