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Old 08-29-2011, 07:55 AM   #1
Mark5PA OP
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Sprocket ratios, F800

This from my ratio chart, in the only available sprocket for the F8

.....15 ...16... 17
41- 2.73 2.56 2.41
42- 2.80 2.63 2.47
47- 3.13 2.94 2.76

Like others, 1'st gear is a tad tall for me with 16/42 sprockets. I have heard some people say the the 15/42 revs a bit high on the freeway. Between those, 2.63 & 2.80, is 2.73 (15/41) and 2.76 (17/47).
I like a bigger front sprocket. Other than guessing on chain length, any problems running the 17/47?
I know, picky. But I am changing the chain/sprockets soon, so I should get what gearing I want.
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Old 08-29-2011, 08:31 AM   #2
itsatdm
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My view of what the problem is on this bike is, the very very lean AF fueling on this bike between idle and 2,200 rpm. From one dyno run I saw, AF ratios range from 17 to 1 to high 14/1 in the space of a few hundred rpms. The result is a jerky throttle response at low rpm with gradual throttle input.

You can improve that with an Accelerator module, Booster Plug or Coon Ass module. It will improve low end torque and allow modulation with the throttle. A G2 eccentric throttle tube makes it even better.

I have run the 15/42 and it does mask the problem due to running above the problem area for a lot of terrain, but it is still there. The bike will easily run highway speeds at the expense of mileage loss and vibrations at higher rpm.

I have also run the 17/42 with the module and it will pull any logging rd I have run. It actually can be lugged at lower rpm than stock

Currently back to stock gearing and see no need for the 15/42. What you propose is a compromise, I just think there is a better solution, unless you are running single track.
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Old 08-29-2011, 09:26 AM   #3
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Quote:
Originally Posted by itsatdm View Post
My view of what the problem is on this bike is, the very very lean AF fueling on this bike between idle and 2,200 rpm. From one dyno run I saw, AF ratios range from 17 to 1 to high 14/1 in the space of a few hundred rpms. The result is a jerky throttle response at low rpm with gradual throttle input.

You can improve that with an Accelerator module, Booster Plug or Coon Ass module. It will improve low end torque and allow modulation with the throttle. A G2 eccentric throttle tube makes it even better.

I have run the 15/42 and it does mask the problem due to running above the problem area for a lot of terrain, but it is still there. The bike will easily run highway speeds at the expense of mileage loss and vibrations at higher rpm.

I have also run the 17/42 with the module and it will pull any logging rd I have run. It actually can be lugged at lower rpm than stock

Currently back to stock gearing and see no need for the 15/42. What you propose is a compromise, I just think there is a better solution, unless you are running single track.
I do have a Booster Plug, works great! I do ride a fair amount of single track, and have to still slip the snot out of the clutch. I was looking for an in between of stock and 15/42. Any reason I shouldn't use the ones I mentioned?
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Old 08-29-2011, 09:49 AM   #4
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Not really, other than the mileage, hwy vibrations, and adding 2 or 3 links to your chain. Might cause some rubbing on the chain guard, but I don't know. You don't state the year of your bike, remember the 2009 sprocket bolts are 8mm.i
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Old 08-29-2011, 10:36 AM   #5
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I run 17/46 and had to get a 120 link chain. It's a tad long - the adjusters are almost all the way out but removing links won't be a problem. How did I get a 46t sprocket you may be wondering - Woody built me a 18" rear using a super sprox for a KTM.

You will need a longer chain with 17/47.
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Old 08-29-2011, 11:08 AM   #6
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Quote:
Originally Posted by Lounge View Post
I run 17/46 and had to get a 120 link chain. It's a tad long - the adjusters are almost all the way out but removing links won't be a problem. How did I get a 46t sprocket you may be wondering - Woody built me a 18" rear using a super sprox for a KTM.

You will need a longer chain with 17/47.
I wasn't going that crazy with the ratios (rear wheel), although I would like to have some more tire options. I am going to get a chain w/master link. Would I be safe getting a 122 link, and chop down as needed?
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Old 08-29-2011, 11:21 AM   #7
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I don't see why a master link chain wouldn't work. The DiD 120 that I'm using is plenty long enough for me - it will stretch also - and if youre not "going that crazy" I think a 120 would be fine but your bike your call. I still need to chop a link or two off mine to get the adjusters more towards the middle.
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Old 08-29-2011, 12:12 PM   #8
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Originally Posted by Lounge View Post
I don't see why a master link chain wouldn't work. The DiD 120 that I'm using is plenty long enough for me - it will stretch also - and if youre not "going that crazy" I think a 120 would be fine but your bike your call. I still need to chop a link or two off mine to get the adjusters more towards the middle.
Thanks.
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Old 08-31-2011, 12:08 AM   #9
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I'm still running the 15/45 I set up last year. Gives me what I wanted; better low speed control, although it's at the expense of highway mpg.
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Old 09-01-2011, 10:41 AM   #10
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Where is this allusive 45 tooth rear sprocket hiding? I could never get anyone (human or otherwise) at Supersprox to confirm they have one available. I want to swap between 17/45 & 15/45. That would be ultimate combo for me.

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Old 09-01-2011, 11:42 AM   #11
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Where is this allusive 45 tooth rear sprocket hiding?...
On their website in plain view.
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Old 09-02-2011, 08:15 AM   #12
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After I thought about it, I may go with the 15/41. It is just a little lower than mid way between stock and 15/42.
The 17/47 is real close to the 15/42.

I have been experimenting with holding a steady GPS speed, and down shifting to 5'th, and watching the instant gph readout. Up to mid 50's, not much difference. 60 and over the difference gets substantial. Guessing that is where the parisite drag digs in.
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Old 09-05-2011, 05:02 PM   #13
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........15 ...16... 17…18
41- 2.73 2.56 2.41 2.27
42- 2.80 2.63 2.47 2.33
43- 2.87 2.69 2.53 2.39
45- 3.00 2.81 2.65 2.50
47- 3.13 2.94 2.76 2.61


http://www.touratech-usa.com/Store/3...unter-sprocket


I just threw in the 18 tooth sprocket that touratech has.


How long does it take to change the front sprocket. For instance, if you wanted to carry a 15 and an 18. traveling a few hundred miles to the trail.... that kind of situation. and would there be enough adjustment in the chain to facilitate this??

thinking like an 18/45 15/45 combo.


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Old 09-05-2011, 06:30 PM   #14
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Perhaps its just me but I dont really see the problem with the 15/42 combo. I switched to this from the stock 16/42 and have been very happy. In slower technical stuff, first and now even second gears are much more usable. As for losing it on the top end, I guess I do use 6th gear more now but its just fine up over 80 mph and for me much beyond that with knobbies is not too great anyway. Its such an easy switch from 16 to 15 that before you go to the effort to modify your chain, etc, you might just get a 15, put it on and see what you think.
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Old 09-05-2011, 06:50 PM   #15
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I am sure the 15/42 isn't that bad, but I have heard the mpg complaint. Going to replace the set anyway, so something not that low might be the nuts. Or not. Worth a shot.
I thought about the switching sprocket thing. Not that hard. But most of my dirt is impromptu. I see a butterfly, off on the dirt I go.
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