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Discussion Starter · #1 ·
What are most of you guys running for XR100 gearing witj a stock engine? I realize that it is track specific but what will get me into the ballpark?
 

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Short tracks I've been running with the stock gearing. Short track being a 1/4 to 1/3 mile road course.

Going to talladaga next month(hopefully), and will be trying 15/48.
 

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Discussion Starter · #3 ·
How long is the track at Talladega? Both of the tracks that I'll be spending the most time at are around 0.8 miles.
 

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You probably already know this, but XR80 sprockets fit the XR100, and use a lighter 420 chain. I run 15-46 on my CRF120 and it hauls ass, but I don't think a stock motor would pull that gearing too well. Luckily, sprockets for these are really cheap! :thumbup:
 

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You probably already know this, but XR80 sprockets fit the XR100, and use a lighter 420 chain. I run 15-46 on my CRF120 and it hauls ass, but I don't think a stock motor would pull that gearing too well. Luckily, sprockets for these are really cheap! :thumbup:
Good to read, I didn't know if the motor would pull that setup. My 120 kit is sort of installed, I got stuck w/o a proper valve spring compressor. It'll be buttoned up when I get back home next weekend.

Question for you on the gearing setup, what length chain does that leave you to run in 420 size?
 

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Discussion Starter · #7 ·
Good info on the XR 80 sprockets but the class I'll run requires stock chain and sprocket sizes.
 

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I ran the stock 428 on my xr100 for a couple races. The stock engine could keep up with the modified mini's in the F7 class at the start, but it be all wound out in the straights and it was hard to keep up.

Just realize that the stock engine is going to be working against you with gearing up. You'll be trading what might be a good off the line performance for the straights. Which is more important?

I agree with 15/48 being a place to start. I know you could go as high as 18/36 with 420.

Here's a quick way to estimate the top speed change from gearing changes:
((new_Front/new_Rear)*Current_Topspeed)/(cur_Front/cur_Rear)=new_Topspeed

Like this:
((15/48)*50mph)/(14/50)=55.8mph
 

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Discussion Starter · #9 ·
The math isn't any problem for me. I've developed full spreadsheet graphs that do the math for me in every gear, and give my info in table or graphic representation. I just don't have any good estimate of what it will actually pull since I don't even have my rims and tires yet. I'm still running around on the dirt stuff. I need to get sprockets ordered but don't want to be wasting money. I'll probably order a 15T for the front and end up with a couple rears. Where are you guys ordering from?

Also if ou aren't aware of gearingcommander.com you should check it out.
 

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You will find it very difficult to find a wide range of sprocket sizes in the 428 chain. They are out there if you look hard, but not for as good of a deal. Whatever organization you are running with, with rules that say you have to stick with 428 chain in the stock class... sucks! :lol: Heavier and hard to find in the right sizes.

Send them an e-mail or call them, ask WTF, 428, really? Its a 6hp kid's bike, targeted for affordable racing!? Then go to Motorcycle Superstore and order the 420 stuff. They have 13-14-15, 36-45-46-49 for sure. 16-17 and 40-47-50-51-52 can be found elsewhere.
 
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