atc 250r gearing

[william16339]

hi, i have a 86 atc 250r, 38mm carb, boyesen power reeds, fresh rebuild, and pipe and other stuff...i hve 13-39 gearing now...my friend has 14-39, i notice its a little faster, but it d0sent seem like i felt power los, and his is all stock, his 250r...so i was thinking a 14-37 setup? how much speed do you think id gain from a 13-39 to a 14-37? thanks

[JasonB]

Depends, what kind of riding do you do? I am running a 13 up front and started dropping rear teeth to achieve different results w drag racing but it kills your use for trail riding. I was running a 37 or 38 tooth for racing and tried trail riding and had issues even using 1st and 2nd like normal. I have a 14 tooth front I haven't tested out yet, I forget how the ratios go and what sizes get you what results. I would recommend heading over to trx250r.net with a question like that, it's where I go for my 86 250r inquiries lol they are very thorough with their 250r jetting, gearing, racing and riding info. Very trike friendly too!

[bannedbrraap]

i posted this in another thread but i will do it here again......this is a gearing calculator, its preloaded with a few different machines....86 250r is in there. works really good.

http://www.filefactory.com/file/17pu...quad_calc1_exe

If you cant get the link to work PM me with your email address and i will send the file to you.

When you open the link...scroll down to the bottom left, and click the red download button, it will ask you to type in some words, then you wait 30 seconds and then you can download it.

[Vealmonkey]

You need to invest in some quick change rear sprockets and start experimenting. Let us know what you find out.

[dcreel]

You need to invest in some quick change rear sprockets and start experimenting. Let us know what you find out.

Wow.. Sidewinder still sells the 2 piece sprockets.. They are a special order item.. I had no idea, I thought they quit selling them.. Made changing rear sprockets a lot easier..

[rayatc84]

Here is a table I made few weeks ago of speed calculation in function of the final gear and rear tires diameter.

Of course they are theoretical speed, but it gives you an idea of the impact of front/rear sprocket / tire diameter modification.

Speeds are calculated taking into account:
• Primary and secondary gears transmissions given in the 2 250R Shop Manuals,
• Theoretical tires diameter: 18", 20" and 22",
• Speeds calculated on the last gear: 5 for ’81-84 250R, 6 for ’85-86 250R
• Speeds calculated at 8500 rpm (supposed to be around the highest rpm)

Speeds are classified in ascending order, and are in km/h (it’s what we use here…); I let you do the conversion in mph…

The 3 colored cells are the OEM combination (front/rear sprocket + rear tire diameter) for each 250R generation.