Please post up your experience with gearing combinations and chain lengths. I'd like to compile into a table in the FAQs to add to the collective knowledge base.

For example:
Stock sprockets for the KLX250s are 14 front and 42 rear with 106 link chain. 13 & 15 fronts also work with the same chain length.

13/45 w/ 108 links is popular. The 14 & 15 work with same chain length.

What do you run or have you ran in the past?

Thanks!

What works:

Front / Rear, Links
15 / 39, 104 (snappster, post 48)

13 / 42, 106
14 / 42, 106 (stock for s model)
15 / 42, 106
15 / 42, 106 (2009 model, tight fit, atleastbehandy)

15 / 43, 106 (snappster, post 48)

12 / 45, ??? (moabmike)
13 / 45, 108
14 / 45, 108
15 / 45, 108

13 / 47, 108 (rgmr)

13 / 47, 110 (Lutz)
14 / 47, 110 (Lutz)
15 / 47, 110 (Lutz; AdventuresinRealLife, snail adjuster at 5)

14 / 48, 110 (reinigef, middle of adjustment)

13 / 49, 110 (IDRIDR)
14 / 49, 110 (IDRIDR)
15 / 49, 110 (IDRIDR)

13 / 50, 110
14 / 50, 110 (TNC's favorite, 2006 snail adjuster at 1.5)

13 / 51, 110 (2006 snail adjuster at 1.5 with a new chain, IDRIDR)
14 / 51, 110 (adjuster at -0.5, IDRIDR)

15 / 51, 112 (IDRIDR)

What doesn't work:
Front / Rear, Links (Notes)

13 / 49, 108 (seemed too tight with axle adjusters forward, insufficient slack)

15 / 51, 110 (IDRIDR - needs a 112 link, see 14 / 51, 110 notes above)

 

IMO you dont need to replace the rear sprocket or change chain size. With 13 fornt is enough for trail, with 14 perfect for dual sport and 15 perfect for dual sport and more than 24 hp wheel power

 

Running a 13/47 on mine with a 108 link chain. My son's KLX250s is running a 13/49 (he's a big guy, so the even shorter gearing helps) with a 110 link chain. The 108 link with the 13/49 seemed too tight even with the axle adjusters all the way forward, so we went to a 110, to keep proper slack on the chain.

I'm running a Moose Racing rear chain guide (stronger than the stock one), and with the 47T sprocket, I had to cut a little out of the upper wear block on the chain guide or the sprocket teeth would gnash on the wear block.

We do 90% tight woods single-track riding, so the 13/47 and 13/49 combinations are great for it - I wouldn't want to ride with any taller gearing now that I've had a chance to try this gearing. If I was commuting, I'd probably leave the stock 14/42, though.

 

It really depends on what type of riding you're doing, and the bike. My friend has a WR250R, and has a 12/47 setup on his, but the gearing (coming out of the transmission) on the Yamaha is different than our KLX's (I think his is listed on GearingCommander.com as a 3.120 and the KLX as a 2.800), so it's not really an apples-to-apples comparison.

If you're doing tight single-track with lots of steep hills like I'm doing, the 13/42 just doesn't cut it.

 

rgmr:
Thanks, exactly what I'm looking for!
I too ran 13/49, and also 14 & 15 with the 49.

I'm currently running 13/51 (and need to re-count links). You don't want to ride 13/42 to Wildhorse Lookout. But, please, let's keep this thread to what works (and what doesn't work). Let's not turn it into a "what gearing is best" thread, nor into a "what oil is best" thread .

 

Scott, 14/50 is "the best" setup for off road. Oh...sorry...I just now read your warning about not making this thread a "what gear numbers are best" thread...LOL!

But seriously, that's what I run on my '06 with a 110/100 18" rear tire. My chain is a 110-link, and the adjusters have the axle pretty close to max forward position at the 1.5 number on the snail adjuster number range. For off road I prefer the rear wheel as close to the front as is reasonably possible on this bike for my riding. While agreeing with you on not making this thread a "what's best" issue, I would say that the 14T front sprocket is probably the best selection sprocket as the 13T really tightens the chain arc for the 520 chain. I think it's best to do a larger rear sprocket to lessen this issue. And if someone actually even makes a 12T for this bike, I think that's a formula for serious chain abuse. A 520 chain will not like that at all.

Here's a link to a nice, concise Thumpertalk thread on a 10-point issue about dirt/DS gearing. Hardly the "do-all", "end-all" for the issue, but it's a nice reference point.

10 Secrets Of Motorcycle Gearing - General Dirt Bike Discussion - ThumperTalk

 

Thanks, Thad.
So, can I assume that although not ideal for chain karma, a 13/50 would also work with the 110-link but a 15/50 is questionable and may need 112-link?

Good article.

 

I have run 12,13,14 and 15 with the same chain. Now I mostly run the 13 with the chain shortened for the shortest wheelbase[ my fav].

 

Is the effective chain adjustment distance the same on both models of the KLX (I mean '06-'07 and '09-'15, not the S and SF)?
I know any gearing/chain combo has worked for me on a '12, just as it has for you guys with the older model. That's where I got the gearing info.
More curious than thinking it's a problem...

I think a 108 gives the most options if you want to go from street(stock equivalent) to a good trail set up. I've run a 14/47 108 but it was tight to the front of the swinger, almost too tight with a 120/80 D606.

 

15/42 even with the BB is a bit tall for tight trails. Great on the road and more open trails though!