i have acquired a set of 2009 klx250sf rims and tires for my klx 250s 2009. the rear is a direct swap no issues there. (i do need to mess with the gearing ratio if anyone has any idea. i saw on another forum that someone was running a 39 rear and a 15 front? anyone want to confirm that this works well . i do mostly city riding but hopping on the highway and being able to go more than 60mph would be nice)

my main issue is with the front im getting a crazy squeaking sound. my assumption is that the disc is rubbing against the pads because after a test ride the front disc is really damn hot. upon further inspection comparing the seal from the old rim(250s) to the new (250sf) they are different maybe causing a spacial issue making something rub where its not supposed to... also not sure about the disc size difference i swapped out my old disc to the new sf rim and it was making the sound worse. i swapped back the sf disc to the sf rim and it was still making the sound but not nearly as bad.

has anyone done this exact swap themselves. im pretty stumped and was under the assumption that it would be a direct swap. im seemingly being proven wrong.

is there any way the speedo not being notched properly into its slots would be causing this sound? ( a possible error i made while installing the new parts)

 

15/39 will work, but will be tall. I'd say a 14/39 would be a better choice, but set it up with the 15/39 for the chain, keeping it as short as possible, that way you can use a 15, 14, or possibly a 13 without changing anything other than chain adjustment.

The SF uses a 300mm rotor the S uses a 250mm rotor. You need to use the 250 rotor if you didn't change the caliper carrier. If you tried to run the larger rotor with the stock S front end the rotor should rub on the caliper, the reason for the rotor being hot. The SF wheel with the smaller S rotor should have worked but you may need to verify you have the left side spacer in there and the speedo drive with the spacer in the right side properly. Look here - click - to see the spacers with the hub.

You should buy a used 250mm rotor to put on the SM wheel if you want quick swaps, they're usually on ebay for around $30 or so, I even got one for $20 one day. They may not be the petal cut, but they will work. My 2009 has rotors from a KX250 on the front and a KLX300 on the back, no idea what year either are. All KLX250R or S, KLX300R, ir KLX650R will fit the front. If you want the large rotor you will need the caliper carrier for the SF to work with the larger SF rotor.

 

I am the one with 15/39 BUT it’s on a 2022 Klx300. I am not sure it will work that well on a less powered 250. The best thing to do is try different gearing and chose what works best for you and your riding style. Front sprockets are pretty inexpensive and easy to swap back and forth. Let us know what you end up with.

 

When it comes to the gearing, the stock 2009 SF used a 14/39 sprocket set, so going one tooth higher on the front will work. I ran that gearing on my 09 KLX250S model. It works, but you have to shift more frequently at higher speeds keep the rpm in a good range. I found I wasn't shifting into 6th gear until around 60-65 mph and the tall gearing made downshifting on some larger rises a necessity.

I'd do the stock 14T if it was me. There is no reason to not to let the engine rev. Small bores easily handle high rpm because the reciprocating parts (piston/rod) are very light, figure about the equivalent to the pistons in a ZX10. You can go out and rev the engine all day long at 6000-7000 rpm without hurting anything in the engine, yet still get decent gas mileage, been there done that when dual sporting with a 13/45.. That small a single is running 10,000 rpm, maybe more in motocross engines and holding up fine. Dual sport and road riding don't hold a candle to that kind of riding.
I just did the gearing to see what happened. As said, I'd do the 14/39 on a street bike just to avoid a bit of shifting at higher speeds based on personal experience.

For tires, when I was looking at supermoto-ing my KLX650 I did serious research including tire diameters to know what gearing would be needed. Fact is often the 17" dual sport or knobby isn't than much larger than a similar street tire. You have to look at the manufacturer sites to see what the inflated diameter is on the tire.

Here is an example:So it is between .50-1.30" smaller diameter on the road going tire Comparing the 120/70--18 to the 140/70-17 there is 4.09" difference in circumference or around 5% smaller. That might increase rpm by around 300 rpm higher with the smaller SM set up.. I'd say not that much difference to really matter, Otherwise I would say do some calculating on the sprocket ratios to see what sprocket sets would work if you were trying to get equal rpm. There are some calculators online to work with it. I had an excel chart, but my microsoft license has expired and I'm not sure I want to spend the money to renew it. Might do the chart in a google sheet.

 

hey guys so i got to the bottom of this and it was the simplest little fix i think ive ever dealt with. when i first put the new set on my speedo had chewed into the old seal , i just swapped the seal turns out that was what was throwing off my front alignment. now to **** with some gearing.