Just got my 250 a 12 model. I'm curious as to how fast it will go stock, not blowing the motor fast but what's it capable of? I'm older and will probably never know cuzz I believe in speed limits and will never take this light bike on the interstate in a major metro area cuzz of the crazy cagers.

 

It's kind of a case of how fast do you need to go, plus how slow do you need to go.

According to the shop manual supposedly the stock 09 KLX250S has a 14/42 final drive which puts the engine around 58 mph at 6000 rpm, and only 7000 rpm at 70, right in the good part of the power band. The engine will handle it better than most riders with a tachometer in front of them. Seems most scooters rev 6500-7000 most of the time when accelerating and doing highway speeds. They last a lot of miles too.

I've run a 15/39 sprocket final drive, which is more of a road gear. It is high enough I didn't shift into sixth unless doing about 55 mph at around, the rpm was just too low for reasonable acceleration at 5500 rpm. Top comfortable cruising speed easily 65-70 with more to spare.

On the other hand I presently am running a 13/47 which gives me a walking pace first gear and should handle all off road work I would do. I am still waiting to really test it. If it is lower than I need, I will step it up a bit. About 50 mph at 6000 rpm in sixth gear. Can you say "not a highway gear"?

So you weigh where and how you're going to ride then gear appropriately. The stock set up is a good general setting.

 

As Mark said you first have to look at your gearing. I'm running 15/42 and top out at 80 mph.

 

I'm running a 13 Tooth and top out at an indicated 83 MPH.

Speedo is supposedly out by 10% from the factory on the S models though. Sooo maybe 75 mph actually. Depends on tires size and tread life a bit too.

 

95 mph downhill slightly in a tunnel. MCM hurting me here a little perhaps. Perhaps the 3N DJ136 was the problem.
If I needed to see 100 I'd undo the MCM and probably get it. 15x39 on a 130/70-17 tire, bout an inch smaller radius than the DS tire.

 

I went for a ride out on a beautiful day last week with a few guys after work.
They were riding 600cc / 1000cc bikes, obviously bikes well out the league of our klx's.
Anyhow we got to an open straight were we all just pinned it.
I saw 90mph on the speedo, this felt like the bikes absolute limit.
Handle bars shaking, vibrating etc it did not feel safe at all.

I know the speedos mph is off but not sure how much, I also had a gps app running on my phone recording my route and average and tops speeds etc. this read top speed as around 75mph. I don't think the speedo is off by that much though.

 

Everything stock on mine, except a DynoJet kit installed by a local motorcycle shop to make cold starting easier, and the bike does not need warmed up and runs like a champ.

I've been 75 on the highway, 0-60 is quick on this bike.

at first I read the manual and never ran it over 6 thousand RPMS, if you do that by the book though you'll run out of gears and be going slow.

Some gears I rev up to 9 thousand RPMS, it will get to 65 MPH quick! hold on!

 

I rode to work one time running 14x43 and saw similar revs. 60mph at 7000rpm. I was a little surprised you got those revs with that gearing.

 

My numbers were off a bit.

My error was I had my tire diameter too large by .7" the fact is the speed with the 13/47 shows 7000 at roughly 55 mph, where the 15/39 will show about 75 mph at 7000 rpm. Fact is the low final drive set will have 6th gear near equal to 4th gear on the high final drive set. That's why I don't shift into 6th until about 60 mph with the high final drive set Serious difference.

As for comparison to your bike, one difference is running a 17" low profile tire and I am running an 18" higher profile tire with probably around at least 1/2" difference in diameter. It's all in the numbers.

 

My 2009 when it was bone stock: One time, with a very, very strong tail wind, body in tightest tuck possible: 101 mph indicated at redline in sixth gear. Opposite direction into same wind, same tuck, I was struggling to maintain 65mph indicated. Normal conditions, it could do 80-90 mph indicated in 6th. I figured with the OEM front tire, the indicated speed was 10% fast.

With mods and stock gearing, it still does about 80-90 in normal conditions in 6th.

Just today, with 13/47 gearing it did 79 mph indicated at redline.