I have an entirely stock bike, still running in.

I'll be putting my poor wifey on the back. Between the 2 of us we weigh 308lbs (140 kg)

The bike is able to pull both of us OK, but judders a lot in 2nd, so I want to gear it down a bit.

My original plan was to turn the 14 tooth (correct me if that's wrong?) front for a 13 tooth... but my local mechanic tells me no such part available, only option is to change the rear from a 42 to a 48, which also means a longer chain ($$)

I know I can order a 13 tooth front sprocket online, but that could take weeks and then no guarantees it will even arrive...

Standard 42 / 14 = 3.0

Changing the front means 42 / 13 = 3.23 About 7% reduction

Changing the back would be 48/ 14 = 3.42 14% reduction


I'm wondering if that's too drastic a difference, or would it be about right, considering the poor thing is going to be carrying me, wifey and about 30lb of camping gear, over rough terrain with some steep hills?

Before y'all inform me I need a biturbo 'Busa or at least another 900 or so cc, I ride in Borneo, where the traffic is pretty slow and many people ride with pillion passengers on 90cc step-thrus. The KLX 250 is actually considered a "big bike" here, and even while running in I easily pass most traffic :P

But 14% reduction... is it going to buzz like a bumble bee on the road? I'll be happy if it can cruise comfortably at 90-95 kph (60 mph)

Sez you, wise Klixers?

 

i put a 43 on the rear for street tires, it made second more usable. 45 i lost on top end but low end is a lot better

 

This site might help you out on your gearing calculations.

Gearing Commander: Motorcycle Speed, RPM, Chain & Sprockets Calculator

Also, I'm pretty sure they make a 13 tooth front sprocket. I'd change your front sprocket first (since it's the easiest to do) and see how it goes.

 

Cheers.

Did you really notice the loss on top end?

If you only went down by 1 tooth on the back I don't suppose there was much difference at all?

I guess ideally what I'd like would be a 46, rather than a 48.. though that would be virtually the same as a 13 on the front..

I'm also curious if the chain guard will fit OK while using a 48?

Brieninsac - thanks, I'll check that out. A 13 tooth is available, but not here in Borneo

 

Well according to that gearcommander thing, it would be around 6500rpm at 100kph/60mph, which is OK I think.

Means it would be just below it's peak power curve, yet nowhere near the redline.

Should also be a bit of a beast off road, which I like...

I'll deffo need a bigger fuel tank though!

Actually that calculator shows that even with the 48 rear, it will still be higher-geared than my little KLX150S was stock (and I changed that to a 13 front...)

Yeah that should be fine then

 

Well, did the change today, including a longer, o-ring sealed chain.

On the ride home I could clearly feel the difference, it certainly is lower geared now, but not excessively.

It does indeed cruise at about 90 kph somewhere around 6500 rpm, which is OK. Not too buzzy, and nice to feel such a surge if you crack it open, even in top gear - but according to that website it should be 100 kph at 6500? I'll take a closer look next time but I'm finding it fine.

The extra torque makes it easier to ride, I think. Can easily burble around in a high gear, but for swooping past traffic or accelerating out of bends can just open the throttle a bit.

Before I remember thinking it was nice to have 6 gears rather than 5, but it needed them, as I often found myself having to downshift if I slowed down for anything. I seemed to be busy changing gears, more so than on my little 150 - but now it's actually better than the 150.

A few times found myself checking to see if I had a higher gear..? Nope, already in 6th, but like I say, it doesn't seem excessively buzzy, just more punch and torque.

Disclaimer - on a tall, dirt-orientated knobbly-tired bike, my arms wide and my peaked helmet catching the wind, I'm perfectly happy to cruise at a steady 55mph (88 kph). If you're someone who demands to go faster than highway traffic, then your results may vary

To me, enduros are not about high speed. Heck, I had a 30 horsepower Honda MTX screaming 2 stroke, gobs of arm-wrenching power - but I would be regularly overtaken by locals on scooters. Why? Because it was low-geared for the dirt and outright unstable at high speeds. That bike actually had a redline section on the speedometer as well as the rev counter - above 80 kph you were in the red zone.

So I'm always a bit confused when people ask if this, or any dirt bike, can cruise at high speeds on the freeway? No, and why would you want to? That would be an unstable, uncomfortable ordeal; no fun at all. Would you take a Jeep Wrangler on the autobahn and expect to keep up with 120 mph traffic? No. Would you take a Merc' SLK off road? No.

I'm finding the KLX250 is pretty much the ideal dual purpose, and I think this sprocket change has settled my mind about it. Now I'm looking forward to my luggage racks (already ordered) and going on adventures!

 

Actually cruising on freeways can be done on anything that can maintain the minimum speed. In Ohio that is 45mph. Of course that isn't very safe in some urban areas where traffic is heavy and fast. I remember someone posting they got pulled over in CA for doing the speed limit, being informed they needed to speed up to stay with traffic. At the legal limit they were fouling traffic!

We used to ride Honda MB5 50cc 7hp motorcycles on the freeway where I used to live. Of course heavy traffic was having six cars within a quarter mile of each other in 4 lanes...

 

Well that's another happy aspect for me, as most of the roads here aren't great, and with 100% import tax on cars most people are driving small cc cars, and driving them slowly.

Drove me nuts when I first came here, but I've settled into the relatively easy pace - and it also means a 250 can easily keep up with 97% of "highway" traffic

 

Update - today's ride has changed my mind a bit. Deffo a bit too buzzy on the open road, and that website is wrong.

For me to reach 100 kph it's buzzing over 7000 rpm, not 6200 or whatever that website said. I find it's only cruising comfortably about 85 kph, ie the same as my old 150.

Will see how it goes with wifey on the back and some luggage. Certainly it seems a bit too low geared for just my weight. Earlier I overtook a car on a long, steep hill, whooshed past the car, gathered some decent speed, went to change up into top gear, realized I was already in it...

What would be perfect is if this thing had a 7 speed gearbox

 

Get a 15T front sprocket to lower rpm and vibration.