Now who said this was going on a stock 250 :-).

Reason I'm inquiring, I want to put on a set of motoz tires. Sizes offered exclude 120 which I would have preceded

I end up in to much sloppy deep mud to be comfortable going 110 on the back.

 

I put a 130/90 d606 on 2 weeks ago and have not noticed any decrease in performance. the 250 handles it easily if you've done the basic uncorking mods.

 

Even the mighty KX450 only has a 120 on the back.

if you want phat tires I would suggest upgrading to one of these -

 

Geez, you guys both need to tell the riders running the KXF250 motocrossers. They run the narrower tire.

You may not notice any decrease in performance unless you actually did the testing to know so. It may not be huge, but it is real. We saw guys running 5" wide (aka 130) knobbies on 125 motocrossers and enduros back in the 80s. They took horsepower from the bikes, especially in muddy conditions where the fat tire dug in too much for the power available. They bogged down sooner and easier than the bikes running 3.50-4.00 knobbies. Same is clearly true with the 250s considering what is run by racers on bikes with about 10 more horsepower than any uncorked KLX. They run the 100, which is about the equivalent of a 110 to 120.

If the 250s were truly capable of taking advantage of a 130 you'd see them on competition bikes. They don't. It is hard to argue with what has been learned by the factory in putting tires on their bikes and the racers who go for maximum performance. I see the same practices on sportbikes and supermotos - too wide tires that affect performance and/or handing.

But hey, have at it. I just pointed out the facts. Do as you please.

 

So 100/100 or 110/100 is what you're suggesting? Me personally I was just looking to replace the stock tire with equivalent.....the 605 is a 4.60. So a 4.10 might be better in your opinion?

 

Hey, when the heck did facts have any bearing here????

 

The 100 and 110 are the new size designations for full knobbies, not dual sport, taking the carcass into account, not the tread. The 110 has a tread width bigger than the 110, more like a 130, and the 100 has a tread width on par with a 120. Don't ask why, I don't know why they can't simply do a tread width measure on all tires. I guess it makes too much sense.

The 4.60 is the same size as a 120/80 at about 4.5" wide, so that is OEM size. I am trying a smaller size, the 4.10 is a lower profile 4" wide tire. I am looking light and less bog if I get into mud and crap. Just something I learned back in the 70s running a small bore MX bike - bigger wasn't better. Also learned that with some of my road bikes. Bigger made them handle slower and didn't really gain a bit. So I kind of got off the "fat tire" look bandwagon. Now it's function first. I'm thinking the smaller tire will break loose a bit easier when I want it to.

Summary:
If you go full knobby use the 100, if you use dual sport you can go 120 or 4.60 for similar sizing.

 

Man's got a point there.

The question was posed and I answered. Riders can take it however they want. Fact is clear heavier and wider takes more power to spin no matter whether it is 5 or 500 hp driving it - pure physics.

 

No one is doubting your logic, just pointing out the differences in power are negligible.

Mabye if your racing the little KLX, but for general everyday use you wont see a difference.

 

You could be amazed at what another +/- 1/2 inch does when off road. I can tell you it's a big difference in mud. I've dealt with it before in trail riding and harescrambling. I've also dealt with various width and profile tires and know what they do to handling on street bikes. They are not all the same and it isn't obvious only when racing.

The pros were the pros, the cons the cons. I answered a question with actual real answers, no guessing, just fact. It isn't about racing, it's about how extra weight and traction affects a smaller low horsepower engine. It is what factories see as the best sizing for the bikes they design. Even Yamaha with the significantly more powerful engine runs a 120/80 on the back. I also used past experience being in around motorcycle sales and accessories, knowing what the riders that knew what they were doing were using. The motocrossers just exemplify what I'm talking about - 250 runs smaller tires for best performance. Make a choice from there.

Can you detail any other pros and cons, backed with something besides rationalization? If so, do so. I just don't see "it works on mine" as the absolute end answer. Guys claim their sport bikes work fine as dual sports too. Do you buy that?

Besides, honestly I don't care what tire you run... run a mud tire off a Jeep.