When I bought a 09 KLX250S last year there were slight dents in the front rim. I'm sure I made them worse by hitting some big rocks and ruts at low pressure before switching to Tubliss. Tubliss is very tolerant of bent rims so I thought this solved the problem.

Lately I have noticed the front brake is pulsing noticeably. I ride 95% off-highway but am concerned about having good emergency braking under all conditions.

I put a dial gauge on and measured:

Front rim axial deflection: varies up to 0.070 inch. Spec is 0.080 inch.

Front brake rotor axial deflection: up to 0.020 inch. Manual says "Runout TIR 0.12 mm (0.0047 in.) or less"

I don't know much about rims or rotors. It seems like the rotor is bent enough to cause the pulsing. It's around 4x spec by my measurement: 200/1000 vs. 47/1000 if my calculations are right.

It is quite possible I smacked it on a rock and that's why it has suddenly become noticeable.

So could the rotor issue be independent of the rim issue?

OEM rotor is $235. Looking for a cheap and tough solution. Cosmetics are not important, toughness is.

Thanks for any words from experience.

 

Rotor and rim issues should be separate. Although the same rock can damage both.
You're going to need a new rotor unless it can be bent back (personally don't see that happening).
I'd buy a nice aftermarket disc for the same cash.
Or look for a whole wheel for $300 or less?

 

what shows as bent rotor could also be bent hub flange.

 

KLX300 rotors fit, I have one on the front of my 09, just not the trick petal cut, but it works extremely well. I have one on the back too, but had to get the 06-7 carrier to suit the smaller 300 rotor.

You can find them on ebay easily for less than $100 all day long, in fact there is one on ebay exactly like the one on my bike for $37 and free shipping. I picked up a spare for less than $20, since both my brother and I have 250s. They had a photo of a front rotor listed as a back rotor at a buy it now. I asked if the picture was the part, they said yes so I bought it... it was the front rotor that I knew was a great deal.

Looks like this:



The seller, a salvage shop, on ebay guarantees the rotor to be true. Others are there ranging on up to the high dollar used replacement for $142 if you must have the petal cut. I didn't care, mine actually has a note KLX300 in Sharpie on it.

I'm betting on the bent rotor over the flange, but you can check the flange with a dial indicator in on the inside of the rotor to verify which it is.

As for the rim, if it is flaired you may be able to "influence it back with a big dead blow plastic mallet. If the rim has a bow in it you may be able to pull it back in line by truing the rim, some spokes may have loosened to the point where it will wobble. If the rim is bent beyond repair almost any KX or KLX 21" rim has 36 holes and the same basic hub, making them a direct fit. Another ebay item.

The only negative on the 09 and later is that the hub machining for the electronic speedo makes it so you can't swap out the wheel with an earlier KLX250 or 300. That sucks because it wouldn't be too hard to find a good deal on a whole KLX300 front wheel in decent shape.

I know a fair amount about this because my 650 uses a similar hub and the rotor from it would fit the 250 hub, but is a 300 mm rotor so it won't work with the caliper position. I've done a lot of research because of wanting to do a set of SM wheels for the 650 and needed to know what works and what doesn't. Since the hubs are nearly the same on a large number of Kaw off roaders I learned what works... and what doesn't, like the elctronic speedo drive issue for the 09 up.

Recap - find a KLX300 rotor if that needs replaced then try it. See if you can pound flairs out of the rim (loosen spokes before doing so to give it room to move). Get a KLX/KX/KDX 21" rim if you can't fix the rim.

Hope that helps a bit.

 

The rear rotor was bent/warped on my 09 and I was able to straighten it with a hammer

 

Thank you for all the info. I will update with results.

 

I ordered the linked one: 143 2000 KAWASAKI KLX 300 FRONT BRAKE ROTOR

Everything aligned but my 2009 KLX250S has 10 mm holes (for a flanged 8 mm threaded, 10 mm hole) bolt. The item above has 6 mm (I'm almost positive) holes. Way too small.

So confirm sizes not just pattern.

 

Sorry, forgot to mention sometimes you may have to drill out the rotor mount holes. I did with my rear rotor and after looking just now, I saw the front had been drilled out. The only concern would be if you wanted to fit the 09 and up rotor on an earlier model, it's easy to drill out, you just can't easily add material. I will remember that next time.

The drill size should be 13/32" or 7/16" the countersink in the holes will automatically align everything, as will the raised inside ring on the hub. The fasteners will stick out a slight bit further due to a shallower countersink used with the smaller fasteners. No big deal mechanically. Few would ever visually notice the difference.

Drill holes to suit the 10mm fastener... small price to pay when saving how much money on the part?

 

Actually I did try drilling out the rotor. The material is very hard. The first two holes burned up two "Harbor Fright" TIN bits. For the next two holes, I drilled them 1/64-inch larger at a time which worked better.

But for the 8 mm thread, 10 mm "shoulder bolts" on my wheel the hole has to be 10 mm. I used a 25/64-inch bit. So the countersinks for the 6 mm flat head bolts are long gone: drilled away.

The 10 mm shoulders spread force out over a large diameter but they have no wedging action like a countersink. Still, when bolted up the rotor is very tight.

There is another problem. One side of the rotor is lightly scored. Not deep but certainly not smooth. Not enough to catch a fingernail but noticeable. I'm sure the seller would say this is insignificant, but wonder if it will reduce braking slightly. A little braking loss can have bad effects.

Any experience with rotor scoring and impacts on braking?

At this point I am tempted to go for a brand new EBC rotor for a hundred bucks.

Supposedly the "steel used in the rotor blades is a special stainless blend with higher friction effect than the normal heat-treated stainless steel found on stock discs. It boasts up to 10% improvement in friction. The weight of the new contour series rotor is reduced by 5-10% by using a 6 (only) button square drive system (SD-System™) on a lightweight alloy center hub."

Sounds like a good placebo effect if nothing else.

 

I've never had any luck with Harbor Freight on that sort of stuff. I destroyed a step drill in no time on mild steel angle iron. Never again. One place where the quality stuff works best. You could get flat socket cap screws at Fastenal to secure the rotor if preferable.

Now on rotor grooves... An engineer/road racer acquaintance, Doug Libby, gave his buddy, my neighbor, hell for turning rotors on his car. His logic made total sense if you think about it:

• New pads will bed into the grooves, so there is no problem there.
• The grooves actually increase braking swept area - think about it...
• The ridges are essentially "fins" and will aid cooling - however negligible it may be.

Totally logical and true, plus turning rotors, which for a motorcycle and the hard rotors would actually involve surface grinding, is removing more material yet. Makes sense to me so I refuse to turn rotors when brake pads are changed. Let 'em bed in and go.

A few notes on Doug. He raced a TZ750 in the 80s AMA F1 class. Libby was one of only two riders that survived a blow out on the banks of Daytona at about a buck eighty, the other was Barry Sheene. Doug spent some time after retiring as a cop in Michigan, doing engineering at Crane Cams, with some focus on Harley cams.



In a side note on car rotor turning it seems a warped rotor will simply warp again when it gets hot and if it isn't an actual warp it is a hard/soft spot so the pulsating will return soon. In those cases get a new rotor.