I've been toying with the idea of somehow fitting a longer swingarm to my KLX. I'd like to get the wheelbase in the neighborhood of 58 inches vs. the 56.5 that it is now. Why? Improved high speed stability, better fit for a big person. I see two ways to go about it. One would be cut and weld the existing arm. This is a sketchy proposition. The other would be to see if a swingarm from another model, maybe a KX or KLX450 would fit, or even another manufacturer. The crux would be fitting it to the frame at the swingarm bearings. Width and diameters would have to be made to work. Then the brakes assembly would have to match up with the rear wheel, brake line would have to be longer, etc.

Why not just buy a bigger bike? Well, 'cause I have the KLX. I like it. I like to modify. And maybe I'm irrational. No good reason really.

Any ideas or insights, especially as to the fitment of another model/manufacturer's would be appreciated!

 

Guido, it's an interesting idea, but I think it has some major challenges. Even if you find a compatible interface at the main swingarm pivot with regards to bearing/pivot bolt/width issues, you have to worry about how the dog bone links will hook up and the exact point on the new swingarm. Just a few mm's at any othese points makes a dramatic impact on the suspension rate characteristics.

In the long run, a good fabrication shop would probably be a better way to go with the stock swingarm. A good fabricator could lengthen the arm in a very structurally sound manner while retaining all the OEM issues that could also cost a great deal of money to address...rear wheel, disc brake tabs/components, etc. Once again, however, your suspension rate will still change a bit due the leverage of the extended rear wheel being further away from the pivot. Also you may have to make alterations to the rear fender/subassembly for the new arc of the rear wheel.

This project would have "can-o-worms" written all over it. Not impossible but perhaps one of those diminishing returns type of deals. If I'm hearing you right, stability is one of your goals. Are your forks all the way "down" in the triple clamps, thereby raising the front to its max...giving a more stable headtube angle. Are your fork springs stiff enough for your weight and riding style, thereby preventing fork dive or excess sag which steepens the headtube angle taking away stability. A stiffer spring in the rear with soft fork springs can cause high speed instability.

Damping quality is often overlooked in its contribution to stability, and both ends of the KLX have a serious lack of compression compliance in rough terrain with successive hits. The front can chatter or porpoise with harsh damping depending the spring weight.

I have an '06 with Race Tech springs and Gold Valve damping, and I find the high speed stability to be very good. The front forks are all the way down in the triple clamps.

 

Yeah, I thought about the suspension issues but I hadn't considered the dogbones. So you think fabrication shop is a better bet? If I went that route I'd get another swingarm off of ebay so I'd have original if things didn't work out.

I really should get the suspension done like you did. I suspect that might solve some of the instability. The problem came up on a gravel road at 40+ mph. The bike got seriously loose, the back end fishtailing like crazy.My riding buddies thought it was the trials tire I'm running but I don't think it was a traction issue. If anything it's because that's a very tal tire and actually steepens the head tube angle (my forks are all the way down in the clamps). I did find that hunkering down a bit and loosening my grip on the bars helped. The next day on a dirt road that was less gravelly I could do 60. But I came home thinking that I'd sure like a little bit longer wheelbase. Does this sound like something a suspension reworking would fix? I'm 6'2'' and 200 plus with gear riding stock suspension on my '07.

 

I was thinking about what you said in also wanting the fit or ergonomics to suit you better. I guess I'm not seeing how lengthening the swingarm will help that unless you're going to do something to the subframe/saddle area to extend that after the swingarm mod. Still, the whole thing sounds like a huge amount of work with some pitfalls that might not play out correctly. Hey, I love to see someone think outside the box and do something creative like this, but I'm not sure this one will be worth the effort. On the other hand, who's really done it to guarantee it won't work?

On the suspension mods, I really do think you'll achieve a great deal to affect stability while also improving so many other aspects about the bike, so maybe the money and time spent on some fabbing would be better spent on the suspension. The suspension will almost positively yield very positive results. The swingarm?...who knows.

 

Well as far as mods for making the bike fit me better I did move the foot pegs back and that made a MAJOR difference in the balance of the bike. That took a little fabrication. However, a bike is what it is. If I want a longer bike there's the Yamaha WR250 (not WR-R), the DR400, and various Euro 250s. And there are a couple bikes out there that share the KLX250s 56 in wheelbase: the WR-R and Honda's XR400. So I guess there's nothing inherently wrong with a short wheel base. I think the re-valve and spring change will be this winter's project, see how that goes. Then a big bore. Still I'd love to find a source for specs on frame components. Wouldn't it be hoot if it turned out that a KX2550 swingarm would slot right in? All in the spirit of modification!

 

Cut it slide some square tubing in and weld it. Did this with a Honda 250x atv with a cb900 motor in it and it held fine it was +4" or have the flat bar at the end re welded with a longer one.

 

Hmmm. . . thanks GreenMonsta. I'll talk it up with a welder I know.

 

So I've finally gotten the swing arm extended and the results have been quite good. I put up a couple pictures on the Bad *** picture thread and talked about it at greater length ( no pun intended) over on ADVRider: Long term KLX250S review - Page 579 - ADVrider

The finished product has the swingarm lengthened 7/8 of an inch (22.2 mm). With 13/42 gearing I'm running a 110 link chain with the adjuster set on the 8 1/3 notch in back. The wheelbase is 58 inches, 1 1/2 inches longer than stock. I have room to run 13/45 gearing which would put the adjuster on the 2 spot. And I learned that each indentation on the snail adjuster is ~ 1mm of length adjustment.

I didn't have to change out any other parts. The stock brake line still works, though the bend as it leaves the master cylinder is a little tighter. The shock spring did not need replacing, though it is heavier than stock, something I changed prior to the swingarm project. The brake mounting bracket was re-welded along with the extension so that orientation is preserved. The chain guide ended up a bit further from the sprocket but I think it is acceptable. I could be relocated by the welder at the time of the extension if one wished.

I've also relocated the footpegs 2 inches further back and raised the handlebars with RoxRisers. The bike now fits my 6' 2" frame really well.

So how's it ride? Really well. It seems more stable in a straight line yet steers a little more lightly. I attribute that to the steering angle having been steepened slightly due to the back end having been raised just a bit. I find myself hitting the steering stops more frequently while practicing figure 8s and such. The bike has lost none of it's nimbleness but it doesn't wheelie as readily. It just feels like a slightly bigger motorcycle.

In addition to the other photos I've posted here's one more. You can see the extension as the scruffy area at the end of the swingarm. Maybe someday I'll repaint the frame.

 

I love a guy who has the conviction to follow his dreams. Nice job!
marc

 

Hmm 7/8" - not enough for you to take a shot at Widowmaker, but it sounds like you've got the stability you wanted

:applause: