Steering Head Angle

[redcouch]

On the handling issue with the later KXs, the front end tucking or washing out beginning to mid corner. I have a 2001 KX125, has this issue though Ive been noticing the handling issue gets more mention with the last generation KX250 models. Been studying bike geometry and came to the conclusion the steering head angle on my frame is too steep, which effects my trail especially when compressing the front end on cornering, and come to find out here re-welding the head tube an additional .5 degrees is a typical fix. So my question for those who have done this is, is this modification really that necessary? Can I get by with a set of ProCircuit linkage tie rods, moving the triple clamps up on the forks, and setting a proper sag? Have you guys tried this and ultimately went with the head tube weld for a significant benefit?

Currently I've installed the PC tie rods and slapped in new linkage bearings, my triple clamps are set to the top of the forks from me previously trying to cure the issue, and I'm going to set my sag at 100mm. Havent tried this setup yet but hoping the bike will corner correctly, has anyone had any experience curing this issue?

[treedodgingfool]

Your situation is a curious to me, being that the only KX (250) I've ever ridden that has a questionable handling trait is the "R" models ('05-07 250, though I didn't notice it on the '05 as much, was a real issue on my '07).  The steering angle is too steep, which is great in a variety of situations in the conditions we use it in, but I put several thousand miles on my '07 the season I chased points in our enduro series with it and was pummeled into the ground more then a few times pretty hard.  It would knife & wash in higher-speed "waltzing tight" trails.  I couldn't figure it out initially & kept playing with the suspension.  My husband thought I was nuts when I'd tell him that it feels like it's knifing and other times washing out (they normally don't go together when dialing in suspension). After a concussion, broken steering dampner, several broken plastics and a seat mount, I nailed down the woe to the steering head angle.  I've abandoned racing that bike, went back to my modded sure-footed & confidence inspiring '04 and gave him the '07.  I use 1" lowered suspension (improves cornering and makes dabing & pivoting in the gnarly stuff easier), that magnified that handling trait.  He swapped on his standard height suspension and did a lot of fine tuning on the suspension adjustments and has it fairly well behaved, for him.  We still don't trust it in the higher speed, sweeping trail stuff and we both agree the front-end needs to be kicked out .5 a degree to truly cure it which we'll do one of theses days. For now it spends most of it's time sitting while the '04s see all the action.

Now on the '04 & older bikes, I have no complaint with the steering head angle.  I do have a complaint, in certain terrain, with the '03 and older style linkage which reacts very fast (rebounds) quickly in the intial part of the stroke, which is great in the rocks & chop but is too busy in the whoops.  No amount of slowing the rebound down in the rear, suspension valving or tuning seems to get it on par with the '04s linkage arrangement (stock-versus-stock).  I have a set of Pro Circuit links to try on my '03 once I reassemble it (chassis overhaul, 10k+ miles on it, it's due) again to see if that slows down the initial part of the stroke, otherwise it'll be the rocks bike.

Your '01 should really have no major, glaring handling issues short of maybe a busy back-end compared to '04-up KXs.  First, I would have the suspension rebuilt/refreshed or revalved if spending your time off a track and in rockier terrain. Set your sag, you can't get a good feel or set-up without setting your riders weight sag & checking your static sag (not having the sag set and/or the wrong spring rates can make a bike feel completely out of whack). If you don't have a service manual, get one.  My '03-04s have a recommended fork height above the triple-clamps of 15mm, check the manual for the recommended height for your application.  I see too many riders set them flush and then wonder why the bike doesn't handle right.  From there, with fresh suspension fluids, proper sag & fork height, correct spring rates & valving for the terrian, you can properly adjust the suspension adjustments.  Now if all those stars align, and you got it right but you still have an issue, then you proceed further, but only after you get everything else in order.  

[redcouch]

Thanks for sharing your experience. Interesting that there seems to be a point were in 04 05 the handling starts to change, even though as far as Ive researched they all have the same steering head angle. Although I'm not sure what this angle is in reference to.

In my situation its purely motocross track riding/conditions. To go more in detail, I have a 2001 KX125, 02 forks and triple clamps(from 46 to 48mm), and the forks and shock have been set to my weight and riding ability by a capable suspension shop. I recently figured out the 02 also had different linkage, rocker and tie rod, and Ive just changed that, not ridden the bike yet. So now its a 2001 bike with 02 suspension, effectively an 02 now the frames are the same part number. Also I recently measured the sag and it seems to sit around 90mm, but this was measured without wearing any gear.

Anyways, if my issue was the fact that Ive been riding on 02 front and 01 rear end I'd be a bit surprised that this was the problem all along, after all its just different forks and I'd like to imagine they are basically identical, at least geometrically, aside from having a thicker lower tube. Havent tried my proper setup yet. My handling issue first came to light when I took my 14 KTM(which ironically is used for desert or cross country racing) on the track, back to back from the kawai, and realized how cooperative and compliant the KTM front end was in berms, really highlighted the kawai's tendency to knife and washout when the KTM showed no signs of even thinking of wanting to go awry. Since then I've upped the triple clamps on the forks, and its made a noticeable improvement, but the harder I'm starting to dive into a berm nowadays I start to get that knife effect. Lowering the rear end with the PC links and proper sag(-10mm) should further correct the issue, as all these adjustments rotates the frame, angles the head tube more flat. I can think of a few more ways to combat my issue if it continues, but at what point are my bandaids just bandaids, and the proper fix is gunna be to reweld the head tube. Note, also ironic about the KTM, its head tube is 26.5 degrees.

That's my rant for now. Still yet to set the sag 100% correctly and try the setup. Might bring back the triple clamps on the forks to the proper height. Is 100mm the sag to set on a KX125 ot at least a good starting point?

[treedodgingfool]

Riding back-to-back with a KTM makes me think what you're expierencing is the chassis & suspension differences between the two bikes, much like when I'd ride a YZ (doesn't turn without a good shove) or any of the other scoots.  KX's (especially the "M" models, yours is a "L") turn really well, maybe a hair-off from a CR or RM of the same year (just a hair) but they split the difference very well between the cornering prowless of the CR/RM and the straight-llne stability of a YZ (that's why I fell in love with them off-road and have yet to ride anything that's sparked my interest as much since, GasGas's, KTooms, you name it).

The two bikes are going to feel different. Age, different development, chassis, etc.  Which one do you spend more time on?  What KTM are you riding?  How long have you had this 125 and what bikes have you ridden before mostly?  If you're used to a slower handling bike, getting onto a slicey/dicey KX/CR/RM 2str is either going to be a love or hate affair.

My husband took a buddies stock '14 KTM 200XCW out and complained about how it couldn't turn to save it's life (after his grumbling, I wasn't interested in trying it myself). We've both ridden different KTM models from a few years ago (08' 300, etc., I used to sell them) and they turned better but still not as knife-like as our KX's do.  If your used to another brand, steering on the front-wheel is going to feel foreign (a front or rear bias handling bike).

As for using the '02 forks, as long as they're valved to match, same length, off-set, you have the right sag & found a level suspension adjustment / set-up, I see no issue.  I'm using my '03s forks on my '04 (same triple clamps, '03s are open-chamber and the plushiest stuff ever with valving off-road), but I use the '04 shock (different shock due to different linkage arrangements from the '03) and my bike could self-pilot between trees (joking, but it's that well-behaved).

We set our sag on every Jap bike we've owned at 3.75" without gear.  We are both so sensitive to this that it being off by a 1/8" can upset our suspension settings. 

[redcouch]

The KX has been my bike for 2 years. Just got the KTM 150xc, so Im used to, was raised on the kawi, its all Ive owned up til recent. Maybe by definition of knifing is wrong, what Im trying to describe is how the front end slips out unexpected and suddenly when Ive entered the berm after turn in, like it is washing out  when I compress into the berm and go to lay the bike over. Thought this was washing out or "knifing", but either way its not right, especially if this bike is suposed to be a turner, cuz the KTM turns practically, as well as a yz250f i rode once turned well like the KTM. Cant wait to test the KX though.

[treedodgingfool]

Knifiing is front-end is turned (bars cranked over) & getting swallowed-up, possibly front-end digging in or the front end feels like it's flopping-over in corners & climbing to the inside (like too much front bias, too soft on fork compression or too slow on rebound and/or the rear shock's rebound is too fast or compression too stiff and/or too soft fork springs or too hard shock spring and/or not enough rear shock rider sag).

Washing is the front-end either not feeling like it biting, bars are turned but you're going straight, climbs to the outside, doesn't stayed compressed in travel through a corner.  Washing can be caused by too hard fork compression, or too fast fork rebound, or too soft rear shock compression or too slow rear shock rebound, too hard fork spring rate, too soft rear shock spring, too much rear sag, forks too low in clamps (less then the OEM recommendation), beat or crappy front tire especially if combined with a fresh rear. 

Did you just start noticing this once aquiring the KTM?  Do they have different front-tires between the two bikes, maybe the KTM's is a lot fresher or a better suited tire for the terrian if it's washing?  Is the rear tire fresh with a beat front tire?  Some of the mods you mentioned (links, fork height, etc), if the bike is washing, is going to make it worse (washing needs more front bias to correct, knifing needs more rear).  Get the sag set correctly (3-3/4" without gear is our baseline, odd? yes, but it works), and get to playing with the clickers to balance that see-saw out (neutral balance). 

[KXDINO]

The kx125 from 99 to 02 had a head angle at 26 degrees with 109 mm trail , the 05 to 08 kx250 had a head angle of 26 degrees also but had only 105 mm of trail ,what kawi did with the 05 to 08 250 frame was steepen the head angle without changing the offset of the clamps to suit the new angle , a new set of triple clamps of less off set helps or what we did was to modify the frame on the 05 to 08 to 26.5 degrees and to lengthen dog legs by 3mm to make it very good, it pushed the trail out to 122mm mark we have raced this bike for years likes this and is fully cured. AS for these model 125 I never herd of problems with this, but I would not touch the frame, I would spend money on gold valves or other brand of suspension mods , correct springs for your weight , than see about a set of triple clamps with less off set , I think rg3 make them , you can research this, all you could try lengthen the dog legs by a 1 mm all so, pc sells these things may be , I usually get them cut and tig welded back together no dramas ,done heaps of them on kx,s. I hope this helps , also the new Dunlop mx 52 works well on kx,s front tyre for grip. note the 04 250 frame had a 27 degree head angle and 112mm trail, also the 04 to 08 125 had 27 and 113 numbers. these model are good handlers.Let us know how you go ?

[KXDINO]

If all this fails than do the frame mod ,26.5 sounds good. its the best mod for the 250 05 to 08, I know 2 other guys who done this and were more than happy with the results , just remember to use a very good welder don't skimp it your neck on the line .

[redcouch]

Hmm, its like a knifing, if it knifes hard enough the front tire is overwhelmed and can washout but I save it before its really a complete washout. I've always noticed this behavior before the KTM, but I just figured it was normal as this is my first bike(well big bike). The KX has new MX52s, the KTM came with MX51s and out in the desert the front MX51 on the KTM actually has a bad habit of not biting for a slight moment when inputting an initial turn, flat tracking on sand, loose dirt, desert terrain, and then before you start to wash out the front end the MX51 will finally bite. Its disconcerting but when diving into a rut or berm, the MX51 on the KTM grips great and doesn't slip. Nontheless, the KTM isn't the issue and I've herd the MX51 fronts tend to do that, I digress.

Thanks KXDINO, a lot of great info I had trouble finding. I have the Pro Circuit links and my triple clamps are Applied Racing, not sure what the offset is because they don't list it on the website. So I would assume 22mm, that is stock I believe, and if they didn't list it maybe that means stock offset. 22mm is pretty short, should be good.

So I set my forks 5mm above the clamps(stock should be 8mm, and this is measured below the fork caps), and set the sag to 100mm, from 90mm, and 5mm more than what treeDfool suggested, and tried it out at the track today. Significant difference, in the right direction. At first, starting out taking it slow turning into berms the bike didn't washout, the front end didn't slip, felt very planted and predictable. In addition I felt the sag change improved the handling on jumps, felt more predictable when seat bouncing and compressing off the face, but this could just be inspired confidence from the turns. Went back out on the track, starting to pick up speed and dive harder into the berms and I could start to get the front end to knife or tuck. Take a typical 180 outside berm, standing up leaning the bike over entering the berm, get settled with the lean angle, letting off the brakes and go to sit forward and slip the clutch and punch the throttle, and the front end tucks, or like the front tire will slip and my bars yank to the inside, I begin fall over to the inside(and a bit forward into my bars), and I throttle through this and stand the bike back up and complete the berm. Is this normal for the KX? It seems to me, as I go 70% into berms the bike handles perfect, as I go 90-100% into berms the bike still has the knife/tuck issue, and it seems to happen when I really move the weight forward, slowing down, going my full speed or pace.

Its mid turn, roughly, from beginning of the turn I set the bike standing up, standing up I weight the front end with my body position, and when I'm ready to go from brakes to throttle Ill begin to sit forward and the bike will tuck, but I haven't necessarily let off the brakes yet and into throttle, safe to say Im still on the brakes and the throttle seems to correct the tuck. Im thinking my front fork low-speed compression needs to be upped a few clicks, slow down the front compressing when all the weight shifts forward so I can get on the throttle before(what seems to me) the front end gets too steep and the trail goes negative and my front tire goes unstable. Didn't touch the clickers today, but I changed my technique by not slamming my butt so far forward when transitioning from standing to sitting, and as I sat I kept my posture up a bit more to weight the back end and keep it from stinkbugging too much. This change in technique never ran into the front end issue, so maybe the bike handles as it should and I just need to correct my technique, although since I'm trying to change my technique Im not going 100%, probably 85-90%.

So I think Im chasing my issue correctly, gunna try the front low speed compression, maybe the rear low speed rebound? All things considered I think 26.5 degrees on the head angle would help, it seems to be just when the front end goes too far forward and the trail decreases to the point the front end gets very unstable and "pulls the chair out" from my weight and inputs, but I'm leaning towards KXDINOs advice and Im gunna leave it alone. Geometrically I've got the bike issue mostly solved, so now maybe fine tune it with the suspension adjustments. What do you guys think?

Setting my sag, my static sag was around 40-41mm. Whats the static sag supposed to be? Is my spring too light or maybe worn?

KXDINO, on a related note was considering buying an 03, 04 05 KX125 and was wondering, whats the head angle on the 03 125? You know if its a good handler 125 like the 04-08 or is it more like an 02? And when we are referring to steering head tube angle, what are we referring to? Is the 26 or 27 degrees in reference to the frame design, or is it in reference to the way the frame sits with the stock suspension setup?

Thanks for all your help guys, a lot of good information here.

[KXDINO]

the 03 125 was a new bike and should have the same numbers as 04 on. The head angle is in the frame , I think most of the late kx 2 stroke offset is around 25mm? The work shop manuals rarely have this info , but some of the triple clamps companies do , I will look in to this a bit further ? I would check to see what you have first ,it might have the std offset? If so , a set with less off set will give you more trail, which should help in the turns, they do this with kxf as well, some people change triple clamps just for looks I only do it for handling improvements .

[treedodgingfool]

We don't play with aftermarket triple clamps either unless an adjustment is needed either (aftermarkets are billet rather then OEM cast, which cast have better flex qualities and less clamping surface then aftermarket, better for some forgiving flex, at least off-road).

I actually have all the dealer new year model updates from '03-up for Kawasaki (worked in the dealership for a decade, kept the literature) which gives a fairly good break-down of changes from model to model year, but those specs are null in this because there is nothing wrong with the geometry of the pre-"R" model KX's.  If y'all want 'em, I can dig it up after this weekend.

If you were to get a different KX125 (in the US), I'd purchase either a '04 or '05 (the linkage arrangment is better on a track).

If it's knifing, try slowing the rear shock rebound down or softing the compression or speed up the fork rebound or stiffen the compression.  Do one click on one thing at a time and do a lap on the same course and see if it improves. If not, go back to where it was, think about what it was doing and chose accordingly the next circuit to adjust.