KDX to KX Geometry Solutions

[IdahoCharley]

There was a post a little while back that indicated a 2 lb reduction in weight if my memory serves me (difference between stock and KX forks) . Don't remember who posted it.

Our KDX 200 did not get ridden very much this year but when I was testing it out (CR Forks w/.40 springs) it seemed close and balanced (stock shock spring adjusted to 102 mm of race sag with my ~ 215 lb sitting on it.)

Trial tire (Dunlop 803) on the rear raised the back-up about 1/2 inch which is very significant change - I would not necessarily recommend it unless your inseam is on the longer side. I don't remember where the top of the fork tubes ended up but I do remember they were closer to flush with the triple tree than up against the handlebar.

[AZRickD]

I measured my KX and KDX front ends and found that KX was about two pounds lighter. But that includes the aluminum KX stem vs the steel KDX stem. The KX TTs were lighter. The other thing is that since there is a rake angle, the big tubie section of the KX forks are farther aft. I couldn't get a reliable balance point comparison between the two, but if the center of mass of the KX forks are higher, then the angle would put the weight farther back.

Rick

[canyncarvr]

Re: 'But that includes the aluminum KX stem vs the steel KDX stem.'

I recall that. Asked about it, too...but don't recall following up on the stem point.

How about posting a pic of your KX'd QC'd bike..upright on level ground?

I'm curious what it looks like.


Statistically, the big tube section is indeed farther aft, as you say..but I don't know that the big tubes weigh more than the littler ones. I wouldn't think so, the upper tubes being aluminium (sic), the bottoms being steel.

In any case, it would take a far better rider than I to tell that difference I would suspect..meaning whatever weight transfer exists.

[AZRickD]

CC, it appeared to me at the time that the center o' mass of both tubes were roughly the same. But the whole KX front end thang is 2-pounds lighter.

Here is my KDX after I cranked the shock spring down about an inch to reduce some static sag and lift the seat a bit so that I'm back on my tippy-toes (in boots) again.

For reference (and of little help), the height of the lower TT pinch bolt is 35" from the floor and the height of the rear silencer bolt is 34".

Another measurement -- lower radiator shroud bolt is 28" above the floor and the lower side panel bolt (under the round sticker on the white plastic) is 27.5". This is with the bike leaning just a few degrees toward the kickstand side.

[Colorado Mike]

Well dang, there's your problem son, you got a third wheel stuck plumb in the middle of your pipe. That's rubbing on your front one (as you're sitting on the bike).
I'm no suspender expert, but that counter-rotating mass has gotta be playing hell with your gyroscrotum inertia. Wish you had posted that a while ago, we coulda got you fixed up promptly.

you're welcome.

[AZRickD]

I had extreee parts left over.



I've re-measured the sag, using what I think is the correct procedure.

I lifted the bike on the jack until the rear wheel hangs freely and measure the distance from the axle to along the swing arc up along the fender. I then but the bike on its own weight, give it a compression or three to get it to rest and measure again. It's just a titch under 2 inches.

I then sit on the bike (I'm using a camera on timer to take a picture of the ruler I have tied to the bike-- I'm so clever). The distance from the bike resting to me on the bike in race position is another 3 inches.

So, is my race sag 2 + 3 = 5?

Should I attempt to reduce the static sag and race by one inch each?

Rick

[AZRickD]

I took the liberty of re-re-measuring sag. I wanted to get the static sag down to about 1" and the total race sag down to 4".

I tapped and tapped, and photoed and measured and tapped and tapped and tappped.

Goal achieved: Static = 1; Race = 4.

I note that when static sag is reduced, race sag doesn't reduce as much (linearly, that is).

I cranked the spring on the shock down about this much...



I'm now firmly on my tippy toes as I was with the original KDX conventional forks and the measurements from the shroud bolt to the skirt bolt is now equal. I've certainly raised the rear end up -- about 1/2 inch or so.

Unless I've totally misunderstood (again) measuring sag, I think this is pretty much to KDXRider forum spec, although the teamgreennews.ca site listed above says static sag should be between 30 and 40 mm (no less than 1.25 inches), I have it at 1".

Maybe I should re-re-measure rake and trail?

Edit: Rake is ~ 69 degrees. Trail = ~4.25".


Rick

[Indawoods]

Time to order the Herman Munster boots from Alpinestar!

[AZRickD]

There is one thing I've learned tonite after cranking on the new 5.2 spring is the comparison with the old 4.9 spring I replaced. What a mushy monster that thing used to be. Much less spring was on there before and much less pre-load dialed into the shock. It must have looked pretty goofy with half my suspension travel taken up in total sag.

I'm going on a 50-mile round-trip mostly jeep trail ride to a BBQ/camp at a ranch on Saturday with my wife and daughter in tow in the Polaris Ranger. This should be a safe test for the suspension as there are a couple of whoop sections and one medium hill climb I can use to test the evil loftiness of the front tire.

What I will have to decide is if I want to mess with the front clickers and reduce compression and rebound. I'll take along a handy screw driver just in case.

Rick

[krazyinski]

I am a shorty and I just ordered tall seat foam and seat cover to help the weight transition from standing to sitting and sliding forward to put weight on the front. along with softer springs this should help.

basically the front forks require more rebound control than I would have thought.
also taller bar mounts allow for the forks to be raised in the triples a bit more.

to each his own but tunning is time consuming but worth the time spent.

[AZRickD]

I can see how those boots would help with her weight distribution problem, but I think she'll need another fork.

Rick

[layoutd]

I have a 3/4 inch stick up on my 96 KX forks. I did feel at first that the front end came up easier, but kinda attributed this to having less weight out on the front wheel. Mine handles well on our tight twisty single track with lots of climbs. I have put a longer length proper spring weight spring on the back.

Really the only times it comes up on hills climbs is during a whiskey throttle event, or if i catche the feathering just right.

I am acutally thinking about lower the fork a little from 3/4 inch to 1/2, no reason, just thought i would see if i can notice a difference in handling

[AZRickD]

I did a not particularly challenging ride yesterday and another one today. My wife and daughter were following along in the Polaris Ranger as this was a "camp & ride" event with our club. I had only a couple modest hill climbs and I noticed no tendency to climb up, even though I wasn't really leaning forward.

Everything else appears to be fine.

I'll have to check again on a better set of hills next week.

Rick

[KDX200Kev]

I had my forks valved and shortened by FC and they work good now. I have a $25 coupon for anyone that plans to send their forks to them.

[AZRickD]

I thought about that as a possible solution but figured I didn't wanna go there $$$.

Rick

[KDXer]

I had my forks valved and shortened by FC and they work good now.

Would that not lose you fork travel ?? I know its a common mod for shorter riders but always wondered about the equal and opposite reaction ??

Cheers,
Isaac....

[AZRickD]

After re-jetting my carb for the *cold* Phoenix weather (60F, 152/40/CEK-4/ AS=1.25) I did some test-riding along some trails. Bike ran well and was developing power. I might have to loosen the clickers in front one or two.

I saw a mountainette about a mile away so I rode over to it to check it out. It was worthy of a test.

It was maybe 100 feet tall, somewhat steep, a bit rocky, a few ruts... well, the degree of difficulty is relative, so for me, the guage is that out of five tries, I made it up twice...

...but none of the abortive attempts were due to my front end coming up. Rider error, loss of traction, getting bumped off course and sideways. I went up in second gear (13/50 gearing) and had to work the clutch, and/or downshift as it got steeper up top. It was a good test for me.

Looks like I'm pretty close to getting the suspension set up. Maybe need to go a little looser in the front end. On one attempt I blasted between to seven-inch rocks that earlier had kicked my front off line only to have my rear go over it and bump me off my foot pegs. I used the lifting momentum to leap off the bike to dismount without falling and keep the motor running. Maybe I need to look into my rear shock as well.

A family group of bikes and quads had gathered below to watch the entertainment.

Rick

[krazyinski]

getting it right is some what of a nut cracker, but once there its magic. mine is all set and I dont even want to touch a clicker now.

[AZRickD]

There *is* one lingering problem...

At speed down a straight long enough to get up above 50 mph or so, the front end gets kinda floaty. This is with my normal, middle-of-the-seat, non-technical riding position.

It almost feels like I need a front spoiler or airfoil to put more weight on the front end.

Also, as a test, if I purposely bump the bars, the front end will oscillate and then calm itself down-- it's right on the edge of this but does require me to initiate this. In the aviation work, this is called "PIO" or pilot-induced oscillation.

Cranking my WER stabilizer to max reduces this only somewhat, but max WER is too tiring for single track.

This behavior didn't exist witht he KDX forks.

Any ideas how to tune this little quirk out of the bike?

Rick

[Indawoods]

Reduce preload.