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View Full Version : Steering guru's chime in



Jay1823
09-28-2007, 10:34 PM
Ok reading up on KPI and scrub radius and i think i'm hosed. Let me know if i drew these lines correctly.
http://img.photobucket.com/albums/v399/boosted_zc/Scrubradius.jpg

The first problem i guess is a have no negative camber. I did take off the top a-arm and try to move it in but it doesn't go to far, the bottom ball joint retricts it. It does look to be a good 6-8 degrees of negative camber when i do that. Not sure if i should knock off my upper a-arm mounts and reposition them to give me more camber. *The scrub radius stays the same though. It seemed to handle pretty well but i'm always looking for improvements.

plkracer
09-28-2007, 10:40 PM
Your lines are correct. The scrub is the distance between the two at the ground, so you may try for more camber, unless you can't get it. Does the steering feel heavy, with a lot of feedback? You have ample caster right? It looks like you have a few degrees of camber, and if it works for you, then it's all good.

greasemnky
09-28-2007, 10:41 PM
Jay, put a strap on it, and edit your post to show the same picture, but with the suspension at full compression. That will give the guys a better idea whats happening. Basiclly, the upper a arm is pushing the tire out as it cycles. I think.

plkracer
09-28-2007, 10:42 PM
Oh, you could try for a taller tire, or a rim with less offset. Are those stock 400ex tires? You have around 3 inches of scrub right?

Jay1823
09-28-2007, 10:47 PM
http://img.photobucket.com/albums/v399/boosted_zc/scrubradius2.jpg

This is with the upper a-arm disconnected and pushed in as far as it can go. The a-arms and spindles are off a mid 80's Honda TRX 250R i believe. Not sure if this is better than the above pic. I don't think i can do much for my scrub radius.

nutnbolt2002
09-28-2007, 10:48 PM
Also I think that your a arms are further apart at the frame than they are at the spindle, not to sure if that is correct.

Jay1823
09-28-2007, 10:50 PM
I'm not worried about the compression angle as much right now. I'd rather start with the basics and work from there. I might just leave it as is. I'm kind of getting sick of working on it. What i think i need to do is build a box and stick it in there since the frame isn't true. It's screwing up all my measurements.

greasemnky
09-28-2007, 10:53 PM
I just ran out and looked at mine. At "rest" my front looks more like your second picture. As it comes to normal ride level, their tilted in slightly, and at full compression, their strait up and down. I think you just need to camber them in like you have it in the second photo. That way at compression, their up and down. GREAT improvement this time. Now for the rear *[smilie=boogie.gif]

Jay1823
09-28-2007, 10:53 PM
Oh by the way, I HATE STEERING!!!!

What really sucks is a welded the HELL out of those a-arm mount tabs. Those are not gonna be easy to cut off. Argh so annoying.

Rorty
09-28-2007, 10:56 PM
I don't consider myself a guru, but I'd like to comment if that's alright. It looks like that wheel may actually have a touch of positive camber. Increasing camber will not alter the scrub radius.

If you want to mechanically reduce the scrub radius, you'll need to reposition the spindle on the upright at a more suitable angle.

I would also re-make the upper arm so the balljoint is closer to a neutral position (actually matched percentage wise to the travel). You may also want to re-make the arm to improve camber and better control the upright.

What I'm saying is that the lower arm and balljoint are probably OK, but the remainder sucks! Sorry.

It's not hard to correct it all, though what upright are you using? Is it off a quad? If so, you would be better off making your own so you can optimise the geometry.

minibajaman
09-29-2007, 08:56 AM
You could fix your scrub radius by getting a different offset wheel. *Or if those wheels are say 10x5 with a 3+2 offset, flip them around and see if that helps. *Given that they are atv uprights the scrub radius with the correct wheel is usually very small. *The blue line in the pic is approx where your scrub might be if you changed the wheels.

To fix your camber problems you will have to remount the upper A-arm. *From the first pic, it looks like the upper a-arm frame mounting points are too far apart from the lower a-arm. *In the attached pic, if the green dots are where you a-arms mount now you could move the upper arm to the blue dot position so that the distance between the inner top and bottom mount points is less than the distance between the ball joints.

Jay1823
09-29-2007, 03:28 PM
I don't consider myself a guru

Yeah well i consider you a guru, your mainly who i wanted to hear from. Yes they are quad a-arms. No i didn't build it i'm just trying to modify it to work better.

mini- i'll see if switching my wheels around helps my scrub radius. Looks like i have more cutting and welding to do damnit. Argh.

My ody build is gonna be so much easier designing it myself and not having to correct other peoples mistakes.