Jumbo240ez Posted June 1, 2004 Share Posted June 1, 2004 Back when I did my swap I didn't move the inner front LCA pivot point up. It's come time to replace bushings and so I 'm considering the mod. I may have experienced "Bumpsteer" on the street, I know I've experienced "tramlining"... but at an open track event (which is 95% of the car's mileage) I never notice any of those phenomenon that I can tell anyway. It seems to make sense that if it improves steering geometry under bump it's a good thing. Are there any telltale signs that this mod is necessary? Has anyone performed this mod and noticed an improvement you'd like to share? Thanks. Jon Quote Link to comment Share on other sites More sharing options...
auxilary Posted June 2, 2004 Share Posted June 2, 2004 not necessary for the track, because there aren't any bumps to induce bumpsteer. In fact, on track your setup is better because you have better camber gain without the bumpsteer mod. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 2, 2004 Share Posted June 2, 2004 Aux, what have you been smoking? Raising the pivot will give more negative camber gain during compression than keeping it at the stock lower location. I've never been on a track that was glassy smooth, and the track is IMO the only place you would ever notice it, unless you're driving on the street like you're trying to get arrested... Here's a good explanation of what bumpsteer feels like http://www.steeda.com/PR/Mustang/bumpsteer/bumpsteer.htm There is one bump at Buttonwillow, go CW over the hill and then there it is, about a 10' rise, then flat again. I used to hit that at the top of 3rd and my Z would do a pretty good twitch every time. Fixed the bumpsteer and it was rock solid through there. Also on the long sweeper there I could keep a steady line, but I was sawing on the wheel all the way through. Did the bumpsteer change, and it is much smoother on the wheel. To get it right you need to MEASURE it, not just move it x inches. Jon Quote Link to comment Share on other sites More sharing options...
auxilary Posted June 2, 2004 Share Posted June 2, 2004 jon, I've seen jumbo's LCAs in person, and I commented to him way back about the pivot point back when he'd drive his car around town. He doesn't drive it on the street, and he's not feeling the effects of the bumpsteer on the track, so does he really need to do it? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 2, 2004 Share Posted June 2, 2004 Well, I guess you have a point, but most people have no idea what the heck it is in the first place. They might have a problem and never realize it. I think that is usually what happens. Or they get some bumpsteer spacers and think that the problem has been solved when it is not. Quote Link to comment Share on other sites More sharing options...
auxilary Posted June 2, 2004 Share Posted June 2, 2004 i have bumpsteer spacers. they didn't help all that much. just moved the problem elsewhere i'm pulling my crossmember out anyway, so it's getting redrilled, probably slotted so i can make adjustments Quote Link to comment Share on other sites More sharing options...
fl327 Posted June 2, 2004 Share Posted June 2, 2004 Ive heard from a few people that the bumpsteer spacers are junk. I know one guy that slotted his control arms and said that was the move. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 2, 2004 Share Posted June 2, 2004 Bumpsteer spacers are a good idea for getting the control arm pointing down more and getting more neg camber gain when the suspension compresses. They just don't fix the bumpsteer problem. I think it was Coffey who said they should be called "camber curve adjusters". Quote Link to comment Share on other sites More sharing options...
Jumbo240ez Posted June 2, 2004 Author Share Posted June 2, 2004 Thanks for the replys. Just to establish a baseline, my only suspension mods are coilovers, shocks and camber plates. jmortensen, there is a turn at SP similar to what you described at BW. There's a dip before turn 2 is at the top of a hill. It's RH turn that's off camber as well. I'm almost the top of third after a downshift but bleed off speed quickly (uphill,braking, etc.) I didn't feel any twitchiness through there. BUT at the (almost) bottom of turn 6 I'd hit a spot that would "Twitch" quick and HARD. Not enough to throw me off line but it sure woke you up! I reviewed some tape and I think it was a DIP. So now I guess "droop" is something I should think about as well? Or was it the bump after the dip...? Side note: That was last Oct-Nov. I was there this May and though my set-up was different (stiffer), I didn't feel the "Twitch" in that section of track. I wonder if it was repaved or fixed? Anyway, it looks like it's worthwhile to invest the time to check both and adjust accordingly. (Damn, here I am getting sucked further into this track stuff... next thing you know I'll be gutting the car, buying scales...!) Has anyone seen the jig in Competition Suspension by Alan Stan-something? It looks like it would work, but I really don't know too much about the author. Guess I'll google him. Thanks again guys. Quote Link to comment Share on other sites More sharing options...
Jumbo240ez Posted June 2, 2004 Author Share Posted June 2, 2004 Oh yea, Aux I know you told me so.... Quote Link to comment Share on other sites More sharing options...
jt1 Posted June 2, 2004 Share Posted June 2, 2004 The track might not be bumpy, but every time you go into a corner and the car goes into roll you get the same effect, the suspension on the outer side of the car is getting compressed. The main benefit of raising the pivot point in the crossmember is to keep the LCA as level as possible in bump, so you don't lose negative camber, therefore keeping the tire planted better. It's a lot more beneficial mod to a car that has been lowered then a car at stock ride height. John Quote Link to comment Share on other sites More sharing options...
johnc Posted June 2, 2004 Share Posted June 2, 2004 Ive heard from a few people that the bumpsteer spacers are junk. As Jon mentioned, bumpsteer spacers are misnamed. They are of some value and I run them on my 240Z. With 275/45-16 tires that are 25.2" tall I have to run the 1" spacers to get the LCA's level at a 6" ride height. When I race 225/50-15 tires and a 5" ride height I didn't need the spacers to get the LCAs level. Move the LCA pivot point up is the better option. Quote Link to comment Share on other sites More sharing options...
Forrest Posted June 2, 2004 Share Posted June 2, 2004 I'm about to relocate my pivot point as well. I noticed horrible bumpsteer once I put 225's on my car. My question is - measure what? I realize that the point is to keep the control arm parallel to the rack, and I've read that the rule of thumb is to move the pivot point the same distance that you're lowering the car. That doesn't seem possible. Is it supposed to be moved directly porportionally instead? If so, what is the porportion? -Forrest Quote Link to comment Share on other sites More sharing options...
johnc Posted June 2, 2004 Share Posted June 2, 2004 I've read that the rule of thumb is to move the pivot point the same distance that you're lowering the car Ignore that rule of thumb, a car lowered 3" would have that pivot floating in air above the crossmember. Each car and crossmember are a little different, so look at moving the pivot point up 3/4 to 15/16". You'll have to check your own car to make sure the LCA doesn't hit the crossmember at full bump. Quote Link to comment Share on other sites More sharing options...
Forrest Posted June 2, 2004 Share Posted June 2, 2004 Exactly, that's why I was lost. Thanks John. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 2, 2004 Share Posted June 2, 2004 I've read that the rule of thumb is to move the pivot point the same distance that you're lowering the car. That rule of thumb probably relates well to bump steer spacers, because it would return the camber curve to stock, be even ther it is flawed. It only deals with the lowering from sectioning struts or cutting springs or adjusting coilovers, and does not apply to lowering that occurs with installing camber plates which doesn't change the control arm angle. If you search on bumpsteer I know I've explained how I did mine a couple times. I did the cheap and easy 2 dial indicators on magnetic bases way, vs buying a $300 bump steer gauge. Worked for me. Jon Quote Link to comment Share on other sites More sharing options...
Jumbo240ez Posted June 2, 2004 Author Share Posted June 2, 2004 Hey guys, for those who need pictures (like me) I scanned the pages describing a Bumpsteer gauge and posted them in a folder here. http://f1.pg.photos.yahoo.com/ph/jumbo30@sbcglobal.net/ It sounds similar to jmortensen's description. Could someone look at it and see if I'm spreading bad info? The way he (the author) makes adjustments is different but I believe the concept is the same. You just want an accurate way to measure toe-in/out through the range of motion your LCA travels. Regards. And thanks again for sharing your experiences and advice. Jon Quote Link to comment Share on other sites More sharing options...
JMortensen Posted June 2, 2004 Share Posted June 2, 2004 Looks a bit funky, but it might work. The hinge is the part that throws me off. I just got a big piece of steel and attached two magnetic based dial indicators to it, which seems easier than building that contraption. Quote Link to comment Share on other sites More sharing options...
Jumbo240ez Posted June 2, 2004 Author Share Posted June 2, 2004 I hear ya... I think the hinge is to allow for changes in camber throughout the arc and keeps the pointer against the board? Though it may be a layer of complexity that is unnecessary. Quote Link to comment Share on other sites More sharing options...
Guest MistressMotorsports Posted June 3, 2004 Share Posted June 3, 2004 This is one of those mods that pays off when you really need those last few tenths of seconds. On a dedicated race car with the rest of the setup done correctly, and a driver with enough experience to notice, moving the LCA points is worth it. For a track toy or street car, probably not. With rubber bushings, probably not. My race car had a combination of pickup points moved, bump steer spacers, and the steering rack relocated, which made it extremely stable over bumps (like turn 8 at Willow Springs), but the setup was done by a professional with the right tools and measuring devices. I would never be able duplicate somethng like that myself in my garage. Mike Quote Link to comment Share on other sites More sharing options...
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