cygnusx1 Posted February 28, 2006 Share Posted February 28, 2006 Why is it that my Z's front tires skip and hop when I am at full steering lock and backing up or moving forward slowly in a parking lot? My wheels are aligned 1/8" toe in and they are dead straight with the steering column lock in center position. The car is lowered 1" and the only geometry change is the addition of the JCR "bump-steer" spacers...that really only keep the control arms at a decent angle. I have 225/50-16 tires on 16x7 Panasports with the near stock offset. I am somewhat puzzled. It is also embarassing when the front end hops and skips while steering in parking lots. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 28, 2006 Share Posted February 28, 2006 Your tires are probably rubbing the TC rod or the frame rail lip. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 28, 2006 Share Posted February 28, 2006 Either that or you could use more Ackermann. Quote Link to comment Share on other sites More sharing options...
2126 Posted February 28, 2006 Share Posted February 28, 2006 Is it possible that its actually the rear wheels doing the skip and hop? If so, it could be a relatively tight, clutch type, LSD causing them to skip and hop in a slow tight turn! Just something to consider! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 28, 2006 Share Posted February 28, 2006 Nah, its the fronts. Especially at full lock the difference in the radius of the arc cut by the inside and outside wheels is pretty dramatic. If you have 100% Ackermann then the wheels follow the arc regardless of the steering angle, then you get no scrub. Z's have very little Ackermann. When you crank the wheel the wheels turn basically parallel. One tire has to scrub. Short steer knuckles make this problem worse too. One test you could do is mark the position of the tie rod, then open up one end and give the car a whole buttload of toe out. Try your cranked turn again. I betcha the skittering is reduced dramatically if not entirely eliminated. Only problem is toe out wears out tires really fast, especially if you've got neg camber too. Quote Link to comment Share on other sites More sharing options...
qwik240z Posted February 28, 2006 Share Posted February 28, 2006 Why is it that my Z's front tires skip and hop when I am at full steering lock and backing up or moving forward slowly in a parking lot? My wheels are aligned 1/8" toe in and they are dead straight with the steering column lock in center position. The car is lowered 1" and the only geometry change is the addition of the JCR "bump-steer" spacers...that really only keep the control arms at a decent angle. I have 225/50-16 tires on 16x7 Panasports with the near stock offset. I am somewhat puzzled. It is also embarassing when the front end hops and skips while steering in parking lots. I have the same size tires and Panasports and I notice at full lock my tire rubs on the bottom edge of the front right fender. Never does a skip or a hop though. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted February 28, 2006 Author Share Posted February 28, 2006 Thanks guys it's definately not rubbing anything and I have an open rear diff and stock steering knuckles, but good points anyhow. I thought it might be Ackermann...I will search the board for Ackermann. Could this also be causing some of my understeer mid-corner? I think I remember someone bending their steering knuckles to increase the Ackermann. NOTE: My steering has always been unusually heavy compared to other Z's. I have driven other 280Z's that steered quite a bit lighter with similar tire size. I have checked everything for mechanical functionality and it's all good. I think I have some strange alignment things going on. The car has never been bonked so at least that's a given. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 28, 2006 Share Posted February 28, 2006 260DET did that, and he had them cut and welded back together at a different angle. Basically you want the line from the tie rod through the ball joint to hit the center of the rear axle line. In this case since we have the steering rack in front of the crossmember that means you want the knuckles bent out towards the rotor to accomplish that. Unfortunately there just isn't much room. On a rear steer you can really change it a lot, since there isn't anything in the way and you're moving the pivot inward away from the rotor. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted February 28, 2006 Author Share Posted February 28, 2006 I just read the article about Tire Slip Angles and Ackermann. I think I might just try my Z with a slight little bit of toe-out as it's only a weekend warrior and rarely sees a straight road. My tires must have low slip angle characteristics which causes them to fight eachother in full lock (Ackermann mode). I will ignore the parking lot antics and just tell people that the Shucking and Jiving is from Ackermann effect found only on "real" race cars. LOL. Quote Link to comment Share on other sites More sharing options...
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