Bump Steer Issue

[Sho Pi]

Hi guys,

I have put aftermarket control arms (as well as a lot of other handling upgrades) on my R33 GTR and I am having bump steer problems. Would anyone know where I could get a bump steer kit to suit my car?

Thanks!

[GTSBoy]

Which arms have you replaced? Which ones have you not?

[Sho Pi]

Replaced everything but the steering arms (with Ikeya Formula).

[GTSBoy]

OK, here's the first thing you have to do. Measure the length of every single one of the arms you took out of the rear (centre of pivot to centre of pivot). THESE are the lengths that you know will work well without too much bump steer.

If you put all those adjustable arms in because you were forced to in order to fit wheels in or something, then at this point you might be screwed. But if you've just done it for fun, then you could set all your new arms to those lengths and probably find it's all better. Then you can make some small tweaks to get the camber right and hope you don't mess it up.

Otherwise, you're looking at an exercise and a half. See here. http://www.sau.com.au/forums/topic/456906-slotting-lca-for-more-cambertrack-what-about-the-rear/?view=findpost&p=7539791

[Dale FZ1]

Starting with the aftermarket adjustable arms at the same centre-to-centre lengths as the OEM gear is a great start.

However if you've dropped ride height as nearly everyone does, then you need to make adjustments. The fact those replacement arms are adjustable takes the hard work out of things, and Duncan obviously needed to comply with race category regs in slotting pivot points.

With a selection of basic tools and some inexpensive to make/obtain gear it is possible to set up the rear suspension without trial/error and guess work. A piece of string, ruler, and a jack can be very useful. It will take time and patience, but you can definitely sort it so that you know exactly what toe change occurs and that you are then not experiencing bump steer if/when it's getting taily.

[hardsteppa]

So, we are talking rear bump steer right? Adjusted through traction rods, which you now have?

if you have a dial indicator, making a bump-steer gauge is pretty easy, no shortage of pics for reference on google. Mine cost me about $20 in materials from Bunnings. The dial indicator is the most expensive part. I can send you some pics of mine if you need.

For reference - my car is dropped about 30mm. It was a while back now I did it but from what I recall when I adjusted for minimal steer under bump, it would then bind more under droop, so compromise was needed. The 'best' setting I found was set the rear camber to where you want first, then start with the traction rod at stock length, and then increase it by the same percentage length as I had increased the camber arm. That setting has worked fine for me and gave the best bump/droop readings so hadn't worried about it any more than that, but then again I'm not track-ing the car.

[Sho Pi]

Yeah the car ride height is lowered as I have aftermarket shocks on which is where the problem has occurred. I'm really way out of my depth here and don't really know what I'm talking about. The guys who fixed up all my handling issues said the last issue they can see with it is the bump steer and said I needed to find a kit / adapter to go between the tie rod and the upright. Something about moving something approximately 40mm down.

Anyway, thanks heaps for the info guys. When I have a bit more time I will look into it more as it looks like their is a lot of info I need to get my head around so I understand exactly what I'm chasing.

[ichi-go]

If you just want to fix the tie rod angle (it should be parallel to the ground like the LCA), moonface or Ikeya formula sell this spaced down Tie rod end:

http://www.rhdjapan.com/moonface-racing-bump-adjust-tie-rod-end-set.html

Or you can wait for GKtech to release their RCA correction kit for R-chassis

http://www.gktech.com/index.php/s14-s15-40mm-roll-center-correction-kit.html

Or you can just get their full knuckle replacement which already has RC adjustment built into it

http://www.gktech.com/index.php/r-chassis-r32-r33-r34-front-super-lock-knuckles.html

Only thing is, they are built for more lock (drift oriented)

[GTSBoy]

If you just want to fix the tie rod angle (it should be parallel to the ground like the LCA), moonface or Ikeya formula sell this spaced down Tie rod end:

http://www.rhdjapan.com/moonface-racing-bump-adjust-tie-rod-end-set.html

Or you can wait for GKtech to release their RCA correction kit for R-chassis

http://www.gktech.com/index.php/s14-s15-40mm-roll-center-correction-kit.html

Or you can just get their full knuckle replacement which already has RC adjustment built into it

http://www.gktech.com/index.php/r-chassis-r32-r33-r34-front-super-lock-knuckles.html

Only thing is, they are built for more lock (drift oriented)

None of those things fix the problem.

[hardsteppa]

OP i am not familiar with gtr setup only gtst but it sounds like they are refrrring to roll centre sdjustment not bump steer.

[ichi-go]

It is somewhat related

http://www.motoiq.com/MagazineArticles/ID/3608/The-Ultimate-Guide-to-Suspension-and-Handling--Bump-SteerToe-Steer.aspx

In terms of Macpherson design anyway