R33 Gtst Handling Advice

[hrd-hr30]

you can't totally eliminate it, but you can certainly get it to within acceptable limits over the most important 3 or 4" of travel around your static ride height.

[Dale FZ1]

Harry was on this one early.

Custom or altered pickup points are not necessarily anything you need to look at. You already have the right sort of adjustable parts installed. It is the case that you need some gear, and some know-how to make the right sorts of adjustment to dial bump steer (aka dynamic toe change) out of your suspension.

That comment holds true for both front and rear ends.

People get fixed on the notion that if they get static toe/camber/caster right, then it's all right. They forget that the wheels/suspension is in a state of constant movement, and so the camber and toe can constantly change too. What happens dynamically is the bump steer effect, and you should want to work with it and make the car behave predictably rather than try to spit you off the track due to poor setup.

The suggestion was made early on that if you don't have the know-how then get organised and take it to a specialist who can set it up properly. No doubt there are good web-based resources that can help, and you could undertake courses to learn more. There are people who derive a living from understanding and fixing these issues.

This is probably one of the fundamental car setup jobs that enables the car to handle acceptably.

[hrd-hr30]

It's no secret the Nissan multi-link rear is bad for bump steer. I learnt it with my R32 GTR almost 10yrs ago. And my 180SX about 5yrs ago had the same issues. If I ever buy another Nissan, somebody slap me. Dialling it out is pretty tedious!

Edited July 9, 2014 by hrd-hr30

[zebra]

where did the write up go?

was about to note it all down.

would have been handy as ive never seen how to fix it

[Littlehorn]

Cheers guys time to have a look around for a motorsport tuning shop with alignment gear then.

where did the write up go?

was about to note it all down.

would have been handy as ive never seen how to fix it

Did i miss something, i dont think any posts have been deleted?

[hrd-hr30]

I was only about half way through it and somehow hitting return to start a new line submitted the post instead... It was getting really long...

I've set up rear bump steer at home a couple of times before, on my old R32 GTR and 180SX. The process is pretty simple, but time consuming and requires some patience. There are probably better ways if you have equipment but this is my backyard method:

- measure your static ride height and camber. ride height is best measured by hooking the tape measure under the lower edge of the rim and measuring up the the gaurd - that's a repeatable procedure that doesn not involve guesswork/judgement/parellax error that the centre of the hub method does. Camber can be roughly measured if you are careful with a spirit level vertically off the lower sidewall, and measuring in to the top edge of the rim - again it's a fixed reference point that makes for repeatable measurements - don't just measure to somewhere on the sidewall. You'll need to reset the camber after/during bump steer adjustments. I'll expand on that later.

- jack car up and put it on stands. It needs to be pretty level to get meaningful measurements.

- remove coilover

- get a 1m length of timber. Knock a nail in each end to hang plumb bobs off. Attach it to the tyre with ratchet strap or something. About 1m long is good because a longer length gives your measurments more sensitivity/accuracy.

- tape a big piece of cardboard to the ground under the length of timber. You'll be marking points and lines onto this. It's good to have a few different colours as there's going to be alot of lines! lol Even better is to have some big sheets of paper or a roll of butcher paper you can tape over the cardboard for each set of measurements you take - it will be much clearer and less cluttered that way.

- jack the wheel up to the static ride height position, with the timber level. Hang plumb bobs off the nails at each end. Mark those positions on the cardboard. Draw a line through those points and it S1 (or Static position 1)

- jack wheel up 60mm and repeat the process. Label this line B1 (Bump position 1).

- lower wheel to 30mm below static ride height and do the same, labelling it D1 (Droop position 1)

The object of the exercise from here is to get these three lines as parellel as possible. But if anything, gaining a little toe in on bump is OK. You do not want it to toe out under bump.

Use an overlay of paper over the top for your next measurements after making an adjustment, or mark them on the cardboard in a diferent colour, label your second set of lines S2, B2, D2. The important thing it to preserve the original S1 line so when you're finished, you can set your static toe back to where it was. So make sure the cardboard doesn't move or you'll have to do an alignment afterwards.

tbc... (lunch break is over)

Edited July 10, 2014 by hrd-hr30

[zebra]

Thank you

[Littlehorn]

Awesome info cheers!

[hrd-hr30]

the other thing to keep in mind when making adjustments is not to make all the adjustments on the traction arm or you'll end up changing the camber alot. Make adjustments alternately on the traction and camber arms, and measure camber again at static height as you go to see what's going on. Don't get too uptight about keeping camber spot on during this process, just so long as it doesn't get way out of whack. You can set the camber back when finished using the method below... Also best to measure and reset static toe after each adjustment. Leave the lock nuts loose on all these arms until you're finished.

Resetting static camber: you can change the length of both arms by the same % to get camber back to where it was. It's not a perfect method, but it's a decent approximation as long as camber is not a million miles out. You will still need to check bump steer again afterwards, but this whole deal is an iterative process, and just keep tellign yourself you are getting closer! lol

So for example, using nice round numbers... if you need more neg to get the camber back to where you started, the camber arm is 150mm long and you decide to shorten it 5mm, that's 5/150= 0.033' or 3.33%. You need to shorten the traction arm by that same percentage. Say its 120mm long: 120*0.33=4mm. You'll need to check bump steer measurements again after doing that, but it should be reasonably close to how it was.

Alternatively, if the thread pitch is the same on both traction and camber arms, using the above numbers of 120 and 150mm lengths, you can turn the camber adjuster 1 and 1/4 turns for every 1 turn of the traction adjuster, because 150/120=1.25.

If you're like me and have totally had enough by the time you've done one side, just measure the lengths of the arms and copy that for the other side. For this reason I'd do the actual measuring and setup on the most important side - ie if you're local track has mainly right handers, do the left side rear properly and copy the arm lengths to the right rear. If the car is still a bit twitch in left handers, you can repeat the process later on the other side.

[Littlehorn]

Great Thanks for that. Should i be making changes on the tie rod as well as the camber and traction arms?

[hrd-hr30]

normally just called 'toe arm' on the rear. but yes, to keep static toe setting the same as when you started. I think I mentioned that somewhere in that wall of text!

[Littlehorn]

I took my baseline measurements this afternoon.

Results show that the car is toeing out under compression and staying fairly static under droop.

Not quite sure how to calculate what it is changing to in mm but it is toeing out approximately 1.64 degrees under compression from the base of 1.25mm toe in at the static position.

Also the wheel is touching the guard so there is only 23mm of travel under compression.

So i have some fixing to do!

[zebra]

Interested to hear what needs adjusting to fix it

[tweety bird]

Ah setting bump steer, my favourite job!

[Littlehorn]

I had a slight issue with the alignment the car was actually moving on the axle stands, i think it might be the sway bar that was causing this. So after a number of hours working on it i couldnt trust the settings, and im now considering one of these to make life easier.

http://www-en.ikeya-f.co.jp/category/1983343.html

[White GTS-T]

I have a set of those, and they're only really good for static alignments. If you want to tune out bump steer, then you need a bump steer gauge; like the longacre ones.

http://www.longacreracing.com/technical-articles.aspx?item=8162&article=Bump%20Steer

[White GTS-T]

On skylines, you tune out the bump steer by adjusting the traction arm, which in turn, effects the static alignment, which, once corrected, effects the bump steer...

[hrd-hr30]

ah, should have mentioned to disconnect the sway bar also if you still have one. Had to miss something, I suppose...

[Littlehorn]

No prob i am going to have another crack hopefully this weekend. Considering using a mates garage with a proper hoist and strapping it down to make sure there is no chance of movement.

[Littlehorn]

Spent the day in the garage sorting this out today, started with the car increasing toe out from static by about 6mm at full bump and ended with the car increasing toe out from static by about 0.5mm.

What i found was even disconnecting the sway bar the car still moved slightly when jacking up, i guess it must be the shock not compressing easily.

So that meant i didnt have an original group of measurements to look back at and means i dont actually know what my standard ride height toe is currently set at, but what it does mean is that the car is now only slightly toeing out at full bump. So if the car is set to 1.25mm toe in at static ride height under full bump it will now go to approximately 0.75mm toe in.

I will pop into an alignment shop next week and get them to check what my static toe is set to and get them to adjust only from the lower toe arm, which means that the ratio of the camber to traction arm will remain the same and they will continue to swing on a similar arc.

I think camber i wont be fussy with as long as it is somewhere between 0 and -1.

So my actual adjustment on the arms ended up being to decrease the traction arm length by 4mm and increase the camber arm by 2mm. Traction arm is now 1/2mm of the shortest it can be set to.