Swapping Upper Control Arms For Track Day

[MrStabby]

I only run 2 degrees neg camber at the front, and dont want to run more permanently as the car is mostly street. I use r spec at the track so i'd like to run more like 4 degrees on track days - would it be feasible to just swap upper control arms, or would that also effect toe? (or something else?)

[Risking]

For a lot of our GTR's we have several sets of upper arms from 2.5 to 5.0 in .5 deg increments.

A camber change effects the entire alignment, only mildly but it does.

Best to get a base line alignment and note the settings. Change only the Camber and then check toe and castor again. Note them down and work out the difference.

Typically a GTR will loose castor and toe out when adding camber. The toe out is okay providong its measured and desirable. but the castor loss is difficult to rectify without massive strain on the radius rods and bushes.

[Duncan]

ahh Brad has already put together a more complete response....but my car handles terribly in the wet, so I have a lengthened pair of upper arms to swap in.

of course, it has never been wet once since I started taking the spare set

[MrStabby]

For a lot of our GTR's we have several sets of upper arms from 2.5 to 5.0 in .5 deg increments.

A camber change effects the entire alignment, only mildly but it does.

Best to get a base line alignment and note the settings. Change only the Camber and then check toe and castor again. Note them down and work out the difference.

Once i know the difference, what do i do with that info?

Typically a GTR will loose castor and toe out when adding camber. The toe out is okay providong its measured and desirable. but the castor loss is difficult to rectify without massive strain on the radius rods and bushes.

I'm currently zero toe front and rear. I know loosing toe will make the car less inclined to turn in, but is that just a feeling at the steering wheel or does it equate to more understeer?

The car is running factory castor (nismo radius rods with the wider bush) and superpro adjustable bushes. I assumed that the extra castor that's popular is what puts strain on the outer bushes on the upper arm and chews them out - is that right?

Given my setup, do you think i'm likely to have problems if i swap in arms to get 4 degrees neg and make no other changes?

Thanks Brad and Duncan!

[Duncan]

well Brad is better to answer that more fully...and he is the person who has got my car handling so well

in my case I run a little toe out with the standard upper arms, and therefore little to no toe if I swap to the longer arms. but since I only use the longer arm when it is wet, loosing toe out is actually desirable anyway, because you just don't have the grip to use the extra turn in from the extra toe.

do keep in mind that shorter upper arms are not a good thing really....they affect the geometery, flog out the caster and upper arm bushes, change the camber gain in corners and result in a narrower wheelbase. yes they are the easy way to get more camber and are commercially available but not really the good way. Lengthing the lower arms, or moving the lower arm mounting point outwards is a better idea - and in my case is one of the few freedoms allowed in production cars.

[Risking]

It's impossible to tell you what changing your upper arms will do without trial and error. Every car will change the alignment by various amounts.

One of the cars we prep it makes .5mm tow change. Another its a 1.5mm change.

You want it to toe out for circuit duties but tow in for a comfortable predictable street driven car

Unfortunaltly your going to have to compromise one or the other to go half serious at the track and be comfortable on the road. Or get an allognment before a track day and again after

[Risking]

It's impossible to tell you what changing your upper arms will do without trial and error. Every car will change the alignment by various amounts.

One of the cars we prep it makes .5mm tow change. Another its a 1.5mm change.

You want it to toe out for circuit duties but tow in for a comfortable predictable street driven car

Unfortunaltly your going to have to compromise one or the other to go half serious at the track and be comfortable on the road. Or get an allognment before a track day and again after

[djr81]

I only run 2 degrees neg camber at the front, and dont want to run more permanently as the car is mostly street. I use r spec at the track so i'd like to run more like 4 degrees on track days - would it be feasible to just swap upper control arms, or would that also effect toe? (or something else?)

Isnt the easiest answer is to find a pair of adjustable arms that can go to 4 degrees? Because I can promise you changing suspension arms just for a track day is a major pain.

well Brad is better to answer that more fully...and he is the person who has got my car handling so well

in my case I run a little toe out with the standard upper arms, and therefore little to no toe if I swap to the longer arms. but since I only use the longer arm when it is wet, loosing toe out is actually desirable anyway, because you just don't have the grip to use the extra turn in from the extra toe.

do keep in mind that shorter upper arms are not a good thing really....they affect the geometery, flog out the caster and upper arm bushes, change the camber gain in corners and result in a narrower wheelbase. yes they are the easy way to get more camber and are commercially available but not really the good way. Lengthing the lower arms, or moving the lower arm mounting point outwards is a better idea - and in my case is one of the few freedoms allowed in production cars.

The bush flogging out problem is because of two reasons (mostly)

The compliance in the suspension is in the castor rod. If you put rose joint rods on it you lose most of the compliance. It then gets transferred to the upper bush. Which gets trashed really quickly.

The mounting points for the inside of the upper suspension arm need to be rotated - this is what you get when you buy a Nismo bracket. Also the Nismo kit gives you a longer lower arm and a shorter castor rod. Unfortunately it is $$$$$'s.

[MrStabby]

Isnt the easiest answer is to find a pair of adjustable arms that can go to 4 degrees? Because I can promise you changing suspension arms just for a track day is a major pain.

Oh - my memory was that its easy, just two bolts - the inner and outer pivots. I'll have another look.

Also - i thought you would only need to rotate the upper arm if you were winding in more castor, and there would be no or very little effect from camber change.

[djr81]

Oh - my memory was that its easy, just two bolts - the inner and outer pivots. I'll have another look.

Also - i thought you would only need to rotate the upper arm if you were winding in more castor, and there would be no or very little effect from camber change.

Yeah there are two bolts but the inner one is about 150mm long and fouls on assorted bits of bodywork when you try and install it. Easiest way is to loosen the bolts on the inner bracket until you can get the bolt in - on the drivers side anyway. Hard to do that on the pasenger side as the ABS gets in the way.

If you have an adjustable outer bush there are two bolts to put in which are difficult to align and get started on the threads.

Basically if you do the inner first the outer is a %^*@ to get in and if you do the outer first the inner is a (%*@ to install.

Anyway it is quite a bit of messing about and more than just an hour of work. Then you need a wheel alignment.

[Duncan]

thanks mate

Yeah there are two bolts but the inner one is about 150mm long and fouls on assorted bits of bodywork when you try and install it. Easiest way is to loosen the bolts on the inner bracket until you can get the bolt in - on the drivers side anyway. Hard to do that on the pasenger side as the ABS gets in the way.

thanks mate, that is the kind of really simple and obvious ideas that really shit you when you've never thought of them I know how I'll be installing upper arms from now one, on my car they are an absolute bastard