alignment question

[32york]

I seem to have run into a problem and I am hoping someone can help. I have a new set of Kumho Ecstas on the car (17/17) and my son and I installed a set of the Bilstein shocks all around set on the lower perch. The car sits real nice. I brought it in for an alignment and the tech told me that he couldn't set it to factory specs (2002-2005) which I asked for because he says the shocks have lowered it out of range on some of the values. The RR camber for one.
We hemmed and hawed and these are the values he came up with:

Front camber -0.7/-0.7, caster 8.0/8.0, toe in .04/.04
Rear camber -2.0/-2.0, toe in .05/.05

I don't remember seeing any threads on Prime where there was similar issue with out of range values after lowering the car. I'm not sure that these settings work for the car and was hoping one of you could verify that they would. He did say that he would change the settings if I felt that they were not right. The car is will be used only on the street and I did ask that the settings wouldn't eat up the tires.

Thanks guys.

 

[jwmelvin]

It is true that lowering affects the range of possible camber. Your numbers seem pretty good really. But you want the front toed out, not in.

 

[stuntman]

Rear camber looks fine. Factory spec is toe in at the front and that improves steering response and turn in at the expense of front grip.

 

[jwmelvin]

Factory spec is toe in at the front

Can you provide a reference for this? I have always understood the opposite. As per comments in the wiki. http://www.nsxprime.com/nsx-faq/tires-and-wheels/alignment/

Or this thread: http://www.nsxprime.com/forum/showthread.php/176801-Front-toe-in-versus-toe-out

 

[stuntman]

I was mistaken on the factory setting.

 

[jwmelvin]

Okay but aren't I correct that you personally like to run toe out in front?

 

[darock]

Totally normal. I have done an alignment on my car before I put it into hibernation last fall and I got the same measurements beside, I used toe out in the front. I have bilsteins with stock springs. got 2.2° rear camber as minimum possible adjustment.

Bernhard

 

[stuntman]

It depends on what you're looking for. If you want to make the steering more responsive at initial turn-in, then toe-in will improve that at the expense of front gripid corner.

 

[32york]

Well I've had my car out now since the alignment and have noticed this. Going down the road at low speed it seems fine. Increase speed to 60 mph and above and a definite steering wheel 'shimmy' or vibration starts and just gets worse the faster you go. Is the alignment related? How do I get rid of this?

 

[jwmelvin]

That sounds like an issue with wheel-tire balance.

 

[32york]

jwmelvin- thanks I will check this tomorrow.

 

[32york]

Checked balance today- was OK. Was a bit more careful centering them on the studs (with my spacers) when reinstalling. Seems to have taken care of the vibration. However I had it out on the highway at 75 mph the car didn't seem as stable as I thought it should be- I was holding onto the wheel with both hands tightly to keep it straight. Is this normal? I couldn't imagine going any faster it was white knuckles as it was.

 

[jwmelvin]

It sounds good that the centering improved. (I count that as a type of balancing.) But I'd like to understand the issue with stability. I have some vibration around 75, which irritates me and which I ascribe to wheel centering, but the car is very stable.

I have seen posts on Prime where others do not like front toe-in. I'm not sure that switching to toe-out would improve straight-line stability though.

 

[32york]

I'm due back Friday with my alignment guy to do some fine tuning this time with me in the car. Is there anything I could do to improve the high speed stability- it was a little scary to be honest. It felt like the car wanted to move side to side. I listed the settings I'm at now at the top of this thread.

 

[jwmelvin]

The only thing that seems odd about your setup is the front toe. I am not the expert here, but my car is running -0.26 deg total front toe, which is toe out. You are running 0.08 deg total toe (toe in). That's a pretty big difference.

In the rear, you are running 0.10 deg total toe, whereas I have 0.19 deg total. Again a significant difference.

My camber is a little higher at -1.2 in front and -2.5 in back. Your seems well within what one would want.

It would be nice if some of the experts here can help you out but I spent a lot of time reading threads about alignment (and a lot of info came from Billy aka stuntman) before deciding on my targets. The only thing I wanted different was more camber in front, but apparently that was not possible.

You will sometimes see toe represented as mm rather than deg. I have always found that unsatisfactory, as it requires the introduction of the wheel width. Since many of us do not run the factory wheel sizes, 2mm of toe on the factory wheel is not the same as 2mm of toe on our wheels. So I much prefer degrees.

PS: as another data point, I looked up the alignment from my last NSX. It was
Camber: f: -0.3, r: -1.5
Toe: f: -0.27*, r: 0.33*

I think you need to switch to toe out in front, and more of it. That will improve your straight-line stability.

 

[stuntman]

Jwmelvin -0.3 camber is way too little, especially if you do any spirited driving.

OP - which Kumhos did you buy? How was stability at 75+mph before the tires? What's it doing now? Your alignment looks fine.

 

[32york]

Kumho Ecsta LE Sport, they probably have 100 miles on them now. The car was bought in St. Louis and my son drove it back to Maine last fall on crappy mismatched weather cracked tires. He didn't speak of any stability issues and knowing him he drove fast. This spring we swapped tires and shocks but haven't driven it till now after the alignment.

 

[jwmelvin]

Jwmelvin -0.3 camber is way too little, especially if you do any spirited driving.

Thanks, I agree, and that's why I have -1.2 now. That's the most I can get.

OP . . . Your alignment looks fine.

It's very unclear why you say that when his toe is the wrong direction from and much less than the spec. The factory spec is -3.5 mm total toe. Depending on whether you use wheel or tire diameter to convert that, it is at least -0.3 deg. He has +0.08 deg.

 

[stuntman]

I'm just skimming this thread and not being too helpful. His front toe is pretty much zero. Even slight toe-in is fine if the steering response and front grip characteristics is what you're looking for.

The Kumho isn't one of the best tires for dry grip and steering response and the tread pattern has a lot of little tread blocks that increase squirm, but his major problem is probably not enough toe-in at the rear. I would double it and tell the alignment guy he screwed up the toe, and try the increased rear toe-in and see how it feels.

Sorry for being somewhat useless so far.

 

[jwmelvin]

That's very helpful, thank you. I didn't realize the problem was more likely rear toe than front.

 

[32york]

Thanks guys, I'll give this a try and let you know.

 

[HDA]

it happened to me that when I went from stock alignment to negative rear camber the car would feel any imperfection on the road, especially uneven pavement. Thus whenever I was between the 2 "grooves" the car would pull to the side.

 

[32york]

Well, I had the car realigned to these specs: (in degrees)

Front: camber -0.9/-0.9, caster 8.0/8.0, toe 0.01/0.01

Rear: camber -2.2/-2.2, toe 0.12/0.12

This time it was done with my weight in the front seat. What a difference. At 80mph its steady on the road, the instability I felt before is gone. It drives beautifully. Thanks Stuntman and jwmelvin for your advice.

- - - Updated - - -

 

[jwmelvin]

Glad it worked out. Go rear toe!

 

[DDozier]

At 80mph its steady on the road, the instability I felt before is gone. It drives beautifully. Thanks Stuntman and jwmelvin for your advice.

- - - Updated - - -

One other issue that shows up at higher speeds is the front sacrificial lip spoiler may be missing. If it is as the speed increases so will front instability and front end lift. Make sure you have one on the car if you are going to be doing high speed runs.

Dave