Whats the sweet spot for caster on these cars?

HwyStar

Registered User
I never experienced it before but now I have. I didn't think it was possible to have too much caster. I set my Cougar to +6* caster and the car is all over the place on the highway. I've heard of this, but after all these years this is a first.

I'm going to back caster off to +4.5* this weekend. What do you guys think?
 
My lowered Anny is at +5°. Tires are staggered front/rear. Tracks perfect.

+6 should make it track like a tank, tho. The closer you get to zero, the more it should wander, not the other way round.

Are you sure your power steering module isn't acting up?
 
It does wander when I go through dips in the road at speed. Strange. Goes toward either right or left. Not death wobble though. Read about having too much caster before and it matches exactly. Maybe +5 is good. I remember setting these cars at +5 before and being good.
 
That's what I thought too. Nothing is loose, or bent. I'll give backing off caster a bit. This is the first time I've put this much caster in a fn10 or a mn12. Think I will put a little positive toe in it too. Maybe .10* total.
 
I generally run 6.25 degrees of caster on these cars, and it makes it track great down the highway. I would suspect that you have some other problem. Did you adjust all the other alignment angles after setting the caster? If not, then that is your problem because changing the caster will throw everything else off.
 
Yeah, set total toe to 0.0* front, -.1* total toe rear and camber to -1* all four wheels. I could put it back on the machine do another sweep and find something off. I do remember this was the last car I did on the machine before the memory burnt in the computer. And, the aligner was acting funny then. Fixed the machine and did a couple cars since and things seem ok.
 
I would do that first and see if anything is off. It just doesn't sound right that the added caster would cause your issues.
 
I was thinking that too. I mean, you see Mercedes with +10* and bimmers around +7*. But, have read ASE questions that said too much positive caster will cause wonder. Too negative causes bump steer. I've seen bump steer. But, I thought wonder would mostly be caused by zero total toe.
 
I'd agree that caster isn't causing your wander. I posted this awhile back, and I thought it would be relevant here, too.

racecougar said:
As far as recommended specs go, this is what I would suggest:

Front:
Camber: Negative 0.8-1.3 You can go further, but you'll start wearing the insides of the tires. I typically prefer mine at ~ -0.8-1.0.
Caster: Positive 5.0-6.0
Toe: Positive .05-.15 On a autocross car, you can go slightly negative, but you'll give up stability at speed. I keep mine at ~ +0.1.
Cross Camber: As close to zero as possible.
Cross Caster: 0 to -0.3 Going negative helps on crowned roads, but will cause a slight drift to the left otherwise.
Total Toe: Positive 0.1-0.3 Once again, this is for a car you'll be driving on the street. If it's an autocross car, a little negative toe will help on turn in.

Rear:
Camber: Negative 0.5-1.0 Same as the front, you can go further, but you'll start wearing the insides of the tires. Also keep in mind that as the rear squats, the camber will tend to go further negative. I like mine set at ~ -0.5.
Toe: Zero to +0.15 I'd lean toward +0.1 on both sides with Delrin LCA bushings and toward zero with the stock LCA bushings, as they'll allow an increase in toe when under power.
Cross Camber: Same as front. Keep it close to zero.
Total Toe: 0-0.3


These settings have worked well for me as an all-purpose alignment (drag racing, corner carving, and highway cruising) on this chassis without any real adverse effects on tire wear. If the intended use was autocross-type events only, drag racing only, etc., I'd set things a bit differently. These are just my recommendations.
 
I'm going to reopen this thread once more because baby needs a new pair of shoes. I have three questions.

1. What are the OEM specs?
2. What is the difference between them and the ones everyone seems to be discussing?
3. Which is better and why?

I understand very little of how to align a car, other than to know the difference when the car is tight or it's loose. I plan on getting a set of 245/45x18's and the car may be slightly lowered and still has the stock Tokico shocks.

So before I have this discussion with the guy who is going to do the alignment, I thought it might be nice if I understood what it is I want and why.

Anyone? Everyone?
 
It sounds like you expect to find a shop and then educate the guy that will align your specific example of a car.

I'd recommend to find someone already familiar with these cars, instead - it's a given they understand when a vehicle has been lowered or lifted, etc. A modern shop that routinely performs 4-wheel aligns will have the specs in their alignment machine.

That said...

1.) Specs should be here: http://www.sccoa.com/articles/scspecs.php

2.) Very little, based on personal preferences, I'd say. Stock sway bars? Special offset wheels? Deleted power steering? Auburn diff? Relocated battery? Poly? I prefer just a touch more caster and very, very minor toe because of the steep crown some of the local roads have in order to help shed the frequent rain.

3.) It's not that simple, I think. Two cars set up identically the same can supply different feedback on different roads when commented on by different drivers. You may need to detail your needs, style of driving and any subtleties such as do you frequently drive two-up with the trunk full of camping gear or are you only concerned with getting it off the trailer and thru the traps.
 
Ira: this article does a pretty decent job of explaining how alignment settings affect handling and wear.

As it pertains to the MN12, my personal theory is that with the slow steering rack, there's no down side to lots of caster. I ran -1.5° camber on all four corners of my SC for years with no real problems--I've had the same tires on the car since late 2007. Contrary to popular belief, excess toe kills tires a lot faster than camber. I don't know what the factory recommendations for toe settings are, but I like a little bit of toe out to help the car steer. On a street car, 1/16 toe out should be fine. Much more than that will begin to wear fairly quickly. I had something like 3/16 toe out on my MR2 because it had the Worst Push in History (TM) and it looks as if something tried to eat the tires' inner edges.
 
If you were closer I would align your car for you...I have done more than a few....

Yeah, I used to run -1.5 deg camber on all four. Normal driving and hitting the clover leaves every now and again I would expect 30k miles out of a set of Goodyear HPs. I decided to back off to -1.0*. That would get me no camber related wear at 60k miles plus on the same set of tires. -1.0* is max negative camber factory spec. Factory caster spec is 4.5-5.5*. I usually set it around 5.5. I put the front at zero total since I've never had a problem with wander in one of these cars. I set the rear to slightly negative to offset the load under acceleration that tends to force the rear arms positive.

Now, if this were a straight axle truck I would set the front slightly (.1*) positive to help with wander and prevent 'death wobble.'
 
Interesting that lots of specs being mentioned with no regard to the tires. In my experience the wider and firmer the tire construction, the more sensitive it is to camber. Alignment specs for the stock 225/60 tires are going to be different than 245/45's (IMO). I just say this because when someone says they have no issues with tire wear at xx negative camber, I believe there are other things to consider.

I've been through many sets of 245 and wider tires on my various SC's over the years, some driven aggressively and one in particular driven by my wife at a most leisurely rate. lol The insides of the tires always wear out, and I always run toe in. The only time the rear tires (285's) have come close to even wear is when the rear of the car is set up for no more than -.5deg camber. -1deg will tear up 285's.

On a car with wide tires that is driven mostly straight ahead or at less than .5g cornering, very little negative camber is needed or desirable. Running over -1.0g negative with a wide tire in the front will make the car feel more edgy, but if you aren't competing then you aren't going to get anywhere near the limit anyway so why chew up tires? At -.7 to -1.0 in the front the car will still handle great but inner edge wear will be reduced. Then to keep the car handling neutral, you need to make sure the rear has less negative camber than the front. I often go for -.3 to -.7. Usually I'm limited by the maximum adjustment of the car and it varies a lot from one SC to the next.

In most cases with a lowered SC you will find that they can't get it any more positive than that, and in fact I've seen some where they can't get it any higher than -1.3deg in the front. The suspension just doesn't often accommodate any more without modification. In the case where you find one that won't go higher than that, then I recommend planning the rest around that one rather than having 3 where you want them and one off in left field.

As for toe, yes I fully understand the affects of toe in and toe out in both terms of standard tire wear and handling as well as high performance and racing. but that being said it is always better to toe both in than to have any toe out on a street car. An enthusiast who manipulates the handling of their car with alignment specs will not be asking questions about what to do because they already know or are experimenting based on their own driving style, tires, and type of track, etc. For the rest of the world, a bit of toe in or at most -0- should always be the guide. Never toe someone's car out without them knowing what it does and wanting the result. It's not worth it!

In my experience with MN12's, some of them handle oddly where the next one is a model of perfection. There are several possibilities for this that need to be checked into. Steering racks are a problem with these. OE units are just plain old, and reman units can be poorly done or even the wrong ratio. It's a bit of a crap shoot in my experience, but in every case where I replaced a steering rack, overall handling and steering response has improved so don't overlook that. Then another thing that can be an issue is that the subframes (both front and rear) are OE aligned to the frame. In the cases of both front and rear it is possible that they are no longer aligned, and since the upper arm hinges from the frame and the lower from the subframe, if they are not properly aligned, the geometry will be off from side to side, no matter what you do. Another thing to consider is that if the suspension has ever been apart it's quite possible that there is bushing windup in one or more component. This will affect spring rates and weight distribution which will give the car screwed up handling. To fix that requires loosening nearly all the suspension components, resettling the car, and then retightening everything with the weight on the wheels. Then there is still the question of bushing and other component wear. I have seen shocks that do not match each other. A stiffer or looser shock in one location will cause erratic handling. I've seen this on brand new Tokico's, so don't assume just because you have new(er) parts that this isn't happening. It can happen with brand new shocks and it's hard to pinpoint.

The last thing I have to comment about regarding the vehicle's tendency to sway as the suspension compresses, is that I'm while I'm not sure how modern alignment equipment determines thrust angle, I suspect that sometimes alignments are done which set the thrust angle off and making the vehicle dogtrack slightly. Maybe someone can comment on how that is measured on a modern machine, but on an older machine it has to be manually set and cars with staggered wheel sizes would cause serious issues with how the machines measured each wheel in relation to the others.
 
Not that it's relevant, but I unintentionally found my last alignment sheet for my MR2 and I was actually at 5/16" toe out on the rear at one point...
 
Trying to go for four-wheel steering, eh? lol

That's essentially what rear toe-out does. The outside wheel, the one that has all the weight on it, is pulling the rear of the car outward, turning the nose inward.

I have no idea what the degree measurement would be, but it's a lot. I changed some things on that car, reducing the front camber from around -3° to around -1.8°, reducing rear toe to 1/8" out and it works better.
 
Thanks guys. So pretty much plan on staying close to the stock settings and let the tech do his. I get that.
 
Back
Top