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April 30, 2009 10:52 p.m. Salanis SuperDork

I am having a heck of a time trying to get the Miata aligned. I'm suspecting that the culprit may be old suspension bushings.

I discovered that I was getting more wear on the outside of my tread, than the inside, and figured that's a sign that I needed a more aggressive alignment. I was at -1.5* and -2.0 for camber, with about 6.5 caster. I'm trying to go for -2.5 and -3.0. I'm not too picky about caster since I'm really not sure how to check it.

So, I tried cranking the suspension bolts as far to the outside as they could go. I was only about to get -2 and -1.7 in the front, and -3.0 and -2.6 in back. I feel like I should be able to get more.

Additionally, when I made a quick circle on the road to test my suspension, the steering feel was wonky. It felt much lighter than it was, and when I started to turn in, the wheel would turn itself harder into the turn. That didn't seem right.

Checked the toe, and I had massive toe in. I don't know if that was the culprit (I straitened it out, but haven't tested it again). I couldn't check caster angle, but it clearly has some. I don't know if it maybe doesn't have enough or maybe has too much. Could it be that there's too much caster and the weight of the car is pulling it over the wheels at low speed?

Do I just need to get new control arm bushings? Would that solve my issues trying to get a consistent alignment?

Please help! I was about ready to start crying and bang my head against the wall when I couldn't my camber and caster how I want them.
May 1, 2009 6:25 a.m. 44Dwarf Reader

Question. Do you have the stock sheild over your brake rotors? If not go get a magnetic angle finder. Place on the rotor (a cold rotor!) point wheel straight. Now hang plumb bob off tread. Mark spot on ground now turn wheel so the plumb bob moves 4 inches.mark spot. and write down angle from the angle finder. Now crank wheel the other way so the bob is now 8 inches from the other mark take angle reading. subtract one from the other theres you caster reading.

Toe in will make car strange to drive. toe in is only used on some FWD with bad geometery.

Remember caster will add camber in turns so it will afect the wear of the tires too.
May 1, 2009 6:38 a.m. Jensenman SuperDork

It sounds to me like an Ackerman problem, based on your description of the wheel trying to turn itself tighter into the turn. Quick check: Turn the wheel all the way one way or another, then check the relative angles of the front tires. The inside tire should turn more than the outside, somewhere around 2 degrees more (roughly). If it's vice versa (outer turns more than the inner) or there is a HUGE difference, the Ackerman is wrong. Check this both ways; if the relative angles are different for different sides the rack may not be 'centered'. On Miata stuff, the inner TR pivot should be almost perfectly in line with the inner lower CA pivot when the wheels are in the straight ahead position.

6.5 degrees is a BUNCH of caster. I'm not sure there's that much caster adjustment in a Miata SLA suspension. I ran 4.5 degrees on Stinky, but that was on a strut type front suspension. It was a compromise setting which really wasn't anywhere near ideal and it required a lot of cutting of the strut towers to get that much. A whole bunch of caster should make it harder to turn, not easier. A sorta kinda way of checking caster (may be acurate enough for your purposes) is to put jackstands under the front CA's as far out as you can get them, make sure the suspension is as close to settled as possible and that the car itself is level. Then put one of those hardware store angle finders against the vertical part of the 'knuckle' (front or rear, doesn't matter) and the resulting difference from vertical is a rough approximation of the caster. I run ~ 2 degrees caster on the Abomination.

44's way is about as good as it gets when checking caster.
May 1, 2009 6:55 a.m. petegossett Dork

I know on a Miata, as you dial in more negative camber, you loose caster which will make your steering light.
May 1, 2009 7:18 a.m. Jensenman SuperDork

You mentioned the tires wearing on the outside even with -1.5 camber. There's other factors which lead to outside tire wear, mostly due to hard cornering (yay!) with low tire pressures.

That means it's pyrometer time. My suggestion: put the camber angles back where they were (the -1.5 and -2.0 figures you mentioned), see where the caster is, then try to get it as close to even from side to side as possible. You do this by turning the adjustment cams, if the rear pivot is moved outward it will increase caster, if the fronnt pivot is moved outward it will decrease caster. Then set the toe at zero (to start), borrow a memory pyrometer and drive about 5-10 miles (con brio if you can), then jump out and check the tire temps. The hottest part of the tire is doing the most work and now you have an idea of where you need to adjust what.
May 1, 2009 11:02 a.m. Stargazer HalfDork

I had that same problem with the steering turning harder onto itself. I always chalked it up as a side effect of my alignment, until I changed my tie rod ends and lower ball joints. I did them both at the same time so I'm not sure which fixed it, but it's gone now. If your car has a bunch of miles on it and you don't have any history of the tie rod ends or lower ball joints being replaced, I'd recommend doing them. The parts aren't too expensive and it really tightens up the steering and suspension feel.
May 1, 2009 11:47 a.m. John Brown SuperDork

Funny thing is Pimpish disassembled his wrecked car and slammed it back together drunk and in the dark and the new car tracked straight. You Miata is broken beyond repair, I will take it off your hands for $9.25 delivered.
May 1, 2009 11:55 a.m. ansonivan New Reader

Excessive negative toe will always cause tire wear on the outside shoulders, wonky/light feeling steering as well.

Bet you a nickle that just setting the toe will have fixed most of your issue.
May 1, 2009 12:07 p.m. Salanis SuperDork

The Ackerman issue makes sense. Measuring my toe, I think I had around 2" of toe in when testing it. Sounds like that could have caused that problem. I probably need to test drive the car again now that I've got it set to about 1/32" to out.

Jensenman wrote:

You mentioned the tires wearing on the outside even with -1.5 camber. There's other factors which lead to outside tire wear, mostly due to hard cornering (yay!) with low tire pressures.

The wear issue is definitely occurring under hard driving. I really noticed it after a day of two people flogging the snot out of it at an auto-x. We were running about 31psi hot. Maybe that was a bit too low, but there wasn't any scrubbing down the sidewall. I suppose it's entirely likely that I need to run more pressure still. I'm running more like 36-38psi on the track, which is even less than what Spec Miata folks run. I still haven't figured out what my optimal tire pressures are.

I kind of suspect that I need more camber since I'm running this car at so many track days. -2.5 and -3.0 are popular for spec Miatas, and I've heard other people say they like that alignment. I'm a bit perturbed that my suspension does not seem to want to get those numbers. I thought there would be more adjustability in the suspension.
May 1, 2009 12:16 p.m. Salanis SuperDork

ansonivan wrote:

Excessive negative toe will always cause tire wear on the outside shoulders, wonky/light feeling steering as well.

Bet you a nickle that just setting the toe will have fixed most of your issue.

Okay, the earlier part of the story is that I also changed my ride height. I figured the car was too low on the Fat Cat NB mounts I had on it. So I raised it on NA mounts, since I had to change the alignment anyway.

Prior to that, I'd had the car professionally aligned and it had zero toe at that time.

That's another thought for getting the camber how I want it. I could go back to the NB mounts to drop the car back down. I'd rather not though, it would occasionally scrape on speed bumps and rub on the front fenders during hard cornering.
May 1, 2009 12:27 p.m. John Brown SuperDork

It is all relative, camber numbers on worn suspensions will vary a bit. What you need to do is get it to turn as well as possible with the springs, shocks, bushings and tires.
May 1, 2009 12:36 p.m. Jensenman SuperDork

Ahh, extra adjustability. It's amazing how much more you can get with a well placed Powr-pull. Or even a lil' strategically placed filing/grinding.
May 1, 2009 12:37 p.m. Salanis SuperDork

Jensenman wrote:

Ahh, extra adjustability. It's amazing how much more you can get with a well placed Powr-pull. Or even a lil' strategically placed filing/grinding.

The Miata shock mount doesn't affect camber angle though, does it? I thought, since it's not a strut suspension, that the camber was solely a factor of the A-arms.

John Brown wrote:

It is all relative, camber numbers on worn suspensions will vary a bit. What you need to do is get it to turn as well as possible with the springs, shocks, bushings and tires.

So you're saying not to worry too much if they're close but not perfect?

Sounds like it's time to bite the bullet and order up new bushings. I'm sure they'll net me more consistent numbers between the corners. Do you think they'll also get me more camber?
May 1, 2009 1:36 p.m. Jensenman SuperDork

The shock mount does not DIRECTLY affect camber. Since the MeOtter is a short/long arm suspension, it has camber 'gain' as the suspension is compressed. That means if you have the suspension set at a given camber angle with the stock hats, then swap those for hats which lower the car you'll gain some camber that way, unless the car is brought back to stock ride height or realigned at the new lower ride height.

As far as replacing suspension bushings, if they are worn yes you can get some pretty big changes in camber as the bushings deflect under load. You can put in new stock bushings but they too will deflect, since they are made of rubber. They just won't deflect as much as worn ones.

Urethane suspension bushings have much less deflection than rubber bushings (lessening camber/toe changes) and more important they allow the suspension to move more freely. BTW: Urethanes will 'stick' when the car is first moved after sitting a while, then free up.
May 1, 2009 1:50 p.m. Salanis SuperDork

Yeah, I'd be replacing them with Urethane bushings. Will new bushings likely result in more or less maximum camber?

I could probably get to the camber angles I want now by switching back to the NB mounts, to drop the car back down that 1/2". But that low ride height was about the same as the local speed bumps, and resulted in rubbing occasionally in the top of the wheel wells under hard cornering. I guess the rubbing wasn't too frequent though, and I'd be able to actually get the alignment where I want it.

Or I get it a little bit more dialed in as it is now, and see what I think of that.
May 1, 2009 3:11 p.m. Jensenman SuperDork

If the original bushings are worn enough that the sleeve is no longer centered in them, then yes the urethanes will change the camber, they will probably reduce the max amount you can get.

If the stock bushings are in good shape, then urethanes won't change the camber since the steel sleeve is centered in the bushing or at least it is in most cases. The slots in the subframes, the 'semi circles' welded to those same subframes and the eccentric on the bolts are what control the camber. Those have been known to mysteriously migrate. Damn migrating parts.
May 1, 2009 3:19 p.m. Salanis SuperDork

The car has 136k on it. I'm betting these are original bushings.
May 1, 2009 4:25 p.m. Kendall_Jones New Reader

Salanis wrote:

The car has 136k on it. I'm betting these are original bushings.

Thats not a terrible amount of miles on the original bushings. The bushings usually get harder as they age (and then they fragment). If you need a set of Delrin bushings, I have a set w/ control arms on ebay ;)

Kendall
May 3, 2009 2:34 a.m. Salanis SuperDork

I think I've decided on the best course of action. I'm going to go with the NB upper mounts, and then run 1/8" or 1/4" spring spacers. That should get me high enough to not rub, but low enough to get the camber I want. Plus, that also gains me some suspension travel.

What is the diameter of Miata springs so I know what size spacers I need?
May 3, 2009 12:04 p.m. joey48442 SuperDork

John Brown wrote:

Funny thing is Pimpish disassembled his wrecked car and slammed it back together drunk and in the dark and the new car tracked straight. You Miata is broken beyond repair, I will take it off your hands for $9.25 delivered.

It wasn't dark! The new garage has decent lighting.

But it does track straight.

Joey
May 4, 2009 1:26 p.m. Salanis SuperDork

Screw doing this job myself. It has just about brought me to tears, and driven me nuts. I will almost certainly upgrade the suspension on the car before too much longer and will have to go through the cursing and everything all over again.

I'm going to do what I should have from the beginning and get a Lifetime Alignment package from Firestone.

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