Negative Camber in the Rear and Expensive Tires

[linkster]

Most of the original postings had to do with the air spring P85+ cars with 265/35ZR-21 tires that, because of their profile, amplified toe errors, and to some degree, benefited from aftermarket camber-reducing parts and careful attention to rear (toe) alignment. In large part that issue has been sorted as those cars are ~~5 years old now and the owners have figured this out.

19s have shown more tolerance for alignment errors, but still need thoughtful alignment skills

Dat wud B me with Veronica over 5.5 years old now with 82K+ miles on 2nd set of (50 % tread remaining) 21s. Removed a $hitton of tire shredding, costly, energy consuming unnecessary camber from both front and rear. Btw, Veronica never drives in low except when we were forced to at highway speed for much of 2013. Aftermarket adjustable UL options are now available, however, I prefer a fixed approach in similar fashion to my mentor @lolachampcar/the suspension maven/TMC Titan on this forum with an in depth explanation on this topic by @HyperMiler.

And yup, the 19s tend to camouflage this issue.


Good-Luck!

 

[sorka]

jerry and I have slightly differing opinions in that I am reasonably sure from past experience that -2 degrees of rear camber will still wear the inside shoulder of the tire even if you are running near zero toe in. It is a matter of degrees (pun intended). High negative camber with lots of toe in or out will chew up your tires very fast. High negative camber with little toe will chew up your tires but take longer to do so. The moral for me was to make sure I was running the toe I wanted while getting rid of the negative camber.

Tesla has helped with newer cars by running them at a higher ride height. They have updated code on the air suspension on older cars to run them higher as well.

I know this is an old post but wanted to point at that the added height is what's destroying cv joints (on AWD cars) due to the increased angle. In my case it was even worse because the steering stops weren't exactly symmetrical and an all the way left turn with the car in highest was exceeding the joints angle and bending it. This is why my passenger side front cv joint went bad 5 times while the left never went bad. The result was vibration during acceleration between 28 and 35 mph.

The car has since been lowered an inch with lowering links I printed and the problem hasn't retuned again.

 

[sorka]

here ya go arijay:

Adjustable rear camber links and tire rotation result in perfectly even tire wear


View attachment 97125
pic courtesy of SUPRKAR

Is there any concern that the bolt/thread are strong enough on the outside of a corner which is trying to pull the link apart?

 

[sorka]

Lastly, you do not want to run zero toe in the rear as the rears will tend to toe out under acceleration loads. The wheel is pulled forward against the lower a-arm which causes the front side toe link to toe the tire out. I've used toe out on the rear of race cars to get them to rotate under acceleration but I would not suggest getting anywhere near this on a street car unless you are adventurous I set mine at 0.15 total (both wheels together) toe in on the rear.

Totally confused. Isn't this backwards? A rear wheel drive car when accelerating will pull the wheels forward compared with the rest of the car resulting in the front of the tires rotating inwards, not outwards.

What am I missing?

About to get alignment done. The rear total toe spec is 0.30 to 0.50. I'd think you'd want it as close to 0.30 as possible and given that I tend to prefer oversteer to understeer then shooting for the least amount of toe in that the spec allows should fit my preference and also reduce tire wear.

The front seems to make sense. The spec is -0.30 to 0.10 so most of that range is negative or toe out. Given that the AWD car is mostly a front wheel drive car when cruising, the wheels are going to get pulled slightly forward and hence the fronts will rotate towards the centerline reducing the toe out to close to zero toe while driving at freeway speeds.

 

[sorka]

It's BBC Speed & Machine . Joe there is very knowledgeable, but he dislikes email.

He hand-machines them from a billet of high-strength aluminum alloy. He needs your cores or else he has to buy the upper struts from Tesla to get the bushings.

Because it's a specialty part it's $1,000 for a pair. (How much are tires?)

If you have a dual motor car you have a ball-bushing on the hub end and a regular bushing on t'other; be sure to get it the right way on.

FYI, Joe will no longer use your used bushings from your links. He will only make arms with fresh bushings that haven't been used. Easiest way to get them is to buy a rear wishbone link 1021422-00-B and he will press out the new bushings from those and use them.

 

[lolachampcar]

Totally confused. Isn't this backwards? A rear wheel drive car when accelerating will pull the wheels forward compared with the rest of the car resulting in the front of the tires rotating inwards, not outwards.

What am I missing?

About to get alignment done. The rear total toe spec is 0.30 to 0.50. I'd think you'd want it as close to 0.30 as possible and given that I tend to prefer oversteer to understeer then shooting for the least amount of toe in that the spec allows should fit my preference and also reduce tire wear.

The front seems to make sense. The spec is -0.30 to 0.10 so most of that range is negative or toe out. Given that the AWD car is mostly a front wheel drive car when cruising, the wheels are going to get pulled slightly forward and hence the fronts will rotate towards the centerline reducing the toe out to close to zero toe while driving at freeway speeds.

You are absolutely right about what the rear uprights and tires are trying to do under acceleration loads; they are moving forward WRT to the car. Now consider that the toe link is in front of the upright. When the upright pulls forward, the toe link pushes the front of the upright outward and, viola, you have a decrease in toe in.

As for amounts, per my original post, I run as near zero as possible without getting drive induced rear wheel steering oversteer on hard corner exit. That has worked out to about 0.1 degree total for me and the way I drive.

Lastly, AWESOMEly good info on the CV joint alignment. Thank you!!!!!!!

 

[sorka]

Nix my previous question about whether the bolts would be strong enough. These are WAY larger than I thought they would be. Works of art.

Anyone know what the bolt specs are for the upper links?

 

[sorka]

@lolachampcar, you mentioned way back about toe in being limited when removing negative camber.

My alignment was done recently and it's sagged to -2.0 on both sides (rear). I'm in the process of lowering the car 1" primarily to decrease the angle the cv joint is when under load.

I didn't do the back yet so the front has been an inch lower than the back.

So my question is, if I lower the rear 1" AND adjust the new arms I'm about to put on to have -1.2 at the lowest setting, do you think I won't be able to get enough positive toe on the ear? I noticed you're already running less toe in than spec allows on purpose and I understand the reasons. I myself am after maximum range rather than novice driver understeer support. I actually prefer oversteer myself.

Is the .15 you're running the maximum toe in you were able to get?

 

[sorka]

Well, without any response on torque specs and not being able to find them anywhere on this forum or google search, I used my snap-on to measure the torque needed to free the bolts. Fortunately the static co-efficient of friction did not exceed the dynamic i.e. there was no sudden release to get the bolt turning and it was very progressive.

Still not the way to go but better as fallback than nothing at all.

The upper bolt only too 50 ft lbs to release. The bolt in the hub took 95 ft lbs which seems quite odd. The upper bolt really seems like it should have been more than 50 ft lbs. I'll do the same thing on the other side.

 

[lolachampcar]

The maximum extension of the upper link was 0.210" before I ran out of ability to adjust toe (ran out of eccentric). IIRC, that equated to about a 1 degree change in camber. To get more, I would have to make toe links. I believe one other forum member went that route and is running something like half a degree of negative in the rear and getting big milage from his tires. (that person can feel free to step in here if he wants ).

I did run into one situation where the drive unit was pre-loaded to one side in production. I put on the longer links and one side would not come in on toe. We loosened the four (IIRC) bolts that hold the drive unit assembly to the chassis and it "popped" back to the center. We then had equal (and enough) toe adjustment on each side of the car. Smart alignment tech to know to do that; I learned something that day.

Are those rubber bushings in each side of those links? If they are, you are loosing the improvement Tesla made when they put a solid ball style joint in one end of the links.

 

[dark cloud]

Nix my previous question about whether the bolts would be strong enough. These are WAY larger than I thought they would be. Works of art.

Anyone know what the bolt specs are for the upper links?

 

[sorka]

Thanks. The knuckle bolt on drivers side came off with 95 and the passenger side came off with 105 ft lbs so that spec jives.

The subframe bolts both came off with 50 ft lbs which is half of the spec it appears. The bolts are the same size so it makes sense.

OK, I get it now. The subrame link mounting bracket will have compressed just a little bit over time. So I should put it back on at 95 ft lbs.

Thanks.

 

[lolachampcar]

Do not forget to torque the rubber bushed sides when the car is in neutral ride height (and not droop). Tightening in droop puts a torque load on the bushing at ride height and they will fail that way (and no, do not ask me how I know )

 

[sorka]

Do not forget to torque the rubber bushed sides when the car is in neutral ride height (and not droop). Tightening in droop puts a torque load on the bushing at ride height and they will fail that way (and no, do not ask me how I know )

Oh geez. Glad I saw this post.

So I have lowering links. Neutral setting with it lower than stock?

What actually failed? And when you say torque you mean just the upper link bolts?

 

[sorka]

Do not forget to torque the rubber bushed sides when the car is in neutral ride height (and not droop). Tightening in droop puts a torque load on the bushing at ride height and they will fail that way (and no, do not ask me how I know )

So I'm still not getting this. Are you saying I need to torque the upper arm while the car is loaded on the wheels at the normal height setting?

 

[AWDtsla]

So I'm still not getting this. Are you saying I need to torque the upper arm while the car is loaded on the wheels at the normal height setting?

All modern rubber suspension bushings are used as pseudo-bearings, except they have a neutral position instead of being allowed to freely rotate, and are pulled elastically in any direction away from neutral. If you allow the bushings to assume their nominal position before applying torque, it means they will be least stressed.

They have high failure rates but are super cheap to manufacture

 

[sorka]

All modern rubber suspension bushings are used as pseudo-bearings, except they have a neutral position instead of being allowed to freely rotate, and are pulled elastically in any direction away from neutral. If you allow the bushings to assume their nominal position before applying torque, it means they will be least stressed.

They have high failure rates but are super cheap to manufacture

I think I understand. But that means I need to:

1) Go back out and remove the wheels.
2) Loosen the bolts on the arms.
3) Put the wheels back on.
4) Lift the car a far enough on the rear wheels to allow me to get underneath and tighten the bolts tight enough to keep the bushings from loosing.
5) If I can't use the torque wrench from underneath, I'll need to jack the car again, remove the wheels, and then torque the bolts.

Or is there a way to compress the suspension enough to bring the hub into the neutral position? i.e lower the car all the way and then go into jack mode to reduce as much pressure as possible?

Is there a way to release all remaining pressure manually from the air springs after I've gone into jack mode? If so, is that enough to manually move the hub up far enough to be in the neutral position?

 

[AWDtsla]

I think I understand. But that means I need to:

1) Go back out and remove the wheels.
2) Loosen the bolts on the arms.
3) Put the wheels back on.
4) Lift the car a far enough on the rear wheels to allow me to get underneath and tighten the bolts tight enough to keep the bushings from loosing.
5) If I can't use the torque wrench from underneath, I'll need to jack the car again, remove the wheels, and then torque the bolts.

Or is there a way to compress the suspension enough to bring the hub into the neutral position? i.e lower the car all the way and then go into jack mode to reduce as much pressure as possible?

Is there a way to release all remaining pressure manually from the air springs after I've gone into jack mode? If so, is that enough to manually move the hub up far enough to be in the neutral position?

I'd leave the wheels on. You will have to go through some contortions to reach the bolts, assuming you don't have the right lift. No guarantee you'd actually get neutral position unless the car is on wheels and leveled at ride height.

1. Jack up the car enough so you can reach around
2. Loosen the bolts to barely hand snug.
3. Lower the car, ensure it's in neutral ride height (toggle park/air suspension)
4. Reach around and tighten the bolts enough so they won't move
5. Jack up and use torque wrench properly.

In the end it comes down to how much OCD do you have...

 

[sorka]

I'd leave the wheels on. You will have to go through some contortions to reach the bolts, assuming you don't have the right lift. No guarantee you'd actually get neutral position unless the car is on wheels and leveled at ride height.

1. Jack up the car enough so you can reach around
2. Loosen the bolts to barely hand snug.
3. Lower the car, ensure it's in neutral ride height (toggle park/air suspension)
4. Reach around and tighten the bolts enough so they won't move
5. Jack up and use torque wrench properly.

In the end it comes down to how much OCD do you have...

I tried that and I could reach the bolts but no way to get them tight enough.

Instead, I jacked a rear corner up then used another jack under the hub. I aligned the jack under the hub and very slowly lowered the other jack so the hub rested on the jack. I then raised the hub about an inch to get it exactly where the wheel was. I first measured the wheel under load to the center of the center cap and then made sure to lift the hub so the shaft was exactly at that level within a mm. At this point the jack on the hub was the only jack supporting that corner but the other jack was within a mm of touching the lift pad on the side of the battery just as a safety catch.

I then unbolted everything. I heard the bushing snap as I loosened it. I put a paint dot to make sure the bushing didn't slip given this upright position I couldn't reach it with the torque wrench. I was able to get it about 65 ft lbs by hand. The paint dot assured me that it didn't slip when I jacked the corner back up and let the hub down.

 

[lolachampcar]

Wow, lots of posts.

Yep, that is what I do. I jack the upright until the car is supported by that jacking point. The car has to be in its normal ride hight setting when you do this which can be tricky (getting the initial jack under the car when it is sitting so low so you can take the wheel off and jack up the upright). Once sitting comfortably on the jack/upright, I carefully reach in and snug down the bolts on both sides of the upper links. Once snug, friction between the bushing inner race and the bracket it resides in (chassis side) will hold it from rotating. I then better support the car and fully torque both bolts.

Be safe.

Also, I somehow screwed something up the first time I put my links in and my car ended up pumping up to the very top of the air springs. I looked like one of those silly 4x4s on a big lift kit with tiny tires. I started to freak out but found I had done something really silly. It was something like the ball link on the suspension arm is not on the center line between the two bushings, its offset a bit. If you put the link in "up side down" the ball ends up on the wrong side of the link center line and thus gives radically false feedback to the ride height sensors. Viola, you have a clown ride

I wish I could remember exactly what the problem was. It's been, what, four or five years ago. If this happens to anyone, do not freak out. It is a simple fix and completely reversible when you do fix the silly problem.