Tutorial: Rear tire alignment

[bwilson4web]

Hi folks,

After a season of pot-holes and with the spring soon upon us, it is time to plan the spring tune-up and getting the tires ready for vacations. This note covers why wheel alignment is important, an approach and lessons learned.

Wheel Alignment

Wheel alignment toe, the angle in direction of motion, impacts vehicle stability (rolling straight hands off,) drag and tire wear. So high performance race car crews make temperature profiles of their tires after a run to diagnose alignment problems. With an infrared temperature tool, ~$40, anyone measure the tread temperatures just like the race car crews:

In these tests, I drove down the highway at different speeds and inflation pressures for about 5 miles and then pulled off to measure tire tread temperatures. Higher tire pressures reduced the temperature showing reduced wear from lower tire drag. Also, the right side tire had (and still has) an alignment problem, excessive camber. This caused uneven wear and premature replacement of my original tires. But notice that at higher tire pressures, not only were the right-side, tire treads cooler but the wheel camber problem was reduced.

Based upon these tests and having bought a new set of tires, I bought a 'life time alignment' service from Firestone to have it checked anytime I want. Other independent tire shops have similar programs with different terms and conditions. Every Spring and Fall, when I do my twice per year oil change and preventative maintenance, I also check the alignment.

Miss-alignment can occur from hard parking into a curb, a pot-hole or other road stresses. But early detection, before the tire wear is evident, allows us to avoid premature tire replacement and minimize handling issues like trying to wander off the road while changing radio stations.

Adjusting the front wheel toe alignment is easy by tweaking a threaded strut and locking nut and is included in the "life time alignment" service. In contrast, Prius front wheel camber requires loosening and tightening a bolt and in severe cases, the bolt needs to be changed. Yet curiously, neither the tire shops nor my local Toyota service center has shown any interest in equalizing the camber to my specifications since "it is in the green."

Tire alignment systems have a wide range of acceptable Prius toe and camber values. Of the two, toe is more important since this is the angle relative to the direction of travel, the same forces that steer the car. Camber is the vertical angle that helps the outside tire take the turning, centrifugal force but it has less impact on straight-line, tire drag. As my earlier temperature profile shows, keeping the tires well inflated to 50 psi, 345 KPa, reduces the effect of excessive camber and reduce rolling drag:

Image copied from: Tires, Page 3 of 4

Since most of the weight is on the front tires, we rotate them with the rear tires to equalize the overall wear. When tires are rotated each should have an inner and outer tire tread depth measurement. Tire tread depth lets us know how the side-to-side wear is working out, the combination of toe and camber. In the USA tread depth is traditionally given in "1/32" of an inch, ~.8 mm. If the inner and outer depths are off by even one unit, there is a problem that needs to be diagnosed and corrected!

Prius Rear Wheels

Prius rear wheels are bolted, 38 ft-lbs 52 N-m, to a solid axle that ordinarily is not adjustable:

Toyota has a special tool that can change rear wheel toe geometry but usually the dealer just replaces the axle after an accident. Independent shops lacking both the manuals and tool are even less able to deal with rear wheel alignment. Everyone will report a rear wheel alignment problem but typically only adjust the front wheel toe.

Shim Kits

There are after-market, wheel shim kits available that come with sets of metal tabs at "1/64", "1/32", "1/16" and even huge "1/8" shims (if you need a "1/8" shim, there is something dreadfully wrong!) Unfortunately, these kits don't come with Prius rear wheel instructions or even how to use the shims safely.

My rear wheels had both excessive toe and camber but nobody would correct them to my requirements. So I bought the Firestone "life time alignment" service, a shim kit and figured it out:

Since toe impacted rolling drag, I started with the left wheel (the upper pair of graphs) and installed a pair of 1/32 shims on the rear bolts. Shims must always be installed as same sized pairs because with four bolts, if there is any misalignment, the bolts that hold on the wheels can not tighten evenly. This is very, very important since a mismatch can lead to a loose wheel, rocking, and over-stressing the bolts and a wheel falling off!

Unfortunately, I guessed wrong and the toe was worse than ever. But I was able to use the error to calculate that a 1/64 shim on the front bolts should minimize the rear wheel toe and they did a perfect job. Due to the bolt geometry, this also changed the camber angle.

To fix the camber, I used a pair of 1/16 inch shims on the opposite side wheel only to find I over-corrected the camber. I replaced them with 1/32 inch shims and the camber was as near perfect as I could want and the toe remained perfect.

Now there is a small, shim-sized gap between the wheel and axle plates. This gap can allow salt-water from road ice and snow clearing or coastal areas to invade and attack the metal surfaces. The shims have a zinc coating, which protects them. However, if you live in areas with a lot of road or sea salt, it makes sense to fully remove the wheel from the axle and treat both surfaces with an anti-corrosion compound. Eventually, after two years, I plan to inspect my rear wheel and axle plates for corrosion and compare the rolling drag with and without the shims.

So far, the tire wear has been excellent. The tread depth has been even and the rate of wear per 10k miles indicates I will easily meet the expected tire life.

Questions? Comments?

Bob Wilson

ps. Since I have left-over shims, send me a PM and I'll send a set for your rear wheels for $20 and postage. Alternatively, the shim kits are readily available and feel free to use these instructions. GOOD LUCK!

[Pinan]

Fantastic Bob. Thank you very much for taking the time to post this. Once I've had my coffee I'll read it again. Heh

We need a thumbs-up button here!

[wolverine]

Thanks for the tutorial! When I first got my 2008 Prius, I could tell that it was not aligned. The dealer, Don McGill in Houston, lied of course, and said it was. My alignment guy, the owner of Southwest Alignment in Houston, found the proiblem right away, and it was just what you found. He put a shim kit in, but now I'm going to take your instructions to him and see if he needs to make any more adjustments.

Strangely, when I got my Subaru LW200, back in 2001, it had the same problem, and, again, SWA fixed it, but only after I'd been thru 5 sets of tires (on their $) in 25,000 miles. Later, Saturn came out with a recall to fix the LW200's, which were based on an Opal chasis.

Thanks again for the great work!

[Bill Merchant]

Fantastic job, Bob! This is really great.


I nominate this thread for stickyhood!

[Tideland Prius]

Slightly OT.

You can see how Toyota really went to lengths to lighten the alloy wheels. They've removed a bit of metal from each of the spokes at the rear to reduce weight.

[wolverine]

I had a misaligned 2008 Prius, as I've said here, and a local alignment shop found exactly what Bob did.

So, I went down to Don McGill Toyota (Houston) today and took them some print-outs of this. The service manager was very defensive and said that he wouldn't do anything that wasn't in the manual, which is understandable.
Mostly, though, he had this attitude:

I then talked with the General Manger, Kirk Wilson, and we Wilsons (Kirk, me and - indirectly, Bob) came to an agreement that Kirk was going to call Toyota corporate, pass this information to them, and encourage them to add a fix kit, unless some other fix was forthcoming.

Failing that, I plan to have my attorney file a class-action lawsuit to force Toyota to issue a recall on the cars - the thrust of which would be that each Prius would be checked for correct rear-wheel alignment and a shim kit put in, if required. I don't want any money; I just want Toyota to do the right thing - fix their frickin' cars.

If you've had problems with rear alignment, then I would ask that you go to the general manager of your local Toyota dealership and give him/her this information, and encourage him/her to also contact Toyota; this might save us all some headaches. Mostly, though, I'm sure you can tell that I'm trying to save myself the headache of a suit; I have no desire to become involved in this, but this 'no-fix' situation with the rear alignment simply cannot continue.

Naturally, of Toyota doesn't do it of their own volition, then the attorneys will make them do it; their attorneys as much as mine, and if it gets to that point, anyone wanting to join in would be more than welcome.

Toyota's non-fix policy will not stand - I can promise you that.

Any thoughts?

[wolverine]

Originally Posted by Tideland Prius

Slightly OT.

You can see how Toyota really went to lengths to lighten the alloy wheels. They've removed a bit of metal from each of the spokes at the rear to reduce weight.

I hadn't noticed that until you mentioned it. Unsprung weight is always a huge factor is mileage and acceleration, not to mention handling. I wonder if it's possible that the could have cut too much weight out, and made the wheels not robust enough to survive a curb hit (not that I plan on doing that anytime soon). Maybe this is one of the main reasons why the car seems (to me) to float so badly at high speed (> 70) and be at the mercy of winds.

Granted, I'm on OE tires, and I plan to change to the Dunlop A2 Sport in the near future (touring with 16" wheels); I'm going to go to a 205/85/16, I think. I'm hoping that will help the car hold the road. This is important to me because I speed - oh, sometimes - and I was doing 80 on a secondary road in North Texas and as I hit got > 70, the car started to feel squirrely on the road, and at 80 I thought it might leap perpendicular to the roadway and try to take a side road at any moment. Either that, or become airborne like a hyrdofoil race boat on a windy day. (hmm.. no pilot compartment that is - well - Death Proof!)

I'm running 42/44 (front/back) in the tires.

[galaxee]

Originally Posted by wolverine

Failing that, I plan to have my attorney file a class-action lawsuit to force Toyota to issue a recall on the cars - the thrust of which would be that each Prius would be checked for correct rear-wheel alignment and a shim kit put in, if required. I don't want any money; I just want Toyota to do the right thing - fix their frickin' cars.

...

Any thoughts?

dear god man. first of all, wake up. a class action lawsuit over a little alignment issue?

second, toyota does not make shim kits. shim kits are made by aftermarket manufacturers for various types of cars. apparently bob has found an aftermarket kit that fits the classis (and 2g?) prius. but afaik there are no all-in-one kits that specify they work on a prius. at least none that we could find at the time. that has nothing to do with toyota, that is the aftermarket business missing an opportunity, for which we just sit and wait.

for a while, we learned handmade shims were being approved on a case by case basis under the alignment warranty period after DH spent a lot of time on the phone with tech over how to set ours straight. since, apparently that has ceased or dealers are not willing to do it. we personally have gotten burned very badly by someone coming to us from this very site asking for a handmade rear shim job.

if i were in your shoes, i'd find an aftermarket shim that works and have the alignment shop install it. and then calm down and let the issue go. prius is not the only car with a rear beam axle, so you're going to have a hard time finding any sympathy.

[ksstathead]

Every tire pressure thread I've seen for the Prius say 2 psi more in front than rear due to weight up front. Did you reverse your pressures in the post before last?

[wolverine]

Originally Posted by galaxee

dear god man. first of all, wake up. a class action lawsuit over a little alignment issue?

What - no "Flame On!" sign??

second, toyota does not make shim kits. shim kits are made by aftermarket manufacturers for various types of cars. apparently bob has found an aftermarket kit that fits the classis (and 2g?) prius. but afaik there are no all-in-one kits that specify they work on a prius. at least none that we could find at the time. that has nothing to do with toyota, that is the aftermarket business missing an opportunity, for which we just sit and wait.

I know that Toyota doesn't make the kits.

for a while, we learned handmade shims were being approved on a case by case basis under the alignment warranty period after DH spent a lot of time on the phone with tech over how to set ours straight. since, apparently that has ceased or dealers are not willing to do it. we personally have gotten burned very badly by someone coming to us from this very site asking for a handmade rear shim job.

if i were in your shoes, i'd find an aftermarket shim that works and have the alignment shop install it. and then calm down and let the issue go. prius is not the only car with a rear beam axle, so you're going to have a hard time finding any sympathy.

My shoes, thank you, per my previous post, already took my Prius to Southwest Alignment, here in Houston, who's been doing alignments for 30 years. He figured out the problem, post haste, and put in a shim. No muss, no fuss.

Why try to persuade Toyota to issue a formal kit and fix instructions? It's called a WARRANTY. If you have a shim put in, and if something goes wrong, and if Toyota can prove that it caused, or helped to cause, the problem, then you have no recourse.

Apparently, you have no experience with these legal-type things, so leave it to the ones that can handle it.

I had this same type of issue with my Saturn LW-200, and when I (or someone else) was done with them, they issued a recall and drilled out ALL of the rear-ends for people who brought their cars in, and installed a kit to make toe and camber adjustable. It also cost me Zero for lawyers, since I didn't have to use one; I just suggested that they talk to THEIR lawyers and give them my write-up on the issue, explaining their liability. I was not the only one pestering Saturn about this, so I don't know if I can take any credit, really.

Why is it important, beyond the risk that people with misaligned back-ends are at? Because it's the right thing for Toyota to do. Perhaps you're not a believer in corporate responsibility, but I am. And next time, before you think you might belittle someone, you might size them up a bit better and not bite off more than you can chew.