Purposely mis-aligned and mis-matching tires

A couple weeks ago another driver decided to merge into my lane and hit me in the process. When I got my car back from the repair center they told me two things that seemed fishy. The first thing I noticed was the replacement tire they gave me was a different model, but the same size, as the other three tires. They claimed that a matching tire was not available since my car is new, and that the replacement tire will drive identically. This does not make sense to me because the tread pattern is different. What can/should I do?

Secondly, the paperwork they gave me about the alignment calls for a castor of 5.1 to 6.6 on my left (driver’s side) front tire. It is also important to note that this is the primary area that was damaged in the collision. The measurement after my crash was 4.9 and the measurement after my crash was 4.9. When I asked the repair center about the discrepancy they told me a) that the castor on my 2011 Prius III is non-adjustable, and b) that the auto manufacturers will set the castor out of spec because of the camber found on the roads to drain rain. Furthermore they said that this amout of castor will not affect tire wear. The idea that the vehicle would be setup outside of spec to correct for the camber of the road seems bogus. Especially because I believe that divided freeways have a similar camber as a non-divided highway. What do you think? Are they trying to sell me halogen fluid for my headlights?

Yep, specs are specs, Toyota doesn’t set them up out of spec. That said, 4.9 vs. 5.1 is a very small difference. But I think they’re right about caster not being adjustable, fwd cars are typically camber and toe adjustable, but not caster (‘castor’ is the oil).

I think you’re dealing with a shaky shop. As to them not being able to match a tire you should take that statement with a grain of salt until proven otherwise. Do a net search (tirerack.com is one) and determine if they’re lying or not.

Tires with different compounds and tread patterns may handle differently and at the very minimum I’d want the oddball on the rear of the car.

They’re correct about this amount of caster not causing tire wear but what they didn’t say is that caster also affects the handling.
If the caster is knocked out of whack, even by a slight amount, then something is likely bent. (control arm, strut, strut tower, subframe, or even the steering knuckle.)
They’re also BSing you about the car makers purposely setting them out of spec although there is a bit of truth about having the RF camber and caster a bit different than the LF to account for the road crown.

The matching tire should have been available through the dealer. You can call the dealer to confirm this.

While 4.9 vs 5.1 isn’t much, it is out of spec. The caster is not adjustable by a mechanic or front end man, but it can be adjusted by a frame shop. Obviously your frame was bent and either the shop did nor get it straightened or straightened enough.

As for the road drainage, there is some truth to that, but I think its the camber that is slightly different from one side to the other, not the caster.

Thank you for your responses.

Texases, thanks for the spelling correction. I was definitely thinking caster while writing castor.

ok4450, Your answer that something is probably bent is what makes the most sense to me. The crash was relatively low energy, so I don’t think that the frame is bent like keith suggested… At least I hope not! That would be rotten.

That is interesting that there is some truth to setting one tire differently due to the crown or camber of the road. Wouldn’t doing this be counter productive if the road is banked like on a turn, or when you’re driving in the left lane of a divided highway?

ok4450, I found the ep20’s online. So they are available. The ep422’s are a longer wearing tire, but it seems to me that it is preferable to have matching tires…

To answer your question about this being counter productive I would add that any differences between left and right are very subtle. This would counter any pull but would not be noticeable on a completely flat road or during a turn.

When it comes to camber a car will pull in the direction of the most positive camber and in regards to caster it will pull in the direction of the least force. This is why a good alignment tech will adjust camber and caster to compensate for road crown; generally with more negative camber and/or positive caster on the right front.

Consider this example and assume the camber spec is 30’ positive +/- 30’. This means the top of the tire is tilted out 1/2 a degree at 30’ positive. If the car were aligned to this spec on the left front and the right front was adjusted to 15’ (1/4 degree) or at dead zero this would compensate for any pull to the right and would never be noticeable while driving nor would it create a tire wear problem. The vehicle would still be within the given specifications.
Hope that helps.

“Tires with different compounds and tread patterns may handle differently and at the very minimum I’d want the oddball on the rear of the car.”

Note: OK is, IMO, correct. This situation is different than the best tires on the …. " issue.

To OK4450’s post, I would add that even multilane highways have a slant across the lanes to drain water off.

If your car drives as you like it, then there should be no problem with mismatched tires and caster setting slightly out of spec. Caster error has little or no effect on tire wear, camber a little and toe, a lot. The caster error can be corrected in one or more of three possible ways: 1: Body pull which is expensive. 2. Adjustable Caster/camber plate. 3. Elongate the strut mounting holes at the top of the shock towers which may or may not be possible with your particular car. Some might think this as being a desperate move but it worked for me with large flat washers to cover the slightly elongated holes. I did this at home but a pro might be reluctant to do it for whatever reason he feels is appropriate.

Unequal caster will result in steering pull. It is possible that you might want a little of that as was mentioned to compensate for a crowned road but I, for one, have not done that for my cars and don’t feel a need for it.

Mismatched tires are a fact of life in the auto world. If you would like, make sure that the replacement tire has the same traction rating as your other tires. I have been mixing tires for many years with no apparent traction problem and certainly no handling problem or even a detectable change in handling. If a Prius is a special situation regarding tires, then I plead ignorance.