^^^^^^^
New tires tend to be slippery until the mold release agent wears off, usually a coupe hundred miles. Also, there are roads which have a high crown in the center of the roadway for drainage purposes, even a properly aligned car will tend to drift on these type of roads.

 

Why is there no caster reading? Front caster is a stability issue if not set properly. They didn't even measure caster. Take it to another shop that will do the whole job.

 

Thanks for all the inputs! They are extremely helpful!

I contacted the shop (very famous S2000 shop here in SoCAL), they asked me to check my wheel balance weights. Sure enough, I don't have any balance weight on the front passenger side wheel, I somehow lost all of them. Since my front tires are quite old, and I never really liked the RE760 tires, I will take the chance to replace them to match the new rear S-04's and get a balance at the same time. If new tires & balance don't fix the issue, another alignment or subframe check will be next.

Just a side note, I was taking a 70mph slight left turn to merge onto another freeway (by the way, even my Honda Fit could take this turn at 80mph on all seasons). I noticed a slight tire twist from the front passenger wheel, then it came with the familiar feeling of swinging left & right. It did feel like wheel balance issue to me, so will see how it goes after I get the front wheels balanced.

 

How can wheel balance relate to stability? Typical wheel balance issue is felt as vibes in steering wheel or chassis. I cant see how wheel balance could affect stability like you have been describing. That just doesnt make any sense.

Missing weights doesnt necessarily mean there is a balance issue. Sometimes a wheel/tire combo ends up being perfectly balanced, and doesnt need any weights.

Still, I think its a good idea to have wheels rebalanced, to make sure that wheel is ok. Not as part of efforts to address stability, but just because.

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I agree with Billman. At high speeds my car tramlined (wandered) with 0 toe. Adding a small amount of toe in the car feels noticeably more stable at high speed.

 

My car will do this only on roads with rain grooves the same direction as travel, and only when going straight. It goes away if I'm going around a corner or accelerating, but it is a bit unsettling until you get used to it. It's not a big enough problem for me to adjust my alignment specs.

 

Personally I've had the same tramlining issue on my car. I could feel it was more a rear-end tramlining than the front actually. It was/likely is possible to happen for a variety of reasons. I too originally thought it was alignment. the car didn't drive this way before, and didn't have any loose/moved adjusters. The problem has come/gone as i've changed tires over the summer this season. here's how it went:

- Tramlined bad out of storage in April. Was running michelin PSS in base AP2 sizes. Rears were worn to the cords. Changed out my tires for half-worn Yokohama S Drives in AP1 fitment. Tramlining completely went away
- Tramlining came back again after 1-2 months. Rear S-drives were worn now to ~ 1mm tread depth. Replaced rear tires only with half-worn General Exclaim UHP in AP1 fitment (much higher treadwear and softer sidewall tire i believe). Tramlining became worse.
- Drove on the street for ~20km on autocross tires (255 Rival S Square). Tramlining seemed to disappear (from the rear at least, front is now tramlining)

Meanwhile i made no alignment changes this season. So my issue appears to be very dependent on the quality of the tires and having them matched front/rear. Keep in mind this is only for my car, with a pretty standard STR autocross alignment. This may not be relevant to your car with factory settings

 

Hope you dont drive in the rain! :-O

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Agreed, balance has nothing to do with the problem based on the description.

 

Lol. I live in Nova Scotia, so it's always wet. I'm nursing myself off the S2000 as a DD for this reason. I can't afford to replace tires this often with this alignment!