ABS+Traction Control Lights
 

So first, I've done some searching and can't find a definite answer so...

Background: I had some work done last week (Stillen CAI & Exhaust +tune, new wheels/tires). I pickup the car today and it all sounds & looks great. HOWEVER, the ABS light & traction control lights are popping up on the dash. the shop (JTRAN) acknowledged this and said it was due to the size difference in tires. They also indicated that the car should 'learn' the new sizes and adapt, thus making the lights go away. After reading on here, it seems like there is a risk of damaged speed sensors as well. I'm going to examine the speed sensors tomorrow.

Wheels/tires:
255/35/20
295/35/20

Does anyone have an answer/solution if it is the difference in wheel/tire diameter? Any help/advice would be appreciated!

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Yeah, as I said, I found those posts. The main question is in order to get rid of the christmas tree of lights, do I need to get new tires that are in closer in size or will the ECU adapt & learn the size difference?
Also, the lights are obviously an indicator, but is there much of a risk running as-is? I'm assuming that my ABS will still work properly

ABS+Traction Control Lights
 

I'm not sure what issues running like that will cause, but the ecu doesn't adapt to tires being the wrong size. I'd swap out either the fronts or rears to a size closer in height to the other axle.

It would be pretty easy to make sure abs is still working. Go try to lock up the brakes.

The posts I quoted answer the only question you initially asked. It is the difference in tire size.

The answers to you other questions (which were not asked in the OP) is in Chuck's post above.

If the ABS indicator is on, you do *not* have ABS.

Check the ABS sensors at the differential, cables are near the exhaust install It is not the tire size.

So after some digging into the issue today, the speed sensors seem fine. The lights only seem to come on initially when getting over ~40. Once they're on, they remain on the entire time until I restart the car and get back up to that speed. While the ABS light is on, the ABS still functions 100% as normal, so I don't think it's the ABS cable. You can feel the pulse when braking hard.

So I think its narrowed down to the difference in wheel size. I don't think there is anyway to make the ECU adapt or flash a new program. Think I'll be making the rear a bit smaller to get into that 3% sweet spot.

Right now I'm at 4.1% difference
255/35/20
295/35/20

dropping down to a 285/35/20 makes it 3.1%. and then 275/35/20 makes it 2%.

What make tire you running? Just checking on Tirerack for PPS sizes.
What you have now is;
255/35-20= 27"
295/35-20= 28.1"

You need to go to a 295/30-20 in the rear which is 27" in height. Or go to a 275/35-20 in the front which is 27.6. Going to a 285/35-20 will not help much. It's 27.9"

Rule of thumb ~3% difference, no more, or live with Christmas tree.

any chance it could also be the rim offset? the shop said they used the same tires on another Z without issue...

I don't think so.

Why are they even arguing with you. You are the customer, if you want a different tire, it is your right.