Best Alignment for Spirited Driving on 18" Wheels
 

Hi - Any recommendations for alignment specs for an S that is mainly used for spirited driving and back road carving? Not sure if the UK alignment spec can be used on 18" wheels?

My wheel/tire set up is F: 18x8.5 +42; 215/40 and 18x9.5 +42; 245/35

Open to suggestions and experiences from others on a similar set up. Also interested in ride height suggestions and whether any positive rake should be set. Definitely not interested in setting the ride height for looks; main priority is performance and obviously not rubbing lol.

Thanks in advance!

Wheel size doesn't matter regarding alignment choices.
Regarding ride height, I think it's best to go for the lowest possible where you aren't rubbing, for the sake of having the lowest center of gravity. But you might want roll center adjusters if that is very low.

What suspension / springs? Not relevant for alignment but would impact how low you could safely go.

Regarding alignment for street driving, deviating much from stock doesn't gain you much....UK alignment will be fine. Don't over think it.

Thank you both! I'm on Ohlins DFV R/T. Fenders are rolled already and my current alignment spec is:

Front:
Caster: 6.6 deg
Camber: -1 deg
Toe: 0 deg ; Total Toe: 0 deg

Rear:
Camber: -2.7 deg
Toe: 0.1 deg ; Total Toe: 0.2 deg

Compared to the UK spec, it looks like I need more toe and less camber in the rear, and less caster in the front? I hear more caster is good for cornering but am I gaining any benefit over 6.0 deg? Similar question for rear camber.. A lot of noob questions, I know...

On my current set up, turn-in feels sharp but heavy. I'm thinking I need more front camber than recommended by the UK alignment spec. Any other changes to the UK alignment that people have found helpful?

Thanks.

More front camber. Most people max out the adjusters, shoot for at least -2. By lowering the front more you get more negative camber. I would not go too aggressive or you might hurt braking with only 215 up front (depends on tires and how hard you are carving these backroads :hello:)

The rear camber does seem too high. I would shoot for -2. You didn't mention the car's year, if it's the AP1 geometry maybe a little more toe in (0.2 toe in per side). If AP2 geometry that number is ok.

UK spec rear toe is absurdly high, -1 camber front and -2 rear is fine and all, but for better handling more front camber is better. I would forget "UK spec"...

0.2 degrees total rear toe is fine for AP1 or AP2. Honestly I wouldn't run more than that on either. Big rear toe was/has been overprescribed to "cure" AP1 handling weirdness but in my experience it's way WORSE with a lot of rear toe-in. I ran 0.1 degrees to 0.2 degrees total rear toe on my AP1 on road and track and it handled much more linearly and predictably vs. "UK spec" of 0.64 degrees. And tire life benefited GREATLY.

Agree with Zdan here on the rear toe and generally for the street I also tend to agree that -1 front and -2 in the rear is a sound and effective camber alignment. Running too much more then -1.5 up front you start sacrificing some grip in most situation because the tires never get up to full temp, and breaking effectiveness is also reduced. Significant inside tire wear as well. Caster is a preference, but oem range 5.5-6.5 is generally where you will find is best for good feedback and stability at speed. More caster you have, the more the car wants to point strait and self correct.

With the rear toe, as you increase your rear spring rate you need less static toe to 'minimize' the AP1 trait. I agree the UK spec on toe is definitely overkill here, but I don't think overkill for factory suspension (Zdan curious to know whether your car was factory or modified suspension with the UK spec).The Ohlins kit has an 8k (possibly 7k based on recent changes) rear spring which still allows decent travel. I have this kit and with 0.2* toe in the car still likes to oversteer if you lift, turn, and brake hard enough, on both 225 square and 255 square. Even with his staggered setup, I imagine he will not want this trait for a street car. A factory aligned AP1 with an unaware driver will get nasty tank slappers, even with the increased stagger of AP2 wheels and tires.

I have -2 and 0.2* toe in the rear, and my tires wear quite evenly across the face and life seems good. Camber doesn't hurt wear much long as your toe is within reason, especially when the car is driven spirited often. Of course, this is my experience/results and no two cars and drivers respond exactly the same.

I disagree! 40 arc-minutes or 0.67 degrees is EXTREME and excessive for *any* setup including stock.

I ran my car totally stock in a showroom stock time trial class for several years (won class 3 times) and the first thing I learned was that everyone prescribing this amount of toe-in could not be more wrong... I tried it my first event with the stock '01 at Watkins Glen, and handling was every bit as weird, nonlinear, spooky as its reputation suggested. 2nd event at Mosport (sharing the car) handling got weirder and weirder, and more oversteer on day two. After TT before heading back for home I noticed the rears were both corded! Prior to next event I knew I had to do something to preserve rear tire life, so instead of "UK" rear toe (or max US AP1 toe), I asked for MIN spec US rear toe-in or about 0.3 degrees *total*, 0.15 degrees per side. When I picked up the car before heading to next event, I found that instead of 0.15 deg per side, they had given me 0.15 degrees *total* rear toe-in. Given AP1 handling weirdness I had experienced, I was a bit worried that the car would be an undriveable oversteery mess. Quite the contrary! The car behaved more linearly, turned in better but generally MORE stable and driveable. Sweet! And the rear tires lasted more than twice as long as well! Major positive improvements all around :)

I have a couple more anecdotal experiences I could share including unintended blind tests that reinforced my conclusion that a lot of rear toe-in SUCKS, REAL BAD, for EVERYTHING. Yes, even on a totally stock factory suspension.

Run minimal rear toe!

I also think the "UK spec" rear toe is based on an *ERROR*. They mistakenly got the rear toe spec as 2x the US spec, giving a MINIMUM of 0.67degrees and a MAX of 1.33 degrees(!!!)! THEN they no doubt had to "recommend" the minimum end of that *erroneous* range as customers *surely* complained about handling weirdness and incredibly short tire life with as much as 1.33(!!!) degrees rear toe.

IMO even the US spec range for the AP1 (~0.32 to ~0.64 degrees *total*) is excessive, and based on the (IMO) wrong idea that "more rear toe-in => more stable". I would run 0.15 degrees total. I wouldn't recommend more than about 0.2 degrees total.