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      01-20-2016, 10:33 AM   #1
intoflatlines
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Tire size vs. camber vs. handling/balance dilemma

I have a Z4M Roadster. Stock suspension. Camber washers in front for -2.7*. Rear at -2.0*. Tires are BFG Rival 245/40 front, 275/35 rear.

Since I set up the car that way, it seems to be pretty balanced in terms of autocross handling and bit tail happy on track. Even though the fronts are narrower than the rears, I think the additional negative camber evens it out.

My tires are dead so I'm looking to replace them. I've been looking into square setups since I will be able to rotate them more easily. But since I am limited in terms of front clearance, that means I'd have to try out 255 or hopefully 265 square. To do that, I'd need to pull out my front 5mm spacers which are necessary because the camber washers plus the 245/40/18x9 ET42 pushes the top of the tire too close to the strut. So I'd pull the camber washers and get camber plates instead.

Wouldn't a square setup with more front camber make the car way more tail happy on track? Not really a big deal at autocross but my skill level for track makes me weary of having more oversteer.

Or should I do a square setup and also increase negative camber in the rear using something like this? http://www.bavauto.com/fland.asp?par...FRApaQodYewCQg
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      01-21-2016, 10:37 PM   #2
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I dunno man, sounds like you have the car set up well for what you do. Neutral on AX and slight propensity to be tail happy is exactly what we all wish our cars would do.

To give that up just so you can rotate tires seems like such a waste.

Take an infrared thermometer to your front tires and see what your temp range is after a hot run, and see what the temp differential is between the inside, middle, outside is. If you're not overheating the tires I would leave well enough alone.

Just my opinion.
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      01-22-2016, 03:14 AM   #3
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I'm going to agree with The Hack (yeah, I know, big surprise right). Sounds like the car is well dialed, why not keep it as is? I think it's better with a staggered setup. Here's why.

I've run in two Z4Ms same day same track. One with a 235/265 set up, -2.7 front -2.0 rear stock suspension and camber washers; the other 265 square and a corner balanced TCK coils and camber plates and -3F and -2R IIRC. Same tires on both cars, much better driver (as in competitive track experience) in the square configure car compared to semi-noob guy here (at the time). We both took turns in the other's passenger seats.

The square set up was much less balanced, very prone to "ultra quick rotation" (lots of quick correction inputs and fighting continuously required) and generally a handful to drive and an unhappy driver. We ended up disconnecting the rear sway to try and dial it a bit and keep the rear planted, but it still proved to be quite scorpion like even with that change.

The stock setup didn't require the same saves and fast hands and it was easy to exit corners quickly and put down power comparatively easily without drama. Add in the driving instruction I got that day and I was all smiles dancing the car around the track. The real kicker was that our times weren't too far different, a couple seconds, which was totally off kilter to the skill level variance. That should not have been but the square set-up as configured was a huge handicap that day for a really good driver.

Wish I'd let the other Zed owner drive mine--wasn't thinking--missed chance there for a direct comparison. But based on what I saw that day no way I'd run a square set-up at this point.

I bet with time and effort one could get the square set-up to work pretty well--but if it ain't broke, well, you know.
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      01-22-2016, 01:08 PM   #4
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Thanks for the input. I love this forum!
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      01-25-2016, 01:40 PM   #5
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Quote:
Originally Posted by intoflatlines View Post
Thanks for the input. I love this forum!
The Z4M in general has no problem rotating with throttle , and I find that it does better on track with some stagger. I have found my -3.4 front / -2.4 rear, with 265/285 to be optimal for my car with MCS coilovers. It is def faster than with a 265 square but i do have added power. With my 750 front 900 pound spring setup rear, fast hands are not optional though lol.
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      01-25-2016, 09:11 PM   #6
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Keep your staggered set up and side swap the tires periodically. It costs a bit more since you have to get the tires demounted, remounted and balanced, but you'll get about the same wear as if you had a square set that you rotated.
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