RTAB Shims...why?

Ryan13 · 01-26-2016, 11:31 AM

I could ask the race shop, and I'm positive they would give me an answer, but I wanted to check with the experts. The RTAB are OEM and they look perfect. The shop wants to insert some shims. Does anyone know why and what they would change/accomplish?

Finnegan · 01-26-2016, 01:04 PM

The shims are to reduce play around the bushings. That play causes changes in rear toe, which negatively affects handling. The bushings are going to help lock in those toe settings and prevent dynamic changes.

Note: Many of us have found that setting rear alignment with more toe-in (higher end of stock) improves the ability to put down power mid corner and on exit. It's at the cost of some tire wear, but worth it IMO.

I hope that helps!

It's a good low cost mod.

http://www.turnermotorsport.com/p-96...-shim-kit.aspx

Ryan13 · 01-26-2016, 07:58 PM

Makes sense...understand now. I also added H&R coil overs, which got -1.5 camber left and right for the front, and -1.8 left and right in the rear. Toe came out to 0.04 in front and 0.22 in the rear (these are left and right measurements as well).

Sounds like the shims attempt to keep those measurements consistent as the car gets loaded side to side. Thanks for the info.

Finnegan · 01-28-2016, 03:04 PM

Quote:

Originally Posted by Ryan13

Makes sense...understand now. I also added H&R coil overs, which got -1.5 camber left and right for the front, and -1.8 left and right in the rear. Toe came out to 0.04 in front and 0.22 in the rear (these are left and right measurements as well).

Sounds like the shims attempt to keep those measurements consistent as the car gets loaded side to side. Thanks for the info.

^Exactly.

You might find shimming the front a cheap way to get more negative camber up front. If you're a track rat -2.5 to -2.7 front is going to prolong tire life. Of course it changes the handling characteristics, less understeer, etc. Turner has these for about 20 dollars.

http://www.zpost.com/forums/showthread.php?t=679303

pokeybritches · 01-29-2016, 09:21 AM

OP: Was this at RRT?

Ryan13 · 01-29-2016, 10:45 PM

Yes...RRT. They did a great job on the car setting it up for me...very happy with the work. Just wasn't absolutely sure what the shims would accomplish. Also had a lot of maintenance work performed just to get a solid starting point. Car is ready for spring and Summit Point.

Just need to figure out tires now. I thought about getting some Apex wheels, but I went with two sets of stock. That may sound like a bad decision, but my logic was I'm not sure I'll ever be a good enough track driver to feel the difference in a few pounds of unsprung weight and since I have two Zs that I plan to keep, if I ever damage a wheel, I've got replacements. Can always add a set in the future if something changes...probably break even on selling the wheels if needed.

I've read a couple of posts about using 4 fronts or 4 rears...obviously some trade-offs each way. 4 rears with a front spacer may work, but since I added the H&R coil overs, not positive that will work without some rub and the need for a lot more camber than -1.5. I can experiment.

Probably just stay staggered with 235 and 265.

Notice you are local. Maybe we can grab a beer one afternoon?

01-26-2016, 11:31 AM	#1
Ryan13 Private First Class 73 Rep 128 Posts Drives: Z4MC, Z4MR, M3, E36, M2, 535 Join Date: Jul 2014 Location: Leesburg, VA iTrader: (0)	RTAB Shims...why? I could ask the race shop, and I'm positive they would give me an answer, but I wanted to check with the experts. The RTAB are OEM and they look perfect. The shop wants to insert some shims. Does anyone know why and what they would change/accomplish?
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01-26-2016, 01:04 PM	#2
Finnegan Dog Listener 701 Rep 7,850 Posts Drives: Z4M/. Z3M, E36/46 M3 Join Date: Oct 2008 Location: Teaching the dog to slalom iTrader: (22)	The shims are to reduce play around the bushings. That play causes changes in rear toe, which negatively affects handling. The bushings are going to help lock in those toe settings and prevent dynamic changes. Note: Many of us have found that setting rear alignment with more toe-in (higher end of stock) improves the ability to put down power mid corner and on exit. It's at the cost of some tire wear, but worth it IMO. I hope that helps! It's a good low cost mod. http://www.turnermotorsport.com/p-96...-shim-kit.aspx
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01-26-2016, 07:58 PM	#3
Ryan13 Private First Class 73 Rep 128 Posts Drives: Z4MC, Z4MR, M3, E36, M2, 535 Join Date: Jul 2014 Location: Leesburg, VA iTrader: (0)	Makes sense...understand now. I also added H&R coil overs, which got -1.5 camber left and right for the front, and -1.8 left and right in the rear. Toe came out to 0.04 in front and 0.22 in the rear (these are left and right measurements as well). Sounds like the shims attempt to keep those measurements consistent as the car gets loaded side to side. Thanks for the info.
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01-29-2016, 09:21 AM	#5
pokeybritches Colonel 479 Rep 2,782 Posts Drives: ESS/G-Power Z4M, VF Z4, 996tt Join Date: Sep 2009 Location: Los Angeles iTrader: (12) Garage List 2006 BMW Z4M [10.00] 2006 BMW Z4M [8.50] 2003 BMW Z4 3.0i [9.00]	OP: Was this at RRT? __________________ VF Engineering Z4 3.0i, ESS Z4M, G-Power Z4M, 996 Turbo
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01-29-2016, 10:45 PM	#6
Ryan13 Private First Class 73 Rep 128 Posts Drives: Z4MC, Z4MR, M3, E36, M2, 535 Join Date: Jul 2014 Location: Leesburg, VA iTrader: (0)	Yes...RRT. They did a great job on the car setting it up for me...very happy with the work. Just wasn't absolutely sure what the shims would accomplish. Also had a lot of maintenance work performed just to get a solid starting point. Car is ready for spring and Summit Point. Just need to figure out tires now. I thought about getting some Apex wheels, but I went with two sets of stock. That may sound like a bad decision, but my logic was I'm not sure I'll ever be a good enough track driver to feel the difference in a few pounds of unsprung weight and since I have two Zs that I plan to keep, if I ever damage a wheel, I've got replacements. Can always add a set in the future if something changes...probably break even on selling the wheels if needed. I've read a couple of posts about using 4 fronts or 4 rears...obviously some trade-offs each way. 4 rears with a front spacer may work, but since I added the H&R coil overs, not positive that will work without some rub and the need for a lot more camber than -1.5. I can experiment. Probably just stay staggered with 235 and 265. Notice you are local. Maybe we can grab a beer one afternoon?
	Appreciate 0 Quote