Posted by Walt Barie on July 30, 1999 at 15:54:07:
In Reply to: Re: Rear Rear Stress Bar / Korman Autoworks / Top-End Performance posted by Gregory Szczyrbak on July 29, 1999 at 15:07:03:
Be very very careful about this stress bar if it is the same design as the E21 bars. As an avid E21er I also follow the E21digest. There have been reports on the E21 list about metal fatigue/cracking occurring where the Top End rear stress bars mounts to the side of the spring hats. Apparently these "hats" were never designed to take the concentrated side loading in the lateral direction and being concentrated at the mounting points of the stress bar.
If I recall this problem has only occurred on E21s that were tracked/autocrossed however if I recall correctly one person only had the bar for a few months before he saw cracks. I don't see what real good that a rear stress bar would be in the E12 or E21 case since unlike the front where the struts experience side loads there are not really any lateral cornering forces on the rear springs/shocks (can't be since there is a rubber mount at the top and rubber bushing at the trailing arm. The trailing arms and rear subframe take all of the side loading due to cornering. The spring perches just see an upward spring force of the weight of the car + weight transfer due to cornering.
Obviously some frame twisting is taking place but I don't think the spring hats which are not super thick steel are the place to concentrate the forces to try to reduce the twisting. To me the rear wheel wells are actually one of the stronger areas of the car since the panel behind the rear seat and the package shelf (assuming you haven't cut major holes out for things like speakers) reinforce the area pretty well.
In conclusion all I will say is think about the direction of forces involved for yourself and decide if a rear stress bar of this design is the right way to go.
Walt Barie
'80 528i
'82 320i DSP Solo II car
'79 320i (retired Solo II (150+ events) and drivers school car for 10years without a rear stress bar and without any cracking of the rear spring hats)
: Thanks Troy. I just contacted Kroman today about this exact thing. I noticed in the Roundel in the "new products" section, they covered the rear stress bar/battery relocation offerred by Top End. I contacted them to get a price. They quoted me $199.00. I figured I'd contact Korman to get their price since I heard they offerred something similar. Of course, now that I know who the supplier is, I can see that the Top End price is the better.
: I too, was curious about how it would attach to the shock towers. I figured it would work the same way that front bars work, but from pictures on Top End's web site, it looks like the 320i and other rear stress bars bolt into the side of the shock tower. I didn't understand why they did it this way. I'm not one for making uneccessary holes in my car. If possible, I'd like to see it bolts right to the top of the shock tower. That would be the way to go.