This product entry is for a complete set of Vorshlag built RTAB limiters for a BMW E36 or E46 chassis - this is enough to reinforce both rear trailing arm bushing locations on these cars. The purpose of these limiters is to minimize toe change during excessive movement of the rear suspension trailing arms. These bushings will not affect ride comfort and allow the stock bushing to perform its regular duties while allowing toe control under the extreme conditions of autocross or track duty. We use these on our shop's V8 powered BMW E36, with 315mm R compound tires on 11" rear wheels, and they work great - so they should work well for just about any BMW out there.
In the Rear Trailing Arm Bushing (RTAB) location on the rear suspension of an E36 or E46 BMW the bushing has to pivot on two axis. Unlike other suspension bushing locations that only have one axis of rotation, swapping in excessively stiff replacement bushings using materials such as Polyurethane can and will cause suspension bind. The stock rubber M3 bushing is fairly compliant and effective when brand new but wears quickly over time, and doesn't cope with the added forces from race tires in perfect condition. Added wear adds excessive toe change under suspension movement, acceleration and braking. It is compounded greatly with additional power and grip from racing compound tires. If your stock RTABs have more than 20K miles and/or you've used the car for more than a season of racing, they are likely shot.
We use Vorshlag RTAB Limiters on all of our street and race E36 and E46 cars, even on 500 whp versions
We've seen some significant toe change on some cars with stock (and/or worn) RTABs - usually evidenced by toe induced tire rub where there shouldn't have been any. These Limiters do work - they limit the deflection of the rubber mounts but they do not add additional noise or bind, and will extend the life of a rubber RTAB bushing considerably.
Many racers just blindly install polyurethane into this and all bushing locations as a "fix" for a worn OEM rubber RTAB bushing. Polyurethane is a bad choice for a bushing material if it has to deflect - such as in a multi-axis suspension bushing location like the RTAB. Rubber bushings + limiters or a complete replacement with a custom steel spherical bearing are the only two textbook choices for this location. We cannot count the number of times we have seen RTAB or front LCA failures on BMWs that were using poly in these areas - an expensive repair and dangerous racing situation. At the very least poly will add bind during significant suspension movement, and this can make the handling feel odd (unexplained oversteer) as well as add significant stress to the suspension-to-chassis mounts (which is how they can fail over time).
That said, some folks with fully track prepared race BMWs have had OK results with polyurethane RTABs. This is due to the much higher spring rates and smoothness of tracks they tend to run with - higher spring rates and smooth tracks limit suspension travel, and thus limits the potential for bind from a polyurethane bushing at this bushing location. So even though you may hear good results from one racer, it doesn't necessarily mean that poly RTABs are the right choice for you. If you have a street car or dual purpose BMW you should always stick with OEM bushings and RTAB limiters, and even many race prepped BMWs use this setup with excellent results.
We recommend using the latest version of the BMW M3 replacement bushing (sold separately and available from Vorshlag) for all E36 and E46 chassis BMWs + a set of aftermarket RTAB Limiters. We have been making our RTABs since 2003 and machine our products from a very unique (and expensive) material, Ultra High Molecular Weight polyethylene (UHMW or UHMWPE) , which is the best material for this application due to its strength, corrosion resistance, self lubrication, and high wear properties.
Detailed specifications on the UHMW material:
- Extremely long molecular chains, with a molecular weight numbering in the millions, usually between 2 and 6 million.
- The longer chain serves to transfer load more effectively to the polymer backbone by strengthening intermolecular interactions. This results in a very tough material, with the highest impact strength of any thermoplastic made.
- It is highly resistant to corrosive chemicals.
- It has extremely low moisture absorption, has a very low coefficient of friction, is self-lubricating, and is highly resistant to abrasion (15 times more resistant to abrasion than carbon steel). Its coefficient of friction is significantly lower than that of Nylon, and is comparable to that of Teflon, but UHMWPE has better abrasion resistance than Teflon.
These are a "set and forget" item - install with a new set of factory RTAB bushings and they should be good for many tens of thousands of trouble free street and track miles. Instructions for RTAB Limiter installation are found on our Instructions page.
Shipping weight is 1.0 pound.
If you are replacing everything you can bundle a set of Vorshlag RTAB Limiters with a pair of OEM replacement E36 or Z4M RTAB replacement bushings and save! This bushing is described in detail in this product entry. This is how a vast majority of our RTAB limiters are sold - bundled with new E36 or Z4M bushings.
Click to enlarge. E36 RTA bushings shown above, Z4 M RTA bushings shown below.
