The best answer here are the new OEM, or OEM style replacements... no spacer needed and they just fit. They are in stock too. Rubber stops (also in stock) are still cheaper and because of that many still go that way. But urethane is the least good, let alone with a spacer. They are way too stiff, and their size teamed with a spacer means you get on them even sooner than any stock or stock type setup.

 

I respectfully disagree with this analogy, I don’t need my rear axle riding up upon aggressive acceleration, I want it being pushed down for traction purposes. I have experienced no adverse reaction to the urethane stops with the SLP spacers. My vehicle is stock height.

 

Ok. I mean I made a jig with a load cell and all and tested all this. Without spacers the urethane stops are significantly taller than the OEM SS/WS6 stops, about the same as the normal Z28/V6 type stops in height. No GM or SLP stop that height ever had a spacer in conjunction. So you are stacking a significantly stiffer stop, with a spacer too. You might like that fine, that's ok. I'm not sure what you would have to have happen to be considered "adverse" reaction. To be honest I've heard that so many times from folks about so many things it means little to me these days. I certainly don't like the urethane stops even with out the spacers. The urethane stops at .4" of travel are 650 pounds. An OEM/OEM replica stop isn't that stiff until over 1.2" of travel. Now, add the spacer in, where you contact the stop that much sooner, you get a BIG spike in wheel rate and get it almost instantly. Maybe you want that, I don't know, it just isn't how the system was designed.

Below is the article I wrote and put on my website, along with the graph comparing the various stops, without spacers, using the body as the mounting point with nothing taking up room in between.

1982-2002 F-body rear Bump Stop test:

My friend and longtime customer, Phil Knowles helped me in quantifying the actual rate of various bump stops for the 1982-2002 F-body. Phil is a test engineer, doing this like this all day, The 3 most common setups were used. The squarer Camaro SS/WS6 stops with aluminum spacers were not tested because they are no longer available, and there is no aftermarket equivalent. Aftermarket OEM replacement stops were not tested as they are replica5 copies of the OEM non SS/WS6 part
Force verses compression was measured for three bump stops that fit both the 3rd and 4th Gan F-body. Polyurethane, Rubber, and OEM GM Polyurethan Foam. These will be referred to as Red, Black Rubber, and Foam, respectfully.

For force measurements, a Valve Spring tester was used in conjunction with a vice, using pieces of steel plate to apply even force evenly across the bump stops. To precisely measure the compression distance for the stops, the vice handle was rotated in ¼, ½, and 1 full turn increments on the vice handle. Each full turn of the vice is .160” as measured with calipers, all raw data was converted from vice turns to inches.
All bump stops were rested on a table with the backs against the flat surface, using a tape measure to compare uncompressed heights, results were 1-15/16” for both the Red, Black Rubber, 2-5/8” for Foam. Each stop was placed in the vice with a small amount of force, so they wouldn’t fall out. To find the initial compression height, it was assumed the initial compression would be linear and linearly extrapolated from the first two measurement to find that height, then account for it. It should be noted that only the OEM Foam and certain aftermarket parts have a stepped and direct fit mount.
Results show the Foam soft and progressive, while the Red is very stiff and nearly linear. The Black Rubber stop was linear and slightly softer than the red Energy suspension stop.

What else do these results show? Mainly that those who believe bump stops do nothing and remove them, are very wrong. The softest of these adds 100 pounds of wheel rate at only 1/2” of compression, and almost 700 pounds of force at approximately 1-1/4” inches of compression.

Where bump stops are used, they combine with spring rate which act together to give you much of your wheel rate in ride. Wheel rate in roll includes sway bars. And there are some other details that can change the rate in minor ways, bushing or suspension bind would be examples of this. All these details need to be considered when designing spring rates, ride heights, even shock damping forces since bump stops can add wheel rate in ways springs cannot easily, and do not return energy in the same way as a compressed, higher-rate spring setup. Wheel rates are a thing on both ends of the car. It is common to read some think their higher rate springs used without bump stops result in something “stiffer” compared to a softer spring and properly chosen bump stops. For example, a 550 lb/in spring on a setup that uses bump stops results in wheel rates than another setup that uses the same spring rate, without bump stops present can offer, additional to that bump stops can be used to tune how and when that wheel rate is used, and that is a critical part of making a car ride and handle properly.

 

Thank you so much for the detailed information a lot of which has gone over my head. The bump stop and spacers sit 2 1/2 to 3 inches away from the rear axle, what should I expect to feel or hear if going over a bump or a depression and the axle hits the stops? I have a lot of aftermarket BMR suspension components on my vehicle and it is very stiff riding in the first place, The term would be like riding on rails. Thanks in advance

 

Well, I guess Mr. Strano does not have an answer that he can put into common language (that a dope like me can understand), however I thank you for your time sir.

 

Mr Strano has lots of things to do SteveC. I'm sorry if you think my delay in answering is because you think I have no answer.

Look my man, on the daily, I hear some pretty weird things. You know what other things I have heard "work fine"? No front sway bar, 150k mile shocks. Cheap tires. No bumpstops at all, and the list goes on and on.

 

The bumpstop and spacers sit 2.5 to 3" from your axle? Your car must sit sky high for that to be the case.

I can't tell you what you think you should hear or feel, I'm not you. Hear? Nothing, it's not like a carnival game with a bell and when you hit the stops it goes ding. Feel, well the wheel rate is way higher, way faster than designed. That means it gets stiffer much quicker. I don't know maybe you like that. After all, like I said before I can't really account for all the things people think, assume, and feel. I have seen lots of folks who have garbage on their car, and it rides badly tell me it is ok because it handles well, or rides on rails. Subjective at best and totally up for interpretation. But here's the thing, those cars tend to be jittery and stiff and skip around. Things that happens less in say, BMW's and Porsches, and higher end Corvettes and things like that. Just that some people think stiffer is better.

Take it all for what you think it's worth. I'm answering this because others are reading it too. Seems like you are pretty set, and also pretty snarky about it when I didn't answer you as quickly as you think I should have. I don't see your bumpstop rate test anywhere. The stops you are using are much less progressive and made for a Jeep. Then they have the spacers added, totaling up to a much taller stack high than any setup GM used or developed. Anytime I use a triangular stop, Rubber, OE style or even what you have, I don't use it with a spacer which just cuts working travel away. If it works for you, ok. Others reading can decide what they think for themselves. Hell, they can measure the space from their stops (if in good shape) to the axle, and see if they have 3" of travel to start with.

 

thank you so much for the answer, I appreciate it very much.

 

Say Sam, what needs to be done to use your rubber stops? Spacers? Trimming?

 

Want to make sure I have this right after reading all of the latest replies. I have UMI stops that have not been installed yet and this would mean not using my SLP spacers correct?