Sam Strano

iTrader: (41)

The Article below is part of what makes Strano Performance Parts different than most. I often have to remind people that selling you parts isn't the hard part of my job, but offering GOOD advice, based on something more than what someone "heard on the internet". There are more to springs than the spring rate. There is more to Master Cylinder brace design than bending a piece of metal. There is more to sway bar sizing/use than having sway bars to sell. This applies to everything, from brake parts to steering wheels.
Feel free to share this, but please give credit.
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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.

sjsingle1

iTrader: (1)

and here I thought the bump stops were only to keep stuff from hitting other stuff at full compression....good interesting stuff

Sam Strano

iTrader: (41)

Absolutely not. In fact for years I've been trying to tell people that that's not their job. Certainly not their only job. If that were the case then we wouldn't touch them on the regular. And as much as some people think that's not true all you have to do is look at your axle on almost any of these cars and you'll see a nice little shiny clean spot where the rest of the axle has surface rust on it. That's because we are in regular contact with these.

I actually prefer to use the term bump rubber, more than bump stop. Because the former seems to click in people's heads more that this is actually a tool for changing and adding wheel rate, and even doing it with different profiles.

wannafbody

iTrader: (2)

Bumpstops act as a secondary spring under compression.

The rubber ones you tested, are they fbody specific or generic?

pdxmotorhead

Look at bumpstop tech in desert trucks,, king of the hammers etc,, the tech there is amazing.. just for a bumpstop! Crazy stuff when you want to hit 140 on a dirt road...

Sam Strano

iTrader: (41)

There are no specific rubber stops for the car. The polyurethane and rubber are generally close but not exactly the same. They are shorter with a bigger increase in stiffness when you first touch them.

OEM or OEM direct replacements, and I have both, are the only 100% direct fit stops there are.