Strut Bump Stops: Dangeriuosly important!

[chiuchimu]

Bumpstops are important on lowered car! Make sure you put them back on when assembling your strut.

I bought shocks and springs to lower my 2G a few years back. I noticed that one of my bump-stops was starting to deteriorate. They didn't sell replacements at Autozone so I just re-installed the old one. Recently, I started notice a lot of hard suspension action like those you get when bottoming out but on much smaller bumps. Then about 2 weeks later, the right upper control-arm ball joint broke free while driving. On replacing it, I took apart the strut and found the bumpstop gone. Since I still couldn't get a new replacement and I wasn't sure if the bumpstop made that much difference. So I took the left bumpstop out and installed it into the right strut. Sure enough, the hard hits occured on the left side this time and not the right. It feels like the shocks might have gone since every bump seems like the car is bottoming out.

Driving carefully, I was trying to find a replacement bumpstop, but just 9 days later, the left ball joint tears free of the upper control arm WHILE DRIVING ON THE FREEWAY! This time I went to a pick -a-parts and got a used control arm and used bumpstops.(I took off car and disassembled the strut at a junkyard just to get the bumpstop.)

I believed for lowered cars the bumpstop plays a crucial role in the suspension unlike on stock cars. I found out by searching the internet that lowered cars for the most part 'bottom out' many times a day. The bumpstop acts as a shock absorber rather than letting metal to metal clash.

Knowing this, I'm against even cutting the bumpstops since many are already rather short and the material is relatively soft for the task it serves.

Anyway, i wanted to make sure this info gets on the forum since not knowing the importance of a simple tiny thing could cause a major accident.

 

[bjones18]

Yes, rubber and micro-cellular urethane are great for increasing suspension/body durability.

We (suspension designers/guru's/modifiers) think of suspensions as means to achieve roll-centers/cambergain/roll-steer etc. In reality, the best "handling" suspension is on a shifter kart. (none)

Suspensions are primarily needed for ride quality and improved vehicle durability. It is not un-reasonable to see 7g's at your jounce bumper due to a pot hole. You can take your corner-weight x 7 to figure out that force. Also, you can use F=ma, E=1/2mv^2, F=kx, E=Fd to figure out that removing energy by compressing a jounce bumper over a long distance ~50+mm lowers the force into the body TREMENDOUSLY compared to a "hard-stop" which uses "body sheet metal's" elasticity & metallic-plasticity as the "distance" in E=Fd. (E is from your speed and the pothole - given - NOW you can use "F "and "d" to achieve E. Soooo....

a. d=~2mm (no jounce bumper) F=HUGE
b. d=~50mm (jounce bumper) F= twenty five times smaller than a - 50/2)

If you are interested in vehicle durability, look at four things:

1. Baja truck wheel travel & length of dampers/springs.
2. Baja truck tire section height - rim to road.
3. Pound on your shock tower with a sledge hammer (notice the damage?).
4. Pound on a jounce bumper with a sledge hammer (it protects whats underneath!)

I can guarantee NOBODY can swing a sledge hammer any where near the velocity that a pot-hole can throw your corner mass.

Racing on a smooth track has different requirements as compared with driving on Michigan roads.

 

[RamenPride]

Knowing this, I'm against even cutting the bumpstops since many are already rather short and the material is relatively soft for the task it serves.

Depending on how much the car is lowered, you may be left with zero suspension travel if you don't trim the bumpstops.

 

[knochgoon24]

If that's the case, you should be looking for shocks with a shorter body.