Bump stop selection

[mikedc]

The right bumpstop depends on how much clearance you have and how often you're getting close to using it up.



And, whether you are trying to mimic the modern OEM approach. These days "micro-cellular jounce bumpers" (read: yellow foam) serve as secondary progressive-rate springs.

I like the idea of the modern foam ones as secondary springs, but some of them feel alarmingly soft for the original job. It's pretty easy to compress them pretty far with a 10-lb sledgehammer (yes I have tried it.) Bumpstops were invented as the last line of defense against IMPACTS. I might be more comfortable using foam ones as additions alongside the old rubber stoppers rather than replacing them.

[stab6902]

I might be more comfortable using foam ones as additions alongside the old rubber stoppers rather than replacing them.

I've never seen a modern car run both. The foam ones are very progressive - the force they provide "hockey sticks" as they compress. That's what makes them desirable.

Example force curves: https://www.virkki.com/jyri/miata/bumps.html

[mikedc]

I've never seen a modern car run both.

Modern vehicles are more fragile than they used to be. Even the trucks & SUVs.

The foam ones are very progressive - the force they provide "hockey sticks" as they compress. That's what makes them desirable.

I know. I've played around with various bumpstops and read about their properties.

You could get a pair of shoes with the soles made of the same modern foam material. But it still won't be safe to step off 4-foot drop and land with your legs straight & knees locked. The 'hockey stick' property of the resistance isn't enough to make it safe if the impact is still too abrupt in the big picture.

[dontlifttoshift]

Modern vehicles are more fragile than they used to be. Even the trucks & SUVs.

LoLwUt

I know. I've played around with various bumpstops and read about their properties.

You could get a pair of shoes with the soles made of the same modern foam material. But it still won't be safe to step off 4-foot drop and land with your legs straight & knees locked. The 'hockey stick' property of the resistance isn't enough to make it safe if the impact is still too abrupt in the big picture.

With the right amount of foam with the proper curve it would be fine.....you know, properly sized for the application. What you said was equivalent to coil springs don't work because the spring out of my bic pen won't hold the car up.

[mikedc]

Lol no they aren't, stop speaking nonsense.

https://www.youtube.com/watch?v=fUtR9eb8zpw

2:54. 4:05. 9:26. Go ask GM about doing this stuff with a 2020 Malibu.


https://www.youtube.com/watch?v=8DV-josbxeA

0:10. 3:28. Go ask Ford if they will demonstrate this stuff with a 2020 F150.

Without getting too far off into the weeds, I can say that I've never had a foam bump stop somehow "crush through" to the point where I felt an abrupt impact. My experience is with GM A, B, and F-bodies, and my cars are often loaded up with my family and driven on famously bad Michigan roads. It's not just me either... A and B-body guys have been running the "ZQ8" foam bump stops for 15+ years with good results.

Take one of those ZQ8 stoppers, put it in a bench vise, and let a 40lb weight fall down onto it from about 3 feet up. This stunt is easier if you're standing on a stool. Keep your hands touching weight all the way down so you can feel the jolt and control the rebound safely.

Then consider that the speed the weight reaches after falling 3 feet is nothing out of the ordinary for hitting a pothole/bump on the highway.

Then consider that each corner of your car is about 20x that heavy.

Then try the same experiment with a (brand new) stock rubber bumpstop. It doesn't make it SOFT but it's noticeably better.

My 2 cents: if you're running a car that's lowered more than an inch and still have the stock bump stops (especially if they're rock hard or dry rotted), foam bump stops have to be the best $30/axle you can spend on your car.

I'm not gonna say that's a bad idea. But I would be extra careful about BAD hits . . . which is already standard procedure for a PT classic car anyway.

I just think running both stoppers (if space on the control arms hypothetically allowed it) would be better. Even if the rubber one is a bit shorter than stock to help you stay out of it.


The factory is liable to go with foam these days because modern cars live on smoother roads in general these days (look at how ground clearance and total suspension travel have reduced in the last 50 years). They look at foam bumpstops and see a way to add a secondary progressive spring rate that is almost scot-free from their position. It's very small, very cheap, and weighs almost nothing.

Another factor that the OEMs might want to consider (as long as I'm telling them how to do their jobs here) is the long-term servicing. It's entirely normal for foam stoppers to be worn out & crumbling after only 10 years - and it's entirely normal for the repair shop to never glance at them, and entirely normal for the owner to have no idea that problem might exist. The OEMs need to raise awareness about the servicing issue if foam bumpstops are going to be the last line of defense against bottoming-out. This is another problem that wouldn't exist if the car had both bumpstops.

[SPG]

https://www.youtube.com/watch?v=fUtR9eb8zpw

2:54. 4:05. 9:26. Go ask GM about doing this stuff with a 2020 Malibu.


https://www.youtube.com/watch?v=8DV-josbxeA

0:10. 3:28. Go ask Ford if they will demonstrate this stuff with a 2020 F150.

Going to let ya on a little secret
a car maintaining it's shape after a crash does not mean it's stronger. If you're dead you're dead.
New cars are designed to crumple to absorb the inertia so you don't die, that does not mean they are weaker.

[mikedc]

Going to let ya on a little secret
a car maintaining it's shape after a crash does not mean it's stronger. If you're dead you're dead.
New cars are designed to crumple to absorb the inertia so you don't die, that does not mean they are weaker.

I know that.

I didn't argue that modern cars are "weaker" in a crash. I was saying they are more "fragile" on bumps & potholes.

A full-framed Ford Crown Vic from 20+ years ago would get a much lower crash test safety score than a comparable modern sedan. But police will tell you the old CV holds up better driving across grassy medians and bumping curbs.

[SPG]

Modern vehicles are more fragile than they used to be. Even the trucks & SUVs.

Lol no they aren't, stop speaking nonsense.