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    Results 1 to 14 of 14
    1. #1
      Join Date
      Mar 2020
      Posts
      199

      Bump stop selection

      After lowering & changing suspension, spring rates etc., we are often faced with a multitude of different modifications that require different bump stops, either in rate or height.

      After installing a new rear end, the factory stop no longer functions. I would like to add one on a different frame mount or to the shock location.

      There are different foam & rubber combinations, plus high rate "bump springs" that can be used in the top of many shocks for travel limiting.
      Obviously, running over a road imperfection mid corner & landing on a solid bump stop can end badly.

      I'm assuming the stops should never come into play under normal conditions.... even though many aftermarket lowering kits make the bump stops part of the normal working suspension.

      Does anyone have a starting recommendation as to the spring rate & amount of compression you shoot for with respect to the final suspension limit?
      Should you start with a percentage of the vehicles spring rate & have it come into play at say 1" from maximum travel?

      For example with a 250lb rear spring, do you choose a stop with a 500# rate starting at 1" from mechanical interference?

    2. #2
      Join Date
      Apr 2009
      Location
      Michigan
      Posts
      322
      Country Flag: United States
      You're right, bump stops are generally not engaged at normal ride height. However, some modern cars are very close to their bump stops (these days they're micro-cellular foam rather than rubber) at normal ride height, and get into them as soon as you corner/brake/load the vehicle. This is the exception rather than the rule though.

      On my lowered old cars, I like to see 2-3" of compression travel before getting into the jounce bumper, and then have another inch or so of usable bump stop compression. More is better if you have the travel/ride height. The micro-cellular foam jounce bumpers are a must have in my opinion. Usually you can't even feel them engaging, and they're smooth and progressive. Another advantage the "new school" foam has over rubber is that it has more internal damping. The polyurethane (often red) bump stops are way too hard to be of any use.

      Unfortunately I don't have any real engineering numbers regarding what to shoot for, but here are some foam bump stops I've used successfully in the past:
      https://www.amazon.com/Belltech-4922...8899241&sr=8-1
      https://www.amazon.com/Belltech-4923...8899286&sr=8-2
      https://www.amazon.com/Dorman-31064-...8899425&sr=8-1
      - Ryan

    3. #3
      Join Date
      Sep 2007
      Posts
      424
      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.

    4. #4
      Join Date
      Apr 2009
      Location
      Michigan
      Posts
      322
      Country Flag: United States
      Quote Originally Posted by mikedc View Post
      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
      - Ryan

    5. #5
      Join Date
      Sep 2007
      Posts
      424
      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.

    6. #6
      Join Date
      Apr 2009
      Location
      Michigan
      Posts
      322
      Country Flag: United States
      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.

      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.
      - Ryan

    7. #7
      Join Date
      Nov 2006
      Location
      Mountain Springs, Texas
      Posts
      4,488
      Country Flag: United States
      Lots of good tech here. Thanks.

      Anyone added foam bumpstops to their coilover shock shafts?

      Don
      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain
      1959 Apache Fleetside

    8. #8
      Join Date
      Sep 2010
      Location
      Beach Park IL
      Posts
      2,838
      Country Flag: United States
      Quote Originally Posted by mikedc View Post
      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.
      Donny

      Support your local hot rod shop!

    9. #9
      Join Date
      Feb 2020
      Posts
      76
      Quote Originally Posted by mikedc View Post
      Modern vehicles are more fragile than they used to be. Even the trucks & SUVs.
      Lol no they aren't, stop speaking nonsense.

    10. #10
      Join Date
      Sep 2007
      Posts
      424
      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.

    11. #11
      Join Date
      Feb 2020
      Posts
      76
      Quote Originally Posted by mikedc View Post
      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.

    12. #12
      Join Date
      Sep 2007
      Posts
      424
      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.

    13. #13
      Join Date
      Oct 2006
      Posts
      634
      Country Flag: United States
      I raised my rear stops so they are 1" away from the frame. They are progressive rate... With the new Hellwig #55703 front sway bar, my 69 el Camino is almost level during a deep turn..
      Attached Images Attached Images  

    14. #14
      Join Date
      Nov 2014
      Location
      East Tennessee
      Posts
      163
      Country Flag: United States
      Man this one really got off topic fast.



      Quote Originally Posted by Lonnies Performance View Post
      I'm assuming the stops should never come into play under normal conditions.... even though many aftermarket lowering kits make the bump stops part of the normal working suspension.

      For example with a 250lb rear spring, do you choose a stop with a 500# rate starting at 1" from mechanical interference?
      If you are using coilovers, I would install the jounce bumper on the shock shaft. The height of the bumper will determine when it engages relative to the end of the shock travel. This actually works out really nicely because you don't have to worry yourself with engagement point and the bumper serves a cushion for the damper, preventing the internal piston from impacting the shock body. If you install a jounce bumper in a remote location you have to be very careful to ensure the shock/damper will not bottom out. Bottoming out a shock should be avoided at all costs.

      There are tons of different rates available of jounce bumpers. They are also cheap. Buy 3-5 different kinds and see what you like. I think this is more of a "feel" thing for most people. The only material to use is the foam like others mentioned (pale yellow color). The foam is actually made of polyurethane but in a microcellular structure. The density, ratio of open to closed cells, and geometry all affect the rate of the bumper.
      Electrical/Mechanical Engineer
      1968 Camaro RS - Flat Black






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