bump springs

[riddle28]

pros and cons?

[MasterSbilt_Racer]

pros and cons?

Pro:. Is linear until it isn't

Con:. Is infinitely stiff when it quits being linear

Pro:. Just a spring, but lighter than dual rate

[Len72P]

is there a different rate of release of the stored energy, between the bump spring and bump stop, and does that effect shock rebound?

[riddle28]

everybody has told me to stay away from them, but in my mind they seem more consistent for what im fighting than rubbers or bump stops do. ive got an older bwrc that drives great with the car laid on the rf, but its a fine line to bottoming the ball joint in the shock

[Kromulous]

Go to that new Howe Upper with the smaller ball joint mount. Basically the pin and bearing is made into the A arm. Makes quite a bit of room.

[Matt49]

If you want to avoid damaging your shock, you can cut out a piece of an old tire and use hose clamps to wrap it around both sides of the upper so it protects the shock if it ever hits the ball joint.

[billetbirdcage]

riddle28: Why don't you just update/move the Upper coilover mount so it doesn't hit? The car should bottom out before this hits on any newer car. Maybe it's not possible on your car is built and how things are set up, but that would be the first thing I'd do......

Also not a fan of bump springs, but there are newer ones out there the might solve some of the issues but I don't feel they are enough for me to actually test any of it. Again just my personal preference, don't mean it's right or wrong just different.

[MasterSbilt_Racer]

is there a different rate of release of the stored energy, between the bump spring and bump stop, and does that effect shock rebound?

The force released is the spring rate over the distance. Springs are linear so rate is always the same. Bumps depend where you are in the travel.

[Burke1118]

The force released is the spring rate over the distance. Springs are linear so rate is always the same. Bumps depend where you are in the travel.

Do you think the hysteresis of foam/urethane is note worthy?

[billetbirdcage]

Do you think the hysteresis of foam/urethane is note worthy?

I think you need to also look at force/travel over time. Meaning say you had a bump that was indeed linear just for ease of discussion. Lets say it's a 200# rate so take that bump and a 200# spring and compress both 1" or 200# of load.

Now release both of them, what is the time difference to come back up 1"? Then how much spring surge does the spring have at that velocity and how much is that effecting the static load on the spring as it will drop momentarily and increase then slowly stabilize over time depending how bad the surge is. Not sure how much a bump can actually surge but it's got to be a huge amount less then a spring.

Say the spring rebounds 1" in .002 seconds and the bump at twice as slow at 1" in .004 seconds, if the car/coiliover is traveling 1" in .003 seconds then the spring is pushing on the car but not so much with the bump.

Hope that makes sense.

[Burke1118]

I think you need to also look at force/travel over time. Meaning say you had a bump that was indeed linear just for ease of discussion. Lets say it's a 200# rate so take that bump and a 200# spring and compress both 1" or 200# of load.Now release both of them, what is the time difference to come back up 1"? Then how much spring surge does the spring have at that velocity and how much is that effecting the static load on the spring as it will drop momentarily and increase then slowly stabilize over time depending how bad the surge is. Not sure how much a bump can actually surge but it's got to be a huge amount less then a spring.Say the spring rebounds 1" in .002 seconds and the bump at twice as slow at 1" in .004 seconds, if the car/coiliover is traveling 1" in .003 seconds then the spring is pushing on the car but not so much with the bump. Hope that makes sense.

So what you’re saying is, if you compressed a 200# small bump spring, and a 200# regular coil over both 1”, then magically were able to make what was compressing the spring vanish and you were able to time how long before both springs rebounded the inch the coil spring would resume quicker?

[billetbirdcage]

Sorry if I wasn't clear, I meant bump as in some rubber/urethane (not steel type spring).

[Burke1118]

Ok that makes more sense. Misunderstood the first reply

[riddle28]

ive got an 09, the upper shock bolt is ran thru a tube in the upper bar. it really gives me the most travel out of any other way i see. im just trying to come up with something as a "soft" limiter say a 1/4" before the BJ hits

[billetbirdcage]

ive got an 09, the upper shock bolt is ran thru a tube in the upper bar. it really gives me the most travel out of any other way i see. im just trying to come up with something as a "soft" limiter say a 1/4" before the BJ hits

If that is all your after, then look at either the 1/2" tall RSW series bumps or the Apollo series bumps. Pick one medium to hard and just shim with packers until the arm just misses the shock without the spring on it. Just leave a little room for compression on the bump but with those styles you only talking 3/16" or 1/4" at most depending on which one you pick.

[riddle28]

Thanks man I’ll check those out now

[Matt49]

This is what I had in my head and it may be completely wrong:
Take a block lead that weighs about 10 pounds figure out how to attach a bump stop to it.
Then take another block of lead the same weight and figure out how to attach a bump spring to it (one that achieves the same load numbers your looking for at your travel). No drop both of these from about 6 feet in the air so they both land on the bumpy side and see which one bounces highest. My guess (and it is just that, a guess) is that that you better have your head on a swivel for the bump spring one to hit you in the jewels on the way back up but the one with rubber bump stop is going to put on far less of a show.
If anybody decides to actually do this, please video and post for educational and comedic purposes.
But in all seriousness, this bounce is exactly what the shock is attempting to control for maximum grip. So if I'm right in my guess above, they would require drastically different rebound curves to achieve critical dampening.

[TheJet-09]

I'm starting to worry about you Matt, with your test procedures for aerodynamics and now bump springs! Lol!

Good information overall though.

[billetbirdcage]

This is what I had in my head and it may be completely wrong:
Take a block lead that weighs about 10 pounds figure out how to attach a bump stop to it.
Then take another block of lead the same weight and figure out how to attach a bump spring to it (one that achieves the same load numbers your looking for at your travel). No drop both of these from about 6 feet in the air so they both land on the bumpy side and see which one bounces highest. My guess (and it is just that, a guess) is that that you better have your head on a swivel for the bump spring one to hit you in the jewels on the way back up but the one with rubber bump stop is going to put on far less of a show.
If anybody decides to actually do this, please video and post for educational and comedic purposes.
But in all seriousness, this bounce is exactly what the shock is attempting to control for maximum grip. So if I'm right in my guess above, they would require drastically different rebound curves to achieve critical dampening.

You don't need to put 10# on top of them to get a fairly accurate assumption, just drop both of them.

[TheJet-09]

Hopefully not high jacking too bad, somewhat related, but I'm new to actually being able to put a number (force) with travel. My question is, at say 3 1/2" of travel on the RF, if one set-up (shock/spring) I have with a bump is only at 1680 lbs, and a second set-up I have is right at 1900 lbs, is that enough you would notice a difference on the track (at least to the driver)?

Or I guess, how sensitive to change around that travel does any set-up need to be to make a difference?