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.

https://i.imgur.com/PazsN4z.png

[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?

[Punisher88]

I'd say in certain track conditions the higher number would go in the corner and want to shear traction on the rf and push the nose. And the lighter one won't. But that's on slicker conditions. On a tacky track you'd probably want the higher number and dif the nose on the softer.

[TheJet-09]

Okay. So along those lines, I've also heard that you can start with the bump engaging at say 2 1/2" of travel when the track is fast, then when it slicks off remove some shims so it engages later (say at 3" of travel). Is that to keep the RF soft for a longer time to aid in its turning ability (and because there is realistically less force going into the corner when slick as opposed to heavy)?

Thanks for any and all input, everyone!

[7uptruckracer]

Its because the track has slowed down so the force that travels the car is less. Your goal is always max travel. So you need to take shims out so it still travels to your max number.



Okay. So along those lines, I've also heard that you can start with the bump engaging at say 2 1/2" of travel when the track is fast, then when it slicks off remove some shims so it engages later (say at 3" of travel). Is that to keep the RF soft for a longer time to aid in its turning ability (and because there is realistically less force going into the corner when slick as opposed to heavy)?

Thanks for any and all input, everyone!

[TheJet-09]

Makes sense. With that in mind, is it fairly guaranteed that an adjustment to the LR will then be necessary when taking shims out of the RF, to keep the car tight enough coming off the corner?

Thanks.

[MasterSbilt_Racer]

Makes sense. With that in mind, is it fairly guaranteed that an adjustment to the LR will then be necessary when taking shims out of the RF, to keep the car tight enough coming off the corner?

Thanks.

If you lose rf travel because the track is slick and then take your bump stop further away from the shock body to compensate, you potentially lost a whole lot of dynamic wedge. I don't want to talk to much about what to do specifically, but certainly you need to do something.

[TheJet-09]

Excellent! That makes me think I at least understand what I have experienced, so still very helpful.

Thank you!

[7uptruckracer]

Its Definitely a slippery slope. You want max travel but the correct load. Softer ride spring well get you to your bump. I've seen guys run a spring rubber on the ride spring and remove rubbers and keep air gap on the bump the same as well. Its not just final load but also the timing off it all too. It can make your head spin. On asphalt if we find a bump load that works we change ride spring load to control travel distance. If i engage my bump 3/4 and I go elsewhere and i don't have the same engagement or too much engagement i change the ride spring. Smooth tracks you can run harder bumps and hold your aero platform rough tracks you cannot because you spike loads.


Excellent! That makes me think I at least understand what I have experienced, so still very helpful.

Thank you!

[TheJet-09]

^^^ Excellent info, and actually what I was thinking but needed someone else to explain it better than I can. The examples help greatly too.

Thanks!

[fastford]

the more you lower the right frt , the more rear steer you will get with out changing any thing else , which is a good thing some times , like with a slight throttle push on the bump.......

[Kromulous]

Lowering the RF (to much) then get into the bump and then hit the limiter on the LR to soon would be counter productive i would think? Always thought that hitting the Limiter on LR on exit is a bad thing?

I guess it all speaks to the engagement timing of the bump stop.

[fastford]

it is to me to krom , thats why when I start working with a bump or 2 stage rt frt , I dont want anything limiting the left rear , some time spent working here will gain speed through the turns , still cant let shock bottom out though ,

[Kromulous]

An interesting trend i see now is putting a jack bolt (adjustable upper mount) on the front shock mounts. I think i am going to cut on our Swartz chassis to add this to the RF, so i can play with this very thing. Should make it easy, altering the pin to pin at ride, of course you would add or subtract on the ride spring but that should be easy enough. If the thread count was the same, shock to jack bolt, that would be even nicer.

[fastford]

i have thought about this to , as well as on the left rear , the only thing is , your changing your static ride height , not that it matters as much now , where as shimming the bump does not change it , now on the left rear it might be good for lowering shock mount if more drop is needed to keep shock from bottoming out..

[grt74]

An interesting trend i see now is putting a jack bolt (adjustable upper mount) on the front shock mounts. I think i am going to cut on our Swartz chassis to add this to the RF, so i can play with this very thing. Should make it easy, altering the pin to pin at ride, of course you would add or subtract on the ride spring but that should be easy enough. If the thread count was the same, shock to jack bolt, that would be even nicer.

its been in asphalt for years

[Kromulous]

Fastford, keep in mind that if you lower the mount, say 1" and then raise the ride spring (shock body) 1" the net result is the same ride, but your 1" closer to the bump (@at ride). Plus the Mod guys have been using the jack bolts on the rear shocks for awhle, always thought about this.

I wish i had more free time, be fun just to make my own chassis. I have been working on one in NX on government time LOL, but a long way to go.

I seen them in the Asphalt cars, where i 1st seen the Allstar mount, Port City i think, great i dea i think.

[7uptruckracer]

With all of this you HAVE to keep spring preload in mind. We are getting ready to put a bump stick on mine that way you don’t have to worry about some of these issues. You can always ask your shock builder if you have room to cut down the shock body as well. You want the right static spring preload so you have the right dynamic spring load. You also want to take advantage of any aero rules for example raising RF pin height to drop LR deck height so you can builtit back up to tech. ALLL of this is why you started seeing shock strokes of “untraditional lengths”. All your numbers are based off max travel then your ideal max spring load know that number and work backwards. Don’t forever these days aero can mean more then mechanical load...we see that more and more with touring cars.


Fastford, keep in mind that if you lower the mount, say 1" and then raise the ride spring (shock body) 1" the net result is the same ride, but your 1" closer to the bump (@at ride). Plus the Mod guys have been using the jack bolts on the rear shocks for awhle, always thought about this.

I wish i had more free time, be fun just to make my own chassis. I have been working on one in NX on government time LOL, but a long way to go.

I seen them in the Asphalt cars, where i 1st seen the Allstar mount, Port City i think, great i dea i think.

[Kromulous]

I thought about the 6" body, is there any counter productive / adverse effects if you move the shock mounts (both) up vertically? Seems like there is plenty of room on the RF and LF under the hood, to bring the shock mounts up. I have thought about cutting the upper bar out and redesigning it it to more a hoop design, similar to off road cars and adding more travel.

Modifying the spring base, higher, would make the movement of the 2 points slower, but more travel. Although i think moving the shock mounts up say 3" wouldn't have that big of an effect, not sure thou.more stuff to research i guess.

[Jking24]

I thought about the 6" body, is there any counter productive / adverse effects if you move the shock mounts (both) up vertically? Seems like there is plenty of room on the RF and LF under the hood, to bring the shock mounts up. I have thought about cutting the upper bar out and redesigning it it to more a hoop design, similar to off road cars and adding more travel.Modifying the spring base, higher, would make the movement of the 2 points slower, but more travel. Although i think moving the shock mounts up say 3" wouldn't have that big of an effect, not sure thou.more stuff to research i guess.Look at some pictures of the newer jimmy mars cars they are built like this

[JustAddDirt]

its been in asphalt for years

Donnie @ Lightning Chassis (UMP Dirt Modified) has been doing the adjustable jack bolts on
LR for 10 years. been using an adjustable RF mount on RF for 4-5 if you order car with one.

Works really well. just have to watch what size adjusting rod used, and make sure it is strong enough for the loading it will take.