43 replies to this topic

[Antoine]

Does someone have some good address for bumstop manufacturer?
I search to made specific bumpstop for my hillclimbing car.

thanks

[Greg Locock]

What style of bump stops? old style conical rubber things, or the long foam ones?

[Antoine]

Rubber bumstop in all size and why not in foam

[Greg Locock]

Dunno about the old ones, but the foam ones you just buy the foam and turn them on a lathe. So you need a source of high density polyurethane foam.

[just me again]

Why not just go through pictures of produktion car suspension until the right bumpstop emerges, then just order it.

Bjørn

[macoran]

Henzo site picture

Antoine,
Check out the Henzo rubber spring people
www.henzo.com

they seem to have quite a range

[Fat Boy]

Greg mentioned this manufacturer not too long ago.

http://www.powerflex.co.uk/

I've actually ordered a couple to test out over the next month or so. I hope they work well. They seem a little more technically savvy than most of the competitors I'm aware of.

[tyjak]

Koni makes bump rubbers for their shocks. they are available in different IDs. Due to their design the "spring" rate is progressive. If you have a valve spring tester, you can put the bump rubber in it and measure the rate.

[Lukin]

http://www.autosport...l_longbeach08-2

I assume different colours for different rates?

[Fat Boy]

Originally posted by Lukin I assume different colours for different rates?

Those look familiar......

The different colors of those particular bump rubbers are just a matter of manufacturing. They are from Koni and for one reason or another, they come out with the color variations. I haven't seen a difference in spring rate due to color.

[Fat Boy]

Originally posted by Fat Boy
Greg mentioned this manufacturer not too long ago.

http://www.powerflex.co.uk/

I've actually ordered a couple to test out over the next month or so. I hope they work well. They seem a little more technically savvy than most of the competitors I'm aware of.

Having ran the Powerflex stuff now, I can tell you that it's pretty good stuff.

[NRoshier]

Thanks for the report. I'd be interested in how you select your bumpstops.

[Fat Boy]

Originally posted by NRoshier
Thanks for the report. I'd be interested in how you select your bumpstops.

Well, I'd love to tell you that it's all part of a well thought out simulation program and extensive research project...but it's not.

I use bump rubbers mainly as a form of ride height control. For the slower corners, I make a conscious effort to stay away from them. Often you have a single big bump in the middle of a slow corner. When you have this, there is a compromise. Do you run a larger gap and a stiffer bump rubber or a tighter gap and a softer bump rubber? I've found that running a tighter gap and a somewhat softer bump rubber is easier to tune, if not ultimately better.

If the bump rubber is initially soft (although it can have a fair bit of progression), you can hit them in the middle of corners and the driver can't particularly tell. Maybe you're only into them 2-5mm, but if you were using a very hard chunk of polyurethane (Shore A 90, for example), it would upset the car. As the car settles onto them down the straight, or in a brake zone, you want them to hold the thing up enough to buy you some ride height (the end goal of running them). It depends on the track, but I've had bump rubbers buy me 8-10mm of ride height (and a bunch of lap time). There are other tracks where they don't seem to do squat for you. Generally, they're best at street courses where you have long straights and slow corners. Natural terrain road circuits can get a bit more difficult because you want to be into them in some corners and out of them in others. The trick is to never be in between. In fast corners, you'll be fine if you're firmly planted in the bump rubbers, but if it bounces into-out of-into-out of then the driver tends to report a lot of strange handling traits.

There are rare occasions where I've ran no bump rubbers and put the car straight down on the packers. It makes for weird damper traces, but done properly it can buy you some more ride height. It's very knife-edgey to set up, though, and easy to get _really_ wrong.

Also, when setting up bump rubbers, you have to anticipate what your driver will do. I had one guy run his FARB stiff all weekend and I set up the packer gap around that. In the race, he picked up push and softened the FARB way off. We went from a reasonable packer engagement with the FARB stiff to complete overkill with the FARB soft. The understeer didn't go away when he softened the bar because the spring rate of the bump rubber was at least as much as the ARB. I ended up with a somewhat confused and unhappy driver.

So how's that for a non-answer? You'll generally end up with a few bump rubbers that fit. Run the stiffest one you can get away with until you have trouble setting it up. Don't try to set them up without good data. Don't expect to get them set up perfectly without a lot of testing. Once you do, it's a good time gain, but get the other stuff done first. They aren't magic, just an extra spring to monkey with.

[NRoshier]

thank you, very helpful.
Have you changed the shape of the bumpstops as supplied to get a different performance or do you think it is better to reply of the material specification?

[Fat Boy]

I've played with shape somewhat while bench testing, but not on the track. I've also played with changing the shape of the packer that initially contacts the bump rubber. By playing with how the final packer contacts the bump rubber you can change the characteristics quite a bit. In the end, though, I have reverted back to a pretty straight forward packer/bump rubber package. They're just another spring, and if you can get that spring to work consistently and smoothly, then you've done what I do with them. If you try to make the initial progression super soft, then to get anything out of them, you have to engage them very early. We're back to the wide gap/stiff rubber or narrow gap/soft rubber compromise. There really isn't any one answer, it's salt to taste.

[Greg Locock]

If you look at the commercial foam ones you'll see the shape is quite complex, particularly around the nose. The idea there is to get a very progressive take-up, which they do by actually bending the foam rather than just compressing. Designing that for a long fatigue life is non trivial I suspect. Further up the engagement you'll see a series of waisted sections. That gives the foam somewhere to go as you really start to compress the thing. You are pretty safe turning that part down in a lathe if you want to soften it off.

If you want to stiffen up the last little bit, put a heat shrink tube around the last few inches, then cut it away until you get the performance you want.

[NRoshier]

I've found the Koni bumpstop information interesting, but of course buying those locally and changing the shapes etc rapidly becomes an expensive exercise. I imagine I could make a rig like a valve spring tester to check progression in modified bumpstops, though I am a very long way from needing to do so.
The F3000 2812 dampers I purchased simply had a very large rubber donut, much like a huge O ring and I'm damned if had any progression. Could they have built the bumpstop into the bellcrank system? Would seen an added complication if they did.

[Fat Boy]

Originally posted by Greg Locock
If you look at the commercial foam ones you'll see the shape is quite complex, particularly around the nose. The idea there is to get a very progressive take-up, which they do by actually bending the foam rather than just compressing. Designing that for a long fatigue life is non trivial I suspect. Further up the engagement you'll see a series of waisted sections. That gives the foam somewhere to go as you really start to compress the thing. You are pretty safe turning that part down in a lathe if you want to soften it off.

If you want to stiffen up the last little bit, put a heat shrink tube around the last few inches, then cut it away until you get the performance you want.

I think the nose portion of the road car bump rubbers are shaped to make the initial contact much softer. If you consider the spring rate and damper travel involved between a road car and an open wheeler you would have to make the initial contact on a road car much softer. Incidently, Powerflex does have a lot of the convoluted shaped B.R.'s. None of them had the rates that I was looking for. The material they use is a closed cell foam, which seems to have a very respectable life.

Dynamic Suspensions uses silicone 'Fruit Loops' of varying colors for bump rubbers. They have the tendency to degrade from the inside out. You end up with a thin outside material holding together rubber-like swarf. Naturally, they don't work very well that way.

I've completely destroyed very hard polyurethane bump rubbers on the track. It's a trick to find something that will live sometimes, depending on the application. On the rear of a high powered car is really tough because you're putting big loads into it and high temps. It's a bad place to live.

In terms of testing, I've found the easiest test rig is a damper dyno. Drop all the oil out of a damper and install the bump rubber to engage various amounts. Plot load vs. displacement for a couple different speeds/frequencies and you have a nice little snapshot of what's happening. Kick it over into Excel if you want to get a little more tricky.

[ben38]

Hi everyone!

I'm back ^^

About the bump rubber thing, I'd say that I also use them to get like 2 different suspension stiffness on the car.
The point is get out of any bump rubber on slow parts and use soft springs to get the best mechanical grip you can.
But if you do use such spring on a high aero car, you'd be bottoming pretty soon as the downforce start to work.
Here comes the bump rubber and the trick is to set your gap Vs spring stiffness right to be effectively on bump rubbers and never in transition in high speed corners.
The question then is what do you do in middle speed corners?
Well then it is up to you, you generally have two choices, sacrifice them a bit or reduce the bump rubber / Springs stiffness difference by softening the initial bump rubber deflection. In the latter case the ride height control by bump rubbers is reduced but then you can balance that by using some packers. The margin to get it right is pretty thin yeah, but it can do wonder.
If you really control the thing, you can also use that to change your rake angle for the straight line to hide some wing and gain a bit in drag.

All this really can make a difference but that needs a guy who really knows what he is doing or it will be endless tests. I generally try to use lapsim or equivalent to see what my spring deflections are. Then you get a quite clear image of it before going to test and you can then already get a not so bad idea of what gap you need for different bump rubber rates.

The other way to "predict" is to use your data logging system and make some calculation on data you already have.
Just calculate an equivalent spring deflection for different spring rates then see where you would engage the bump rubber. The gap then is quite easy to find out but check out your rate for transitions as you will generally find that you can not set any gap that will work perfectly for every corner unless you pick a very big one.
The final decision will really depends on your driver's style and on the track conditions (namely level of grip).

That's how I do.

Any way, i also have little problems to find good bump rubber these times and the biggest one I face is to find good ones for compression and rebound.
The manufacturers generally ensure the caracteristics only in compression and I noticed some funny answer in rebound like delay or different stiffness.
Anyone know where I can find this kind of magic rubber?
I also need all kind of stiffness shape from progressive to linear (the hardest to find for bump rubbers)

[Fat Boy]

Originally posted by ben38

The question then is what do you do in middle speed corners?

100%. Really bumpy low speed stuff is similarly tough to predict. In these situations, I start with a larger gap that I'm sure won't cause problems (although it also won't get me much ride height). Then as a test I close the gap up fairly aggressively and lower the car. It's important that you do both. And see if that is better or worse. If it upsets the car too much, then I back out of the B.R. and ride height until I find the happy medium. Sometimes that's all the way back where I started, but often a little less of a gap and a little lower than the 'safe' starting point.

In places like this it really is a 'Salt to taste' type of deal. Some guys are OK with what it does and some aren't.

[Paul Vanderheijden]

I read this thread with interest. I prepare and race historic touring cars (rear engined Abarth ) and have found the with judicious use of "bump stops" I get much better corner entry and exit. Generally I treat the bump stop as a second "progressive spring system". The bump stops that I use are not part of the shock, but between the lower a-arm and the chassis, both front and rear.

I looked around for alternate materials to the standard Fiat square black rubber unit and found something that I can use at the local hardware store. This was actually a rubber door stop, with a single stud moulded into the back side. I played around with these and final came up with a shape that I like by turning them in a lathe.

The idea was to retain relatively soft springs for good road following compliance, setting the ride height so that there is some wheel motion before the lower a-arm contacts the bumpstop. This allows that car to "take a set" when entering a corner and then the progressive nature the bumpstops comes into play. About mid-corner the car is still quite stable and as I transition into corner exit and transfer weight to the rear, the same process occurs at the rear of the car. I have found that this allows for very stable corner entry and exit. I combine this with a relatively stiff front stabilizer bar.

While this may be a very much less sophisticated example, as compared to a modern formula car, it does work and is results in significant reduction in lap times.

Paul Vanderheijden

[zac510]

ben, Fatboy, etc, when you guys are talking about using the bumpstop as a spring, it is still being damped by the damper isn't it?

[RDV]

zac510 ben, Fatboy, etc, when you guys are talking about using the bumpstop as a spring, it is still being damped by the damper isn't it?

Yes, but much less, bump rubbers slow damper speeds dramatically...one of the reasons damper manufacturers dont like you running on them....let's put it this way, the original use of bump-stops was to stop metal-to-metal contct on the damper itself...but racers hijacked them to be used as progressive springing.

re ben38 quote on bump and rebound rates, it depends a lot on the velocity rates (or inverse motion ratios if you wish) that is being used on the suspension....on a 1.0 ratio or thereabouts, which is usual on racing cars, that means the rubbers have to work in a very limited range, @ 15mm deflection, which calls for rather hard polyurethane rubbers and hard shore values

...the original koni brubs were much softer and were designed to be use in a higher stroked suspension, say 30 to 40 mm....in that case a nose made sense...but coming back to rates, this varies with the speed of cycling...you will get different curves at different speeds at the same stroke, and the rebound values will depend on the hysteresis of the rubber, or urethane foam or what-have-you.

Another way also of changing the curves is to have different machined seats for the brub on your spring seat( a bit like the moulton hydro-elastic suspension, enclose them in housings, of even , in the case of urethane rubber, using different lenght rings...one , say 50 mm long cylinder will be harder and have a different curve from 5 * 10 millimeter cylinders of exactly the same material.....fun stuff and multi-tailorable, to coin a neologism....any elastic hydrocarbon polymer for that matter...

down side to all this, with heavy use and cycling urethane rubber degrades, they will also degrade differently on front and rear suspensions, e.g. on a rear engined single seater the fronts last a long time, rears degrade fast as usualy damper attached to gearbox...so living in a very hot environment, apart from stroking more...

Dynamic bump rubbers degrade and split as FB mentioned, but are quite useable, if replaced regularly....also prone to splitting on mould line on some faulty production runs...I bloody lost a race on one of those, despite fitting a brand new one for start of race....my mistake...arghhh

Ohlins rubbers are very reliable, are a bit softer than the Dynamics, Konis of course useable still in a wide variety of formulas, Smacbump in France produces a good series, much used in LMP, GP2 and A1, plus the ones quoted above....

Bump rubbers are an art to work with, but can give excelent results if inteligently used...

...and ben, you do your own curves, as I mentioned before, they vary with speed....a good damper tester should be ok ....
...also linear rubbers? ...rubber is not linear..... :

[Fat Boy]

Originally posted by RDV

Bump rubbers are an art to work with, but can give excelent results if inteligently used...

...and ben, you do your own curves, as I mentioned before, they vary with speed....a good damper tester should be ok ....
...also linear rubbers? ...rubber is not linear..... :

I was hoping you'd join in on this thread.

Sure rubber is linear. You just have to really zoom in on the graph and draw a really thick line with a crayon!

[RDV]

Fat Boy-I was hoping you'd join in on this thread.

...oh, I can go on about bump rubbers for hours....more next week, am in middle of race weekend, so a bit busy....

[Andrei]

German automotive industry is working mainly with a company called Elastogran - http://www.elastogran.de. They are supplying us with different kind of shaped bump rubbers for series production, but for testing and finding out different setup's we are getting rubber parts in cylindrical form - Lengths of 30-50 cm, diameter of 10 cm and different shore. We are forming an cutting them with a lathe.
For the touring cars I have worked with, we chose rubbers of different shore (30 - 60+) with a thickness of 10 mm. We can play with these parts, or, for certain tracks, we could build some with 5 mm thickness to play around. For racing, we have never tried to make formed bump stops. What we have already done was to build bump rubbers of, lets say 10 mm of 60 shore and 5 ore 10 mm of 30 shore.

[OfficeLinebacker]

So do you mean the things that ride on the plunger of the damper or the thing screwed into the chassis that makes contact more or less at coil bind?

In the case of the former, I suggest googling the term "packer" as they're commonly referred to using that term in the US while "bump stop" usually means the latter.

In the case of the latter, polyurethane is the best, I imagine. You can make them yourself or Energy Suspension likely has a thread pitch that fits.

[Fat Boy]

Originally posted by OfficeLinebacker
So do you mean the things that ride on the plunger of the damper or the thing screwed into the chassis that makes contact more or less at coil bind?

In the case of the former, I suggest googling the term "packer" as they're commonly referred to using that term in the US while "bump stop" usually means the latter.

In the case of the latter, polyurethane is the best, I imagine. You can make them yourself or Energy Suspension likely has a thread pitch that fits.

You're talking more production type stuff when you talk about a bumpstop that is fixed to the chassis.

On any racing car I've ever dealt with, both packers and bump rubbers are concentric with the damper shaft. Packers are made of nylon 6/6 or something similar. They are either cylinders which need the damper to be partially disassembled to remove or split which allow for fine (1mm or less) adjustments in contact adjustment in pit lane. Packers are not meant to deflect (although they, of course, do so a small amount).

Bump rubbers can be cone, cylindrical, or other elaborate shaped bits of foam, polyurethane, etc.. They are meant to be engaged at some point in the stroke of the damper to give the car a stiffer ride spring rate or prevent bottoming.

[OfficeLinebacker]

Originally posted by Fat Boy


You're talking more production type stuff when you talk about a bumpstop that is fixed to the chassis.

On any racing car I've ever dealt with, both packers and bump rubbers are concentric with the damper shaft. Packers are made of nylon 6/6 or something similar. They are either cylinders which need the damper to be partially disassembled to remove or split which allow for fine (1mm or less) adjustments in contact adjustment in pit lane. Packers are not meant to deflect (although they, of course, do so a small amount).

Bump rubbers can be cone, cylindrical, or other elaborate shaped bits of foam, polyurethane, etc.. They are meant to be engaged at some point in the stroke of the damper to give the car a stiffer ride spring rate or prevent bottoming.

OK so you mean something like this:

http://www.energysus...ges/bumpst.html

[Greg Locock]

We use elastogran or equivalent polyurethane foam ones on each end of the car. On the front they are on the shock, on the rear they are alongside the spring. The parts are very similar, and are obviously tuned in a somewhat similar fashion. Given the choice, putting them on the shock is a better move, so long as your shock mounts can withstand the very high compressive forces.

[RDV]

Mmm...think we should differentiate between bump-stops and rubber spring in the application....if the dampers are also the spring carriers its easy to work-out the brub characteristics we are looking for in the case of coil-springs.

Bump-stops used as end-of-motion limiters would have an entirely different curve/hardness requirement.

[ben38]

Hi all,

Thanks RDV!
But as I told you before I do not have any damper dyno available nearby
I'll have to test different stuff based on manufacturer specs and give it a shot on the track.
Well I might also teach my driver how to drive somewhere in the process

As I already offered you my dear RDV, you're more than welcomed in here and we already prepared all the required stuff needed to welcome someone from your country

I am in Sepang rigth now and I can maybe find some new stuff here to play with!

I'll keep you updated ;)

Now I go back to my towel to clear that sweat from my forehead that appears everytime I go more than 5 metres from the nearest aircond

[Ben]

Originally posted by ben38
Hi all,


Now I go back to my towel to clear that sweat from my forehead that appears everytime I go more than 5 metres from the nearest aircond

Gotta love Sepang. I'm off to Spa this weekend - probably going to be moisture of a different sort there :-)

The car I'm looking after the tyres for at the moment is being engineered by a really smart guy who's doing much the same thing that's being discussed by RDV, FB, and ben38 - i.e. bump rubbers for high speed, off them at low speed and a lot of fiddling in the medium speed stuff.

Just wanted to throw something else in - a while back Racecar Engineering ran an article on Eibach's F3 damper and the helper spring cartridges you could run with it. Anyone here have any experience of that? The thing it seemed to allow you to do was run a dual rate spring with a bump rubber on the end.

Naively I'm thinking you could have a soft initial rate for the slow speed, a somewhat stiffer second rate for medium speed and then working into the bump rubber at high speed/ under braking. I guess it would be damn hard to ensure you ran in the correct part of the curve though.

Off-Topic - I didn't want to resurrect the thread on third springs from last year, but I was wondering about the damper characteristics of third dampers (specifically at the rear). I'd always assumed you'd want them soft at low speed to allow the rear to sit down fairly quickly as the aero load builds. But it also occurred to me that you might want it to be quite progressive in medium speed to help build the load on the tyres quickly without having to run that on the side dampers where it might hurt mechanical grip - anyone got any experience of that?

Ben

[murpia]

Note that all of this applies mainly to cars with significant downforce, i.e. cars where the ride heights change significantly with speed...

Originally posted by Ben
The car I'm looking after the tyres for at the moment is being engineered by a really smart guy who's doing much the same thing that's being discussed by RDV, FB, and ben38 - i.e. bump rubbers for high speed, off them at low speed and a lot of fiddling in the medium speed stuff.

Does this car have 3rd springs or dampers at all? If it does I would expect all the ride-height control fiddling with bump rubbers be done on the 3rd leaving the sides never to touch the bump rubbers except in extreme situations like giant kerbs.

Just wanted to throw something else in - a while back Racecar Engineering ran an article on Eibach's F3 damper and the helper spring cartridges you could run with it. Anyone here have any experience of that? The thing it seemed to allow you to do was run a dual rate spring with a bump rubber on the end.

Naively I'm thinking you could have a soft initial rate for the slow speed, a somewhat stiffer second rate for medium speed and then working into the bump rubber at high speed/ under braking. I guess it would be damn hard to ensure you ran in the correct part of the curve though.

If remember right Eibach offer two kinds of additional spring. One is designed to 'fill in the gap' if you're using a spring too short (or a damper too long) to be on the spring platforms at full droop for the preload you need. Usually seen on direct-acting coilovers where the ride height is adjusted on the spring adjuster not a push / pull rod.

The other kind is meant to go coil bound at some point in the working travel of the spring and provide the dual-rate effect you describe. Again I suspect it's more useful on direct-acting coilovers as with a rocker system you can build in this rising rate effect into your rockers in a more progressive manner.

Ensuring you run in the correct part of your spring rate curve is just standard (professional level) race engineering - you should do a static test in the workshop to determine your vertical stiffness curves vs. wheel displacement and to calibrate your damper pots. You can take aero data and work out a speed vs. wheel displacement curve, plus a roll couple distribution vs. speed curve. Look at the likely corner speeds for the track you're going to and a base setup should present itself.

On the track after your first session you can see from data where you really are in all the corners and adjust accordingly. If it were me running the car I'd have insisted on a straightline shakedown test to check the car data against the theoretical data in advance.

Off-Topic - I didn't want to resurrect the thread on third springs from last year, but I was wondering about the damper characteristics of third dampers (specifically at the rear). I'd always assumed you'd want them soft at low speed to allow the rear to sit down fairly quickly as the aero load builds. But it also occurred to me that you might want it to be quite progressive in medium speed to help build the load on the tyres quickly without having to run that on the side dampers where it might hurt mechanical grip - anyone got any experience of that?

By speed do you mean car speed or damper velocity?

Often 3rd dampers are tuned on a 7-post to minimise the tyre load fluctuations and enhance grip. In my experience that's worth far more laptime than trying to tweak the car balance a little bit with the dampers (side or 3rd). Of course that relies on the fact you have the tools to re-balance the car without resorting to damper fixes...

A position sensitive 3rd damper seems like a good idea. With the use of gapped bump rubbers the damper might need to be stiffer once the car's on the rubbers compared to just on the springs...

And of course you can always consider the latest idea in F1, the 'J-damper'...

Regards, Ian

[Ben]

Originally posted by murpia



By speed do you mean car speed or damper velocity?


And of course you can always consider the latest idea in F1, the 'J-damper'...

Regards, Ian

I meant damper shaft speed.

Care to explain the "J damper" to someone who hasn't had time to trawl the comics recently?

Ben

[Ross Stonefeld]

The very crude drawing/explanation I saw seemed to think it was on some sort of a thread? So instead of sliding back and forth it advances through a groove?

[Ben]

Originally posted by murpia

The other kind is meant to go coil bound at some point in the working travel of the spring and provide the dual-rate effect you describe. Again I suspect it's more useful on direct-acting coilovers as with a rocker system you can build in this rising rate effect into your rockers in a more progressive manner.

Surely most people would rather tune the progression using spring elements rather than assuming an optimum amount of progression and building an expensive part like a rocker.

Most customer cars I've come across are fairly linear in the rocker.

Ben

[murpia]

Originally posted by Ben
Surely most people would rather tune the progression using spring elements rather than assuming an optimum amount of progression and building an expensive part like a rocker.

Having recently tried to 'fix' a badly designed rocker with off-the-shelf spring parts, it's not as easy as it sounds. Of course a spring manufacturer can offer you a fully customised progressive wound spring, but that costs more than the average rocker...

With a twin-rate side spring setup I'd be wary of the rates 'transitioning' in roll in a corner giving an inconsistent roll couple distribution. At least a fully progressive setup is smooth in this case.

A twin-rate 3rd spring setup would be a lot easier to tune I expect, with little effect on roll couple distribution.

I haven't seen anything other than a twin rate spring stack for sale (Eibach), and that's only available in a few diameters. It wouldn't fit our dampers or maximum spring free length for example but it obviously works for others.

Regards, Ian

[murpia]

Originally posted by Ben
Care to explain the "J damper" to someone who hasn't had time to trawl the comics recently?

It's supposed to be an acceleration sensitive (as opposed to velocity sensitive) device that uses masses and a mechanism instead of fluids and valves.

Regards, Ian

[murpia]

Full write-up of the J-damper in this weeks Autosport.com Journal.

Regards, Ian

[McGuire]

The forward-looking conclusion here is that race cars don't need metal spring systems. Get on it people.

[Fat Boy]

Interestingly enough, NASCAR is now pushing the limits of bump rubbers. Gotta love the COT.

[Greg Locock]

Well, now we've done bump rubbers, what about rebound rubbers?

For years we used fancy plastic (probably polyurethane) ones buried in the bottom of the shock, now we've gone back to steel springs. From a modelling perspective I don't like them as the sudden engagement sends the computer off into a numerical nervous breakdown. Still, they work. The idea is that they give a rising roll rate. The fun coms when you use it to change the weight transfer at the limit.

Since by definition a racing car is at the limit all the time perhaps they are less useful on tracks.

[McGuire]

Originally posted by Fat Boy
Interestingly enough, NASCAR is now pushing the limits of bump rubbers. Gotta love the COT.

This is just their latest go-around with bumpstop setups. Back in 2001-ish was the last time... then NASCAR took that away so the coilbind setup evolved.

This latest deal developed over the winter as the shakers and shock dynos were stroking away 24/7. Teams are now searching the globe for new and magical bump rubber materials. I knew it was going to be an interesting year when the 24 broke the control arm brackets out of the frame at Daytona. People are bending lower control arms. In my whole life I had never seen that.