Suspension rate questions

[Mos]

I didn't run bumpstops in the sprinter with the short stroke shocks Can't remember it ever bottoming out.
You could always pretension the spring if you want a taller rest position, you just won't have as much droop.

Mos.

[The Real Roadrunner]

always run bumpstops on the front, doesnt matter if you only get 40mm of free travel to the stop as that is all a normal low G bump will compress the damper.

consider the bumpstop as being a variable rate spring and shortening it will generally only make it stiffer therefore the transition from normal damping to "jounce" will be harsher.

if it was mine id leave it the way it is, that way on high G bump it will give you a nicer transition and less jerky ride, the car would also be easier to drive when it goes thru that transition point.

cheers
linden

[MWP]

I wonder if trimming down the outside of the bump stop would be a good alternative to cutting it shorter.

By trimming it down (making it narrower), itll give more travel like shortening does, but itll be more progressive.

[30psi 4agte]

From what i have read and the length of the bilstein bump stop ( ~75mm ) I wont loose any sleep over removing 25mm fromt the biggest end.
That way i will keep some of the "jounce"

As linden said i would never run a front shock without some form bump stop....... not when you spend big dollars on bilstein shocks anyhow

Linden :"doesnt matter if you only get 40mm of free travel to the stop as that is all a normal low G bump will compress the damper"

It will also depend on your spring rate....... but i know you already know this

ATM with my current spring rate i dont feel 40mm travel is enough..The spring rate is only 250lb .... So even if i do the ol' pusn on the front gaurd test i can get it to touch the bump stop fairly easy

So my plan of attack is going up in spring rate to 325 -350lb and removing 25mm off the stop.

This will give me 65mm travel before the start of the stop ~ 50mm of travel in the jounce of the stop and have the up rated spring to help keep shit in order .

[The Real Roadrunner]

250lb is very much in the pensioners turd range ie soft. id probly go 300lb minimum.

if you can compress it that much the valving musn't be doing alot at that point cause most cars i do will only move 20-25mm by pushing the guard.

what car is the insert from?

cheers
linden

[oldcorollas]

i see the bump stop as a "shock absorber saver"
don't need to run one, but stops shocks bottoming out...

if you are cornering hard and hit a big enough bump to bottom out.. chances are you shouldn't have been trying so hard on that corner anyway

[1jzracing]

once a bump stop is active during a hard corner (... ie suspension is bottoming out) then all your handeling and grip is lost no matter how soft or tapered the stops are, the instant 200% increase in spring rate causes immediat understeer (or over steer if its rear)
travel and spring stiffness sould be set so they never touch at any time around a lap

this has been the cause of much confusion about the right spring rates when its just a suspension travel issue, where the car acts as if the springs are too stiff when in fact they are too soft and/or ride height is too low

hence i run the smallest stops possable, about 20mm thick on every car to see any race or track time. i generally use a disc of polyurtethene like an aftermarket sway bar link bush, something tough and durable that wont split, some long tapered ones are not elastic enough when you cut them down and they split

you want the maximum travel b4 they hit allowing the lowest ride height for best cornering

incedently i never had any damaged shocks in 15 years experience

[30psi 4agte]

if you are cornering hard and hit a big enough bump to bottom out.. chances are you shouldn't have been trying so hard on that corner anyway

Your right ....but thats not to say in the real world that it doesnt happen.


Linden : The insert is originaly from a commodore ..... but i ordered the insert directly from bilstein in melbourne. I told them what car it was for, what springs i intended to use ,the weight of the car and that i intended using it out on the track.

They helped me pick a insert to suit. So they set the valving to suit.

Now : It does feel alittle soft to me ( when pushing on the guard ) but im not sure if that is to do with the spring rate or not , or the fact im just a big **** that it moves 40mm.

As far as the shock stopping/ slowing the compression and rebound they seem ok but just have that bit too much travel .. So I reckon thats the grandpa springs .


Im gonna call em anyhow when they are back from the chrissy holidays ......so ill quiz em about the valving and the fact that i have 40mm travel + can get it to hit the stop.
l also want to know what effect going up 100lb (250 -350 lb) will have on the way the shock is valved.

Will going up 100lb on the spring rate require shock re valving or will it still be ok??

[MWP]

Im running 300's on the front of my RA28 with the Koni racing inserts (on softest).
Jumping up & down on the engine xmember moves the car 10mm or so.
Rather firm.

[craigsimon]

the other thing to remember MWP is that the spring and shock won't be at 1:1 motion of the wheel so your wheel is going to "see" the spring rate as greater than the 300lb spring i.e. it won't compress as much as you are expecting. If you calculate how much the shock moves compared to wheel movement you will get your ride rate.

[The Real Roadrunner]

the other thing to remember MWP is that the spring and shock won't be at 1:1 motion of the wheel so your wheel is going to "see" the spring rate as greater than the 300lb spring i.e. it won't compress as much as you are expecting. If you calculate how much the shock moves compared to wheel movement you will get your ride rate.

mac strut front end, theyre pretty much 1:1 or close enough to. if it was a double A arm setup then the above holds true but the strut angle is within 7 or so degrees of vertical so the difference will be minimal.

cheers
linden

[craigsimon]

sorry my bad I've been thinking too much about my double a arm design

[30psi 4agte]

Thought i post this as its useful


I ended up ringing bilstein in sydney and speaking to their tech guys about shortening bump stops , the effect of running the shock in its last 50mm of travel etc.


In short: Shortening the stop by 25mm will have no great effect to the shocks life. The std stop length is 50mm.
I was told to cut the stop from the bottom leaving the softer "more absorbing" part to do its job. So basicly when the stop is hit it wont be like hitting a rock hard stop there will still be some give , or as linden ( Road Runner) commonly calls "jounce"

I also question him about the shocks overall travel... So basicly i said ...... If i ran NO stop at all would i blow the seals out and fuck the shock ?

I was told its not a good idea but .... The shock is designed to compress fully without a bump stop , so what would happen is the end of the shock would smash into the housing but it wouldnt effect the internals so to speak --- That is depending on how hard you smash them together
So all in all i guess you can in theory run the shock without a stop but you would want to make sure that something else is gonna bind / smash / crunch and not the shock.

Like i said its isnt suggested !!!!

Lastly i questioned him about the valving of the shock and running it in its last 50 - 60mm of travel.
My question was : Because the shock is running at its last bit of travel does this effect the feel / opperation of the shock because it is coming to the end of its travel?
( some shocks will become alot firmer in at the end of their travel )

His answer to that was : My particular model of shock ( the P36 ) has a constant valving. In other words.... No matter how far the shock is compressed it will be the same rate throughout its travel.


Hope this answers some of those questions im sure alot of people and not only myself have had