Suspension rate questions

[MWP]

Hi all,

Ok, i just bought myself some nice new Koni racing inserts to go in my RT132 struts.
They have a full stroke distance of 155mm.
I thought this would be enough when i ordered, now im not so sure...

Installed in the struts im measuring 100mm before hitting the bumpstop, then another 40mm until hard stop.

Some numbers (my approx)...
RA28 weight: 1150kg
F/R split: 55/45 (632kg/517kg)
Front springs: 300lb/in (=5.35kg/mm)

So, at rest, the suspension will sag 59mm (632/2/5.35).

This means when installed in the car, ill only have 40mm (214kg/corner) of suspension travel until i hit the bumpstop.

Will this be enough?
Will hard cornering + hitting an avg sized bump put me well into the bumpstops?
Im not sure how to calculate these bits...

Obviously i dont want to be riding on the bumpstops during cornering, and still have a little travel left for soaking up small bumps before hitting the bumpstops.

Thanks for any advice.

[oldcorollas]

soudns about right... ar ethe springs compressed in the strut when at full droop? or they just reach their free length? or they are not captive? that will make difference..

i guess you are finding out why they are called "racing" inserts deigned for when you only need sayy.. 90mm bump and 60mm droop
to be honest , having 40mm bump stops on a shock with 155mm stroke seems silly.. 1/4 of the stroke is taken up by the bump stop?

can you get shocks with longer stroke?

[MWP]

Yeah, the bumpstops are quite large... i could cut them down quite easily.
Doing that of course also means hitting full travel is a lot more harsh.

That figure for the spring sag is with the spring just under tension (so just captive) with no weight.

This is the longest stroke unit they make in the 8611 series (replacement for the 8610 series).

[MWP]

For reference:


... thats fully extended.

[pisso001]

I have no idea about this stuff, just subscribing to learn..

They are beautiful. ^^^^

thanks,

Chris.

[oldcorollas]

well.. typically you want something like 60/40 bump/rebound (or 70/30 or whatever)... and that should be disregarding the bumpstop.

once you hit bumpstop, your suspension effectively binds, and if you are cornering, you will more than likely lose traction as the tyre bounces...

on the track, short stroke is fine, but on the road.. is not so good.

the bumpstop is there to stop the shock bottoming out. if the stop is solid, maybe cut it down to 20mm? so that it does only that... stop the shock just before it bottoms out... ie.. cut it to 20mm before bottoming out.. hopefully the increased rate from the stop prvents the shock destroying itself.

you also don7t want it to top out every time you go over a bump.. that will also kill the shock eventually.

so... work out yout 60/40 or 70/30 position, and set that as your ride height (or adjust the shock in the strut body to that position).. and that is all you can do for it except fro drive slowly and carefull like a granny on roads that have any form of bump or pothole.... (and annoy those in cars with suspension that works properly )
heh heh

[The Real Roadrunner]

touchee oc the bumpstop will act as a variable rate spring my good man.

shorten the stop to give you 50mm bump b4 it hits (at ride) and you will be sweet.

if this is for the from of the v8/28 id go for 350-450lb springs but thats just me.

cheers
linden

[TA23 Racer]

The bump rubber in the photo is whats called a silasto it's tapered on the inside & outside giving a rising rate bump rubber very usefull, so the suspension doesn't go from 300 lbs to nothing in a mm. I'd try it out first then maybe if bump travel is a prob shorten the bump rubber from the top of it.
Is the 300 lb for road use? which I think would be OK. I have a TA23 IPRA Celica which is 1009kg, I use between 375lb & 450 lb on the front which feels very harsh on the road.
Nicely done strut leg by the way.

Cheers Dave.

[MWP]

Whew, thanks guys... hearing that makes me feel rather relieved.

Yeah, the Koni bumpstops are very nice looking units.
Ive got 4, so ill have a spare set if i cut a pair down too far.

Yup for the 1UZ RA28, road use with the occasional track-day/hill-climb.
300's on the front, and i think ill try 220's on the back.

[The Real Roadrunner]

Is the 300 lb for road use? which I think would be OK. I have a TA23 IPRA Celica which is 1009kg, I use between 375lb & 450 lb on the front which feels very harsh on the road.
Cheers Dave.

harshness is in the valving not the spring.
spring rate just dictates how much force is required to move the spring by a certain amount.

i put 475lb springs in a daily driven 1j cressy with koni yellows for a commy and they were
great to drive on.

not harsh but firm once adjusted, didnt bottom out and was super responsive to drive.
yes there is a big weight difference between the 2 cars but the 1uz aint a light motor.

cheers
linden

[amichie]

Have you considered the spring preload??

[30psi 4agte]

How did you end up going with this ?

[30psi 4agte]

I have finally had a chance to get my car on the ground over the past few days...... and it turns out im in a similar boat.

I have 40mm of travel to the bump stop... On the bilstein the bump stop is about 3" long.....so it looks like ill be cutting it down 25mm to give me 65mm travel before the bump stop engages.

The rear only has 60mm of travel too

But the car looks tuffer than ANY corty i have EVER seen !!!------ will have fresh pics up in my rides thread soon

[MWP]

My RA28 that these struts are going into is still a long way from being on the road.
I wont know what they are like until it is

If its not an everyday car, and you can put up with a harsh ride (hard springs = less travel = doesnt bottom out), itll be fine.

Ill be waiting for those photos

[30psi 4agte]

I have been doing some research and apparently shortening the stops 25mm will have no drastic consequences.

I have also read that it wont void warranty either but im yet to confirm this. --- Ill have to wait to the 10th of jan to contact bilstein directly to get the low down..

Shortening the stop is a common practice for the bmw guys. I have read that even with std springs and the recommended bilstein insert they hit the stop quite easily..

The is a heap of info out there about those guys shortening stops..


Food for thought..

P.S MERRY CHRISTMAS BITCHES !!

[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