Importance Of Sprung To Unsprung Ratio

[Batfink 201]

True but we could be looking at simply driving style and preference. It could be simply too low at the rear and is hitting the bumpstops

[Castorkid 11 1 Cars]

Thanks all

Have actually got some 600/300 306 tarmac Bilstein dampers on the rear at the moment which I like. The rear is much softer and more compliant than the front using my crude bouncing on the car test. The front is absolutely rock solid and the most functioning area of the suspension at the front is the side wall of the tyres. The rear is lower than the front, which I plan on correcting but I'm def not hitting the bump stops.

 

What do you think the effect of using high quality coilovers on the front (Proflex or AST) and standard spring rates would be??

[welshpug 1,626]

are you sure its not leaning on the stops?

 

got a pic of the ride height?

 

I doubt you will get a damper like proflex or ast running a standard spring rate without a totally custom set, the lower spring rate necessitates a larger diameter spring to allow for travel, a small dia spring will just go coilbound.

 

damping though and its consistency will be excellent, as it happens I run AST's on my ZX with 185 lb springs, purely as that's what came on them, but they worked nicely with the standard 21mm rears and a standard 24mm arb (actual rates will be slightly less than 205 due to the length) though a heavier car, a friend described it a a grown up 205!

[Castorkid 11 1 Cars]

Thanks Mei

Are there any other lowering spring/damper set ups which would be softer than my current bilstein-eibach combo?

[welshpug 1,626]

I wouldn’t go softer, but standard would be softer

[Castorkid 11 1 Cars]

Can you still buy new standard dampers and springs from Peugeot or do you need to go for an aftermarket equivalent?

[Castorkid 11 1 Cars]

Can you use a B4 or B6 Bilstein front damper with the Eibach 30mm lowering spring?

[Cameron 16]

Running the standard spring rate with a lowered ride height will be terrible, I guarantee it! Think about how your suspension's travel is defined: you have a Max Jounce position determined by the upper spring seat, the Jounce bumper ("bump stop") block height (height at which it compresses solid) and the strut body length. This does not change as you change springs, so by lowering the ride height you are reducing the distance between your ride height and Max Jounce position i.e. reducing Jounce travel. If you take 30mm out of your Jounce travel then you're 30mm closer to the point at which your suspension is solid, so you need to increase the spring rate to avoid running out of travel all the time. If you want the standard spring rate then you'll need to keep the standard ride height, similarly if you lower the ride height you need a stiffer spring rate.

[EdCherry 34 1 Cars]

Unless you have 30mm of unused travel to begin with...

[Cameron 16]

Which you don't..

 

Edit: The reason I say that is a 2g bump (experienced often) will fully compress the spring and most of the JB too.

Edited December 29, 2012 by Cameron

[Batfink 201]

Can you use a B4 or B6 Bilstein front damper with the Eibach 30mm lowering spring?

Yes both are full length dampers. The b4 is own damping, the b6 30% uprated

[kyepan 291]

I think we need to go back to Cameron first post, it's worth exploring in more detail before thinking about changing the suspension setup. imagine removing some of the suspension, removing the standard seats and putting in buckets is basically replacing soft compliant standard seats with perhaps some travel in them for tight wedged in no movement buckets..it's going to turn up the volume on all the signals from the chassis to your ass. those will go up through your body and down your arms, messing up your fine motor control on the wheel, add some nervous tension in from the new sensations, and you've got the reason it's slower. what I'm saying is its not slower, you are slower because your getting jostled about in the seat.

 

 

try giving the wheel a lighter grip, move the seat a bit closer so your arms are relaxed, bent, and able to give the wheel a smidge more room to react to the road surface.

 

 

relaxed and alert is fast, smooth is fast, smooth is safe.

 

Reducing the rotating mass will reduce the gyroscopic effects and make the steering feel lighter. Light wheels are a quick solution. Lighter discs that use alloy bells are a more expensive second option. But as above, make sure your performing at your best before changing the hardware

Edited December 29, 2012 by kyepan

[Cameron 16]

Amen.

[Castorkid 11 1 Cars]

Dear all,

Thanks again for all your input. Here's a pic of my 205 as it is currently set up. Its sat on a slight downwards slope. After reading all of the responses, I think that I'll wait and review the situation once the 21mm bars have been put in and the rear has been raised to match the front. Might try putting my old challenge rear dampers back in (currently have a pair of 600/300 in at the moment).

 

Perhaps when the rear is raised, it will put more weight over the front wheels improving the understeer and reducing the 'bobbiness'.

 

If all this fails, I might just go back to standard ride height and try softer settings all round.

 

Still fancy some lighter alloys and callipers though!

[Cameron 16]

That doesn't look bad at all.

[Castorkid 11 1 Cars]

I previously had a 25mm rear ARB in it and had the rear a little higher than the front and the car felt oversteery. I've put a 23mm rear ARB in and lowered the rear and now I have the opposite problem. I've been advised that my newly manufactured 22mm rear torsion bars can be more of an unknown entity than the PTS originals. So, I've sourced some original PTS 21mm rear bars and plan to fit those. Do you think if I raise the rear a bit aswell it will eliminate the understeer i'm getting? Given the front is on eibach 30mm lowering springs with bilstein challenge dampers what rear ride height do you think I should be aiming for to make the handling more neutral?

[Cameron 16]

Raising the rear isn't going to have any effect on over / understeer, I don't know where that idea has come from.. unless you lower it to the point where you run on the bump stops. The amount of longitudinal weight transfer you get from adjusting the rear ride height is minimal (you'd get more by sliding your seat a few notches) so that isn't going to be the cause, and either way if that had a large enough effect to make a difference, you'd want to put more weight on the rear rather than the front.

 

Your setup change speaks volumes, 2mm of thickness on the ARB may not sound significant but it does actually count for quite a lot in terms of stiffness, so it's not surprising you saw a change to understeer. Unfortunately a stiff rear end is the way to get a FWD car to grip and handle, so if a 25mm ARB was too much and a 23mm too little with 21mm TB's.. fit 22mm or 23mm TB's with your 23mm ARB and see how that feels.

 

Are your front dampers adjustable?

[Castorkid 11 1 Cars]

Thanks for the reply

Im using 22mm torsion bars at the moment and the only changes thus far are a drop from a 25mm rear ARB to 23mm ARB and a reduction in the rear ride height, but as advised, im due to swap to 21mm PTS bars as they are a more 'known' entity in rate terms. The front end is bilstein challenge dampers so non-adjustable.

 

Amazing that a 2mm change in rear ARB would have such an effect. I've read about the Skip Brown phase 2 set and thought if I copy that, i'll be closer to the mark.

 

Still think the way forward is to look at the unsprung to sprung weight ratio as previously discussed. I fully expect that now i've put the interior back in and piled on a bit of success ballast over Christmas that the car will perform even better!!

 

Cheers

 

Nick

[Anthony 1,000]

Am I reading it correctly that you're running 600/300 inserts and Eibach springs? That sounds massively over-damped to me, and I would think that refitting the softer (but still fairly highly damped for a road car) Challenge inserts in would be far more appropriate for B-road use.

[Castorkid 11 1 Cars]

Anthony

I'm running 600/300 dampers on the rear. On the front its challenge dampers and eibachs. Rear feels way softer to the bounce test than the front.

Edited December 30, 2012 by Castorkid

[welshpug 1,626]

It shouldnt be, that may be part of the problem, i have 205 gravel bilsteins and it doesnt bounce.

[Cameron 16]

Thanks for the reply

Im using 22mm torsion bars at the moment and the only changes thus far are a drop from a 25mm rear ARB to 23mm ARB and a reduction in the rear ride height, but as advised, im due to swap to 21mm PTS bars as they are a more 'known' entity in rate terms. The front end is bilstein challenge dampers so non-adjustable.

 

Amazing that a 2mm change in rear ARB would have such an effect. I've read about the Skip Brown phase 2 set and thought if I copy that, i'll be closer to the mark.

 

Still think the way forward is to look at the unsprung to sprung weight ratio as previously discussed. I fully expect that now i've put the interior back in and piled on a bit of success ballast over Christmas that the car will perform even better!!

 

Cheers

 

Nick

 

I don't know why you've got this idea that sprung vs unsprung mass ratio is a critical factor, but I would forget it as quickly as you Googled it.

 

From a quick search it's clear that this idea is tossed around a lot by Internet Dynamicists, and I think you've read far too much into the effect it may have. Taking 40kg or so out of the sprung mass really isn't enough to have a significant degradation in ride. Notice I say ride, not handling, as that's the biggest effect this ratio has on dynamics.

 

Adding weight is never a way to get a car to perform better.. you ever notice F1 cars get faster and faster as a race goes on and they burn off the heavy fuel load?

[Castorkid 11 1 Cars]

Everywhere I read it says raising the rear and lowering the front end will reduce turn in understeer.

This makes sense to me as surely by making these changes, it places more weight over the front wheels. The more weight there is placed over the springs, the more compressive force is available, and the harder it is for vertical wheel movement to overcome the inertia of the car and lose contact with the road.

 

As Allan mentioned, 'it's never going to glide down a uneven pot holed road like a mk 5 golf etc, its what makes them fun ;)'

 

Is that partly because a Mk5 golf weighs 1400kg and has a similar unsprung weight to a 205?

[brumster 135 1 Cars]

Just on the topic title a little, I remember many moons ago I built a GTM kit car - original spec for this was the original 13" Rover Metro rims but of course those didn't look cool enough in the day so I made the rather poor judgement of putting it on 15's (well, it would look well wicked wouldn't it :] )....

 

I never drove it on 13" rims so basically how it felt, rode and handled was how I thought they all were - and drove around on them for years. Hulking great 15" TSW rims and some ridiculously low profile tyre (40 I think).

 

Then one day for a TV shoot I put it back on some borrowed 13" rims and fook me sideways what an improvement. Not only had the steering and general ride improved shed loads (probably more down to reduction in tyre width and increase in profile than unsprung weight) but the acceleration - and particularly the braking - was NOTICEABLY better. So much so that I ditched the 15's like a hot potatoe and bought some middle-ground 14" rims.

 

I now pay more attention to the weight of things I'm bolting onto cars

[Batfink 201]

Make sure the dampers are working (it sounds like your rears are dead), check the ride height at the rear and make sure there is enough suspension movement before hitting the bumpstops, then drive the car again. Then you've got a proper evaluation point.

 

Theres no real ratio needed for unsprung weight, remove as much as possible. Its not going to affect the balance of the car though (front to rear). Its not going to mask duff suspension either.