Shorter & uprated Springs

[Monty]

I found that the factory damping knob position doesn't go hard enough to cope with the 20% uprated springs. The ride is quite good now but firm.

Candles.

Think thats more to do with that the uprated front springs you have, as there the same length as the stock ones which only means you need to lower the damper seat to keep the same ride height, so really you need shorter springs when uping the rating and thats why you need to turn the dampers seetings to right up to try and compansate, hence why i started this thread

[Nige]

Candles, do you know that according to the protech website you can adjust the the damping range and then use the adjustment knob to fine tune within the selected range, ie your damping options are not limited to the 13 clicks of adjustment (or however many it is) on the knob alone? I'll find the link when I get home and post it. Is the damping insufficient in bump or rebound (or both)?

Edit: Link http://www.protechshocks.co.uk/products.htm see para 8. It's this feature that makes the pro-tech dampers attractive to me.

[Candles]

Yes, thanks for that Nige, I had seen it in another thread and was planning to give it a go. I noticed the lack of damping mainly on the rebound: Over a certain type of bump the car would overshoot the neutral point a couple of times. It felt like a ship!

[Nige]

Think thats more to do with that the uprated front springs you have, as there the same length as the stock ones which only means you need to lower the damper seat to keep the same ride height, so really you need shorter springs when uping the rating and thats why you need to turn the dampers seetings to right up to try and compansate, hence why i started this thread

I'm struggling a bit with the logic of that Monty . There are real experts around here who will put me right but I can't see why the spring length is going to impact on the ability of the damper to control it? I can see why you would want a shorter spring if it were stronger, in order to maintain the same ride height as the static weight on the spring won't have changed so a stronger spring will be less compressed by that weight.

[chrishewett]

Candles,
I have sent you a pm.
Chris

[Nige]

Chris, I'm very interested in the work you are doing with Andy in finding a setup for your car. I'm also interesteddin and grateful for all the good advice and thinking from F1 Lotus and Bob as well. Keep us informed how your developments go please and I hope we will be able to move this on with benefit to all who want that little bit more.

Lincolnshire is a good way from me now but being born and brought up there it seems I might well have a good reason for a return visit .

[Specky]

This is a crakin little disscusion... I like this one Monty...

I like the idea of Niges doulbe shock..(Sound brillant in theory, but so does communism)

But one things strikes me... It's candles.... (Not that sort of strike)

Here's why...and it a laymans view as I know bugger all on suspension set ups

All systems have there pros and cons...

All cars are different...

All driving styles are different...

All tracks are different...

There are just to many variables...

SO candles with his more than adquate adjustable set up seems the way forward...It just seems sensible...



Oh well...What do I know...

TTFN

[Monty]

Think thats more to do with that the uprated front springs you have, as there the same length as the stock ones which only means you need to lower the damper seat to keep the same ride height, so really you need shorter springs when uping the rating and thats why you need to turn the dampers seetings to right up to try and compansate, hence why i started this thread

I'm struggling a bit with the logic of that Monty . There are real experts around here who will put me right but I can't see why the spring length is going to impact on the ability of the damper to control it? I can see why you would want a shorter spring if it were stronger, in order to maintain the same ride height as the static weight on the spring won't have changed so a stronger spring will be less compressed by that weight.

Not sure what you mean Nige, but i`ve got the Fed springs on the front with my AVO`s but because i had to lower the spring seats for a better ride height the spring is not under it`s normal compression so it was like being on a boat, so i had to turn the damper settings right up to compansate but IMHO opinion it`s the wrong to do things as the ride is very hard and get bump steer, moe than likely cause more understeer etc. I`ve got very little knowledge on this subject thats why i started this thread to get comments/views from the peeps with more brain power lol

When the elise lads do suspension upgrades there kit comes complete with damper & uprated spring and this is the route i`d like to take but it`s more difficult for us Elan`ers as we don`t know the stock spring ratings, so we need to know these figures before we can move on.

[dapinky]

It is my understanding that shocks should be married to specific springs (length/rate), and any change in any variable will have an effect on any other.

ie, if you fit stronger springs, to get the same ride height you need to lower the shock platform, or use shorter springs. But as the shock will have been designed (hopefully) for the original springs, either option will allow the stem of the shock to have a shorter range of movement than its maximum, which will have an effect on the amount of 'wallow' you get.

In simple terms, if a shock has a movement of say 5" with stock springs, by using shorter ones, you may have a full movement of only 4" (the same as if you drop the platform by an inch to compensate for extra strength in the spring).

This will have little effect on a road (usually), but on a track, with full body roll and high G forces, the movement of the shock could be the limiting factor???

As it gets to maximum extension/compression, there is no more absorbing of shocks, and just body roll - like if you had solid bars instad of hydraulics.

I'm not suggesting that any of the shocks in use would necessarily suffer from this phenominon, but i have completely different length units for the track dolly with short, hard springs (koni) than for the road car with medium length ones (spax) - and stupidly long thick bilsteins on the rally car.

When i put the Bilsteins on the track car with short springs I couldn't get the platforms high enough to allow the spring to touch the top mount on full travel on the rear axle, and found both springs popped out of their mountings at Llandow circuit with interesting results (a 'brown trouser' moment for my passenger more than me).

I'm not wanting to state this as fact (i'm not a dynamic engineer), but just as a few random thoughts.

[chrishewett]

Nige,
I will happily pass on all information to any interested parties. Andy has my car at the moment fitting a chip so I will ask him to investigate the corner weights while it is in the workshop. We can't go much further until I pick up the springs and dampers from dapinky.
By the way, when Andy fits the springs he has made up he will also have appropriate damper inserts made.
Chris

[Monty]

Dave, that makes sense to me but i certainly don`t know the answer, i suppose in the ideal world we need a full kit to be made were the springs and dampers are matched and made by the same company so there set up correctly but i didn`t really want to be spending money on a full setup as i`ve got AVO`s already and i seem to be having to do everything twice ie brakes, roll hoops and now suspension lol


Chris,
Yep keeps us all up todate on how things go, when you said

he will also have appropriate damper inserts made

are you talking about the rubber parts the spring sits on?

[Monty]

I think you will have trouble with just springs as the rates can be calulated but the ride height is dependant on the shocks as well or rather the position relative to the top mount.
It all gets a bit complex, OK you have a certain amount of adjustment in coil overs but that is not the full story if you increase the spring rate from say a 300lb/inch spring to say a 450lb/inch spring and the car from just off the ground to ride height will be higher with the stronger springs.
Reason: if the car corner weight is say 600lbs with the 300lb spring it will go down 2" but with the 450lb spring it will only go down 1.33" so the ride height will be raised by 0.67"
If the shock assembly complete with spring is 1" shorter this will lower the car by 1" and still retain any pre load on the spring, but again if you increase the spring rate the car will not drop by that 1"
If you were fitting uprated springs then the car needs to have shorter shocks as well.
If the load on the wheel is 600lbs and the preload on a 300lb/inch spring is 100lbs then the cars height from no load on the wheel (tyre just off the ground) to ride height will be a drop 1.67".
Do the same thing with a 450lb/inch spring and the car will drop 1.11"
Shorten the shocks and what ever you shorten the shocks by is the amount the car will be lowered if using the same spring.
If you lower the car by just winding the platforms down you come to a point where the spring is not under any load when the car is off the ground.
Thown in to this mix is the effect this has on the shocks travel.
If the shock has a travel of 6" and with the car at normal ride height sits at mid travel then you lower the car by 2" by just lowering the platforms the you effecivly reduce the shocks travel by 2" so you are then sitting with only 1" of travel before the shock bottoms out. This can in extreme cases break the suspension by forcing the top mount to explode out of the bonnet.
As I said all a bit complex.

Are your springs loose when a wheel is off the ground?

Not on the front but i do remember that when i was fitting the rear springs to the Avo damper that i could screw the top hat on without spring compressor and i`ve lowered it since IIRC the stock rear damper & spring wasn`t under much compression I`ve had the Avo`s on now for about 3 years and haven`t busted one yet

[chrishewett]

Dave, that makes sense to me but i certainly don`t know the answer, i suppose in the ideal world we need a full kit to be made were the springs and dampers are matched and made by the same company so there set up correctly but i didn`t really want to be spending money on a full setup as i`ve got AVO`s already and i seem to be having to do everything twice ie brakes, roll hoops and now suspension lol


Chris,
Yep keeps us all up todate on how things go, when you said

he will also have appropriate damper inserts made

are you talking about the rubber parts the spring sits on?

No, the length.

[bobbrown]

It is not unusal for stronger springs to reduce the amount of suspension travel required.
Take a 200lb/in spring and 6" of travel to get full compression you have to apply 1200lbs if you uprate the spring to say 300lb you only need 4" of compression to achieve the same loading.
It may be possible to shorten existing shocks by machining the top of the piston rod, this assumes that the top of the piston rod is removable.
Ok you reduce the travel but lets say you wanted to lower the car by 1" and increase the spring rates by 50% the top mount would need to be machined back 1.75" to get the car 1" lower while retaining the same preload on the spring.
At full compression the load would still be about the same as on the standard shock and in the same position.
Not ideal but a compromise.
In an ideal world the shocks length should be matched to springs and ride height required.
Spring lengths on coil overs are not so critical as the platform can be lowered to accept a longer spring or raised to accept a shorter one as long as the spring does not go coil bound and the spring rate is correct this should be fine.
Monty
Do the AVO's allow you to remove the top mount e.g. is it screwed on to the piston rod?

Bob

[Monty]

Do the AVO's allow you to remove the top mount e.g. is it screwed on to the piston rod?

Bob

Yep, as the AVO`s only come with the lower seat and you need to use the stock top.

[bobbrown]

As theses shocks use the standard top mounting they could be machined back to lower the car

Must say I am not that impressed with the locking arrangement of the lower spring carrier, a grub screw, not the best way as it tends to damage the thread!
Much better with 2 rings one locking against the other, then there is no chance of damaging the threads.
When I have used this type of spring mounting I have always applied grease to the threads and then wraped the whole threaded area in duck tape to keep the grit and dirt out of the threads other wise when you come to make any adjustments its a pig as you have to clean all the threads up or risk damage.
Also I would have prefered to see the lower spring carrier as one piece with the adjustment ring and a locking ring under that.

[Monty]

I agree the grub screws and not the best idea in the world but i don`t have trouble adjusting them. I like the seperate seat as its a has an outter ring for the spring to sit in to, but the hole IMHO is to large and don`t like the way it sits on the adjustment nut so i may have to get some very large washers made up to go between the nut and seat.

Found a pic of the Protecs on the wiki, and seem to have the one piece adjustment nut and seat but how does the spring stay central?

[dapinky]

Monty,

If you look at the photo from the back, you will see that the rings have a step in them to hold the spring in place (the photo shows the face which goes to the bottom of the shock).

There is no locking mechanism on the protechs, but i just used 2 sets of platforms, so they would lock together.

[bobbrown]

It is better to have the spring seat built into the adjustment ring not a seperate piece on top of the adjuster.

I hope the protech's are not an aluminium shock with an aluminium spring seat as that is a disaster waiting to happen!
I can see the thread getting a small pickup and it will drag its self round till you can turn it no more and you are forced to cut it off.
I have had to cut the rings off a Bilstien shock and that was a steel casing with an upside down shock in it (like you see on WRC cars)

[dapinky]

I hope the protech's are not an aluminium shock with an aluminium spring seat as that is a disaster waiting to happen!

Bob,

The spring seats are steel, not Aluminium.