andyd
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| posted on 24/3/03 at 12:54 PM |
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Shock/Spring length
Does anyone know if it's really bad news if when a shock is at it's maximum travel the spring is loose.
Reason for asking is that we've got 12" max travel shocks (AVO) and 8" springs on the front. When the ride height is ok, the shock
isn't at it's maximum travel. If the wheel then deflects downward (ie into a pothole or after launching over a hump backed bridge  )
surely the shock will extend to it's maximum (in extreme cases) but the spring will not keep up.
This then means that the spring will for a moment be free floating and when the wheel then returns to the normal ride height, the spring may not be in
the correct position. I'm worried that this may be a) dangerous and b) may knacker the spring seats top and bottom.
Any opinions or am I worrying too much?
Andy
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JohnFol
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| posted on 24/3/03 at 01:56 PM |
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The spring is pushing the shock as far apart as possible. Therefore the spring needs to be compresed to be fitted onto the shock. This is irrespective
of being fitted to the car.
So if you hit a pot hole, you would need something actually trying to pull the shock apart before the spring would move.
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dozracing
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| posted on 25/3/03 at 01:35 PM |
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Hi ,
I believe for SVA you must have a shock with spring load at all extremes of travel.
But as far as the operation of the shock is concerned you should have no worries about it being loose in full droop. Most race cars are like this.
All that is pulling the shock is the weight of the wheel and when you hit a pot hole things happen so fast it is unlikely the wheel weight will pull
the shock apart against the rebound damping enough to unseat the spring anyway.
Kind regards,
Darren
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JohnFol
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| posted on 25/3/03 at 01:58 PM |
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Feel free to correct me but the maximum extent of the shock doesn't suddenly become longer just because the shock is fitted to the car . . . . .
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andyd
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| posted on 25/3/03 at 06:06 PM |
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Darren,
As I need to pass the SVA then I do have to have the spring load throughout the travel if that's what's required.
John,
Forgive me for being dim but... what?
I don't understand your last post. Are you questioning Darren's statement about the rebound damping?
For what it's worth I'd feel happier if the spring was rigid and if SVA requires it anyway then I have no choice.
Since my original post I've adjusted my rear spring seats so that the spring is under pressure when the wheel is off the ground and when lowered
the spring/shock compress under the weight nicely to give me the correct ride height (trailing arms parallel to the ground). However the fronts are
still too high. I think the only cure for this is to buy lesser poundage springs. The ones Luego supplied are 300lb which seem too much for the
Fireblade engine. The only other options I can think of would be to buy shorter shocks so the spring is more compressed to start with or the lighter
springs maybe 250lb so that the weight of the front end pushes them down the the right ride height.
Any thoughts on a solve for this are as usual gratefully received.
Andy
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dozracing
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| posted on 25/3/03 at 06:22 PM |
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Hi Andy,
It woul dbe worth checking the SVA regs, as i am not building mine for the road i am only recalling that from other peoples comments over the
years.
If you need longer and softer springs i have 275 and 175 springs in stock that are longer. Also if you need the correct length shock i sell a kit for
£220 for 4 with springs, and i often split them into pairs for people in your position.
You might also consider using helper springs, which are very soft spring made from flat coils that are only there to prevent your type of problem. I
can get hold of these for you if you need them, but, i will have to check on spring diameters first. I guess yours are 1.9" ID?
Darren
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Spyderman
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 posted on 25/3/03 at 08:50 PM |
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quote:
Originally posted by andyd
Does anyone know if it's really bad news if when a shock is at it's maximum travel the spring is loose.
Reason for asking is that we've got 12" max travel shocks (AVO) and 8" springs on the front. When the ride height is ok, the shock
isn't at it's maximum travel. If the wheel then deflects downward (ie into a pothole or after launching over a hump backed bridge )
surely the shock will extend to it's maximum (in extreme cases) but the spring will not keep up.
This then means that the spring will for a moment be free floating and when the wheel then returns to the normal ride height, the spring may not be in
the correct position. I'm worried that this may be a) dangerous and b) may knacker the spring seats top and bottom.
Any opinions or am I worrying too much?
Have you checked to see how much free space there is when shock is extended?
If spring is coming off it's seat then yes it could be considered dangerous. If there is only a few mm of free space then you might get away
with it. Otherwise you could always put a spacer onto the seat to pack it out.
Terry
Spyderman
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stephen_gusterson
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| posted on 25/3/03 at 11:04 PM |
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quote:
Originally posted by JohnFol
Feel free to correct me but the maximum extent of the shock doesn't suddenly become longer just because the shock is fitted to the car . . . . .
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I think that what he is saying is that when the suspension is loaded by the weight of the car, the spring is ok. However, when the car would be jacked
up allowing max droop - like hitting a hole - the spring will rattle around loose.......
sounds bad to me.
atb
steve
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JohnFol
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| posted on 26/3/03 at 09:28 AM |
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Imagine a shock with no spring fitted. Now pull the shock as far apart as it will go. It will hit a mechanical limit (bump stop or whatever
it's called). Measure the distance between the top and bottom spring mounts. Measure the height of the sping.
For me the spring is the taller of the 2, therefor even when the wheel has hit a pot hole, the spring is still being held in compression.
Might be a different design, but that was my concern. .
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Fast Westie
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| posted on 26/3/03 at 10:58 AM |
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quote:
Originally posted by andyd
Does anyone know if it's really bad news if when a shock is at it's maximum travel the spring is loose.
Yes it is, the top spring mount is only clipped in place and held by the spring pressure. If the suspension goes into full droop the top mount could
come loose and fall out. This would be the reasoning behind the SVA regs I would think.
You should be alright with 12" shocks and 8" springs. Have you tried winding up the spring seats?
The car in front is a Westfield
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andyd
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| posted on 26/3/03 at 12:12 PM |
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John,
Thanks, I understand what you meant now.
FastWestie,
Yes we have adjustable springs seats but this will a) make the spring "harder" which will mean that the weight of the front end will not
compress hardly at all and b) it will not lower the ride height which is really what we are after.
You're right about the top spring seat. Obvious really but I didn't think of that
Andy
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dozracing
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| posted on 26/3/03 at 01:42 PM |
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The only way to achieve what you want is a longer spring or shorter shock.
If you wind up the spring platform this will not stiffen the spring! It will add preload and hence raise the ride height, its different to stiffening
the spring. It will of course stop it coming of its platform and one cheat will be to run the higher ride height for SVA and then lower it again
after.
You really need not worry about unseating the spring in operation. Like i said most race cars will run in this condition. If you run over a pot hole,
the spring load cannot possibly push the shock to the limits of travel against the rebound damping force fast enough for it to unseat the spring,
before the wheel is back out of the pot hole or the chassis has caught up with the wheel in the pot hole. Believe me it just doesn't happen.
Darren
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andyd
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| posted on 26/3/03 at 06:19 PM |
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quote:
Originally posted by dozracing
If you run over a pot hole, the spring load cannot possibly push the shock to the limits of travel against the rebound damping force fast enough for
it to unseat the spring, before the wheel is back out of the pot hole or the chassis has caught up with the wheel in the pot hole. Believe me it just
doesn't happen.
Darren
What about over a humped back bridge when the car's off the deck for seconds? (Just kidding, btw).
Thanks for the info Darren. Incidentally, the shocks/springs you sell. Can you give me a breakdown of the lengths etc? As I have 12" shocks
and 8" 300lb springs what springs could you sell me that would lower my ride height by say 2"? You can email off forum if you like. Just
take out the trash bit.
Oh well you could but the email details seem to have gone from my profile. Just U2U me if you don't want to post here.
[Edited on 26/3/2003 by andyd]
Andy
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Rorty
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| posted on 27/3/03 at 03:53 AM |
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andyd:
quote:
Yes we have adjustable springs seats but this will a) make the spring "harder"
I wasn't going to put my oar in, as Darren has effectively answered the query, but I would like to expand on something he said.
A lot of people are under the misconception that winding up the spring seat will stiffen the suspension. It doesn't! All it does is change the
amount of preload, causing the car to rise.
The rate of a linear spring remains constant under all loads. In other words, a 200 lb/in spring requires 200 lbs to compress it one inch. It will
require a further 200 lbs to compress it another inch, and so on.
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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dozracing
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| posted on 28/3/03 at 02:17 PM |
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I have 12" front shocks, with 8 or 9 inch springs, adjustable ride height 275lb/in rate
I have 11.5" rear shocks with 7 or 8" 175lb/in springs. I can also get practically any spring rate you desire for a good price (depends on
rate).
Shock kit (4 off with springs) is £220
See website www.gtscougar.freeserve.co.uk for full details, or email off list doz@gtscougar.freeserve.co.uk
Kind regards,
Darren
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andyd
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| posted on 28/3/03 at 03:07 PM |
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Thanks for all the input.
Rorty, thanks for explaining the spring "hardness" thing. I didn't realise that these springs are linear.
Darren, we are going to wait until we've got all the weight that we'llhave over the front in before making the change. I'll maybe
contact you then once we've decided how low we need to go. Thanks.
Andy
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