Ride height & spring rates

Ride height & spring rates

Author
Discussion

gizzardio

Original Poster:

210 posts

153 months

Thursday 29th December 2016
quotequote all
Hi

Quick question. I am thinking of increasing my spring rates but I'm conscious that increasing the rate has an impact on ride height due to static load.

If I understand my physics right, if I increased from 300 to 400 lbs/in, then if I kept the spring length the same, it would only deflect to 0.75 (300/400) of the original which means if I had a 9" spring originally, then I would need a 0.75 x 9" = 6.75" spring to account for the increase rate.

Is this right?

I need to consider my spring seats, which are adjustable, to make sure they can crank down another nearly 2" though.

Also, I take it that buying the same length and then crushing the spring 2" using the adjustable spring seat isn't a good idea because the spring will fully compact under driving conditions as its already been squashed 2" before a load is applied.

See the image to see what I'm trying to say if its not clear.


phillpot

17,105 posts

182 months

Thursday 29th December 2016
quotequote all
gizzardio said:
Is this right?
Can't explain the mathematics of it but I don't think so.


take a look at the suspension wiki, lots of people using 400+ springs without issue and I doubt they are 6 or 7" long, mine certainly aren't.

GreenV8S

30,150 posts

283 months

Thursday 29th December 2016
quotequote all
The springs have a certain load on them which is determined by the weight of the car and the geometry of the suspension. For the sake of argument let's say the spring load is 1000 lbs.

The 300 lb/in spring compresses by 1000/300 inches, call it 3.3".
The 400 lb/in spring compresses by 1000/400 inches, call it 2.5".

If you leave the spring seat the same and the two springs were the same length when unloaded, then the stiffer spring would be about 0.8" longer at normal ride height. This means you'd need to adjust the spring seat down by about 0.8" to get back to the original ride height.

Note that the stiffer spring will also need very different damping rates and the general increase in stiffness will show up any deficiencies in the quality or condition of your dampers. You don't say what dampers you have, but some aftermarket adjustable dampers behave quite poorly at the extremes of their adjustment range and some are only adjustable in rebound, leaving some really unpleasant characteristics when you stiffen them up. At this sort of spring rate you're really going to need some good quality dampers.

You don't mention which springs you're thinking about changing. The front and rear suspension need to be altered together to maintain the ride and handling balance of the car but they are typically NOT the same spring rate or damper rate front/rear.

Changing suspension components and settings is very easy to do in terms of wielding the spanners but involves a lot of knowledge and experience to specify a setup to give the handling and ride characteristics you want. No offense meant, but from your original post I'm not sure you understand it well enough to design your own suspension upgrade. Have you taken the specification from somebody else?

Edited by GreenV8S on Thursday 29th December 15:06

magpies

5,129 posts

181 months

Thursday 29th December 2016
quotequote all
Your calculations are not correct - you will notice that the springs operate at an angle and not vertically, they are also some distance between the pivot points and the wheel hub - both of these affect the spring length / rate / ride height. Small adjustments at the damper will give larger movement at the wheel.

Best way would be to try adjusting what you have - At the front (cos it is the easiest) count the number of threads available below the seat and the ride height, spin the seat down say 5 threads on both dampers, measure the new ride height and the 5 thread distance and see what the ratio is. Jack up and return to original position.

Looking at the suspension wiki you will notice that the ride height should be set slightly nose down at approx 10mm lower at the front. These measurements are taken at the front and rear outer corners of the chassis outriggers i.e just behind the front wheels and just in front of the rear wheels. Most people are setting front between 170 and 180 front and 180/190 rear.

Spring wise most are using 400+/- 50 front and 350+/- 25 rear at standard original length, the amount of threads being sufficient to adjust the ride to the figures above.

You have not said which dampers you are looking at fitting - again different ones available and various quality and adjustabilities.

All the above is subjective and some experimenting may be needed to obtain YOUR ideal or as close as you can get.


Edited by magpies on Thursday 29th December 15:16


Edited by magpies on Thursday 29th December 16:13

phillpot

17,105 posts

182 months

Thursday 29th December 2016
quotequote all
magpies said:
Spring wise most are using 400+/- 50 front and 350+/- 25 rear
wink

gizzardio

Original Poster:

210 posts

153 months

Thursday 29th December 2016
quotequote all
Hi

Thanks. Yes I see that I got the maths right but the application wrong. If for example I had 250kg in the corner, then that is 550 lbs and so I can work out deflection in a 300 and a 400 lbs spring and that's the difference.

As has been said, its not exact due to the various angles in the suspension set up so its only applicable in a linear vertical situation.

I have AVO adjustable dampers (apparently bump and rebound in the one adjuster). I can probably get advice from the manufacturer on the limits of spring rates to give me an idea on this.

It was the suspension wiki that I was looking at that made me think to increase spring stiffness based on comments and settings in there.

I suppose that's why I'm asking here as it'd be good to hear what happened to others when they changed their setup and what else to watch for. I hope I don't have to do a full geometry set up as if all returns to the same ride height wouldn't that mean camber, toe in/out, etc are unchanged?

If I do this, I'm changing both front and rear to probably 400 / 375 F/R.




magpies

5,129 posts

181 months

Thursday 29th December 2016
quotequote all
phillpot said:
magpies said:
Spring wise most are using 400+/- 50 front and 350+/- 25 rear
wink
oooops biggrinidea

magpies

5,129 posts

181 months

Thursday 29th December 2016
quotequote all
magpies said:
phillpot said:
magpies said:
Spring wise most are using 400+/- 50 front and 350+/- 25 rear
wink
oooops biggrinidea
Just checking to see if any-one actually reads my posts - Step forward Phillpot readthumbup

DamianS3

1,803 posts

181 months

Friday 30th December 2016
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We read them fella... smile

Personally I would advise not going too hard on the S I started with 375 rears and it was very harsh and jumpy down at 300 now and I find it much more planted over Yorkshire roads.

Damian S3

magpies

5,129 posts

181 months

Friday 30th December 2016
quotequote all
a good person to ask would probably? be Alan461 as he has not only an S but also passengered in a number of other S's (including mine) on various run outs. So he (if he wants) could confirm how some cars ride.

Alan461

853 posts

130 months

Friday 30th December 2016
quotequote all
Lol. sorry, no use asking me, not something on which I could give useful comment.
Most of the S series I've been in feel planted but I couldn't identify whyconfused
375/450 f/r btw
This might help;
http://www.pistonheads.com/gassing/topic.asp?h=0&a...

magpies

5,129 posts

181 months

Friday 30th December 2016
quotequote all
I think ! that most people stiffen up their car is to stop it from bottoming out on classic UK B and C roads

The Big G

990 posts

167 months

Tuesday 3rd January 2017
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Think I'm running 500 at the front and 400 at the rear. Gaz gold fitted and all springs are the same length of 8 inches if I remember corrrectly. It doesn't ride sooothly but is really secure and planted at speed. Was one of the best things I've done to mine, only changed them last year as I found out I had 275 on the front and just as soft on the rear. Is night and day on the handling front, wish I had done it a lot sooner. So much more planted now at speed.

I think I'm just round the corner from you, so you're welcome to see what it's like. If you're who I think you may be the. You may remember being followed rather noisily by me through the airport tunnels into wilmslow last summer.

gizzardio

Original Poster:

210 posts

153 months

Thursday 5th January 2017
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Hey there. Very kind offer of you. Yep I'm just nearby. I'll PM you on here and I'll come check out your setup if that's OK.


phillpot

17,105 posts

182 months

Friday 6th January 2017
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The Big G said:
all springs are the same length of 8 inches if I remember correctly.
Original springs are around 10-10.5" long

magpies

5,129 posts

181 months

Friday 6th January 2017
quotequote all
phillpot said:
The Big G said:
all springs are the same length of 8 inches if I remember correctly.
Original springs are around 10-10.5" long
probably 8" under stationary load and 10" when off the car and separated from the damperthumbup

GreenV8S

30,150 posts

283 months

Friday 6th January 2017
quotequote all
magpies said:
probably 8" under stationary load and 10" when off the car and separated from the damperthumbup
Aftermarket dampers with adjustable spring seats would probably require shorter springs than OEM.

greymrj

3,316 posts

203 months

Sunday 8th January 2017
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Just a couple of bits to add if I may.
I could not get any consistency with the original units. When they were all stripped it was pretty obvious that there were now small differences in spring length and much bigger differences in damping and that the adjusters on the Konis were no longer effective enough. I went for Gaz units as recommended by Gaz(I think the details of my set up are in the wiki, I cant remember!). I set them for correct ride height using a garage ramp.
1. Do not assume the outriggers are necessarily a good reference, check the chassis and the relative angle of the suspensions on both sides. My outriggers are a good 1cm out.
2. First time I did it I forgot one crucial thing...set it with a full tank and someone in the drivers seat! Errm..just a bit of a difference!
3. That will give you a good starting reference but each of these cars are different (The S1 is lower and has different rear swing arms which makes this even more crucial), each of us likes a slightly different mix of roadholding/compliance, and many of us have different wheel/tyres which affects ride height and compliance.
I like the front stiffer than the back (both for 'feel' and because my back isnt good) that means I have had to add a little rear ride height to get the compliance without bottoming out too much. The S1 will always be a more difficult compromise that is why I have sacrifical plates on my exhaust!!
4. Add a heavy passenger and your settings are now out! Mine is now set as best I can for use by my partner and I. With no passenger or a heavy passenger my driving has to compensate a little.

The Big G

990 posts

167 months

Wednesday 18th January 2017
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Was great meeting you the other day. Hope you manage to get it sorted out over the winter months.

Was looking on eBay and wheels popped into my mind. The eight spokes are difficult to find, but imolas such as these were fitted to some s4s' and V8s'. This would give your car a more stock look instead of slot mags while waiting for a set of eight spokes to come up on the market.

https://www.ebay.co.uk/itm/142246605309

thumbup

phillpot

17,105 posts

182 months

Thursday 19th January 2017
quotequote all
greymrj said:
With no passenger or a heavy passenger my driving has to compensate a little.
Longers, think my compensation was a bit out at the
Mulsanne chicane? .. wink