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Spring rate/ length 
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Joined: Tue Oct 30, 2007 8:44 am
Posts: 625
Location: Chester le Street
Post Re: Spring rate/ length
We did all the sums at Newark and with the data Bob provided {Very accurate it was too.} we worked out that his Libra should be running with 200 lb/in front springs and 310 - 320 lb/in rears.

These would put the car at the upper end of the sports car wheel frequency range.

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Sun Jul 06, 2008 7:56 pm
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Post Re: Spring rate/ length
I've decided to update to 2.25" springs and new dampers -- which is it to be -- 450/250 as per original spec or follow your route with 300/200? Any chance of an update on your experience?


Mon Feb 16, 2009 6:54 pm
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Post Re: Spring rate/ length
I tried the 300/200, well 325/200 and didn't really like it. The ride was better but the handling wasn't as good. I run anti roll bars and found that with the rear set to it's softest setting it spun the inside rear much more readily. I have gone back to 425/250.

I am about to have a Z Cars rear fitted so I have given up messing with tham for now.


Mon Feb 16, 2009 9:33 pm
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Joined: Sat Sep 29, 2007 3:45 pm
Posts: 943
Location: SL2 4JW
GTM: Libra
Post Re: Spring rate/ length
Update

Yes luckily I did manage to find some time last year to play around with this.

Rover engine'd [1800VVC + PG1 box] car without anti-roll bars.

Took our calculations along to Andy Robinson Racing and his recommendation was 8" 300lb rear, 8" 200lb front.
I opted for 10" 300 rear 8" 200 front [because I already borrowed and tried 10" 300's] which was a mistake because I had trouble raising the front of the car.
Spoke to Andy [unequal length of spring causing problem ?] and he said to try 8" 225's on the front.
So I put my 8" 250lb's back on and hey presto problem gone.

I would now opt for 8"300lb rear, 8"225lb front [if I could afford to keep changing them].

Apparently GTM are now supplying 8"250lb rear, 8" 225lb front on a Honda engine'd car with anti-roll bars. If you have a Rover powered car without roll bars we are basically on our own.

Other factors you need to consider are front and rear Toe-in and Tyre pressure's.
Both play a major part in your set up.

At the end of the day it's all down to personal preference.

Good luck.

Bob S.

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Tue Feb 17, 2009 6:11 pm
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Joined: Thu Jan 16, 2014 5:54 pm
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Post Re: Spring rate/ length
My Honda b series libra has 9x250 front and 9x450 rears. I need to send the shocks away to gaz as two are leaking. Do people think these sprigs are OK for fast road use?


Sat Nov 12, 2016 10:55 am
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Joined: Tue Oct 30, 2007 8:44 am
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Location: Chester le Street
Post Re: Spring rate/ length
You will probably be close enough with the front springs but the rears are likely to be at too stiff.

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Sun Nov 13, 2016 9:43 pm
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Joined: Sun Feb 15, 2009 9:00 am
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Post Re: Spring rate/ length
octance wrote:
My Honda b series libra has 9x250 front and 9x450 rears. I need to send the shocks away to gaz as two are leaking. Do people think these sprigs are OK for fast road use?


My Honda B18C Libra is on 450 rear 250 front too, not sure on the lengths. A few people have ended up with the same or near as damn it and the Honda engine/box is a bit heavier so can't be a million miles away?

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Mon Nov 14, 2016 11:11 am
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Joined: Sun Oct 19, 2014 10:10 pm
Posts: 1038
Location: Bristol
GTM: Spyder
Post Re: Spring rate/ length
I'm on 425 rear, 250 front on my Spyder, both 8". TBH feels about right. Rides the bumps fine on the road with the dampers turned down a bit and firms up nicely on track with the dampers wound up. I've no ARBs though and I do get quite a bit of body roll on track even with the dampers set pretty hard so I'm thinking of going down the ARB route and maybe then softer rear might be in order. Mine is a VVC K series.


Mon Nov 14, 2016 6:55 pm
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Joined: Sat Oct 22, 2016 12:41 am
Posts: 126
Location: Brisbane Australia
GTM: Spyder
Post Re: Spring rate/ length
Just replaced the rear springs. Went from 450 lb 9" to 300 lb 10" (on GAZ dampers). Fronts are 250 lb. I wanted to soften the rear - the rear ARB was set full soft and I have still had it very sideways a few times - no spins yet though.
The length is good - fitted length is only about 5mm different to before. I thought it would become an understeering monster but no - it still turned in OK and goes neutral with the right amount of throttle. I stiffened the rear bar three notches and the balance improved. Just need to spend some more time driving it now before making further changes. So far I think it was a good move - I have some room to move with ARB adjustment and the ride is a lttle better and will probably be even better with the dampers set a bit softer.


Thu May 20, 2021 3:47 am
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Joined: Sat Oct 22, 2016 12:41 am
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Location: Brisbane Australia
GTM: Spyder
Post Re: Spring rate/ length
Recently did a tarmac autocross session. These cars are made for the tight stuff!! They just turn in so quick.

Balance feels about right - maybe slightly loose for an amateur driver like me. I think I will soften the rear bar one notch. Finally about to get rid of the old Toyo Proxes T1Rs that came with the car and fit Nankang AR1s. Apart from the expected huge step up in grip, it will be a square setup. Same MG 11 spoke 16 x 7" rims but going from 225/40R16 rear and 205/45R16 front to 205/45R16 all round. I don't expect a massive difference in balance - the wider rears were a bit under-rimmed and that tends to make the tyre a little bit slower to load up on corner entry. 8" rims on the rear would be ideal.

I know most Elises run staggered tyre and wheel sizes so I am surprised that most Libras and Spyders run a square setup - considering weight distribution is very similar to the Elise.

Anyone have thoughts or experiences to share?


Fri Oct 08, 2021 9:22 am
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GTM Nirvana
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Joined: Sun Oct 19, 2014 10:10 pm
Posts: 1038
Location: Bristol
GTM: Spyder
Post Re: Spring rate/ length
A guy came up to me in the paddock at Llandow a few years ago while I was there for a track day in the Spyder. He was really interested to look around it. He was aware of these cars but had never seen one. He claimed to have been part of the suspension design team for the MGF and later the TF at MG Rover back in the day. He was saying that they had tested various configurations and wanted to go with staggered rim sizes but the bean counters wouldn't let them. Best they could do was stagger the tyre sizes and the VVC TFs came with 215/40 rears and 195/45 fronts. 215 was the biggest they could fit on the 7" rims.

For the road I'm happy with 205 all round but I've definitely found it works better on track with wider rears. I've been using 225/45/16 on 7.5" rears and 195/50/16 fronts on 7" for semis and for slicks I've used 210/610/16 on 7.5" on the rear and 200/580/16 front and found it nicely balanced.


Fri Oct 08, 2021 8:47 pm
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Joined: Sat Oct 22, 2016 12:41 am
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Location: Brisbane Australia
GTM: Spyder
Post Re: Spring rate/ length
That's great feedback thanks Sanz.

With staggered tyres and rims, did you find you could move the tyre pressures closer to equal F/R?
I've been running about 4 psi higher in the rear but suspect I may need to increase that to 5 or 6 going from 225 to 205 at the back.


Mon Oct 11, 2021 12:45 am
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GTM Nirvana
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Joined: Sun Oct 19, 2014 10:10 pm
Posts: 1038
Location: Bristol
GTM: Spyder
Post Re: Spring rate/ length
Tyre pressures I've found work best:
Road (205/45/15 all round) 18psi front 22 rear
Track semi's (195/50/16 front, 225/45/16 rear) 16psi front 20 rear
Track slicks (200/580/16 front, 210/610/16 rear) 16psi front 18 rear.

These are all cold pressures. When it gets really hot I let a bit out but I find if I start lower it feels a bit unsure for the first couple of sessions in the morning. When I re-check them (if I remember to) after they've cooled back down they end up as 15 front and 16 rear. When fully hot they increase by about 6psi on the rears i.e. 22 hot

For my Locost (460kg) I'm right down to 14psi cold!


Mon Oct 11, 2021 9:29 am
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Joined: Mon Apr 17, 2017 10:05 pm
Posts: 38
Location: Bristol
GTM: Libra
Post Re: Spring rate/ length
Hi Sanzomat,
Slight deviation from topic but what steering rack are you using?
I have a little play in my rack so it will be changed and I was looking at a 2.8 ratio to replace the 3.7 currently fitted - just after some feedback from anyone who has swopped on how it will affect the car's feel at manoeuvring speed as well as on the road/track.
(I had an interesting moment on a wet roundabout which involved quite a bit of wheel-twirling, so hoping a quicker rack will make up for age-related deterioration in reflexes :shock: )
Another deviation - whereabouts are you in Bristol? It would be good to meet up and compare notes! I always seem to be unavailable for the KitNet gatherings.
Thanks in advance.


Tue Oct 12, 2021 9:14 am
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GTM Nirvana
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Joined: Sun Oct 19, 2014 10:10 pm
Posts: 1038
Location: Bristol
GTM: Spyder
Post Re: Spring rate/ length
I'm using the TF 2.7(?) one. Mine came with the Metro 3.6 and it felt far too slow steering. The TF one was a big improvement and whilst it is a bit heavier at parking speeds its not a big problem and the benefits once you are rolling make that seem insignificant.
Don't forget you need a left hand drive one as its upside down/forward of the axle. Mike Satur sometimes has them and at a reasonable price for brand new (well it was when I bought mine)


Tue Oct 12, 2021 11:33 am
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