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Author: Subject: Rear Spring ' poundage' - spring rate??
greenwood03

posted on 15/8/11 at 01:27 PM Reply With Quote
Rear Spring ' poundage' - spring rate??

OK this is a bit of a generic post - basically looking for 2 things please.
a/ some guidance as to what others are using spring wise on their 7esque cars ( rate + length ).

b/ a bit of sanity checking of my likely flawed logic.

So, i had a Tiger Cat which i think is overly sprung. As standard they come with 9inch springs of 300lb. Many have gone further to 350lb to alleviate bottoming out when there's a hefty passenger in teh co-pilot seat. The resultant ride (imho ) is a tad harsh, brilliant on a smooth road/track, but difficult to drive swiftly over a bumpy surface as the rear of teh car isnt in contact with teh black stuff.

My simplistic thoughts were, instead of raising the poundage, wouldnt it be more effective to lower the poundage and lengthen the spring, ie/ 275 and 10 inch. The extra length could soak up part of teh driver/passenger + car weight and hopefully give enough travel for the springs to work effectively.

i've tried both 300 + 350's in the 9 inch. the 350lbs make the car very very firm, the 300's feel better and soak up more of the bumps, but i still think there's room to soften it a little further, although i imagine that that in turn may mean changing teh front springs so that they aren't out of whack with teh rears?

anyway, as a starying point grateful if a few folks can post up what they're using and from that may get a bit of a feel for what i could trial on mine.

cheers
Mark





http://southernkitcars.comIntermarque Club for owners in the South/South East

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myke pocock

posted on 15/8/11 at 02:54 PM Reply With Quote
Well, I originally built mine with ex Lotus 7 coil over units front and back. One was leaking so I bought replacement Gaz units for that king of car and the back springs are rated at 190 lbs ( cant remember what the fronts are). I have been told that they may be a bit soft but with the adjusters backed right off it only bottoms out at the back very, very occasionally and rides nicely. As you say, heavier poundage is OK for billiard smooth roads but life aint like that, certainly not in Cumbria anyway!!!
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Mal

posted on 15/8/11 at 03:15 PM Reply With Quote
If it helps, commonly used spring rates on a Westfield with IRS is 275 lb/in( 7" free length) on the front and 180 lb/in (9" free length) on the rear.
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greenwood03

posted on 15/8/11 at 03:48 PM Reply With Quote
thx guys.....anymore care to shed light on what they're using ???





http://southernkitcars.comIntermarque Club for owners in the South/South East

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pewe

posted on 15/8/11 at 05:01 PM Reply With Quote
Matt at Procomp on here is always very helpful.
If yours is a live axle set-up it requires different poundage springs and specific valving in the shocks due to higher unsprung weight.
Mine is a live axle with 150lb springs and Matt supplied the Protech shocks suitably re-valved.
Suggest you sort it out prior to the Northern trip as some of the roads are pretty undulating!
HTH.
Cheers, Pewe

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GeoffT

posted on 15/8/11 at 05:07 PM Reply With Quote
My car is a 'book' live axle Locost - originally had 150lb rears (8" ) but I found I needed the shocks a bit harder than was comfortable to prevent bottoming, so just recently upped them to 200lb and backed off the shock settings. This gives a nice compliant ride with no bottoming out.

I also felt that on a recent trackday the rear end breakaway was a bit more progressive, it would snap out very suddenly with the previous setup......faster than my grey haired reactions could keep up with most times....

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macc man

posted on 15/8/11 at 05:56 PM Reply With Quote
An alternative to high spring rates is to fit a rear anti roll bar. This will stiffen up the handling in the corners and allow lower spring rates. Just a thought.






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Surrey Dave

posted on 15/8/11 at 07:08 PM Reply With Quote
140 lbs

Originally fitted 140lbs ride was good but not enough travel in the damper, so they bottom out , so I fitted 225lbs to limit travel.

Ideally it would be nice to re do the mounts to fit a longer damper or the other option is to angle the damper to give more travel from the shorter damper.

Jon Ison angled his in towards the centre of the car.

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franky

posted on 15/8/11 at 07:24 PM Reply With Quote
quote:
Originally posted by macc man
An alternative to high spring rates is to fit a rear anti roll bar. This will stiffen up the handling in the corners and allow lower spring rates. Just a thought.


My understanding is that if you've got the right spring rates/dampening there's no real need for an ARB.

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Marcus

posted on 15/8/11 at 08:13 PM Reply With Quote
I use 150lb 9" on the back of my live axle Locost with Gaz shocks. Don't think I've bottomed out yet, but may change them next year when I hope to go hillclimbing





Marcus


Because kits are for girls!!

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