Brad Tipp Posted August 28, 2001 Share Posted August 28, 2001 Having had lots of work done recently I think I need to up the spring rates on the front. What are the recommended rates for a track biased car with the following spec? 1.6 K Superlight upgraded to 180 BHP - wide track with adjustable platforms. running ACB10's 6X21 at front and 7X22 inch at rear. I’ve already had the back uprated and it rides MUCH better. I'm looking for a similar improvement at the rear. T 1 PPB - Superlight "Well yes officer i'm not arguing, it's just that [insert excuse here]..." Link to comment Share on other sites More sharing options...
Peter Carmichael Posted August 28, 2001 Share Posted August 28, 2001 Anything in the 250-350 lb/in range will suit. If you go very stiff, you should think about a softer front ARB. Link to comment Share on other sites More sharing options...
Brad Tipp Posted August 28, 2001 Author Share Posted August 28, 2001 Thanks Peter, any idea what the standard ones are? T 1 PPB - Superlight "Well yes officer i'm not arguing, it's just that [insert excuse here]..." Link to comment Share on other sites More sharing options...
Peter Carmichael Posted August 28, 2001 Share Posted August 28, 2001 Standard are 150 lb/in Link to comment Share on other sites More sharing options...
Paul McKenzie Posted August 28, 2001 Share Posted August 28, 2001 I seem to remember reading that the general opinion was that the 1996 onwards progressive rear springs were good for track work and the emphasis needed to be on uprating the fronts and also fitting a rear ARB. What do people think?, and what is the rating of the original rear springs? Thanks, Paul Link to comment Share on other sites More sharing options...
Brad Tipp Posted August 28, 2001 Author Share Posted August 28, 2001 I don't know the rating of the original rear springs but I've been told that rear progressive springs = badness. T 1 PPB - Superlight "Well yes officer i'm not arguing, it's just that [insert excuse here]..." Link to comment Share on other sites More sharing options...
Paul McKenzie Posted August 28, 2001 Share Posted August 28, 2001 Brad, What rate did you change to on the rears? Paul Link to comment Share on other sites More sharing options...
Brad Tipp Posted August 29, 2001 Author Share Posted August 29, 2001 Paul, I went to 180 lbs on the rear with slightly shorter springs to lower the rear ride hight after the 22 inch rears were fitted. I think I'll go for 250 lbs on the front and see how that goes. T 1 PPB - Superlight "Well yes officer i'm not arguing, it's just that [insert excuse here]..." Link to comment Share on other sites More sharing options...
Brad Tipp Posted August 29, 2001 Author Share Posted August 29, 2001 Peter, Can you tell me what the inner diameter and free length should be? It looks like 1.875 inch and 7 inch respectively. T 1 PPB - Superlight "Well yes officer i'm not arguing, it's just that [insert excuse here]..." Link to comment Share on other sites More sharing options...
Peter Carmichael Posted August 29, 2001 Share Posted August 29, 2001 The free length of the spring is not really the problem. For the 250 lb/in springs I got the Vauxhall green race springs from Caterham. These are 2.25in diameter. You need to get a new end cap for the damper, again from Caterham parts (note the adjustable spring seats are reversible to cope with the other size.) To get the ride height right you have a problem with the *damper open length*, rather than the spring free length. The problem is that the springs are stiffer so they don't sag as much just under the static weight of the car. If the springs are going to be touching the platforms at fully open for safety's sake, then they are going to be longer than you need at static equilibrium. Your ride height will be wrong. There are a number of options: 1. Run with springs that will go slack at full droop and slow down for hump back bridges and the Mountain at Cadwell. (Eeek! Although not uncommon practice) 2. Lockwire/tywrap springs to the platforms. (Its not really solving the problem...) 3. Remove the spacer from the damper to shorten the open length. (This sorts out the ride height, but renders the bump stop inoperable until your sump is ploughing an inch deep furrow in the tarmac. You can shim the bumpstop back into action on the piston.) 4. Run a helper spring (Solution that I have. A helper spring is a flat section spring of low stiffness that lets you set up the spring to be slack and then fills in the gap between the platforms and the springs. In normal use the spring is fully compressed). Hope this helps. Link to comment Share on other sites More sharing options...
Peter Carmichael Posted August 29, 2001 Share Posted August 29, 2001 180lb/in is pretty damn stiff for a rear spring and means your ride frequency will be quite abrupt. It also means you ought to aim a bit stiffer for the front to keep things matched. It might make more sense to aim for the ~350lb/in range at the front and downgrade from an 18mm ARB to a 5/8in ARB (~16mm). The angle of the spring/dampers at the front means that the effective wheel rate is less by a factor than the spring rate. The factor for a widetrack car is ~2.7, so a 350lb/in spring actually only has a wheel rate of 130 lbs/in. The rear springs are direct acting (more or less), so you get your 180lb/in at the wheel. Consider that the original front springs give a wheel rate of 55lb/in and you can see that this is much too soft. The ride frequency at the front should be slightly slower than for the rear. The rear carries a bit more load, so the combination of 350lb/in front and 180lb/in rear keeps you balanced for ride frequency front and back. My own preference is for a softer rear end to help with traction, so I would probably not have gone beyond 160lb/in. The original rear springs vary from ~110lb/in at full droop to ~170lb/in. They usually ride at about the 130-140lb/in range. Link to comment Share on other sites More sharing options...
Brad Tipp Posted August 29, 2001 Author Share Posted August 29, 2001 Peter, Thanks for the advise. I always have trouble visualising this, but after reading your explanation 3 or 4 times I think I understand. Can you suggest the the correct length of spring and helper spring I should go for? And should I go for 2.25 or 1.875 internal dia? You are correct in that other people have said my rearend (oh er) is very stiff. it rides fantastically though, so I'm very happy. Interestingly Caterham tech suggested if I have 180 rear I should go for 215 front!! Away from the 250 I asked them about! Bit of a difference of opinion with your 350 subsequent suggestion. God I wish with suspension settup was easier! T 1 PPB - Superlight "Well yes officer i'm not arguing, it's just that [insert excuse here]..." Edited by - brad tipp on 29 Aug 2001 13:16:04 Link to comment Share on other sites More sharing options...
Peter Carmichael Posted August 29, 2001 Share Posted August 29, 2001 I will measure up the springs tonight. Link to comment Share on other sites More sharing options...
Brad Tipp Posted August 29, 2001 Author Share Posted August 29, 2001 Cheers Peter, I'll look for a post tomorrow. T 1 PPB - Superlight "Well yes officer i'm not arguing, it's just that [insert excuse here]..." Link to comment Share on other sites More sharing options...
Swiss_Tony Posted August 29, 2001 Share Posted August 29, 2001 Sorry to change the subject a bit ........... Does anyone know what springs and shocks are fitted to the JPE? James Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now