Sideways Tim Posted March 16, 2012 Share Posted March 16, 2012 I'm about to overhaul the brakes and suspension and have been thinking for a while that the front end sits a bit high. I want to fit new springs while it's stripped down, but what do I need and where from? I've got Spax dampers all round and a newish rear spring, so quite happy with just a pair of new coils. Do I need to measure the old ones first? Weighted or off the car?I only want to do this once ideally, so your help, as ever, is appreciated.Tim. Link to comment Share on other sites More sharing options...
Rumpith Posted March 16, 2012 Share Posted March 16, 2012 I have 330lb springs lowered by 1" - most of the main suppliers will sell these... Link to comment Share on other sites More sharing options...
AndyW Posted March 16, 2012 Share Posted March 16, 2012 Tim, Hello, it largely depends on how complicated you need to go. To calulate the spring ratio of the coil with them off the car follows:The spring rate of a coil =k where; K=(d^4*G)/(8ND^3)where d is the wire diameter, G is the spring shear modulus (around 12,000,000 lbsft/in^2 for steel), n is the number of raps and D is the diameter of the coil.This should give you around 170/180 lbs/ft (if you currently have factory spec springs as fitted to the spitfire). Link to comment Share on other sites More sharing options...
AndyW Posted March 16, 2012 Share Posted March 16, 2012 bugger, didnt get to finish post......Best to do this prior to spending money to check which ones you already have fitted. If they arn't 330lbs/ft, I would agree with rumpith and get a set.Spax are ok, have a search for a previous thread regarding the merits of different shocks. Others prefer Koni as you can adjust the height whilst still attached to the car. Andy. Link to comment Share on other sites More sharing options...
Sideways Tim Posted March 16, 2012 Author Share Posted March 16, 2012 This is where it gets confusticating. One reply saying 330lb and another saying 180lb.Standard Spitfire MK IV, Spax dampers. If I get a standard weight spring, which is shorter, will it be too soft? Does a shorter spring need to be a higher poundage?Thanks :) Link to comment Share on other sites More sharing options...
thebrookster Posted March 16, 2012 Share Posted March 16, 2012 Assuming your shocks are non adjustable (in height that is), then yes you would need to find a spring with a shorter free length than what you have on just now to get the height lower.As the guys have said, 330lbs springs seem to be a good upgrade, not too hard for normal use, but 'smartens' the ride from the soft standard spring. This should help with slightly more spirited driving occasionally without going over the top IMO.I posted recently on another method of finding spring sizes and what you need, I'll try and look it up for you. Link to comment Share on other sites More sharing options...
thebrookster Posted March 16, 2012 Share Posted March 16, 2012 Here we go, the thread in question is over on the darkside (sideways-technologies), however it gives a good description of what you might need to take into account when fitting harder springs, and how to adjust for height differences.http://sideways-technologies.co.uk/forums/index.php/topic/1305-how-to-calculate-front-spring-length/Cheers,Phil Link to comment Share on other sites More sharing options...
Clive Posted March 16, 2012 Share Posted March 16, 2012 3266 wrote:Spax are ok, have a search for a previous thread regarding the merits of different shocks. Others prefer Koni as you can adjust the height whilst still attached to the car. Andy. Spax are adjustable on the car (until the adjuster seizes, which can be pretty fast) as are gaz. Koni need to come off he car to be adjusted.......I would use 330lb 1" lower as supplied by moss and others. Yes, if shorter needs to be stronger as they may bottom out. Link to comment Share on other sites More sharing options...
Sideways Tim Posted March 16, 2012 Author Share Posted March 16, 2012 Thanks folks. Starting to make sense now :) Link to comment Share on other sites More sharing options...
Alex Posted March 16, 2012 Share Posted March 16, 2012 My Spax are about 8yrs old.....I just checked my adjusters and theyre fine ;)Admittedly they are not high mileage and its been off the road 5yrs but some of that it was stored outside. Link to comment Share on other sites More sharing options...
starman Posted March 17, 2012 Share Posted March 17, 2012 2356 wrote:I'm about to overhaul the brakes and suspension and have been thinking for a while that the front end sits a bit high. I want to fit new springs while it's stripped down, but what do I need and where from? I've got Spax dampers all round and a newish rear spring, so quite happy with just a pair of new coils. Do I need to measure the old ones first? Weighted or off the car?I only want to do this once ideally, so your help, as ever, is appreciated.Tim.I second what others have said--the common 330 lb/in, ~9 inch free length springs will do the trick nicely on dampers with fixed spring seats. 350 lb/in, 9 inch free length, 2.5 inch I.D. springs also work great. Nice thing about this particular stiffness and free length is that they are readily available from a variety of vendors (like Faulkner springs from places like Merlin in the UK, or QA1 springs from Jegs in the US). You don't need to measure the old springs, but you will need a spring compressor to remove the old springs from the dampers. The new springs are short enough that they won't preload the extended damper when it's off the car and so you won't need the spring compressor to reassemble.The key to the desired ride height for fixed spring seat dampers is the right combination of spring rate and spring free length. It's not a linear thing--check this out:http://auskellian.com/paul/links_files/performance_enhancements.htm#frontFollowing this link a few paragraphs, there's a calculator that I created that you can download so you can see how this works for the ~1 inch lower front geometry. Enjoy- Link to comment Share on other sites More sharing options...
Sideways Tim Posted April 15, 2012 Author Share Posted April 15, 2012 New springs in place today, along with a full polybush all round, new Mintex pads on the front, electric fan fitted.Looks great at the minute, but I'm a little concerned it will look too low once it all settles in :-/What ya reckon? Link to comment Share on other sites More sharing options...
AndyW Posted April 15, 2012 Share Posted April 15, 2012 Tim,Looks good now! can't really make out from the photo, have you previously lowered the rear or is that just set at standard? cheers. Link to comment Share on other sites More sharing options...
smithy Posted April 15, 2012 Share Posted April 15, 2012 Looks good! And I'm very jealous of the grille. Smaaart. Link to comment Share on other sites More sharing options...
Bainzy Posted April 15, 2012 Share Posted April 15, 2012 Looks great, what spring setup did you actually get then? Link to comment Share on other sites More sharing options...
Sideways Tim Posted April 15, 2012 Author Share Posted April 15, 2012 Standard spring on the rear, all be it a new one fitted by the p.o. About five years ago.The springs that came off the front have a 13" free length. No idea what poundage they are, but it was scary using the compressors to get them off!New springs were from Merlin 9" 350lb Link to comment Share on other sites More sharing options...
starman Posted April 18, 2012 Share Posted April 18, 2012 Nice Tim! Link to comment Share on other sites More sharing options...
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