Spitfire 1500 Front Spring rate

[JB257]

Hi,

I'm currently in the process of refurbing the front suspension of a Spitfire 1500 (1977) and I'm needing to get the last replacement parts which are the shock and spring.

I've decided on going for Gaz fully adjustable shocks (GP4-2271) - I've heard good and bad about these but came to conclusion Koni were marginally better quality but wanted the better adjustability for ride height and dampening even if I rarely touch it once fine tuned. Spax had a few more horror stories found online than Gaz so that sealed it for me.

But am stuck when it comes to the spring I'm unsure what spec to request/order. Through searching here and online I've seen anywhere from 250 to 350 lbs recommended. Apart from some spirited driving down a few lanes I'm generally going for comfort so figure I don't want too much spring rate but either way it will still be better than before.

Has anyone got any experience, recommendations or advice at all? I'm hoping these might be an early Xmas present to myself while I clean and refit the rest of the suspension over the Xmas break! :)

Thanks!
John

[Martins Stag]

I believe that the standard poundage was 180lbs . If it were me i would stick to the lower end unless you are going to do track days?

Martin

[Martins Stag]

I believe that the standard poundage was 180lbs . If it were me i would stick to the lower end unless you are going to do track days?

Martin

[JB257]

Thanks. No plan to ever do track days so will go towards the lower end and see how I fare.

At worst I think a new spring costs £37 so not too expensive a lesson to learn should I find it a little too harsh. May make me get round to re-doing the seats though!

[Taylor bright]

If you have the corner weight and motion ratio i can work the perfect spring rate for you based on what you're going for 

[Clive]

Remember the spring rate is not the same as the rate at the wheel (if that makes sense) as the spring is working at an angle.

Somebody may have the details? But on my Toledo/dolomite I have 175lb springs, considered to be plenty hard enough. Where as on a spitfire 330lb spring are pretty OK. Saying that on my Vitesse I had 440lb springs, and later used them on my herald (used for all sorts of events) and they were a tad hard. Got 480lb springs ob my spitfire, again may be a touch stiff for many people.

[Taylor bright]

Also the other question is how technical you want to go because you could run a nice dual spring set up and remove the anti roll bar if you wanted to go a bit over the top

[JB257]

Thought I better add a further update as I finally rebuilt the front end and got it running again after some brake issues that took longer than expected.

I ended up with 250lb springs but think I need to replace them already after barely getting them run in. I never specified the length on the order just the rate as they did ask for the car model etc and they sent me some 8 inch ones which barely leave any thread left on the adjustable shocks. All seems fine but these leave little room to adjust and suspect they might be bottoming out a bit.

I could do with sorting the rear shocks so may order some new longer springs; at least 10" if not slightly more so then these will sit roughly half way up the shock adjustable range. Might be worth going for a higher spring rate as well if you guys are running much higher with decent drive too!

[Taylor bright]

if the springs are too short then you can just make a spacer(if you have access to a lathe) to put onto the spring seat so that you can gain back the ride height

[Taylor bright]

side note 250lb spring would be a good balance for a road car as by rough calculation(not measuring the car and just taking the gross weight and distribution of a standard 1500) should have a wheel frequency of about 1.5 hertz which makes for a solid road car 440 or 480lb spring would push you up to around 2 and 2.08 hertz which for a road car is about as high as you'd ever think of really wanting to go unless you had some serious extra weight to control, just my 2 cents as it were 

Quoted from JB257-

Thought I better add a further update as I finally rebuilt the front end and got it running again after some brake issues that took longer than expected.

I ended up with 250lb springs but think I need to replace them already after barely getting them run in. I never specified the length on the order just the rate as they did ask for the car model etc and they sent me some 8 inch ones which barely leave any thread left on the adjustable shocks. All seems fine but these leave little room to adjust and suspect they might be bottoming out a bit.

I could do with sorting the rear shocks so may order some new longer springs; at least 10" if not slightly more so then these will sit roughly half way up the shock adjustable range. Might be worth going for a higher spring rate as well if you guys are running much higher with decent drive too!

 

[Clive]

Taylor, when you are doing your calculations do you use the actual spring rate, or the effective rate allowing for the angle? Just a thought.

John, I would wait and see how you get on with the springs before rebuying. Play with the shock rate too, but too hard is usually not good at all. Then decide. Remember if you use a harder spring it will compress less, so take care if you do go stronger and longer that it won't be too high! 

[Taylor bright]

hi Clive i am taking into account the angle, however like i said it was just quick calculations based on assumptions such as the weight and measuring the front geometry by ratio on my monitor ill measure my spitfires motion ratio at work during the week and can give more accurate numbers if you would be interested in that :)

[JB257]

No access to a lathe unfortunately but a spacer might be the cheaper option compared to spending another £70+ on a pair of springs at least at first. I've replaced the rear spring as well now and its still a bit too low at the front when using a level using the lower sill as a rough guide so might be the best next step really. Sadly the due to a short bolt where the brake lines attach to the top rear suspension arm the shocks need to come back off anyway.

Thanks for the advice. I'll try a few things and give it another few longer runs weather permitting and see how I go.

 

[JB257]

Just following up for completeness; all finally sorted at last and have now got 10" length springs fitted and things feel and seem a lot better and the spring when tensioned on the bench and then the car is about mid-way of the threads on the lower shock for adjustment. So not exactly stock but allows proper tension on the spring without any issues that it will bottom out or anything. With the tracking now adjusted due to lack of play in the new parts it drives brilliantly.

Also worth noting that I actually spoke to the guys at Gaz directly and explained and sent photos of the shocks and springs in place and though they made them to the spec according to references they have and I didn't mention any change to length they kindly sent me a new pair at no cost.

 

Now onto the next project!