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Coil Springs - views on "slightly raised" road height.


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I now have everything stripped off my TR5 and the body in off being prepared and sprayed while I clean and treat the chassis and then put all the running gear back on before the body goes back.

 

I want to ensure that it handles well, but is also relatively practical around some of our less than perfect roads. The springs that I have taken off were front yellow/purple, which I believe is "competition lowered", and rear white/red which I can't identify but assume were similar lowered versions, so handling was good if a little harsh.

 

The exhaust manifold and sump had obviously made contact with the road on numerous occassions based on the dents and knocks visible on them, and I want to avoid the scrapes if possible after the rebuild. I'm thinking of road/rally springs from Moss which say "slight raise in road height", but has anyone tried these, and are they good in terms of handling and also how the car looks?

 

I saw another thread on ground clearance, and I know the tyres will reduce ground clearance compared to original as I have 205/60/15 tyres, but with the smaller tyre diameter and slightly raised height will the car look strange?

 

I think I'm going to try these road/rally springs as I can always change later if needed, but with the wealth of knowledge on here thought I'd see if anyone has any views on whether this is a good idea!

 

I'll be putting new polyurethane bushes all round as well.

 

Thanks

 

Parry

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Parry,

Rather than rely on descriptive terms, why not measure the springs' stiffness?

That is measured in pounds per inch (or, I suppose, grams per centimeter, but it never is)

So measure the free length, in compressed, then arrange to compress them by a known weight.

You would do!

Put a plank on top of the spring, and stand on it. You may need a door to steady yourself.

And an assistant to measure the new height of the compressed spring.

Now the difficult bit!

Divide your weight, in pounds, by the number of inches that the spring was compressed.

The answer is the spring's stiffness, in pounds per inch.

 

Now you can ask what is the stiffness of any spring thou fancy and compare.

 

John

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Parry

 

I had the same issue, mainly due to being laden as usually camping is involved, so I put some spacers in at the bottom of the springs at the rear, which don't take long to take out/put in, for weekends when not roughing it.

 

No experience with the springs you are considering, but the above would save you a fair bob.

 

Cheers Carl

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You can also caculate the springrate of a spring by its geometry.

Peter Cobbold provided the formula for this in other threads on this forum.

It is important to measure the spring wire diameter accurately, as this influences the springrate quite a bit.

Regards,

Waldi

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If I'm reading the colours right, my old springs were 420lbs, and the ones I'm looking at are 390lbs. I'm not sure I could stand on the springs and measure accurately the height to calculate that myself in case any changes since they were new John!

 

I'm assuming that this will impact the stiffness of the suspension, so only a small change from my old springs but the slightly longer springs I am now looking at will impact the ride height and how much potential movement will be possible in the suspension, so maybe slightly more body roll, but I may be wrong.

 

Carl, mine isn't just when loaded, so I'm not sure spacers would be a good solution for me. Having said that, two people in the car is almost fully loaded given the laden weights in the manual which surprised me when I first saw that! Good to see another valencia blue TR5, although mines grey primer at the moment before it gets back to its normal valencia blue.

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Coil spring rate calculator post: http://www.tr-register.co.uk/forums/index.php?/topic/63429-rear-springs/?p=547197

Are you sure your front and rear springs are the same?

Peter

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Front and rear springs look different, but just went to the spring rate calculator you referenced Peter and it's beyond my current knowledge - I tried measuring the springs but the answers in the calculator didn't mean anything to me so I probably need to educate myself further on these things if I really want to do scientifically, so trial and error may be my best approach for now, but thanks for enlightening me on the complexities involved.

 

Alan, I think the wheels are 6 inch width, although the markings don't say, the just say KN SCP and 15J.

 

Parry

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In my opinion 60 profile is way too low. NLG (North London) are finding the stuff we had put on, we are taking off because of the state of the roads in modern England. Back to Lever arms, softer road springs, 70 profile (Vredestien classic sprints, wonderful) and makes for a pleasant drive. Maybe, as we are getting older and want comfort these days.Driven thousands of miles and the Mazda seats are the icing on the cake.

Just my/our opinion of course for what it is worth.

Regards Harry

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With that section tyres you would have quite a large arch clearance anyway so raised springs would make it worse. 195/65/15 is the norm for most these days.Your KN wheels should have a width marking somewhere.

Stuart.

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Thanks Stuart, I'll need to replace the tyres as they've been on the car since I got it which is about 15 years now, so even though tread is ok I wouldn't trust them, so I'll look for a higher profile when I get to that stage.

 

Springs are supposed to be just under 4mm height increase against standard so I decided to go for them.

 

Completely agree Harry that I want something I can use and enjoy on todays roads and not something that I occassionally find the perfect road for. Hopefully I'll end up with that car when I'm finished!

 

Thanks all for the input!

 

Parry

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So much for grams per centimeter, and spring stiffness ALWAYS being in lbs/in - that spring stiffness calculator is in Newtons per meter! Well, car coil springs ARE always in lb/in, so there!

 

This is the formula:

k = Gd^4/8D^3N

 

k=spring stiffness

d=wire size in inches (Yay!)

D=coil diameter

N= number of active coils (don't count the ends)

G=shear modulus of spring material. (use 11.5 million)(psi)

 

The symbol "^" means 'to the power of", X^2 means X squared, or X times X.

 

Good luck!

John

Edited by john.r.davies
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