Sping Rates too Stiff?

[ChrisPap]

Hi All,

I've recently had Nitrons fitted on my car and the spec for them is 400 front and 325 rear sping, I imagine that rate is in lb/ft.

However, I feel that the car is stiffer than it used to be and really too stiff for everyday british roads. I travel a lot of B roads and am not doing track days.

I've turned the damping down to the point where the car now feels underdamped and it's skipping across bumps, but it's still too still, so am thinking I need to drop the spring rates by at least 25lb a corner.

Has anybody been down this road before? I don't feel like a 350 hp 1060kg car needs a choppy ride to feel like a sports car. Anyone else?

[ChrisPap]

Walford, I don't know how you'd quantify it, I'm going slower than my other cars because of the jostle-y ride.

Targarama, glad it's not just me! I dislike the audi notion of a car needing to be stiff to be sporty. If the car is light it should be able to float more and still corner well.
To be fair, it is pretty mega on a smooth road, but there aren't enough of them around.

[ChrisPap]

Walford said:

what you have to bear in mind is you don't have massive ground clearance, so limited travel, this is the nature of the beast, don,t compare the ride to cars running higher off the road

Don't think that's it. One of them is significantly lower (have to cross my driveway sideways) and it rides as well as the TVR.


Maybe it's just the roads out my way, but I'm shocked at some of the spring rates mentioned here! How do your teeth not get shaken out?!

Does anyone know what the TVR standard rate is?

[ChrisPap]

Serg,

actually, it's a 40mm set. Had new rear bushes and full geo at Str8six when the dampers were fitted and it has transformed the handling. Car tracks beautifully now, nice balance and great grip in the corners, and nice stability on braking and turn in.
It just feels like the springs are too stiff. The car was set up with 12 clicks front and 11 back (out of 24). I've softened if 3 clicks all round and it's slightly better, but now get the feeling that it's underdamped, pogo-ing slightly.

Glow worm, thanks! My car is a June '05 (so pre august) Tamora with (I think) Green and White spings so maybe the same rate as the Tuscan and if so it looks like they were fully HALF the rate of the nitrons!

Edited by ChrisPap on Friday 3rd May 21:59

[ChrisPap]

Sevenman said:

I have been told that TVR used softer springs and quite a lot of pre-load on the spring, but am not sure how that effects things.

That doesn't sound right. Certainly on my Tamora originally there was no spring pre-load. I only correct your information so as to not go down the wrong path, not sure who told you that, maybe it's for a different model.

As you wind tension on to a spring, it is supporting a greater degree of load, however much weight it would take the spring to compress the same distance. So if you put 250kg on a spring to compress it 1 inch, then by adding that much preload, you will need to add 251kg of weight to that spring before it will move. but when it does move, it will only take the rate of the spring to move it. so if it's a soft spring it will still be soft once you overcome the pre-load. It's a nice idea, but to make it work you need to compress the spring against a stop in it's rest position, and that would be the droop stop. But if that were the case when you jack the car up the wheel would come off the ground instantly, not stay on the ground for the first inch or two of jacking- like my car did and still does.

[ChrisPap]

SergSC said:

how many miles have you put on them so far? Ive done about 120, but have been told they can take 500 miles to breakin and soften a bit... then again Ive also read reports that this theory is bs.
To correct myself when comparing with my s2000, I went up a similar % increase in spring rates on an s2000 and got better comfort and handling, I guess because it was much better damper... but there more variables so hopefully somebody who knows better can chip in and educate better. I guess the actual sr number you get on different cars depends on how much leverage the suspension arms can apply so I guess the sagaris has more because of this and then some...

I've done over 600 miles so far.

When comparing Sags to other T cars, the leverage of the wishbone (wider track) and the inclination angle of the dampers both have an effect on required spring rate.

Not sure what to make of your s2000 experience. Did you really double the spring rate and find it better?

[ChrisPap]

spitfire4v8 said:

you're right in most of what you say about preload, however the droop stop is the open length of the damper, you can have just 5grams of preload on a spring at full droop and it's still pre-loaded .. but you would still get the full droop travel as you raise the car. If you preload a spring you don't lose that droop travel unless you have enough preload to fully support the car at rest onto the droop stop. On a typical tvr this would be around 250kgf per corner as you say, but most preloaded springs will only be around say 100kg at full droop and the rest of the loading is taken by the natural compression of the spring as you lower the car to it's ride height. The std springs are very soft rate and long .. 11 inches maybe?

Right you are. It was late and I wasn't thinking it through properly!I'm not used to the damper body working as the droop stop!

I have access to a range of damper dynos at work but what a pain to strip the dampers back off, and the original set has been binned by now I'm sure.

Not convinced the dampers are the problem, as I say, I've backed the adjuster off to the point the suspension feels underdamped like a pogo even at low damper speeds, and it just doesn't feel right.

I need to get to the bottom of the spring rate issue because if it is in fact true that the aftermarket companies are doubling the original spring rates then I need to sort something out because it seems ludicrous. I have the same ride height, same roads, but suddenly twice as stiff springs and it feels more like a go kart than a sports car now.

[ChrisPap]

To any curious onlookers: No one seems to know for sure but the best guidance I have (from Jason at Str8six) is that the Tamora factory spring rates are 300 front and 250 rear.
If correct that means that the standard Nitron springs are 30-33% stiffer than the factory set up, which may explain why I went from feeling the car was suprisingly good on the lanes to feeling it was quite uncomfortable. Nitron did confirm that them being 30% stiffer sounds 'about right' and that it's something they've done in response to customers desire for 'fast road and track use'- ie, feels like a go kart.


I've ordered a pair of 275 springs for the rear and will move the current rear 325 on to the front and see how I like it. Might stick the dampers on a dyno while I'm at it- just to see what's going on and will report back.

[ChrisPap]

Thanks, although I suspect the Chim and Grif are a different kettle of fish to the T cars.

Maybe the factory rates are too soft for track use, it does feel mighty on smooth roads on the stiff springs, but I don't do track days, I do 80% british B-roads, and I was pretty happy with the car before. I'm hoping to have the springs toward the end of next week and will update once I get them on.

[ChrisPap]

Update:

I have since bought new TVR OE spec springs for my car. The fronts are the original dark green, the rears are the newer spec light blue (originals were white). As they are not marked I got them tested for rate at the only damper place I trust, and WHOA!

The fronts are 195 lb/in, and the rears are 230 lb/in. That means the springs supplied with Nitrons are over TWICE as stiff on the front (205%), and the rears are 152% of the original stiffness!

No wonder my car went from feeling suprisingly nice on B roads to being really quite unpleasant. I can't wait to get them on the car now and see what's what!

[ChrisPap]

No, the eibach free length is much longer and requires pre-load in the spring for ride height. I'll measure the differences once I have the nitrons of the car.