Why not progressive springs?

[Dominic TVRetto]

These seem like the perfect solution to our short suspension travel woes, and I believe they may have been fitted OE to at least the first incarnation of Griff's (if memory serves) - even if they were discontinued...

So why do we not use progressive springs on coil overs - is there some fundamental design issue that prevents us from doing so, or could I order some original Griff progressive springs and put them on my Gaz coilovers without mishap..?

Why do we use standard springs rather than progressive?

Thanks!

[black_potato]

I dont see any reason not to use them as such but its very important that the valving compliments the spring rate. Another option is to go helper/main spring which would give you very predictable results.

[Dominic TVRetto]

Thanks.
Out of interest, why does the valving matter more so than for standard springs? If the standard valving (for example) would work for standard spring rates anywhere between 350-450lb, why would that valving not work for progressive springs with a similar range?

[Barkychoc]

TVR S's OE spec have variable rate springs.
They worked well IMHO. I went to single rate which were not as good. By this time I'd chucked the old ones away

[Equus]

There's a good reason that progressive springs have never gained major popularity: they're anything but progressive when it comes to handling characteristics. They fk up the linearity of weight transfer when cornering, and hence introduce all sorts of unpredictability.

[anonymous-user]

Do spring rates affect weight transfer? I'm not sure that's right. Weight transfer is affected by a change in directional force and happens regardless of the spring supporting that weight. Springs rates affect compression under a specific weight and so affect body roll and ride height. Progressive springs allow for a greater initial compression than a stiff linear spring, but firm up after that. The car will thus roll a little more on turn in but once it has taken a set the results are the same as a linear spring. There are a compromise but the work well if you want reduce roll on track but retain some compliance for road use. You do need to ensure that the progression is correctly tuned for your car but if correctly selected they work well. I have Novitec progressive springs on my F430 - specifically tuned for the car and I'm very happy with them.

[Equus]

thecook101 said:

Do spring rates affect weight transfer?

Hell yes!

Total weight transfer is a simple function of mean track width and height of CoG, but diagonal weight transfer (which affects understeer/oversteer balance) is partly a function of roll resistance from the springs and ARB's.

[anonymous-user]

Ye sure, poorly put - I was referring to total weight transfer where spring changes on all four corners are equal. Absolutely, changing front and rear spring rates and or arb independently will directly affect corner loads and thus balance. My point was more that progressive springs can work well - if correctly tuned to the car in question.

[Equus]

thecook101 said:

Ye sure, poorly put - I was referring to total weight transfer where spring changes on all four corners are equal. Absolutely, changing front and rear spring rates and or arb independently will directly affect corner loads and thus balance. My point was more that progressive springs can work well - if correctly tuned to the car in question.

The problem is that they're very difficult to tune well.

When a car rolls, it does not compress/unload the springs equally, front and rear. With a RWD car, it will usually be 'leaning' more heavily (transferring weight onto) the outside front corner. If you're using springs that don't compress in a linear fashion, it becomes very difficult to predict how much roll resistance you're getting at each corner, particularly if you hit a bump mid-bend.

Then there's the problem that if your spring rates are changing as the suspension deflects, the low velocity damping will no longer be matched correctly to the spring rate.

Complete can of worms...

But then the Griffith's basic geometry is so bad that your best bet for predictable handling is just to stop the suspension moving too much in the first place.

[anonymous-user]

Equus said:

Complete can of worms...

Agreed. But take the situation where someone wants to lower the car for track use but still use it on the road - as per the OP's requirements. IE the performance/GT driver. If you drop it 20-30mm and keep the OEM springs you're likely to chin it on every bump in the road. If you fit stiffer springs to prevent that then you're going to hate it on the road. So in this case progressive springs are a decent compromise - so long as you fit springs specifically developed for the car/weight/driver/etc. Not easy to do and as you say a complete can of worms - although there are companies out there they develop progressive springs for specific cars. OP could also look at stacking two different linear springs for some additional tuning options.

Key thing is to have progressive springs tuned to sit just at the rate transition point when loaded with the cars intended use weight - car/fuel/driver(s). That way the car achieves a set quickly on turn in, and still has some compliance during regular road use. It's not for everyone but it has it's use case.