Hawk Rear Springs

[Griff]

Keith,
I do have longer bump stops, if I remember correctly they were FIAT Coupe 20 valve. What I'm really interested in though, is the idea of going to rising rate springs, so that any transition to the bump stop is linear.
Your thoughts?

[Keith]

Hi Griff,
OK, my thoughts. I don't actually have any experience of using rising rate coil springs. I spent my career working for a number of OEMs: Rolls Royce, Nissan, Bentley and Audi. No car I developed used them. So you can take the rest of what I'm about to say with a pinch of salt, its just my opinion. Achieving a rising rate spring characteristic is desirable but with coil springs there are some downsides: expense, difficulty achieving the right characteristic and spring durability. At Bentley and Audi we achieved a rising rate by using air springs, not the big bag type things you see on trucks but springs with a rolling diaphragm supported by a sleeve in combination with a profiled piston, the combination of which helps to reduce the hysteresis otherwise associated with airsprings. There's no way I'd recommend that as a solution in Strato's world due to expense and the time and effort it takes to get the right characteristic. However, my experience with that setup means I can definitely say that the right rising rate characteristic can definitely improve ride comfort so I guess the same is true of rising rate coil springs. What I also learnt is that a carefully developed spring aid, one with a soft "nose" so that the initial contact is almost imperceptible is a very effective way of achieving a rising rate spring characteristic. Care must be taken to balance the spring aid characteristics on front and rear axles, to avoid a sudden change in roll stiffness distribution and non linear handling effects and that is also a point to note if you decide to go the rising rate coil spring route: you would need to match (or rather balance) the wheel rate change for both axles so you'd need to go rising rate at the front too. If you decide to go down the rising rate coil spring route I'd be very interested to know how you get on.

[Keith]

and another thing to consider - If the rising rate part of the spring characteristic is seen during cornering roll motion it can result in a jacking effect which could lead to a loss of negative camber which might be a very bad idea on the rear of a Strato's with wide rubber.

[ProtoTipo]

'Something like these
but flat ground at both ends.

[Iowstratos]

I have a set of Beta coup struts with cutdown springs you can have as I’ve now gone to the Hawk new setup. I used them for more the 20 year, a bit rusty now but work OK.

[NoCorseChris]

Not something I have personal experience of, but I’ve seen folk in the Westfield community use progressive bump stops to fine tune the suspension to good effect, rather than using the springs. They typically use Mk4 Golf ones

Coincidentally, I did buy some progressive springs for the rear of the Westfield that have been developed by Spax. Excellent things.

[Keith]

Yes Chris, or maybe there's a ford spring seat that would save the need for grinding flat but I've decided to get some made by Faulkners. Thanks for looking.

'Something like these
but flat ground at both ends.

[ProtoTipo]

I've decided to get some made by Faulkners.

That's the best way Keith,
I've got Hawk GAZ struts with 9.5" 320lb, but I'm starting with a Beta engine, so they'll probably be too high in lb.
I could fill the boot with sand bags?

[Normb666]

....or find a willing accomplice to get in the boot. Besides providing ballast, they'll act as a sacrificial crash zone/structure in case you go off backwards. Might wanna carry a sponge and a bottle of Flash to clean up any mess, tho.

[Griff]

This is quite an interesting article Rising Rate Suspension: A Design Guide (waveydynamics.com)
similarly, so is this Linear vs Progressive Rate Suspension Springs | Tech Tips | Hyperco (hypercoils.com)