AST Suspension - Digressive option?

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Hi All

I'm in the process of buying some AST 5100 coilovers for my 172.

It's a track focused car, with very occasional road use (mainly to and from the track).

I think I have decided on spring rates (90nm f / 100nm r) but undecided on whether to go for the double digressive option (DDP).

The responses from AST have suggested DDP for the track (but not for UK roads) and on all four corners.

Does anyone have any real world experience with either the DDP option or the standard option and can recommend which way to go?

I understand the concept of digressive valving (more stable platform on low speed compression e.g. braking, acceleration, cornering) but has a "blow off" for high speed compressions e.g. kerbs. However keen to hear some first hand opinions rather than marketing!

Thanks,
Sam

 

[Mr Underhill]

I have new AST 5100s which I purchased for my 182 RB. The plan was to drive on the road and do the occasional Trackday. Digressive pistons were mentioned by AST to me but as I’m not racing in a series, they didn’t think it was necessary.

I opted for the softer 70Nm springs, without top mounts, then took it to Track Torque Racing in Tockwith to have it set up.

It wasn’t great on the roads to be honest and a bit too bouncy for my liking, although nowhere near as bad as my previous circuit car which had 750 Mc Spax Controlled suspension 750 lbs ft front and 450 rear.

On circuit it was surprisingly good although without solid top mounts it felt a little vague. If you think about it logically it’s understandable really.

I’ve since put the RB back to standard and purchased an ex hillclimber 182 and ordered the solid top mounts and 90Nm/100Nm springs.

So whilst I can’t comment or give feedback on DDP, I’m pretty much at the start of that AST journey myself and so far, I’ve been very impressed. I’m back at Croft in May to set it all up.

 

[Ph1 Tom]

I had DDP on my Mégane AST suspension. And on my Clio I didn't. I didn't feel any difference on track but on the road I felt like there was a bit more low speed compliance (speed bumps for example).

 

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Thanks for the responses. Pretty hard to get a definitive answer on which is the best way to go, so I might have to flip a coin!

 

[Waitey]

Digressive doesn't deal with low speed bumps well.

The dampers essentially get harder faster. Fine on track, horrid on the road.

Nothing wrong with linear for the track.

Also whats the reasoning for 90/100 spring rates, they are huge!

Thats giving a ride frequency of over 3.5hz. Thats not far from what you'd want for an F1 car!

 

[SCB]

Digressive doesn't deal with low speed bumps well.

The dampers essentially get harder faster. Fine on track, horrid on the road.

Nothing wrong with linear for the track.

Also whats the reasoning for 90/100 spring rates, they are huge!

Thats giving a ride frequency of over 3.5hz. Thats not far from what you'd want for an F1 car!

Thanks for the response.

I have opted for standard front and digressive rear on advice from one of the AST UK guys and from someone in Australia who runs the same set up on his production racing Clio.

AST recommend 80/80 spring rates as a starting point for track use but many seem to run firmer spring rates. I have heard 100/110 is not uncommon. So I have gone for 90/100 as a starting point on recommendation from the same guy in Australia. It is a dedicated, stripped out track car so not seeing any real use on the road.

 

[Mr Underhill]

Yeah, 80/100 or 90/100 is pretty common amongst the Clio racing fraternity. Not the most expensive springs to buy, so you can always try different rates and see what works. I originally went 70/70 but found them a bit too soft for my tastes.