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Suspension tuning with packer/bump springs on aero cars

Suspension Tuning & Optimization

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Discussion and questions related to the course Suspension Tuning & Optimization

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Hello all, I've been using bump springs on my aero time attack car and I was wondering what others have observed going onto this setup for suspension tuning.

I've personally observed the car seems to like more rebound and same or a bit less compression. I'm curious if I'm on the right path and what others have noticed moving onto bump springs/packers.

That would make sense - the "bump" springs are acting like a higher rate srping and would need less compression damping as the spring would add more force there, and on rebound the spring would have more force and need more reboun to control that. This would be expected to be especially true if the main spring goes into coil-bind.

However, the bottom line is "what works, works", you don't mention if it's a 2/3/4/5 way damper adjustment available - if you have both high and low speed, might be of benefit to experiment a bit around that, too, for transition responses.

Thank you Gord, This was very helpful.

I'm on 3way rebound, compression low speed, and compression high speed.

Hey Mike, I'm a bit late to the party here but figured I'd toss out my .02.

One of the key factors here is using springs in series. The resulting spring rate is calculated by the sum of the inverses of each spring, so for example if your main spring was a 500lb/in spring and your bump spring was a 2000lb/in spring your effective spring rate would be 400lb/in until the main spring goes into coil bind and then your effective spring rate becomes 2000lb/in. This is important information to figure out because this effective spring rate is what your damper builder will need to know to properly valve them.

Ride height changes through increased and decreased downforce will be handled by the low speed compression and rebound areas of the curves. The tough part about this is that your low speed damping will be utilized for both effective spring rates which leaves you with a compromise, either favoring the effective rate with both springs active during low/medium (vehicle) speed cornering, or the effective rate spring of just the bump spring for cornering during high (vehicle) speed. It's the same deal for high speed damping too, high (vehicle) speed bumps will utilize the high speed areas of the curves and so will low/mid (vehicle) speed bumps, but effective spring rates may not be the same for both of those scenarios.

If you're going to stick with the bump springs next season it would be incredibly beneficial for you to map out which spring rate condition the car is in for different areas of the track. This is most easily done with ride height sensors but if that's not in the budget then a Gopro camera mounted in the wheel well with GPS can get you somewhat in the ballpark to visually show you what areas of the track the main spring is in coil bind.

The compromise on damper valving is why I generally prefer running a bumpstop and tuning with packers; springs in parallel have their rates added together so once the bump stop is engaged the spring rate is more of a progressive gain rather than a switch between two different rates.

Good points, Austin, especially as "bump stops", or "snubbers" can be found with different 'rates', lengths, and progressions.

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