Alex,
As always, thanks for sharing. These discussions are always fun and I always learn a lot.
I think the theory and your starting spring rates make sense, and might get someone to a good starting point for a road race car. But I think there are a lot of shortcomings on our cars that we have to compensate for.
First, the writeup assumes a motion ratio of 1:1, which we're close to with our struts, but I think it's closer to 0.9 or so. That will cause the spring rate to be about 10% higher I think.
Second, as we have been discussing in other threads, we don't have an ideal camber curve (especially in the rear), so body roll tends to hurt us more than it would on a car with SLA suspension. This usually means we spring up a little more in order to keep a decent contact patch when cornering. Something like the Elise, on the other hand, really shines with fairly soft suspension and some body roll, but it also has very well designed suspension and nice camber curves.
Lower frequencies produce a softer suspension with more mechanical grip, however the response will be slower in transient (what drivers report as ?lack of support?). Higher frequencies create less suspension travel for a given track, allowing lower ride heights, and in turn, lowering the center of gravity.
I think the above quote sums it up nicely. It's always a compromise, and a lot of us go with lower ride heights and stiffer springs. I come from the autox world, and I think we tend to put a premium on response since we are changing direction so quickly (averaging a significant steering input every 2-3 seconds--slaloms sometimes require 6 inputs in about 3 seconds). Road racers may be able to run lower frequencies because they have more time to set the car in a turn, and probably average more like one input per 5-6 seconds or more (10 turns a minute or so?).
As an example, I've successfully run spring rates higher than most coilovers come with. I, and others, have also found that running about equal rates f/r works well on our cars, which is probably right inline with the 10-20% higher in front they refer to. I've always been baffled why coilovers come with front springs so much softer than rears. My only conclusion is that they're trying to make the ride more comfortable on the street.
I think if you take all these things into account, you could probably get into the 350-400# range pretty quickly, which is probably the lower end of what most folks are running on race cars (road race and autox). If you've got a severely lowered car, it may take even more spring rate to manage body roll if your roll centers aren't brought back up.
As always, thanks for sharing. These discussions are always fun and I always learn a lot.
I think the theory and your starting spring rates make sense, and might get someone to a good starting point for a road race car. But I think there are a lot of shortcomings on our cars that we have to compensate for.
First, the writeup assumes a motion ratio of 1:1, which we're close to with our struts, but I think it's closer to 0.9 or so. That will cause the spring rate to be about 10% higher I think.
Second, as we have been discussing in other threads, we don't have an ideal camber curve (especially in the rear), so body roll tends to hurt us more than it would on a car with SLA suspension. This usually means we spring up a little more in order to keep a decent contact patch when cornering. Something like the Elise, on the other hand, really shines with fairly soft suspension and some body roll, but it also has very well designed suspension and nice camber curves.
Lower frequencies produce a softer suspension with more mechanical grip, however the response will be slower in transient (what drivers report as ?lack of support?). Higher frequencies create less suspension travel for a given track, allowing lower ride heights, and in turn, lowering the center of gravity.
I think the above quote sums it up nicely. It's always a compromise, and a lot of us go with lower ride heights and stiffer springs. I come from the autox world, and I think we tend to put a premium on response since we are changing direction so quickly (averaging a significant steering input every 2-3 seconds--slaloms sometimes require 6 inputs in about 3 seconds). Road racers may be able to run lower frequencies because they have more time to set the car in a turn, and probably average more like one input per 5-6 seconds or more (10 turns a minute or so?).
As an example, I've successfully run spring rates higher than most coilovers come with. I, and others, have also found that running about equal rates f/r works well on our cars, which is probably right inline with the 10-20% higher in front they refer to. I've always been baffled why coilovers come with front springs so much softer than rears. My only conclusion is that they're trying to make the ride more comfortable on the street.
I think if you take all these things into account, you could probably get into the 350-400# range pretty quickly, which is probably the lower end of what most folks are running on race cars (road race and autox). If you've got a severely lowered car, it may take even more spring rate to manage body roll if your roll centers aren't brought back up.
