Spring rates
- Thread starter Rob1400T
- Start date
Steve Hoelscher
True Classic
That's an excellent question. Rate tuning for caged cars is slightly different due to the additional chassis stiffening of the cage.
Its important to remember that everything to do with a car's chassis is basically a spring. The tires are a spring, the springs are a spring, the top strut mounts are a spring, even the chassis itself is a spring. I learned pretty quickly that if the spring rates got stiff enough the tires would compress enough to reduce the effective spring rates. So I had to understand the tire's spring rate and keep that in mind when tuning the chassis's springs. When I started playing with spring rates I used the stock top strut mounts, which is rubber and also a spring. Remember back to our roll ratio discussion. If one end of the car has a much higher roll rate than the other, the chassis tries to twist in roll. I learned a great deal about the role of tire compliance and chassis flex from GoKart engineers. Modern racing karts don't have suspension. The kart's handling is tuned with chassis stiffeners and tire pressure.
So the roll ratio I used on my DSP X1/9 had to accommodate the chassis flex and a car without a roof typically has a lot of flex. The X1/9 being stiffer than most. Install a cage, which reduces flex, and you can close up the roll ratio some. You don't need as much front bias in most cases. You do want to maintain about the same total roll rate but you can likely back off some on the front rates.
Its important to remember that everything to do with a car's chassis is basically a spring. The tires are a spring, the springs are a spring, the top strut mounts are a spring, even the chassis itself is a spring. I learned pretty quickly that if the spring rates got stiff enough the tires would compress enough to reduce the effective spring rates. So I had to understand the tire's spring rate and keep that in mind when tuning the chassis's springs. When I started playing with spring rates I used the stock top strut mounts, which is rubber and also a spring. Remember back to our roll ratio discussion. If one end of the car has a much higher roll rate than the other, the chassis tries to twist in roll. I learned a great deal about the role of tire compliance and chassis flex from GoKart engineers. Modern racing karts don't have suspension. The kart's handling is tuned with chassis stiffeners and tire pressure.
So the roll ratio I used on my DSP X1/9 had to accommodate the chassis flex and a car without a roof typically has a lot of flex. The X1/9 being stiffer than most. Install a cage, which reduces flex, and you can close up the roll ratio some. You don't need as much front bias in most cases. You do want to maintain about the same total roll rate but you can likely back off some on the front rates.
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