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Just wondering what people are running as far as spring stiffness is concerned . I am reevaluating the situation and would appreciate any imput . I have a Van Diemen RF 81. I am considering 180 - 200 lbs springs in the back and Front as a starting point
Any thoughts?
Robert
Hit the 'search' button
type in 'motion ratio' and start reading.
The motion ratio takes into account the wheel - spring movement ratio (think of it as the leverage the wheel has on the spring). Then you consider the actual weight supported by the wheel. With older FF the "effective" spring rate is often in the range of 50%+ of the supported weight. More is better to a point but it is limited by chassis flex (chassis becoming the spring). I would say the spring rates you suggest are low.
Lots of detailed discussion on this on Apexspeed.
Have fun, Joe Riley
If you are running on Dunlop treaded tires, or probably the Avon equivalent, you will probably find that if you start with wheel rate about 50% - 70% of corner weight you will be comfortable. That's a wheel rate of about 135 lbs to 150 lbs for the fronts on my cars.
You need the motion ratio's to turn that into a spring rate. On our RF83 I am starting with 550 pound fronts and 400 - 450 pound rears.
Brian
You are going to need to do the math, but your suggestion seems low. With Hard Hoosier R-60 and later the ARS Slicks (FR-85), we found fronts in the 350 range and rears about 450 worked for us (after a new bonded belly pan was added). Flex in the chassis negates the benifits of stiffer springs. Best way to stiffen most chassis is via the bonded floor.
On my RF 78, running Goodyear 600 slicks, I have 275# Fr. / 325# Rear. (according to the previous owner, I haven't measured them) I am running competitive times, though many people consider these rates too low. I haven't tried stiffer springs yet, so I can't comment on them.
Steve
All the previous posts are correct. Chassis flex matters in terms of spring selection as does the motion ratio of the suspension in question as well as the tires. Sticky tires will require higher spring rates than harder ones. In my three decades as a professional race engineer, I have also found that the driver matters, too. A driver with little experience generally likes a car set up softer, to give him time to react to the car's antics. A more experienced driver likes a stiffer car which responds more quickly to his control inputs. This goes for anti roll bars, and shocks to some extent, as well. Carroll Smith once said something to the effect of, "Spring rates vary with the phase of the moon!" A slick track will require softer springs than one that sticks well. I agree with an earlier post that your rates might be a little low to be running sticky tires, but consider all the facets of spring selection before you change.
Robert Metcalf