Fortune Auto 510 - Spring Rate & Valving Opinions
06-23-2015, 10:15 AM
#11
Note that there are lots of measurements that need to be made to calculate the critical damping rate. Farnorth recommends, if you can change springs, 65% of critical below 3 in/sec, and 30% above...a sharply digressive valving. He goes further to say that is a starting point. He recommends taking measurements with shock position sensors (he recommends at 500Hz!) and then using the adjusters to get them even. The cheapest recorder I can think of is the RaceCapture Mark 2, and that with 4 sensors and wiring will run about $1400. This is his data acquisition page: http://farnorthracin...secrets14.html; this is use of data: http://farnorthracin...secrets23.html.
Remember that each corner has its own sprung weight. Front and rear will have different unsprung weights and may have different tire stiffnesses. And you will need to add the anti-roll bars, CG, etc. If you added Suspension Analyzer from Performance Trends you could see how the car responded as it went around the track. That would require precise measurements of all the suspension links.
Most people here use the same spring/shock/bars pretty much everywhere. It is also possible to have different setups for different tracks and different weather conditions. A track may have its high speed or low speed turns in one direction; Lime Rock is usually given as an example. Oval racing usually takes place in one day, starting with practice at around 4pm and ending with a feature race maybe after 10pm. Some teams may change their shock/spring packages. In NASCAR, which has several races that begin in daylight and end at night, teams make adjustments and it is often the case that the fast cars when the green flag is waved are not the fastest when the checker waves.
Note that while it is possible to calculate the forces in springs and anti-roll bars at any point, the shocks, which are dependent on the rate of change of the position, bushings, etc. is more problematic. Also note that autocrosses have very limited track time or test time and HPDE track days aren't against the clock. An HPDE car is probably best setup for easiest setup for the driver to be consistent and the car is easily recoverable while the fastest may be something else. Somewhere I read that Formula 1 cars are always on edge while endurance racing cars (e.g. Le Mans) are setup to be easier to drive consistently.
In this case, for HPDE, if FA sets them up for track days with 12/10 spring and whatever anti-roll bars and tires the OP is using he should be fine.
Remember that each corner has its own sprung weight. Front and rear will have different unsprung weights and may have different tire stiffnesses. And you will need to add the anti-roll bars, CG, etc. If you added Suspension Analyzer from Performance Trends you could see how the car responded as it went around the track. That would require precise measurements of all the suspension links.
Most people here use the same spring/shock/bars pretty much everywhere. It is also possible to have different setups for different tracks and different weather conditions. A track may have its high speed or low speed turns in one direction; Lime Rock is usually given as an example. Oval racing usually takes place in one day, starting with practice at around 4pm and ending with a feature race maybe after 10pm. Some teams may change their shock/spring packages. In NASCAR, which has several races that begin in daylight and end at night, teams make adjustments and it is often the case that the fast cars when the green flag is waved are not the fastest when the checker waves.
Note that while it is possible to calculate the forces in springs and anti-roll bars at any point, the shocks, which are dependent on the rate of change of the position, bushings, etc. is more problematic. Also note that autocrosses have very limited track time or test time and HPDE track days aren't against the clock. An HPDE car is probably best setup for easiest setup for the driver to be consistent and the car is easily recoverable while the fastest may be something else. Somewhere I read that Formula 1 cars are always on edge while endurance racing cars (e.g. Le Mans) are setup to be easier to drive consistently.
In this case, for HPDE, if FA sets them up for track days with 12/10 spring and whatever anti-roll bars and tires the OP is using he should be fine.
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