Quote:
Originally Posted by Eatoniashoprat
Thanks Clive, The wheel frequency in these equations is the natural frequency of the spring as installed with the given corner weight right? If this is the natural frequency then intuitively if you push down on the bumper and let go the spring should try to oscillate at its natural frequency (only with the shock trying to dampen it). The reason I started looking it it is because 80Hz didn't seem right but I can definitely see the car bouncing up and down at 1Hz. Wait! I just realized that you are talking in CPM (cycles per minute), and the other page is in Hz (cycles per second) and if you convert they're in the same ballpark.  . Those darn units!
The calculations you did I believe were for Humbles car at 1900lbs, whereas my car is about 2200-2300lb with me in it. And actually the factory springs were measured by topline to be around 63 lbs, and the maxx springs I have right now are 71.5lbs. Without punching the numbers in *guess* tells me I should be in the 105-125lb/inch spring range.
For the rear it's either weld in the 2 extra bars to make mine a 5-bar (do these with the motor/tranny installed?) and go coilovers OR, go the cheap way and put in 944 bars, although with 125lbs/inch springs this is probably going to have a similar CPM to the 125lbs/inch and will need to be even stiffer. Or go 100lbs/inch springs to be on the low end of the spectrum and do 944 bars. Time to crunch some numbers! *grabs calculator*
not to mention the fact that I don't have a rear sway bar (yet?) |
Well Spotted! The CPM rates and Hz rates should be a factor of 60 apart. If you multiply the Hz rate by 60 then the CPM rate is 48 - 60, which will give very soft suspension. Traditionally, spring rates in the States have been softer than European rates so maybe that accounts for the difference.
At the rear I was working on 1.27 as the motion ratio and using one of the webs torsion bar calculators the standard 22mm TB gave a notional spring rate of 186lb/in with a wheel rate of 145.5lb/in (95CPM). The 23.5mm bars gave 216lb/in, 170lb/in wheel rate and a CPM of 103.
Staying with Humbles figures if you use 100lb/in springs at the front the CPM is 93 and with standard 944 TBs the CPM is 103 that is the 10% variation we are looking for. You could also retain the standard TBs and add 30lb/in springs as coil overs.
Clive