Quote:
Originally Posted by Eatoniashoprat
on a macpherson front end shouldn't the motion ratio be measured to the center of the tire? So the lever arm would now be something like 1:1.1 or so?
Also, using a lever arm of 1:1.277 in the back is giving me goofy numbers. I can't seem to replicate the ones you produced in the other thread. I'm getting CPM values that are huge (150+). This is using the spring rate values you gave for the stock and 944 TB at the shock position (186 and 216, respectively).
This is fun 
Good info here at this link also
http://www.swayaway.com/TechRoom.php#MOTIONRATIO |
In a true macpherson strut the king pin inclination goes down through the centre of the strut and through to the centre of the tyre tread. Therefore, the spring acts directly in line with the contact point so the ratio must be 1:1 I appreciate that on negative scrub suspensions that inclination point actually strikes inboard of the centre of the tyre contact point so the motion ratio is marginally larger but not much.
In all this appreciate that the calculated spring rates are in fact only the starting point to achieve the desired handling and ride parameters so dwelling on CPMs in anything other than as an indication of the rate will be counter-productive. It might be of interest that in the early '80s after a great deal of testing the very competitive Talbot Sunbeam Tarmac Rally Car was using CPMs of 128 front and 133 rear and that was much less than the circuit racers.
It's Friday and a long w/e beckons so I intend to cool the brain down with some cold beers - Bye Bye!
Clive