Tony Posted July 11, 2009 Report Share Posted July 11, 2009 Speaking of which, curious there isn't always a Thrust target ? Can't imagine a domestic car having anything other than a zero thrust angle. Good point, in truth i don't know why the thrust target isn't always set, maybe on modern machines the steer ahead over rules the thrust? Quote Link to comment Share on other sites More sharing options...
CIH Posted July 12, 2009 Author Report Share Posted July 12, 2009 are there any specific drawbacks with a deeper catsor angle ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 13, 2009 Report Share Posted July 13, 2009 are there any specific drawbacks with a deeper catsor angle ? Unless ridiculous changes are made then no as a modification. Domestically in the overall scheme of things then yes the castor has many consequences. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 13, 2009 Author Report Share Posted July 13, 2009 should we explore them ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 13, 2009 Report Share Posted July 13, 2009 should we explore them ? Yes. A vast majority of the topics we have had revolved around the castor, to date what is you perception of the castor angle? Quote Link to comment Share on other sites More sharing options...
CIH Posted July 13, 2009 Author Report Share Posted July 13, 2009 Well, for domestic cars I've always figured it to be fairly passive ie; less likely to cause problems, unlike toe or Camber. Maybe not passive, "subtle" ? Possibily that's because they can hide problems with things like modern PAS systems ? For Performance gains on fasty-road/circuit it seems to me more castor is almost a given, without any major drawbacks. Quote Link to comment Share on other sites More sharing options...
Tony Posted July 17, 2009 Report Share Posted July 17, 2009 Have you noticed most FWD cars have a low castor and a deep SAI and that RWD are the oppersite..... why do you think this is? Quote Link to comment Share on other sites More sharing options...
CIH Posted July 17, 2009 Author Report Share Posted July 17, 2009 Beacuse FWD is "pulling the car forward" and RWD "pushing" ? I'd think thrust is much more prononuced with RWD ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 17, 2009 Report Share Posted July 17, 2009 Other than squat on a RWD and droop on a FWD their only difference would be the toe settings?... so why the difference in the castor/ SAI. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 17, 2009 Author Report Share Posted July 17, 2009 something to do with fighting torque steer ? Or are we still talking roll centres ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 17, 2009 Report Share Posted July 17, 2009 something to do with fighting torque steer ? Or are we still talking roll centres ? Obviously it's to do with a build issue.... i want you to think about that before i explain all. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 17, 2009 Author Report Share Posted July 17, 2009 transverse engine & transmission Vs Inline ? Something on those lines ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 18, 2009 Report Share Posted July 18, 2009 A main barrier for the actual castor position is design limitations between the FWD/RWD and the kingpin offset (SAI) in your language. Take a look at these two examples. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 19, 2009 Author Report Share Posted July 19, 2009 Other than the limitations imposed because of the room needed for the driveshaft I'm stumped. Quote Link to comment Share on other sites More sharing options...
Mark H. Posted July 19, 2009 Report Share Posted July 19, 2009 In the pictures you show, the top picture with the driveshaft shows the strut and spring mounted to the top of the hub. The 2nd picture shows the strut mounted the to the bottom. Does this have an effect on movement as the angle the strut moves on is quite different. Ones almost vertical the other is more 45 degrees. Quote Link to comment Share on other sites More sharing options...
Tony Posted July 19, 2009 Report Share Posted July 19, 2009 If the car is FWD, the steering offset SR will introduce torque steer. This is because the tractive force will try to pull the center of contact patch of the front wheels forward, thus the wheel will rotate about the point the kingpin axle projected to the ground. The torque steer moment is the product of SR and the tractive force. Therefore the amount of torque steer is proportional to SR. The solution is to build more inclination to the kingpin to reduce SR. This is easy implemented in double wishbones suspension which is shown in the picture, but not MacPherson strut, whose kingpin also serves as spring and shock absorber. If we incline the kingpin too much, there will be too much lateral force transmit via the spring / shock absorber to the car body. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 20, 2009 Author Report Share Posted July 20, 2009 Isn't geometry a rather blunt tool for controlling torque steer ? Aren't trick diffs the usual "solution" nowadays ? So is this why FWD cars rend to have very pronounced wheel offset too ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 21, 2009 Report Share Posted July 21, 2009 Isn't geometry a rather blunt tool for controlling torque steer ? Aren't trick diffs the usual "solution" nowadays ? So is this why FWD cars rend to have very pronounced wheel offset too ? Trick diffs belay the need for dramatic geometric changes but they seldom totally eliminate to problem.... FWD off-sets are a direct result of the kingpin off-set. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 24, 2009 Author Report Share Posted July 24, 2009 Taken in isloation, does KPI have any dynamic infulence with 4WD & RWD ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 24, 2009 Report Share Posted July 24, 2009 Yes, both 4WD & RWD tend to have a very declined KPI 13 or 14d is not uncommon. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 24, 2009 Author Report Share Posted July 24, 2009 given most modern 4WD cars are essentially frontdrive with occasional rear (granted not all) there must be a compromise somewhere ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 24, 2009 Report Share Posted July 24, 2009 given most modern 4WD cars are essentially frontdrive with occasional rear (granted not all) there must be a compromise somewhere ? Have you noticed they have next to no camber though, this is to ensure the transfer box is not damaged. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 24, 2009 Author Report Share Posted July 24, 2009 how would camber damage the 'box ? Quote Link to comment Share on other sites More sharing options...
Tony Posted July 24, 2009 Report Share Posted July 24, 2009 how would camber damage the 'box ? If say the rear wheels had more negative camber than the front then the rear tyres would be doing more RPM than the front. Quote Link to comment Share on other sites More sharing options...
CIH Posted July 25, 2009 Author Report Share Posted July 25, 2009 Sounds like trying to evolve a 4WD set-up could get tricky Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.