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      11-29-2012, 05:58 PM   #51

Drives: Imaginary M2
Join Date: Jul 2008
Location: Scotland

iTrader: (0)

Originally Posted by NISFAN View Post
Well to compare we would need to understand the 'normal' rack first. It has a relatively small pinion gear running along a rack. Teeth on both are matched to the same pitch and tooth size. The pinion can rotate more than one revolution in either direction. Typically you can turn the wheel over 2 times lock to lock.

In a system with variable geometry, you can't just change the pitch of the rack teeth either side of centre because the pinion would run out, the gear would not mesh.

Soooo.....a variable system has a large pinion, big enough to cover the full rack movement, and has matched varying pitch. The rack and pinion are made as a matched pair. The differing ratio is machined into both the rack #and the pinion to maintain meshing. This system has to be carefully aligned to start with, etc. so quite technical and orders of magnitude more complex than a straight rack. The important feature is the pinion cannot rotate more than 360 degrees like it does on a normal system.

Coming back to what your salesman advised, as it has a similar ratio in the centre as Maestro explained it won't behave much differently, although the large pinion would require less assistance, so could 'feel' different depending on the electronic assist programming. Also in normal driving you rarely use more than 90 degree steering wheel angle where the tighter ratio kicks in, so you are unlikely to feel this action in normal driving, only low speed manoeuvres. Again as Maestro explained hardly a sporty experience on it's own, but with advanced assistance might feel significantly different to matter.
Thanks for the long explanation, but i still don't see how its 250 of a difference in manufacturing costs. To put it simply a larger pinion is used along with the steering rack, obviously the pitch between the teeth changes as you move along the rack. So the rack and pinion will just be made to different size. with different pitch between the teeth than a standard rack.. I don't know why its such a great engineering feet... after all id expect it and and standard rack to be machined to the same tolerences.. thou. Maybe a little more complex not majorly though. As both would need to be machined properly to run true anyway.