big wheels
Hi Nigel,
Just a quick note about the wheels section. It says that fitting bigger wheels will be detrimental to the ride, but will improve the handling. I don't think that's always the case, especially for a car with Macpherson strut suspension.
Macpherson struts were introduced by Ford (I forget when: late 50's early 60's) at about the time that radial tyres first appeared. Macpherson struts are compact, cheap and light, and have a lot of travel, which is good for ride. Unfortunately, the geometry is compromised, when compared to the likes of double-wishbone suspension.
The geometry of front suspension is such that the wheel doesn't move vertically up and down: it moves in an arc. It does this so that as the car leans in a corner, the tread of the tyres stays flat to the road surface. Unfortunately, the arc isn't quite correct for macpherson strut suspension.
The only reason Ford got away with it was because radial tyres have softer sidewalls to crossplies, which allowed 'give' in the sidewall to keep the tread of the tyre flat when cornering.
This works okay until you fit really low profile tyres, which have less movement in the sidewall. If the profile is too low, the tread of the tyres won't be square to the road surface, which means you're cornering on the edges of the tyres, which gives you less grip.
Larger tyres can also cause other problems, such as tramlining, and lowering the car can cause other geometry problems, leading to bump steer and incorrect ackermann angles (the inside wheel turns the wrong amount compared to the outside wheel, which scrubs the tyres).
I'm not trying to pick fault: I just think it might be helpful if people fully understand the changes that can occur when altering suspension and tyres.
