JoeS said:
Comments about alignment issue?
MacPherson strut front suspension isn't the way to do it for either good handling or good tire wear - It's the cheapest way to do it on a small car, but certainly not the best. You only have control of the camber when the tires are pointed straight ahead
The struts are tilted inwards at the top and slightly aft to get the desired caster setting. The spindle is attached to the strut at the opposite angle of the inward tilt, so the wheel is cambered near zero when pointed straight ahead - Pretty much perpendicular to the road. Ok as far as that goes
Now, turn your wheel all the way to the right and look at the outside tire (drivers side) and check the camber - You'll see that the top of the tire is now tilted inward (negative camber) so the inside of the tire is going to take the brunt of the wear when the wheels are turned. When you consider that this car understeers something terrible (tries to go straight instead of turning) you can easily see what's about to happen - You'll scuff the tread off the inside of the tire when cornering hard and fast. The outside wheel takes the brunt of the cornering force and it's tire is decambered so it scuffs tread off the inside of the tire. If you check the passenger side wheel when turned full right, you'll see the opposite - Positive camber and the tire wearing the outside edge . . . . but the outside tire is going to see the brunt of the wear. Also, body roll during hard cornering compresses the strut on the outside of the corner (drivers side when turning right) and as you compress the strut, you add even more negative camber
There is no 'fix' for this - Nothing can be adjusted. The angle between the spindle and the strut is fixed and cannot be changed as the wheel turns left or right, as it really needs to be. You could dial in less caster (tilt the top of the strut forward, more toward vertical which would add positive camber when the wheel is turned) but then you're messing with other things - How hard it is to turn the wheels and whether they will tend to straighten out when you release the steering wheel so you don't want to mess with that
From an online article by
JD Laukkonen "Of course, the overall simplicity of MacPherson strut suspensions also leads to a handful of disadvantages. Although it makes it easier to set the suspension geometry when performing repairs (i.e. if nothing is bent, and you bolt everything in place, then the caster and camber will both be correct), that same simplicity means that the camber angle necessarily changes when the vertical position of the wheel changes. The net effect is that MacPherson strut suspensions are typically seen as possessing inferior handling characteristics to other suspension systems (i.e. double wishbone, etc.)"
The 'solution' is a double wishbone front suspension with unequal length control arms (the upper arm shorter than the lower arm) as is found on many rear wheel drive performance cars - FWD cars almost always use MacPherson struts for space reasons - I imagine Mitsu is using them here because they are CHEAP and this chassis was originally designed as a very low buck city commuter car - In our car, struts also give more front seat legroom
With unequal length control arms you not only have the camber you want when going straight ahead, but you can also alter it as the wheel turns left or right, which gives you not only much better tire wear, but also much better handling as well
Long story short, it was designed as a city commuter car and they never considered we might like to do clover leafs at 50 MPH. Slow down and you get extra range . . . . *and* your tires will last longer too
Don
