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Rear Wheel Alignment?

Johnapool

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That was my question too . . . align with what? I'm having a hard time getting my head around this. Unless something is severely bent or broken, issues of toe and camber would seem to be meaningless.

The rear wheel (or wheels) must be aligned with the front tires, or the situation is kinda like Bob posted, in that rear tire(s) that don't track exactly as the front will be "scrubbed" slightly as they go along, quickly wearing the tire out. Have you ever seen rear tires "scalloped" around the edge?
With a three-wheeled vehicle, with front-wheel drive, all that rear wheel has to do is follow. Caster and camber are not much involved, as the swing arm will be trailing, providing stability, and the entire structure must be absolutely vertical. A simple screw-type sideways adjustment to align the rear wheel with the front can easily be trued with a simple laser-beam alignment machine. Lots of modern cars are designed to allow "four-wheel" alignment.
 

NSTG8R

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If the rear wheel is trying to push the vehicle right or left while going straight the result will be:

Poor handling, the vehicle will try to turn the direction the rear wheel is guiding it.

This means the driver must keep pressure on the steering-wheel in the opposite direction to go straight.

High tire wear. The wheels will act as erasers against the road.

It’s kind of like driving in a curve all the time.

All of this causes higher than normal fuel consumption.

It will also cause driver fatigue from trying to compensate all the time.

I don’t know how the stability control will affect all of this?


Good explanation Bob. That's the condition I was attempting to spit out. If the rear tire is not pointing 'dead straight' in relation to the front wheels/chassis, you'd have to compensate with the front wheels to keep her going straight down the road (crabbing as skygazer put it). I guess it'll be obvious to the driver immediately after hitting something hard enough to jack up the trailing wheel, as you'll have to turn the steering wheel left, or right to keep from turning. Think of it as rear wheel steering if the toe-in/toe-out, or probably more appropriately, toe-left/toe-right with a single wheel in the center of the vehicle.
 

wheaters

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On the chassis production line they will ensure the rear cross member is (welded) at ninety degrees to the centreline of the full length of the car. Simple enough to do, especially as this will be done by robots welding components held on a jig.

From the photo supplied, it appears that the swing arm pivots from bolted on lugs located on the rear face of that rear cross member. If the rear swing arm allows the wheel to point off centre, they can very easily put shims between the cross member and the lugs, to bring it straight.

There's nothing new or radical about this technology, it's all been done before.
 

Bert

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If the toe on a single rear tire is within a few inches, you're golden. The effect of it being off one way or another, front to rear tires, is "thrust alignment", or how it tracks front to rear. While it's true you want it as trim as possible, it won't effect handling or tire wear with only three wheels. Two tires on the front though, need to be very close to "true side to side". (toe in/out) If they're not they grind away at each others tread life, as well as significantly effecting handling.
Camber is the tire leaning in or out from top to bottom. Toe is how they true up to the tire on the opposite side, but same end, as the vehicle. Castor is the two pivot points for the wheel assembly. Positive castor is the upper pivot (ball joint) being behind (look straight down at them, behind equals toward the rear of the vehicle) the lower one. Negative is the upper one being ahead of the lower one. A shopping carts front wheels have negative castor. Too much negative castor causes the wheels to shimmy at higher speeds, to much positive makes the vehicle harder to steer/control while turning. (but does assist as you come out of the corner, the vehicle tries to go straight by itself) If the castor isn't equal side to side, the vehicle will pull towards the negative side. To much camber "can" cause pulling, but mostly effects the side to side tread wear on each tire.
There are more preset, and harder to adjust angles and weights to consider, but I'm not setting up for the track, so my secrets remain with me..;)
 

Bert

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Oh by the way, if for some reason th rear tire isn't "true" to the front enough, the vehicle WILL still go straight down the road, but it will do so at an angle. It will not track straight, but won't pull one way or another. Kind of a pain when the steering wheel isn't pointed straight.
They call this "dog tracking".
 

NSTG8R

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On the chassis production line they will ensure the rear cross member is (welded) at ninety degrees to the centreline of the full length of the car. Simple enough to do, especially as this will be done by robots welding components held on a jig.

From the photo supplied, it appears that the swing arm pivots from bolted on lugs located on the rear face of that rear cross member. If the rear swing arm allows the wheel to point off centre, they can very easily put shims between the cross member and the lugs, to bring it straight.

There's nothing new or radical about this technology, it's all been done before.

Totally agree Wheaters, just curious where the adjustment point was. I couldn't really see with the framing jig/fixture in the way what was going on at the swing arm pivots. I like the simplicity of the hub carrier shim skygazer mentioned. Give me a carpenter's square and a feeler gauge and I could align the rear myself...not a fan of other people messing with my toys.:D
 
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