OT: Wheel tracking - how accurate does it have to be?

I took my SD1 (rigid rear axle) to a four wheel alignment place once. I'd fitted a new steering rack and wanted it done properly. So not the likes of Kwikfit. The rack has a centre finder, so I'd fitted the steering wheel in the straight ahead position with the rack central - as per the BL manual.

The computer print out said I'd too much rear wheel toe-in. ;-)

After they'd finished (and charged rather a lot) the steering wheel was miles out when going straight.

My guess is it's all very well buying expensive sensitive equipment. But like all such likely needs the calibration checked regularly to give the best results.

I got mine from ebay a few years ago. Sorry, the prices seems to have risen since. Cheapest on ebay is £45 new.

I agree. Thanks for looking.

slightly to

Probably depends on what is wrong with the tracking.

Both wheels with an equal toe in/out error ie /\ or \/ probably won't pull but may have a vague straight ahead position and tendancy to lose that vagueness when cornering. or vice versa depending on toe in/out.

One wheel toed out the other toed in, ie \\ or //, will definitley send the car left or right. Hands off the steering wheel it'll naturally align off center.

With one wheel having more toe in/out than the other ie \| or /| the unequal forces from each wheel will combine to create a vector that isn't in the straight ahead direction and the car will drift in the direction of that vector. Agian with hands off the steering wheel I think it will naturally align with the vector so be off center.

Within reason, how is it possible to have a *tracking* (rather than suspension / chassis geometry problem) error like that? I get how the steering wheel / column / rack might have an arbitrary mechanical / hydraulic / electric centre but as long as the steering system was linear, how would it know (if the right was 1 deg toe'd in or the left

eg, I had that on the back axle of a MK2 Escort based kit car because the axle tube was bent (accident). This mean that the nsr wheel was parallel to the direction of movement of the car as set by the other 2 (front) wheels but the osr wasn't.

Cheers, T i m

Too much toe in gives you a tendency towards wavering in a straight line Too little gives you massive tyre wear and a reluctance to turn in

ER Dave, that can be adjusted by the steering wheel. There is no effect from that apart from a c*ck eyed streering wheel when going straight ahead

Think some cars did have steering which centered under power assistance - the Citroen DS?

But on others, if it is pulling to one side, tracking isn't likely to sort it. More likely wear or damage to the suspension or tyre, etc.

Ok and I could see how *they* could steer 'off-centre' but with perfect tracking. [1]

Quite, other than the most wear would be most likely seen on the side doing the most work (and hence scrubbing more, in this country, that would be the front left as that's the one doing all the work climbing up the camber (plus roundabouts etc).

Cheers, T i m

So, if you do them up with the steering off centre, that's where they try to make the car point thereafter. ;-)

That why there is a vice versa in there, can never remember which error gives which effect.

ER, how do you make a car turn a corner? You push the wheels as above, the more you push 'em the sharper the corner the car takes. B-) (each slash in the diagrams is one wheel...)

Hands off the steering wheel be c*ck eyed but the car won't be going straight ahead. Hands on and making the car go straight ahead is "pulling".

The best test of alignment is hands off at 50+ mph on a straight flat road on a calmish day. Long straight bits of quiet (so the bow waves from other vehicles don't shove the car) motorway are good. The car should only drift off course enough to require correction to remain sensibly in lane after 10s of seconds.

Both ends of the track rod are adjustable and we all know how "expert" tyre fitters are at wheel alignment...

Both ends of the track rod have to be adjustable to get the tracking of each wheel relative to the body (or more accuratly the rear wheels) and relative to the other wheel correct.

Experience says otherwise, new tyres from a chain, "your tracking needs adjusting sir" "OK" they tweak, within 50 yds of leaving the place I noticed to drive straight ahead I had to apply correction to the steering. Took it back, they tweaked again, still bad. Took it to local garage, they tweaked, back to normal as it was before the new tyres...

Yeahbut, say you still had a basic rack and pinion steering system, how would anything other than you in the car 'know' where the centre of that system was (the wheel being straight ahead etc)?

So, you have the right hand side with a x deg tracking error and you correct it by adjusting the other side. How does the car / back wheels know it's all straight?

Cheers, T i m

tracking

It's a dynamic system, when moving (hands free) the forces from all four wheels balance out and combine to produce a single vector for the entire system, hopefully straight ahead. The balancing of the forces may mean that some wheels are being forced to run off true and thus have uneven wear patterns.

It depends on steering design.

With older steering and idler box types, you adjust the tracking by altering the length of the tie rod between these two boxes.

With R&P steering, the rack should be centralised first, then both sides adjusted to give the correct toe in. Something it isn't easy or quick to do properly. Many will simply just re-position the steering wheel on its splines, if not looking right.

Yes, it will.

You have some weird misapprehension in your head.

Consider.

You take the steering wheel off and rotate it 5 degrees. You now relaign the stering imnks so that with the steeriung wheel in the centre the wheels track corfrectl;y.

Whast has changed?

Nothing.

Hands on and making the car go straight ahead is

No, it is not what happens., If you have that then you have serious unilaterla m islaignment or a flat tyre or a binding brake

That demopnds on et camber, who is sittmg where, how mucvhj they weigh theh wind and many other factors. Steeriung mislagnment will not be shown by such a test.

Er no, they dont.

Both eends are adjustaable so tiu can get et steering wehel in te centre

You only need one adjustbale end to get the wheels parallel,

The sreeting wheel takes care of the other

Doesnt answer the question

I am afraid Dave doesnt actually understand the question at all

With R&P steering, the inner ball joints need to be in the correct place relative to the suspension pivots. Otherwise you will get some odd effects when the suspension moves. Something many tracking places simply don't understand. There is more to wheel alignment than just toe in.