Toe accuracy query

[Mignon]

stevieturbo said:

To ignore the other 2 wheels is just stupid, because anything could be wrong. Just because there is no ready made adjustment available, doesnt mean you should ignore it.

Yes of course it's nice to know the rear end is out of spec first but you can't compensate for that by adjusting the front end which is what people seem to think 4 wheel alignment does.

With a simple set of Dunlop gauges you can check the rear wheels have the correct toe also. Normally they'll be dead parallel on older cars although fancy modern stuff might differ. But none of this changes how you set front toe which is the OP's question.

[Fastpedeller]

Mignon said:

Nonsense. 1/2 a degree on a 17" rim is 3.8mm! That's a huge amount even if the most accurate piece of measuring equipment you own is a wooden ruler. With a digital vernier or even just a steel rule you should be able to set your own tracking up to under 1mm without breaking a sweat. Here's how to do it.

What you need to do first is set up two parallel beams either side of the car you can drive in between. They want to be a bit longer than the wheel rim and at about hub centre height which is about 300mm off the ground for the average wheel/tyre combo. Two cheap spirit levels will give you a couple of straight edges for not much money but lengths of accurately planed 2" x 2" wood will do just fine. Bolt those down to some sort of base with a bit of adjustment built in and then tweak them parallel using a steel tape measure and nip the bolts up.

Roll the car in between the beams and measure from the front and rear of each rim to the beams. Add both front measurements together, the same with both rears, take one away from the other. That's your total toe in or toe out.

If you want to be ultra fussy then check the wheel rims with a dial gauge first to make sure they aren't buckled. Jack up each side one at a time, set up a dial gauge against the rim, spin the wheel carefully making sure you don't move the steering. Note any high or low spots but if a rim is badly buckled you're probably wasting your time trying to set tracking up properly anyway as the tyre tread will be distorted.

That is literally ALL you can ever do to set front tracking up. What the rear wheels are doing is neither here nor there. If one rear wheel is pointing out on the piss because of accident damage or whatever then there's no way of compensating for that other than fixing it first. If your car drives straight when the steering wheel is straight and the tracking is correct when the steering wheel is straight THAT'S THE END OF STORY!

So called 4 wheel alignment for cars that only have adjustable front tracking is utter BS. The car itself adjusts for everything when it orients itself in a straight line. I'll try and explain.

Imagine one rear wheel is parallel to the centre line of the car but the other rear wheel isn't. Let's say the left rear has some toe out. The rear of the car will try to steer to the left meaning the front of the car also needs to steer left to balance this. If the steering wheel had previously been dead straight on a straight road before this damage then now it will be turned left a bit. But what does this matter? The answer is it doesn't other than that the rear tyres will scrub out a bit fast.

What is actually happening is that the car bodyshell is now oriented a bit one way when the car is travelling straight but both front and rear tyres will be evenly balanced each side for tow in and toe out RELATIVE to the direction of travel. If you've set the fronts up parallel between your beams there's nothing more you can do. The toe out on the rear can only be fixed with new parts.

I know this is not easy to grasp. We tend to think about the car bodyshell being the thing that points straight ahead but if there's excessive toe at either end of the vehicle then it's actually just the bodyshell that ends up not pointing straight. The tyres all balance themselves out side to side so on average they each point the same amount sideways from the direction of travel.

So if your front toe is correct but you have to steer a bit one way then the back of the car is damaged. End of. Fix that first and the steering wheel will end up straight again.

http://www.alignmycar.co.uk/what-is-the-difference...

Read the above. Think about it really carefully. It's all utter nonsense. 4 wheel alignment for cars that only have adjustable front tracking is a con. It achieves nothing that good old Dunlop gauges on the front rims only can't do.

The big problem with 4 wheel alignment laser systems is when they try to compensate for damage in the suspension by NOT setting up the front wheels with the correct amount of toe. Then the front tyres scrub out in a few hundred miles. The operator doesn't necessarily know this is happening, especially if the computer system is working from the wrong specs.

As for why you can take your car to a dozen different places and get told by every one that the last place f**ked things up is they're ALL inaccurate to some extent. Being repeatable does not mean being accurate. A damaged micrometer might read 2 thou too big every time you use it so it's still very repeatable but it's also broken!

Agree all the above. Ref the repeatability, I also see where you are coming from. I mentioned repeatability when using a couple of cheap lasers (and indeed I used a steel rule!). To give more detail to that statement..... In addition to tracking the vehicle on good, level ground, I also measured it on a gravel drive and got the same readings. I guess this is what the manufacturer (or indeed buyer) would desire to happen? By way of explanation, we wouldn't want massive suspension alignment changes every time the highway deviated from smooth/horizontal! It's easy to get fooled by "high tec computer" alignment into thinking it's something special, as stated previously it may not be any better than DIY. begs the question - how did manufacturers/garages set the alignment many years ago pre dunlop or similar proprietary equipment being readily available?

[Mignon]

Fastpedeller said:

Agree all the above. Ref the repeatability, I also see where you are coming from.

Excellent. I know it's a bit hard to understand in some respects but I tried to explain it in terms that were as straightforward as possible. Another way of thinking about all this is just place four wheels so each is either parallel or toed in or toed out the same amount relative to the one on the other side at the same end and the fronts are aligned on average down the same centreline as the rears. Now move the bodyshell a bit one way. Or even a lot one way. You could be staring out of the passenger side window while you're driving straight if the bodyshell is 90 degrees to the wheels but all 4 wheels are still tracking straight ahead and balanced side to side. Nothing you can do with front tracking can alter this or improve it other than getting the toe correct.

[Fastpedeller]

Mignon said:

Fastpedeller said:

Agree all the above. Ref the repeatability, I also see where you are coming from.

Excellent. I know it's a bit hard to understand in some respects but I tried to explain it in terms that were as straightforward as possible. Another way of thinking about all this is just place four wheels so each is either parallel or toed in or toed out the same amount relative to the one on the other side at the same end and the fronts are aligned on average down the same centreline as the rears. Now move the bodyshell a bit one way. Or even a lot one way. You could be staring out of the passenger side window while you're driving straight if the bodyshell is 90 degrees to the wheels but all 4 wheels are still tracking straight ahead and balanced side to side. Nothing you can do with front tracking can alter this or improve it other than getting the toe correct.

I had an interesting 'conversation' many years ago in an exhaust/tyre fitting place (annual car racing championship) After fitting exhaust they said "do you want tracking checked" to which I said "no thanks". Cue much 'persuasion', so I said "does it cost anything?" They said "free check", so I said "you are very insistent, so ok if you must". Paid for exhaust and watched car, nobody approached it! Walked to car and stood beside it - a few minutes later the guy I'd paid for exhaust came over "You can take your car if you want mate, the exhaust is finished". "I know," says I, but your colleague said he would check the tracking". Guy goes out back, returns and says "yes it needs doing" so I said "I know, I've been watching the car and he hasn't done it" So he goes away again, returns and says "It needs adjusting, it's £20 for the front only or £35 for front and rear". So I gave it to them with all guns...... "Has your colleague got laser eyes?, cos he hasn't put any equipment near the car and the tyres aren't worn in any way that would indicate a problem? Tell me how you adjust the alignment on the rears (this being a mk2 Fiesta) as they aren't adjustable." He said "it's worth knowing, cos it may have been bumped and out of alignment" Me "no point knowing, and again no tyre wear to indicate" "What other cons do you do on people who come to you? Do you want to put the old exhaust back on and refund my money?, cos I'm prepared to follow that route, you are a bunch of thieves." I then left, my piss being at boiling point!

[stevieturbo]

Mignon said:

Excellent. I know it's a bit hard to understand in some respects but I tried to explain it in terms that were as straightforward as possible. Another way of thinking about all this is just place four wheels so each is either parallel or toed in or toed out the same amount relative to the one on the other side at the same end and the fronts are aligned on average down the same centreline as the rears. Now move the bodyshell a bit one way. Or even a lot one way. You could be staring out of the passenger side window while you're driving straight if the bodyshell is 90 degrees to the wheels but all 4 wheels are still tracking straight ahead and balanced side to side. Nothing you can do with front tracking can alter this or improve it other than getting the toe correct.

Even today, it isnt uncommon to see cars crabbing down the road, as per virtually every old Mini. I seen a cracker a few weeks ago driving down the motorway. A Transit in front was crabbing like mad, I'd say the front wheels easily 10-15deg turn to keep it driving straight ! Worst vehicle I've ever seen on the road ( even worse than an old Mini lol )

Front tracking might still read ok in a static position...doesnt mean the car is right. The benefit of modern systems isnt so much accuracy, but plain and simple ease of use.

IMO a well setup string system can be very good...but it's a bloody slow process so not practical for something used daily on many vehicles.