Toe accuracy query

[ianmway]

Hello,
After looking at the toe settings in the workshop manual for my DB9, it says that the front toe should be 2.5’ (minutes) each side which on a 20” (515mm) rim works out to be a difference of 0.37mm front to back of the rim.

So even with modern laser alignment machines the slightest error due to;
• Machine being out of calibration
• Poor positioning the reflector mounts to the rim
• Any damage to the reflector mounts (IE they have probably been dropped once or twice)
• The designed slack in the suspension components (rubbers etc.)
of such a small distance will result in a significant error in measurement.

My query is how can you be sure that the measurements of such tiny distances are correct over the width of a car (for total toe)?

Thanks

[stevieturbo]

ianmway said:

Hello,
After looking at the toe settings in the workshop manual for my DB9, it says that the front toe should be 2.5’ (minutes) each side which on a 20” (515mm) rim works out to be a difference of 0.37mm front to back of the rim.

So even with modern laser alignment machines the slightest error due to;
• Machine being out of calibration
• Poor positioning the reflector mounts to the rim
• Any damage to the reflector mounts (IE they have probably been dropped once or twice)
• The designed slack in the suspension components (rubbers etc.)
of such a small distance will result in a significant error in measurement.

My query is how can you be sure that the measurements of such tiny distances are correct over the width of a car (for total toe)?

Thanks

there are many things that can affect "accuracy".....first and foremost the dummy using the equipment.

And you cant be sure. if you want to be sure, get all the gear yourself, ensure you have a totally flat and level working surface, the equipment is calibrated to a level you are content with...then measure it all yourself.

As most of the above is a little impractical...dont get too worried about it. As long as it isnt a mile off, it will be fine, and could change 30 minutes down the road after a few potholes.

[Mignon]

The tolerance on front toe is about the same for nearly every car ever made. For RWD somewhere between parallel and 2mm total toe in. For FWD somewhere between parallel and 2mm total toe out. Your specs are, I believe, 2.5' (+/- 2') on each side so not so far from anything else as the tolerance is almost as big as the base setting. Maybe a tiny bit more tightly specified. As for how accurately any tracking machine can measure that I can't answer. IMO you can't beat a set of good old Dunlop gauges. I've seen some right horror stories on those computer jobbies. And yes, errors on the straightness of the rim can only be compensated for by measuring with a dial gauge and no one does that.

[julian64]

This is why people who measure with rule from a string cage will always be inaccurate. Your two alternatives are

1) just set it up best you can, then drive it around and keep altering it till you find what suits you best.

2) exacerbated the measurement so that instead of measuring 0.3mm you measure a foot or two. This is done by having a reflective beam down a long angle. Imagine a light/laser strapped to the wheel pointing away from the car. For every min you turn the steering wheel it'll make bugger all measurement at the wheel but as the laser goes across the room onto the garage wall there will actually be quite a big movement which you can them work backward to get an angle

[ianmway]

Thanks for your advise, after some fiddling around with lasers, digital levels metal bars & tape measures the car feels really good. The next thing is to take it in some where & find out how accurate I have been.

Can any one recommend a 4 wheel alignment place near Worthing West Sussex?

Thanks

[HustleRussell]

Mignon said:

The tolerance on front toe is about the same for nearly every car ever made. For RWD somewhere between parallel and 2mm total toe in. For FWD somewhere between parallel and 2mm total toe out. Your specs are, I believe, 2.5' (+/- 2') on each side so not so far from anything else as the tolerance is almost as big as the base setting. Maybe a tiny bit more tightly specified. As for how accurately any tracking machine can measure that I can't answer. IMO you can't beat a set of good old Dunlop gauges. I've seen some right horror stories on those computer jobbies. And yes, errors on the straightness of the rim can only be compensated for by measuring with a dial gauge and no one does that.

As you say 5 minutes toe in is in no way out of the ordinary, quite typical in fact.

Proper lazer equipment will perform runout measurement on each of the four rims and compensate accordingly at the measurement stage. Properly used, lazer should be the most accurate method.

[Mignon]

What's a lazer?

[HustleRussell]

Mignon said:

What's a lazer?

It's a spelling error.

This is the type I use

[julian64]

I have to say that setup looks horrendously inaccurate.

The amount of gubbins between the clamps on the wheel rim and the dirty great spindle coming out with with sensor hung on.

If there is any, and I mean any, wobble in any of that the figures would be nigh on useless

Lasers are great for making a straight line, but not good for sensing distance as the speed of light is too fast unless you have a very very accurate clock. So your system is just looking for where the straight line hits a senso to measure an angle rather than a distance which means you have to set any offset manually.

All in all too many ways of an error creeping into your system to measure 5mins.

[HustleRussell]

Ok, whatever you say...

[ianmway]

To round off the thread,

Using lasers, digital levels etc I got the alignment to a position I was happy with. The next step was to take it somewhere with the Hunter alignment system. I went to Setyres in Hove, yep as you have probably have guessed nearly all the settings were out, some how I had managed to get the steer ahead & trust angle pretty much dead on by not having the individual setting s correct!

I must point out that the young man "Chris" at Setyres Hove was very very good, took well over an hour to get it all correct I would highly recommend him.

In conclusion, you need the correct machinery to set the alignment properly. I really can't see that using ebay lasers, string, tape measures & digital levels etc will get you any closer than 0'30" (1/2 a degree) of where you want to be at the very best.

Thanks

[julian64]

I was in the same position as you. I sorted out my M5 as accurately as I possibly could. Even bought a second hand wheel alignment device. Had it calibrated. Spent a weekend on my car setting it up.

I then took it to a laser wheel alignment place in Rochester who ridiculed my setup, and charged me a fair old whack for resetting it up. They were showing how far out it was from their machine. I couldn't really tell the difference driving and to be honest was expecting them to simply confirm my settings but hey ho.

I then couldn't leave it alone so took it back into my garage and re-measured it. The result was I couldn't tell they'd actually moved anything. My wall marks all lined up and the toe and camber where unchanged.

I threw my stuff In the bin believing it to be rubbish. About a week later I was chatting to a friend who works in BMW in Sidcup and spent ten minutes rubbishing the laser wheel alignment place in Rochester saying they'd had a number of BMW's from there after complaints from owners.

I therefore booked it into BMW for a wheel alignment check. They again rubbished the settings, and went through the whole car.

Long story short the car came back from them with a steering wheel off centre but more importantly the steering didn't self correct after a bend and the car was very tail happy. I took it back and they verified the settings to be book

I was unhappy with the car so I stopped arguing, bought it home. Took my stuff out of the rubbish bin and reset the car back up in the original style. It then drove well and I was happy not to go for wheel alignment elsewhere again.

The points I gained from this was that

1) Everyone will rubbish everyone else's settings
2) Book doesn't matter. Its how it drives that matters.
3) Big impressive laser devices are only as good as the people operating them, and even then not so much.

I've been looking for some way of it not taking a whole weekend since.

[GreenV8S]

julian64 said:

laser wheel alignment place in Rochester who ridiculed my setup

rubbishing the laser wheel alignment place in Rochester

They again rubbished the settings

1) Everyone will rubbish everyone else's settings

I think you're absolutely right. In my experience it's very common in the motoring and motorsport trade. I don't know why - in my mind it reflects very poorly on the people offering the criticism.

For a geometry change to cause the effects you describe it would need to be quite substantial, so it would be interesting to know whether you were able to measure the difference between the professional setup and your own preferred one. The DIY 'stick and string' method should IMO be capable of achieving any accuracy you could sensibly need if done correctly, and the main advantage of the fancy tools IMO is that they are much quicker, not that they are more accurate.

[Fastpedeller]

GreenV8S said:

julian64 said:

laser wheel alignment place in Rochester who ridiculed my setup

rubbishing the laser wheel alignment place in Rochester

They again rubbished the settings

1) Everyone will rubbish everyone else's settings

I think you're absolutely right. In my experience it's very common in the motoring and motorsport trade. I don't know why - in my mind it reflects very poorly on the people offering the criticism.

For a geometry change to cause the effects you describe it would need to be quite substantial, so it would be interesting to know whether you were able to measure the difference between the professional setup and your own preferred one. The DIY 'stick and string' method should IMO be capable of achieving any accuracy you could sensibly need if done correctly, and the main advantage of the fancy tools IMO is that they are much quicker, not that they are more accurate.

I agree entirely. Many years ago I worked in the vehicle industry (R&D). I set up my car using bits of string and straight edges. The next week I got an ok from the boss to take it in the workshop to be put on the hunter, and the guys were sceptical and laughing until they checked it and said I was only 6 minutes out of mid-point of tolerance, so very good indeed. It had taken some time to check, adjust, and recheck doing it with string but was ok (and a great sense of satisfaction). Now i use cheapo lasers (as long as it projects a dot it works, as light goes in straight lines!) and can do a check in less time than it takes to drive to a garage. Interestingly on one of our cars I set the lasers up parallel, and thought the data for front and rear track was off, until I realised the (non-adjustable) rear track had some toe-in I hadn't anticipated, but not mentioned in the spec (probably 'cos it is not ajustable!), so nearly a schoolboy error. The method is surprisingly accurate (as evidenced by lack of wear) and repeatable

[stevieturbo]

ianmway said:

To round off the thread,

Using lasers, digital levels etc I got the alignment to a position I was happy with. The next step was to take it somewhere with the Hunter alignment system. I went to Setyres in Hove, yep as you have probably have guessed nearly all the settings were out, some how I had managed to get the steer ahead & trust angle pretty much dead on by not having the individual setting s correct!

I must point out that the young man "Chris" at Setyres Hove was very very good, took well over an hour to get it all correct I would highly recommend him.

In conclusion, you need the correct machinery to set the alignment properly. I really can't see that using ebay lasers, string, tape measures & digital levels etc will get you any closer than 0'30" (1/2 a degree) of where you want to be at the very best.

Thanks

Ahhh..but this assumes their system is accurate and the guy was doing it right.

[julian64]

HustleRussell said:

It's a spelling error.

This is the type I use

Coming back to this is why I don't have much trust. If you look at that system on the rear wheel. You have a wheel clamp followed by a few connections to a spindle going out from the wheel holding a pivoting heavy load of a laser box which is about a metre long.

Its measuring down to five minutes of arc. That means if there is even a couple of microns of loose play on the spindle or in any of those connections there is little point in trying to measure 5 mins of arc.

If I touched that with my finger I reckon the mechanical connections holding the laser to the wheel would change by much more than this. Even its own weight through those connections would render it useless.

I really don't understand anything looking that to be at all accurate.

Surely for accuracy you want something really, really, light weight and precision like a miniature laser and a micrometre so that its weight wouldn't have an effect and with as few connections as possible so the mechanics couldn't have any play.

[HustleRussell]

It's obvious that you've had bad experiences with garages and setup before. Who am I to convince you that ten grands worth of purpose built 3D datumless geometry equipment is better than a laser pen, a garage wall and trial and error. It's not as though we've won a load of races with it.

ETA: little did I know we have since upgraded from the older Beissbarth system to Hunter, which I haven't used yet.

Edited by HustleRussell on Wednesday 21st December 12:14

[Mignon]

ianmway said:

In conclusion, you need the correct machinery to set the alignment properly. I really can't see that using ebay lasers, string, tape measures & digital levels etc will get you any closer than 0'30" (1/2 a degree) of where you want to be at the very best.

Thanks

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 toe 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!

Edited by Mignon on Friday 17th February 02:43

[julian64]

if you look at the original poster he is talking about 2.5 minutes which is 2.5 x 1/60th of a degree. Very much smaller than a degree

[stevieturbo]

Mignon said:

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.

4 wheel alignment is simply a measuring process. What you can or cannot do with the info provided by that process is a different matter.

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.
One way or another a repair to effect correct alignment can always be managed. That repair might be simple or very difficult/expensive...but it is better to know, that just ignore because one thinks nothing can be done about it.