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MG MGF Technical - Four wheel alignment questions

Just few simple questions, honest! I've read Rob's site, I've read the archive, I've looked very hard at the print outs from my first (good result) and second (recent and not satisfactory) 4 wheel alignments. I am going to get the alignment redone by the MGR dealer and want to talk to the MGF expert without sounding too ignorant, so please could the knowledgeabe answer the following:

1) Toe targets on the print are marked + or -. Can someone confirm that Toe-In is positive and Toe-Out is negative?

2) Does anyone know how the Beissbarth laser alignment works, in the sense that the print outs show before and after "adjustment" for camber, castor and king-pin when according to all I read, only toe is adjustable on the MGF?

3) In particular, are the target values set automatically or manually? The latest alignment has target values that are quite off mark - eg a rear camber of +1 deg when it should be -1 deg.

4) If only the toe angle can be altered - does that alter the other measurements on its own?

Many thanks

Chaz
Chaz

Hello folks... is anyone able to help with these questions, please? Rob, Dieter, Bruce, Will?

Yours in anticipation...

C
Chaz

Hi Chaz,

sorry for the late response - too much DIY to do on the kitchen at home! LOL

>>1) Toe targets on the print are marked + or -. Can someone confirm that Toe-In is positive and Toe-Out is negative?<<

Toe-in is positive and Toe-out is negative.

>>2) Does anyone know how the Beissbarth laser alignment works, in the sense that the print outs show before and after "adjustment" for camber, castor and king-pin when according to all I read, only toe is adjustable on the MGF?<<

The principle of all laser alignment systems are the same. The a system of mirrors (prisms?) are connected to each of the wheels, and a series of co-ordinates are established, from which camber and toe angles are calculated. I am unsure how the caster and king-pin inclination are calculated/derived, but I suppose that this is not important, insofar as that they are always determined, irrespective of whether these variables are adjustable or not.

>>3) In particular, are the target values set automatically or manually? The latest alignment has target values that are quite off mark - eg a rear camber of +1 deg when it should be -1 deg.<<

The target values are from the manufacturer - the figures for which are in the machine's database. I'm surprised that you have POSITIVE camber at the rear! Camber is adjutable inthat it is dependent on ride height. What hight is your car's suspension? Should be around 367mm (measured from the front wheel centre to the wheel arch lip vertically above). If too high, you will see positive camber, which will be detrimental to handling characteristics.

>>4) If only the toe angle can be altered - does that alter the other measurements on its own?<<

Altering toe-angle should not impact significantly on the other measured figures, although the measured camber can alter as the wheel rotates through a complex arc of rotation.
Rob Bell

Cheers Rob - hope the DIY was better than mine usually is!

The +1 deg camber is the target on the recent 4 wheel alignment print out, along with +/-0.09 toe in and out instead of 0.10 and +5.06 castor instead of +5.0. The results show negative cambers for all wheels except front right which is +0.25. Toe settings are a little worse than after the alignment done in May, but better than before the alignment. Nonetheless, the car feels floaty, with poor turn-in and feel about the centre and easily knocked off line if the road surface is even a little rough, especially on bends.

Well, this morning I explained what I thought was wrong with the handling to the MGF expert at the dealer. He said that the target data are on a disk and therefore could not be wrong. When I showed him their previous May print out, he fell over with shock and agreed that something had gone wrong! He confirmed that they only adjust the toe settings and is going to check the ride height to see about the camber.

One interesting comment arose because I complimented the guy on the May alignment which achieved -0.07 and -0.05 toe-out at the front (the target was in fact set at -0.05). Neville said, that setting the front too parallel lost steering feel. He explained that the MGF suspension pushes the front wheels into parallel as it drives, rather than the more common toeing-out and therefore the at rest setting is toe-out, to keep some feel in the steering.

Clearly, from studying the online information in the archive and on Rob's site, this runs counter to normal suspension behaviour. Could it be true?

Thanks

Chaz

Chaz

>The principle of all laser alignment systems are the same.

Yep, though dealing with the software is almost a big problem for the user.

http://www.mgfcar.de/tracking/index.htm
This stuff below 'index' was from Beissbarth. :)
Rob will remember. The translation we never got ready :)

The software is done to be quick but correct regarding pre-loaded manufacturer specs, but at old Beissbarth it's a pain cause the alignement process can't be stopped and the final result gets out only in the last step.... on a printer. Also the angles pre-loaded with car affiliated tolerances can be seen normally only on the printed sheet.

Huge problem is that the user choice for the right spec is only *MGF MY 96* without deaper information on included angles. He needs to look up at different place what the manufacturers pre-load specs really include. They almost trust and don't look up.

Alignment process must be made in a fixed sequence though it would be useful for the user to seeing current angles he changed and not only red/green marks on the monitor.

The process is to lock the steeringwheel in straight direction.
Then put the rear wheels toe angles in that manner that the angles are correct AND the cars centre line is vertical to the rear axle.
(The rear steers 'virtual straight ahead)
A problem at the MGF is the weakness of the rear suspension in 'any' direction if no compliance washers are fitted to the tie bars. The user has to shake the car on the moving axle stands before the process starts to get the car in a kind of idle location.

At last the front wheels get aligned with the correct toe angles. Symetrical to the cars centre line, of course.

I haven't seen newer design *Beissbarth's* since about 2 years, but there are better from other companies.
'Hunter' i.e. was said to be better for MGF
http://www.bath.ac.uk/%7Eccsjst/mgf/suspension.htm
http://www.bath.ac.uk/~ccsjst/mgf/suspension.htm

HTH
Dieter
Dieter K.

>He said that the target data are on a disk and therefore could not be wrong.

Ooops, sorry, typed to long and didn't see your post.

Yes, that's exactly what I wrote above regarding 'Manufacturers spec.
Though he can look up the text files on the HD of the Beissbarth Computer in advance. No change possible IMO, but anyone who 'understands' the red/green mark actions will be able to overcome the wrong specs and find a toe IN solution.

HTH
Dieter
Dieter K.

Dieter, I remember well, along with our attempts to sort out a questionaire on how different chassis set ups alter car behaviour! :o)

All alignment set ups are completely dependent upon the competance of the operator using the equipment. What Dieter has summarised really emphasises what has to be done to get the thing working correctly in the first place, which shows the pitfalls!

>>One interesting comment arose because I complimented the guy on the May alignment which achieved -0.07 and -0.05 toe-out at the front (the target was in fact set at -0.05). Neville said, that setting the front too parallel lost steering feel. He explained that the MGF suspension pushes the front wheels into parallel as it drives, rather than the more common toeing-out and therefore the at rest setting is toe-out, to keep some feel in the steering.
Clearly, from studying the online information in the archive and on Rob's site, this runs counter to normal suspension behaviour. Could it be true?<<

I don't believe this to be true at all - but perhaps Neville was over-simplifying a concept?

In forward motion, road resistance will cause a drag-like force on the front wheels, forcing them in the opposite direction to the direction of motion. Thus, when travelling forwards, the wheels will tend to toe-out. This is not due to geometry design, but due to compression of suspension bushes.

Geometry design comes into play when the suspension is put into compression or expansion (jounce and bounce) - which can be due to suspension movement over bumps, or due to roll or even in accordance to steering movement.

There is nothing unusual about the MGF front suspension. It is, as you know, based on the Metro front subframe, and is a double wishbone design. It has been effectively carried through to the TF, albeit with coil springs. You'll be interested to discover that the TF uses a 0 (parallel) degree toe-setting on the front suspension, so it would appear that MGR's engineers would be disagreeing with what Neville has told you. The TF has excellent steering characteristics!

Regarding steering feel, there is truth in what Neville has said. Some toe-out is commonly used to improve turn-in response - especially early turn-in. This is due to the increased steering effort of the inside steered wheel relative to the outside steered wheel. Certainly, as you reduce toe-out towards toe-in, feel through the steering wheel reduces about the straightahead position. But then something slightly odd occurs - once in the corner, steering response actually feels BETTER with some toe-in at the front. The reason for this has never been truely apparant to me, but may have something to do with the load transfer to the outside front wheel away from the inside steered wheel. Overall, IMO, the new compromise brought about by using toe-in to steering-feel feels so much better than the OE settings that it is worth compromising the initial steering response. Many here would agree - and hence the popularity of the BBS tracking settings. The fact that it practically erradicates tyre wear problems is just a nice bonus! LOL
Rob Bell

Rob, the reference to Metro is quite relevant. I had a trusted local mechanic change my front wheels from toe out to BBS recommended toe in. He has lots of Metro experience and sat someone in the car while he did the final set up as he felt that the loading on the suspension had a effect on the setting.
Brian

Brian, your mechanic is clearly someone of great experience, because he is quite right that the laden state of the car will have an impact of the static geometry settings. Mind you, on an F with somewhat firmer suspension than a metro, I'd have thought that the suspension height changes associated with someone getting into the car would be fairly inconsequential?
Rob Bell

The black arts of suspension, is all I can conclude! Prior to the adjustment, I felt the car was well planted and had good feel and turn-in - the measurements showed one front wheel toe-out by too much and one toe-in!! The corrected -0.12 deg toe out on both wheels felt worse as described above. So what do I know!

Rob - in an archived post you explain that on a corner the outside wheel tends to toe out and the inside to toe in, hence setting some toe-in at the rear to counter oversteering. Is the same true for the front wheels?

Could the explanation for what you say about steering feel be that when driving straight the toe-ing out causes a pull to the left and right equally, thus giving the steering more feel? If the wheels are parallel, the toe-out in motion is less and the drag/feel reduced. I can sort of feel this in my head...but when it comes to the explanation about cornering I can't work it out.

Any road, the garage says the alignment has been redone (for free) and the service cost less than I was quoted, so I'm a happy bunny and looking forward to the drive home from Tunbridge Wells. I'll let you know the results (if anyone's interested).

Thanks for helping me learn...

Chaz
Chaz

>>The black arts of suspension, is all I can conclude! Prior to the adjustment, I felt the car was well planted and had good feel and turn-in - the measurements showed one front wheel toe-out by too much and one toe-in!! The corrected -0.12 deg toe out on both wheels felt worse as described above. So what do I know!<<

The total toe-angle would be interesting here Chaz, because the toe-in of one wheel would compensate for the toe-out of the other... (and here I am assuming that the steering rack was properly centred ;o) )

>>Rob - in an archived post you explain that on a corner the outside wheel tends to toe out and the inside to toe in, hence setting some toe-in at the rear to counter oversteering. Is the same true for the front wheels? <<

Depends. Sorry for the enigmatic answer - but the geometry changes are complicated by what happens when the suspension is variously compressed on the outside and unloaded on the inside wheel... For this you need access to the bump-steer data. I've got some, and have been meaning to get it onto the web site for ages. When I get some time, I'll do this soon. :o)

>>Could the explanation for what you say about steering feel be that when driving straight the toe-ing out causes a pull to the left and right equally, thus giving the steering more feel? If the wheels are parallel, the toe-out in motion is less and the drag/feel reduced. I can sort of feel this in my head...but when it comes to the explanation about cornering I can't work it out.<<

That sounds like a very reasonable explanation for the steering feel and initial steering response differences Chaz, and is how I understand things. :o)
Rob Bell

Don't forget to make sure the suspension is set to an appropriate height (and has settled for an hour or so!) before alignment.

368 +/-10 mm from the centre of the wheel to the underside of the front wheel arch. Take off 0.6mm per degree colder than 17 celcius.

It has also been recommended (by Rog, I seem to recall) to set the tracking, drive round the block and recheck it - to make sure all the rubber components were in the appropriate places.

It is actually possible to alter the camber setting, but it involves removing the lower arm (drilling out the rivets) and making the holes "oval" before refitting the arm with nuts and bolts at the correct alignment. Cup cars had this "mod".

Neil.
Neil

Kyp is back to usual, her handling restored to glory. Neville has set both front wheels at -0.04 toe-out and the both rear wheels at +0.09 toe-in and the result is bliss. Interestingly, the "before" measurements are significantly off the "results" measurements from the alignment done a month ago - shows what 4 weeks driving Kent, Sussex and London roads can do.

To answer Rob, the total toe on the front before the December alignment was -0.25 (L:-0.42 R:+0.18). The rear was also out on both wheels (L:-0.16 R:+0.25) but together they were at +0.09. The driving axis was +0.21 before and -0.02 after that adjustment. The before still felt better! The driving axis is now 0.00, by the way.

One further observation: the target data in this print out are the same as those in the May alignment print out. They show standard MGR targets for everything except the front wheels toe-out. This is shown as -0.05, plus or minus 0.03 - ie half of the standard MGR settings (which are -0.10). Unless there has been any user intervention by Neville (and I assume not) these are the standard Beissbarth disk or hard drive target data for a N re 1.8i MGF with standard tyre sizes.

If anyone is interested, I have a question on cambers, whihc I'll post in another thread.

Cheers and happy mototring all.

Chaz
Chaz

This thread was discussed between 03/01/2003 and 07/01/2003

MG MGF Technical index

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