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MG MGF Technical - F suspension geometry
|Some may know I had some problems with tramlining and stability on my F after having the suspension height adjusted and switching to 16" wheels. As suggested on this very BBS I had 4 wheel alignment done on Saturday and the tyre centre gave me a very nice before and after printout - little wonder the car was unstable, rather than 10 minutes toe out at the front I was running 12 minutes toe IN on the front left and 11 toe in on the front right! At the back, the left wheel was 14 minutes toe in (so not too far out) but the right was dead straight!|
Now, a question for the suspension experts! The printout shows toe, camber and caster. I realise that only toe can be adjusted on the F but I appear to have a problem with left rear camber and front right caster. The front right caster is shown as slightly (3 seconds) out of permissable range, but the left rear camber is quite a long way out - 2 minutes 9 seconds, where the maximum permissable is shown as 1 minute 30. Is this something I need be concerned about?
|There really isn't an awful lot you can do about it Tim, so from that point of view, and the fact that the car seems to be driving well now, no, don't worry about it.|
If you look back through the archives, you'll find that Tony Smith had similar issues with some of the tracking parameters. He had PU bushes fitted, and hey presto! The caster/camber abnormalities disappeared.
Difficult to recommend an expensive course of action to a problem that doesn't cause problems on the basis of one report - but if you were thinking of PU bushes anyway, then perhaps this could form part of your self 'justification' for doing the job and spending the cash :o)
|Thanks, Rob - guess it's another case of too much information causing worry! :) The F's given my wallet a battering recently thanks to the service, rear brake pads, clutch cylinder and new wheels plus 2 new tyres needed soon - so I think PU bushes can wait a while! :)|
|Tim - If you have just had your tracking adjusted to the MGR standard of 5min toe out at the front and 5min toe in at the rear then be prepared for your nice new front tyres to be worn out in a few k miles. I gave up running the MGR standard back in 1997 when it destroyed my front tyres inside 5k miles. Since then I have experimented with many changes front and rear to find what I like and what also cures the front inner edge wear. Look up Rob Bells site for the recommended settings which I believe is 5mins toe in front and rear. Also when you get tracking done make sure you tell them what settings you want, not what they have in the machine. Absolutely insist on it and make very certain on the end printout that what you asked for is what you got. And besides the obvious of the toe angles make sure the overall drive ahead settings are not more than a minute or so either side of 0. Otherwise the car goes everywhere on the transition from power to overrun.|
And just as an afterthought on your tramlining experience I used to have this very very badly. Nothing I could set via toe settings or any tyre pressures I could rationally run at (from between 18 to 32psi) made any appreciable difference. I also had PU bushes fitted all round, including the subframes, and that didn't really help either. My car has also been Techspeed'd and although that improved things it didn't cure it. New tyres of the same type also did not change it. Eventually I changed the tyres (back to Yokohama's) and the tramlining was instantly gone and has stayed away for subsequent tyre replacements as well. Investigations I have done latterly show that the major change was the tyre load rating and tyre construction methods. The tyres that tramlined really badly (a very respected make and a very good tyre for grip, longevity, wet performance etc) had a high load rating and the recommended fitment for them is for relatively heavy and powerful front wheel drive cars. Not our beautifully lightly loaded front end on MGF's.
So the real answer is as we all know with the MGF. Choose your tyres very carefully and look after them. They are without doubt the single biggest performance enhancers you can buy.
Thanks, interesting thoughts. Mine has been tracked to the standard settings, which are 10 minutes toe out at the front and 10 minutes toe in at the back. At the moment the car handles very nicely, but of course I haven't yet done enough miles to gauge tyre wear. I'll keep a very close eye on them over the next few thousand miles! I haven't yet changed the fronts so if they get scrubbed it's not the end of the world.
What tyres were you running when you had the tramlining problem (before you changed to Yokos)?
|Tim - I wouldn't wait until you can see and measure the wear. At those settings you are almost certain to get inner edge wear. By the time you can see and measure it the tyre will have a set wear pattern which will probably continue no matter what settings you try. |
Re the tyre make I don't think I ought to name specifics on an open forum. What I can say is that the manufacturer is very well regarded (frequently recommended here) and the tyres are fitted as OE to cars such as the Audi TT, and are very well regarded by the drivers.
Unless there is a professional reason why you should keep quiet, there is no reason not to state personal preferences or experiences in public. Say it in a civilised manner and stick to facts and nobody will think any worse of you.
|Ok John. Persuaded. The tyres that were really bad for me with tramlining were the Bridgestone RE040. Some thoughts/explanations follows.|
One of the reasons for choosing them in the first place was that they were one of the few "performance tyres" in the correct sizes for an F, eg 185 and 205 on 15" wheels. At that time I really didn't want to go away from the standard sizes. I had already run Yoko A520's and B'Stone RE720's as well as the OE rubbish NCT3's. GY F1's and B'Stone S02's didn't come in 185 sizes. Both the Yoko and B'Stone tramlined somewhat, especially the Yoko's as they wore down. But the RE040's did it badly right from the word go. They were so bad I had the tracking done immediately after the fitting (as I always do) and then again a month later as I couldn't believe how bad they were, especially on the bad ruts on the M25 around the M4/Heathrow exit area and under heavy braking.
As I said before I tried various pressures and tracking settings and in reality nothing really helped, although some settings alleviated it a bit. I even went back to the original MGR toe out settings at the front to see if anything at all made a difference. All that did was destroy the fronts in about 2k miles. So I went back to my favourite settings (5min toe in front, parallel rear), and bought another 2 fronts as the rears still had masses of life left and I thought that the PU bushes etc would help. They didn't of course.
I should also add that other than the tramlining the tyres were fantastic. Loads of wet and dry grip, felt great handling wise, were relatively quiet (at least with an MS Daytona exhaust they never intruded) and on the rears at least were showing good longevity, so I persisted. Bad mistake that.
Anyway after another 10k or so miles on them as the rears were by now getting fairly low I decided that enough was enough and went back to Yokohama, but A539's now, and all the same 205 size. No other changes and magically the tramlining has gone (even with the larger tread on the front) and has stayed away for some 8k or so miles to date. And it stays away with tyre pressures anywhere between 18 and 32psi in the front (me playing again).
Since then I have been looking at what I can find out for why this might be and basically I have come to the conclusion that the RE040's were made for heavier load at the wheels cars and because of that have a really solid, inflexible breaker band and sidewalls, and generally a heavier construction. Hence the really good flat and even wear, grip and handling. But the downside is that the relatively inflexible sidewalls accentuate the lightly loaded front end foibles of the MGF suspension, which is especially evident with tramlining. On an MGF with old tired suspension and sloppy bushes/subframe mounts this may not be too noticeable but on my car with it's Techspeeded suspension, TF rack, PU subframe mounts and PU bushes everywhere it was very noticeable and not at all fun on bad roads.
I hope this missive explains my thoughts and what I found/experienced in an understandable way. I really didn't mean it to be this long but you asked....
|Very interesting, thanks for posting that Alan.|
Should I be adding this to the tyre survey data on the website with the tramlining warning?
Would be interesting to hear from anyone else who has tried the Bridgestone RE040s?
|Rob - The interesting thing is if you look on the Bridgestone site the RE040 is not directly listed any more (it is in the size charts) although you can still get it from tyre dealer/distributors. It seems to have been replaced by the RE050 whereas the good old RE720 soldiers on. I wonder why......|
Re the tyre survey data help yourself but my experience is just that. My expectations, my results. Totally non scientific. Definitely non gospel. Probably needs a government health warning (they warn you about everything else these days!)
|The whole tyre survey is in reality just people's opinions - but without scientific testing of tyres, that's as good as it can get!|
This thread was discussed between 25/10/2004 and 27/10/2004
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