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MG MGF Technical - Definative alternative tracking settings
|What are the definative alternative track setting |
I have a pretty standard 1.8i fitted with 185/205 avons
do lots of motorway driving ,and wish for greater stability at speed.have fitted spliter.Micheldever set car last time.
|Rich, unfortunately there is no such thing as 'definitive tracking settings'. This is because by altering ride height and toe-angles, the chassis dynamics are actually very adjustable. Therefore your preference may be different to other's...|
I presume that you do not have rear tie bar bush compliance washers fitted?
To get the dynamics that you desire, ie increased motorway stability, then have your car's ride height set to the low end of the manufacturer's range (about 350 mm from front wheel centre to wheel arch vertically above). Ideally, it should be lower, but this may incur an insurance penalty so I am not sure that this is a route you wih to follow at the moment.
Without compliance washers fitted, leave the rear toe-angles as standard, ie 0 degrees, 10 minutes toe-IN.
Set the front wheels to 0 degrees 5 minutes toe-IN. (Standard setting is 0 degree 10 minutes toe-OUT)
will try the settings as soon as poss,No I don't have the compliance washers fitted.
|Rich, the compliance washers are only 10 quid and should not cost too much to get fitted. If you have the cash, get the polly bushes fitted as well.|
As Rob says, don't change the rear tracking without (at least) the washers, it could be dangerous to radically alter the rear tracking without them :-(
I recon if you get ten Fs you won't find two with the same suspension figures after an alignment check, even if they all have the same height and toe angles set.
|Have changed the tracking settings to toe in 0degrees5mins on the front .Initially the steering feels very slightly heavier,which I find good.Stability it's hard to say because it was very windy this morning,but i believe it is better.|
|Just as a comment, i haven't got the compliance washers on my car but have the back set to toe in 5min, and i have had no problem, and love the way the car feels.|
I have the washers fitted, and the car is lowered with knuckles.
Rears are parallel. Fronts toe in 0degrees8minutes.
I find it very 'pointy' but very tail happy.
On the road it's fun. On the track I find it hard to go quickly.
Can anyone speculate what the rear settings would do before I get
it changed back to parallel all round ?
|Paul, How do you find the car with the lowering knuckles, any problems? And what tyres are you using? It's just that I'm about to put lowering knuckles on mine and was hoping that the car would feel better to drive and not as twitchy. Thanks Sue.|
as we have discussed before my car has, 0 degrees 5 minutes toe-IN on the front and 0 degrees 5 minutes toe-OUT on the back (as set by Mike Satur), no compliance bushes fitted, standard NCTs. I know you don't recommmend toe-out on the back (everytime i see you say that i think am i mad?!), but so far the car feels fine even in the wet and i have had no problems. I am looking for some new tyres after a near MOT failure, so may consider going back to parallel at the back if i go for SO2 PPs as i guess i'll get less warning of a rear breakaway.
|Paul, IMO your guess about the S02s is wrong. i found with the NCTs the rear going could happen at frightening speed in the weight and with little warning. With the S02s however you can play around on the limit as much as you like because you know exactly what is going on and you have huge amounts of warning and loads of time to do something about it. I feel even more strongly about this after my track day on tuesday where i spent most of the day drifting and sliding round corners, (might not have been the quickest way round corners, but it sure was fun) and half the day was in the wet.|
as far as having toe out at the rear, i don't really know much, but with 5 min toe in it can feel like the back end is nicely balanced, not oversteering and not being draged round corners by the front of the car, but i could imagine that with toe out it could constantly feel like the back end was trying to drive past the front end on corners, i'm probably not explaining what i mean very well, but thats probbaly cos i'm not sure what i mean. but anyways, i'm happy with my car at the mo, and looking forward to getting it lowered in the near future.
|I think I have toe-in on all 4 wheels (i.e. toe setting is +ve). Front is +0.08 deg, rear is +0.15 deg. With NCT at the front, and S02 at the back (standard 15inch wheels, standard ride height), the back end is completely stable, with a very predictable front end - I'm very happy with the handling for road use.|
My car does have an out-of-spec camber of -2.10 deg on the nearside rear, but that doesn't appear to affect handling or tyre wear.
|>>I find it very 'pointy' but very tail happy. On the road it's fun. On the track I find it hard to go quickly. Can anyone speculate what the rear settings would do before I get it changed back to parallel all round ?<<|
I found exactly the same behaviour Paul! With the rears set parallel (and the fronts incidently) I found the rear would readily slip into oversteer. Whilst tremendous fun (you have to try it to believe it folks), I too found it to be a pile of pants on the track. But at least the rear was readily recoverable. I have a piccie of me going side ways (90 degrees to the direcetion of the track), full opposite lock, which I recovered. Not good driving, but a symptom of the geometry set up.
I have since converted to 5 minutes toe-in all round which is so massively better on the track. Toe-IN front promotes front end over-steer (which I like- nice 'n' pointy :o). Toe-IN rear conversely promotes rear end 'under-steer' which is far more stable in medium to fast corners, plus you can get more power down out of the slow ones.
>>as we have discussed before my car has, 0 degrees 5 minutes toe-IN on the front and 0 degrees 5 minutes toe-OUT on the back (as set by Mike Satur), no compliance bushes fitted, standard NCTs.<<
Paul, as Paul N mentions, the parallel rear set up feels wonderful on the road, and I have no doubt that toe-OUT rear is going to feel terrific in terms of how the car handles. I just worry about those conditions of 'extremis'. If you had poly bushes all round, then passive geometry changes is going to be very minimal, and Mike's recommended set up that you use is going to be safer than a car fitted with OE bushes. 9 times out of ten toe-OUT rear will be fine. But Paul and I have noted that the rear does come out readily when rear toe-IN is removed- and that's what I worry about it on a standard road car. I'd hate to find myself going side ways into traffic (or worse) during an emergency manoeuvre or braking. Therefore, given that 5 minutes of toe-IN works so well on road and track, this is what I (being cautious) would recommend for a standard MGF- and then preferably with compliance spacers fitted to the rear tie-bar bush.
If that sounds like me preeching, it is not meant to, beieve me!
Regarding tyres, actually S-02s give you MORE warning of impending break away- but I guess one ought be be a little more careful given that the limits of adhesion are higher...
|I understood that toe-in at the rear with standard bushes (ie soft) wasn't a good idea, as the car would become unpredictable under hard braking. IOW, the toe-in would change to toe out under abs-use-type conditions. And if you're on a corner and this happens.... gulp.|
Whereas toe out on the rear just becomes worse toe-out under heavy braking. But this isn't a problem with less pliable bushes.
Or am I braking (sic) up the wrong tree?
|Slightly Hugh, partly because the angle changes you mention are slightly exaggerated (under braking, the wheels tend to splay towards toe-out if not actually toeing out, if you know what I mean), and partly because what happens to the toe-angles is different in a corner is different to what happens to the toe angles under stright line driving during acceleration or indeed at steady state or under braking.|
Take the cornering condition. Because of centropedal forces and frictional loads upon the tyres, the inside wheel (to the corner) tends to toe-IN and the outside wheel tends to toe-OUT. Therefore the rear wheels tend to OVERSTEER, tending the rear of the car to swing out of the corner. Setting the rear wheels to a toe-IN will mean that the laiden outside wheel will tend not to toe out to the same degree, and hence reduce this oversteer phenomena. Setting the rear wheels to toe-OUT will simply exaggerate the oversteer, making it more likely that the rear of the car will swing out.
Reducing the compliance in the suspension bushes will reduce these 'passive' geometry changes. But there are clear potential problems associated with a toe-out rear set up.
Obviously, there is more to geometry dynamics than I have mentioned here- not least what occurs as a result of suspenion compression and the effect of the track control arms upon toe angle, but the above is the jist of the problem as I see it.
Confused? I would be, but I have some nice diagrams somewhere that explains things rather better! ;o)
|Just to double check when tracking is quoted as 0degrees 5 mins is that a total for left and right or each?|
please excuse my ignorance.
0'5mins total has greatly improved my handling would more be a benifit or just eat tyres?
|Thanks for the opinions Rob, noted.|
I think a return trip to Mike may be in order to toe in the backs when the tyres are fitted and i have to see the folks at Christmas. However i've had no problems so far and i do like the feel of the car as it is.
I think that the 5 mins is the total toe angle.
Many people recommend Micheldever Tires. I am in the fortunate position that I pass Micheldever Tires everyday going to work. However, I am in an equally unfortunate position that I haven't a clue about tracking etc. When I have to get my tires changes, will Micheldever Tires be as aware of the various views espressed on the BBS regarding tracking and know the best settings, as opposed to Rover's guidance which sounds rather suspect from the comments made?
I would welcome your views.
|Rich, Fabrice, the toe angles quoted are for the individual wheels, which means that the total toe angle is 0 degrees 10 minutes.|
John, Micheldever tyres are a switched on outfit, and have used alternative tracking settings out of their own initiative in the past. I am sure that if you ask, they'll set the tracking to what ever you ask.
IMHO Rover's settings aren't exactly suspect, rather just 'safe'- designed to get the front end understeering and prevent the rear from oversteering. Remeber the headlines of the Mk2 MR2 being unsafe with snap oversteer? I guess this was a big influence on Rover engineers. The tracking settings quoted above alter this balance- I'd say to the better- but do bear this in mind if you do decide not to use the Rover settings.
Sue: Lowering knuckles are (in my opinion) a very worthwhile modification.
They do improve stability at speed, however the tracking setup of the car
will alter things much more than height alone.
Also, choose who lowers the car carefuly. Good outfits will also check how
the car is setup front to rear.
ie. The front suspension is connected to the rear suspension so how can
a car be higher at one end ? The garage will (should?) put the correctly sized
shimms in to make the car perfectly level.
"Techspeed". That's all I'll say on the matter! :o)
Rob: Think I'll invest a little more money into another allignment before I go
back to parallel all round then. Hope you're right! :o)
After coming back from holiday I jumped in the car and went for a blast up
my favorite road (at legal speeds with no traffic!). Nearly smacked the kerb
with the rear end... ToeIN at front, parallel at rears may be fun, but you just
cannot drive more than 8 tenths without loosing it.
And the bad news is I'm not into Castle Coombe. Did you make it ?
I'd describe S02s as 'progressive'. You can can the slide (many times an Anglesey!)
but you're not fast! :o(
John: Micheldever tyres will set it to whatever you like! Julian is the man with the
best knowledge and is truely interested in how the car handles. They sell v.cheap
tyres too! :-)
|Matt, the standard Rover setting for the F is..|
Front = Toe out
Rear = Toe in
So rear toe in is standard.
I (and others) are using the following
Front = toe in
Rear = toe out
This is the way most rear engined / rear wheel drive cars are set up.
With this setting it is advisable to have the compliance washers and polly bushes fitted at the rear. To avoid tyre wear and make the front more stable it is advisable to have the bushes fitted at the front.
None of this gear is essential, but I think when dealing with a safety issue, it is prudent to do whatever you can to make the car as safe as possible. I would also advise decent tyres as well. Maybe 195x50s on the front if you want less understeer also.
The F can never be set absolutely correct as the Hydragas is not very constant in it's height management. I sometimes wonder what Citroen would have done with the F :-)
|Good luck with the tracking Paul. I don't know where you plan to get yours done, but if you are in the Heathrow area then Feltham tyres do a very good job for 40 quid...|
Regarding Castle Combe, yup, I made it, I got an entry this time :o)
Are you going to Oddicombe? My car's brakes are still in pieces awaiting for parts from B&G. If they're not with me by tomorrow morning then I am stuffed! :o(
Tony, agree with what you said- but not all mid or rear engined cars are set up toe-in front toe-out rear. The Lotus Elise isn't for starters! I think that you'll find quite alot of variability on toe angles from one mid engined car to another- mainly down to suspension and dynamic compliance design to get particular handling traits. If it works on one car, it does mean it'll work on another...
|Would just like to agree with Rob,Feltham tyres set my tracking in the week and did a good job.|
although I asked in error for 0degrees5mins total, instead of both sides on the front but compared to the standard toe out setings the car handles a lot better,but probably will try more next time.
|Just a few comment on my experience with the MGF handling and some thoughts on what my be causing the problem.|
I have had the same experience with the vehicle snapping into oversteer with no warning at low speed. An unnerving experience because of the way it happen.
I was coming around a left hand corner in the middle of Sydney and would have not been doing any more that 40KPH when the vehicle back end come right around with no warning or apparent reason. Negative camber on the road and good tyres on the vehicle.
I have to admit I lost control of of the vehicle in a very dangerous situation with a large truck coming the opposite direction. Although I used to race an MGB some years ago and test drive vehicles, I found the experience quite unnerving expecially in reference to the dynamic behaviour of the vehicle. No warning, lost rear traction for no apparent reason and once it lost traction it snapped into violent oversteer with no way of controlling it.
Some months later I was invited to participate at a MX5 club meeting and the story started to unfold. I managed to spin the MGF three times in the first lap attemping to keep up with stock standard MX5 and it did not get any better for the remainder of the day! Each time the vehicle did a 360 with snap oversteer, no warning and too fast to contoll it. The problem was very pronounced if I backed off the accelerator in the middle of a corner.
Having worked as a motor vehicle suspension engineer some years ago I attempted to understand what was causing this behaviour and found some disturbing facts.
1. The rear wheel can move 5-6 mm backwards and forward relative to the body. This is caused by the amount of compliance in the connection between the radius rod and the lower suspension arm. This results in the toe-in setting changing during acceleration or braking. Hence should you back-off the accelerator quickly whilst going around a corner the toe-in setting will change to a toe out (depends on initial settings). You may also experience this when you go around a large radius corner, keep you steering wheel at the same setting then accelerate and decelerate and feel the back of the car start to come around. Roll Steer?
2. The vehicle has problems keeping toe-in setting. I have found that the toe setting front and rear changes quickly and considerably. I have a kept the wheel alignment print-out reports from my local tyre dealer which shows remarkable changes only a few months apart. This may be related to the hydragas suspension susceptibility to temperature which changes the trim heigh of the vehicle. This in itself would not be a problem, but I suspect that that this changes the toe setting front and rear because of the suspension geometry. Bump Steer?
3. The hydragas suspension design connects the front and rear wheels on each side to reduce the vehicle pitching. However, this is achieved by forcing the front or rear wheel to move up or down as required to avoid the vehicle pitching. The result is that the wheels are forced to move quickly through their travel when you are either accelerating or decelerating. Hence if the suspension geometry causes bump steer (which I suspect is the case at the front and rear) it is possible that this in conjuntion with braking or accelerating forces on the suspension linkages may result in an instantaneous change in toe setting. This may apply in particular to the toe-out at the rear which result in a change the tyre slip angle (loss of the tyre cornering force)loss of adhesion and hence snap oversteer.
4. The vehicle layout with the engine and transmission literally on top of the rear wheels give the car a low Polar Moment of Inertia. This means that the vehicle is very easy to spin, which partly explains the snap oversteer behaviour. Hence once you lost adhesion at the rear of the vehicle it it will spin very quickly and it is very difficult if not impossible to recover.
5. The standard specifications toe-out setting at the front of the vehicle is very unusuals not only it scrubs the tyres out but it also induces instability at high speed and oversteer.
I intend to do some physical checks to test the front and rear bump steer characteristics and will post the results.
I would also like to hear from anybody on this subject.
Many of these characteristics are reduced by fitting of the Polly bushes. The front and rear bushes reduce the bump steer effect dramatically. The rear bushes and compliance washers take out a lot of that tendency for the back to skip out.
Since having the bushes and compliance washers fitted I have now set the rear to toe out 5Min. Without the bushes this could become very unstable.
I still do not understand why Rover set the car to toe out. Since having the bushes fitted and the front tracking set to toe in the stability in a straight line if vastly improved and cornering, it really bites into the road. Tyre wear is also reduced.
I have 195s fitted at the front and they give less understeer which seems to make cornering more predictable. The car feels much safer now. I still need to do some more testing in the wet though.
I think my car was one of those that was not jigged properly as my front left camber is quite different from my right. It's within parameters now since I had the bushes fitted but it is still quite different. I assume that it is easier to get correct readings from the alignment now the suspension is not moving about all the time.
|John, I agree with your assessments on bump steer and roll steer. The amount of toe-angle change for the particular axle is dependent upon the ride height, and hence the angle of the track control arms relative to the position of the wishbones.|
The point about the degree of pitch is interesting- with front-rear connections of the hydragas system one might anticipate greater suspension movement front and rear than a conventional unconnected system with weight transfer, despite the incorporation of anti-dive and squat geometry. Interestingly, Techspeed disconnect the front and rear hydragas spheres for improved suspension control on road cars, and you'll not be surprised that the hydragas is not interconnected on the MGF Cup cars...
Reducing suspension movement by lowering appears to have big benefits on handling- perhaps because bup and roll steer influences are minimised. I've been plannig to check this out myself, but as usual, time is the greatest enemy.
Not surprised that the hydragas ststem are disconnected front and rear on the MGF Cup cars. We use to do the same on the racing Mini Minors with hydrolastic suspension twenty years ago for the same reason.
We either fitted a needle valve in the front rear connection pipe (to reduce the fluid flow and hence slow the pitch correction process down) or disconnecting them all together. We preferred to change Minis back to rubber cones which provided much improved control and predictability.
Which brings me to the MGF, it is apparent that this vehicle was never designed as a sport car.
The hydragas suspension have no business on a sport car, they are ideal for limousine ie. nice confortable ride, but certainly not on a sporting vehicle. Beside they are expensive, heavy and costly to maintain when compared with standard metal springs.
The lack of camber adjustment on this type of car is unforgivable! expecially when this is standard on most inexpensive cars available today on the market.
Having worked as a design engineer for BMC and later Leyland, this car looks to me that it was assembled from bits and pieces left over in the parts bin rather than having been designed from scratch. This may be a inexpensive way of building a car but it forces compromises some of which we are now discussing. If I am not mistaking the top suspesion arms on the MGF look teribly similar to the Mini manufactured 20 years ago and would not be surprised if they were interchangeable. The same applies to the Hydagas units.
As far as the antidive and antisquat from what I remember of the MGF suspension layout (I had a quick look some time ago and could be wrong) it does not appear to have much if any anti-dive or anti-squat designed in the layout. This is understandable as the MGF uses the hydragas units to control the vehicle pitch ie. it does the same job.
nice discussion. I try to follow.
For our other chaps some stuff to look and read:
How a MGF Hydragas Unit looks inside
How a Canadian Student found it should work
I never got an answer from that former student. Sad, it would have been very interesting to see the diagrams of his dampening measurements. Guess that John would be the right to explain some more terms.
|John, you are of course quite right regarding the provenance of the suspension system. The car's development is documented in a book 'Project Pheonix' (which sadly out of print, and I do not personally have a copy, but perhaps David Knowles new book on the MGF has similar details?). Basically the front and rear subframes are recycled from the front subframe of a Rover 100, ne, Austin Mini Metro, a car itself based upon a number of Mini components. There are a few Rover 200 parts thrown in, plus Austin Maestro/ Montego wheel hubs and brakes... Not a complete list I am sure, but you get the impression of a parts bin special!!!|
Regarding anti-squat/ dive geometry- I do not actually know if the MGF has it, but merely presume that it has... What modern car hasn't? I would guess that the F has got anti squat/dive becuase otherwise the car would behave like an old Austin 1100, and pitch horrendously, which frankly isn't something I've noticed...
Anyway, I guess we're stuck with what we have, and the question is, how can we improve things? Techspeed appear to provide one very attractive route, but it isn't available to all of us for various reasons. Answers on a post card to the usual address. ;o)
Dieter- shame that the student didn't get back to you, but the research he did was interesting!
|I do have the Project Phoenix book but have to confess I have not read it yet.|
I rather suspect that the reason the 'bins' were raided so heavily was down to pure cost and budget reasons.
One has to remember that this whole design exercise took place prior to the BMW take-over and at a time when no one had a clue as to how many units they would be able to sell.
And whilst the designers and engineers would no doubt have loved to build a car that we would all agree is fantastic, the accountants would have set very tight budgets for them to work to - hence the use of bits that have already been developed and save on cost and also time.
If someone could have convinced the board of directors in charge back in those days that the MGF would sell 100,000 units in approx 5 years then we may have got a different car.
As the old say says 'It is easy to be wise in hindsight'
|Lets not get too starry eyed about old MGs.. I suspect the A and B were just as dependant on the corporate parts bin as the F.|
I would rather have the cuurent compromised F than no F at all.
|and the fact that it HAS sold 100,000 units shows that they can't have done a bad job of raiding the parts bin.|
probably the best way to improve our "F" is to get as much info from Cup-cars as possible ! It would be very interesting if at least one of the 2 MG-magazines could do a series of technically articles about all the improvements made . Surely not all of it would be suitable for road use but would be as said very interesting ! By now after several seasons all the weak spots would be found and corrected. Dieters pictures revealed some but not all....
|I only asked if anyone had any decent tracking figures!|
Anyway I think it is great that there are so many knowledgeable owners around to pass on info. and idea's.
who said that we got ready ?
MG-Rover-BMW got not ready with the design, so how should we 'half-speciallists' ever get ready talking about it ?
>Cup-cars .. Dieters pictures revealed some but not all....
Yes, Carl, Rob took also, but guess his camera had problems ?
You mean this one, do you?
Extra bar, welded to the front subframe:
Lower wishbones, both adjustable. And non of the crap rubber bushes.
A very interesting term was told by a small raceteams head (sorry, forgot the name) He told us that the rear camber of the Cup-Cars should be about 6 degrees. Otherwise non of the course curves could be done without slipping from the course.
Yes, this is a very interesting thread. I can't do a side-by-side comparison but I think that the subframes, although based on the Metro design, are quite different due to the much wider track of the F and also some crash deformation issues. Most cars from the same marque, regardless of expense, share components both to reduce costs and to retain some common identity. I don't mind too much riding around in what's little more than a fat Metro, after all it's not too obvious. I'm not too keen on the front wishbone and swivel joints though, they look decidedly flimsy.
As to the definitive tracking settings, I don't think that there are any! There's the best compromise for road use, and the best for track use, and any amount of variation to suit the driver and tyres, etc. I'm grateful that there are enough interested parties about to try out all these settings. I'm not sure what cars John has in mind that have adjustable camber. I can't think of one that isn't on the track. It's perhaps a good thing, just think of the additional opportunity to set the car up incorrectly, and all the threads discussing what it should be.
By the way Dieter, your URLs seem to end up a blind alley. Is it me?
Regards, Kes (350mm and parallel f/r, no c/washers, 16" F1's, no scares).
|This is all very interesting, and has given me some insight into the changed handling characteristics of my car, after my rear suspension settings we modified back to within the Specified Rover ranges.. It has made the car worse ! (I did have about 1.5 ~ 2 deg additional -ive camber on the rear wheels..)|
There has been much talk about the Compliance Washers and the Polly Bushes.. Can any one show me some pics of a car with these fitted (both washers and Bushes), and also a picture of the parts that we are actually talking about - What you actually get.
I'm wondering if these items can be purchased here in OZ from the generic parts bin, as the Exchange rate between the OZ$ and UK pound will send me broke if I order them from the UK..
If any one can supply measurements for the above items as well, that would be fantastic.
thanks for your hint on the blind links.
Its a new account there in Austria. Guess those provider guys 'practice' still:(
Sometimes it works, sometimes its down.
Pictures of the Cup-Cars wishbones are as thumbs also on
>Can any one show me some pics of a car with these fitted
I'll try a consumption of where the are.
One of mine: http://members.tripod.de/MGF/bushes/bushes1.htm
|John you say....|
>This is understandable as the MGF uses the hydragas units to control the vehicle pitch ie. it does the same job.
Surely under breaking weight is transferred to the front of the car forcing fluid through the link to the back increasing the pitching moment? Same on corners as the weight transfers, the suspension only locks out after pitching in to the corner. No expert but having had the system split front to rear the difference is amazing. The car doesn't dive or roll anything like it used to and in a corner it goes exactly where you want. Plus there it's stability over bumpy roads is excellent. Push it and it oversteers pretty progrisvely as well. Standard tyre sizes so guess if it had 205s at the front things would be a little more "exciting".
>>It would be very interesting if at least one of
the 2 MG-magazines could do a series of technically articles about all the improvements made <<
Yes, I have thought about this too (and see the thread that Gaz started 'Cup Car 2 road car'). And yes, it would make for a very interesting article in an MG mag...
Actually, the mods that Stuart has had performed on his car is as close as a road car is likely to get to a Cup Car for the road.
Other than this approach, are there any others?
|>> Actually, the mods that Stuart has had performed on his car is as close as a road car is likely to get to a Cup Car for the road ...|
Stu .... speak up man ... give us the details ...
|OK ... I've just read the 'other' thread I started ... no need to explain ...|
You are perfectly correct! The interconnection of the front/rear wheels only reduces pitch at constant velocity when the vehicle hits a bump or ditch in the road. It accually aggravates the situation under braking or acceleration.
As I was experiencing instability under braking and I had another driver take the vehicle around the race track so that I could observe the vehicle dynamics. It was noticeable that the rear of the vehicle would jack up and wiggle when the driver hit the brakes at the end of the straight. This was probably caused by a number of factors associated with the rapid change in pitch. The toe-in/out would probably change and the contact force between the tyre and the road reduced leading to loss of braking force from the rear tyres.
I have since fitted Koni dampers front and back which has greatly reduced the pitch under acceleration and braking and given the vehicle a very solid feel. The koni are double acting whilst the original are only signle acting ie. only work on rebound. To some extent I have probably achieved the same effect that you have by splitting the system.
Stuart, can you provide details of what you actually have had done to your vehicle. Can you now independently adjust the height of the vehcle at each corner without having to fit spacers under the hydragas units?
|Scott, Phew just finished my update to my web pages showing upgrades and additions to my MGF. Shows pictures and a diagram of the bushes and washers.|
Not as technically detailed as others by any means but at least shows you what they actually look like in your hand.
Still needs a bit more work, so if anyone has a good picture of the Mike Satur Walnut Ashtray and a set of his old alli seat recliners and door lock pins please send them to me :-) Cheers
|Pitch under braking is a problem John, as you quite rightly say. In addition to the toe angle changes you get as a result of frictional forces on the wheel causing them to splay outward (pivoting around the kingpin/ steering axis), one also gets toe angle changes as a result of suspension compression at the front, and suspension 'expansion' at the rear. The geometry can be designed in such a way to for this latter phenomena to compensate for the former toe angle changes. Having not done a study of the MGF yet, I cannot say whether this has been done on 'our' car.|
However, I would have said that the squirm of the back end you noted is likely to be secondary to the extreme compliance of the rear tie bar bushes- and the reason why Competition Parts introduced the compliance spacer bushes for motorsports use. The rear end of a car so equipped would be far better tied down than your car appeared.
Adding different shock absorbers is certain to make a difference to the car- the degree of suspension movement will be more contained under extremis to the benefit of geometry control. However, many will have noticed that the Moss catalogue contains a warning about up-rated dampers. Remember that the car was designed with very weak shock absorbers in mind, so the stress transmitted to the bodywork is lower. The stiffer the shock absorber, the more energy the shock absorber mount needs to absorb. And the trouble is, over time, the shock absorber mounts cannot take this kind of use, and will crack. So if using adjustable shocks, use as soft a setting as you can.
Personally, I think that shock absorbers should be one of the last modifications- after uprating the suspension bushes, and perhaps after disconnecting the fore-aft hydragas lines.
|Indeed this is an interesting thread. Now looking a degree further down the line I had some dealings with AP in the late 1970's and expereinced their Active Ride suspension system. Interesting concept which was qyuiet effective, especially bearing in mind the low speed electronics and valving thatw as then available. Actibe ride of course later became a very advanced feature of F1, subsequently banned.|
Recent years has seen the re-establishment of AR in some of the more exotic vehicles. Now however the MGF has a distinct advantage as it starts off with a fluid suspension system rather than seeing a steel suspension have to be converted. In the first instance some of the degree of pitch can be controlled by the simple inclusion of an interconnecting valve between front and rear that can be shut down during brake applications. This would reduce the front to rear fluid displacment. Simplistic I know and refinement would be needed.
Next it would not be beyond the bounds of possibility to create something of an active ride by the use of an ABS pump and some additional 'plumbing' and electronic control. Pitch and ride height sensors could then actively induce not just a stop of front to rear fluid displacement but actually increase front pressure to resist front dive.
Take yet another stage and have side to side interconnection and cornering forces can be resisted in the same way. The base benefit, just as with the old AP AR system is that the suspension allows the retention of the tyre contact patch on the road surface and as such the maximum grip of that patch is retained much more than under normal conditiins where the tyre is 'rolled'.
This thread was discussed between 10/10/2000 and 29/10/2000
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