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MG MGF Technical - The F and Body Roll
Had to rapidly swerve at the weekend (cyclist tried to kill themselves by falling on the A1 in front of me in a 60 strech, was doing 45 at the time). In my last car, you'd get no body roll.
I think you can probably guess what I experienced (major body roll and nearly lost the back-end). Can anyone explain what causes this, and how it can be reduced (or eliminated)?
How old is your car ?
If it's more than two years old (or possibly brand new!) the suspension may be faulty - worn dampers, bushes, mountings, etc.
Alternatively how high is the suspension - if it's pumped up too high then you could see problems like this.
The F should be able to swerve without problem - the limiting factor should be your ability to stay in the seat (which doesn't have a lot of lateral support) !
Have the suspension checked, and replace any worn components. Get the suspension height set low, and the tracking set accurately.
|I had to swerve at the weekend after coming round a corner to meet some twat Jag driver coming at me on my side of the road! Even though my suspension is towards the high end of the recommended range, I thought the car coped pretty well - little roll and no loss of grip. The Jag (an X) on the other hand was strangely all over the place. Hasn't it got the Mondeo chassis that's supposed to be so bloody good?|
I suppose what I am saying is that I would agree with Steve that if body roll really struck you as an issue then something may be faulty. O.k., the F's not an Elise, but I haven't found this body roll thing a real issue.
|The instability may have been in part because you were braking at the same time Leigh. With a mid-engined car, this can mean a very significant weight transfer, which will tend to pendulum the rear end as you steer in avoidance. This effect tends to be exacerbated by the built in passive rear wheel steer - for which I'd recommend it's removal by the fitment of compliance spacers.|
Roll isn't really a problem on the F - but the initial rate of roll is a little higher than on some sportier cars because of the damper design. The standard dampers have little resistance to compression, and work only in the rebound mode. Having had eibach dampers fitted, the initial rate of roll has been dramatically reduced. Makes for a much more confident feeling car :o)
|Rob, sort of related to your comment about compliance washers - do they improve the rather skatey behaviour of the rear of the F on ice? Or is that just a law-of-physics thing that we can't do anything about?|
|A combination of the two I think David - in that the weight transfer and the polar moment of interia tends to unsettle the rear of the car. The passive rear steer may or may not be of benefit under such circumstances - but is usually a hinderence in that the rear wheels start steering out of the slid allowing the rear to swing out (baby! - sorry - saw V Graham Norton who had Mike Myers of Austin Powers fame on his show). |
Best to get rid of the passive rear steer IMO, for more predictable responses :o)
Wasn't breaking at the time, as no way was I going to stop, and swerving seemed to be the best option. Might try getting on to a disused airfield or big car-park and try swinging the car around a bit, to try and get a feel for how severe it is.
The car's on the lower side within tolerance, so it's not a height issue. As I recall there was a significant amount of roll initially, and I think this was exasperated my me having to swerve back in to my side of the road (quick right-left-straighten up movement). Felt like the car got a bit of a lashing on the left-straighten up phase.
Car is 98, and was thinking polybushes might help.
|Leigh, again as mentioned by sTeve already.|
Check the dampers imidiately. I think they will start loosing performance already from above 40k miles. The rubber bushes which hold the dampers should be checked as well.
>compliance washers - do they improve the rather skatey behaviour of the rear of the F on ice? Or is that just a law-of-physics thing that we can't do anything about?
From my own experiance they don't and I also would not think they may do. More camber may do, I do not know. The MGF design makes the rear part of the car much heavier then the front. (60:40 rear:front ?)
If the rear breakes out cause of blocked wheels from braking or a blown tyre or on ice then only very very quick steering to the opposite side can help to give the rear wheels any grip back.
A sliding rear doesn't steer. If the whels roll then there is a chance to lead them back to straight ahead direction. Toe angles of the rear wheels have silly influence as well, making the MGF to a devils tool if it once gets out of straight ahead direction.
I like to remember on the skid course I did two month ago. MPG and AVI files from the damn hydraulic side shift thingy and track are still @ http://www.mgfcar.de/2002.fst/index.htm
Unfortunately they don't show us turning the steering wheel like mad ;)
|The variable torque response of the electronic PAS acts much faster than the more normal hydraulic PAS and can make the car move sideways very quickly. The first time this happens it can feel like excessive body roll when actually the car is responding to the instruction from the nut behind the wheel.|
| I had to swerve last night to avoid a baby!|
cracked my head on the bedside cabinet though.
Yes, major body roll!
That could be it to be honest. I was out in the car the other night, doing a bit of 'waggling' (no idioms please), and found the car was Ok.
May well have been the nut behind the wheel over-reacting. The pugeot I had before had hydraulic pas and was more 'predictable'.
I do find at times with the 'F's steering the car is ahead of where I expect it to be. Wonder if removing the epas fuse for a bit might be worth a try?
Thanks for all replies,
|You may also want to consider the hydragas restrictor valves "nipple job" as fitted to the Cup cars and made available thru Techspeed.|
>> (60:40 rear:front ?) <<
Hmmm, IIRC Rover claimed 55:45 rear:front
|>Wonder if removing the epas fuse for a bit might be worth a try?|
If you're doing more than about 25mph, then the EPAS won't be assisting you anyway - it'll have switched off.
I would check the shock absorbers are still connected to the axles - as the car's a 98, the bushes may well be shot, particularly the rear. I replaced my 97 ones this time last year and they were "bad"!
|Apparently the EPAS kicks back in at high torque. Although I have yet to go to north weild and try this ;-)|
|>>Apparently the EPAS kicks back in at high torque.<<|
This is absolutely correct Will. There is a noticable difference in steering behaviour at any speed with the EPAS disconnected. As you probably know better than anyone m8!
|It does appear better without, but untill I get far enough thru my tyres to justify a airfield day I cannot say for sure. Having fitted the switch I hardly ever switch it on unless manovering in very tight spaces, forgetting to switch it off and the car feels very light.|
I let Becky drive it the other week, and she didn't complain about the lack of PAS, but was shocked when I switched in on just before she pulled into the carpark (I did warn her!) and how light it got.
This thread was discussed between 08/07/2002 and 22/07/2002
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