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MG MGF Technical - aerodynamic data / splitter

I have fitted a KH splitter a while ago and I'm generally very happy with effect on straight line stability on our beloved Autobahns :-)
But when looking at the car and that monstrous splitter I often wonder whether it could possibly have too much downforce at the front and still too much lift at the rear now, which would result in a very oversteery behaviour for example in an emergency stop from high speeds. Now, this is something I would definitely not like to encounter!
I am therefore thinking of fitting one of those small boot-lips that are fitted to BMW M-cars and AMG Mercs these days which are reported to cut rear end lift by around 50 % on those cars.
But as long as I don't have a clue what the aerodynamic balance actually is like at the moment I can't decide whether this makes any sense!
So now the question: does anybody have windtunnel data of the MG-F or information on how exactly a splitter effects the aerodynamic balance (surely KH-Assemblies must have done windtunnel work for their splitter!?) ?
Looking forward to your thoughts!

Nikolaj, as far I know, it doesn't push the front end of the car downwards, rather just reduces the amount of air flowing underneath it (I think). The rearend twitchness you are speaking of can be reduced or removed completely by fitting rear compliance bushes to the rear suspension (the anti-roll bar bushes IIRC). This stops the wheels slightly changing track as the front of the car dips down when you brake. (Again, I think this is what happens, not 100% sure).

Anyway, you don't want a spoiler that would press the rear end down, as that isn't actually helpfull. MG themselves designed all the spoilers on the Z series to be zero lift generating (+ or -) for this exact reason. The trophy rear spoiler is exactly the same.


Steve Childs

>>So now the question: does anybody have windtunnel data of the MG-F or information on how exactly a splitter effects the aerodynamic balance (surely KH-Assemblies must have done windtunnel work for their splitter!?) ?<<

As usual Nikolaj, you raise some very interesting points- and aerodynamic balance is something I have had an interest in. I've noticed on the autobahn at speeds >120 mph that the rear-end becomes worryingly light suggesting that there is more lift at the rear than the front. However it must be said I had a bootrack fitted everytime I've been in Germany and it almost certainly ruins the aerodynamics over the rear bootlid...

KH claim that they tested their splitter at the MIRA wind tunnel, and one assumes that MG themselves tested it- and indeed a number of development MG-Rover cars have been spotted sporting the KH splitter. Unfortunately, if there is any testing data, it is not in the public domain.

I would make one observation though. Note that the Trophy 160 sports a front splitter. Note also that this car ALSO has a rear spoiler. Significantly, both of these spoilers were developed following extensive wind tunnel testing (if we believe the sales hype). Therefore, it would appear that a Trophy front spoiler would NEED to be balanced by a rear spoiler...

I suspect that the best way forward is to fix one of these rear spoilers to your car temporarily and do some high speed testing of your own. If you do this, then please let us all know your discoveries!
I suspect for those of us stuck in speed-limited and congested UK its a 'not-strictly necessary' piece of kit...
Rob Bell

I was on the autobahn recently at >120mph, splitter, no boot rack and felt stable.

Probably the effect of the boot rack then! Useful to know- there aren't any stability warnings associated with the fitment of bootracks to my knowledge...
Rob Bell

Did you have a case on as well?
BTW Sally had never done 140 before:-))) (Going by revs, more on speedo)

>>there aren't any stability warnings associated with the fitment of bootracks to my knowledge
No, but there are with driving at >120mph !!!!


>>>Note also that this car ALSO has a rear spoiler. Significantly, both of these spoilers were developed following extensive wind tunnel testing (if we believe the sales hype).

So is the Trophy rear spoiler actually doing something? I had the impression that the previously available Rover spoiler for the F was just, er, decorative.

I never could decide on that rear spolier. All other mods I have ever though about were either clearcut "I want one" or "Yeuuch". Problem is that the spoiler I like most is the Rover one which is quite expensive.

Especially as it's not chrome....
David Bainbridge

David, I can get the Rover spoilers quite cheap, the Trophy spoiler would be £150.

If you compare the drag figures of the trophy vs the normal MGF, there is a slight reduction in drag with the trophy, so one can only assume that the spoilers do work.

Although the KH splitter is more effective than the trophy splitter.

Steve Childs

Gareth, no case on the bootrack- I usually find I can pack more than enough in the car to not need the boot rack. It's usually fitted so we can get the booze into the car before returning to blighty- or in the case of last years' Treffen, taking home a second hand roof!!!

>>Although the KH splitter is more effective than the trophy splitter.<<

That's an evocative statement Steve- how do you know this? :o) Have you got a Trophy splitter on your car now?
Rob Bell

may have to take my rack on Treffen, case of Mobil 1 to bring back.

>> That's an evocative statement Steve- how do you know this? :o) Have you got a Trophy splitter on your car now? <<

Well, I know someone who was told by someone at MG, apparently the KH is 40% more effective. - going on what he said, obviously no realistic way to prove it.

Steve Childs

>>>>>David, I can get the Rover spoilers quite cheap

(In dodgy James Bond film-type middle-eastern accent:) You give me good priiiice, yeeees? How much you want for ze spoilerrr? You want yankee dollar, yeees?

By the way, does anyone have a picture of an anthracite F with a black K&N splitter on? (Dieter's probably got a gallery of one being fitted, removed, fitted upside down etc.)

David Bainbridge

David, price is above!! :) Haven't asked for the other spoiler, manily because it appears noone wants it and prefers the Trophy spoiler. I would guess it would be the same price though - retails for the same price through the dealer. Plus if yours in Athracite, you wouldn't need it spraying either ;)

Steve Childs

On the subject of Treffen and parts transports: I still have two nearly new 205/50 ZR 15 Bridgestone Potenza S02 PP lying around in my garage that I desperately (->cheaply!) want to get rid off!!! They have around 6mm of profile and have only been used carefully (no curbing etc.) for about 6 months as rear tires on my F. I planned to replace my Michelins at the front with Potenzas as well but Bridgestone doesn't produce these tires any more and as I didn't want to use different tires front and rear any more (resulted in bad handling!) I changed to Toyos all around.
In Germany nobody seems to have Potenzas fitted on their Fs so nobody's interested in my tires, but as most of you do have Potenzas I suspect you might be interested...!!!
Aachen is not far away from where you are going, unfortunately I cannot come to the Treffen myself but we should be able to sort something out in case anybody wants to buy the tires.

my F is charcoal and has a black KH splitter.
But I think you'll find a better picture of Matt's former car (anthracite) on Steve's website (
IMO, a good combination of colours. The paint of the car is dark enough to avoid painting the splitter if you don't like the contrast of the 2 colours.

You're right about Dieter : he has an online "how to fit a splitter" guide. We got our splitters together but he was quicker to fit... anyway, the instructions that KH provide are clear enough to figure how to drill 6 holes ;))

Maybe interested in those tyres Nikolaj- my front 195/50s are starting to look rather ragged on their outer edges thanks to all the track action they've seen ;o)

How much are you wanting for them? Not sure who'll be able to bring 'em back to the UK though... :o( Most of the Treffeners will have their luggage compartments filled to capacity.
Rob Bell

Lots of discussion about aerodynamics, but (unless I have missed it) no discussion on weight and positioning of that weight. The effect of weight is significant as it will compress suspension. More importnatly is where that weight is placed as between the axles it will have a reasonably even effect on compressing the suspension.

However in the boot you are a little distant from the axle line and this creates leverage effect which multiplies the effective weight. Placed behind the rear axle means that the pivotting effect revolves around the rear axle and in doing so compresses the rear suspension and raises the front. This has a huge effect on the airflow over (and under) the car and the lift effects.

The effect of weight will have more impact than the addition of a boot rack or other appendages.

Roger Parker

I'm gonna spout loads of stuff now, and it may not all be true, just basing it on my knowledge of aerodynamics and stuff.

Firstly i would say that the aerodynamics at 120, or the effects of things on aerodynamics would probably be a lot more important than you think Roger, at those speeds the aerodynamic forces are getting pretty big. and would certainly reduce the importants of weight. suspension compression however has a big effect, mainly cos this effects the aerodynamics of the car. and why range rovers of modern day lower themselves at speed, reducing the lift and stability

As for the boot rack making the tail happy, i would think this unlikely. More likely to do the opposite as it would act like a spoiler. Spoiler ain't just a clever name, it does what it says on the tin. Spoils the air flow over the car, therefore reducing lift. If the flow breaks away from the car it is not helping the lift situation anymore, therefore keeping the car nicely on the ground.

This also goes for the comment about the rover spoiler being decorative. People often think that spoilers are decorative purely because they can't see how they can produce down force, and well...none of them do, if they did they would be called a wing (ala the wing on a cosworth escort) i little lip spoiler however insignificant will probably have some spoiling effect and therefore reduce lift.

The clever bit is to spoil the air flow and reduce lift while not increasing drag. because inherintly a messy airflow is more draggy. so that is why they have done a good job on the trophy, making it more slippery while keeping it on the ground better.

what else can i make i think thats it

go on, tell me i'm talking rubbish, and if anymore stuff springs to mind i will be back to share it with you

Rob, I don't know UK tyre prices so I don't know what price would make sense for you. Let's do it the other way round: what would you think an appropriate price ;-) ?
On the subject of aerodynamics: I have kindly asked KH Assemblies whether they are able to quote some data, let's see whether and what they answer...!

The data would be interesting, if only i was back at uni, i could have had an interesting final year project playing the wind tunnels

Nuts- I can't remember how much I paid for the bloomin tyres @ Micheldever- about 50 quid? So scrubbed in 'second hand' tyres about say 20-30 quid each? What do you think Nikolaj?

Rog, for the record, the trim on my car at the time was neutral with the load in the boot (my car unlaiden used to have a nose-down attitude before it got "Techspeeded"). Therefore not sure how much of a difference this would make in this instance. Being roof-down and an empty bootrack fitted probably more of an effect me-thinks...

Matt- D'oh!!! Can't you sneak back to Uni? ;o)
Rob Bell

Rob, I paid around 70 quid each here in Germany so I think 30 quid each should be fine with both of us, shouldn't it? So all you 've got to do now is find someone to bring them to you, which is probably the difficult bit. Good luck to both of us then ;-)

Suppose it will be difficult to persuade a Treffen guy to put two tyres instead of a load of red wine to the boot rack ;)

On the other hand we meet up hopefully with a lot of Belgium Enthusiast on Saturday (arrive at March-en-Famenne on Friday). Could be possible to close up 4you ?

Nikolaj, you also should ask Ralf from Munstereifel for transportation abilities. May be he can help.

Dieter Koennecke

Dieter - come join us in Do't chat room - see the General BBS. :)
Paul Lathwell

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It doesn't like my firewall, dohh.
Will try a different Provider
Dieter Koennecke


I think you miss my point, which was that it the effect of weight and how it alters the attitude of the car, which consequently alters the aerodynamic performance - negatively! We actaully agree completely.

Testing at Bruntingthorpe at up to just short of 170mph I have lots of experience of the effects on how very small changes of attitude really stacks up the effect as speed rises. I would actually comment that around 100mph was one of the thresholds where things started to happen more obviously.


Roger Parker

This thread was discussed between 04/09/2001 and 05/09/2001

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