MG4 Undertray dip/bulge

fnegroni said:
Before I read 40 pages of posts, does the fix/modification (official or not) show any improvements in terms of aerodynamics whether it’s noise reduction or energy consumption?
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Over to our Australian contingent - anyone tried it? Does it actually exist?
I wouldn't notice noise reduction as I always follow the advice of a mate who was a mechanic and have the music loud. Regards energy consumption, again I would imagine it's very difficult to quantify as there are so many contributing factors, certainly by the man in the street. My concerns are crap, specifically corrosive road salt getting up there and corroding parts and going unnoticed and aerodynamics with subsequent effects. It is outside of the designed specification.
 
OriginalBigAl said:
A properly fitting undertray would appear to be a statistical anomaly, possible , but unlikely.
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When I was last at my dealer (getting the SOH checked) I looked at 2x SEs and 1x X-Power in the showroom ... the X-Power had a noticeably-warped undertray but the ones on the SEs were very flat.
 
DaevM said:
My concerns are crap, specifically corrosive road salt getting up there and corroding parts and going unnoticed and aerodynamics with subsequent effects. It is outside of the designed specification.
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Not to mention getting it ripped off or damaged. On the lanes near here some potholes get to 4" deep before they're repaired - even inching through them is a bit worrying.
 
siteguru said:
When I was last at my dealer (getting the SOH checked) I looked at 2x SEs and 1x X-Power in the showroom ... the X-Power had a noticeably-warped undertray but the ones on the SEs were very flat.
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Mine (se lr) was very flat when I collected it at the beginning of March. 3 weeks and a 591 miles later = warped and bulgey.
Definitely the mileage doing it as it had been 'resting' for 10 months between being built and me taking delivery. I e. It has just warped over time.
 
Hi,

Can anybody provide the measurements of the official (Australian) fix?
Thinking of building one myself since the dealer has already reviewed the undertray and they say there is nothing wrong with it...

BR,
 

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You did ask him how it feels driving on a motor bike at 100kmh with his mouth wide open? Pathetic.
Although my gutt feeling says he knows it isn't ok. But he is told to save MG's profits....

DaevM said:
Mine (se lr) was very flat when I collected it at the beginning of March. 3 weeks and a 591 miles later = warped and bulgey.
Definitely the mileage doing it as it had been 'resting' for 10 months between being built and me taking delivery. I e. It has just warped over time.
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Bolts coming loose? Gap increases? Air starts pushing in and deformes the undertray (it is plastic).
If this is correct: once messed up you cannot undo it. The material is stretched at the front side. Cutting it at the sides, create new holes to fit the bolt position and putting an aluminium bar on top of it could fix this.
 
It's probably getting hot and deforming, probably used a plastic with too low a heat deflection temperature.
Installing heat reflective pads may help prevent it.....not much use when it's already warped.
 
Les burrows said:
Ina word NO
Les
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You'd need to do tunnel-testing (as in wind, of the airflow variety) to determine the actual increase in drag. Consider that Honda reckon the drag reduction on the Honda e due to removal of the wing mirror pair is iro 4% of total drag, and VW put flatish covers on their EV wheels (iro 6%(?)), one might estimate the open-mouth mg4 aft tray to be iro 1 to 2% ( the flow speed is quite high in the underpan region -hence the coverall tray), depending on the size of your bulge.
Imo MG are being deliberately obstructive on this issue: even ignoring the, say, 1% drag coefficient increase and neglecting the dust/crap/rabbits ears that collect in the space above the pan, if you drive though water deep enough the pan will get ripped-off, or at least proper buggered.
Anyone know anything about 'class actions'??

fwiw, i was wondering where the 'air' (and muck) is coming from that's making this...
it's a backwash of air that's probably picking-up grot from the wheelarch flow, but a higher-pressure feed is exiting the rear door-wing panel gap into the turbulent boundary layer - i wonder if the positive pressure is coming from the air scoop...
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p.s. Warning - OFF TOPIC: (SE owner): some time ago i told a posh-car mate that the Trophy/LR spoiler 'covers' (fitted to the SE) were auto-deploying emergency air brakes that only functioned under emergency braking at more than 100mph. It was a bit of a joke; i thought he'd just laugh. But now he keeps asking to go for a blast, so's to see it working. I remind him the speed limit in the UK is 70, and that the car is limited to 99 anyway. But he's genuinely keen, not bluff-calling. Any advice, pls?
 
Ah well, lies and deception is it. You could say that they have been disabled via OTA updates because although they drastically improved the MGs braking, they also disrupted the air flow for any following vehicle increasing their braking distances resulting in the MG being rear ended. After that you are on your own!:whistle:
 
turntoport said:
You'd need to do tunnel-testing (as in wind, of the airflow variety) to determine the actual increase in drag. Consider that Honda reckon the drag reduction on the Honda e due to removal of the wing mirror pair is iro 4% of total drag, and VW put flatish covers on their EV wheels (iro 6%(?)), one might estimate the open-mouth mg4 aft tray to be iro 1 to 2% ( the flow speed is quite high in the underpan region -hence the coverall tray), depending on the size of your bulge.
Imo MG are being deliberately obstructive on this issue: even ignoring the, say, 1% drag coefficient increase and neglecting the dust/crap/rabbits ears that collect in the space above the pan, if you drive though water deep enough the pan will get ripped-off, or at least proper buggered.
Anyone know anything about 'class actions'??

fwiw, i was wondering where the 'air' (and muck) is coming from that's making this...
it's a backwash of air that's probably picking-up grot from the wheelarch flow, but a higher-pressure feed is exiting the rear door-wing panel gap into the turbulent boundary layer - i wonder if the positive pressure is coming from the air scoop...
View attachment 26390

p.s. Warning - OFF TOPIC: (SE owner): some time ago i told a posh-car mate that the Trophy/LR spoiler 'covers' (fitted to the SE) were auto-deploying emergency air brakes that only functioned under emergency braking at more than 100mph. It was a bit of a joke; i thought he'd just laugh. But now he keeps asking to go for a blast, so's to see it working. I remind him the speed limit in the UK is 70, and that the car is limited to 99 anyway. But he's genuinely keen, not bluff-calling. Any advice, pls?
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Interesting. I am also getting that, but I hadn't connected it with the undertray.
 
ok, to elucidate: the grot patch was/is noticeable on both rear wings. It is the result of a differential pressure-bleed contraflow of relatively dirty air/water into the turbulent boundary layer along the vehicle side at that point. It is not purely a function of the wheel-tyre chucking muck off; if it were, the grot would be stuck on from the edge of the wheelarch forward. But it isn't; the grot clearly is exiting the rear body panel-to-door gap. Now i doubt very very much it is exiting the door seal - that implies the interior of the car is full of crud, and it isn't (even with the grandkids in there). So the airflow originates between those pressure-zone discrete assemblies; i'm intrigued as to whether the undertray (scoop - fed) airflow is the source of the positive pressure; SAIC should be able to model this fairly easily.

This undertray scoop stuff isn't rocket-science - SAIC should sort it gratis - saying it's 'acceptable' is just total bollocks; the vehicle drag coefficient is not what it was for the wltp/other tests because the build standard is non-compliant to that certified. Simple.
 
You said rear wings. I assume you mean rear doors?
You could start a poll to check if a bulge consistently comes with these dirt patches. But you need two separate questions to make it work. Does you MG have a bulge y/n? And do you have the dirt patches y/n?

Btw, I fully agree with you about the effect on energy consumption.
 
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DaevM said:
Mine (se lr) was very flat when I collected it at the beginning of March. 3 weeks and a 591 miles later = warped and bulgey.
Definitely the mileage doing it as it had been 'resting' for 10 months between being built and me taking delivery. I e. It has just warped over time.
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Heck! Mine as well..
It was close to perfect when I got it. But it isn't anymore. Left and right of the middle bolt you can see slight bulging appearing.
Could it be motor heat softening it?
 
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