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GerrardLFC

Hello,


A few days back I was driving along a notorious road in the welsh mountains that has a lovely little stubborn speed bump over a hill which I happened to hit at about 40 (bare in the mind the limit for this road is 60 and the bump appears from nowhere once you go over the hill) thanks to hitting this bump I've completely smashed the plastic which is under the car and I'm assuming is there to protect the engine?  It also managed to knock the tracking out a tiny bit. 

 

Once I got back home I noticed that a massive piece of what I could only assume is sound proofing was missing 2 bolts and was hanging down from the car, I will be getting this re-attached in the morning.


Is this plastic important or should I not worry about it too much?

 


I have a Focus Zetec 2012.

artscot79
The plastic protects the engine keeps crap off reduces engine noise and should be replaced if it knocked te tracking out it may have buckled an alloy as well
JayTDCI

Sounds like you hit the under tray to me, best to get balancing and tracking sorted, if you've noticed vibrations on steering wheel.

FOCA

You should complain about that bump - i wonder how many others that has happened to?

Andy H Dibley
Lost my under tray when I hit a deer just before Christmas, first car I've owned that's had one. They mainly provide protection from gravel roads and splash protection from big puddles. Been driving without one for 6 months, no issues yet. First car I've had with one tbh.

The only bit that is semi important is the air dam either side of the from AC condenser, that kinda focuses air onto it. Not a huge pain if its not there, just handy.
ffz

I might be talking out of my backside, but is there not some aerodynamic benefit to this panel? 

FOCA

I might be talking out of my backside, but is there not some aerodynamic benefit to this panel? 

Yes, apparently it tidys up the air going under the car, some call it a "fairing" its effect is probably quite subtle though,

 

i was doing some work under my car last year and never bothered to put it back on (its extra weight, anyway) the only difference i notice is the engine is louder and i get a bit more clearance over speed bumps, i possibly get a lttle less traction     

 

some cars came with them fitted, some not  

 

i think it may be an expensive item new and hard to track down one secondhand for a 2012 car  

Andy H Dibley

I might be talking out of my backside, but is there not some aerodynamic benefit to this panel? 


Not really, what you might be thinking of is the same panels that racing cars have fitted. These panels are there to speed up the air flow under the car, from the splitter at the front to the defuser at the back. It makes the car like a reverse airplane wing and offers down force.

For this to work though the car needs to have an almost uninterrupted flat surface from front to rear and needs to be travelling at fair old speeds. Somewhere in excess of highest speed limit for it to be of any use.
FOCA

Not really, what you might be thinking of is the same panels that racing cars have fitted. These panels are there to speed up the air flow under the car, from the splitter at the front to the defuser at the back. It makes the car like a reverse airplane wing and offers down force.

For this to work though the car needs to have an almost uninterrupted flat surface from front to rear and needs to be travelling at fair old speeds. Somewhere in excess of highest speed limit for it to be of any use.

I disagree, road cars have to travel through the air too, and even though they are not designed to produce downforce,  modern cars are aerodynamically designed to slip through the air to get a good fuel consumption, the undertray looks like it fills the space between the bottom of the front of the car and the front of the floorpan where it seems to line up nicely, although there are parts sticking out like the suspension, the exhaust, fuel tank and other components are tucked away out of the airflow

 

The undertray looks like it has aerodynamically designed vents in it  and if you thing about it the air going under the car is going as fast as the air on top (eg, if the air on top is doing 70mph, the air underneath in doing 70mph)  

 

Areodynamic drag is a square law - that means doubling the speed increases the drag by four times,(eg - there is FOUR times the aerodynamic drag at 70mph than at 35mph ) that is why the fastest Veyron had to have the power increased from 1000Hp to 1200Hp just to get a few more mph to retake the "fastest car" catigory - James May drove it but was not allowed to explain the square law - the producers wouldent let him, they thought the audience would not understand it - so he had to say the air was "thick" like treacle at high speed, instead  

 

you can consider the undertray like the fairing on a motorbike, it too, does not produce downforce or does not go all the way to the back of the bike, but helps the bike slip through the air more efficiently  - if you took the bonnet off, do you think that would make a difference to the aerodynamics? its like a bonnet, but underneath instead of on top!   

 

It is hard to say how much of a difference the undertray/ fairing makes, remember these cars are also designed to run at 100mph+ speeds on Autobahns, where it could be very signifcant, but even at 70, it could make a difference 

 

I remember reading that over 40mph, aerodynamic drag is important, at what speed do the active grill vents close?

 

I might put mine back on once ive fitted my new bottom engine mount and q-rusted and hammerited under the car - it only weighs 2.4kilos!       

GerrardLFC

I have a sneaky feeling it's messed the shock absorber or suspension bracket on the passenger side of the car, when I drive along I hear like a spring type noise like an elastic band it reminds me of.

 

I think I may have to get it repaired via insurance claim :(

FOCA

I have a sneaky feeling it's messed the shock absorber or suspension bracket on the passenger side of the car, when I drive along I hear like a spring type noise like an elastic band it reminds me of.

 

I think I may have to get it repaired via insurance claim :(

You could have broken a spring.  Its just a matter of wieghing up the cost of doing it/ the exess and if your NCD is protected etc - i wonder if the peple that installed the speed bump could be liable for your costs?  

jameso

hi

first things first you say you hit a bump in the road have you had a good look underneath the rest of the car because you could have damaged a lot more than you think ie brake pipes fuel lines best option take to a bodyshop that give a free estimate and then you can tell best option

GerrardLFC

hi

first things first you say you hit a bump in the road have you had a good look underneath the rest of the car because you could have damaged a lot more than you think ie brake pipes fuel lines best option take to a bodyshop that give a free estimate and then you can tell best option

 

I've had it checked today, no damage as such. 

I guess this is a case of living and learn, some people learn a life lesson and don't get to drive away like I did :-)



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