Fitting underbody skid trays to improve aerodynamics?

[mfreeborn]

Hi all,

 

I'm toying with the idea of fitting skid trays underneath my mark 3 estate. The motivation would be for improved aerodynamics and thus fuel efficiency. Is this something that anyone else has thought about/done? Or is it prohibitively difficult/expensive for what I'm hoping to achieve?

Edited 2 April, 2023 by mfreeborn

[KenONeill]

2 hours ago, mfreeborn said:

Hi all,

 

I'm toying with the idea of fitting skid trays underneath my mark 3 estate. The motivation would be for improved aerodynamics and thus fuel efficiency. Is this something that anyone else has thought about/done? Or is it prohibitively difficult/expensive for what I'm hoping to achieve?

Do you have free access to a full-size moving floor wind tunnel?

[langers2k]

It's been done on a few Golf's using OEM parts. I doubt it significantly increases fuel economy though...

[mfreeborn]

1 hour ago, KenONeill said:

Do you have free access to a full-size moving floor wind tunnel?

It was just something that I came across on the internet.

 

1 hour ago, langers2k said:

It's been done on a few Golf's using OEM parts. I doubt it significantly increases fuel economy though...

Yea I think that's the sort of thing I came across. Just curious if it was something that was more widely done, or if it's really just a bit niche.

[Ootohere]

Skoda have done it for years with the likes of Greenline models, and lower suspension / tyres so less clearance, or just narrower tyres and less grip / traction / safety.

But then considering the UK NSL's it makes not much or any  difference as you motor along trying to save fuel. 

[varooom]

If the project cost you £200 (2nd hand parts let's say) and you save £1 a week in fuel... it would take 4 years to break even.

 

I do have a Greenline, and it can post some incredible figures, but always depends on how it is driven.  You might be better off keeping a close eye on tyre pressures and servicing, driving with windows up at higher speeds (if you don't already) etc.

[MarkyG82]

Engine tray would make the most difference if not already fitted. I'd be surprised if you didn't have one on a UK car. Next step would be narrow Tyres like 205/55/16 assuming you don't have a vrs and your insurance company aren't numpties.  Next step is lowering as suggested by toot. There is not much else you can do beyond major mods away from OEM parts. Maybe make sure the little lips in front of the wheels are intact. They make a surprising amount of difference for such a small part and often get battered by kerbs. Oh yeah, remove mud guards if you have them.

Edited 2 April, 2023 by MarkyG82
Typo

[ChoonDoode]

do the mudguards make a lot of difference? I can't say about a before and after because I bought them with my car.

 

I'd sooner keep mine on to save 'crud' getting pinged up at the car and save thruppence ha'penny on my fuel bill

[Ootohere]

Best keep the mud flaps and keep the wipers fitted unless you are heading to an arid desert maybe.

[MarkyG82]

Na, bin the wipers off. The more challenging drive will force you to slow down further saving fuel.

 

Re. the mud flaps, everything adds up. If going to the effort to add extra undertrays then the flaps will be a contributing factor.

[langers2k]

Found the Golf thread: https://www.golfmk7.com/forums/index.php?threads/how-to-retro-fit-skid-trays-aerodynamic-under-trays-stone-guards-to-a-mk7-golf.320687/

 

I expect some of the parts will be transferable but that's an adventure for the OP to figure out 😆

[Gerrycan]

While I have long had an interest in the topic of vehicle aerodynamics I have no real expertise or experience other than having followed a few online projects.

Generally speaking it is quite hard to get any significant aero improvements on the basic modern vehicle shape unless you go to extremes like adding huge boat-tails, or covering the wheel arches.

 

First of all you can congratulate yourself on having a pretty aerodynamic car in the first place. Sure it concedes a point or two to the sedans 0.30 drag coefficient but compared to most other estates it rates pretty well and certainly better than any SUV styled vehicle. I believe the Karoq is 0.34 and that is one of the best of its type.

 

When I had an opportunity to look under a raised Octavia mk3 I was quite impressed by how smooth it was for the first three quarters then there is the aero ridge to 'throw' the air across the gap past the rear suspension where the underside smoothness becomes more compromised in my opinion.

 

There is a small feature in the Octavia design that rankles for me and that is the transition from the windscreen to the roofline where there is a centimetre high ridge instead of a smooth contouring as on my 20 year old Toyota Echo (which also claims 0.30 drag coefficient). The 'ridge' collects a huge number of bugs after a fast evening country run and just does not seem right.

 

There were little or no claims of aerodynamic improvements between the mk2 and mk3 Octavii but the mk4 is remarkable for a lower priced, mass produced ICE vehicle by claiming 0.24 to 0.26 for sedan and combi.

The perfectly aerodynamic ŠKODA OCTAVIA - Škoda Storyboard (skoda-storyboard.com)

 

Your post reminds me of a motoring magazine's experiment of attaching a large aluminium sheet underneath a Triumph TR4 (Yes I am THAT old) and claiming they increased the top speed by 10mph.

So by all means experiment and I'd love to read a report from you.

Edited 4 April, 2023 by Gerrycan

[gumdrop]

On 02/04/2023 at 07:31, mfreeborn said:

Hi all,

 

I'm toying with the idea of fitting skid trays underneath my mark 3 estate. The motivation would be for improved aerodynamics and thus fuel efficiency. Is this something that anyone else has thought about/done? Or is it prohibitively difficult/expensive for what I'm hoping to achieve?

Going to work one morning early, in heavy rain, i took a corner at 25-30mph and hit a tempory lake!

In many years of driving this road it was normally dry what ever the weather, so the car surfed across the

deepest part until the wheels found traction at the crown of the road. without the engine compartment pan

I could have ended up very wet. Yes they are of some use.

 

[dieselV6]

Deep water in the road can also tear off the underbody covers, I have one waiting to be fitted to my vrs after hitting a temporary road lake at around 50mph at night just before Easter.

3 out of 7 mounting points of the largest cover on passenger side got torn off. No other damage.

I noticed that, even accounting for plastic ageing, the new cover is more flexible (replacement part number, original no longer available), it might take similar experience better in future.

 

 

[mfreeborn]

I actually went to the effort of crouching, and took a peek under the car. It turns out that quite a lot of the underbelly is already covered, so I don't need to worry about adding anything aftermarket.

[Gerrycan]

1 hour ago, mfreeborn said:

I actually went to the effort of crouching, and took a peek under the car. It turns out that quite a lot of the underbelly is already covered, so I don't need to worry about adding anything aftermarket.

Jeez, you could have done that before you posted. 🤣

[mfreeborn]

8 hours ago, Gerrycan said:

Jeez, you could have done that before you posted. 🤣

Yes, but I don't want to wear out my knees prematurely! There are some interesting replies though, and I learnt that the plural of Octavia is Octavii.

[Gerrycan]

5 hours ago, mfreeborn said:

Yes, but I don't want to wear out my knees prematurely! There are some interesting replies though, and I learnt that the plural of Octavia is Octavii.

The knees I understand, but  from my pearls of aerodynamic wisdom all you got was Octavii! 🤣🤣

Edited 20 April, 2023 by Gerrycan