Rear undertray, aesthetic or performance purpose? - LotusTalk - The Lotus Cars Community
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post #1 of 18 (permalink) Old 05-09-2019, 06:24 PM Thread Starter
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Rear undertray, aesthetic or performance purpose?

I removed the rear undertray from my 94 for some work.

I started wondering what the purpose of the undertray was.

Did Lotus include the tray purely for aesthetics - something they thought buyers of an expensive sports car would expect?

Or, does the tray improve aerodynamics and/or cooling significantly?

If its all about aero I think I will leave it off and save the weight, I wont be spending much time above 100 mph.

What do you all think?
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94 Esprit S4 - Silver
Previous - lots of hot rod Air Cooled 911s
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post #2 of 18 (permalink) Old 05-09-2019, 07:14 PM
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I removed mine several years ago and eventually sold it because I decided to not put it back on...ever. I did find some rather fine, 1/8 inch I think, stainless screen on Ebay to cover the hole where the timing belt is. Just in case a stone happened to rattle up somehow into that tender spot. Aero? I doubt it. Maybe, but it makes access MUCH easier. As well as if something starts leaking being able to spot the source. On my car anyway, '88, the undertray does restrict access from someone if they knew what they were doing, to the fuel pump and lines and electric connections for it. But I never leave my car for any length of time, and never park in questionable areas. The undertray is surprisingly heavy for what it is. As far as cooling, I think that's why the holes are cut where they are, for more air to exhaust manifold. I've not noticed any consequences and I've had it off for quite a while. There may be an argument about this, but, bottom line, It's my car, I think I'll do what I want with it. I recommend you do the same.
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post #3 of 18 (permalink) Old 05-09-2019, 07:55 PM
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I think it was for aero and protection of engine accessories.
I keep mine for protection against road debris and for cooling improvements.
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post #4 of 18 (permalink) Old 05-09-2019, 07:59 PM
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There has been some discussion of the tray protecting the cast exhaust manifold from cracking due to water puddle spray, but most of the later cars seem to have that area cut away so not much help on those. My 'early car ('85) has a solid tray w/o cutouts, so an argument could be made for aerodynamic smoothness under that part of the car. I generally leave mine on to keep water, mud and gravel out of the engine compartment, but it's been off for long periods as I work on stuff under there. In a hot climate I'd be tempted to leave it off for maximum air circulation in the engine bay.

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post #5 of 18 (permalink) Old 05-10-2019, 02:50 AM
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My Fiat X 1/9 came with left and right undershields that were both fairly heavy metal and a pain to work around. Being a cocky teenager, I quickly removed them. Then I discovered that the alternator light would come on when driving through water and that the engine got dirty quickly. I ended up putting the engine side one back on. Lesson learned: race cars can do without a lot of stuff that you might want on your street car.

Point being: your concern about keeping stuff from getting up in the belt area is not abstract. Looking at your pics of the Lotus undertray, I doubt there's anything aerodynamic going on there. Wouldn't be surprised if it kept things cleaner and dryer, though.
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post #6 of 18 (permalink) Old 05-10-2019, 02:59 AM Thread Starter
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I had not thought about the debris angle. I guess because the area is in front of the rear wheels it did not occur to me. I know of one car that ran without it for years. Now that I think about it he had a broken lower timing belt pulley at one point (he checked it after someone here on the forum reported a problem). I never thought that the damage might have been caused by debris getting in there.

Great point about access, it sure would be nice to not have to take the step of removing the panel to get up there.

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post #7 of 18 (permalink) Old 05-10-2019, 03:46 AM
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I had my Esprit for five years, it didn't have the under tray when I bought it, and I never had any problems
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post #8 of 18 (permalink) Old 05-10-2019, 03:59 AM Thread Starter
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Quote:
Originally Posted by DaveS4s View Post
I had my Esprit for five years, it didn't have the under tray when I bought it, and I never had any problems
Hey Dave - yeah your car is the one I thought of.

You did not have any problems....except a lower timing belt pulley....probably unrelated

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post #9 of 18 (permalink) Old 05-10-2019, 04:18 AM
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To tray or not to tray

Penelope came without one and JAE helped me find a used one to put on. I think it keeps water and debris from getting up there which can't ever be good in a mid engine car. It also tidy's up under the car for a more smooth look. We don't have true ground effects so I do not see a car that drives at speeds far less critical then a track car might experience. Although after I installed a flux capacitor it did add a benefit when I could find enough gigawatts.
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post #10 of 18 (permalink) Old 05-10-2019, 05:20 AM
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If anybody has a spare one that's correct for 86/87 HCi, I'd be interested, as mine doesn't have one.

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post #11 of 18 (permalink) Old 05-10-2019, 07:02 AM
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This has been discussed before over the years...on multiple forums.

91MR2 (Joe P) had road debris damage a relatively new timing belt when he was running without it.

Drive-by noise (euro requirement) is another reason cited for Lotus fitting the undertray.


I've always run with mine installed and I gotta say, YES the topside of the engine stays clean.




++++++++++




Since somebody else brought this up first, I'd say INSTALL THE UNDERTRAY, REMOVE THE WING to promote aero and lower the center of gravity.



But, you all expected me to say that, didn't you?
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post #12 of 18 (permalink) Old 05-10-2019, 08:28 AM
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Given what Lotus didn't install i would guess that they designed, created and installed the undertray for a specific purpose, and looks wouldn't have been one of them at that altitude. I have driven both with and without and my observations are that it does keep the engine cleaner, quieter and having found a 1 inch by 8 inch oak tree branch jammed up against the vacuum pump and the hose i would say debris ! I also believe it has an aero component. I get that you can drive 10,000 miles without it and have no issue, but you can drive 10 miles and lose the engine if anything interferes with the timing belt. How lucky do you feel?
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post #13 of 18 (permalink) Old 05-10-2019, 05:54 PM
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Most new cars have some kind of plastic cover underneath now. It is a pain when you have to work underneath but it is probably used for aero, cooling, noise control and debris protection. Especially the ones under the front by the radiator. Consider that when a manufacturer makes a lot of cars, if they can save $50 on each car (let's assume that's what the cover cost) besides the room to inventory the parts, and assemble them onto the car, they would leave it off if it wasn't important. GM had a problem with debris getting caught and binding up the steering column on some models. Their answer was a plastic shield over the steering shaft in a recall. My advice, if the car had it, you should put it back if you can.
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post #14 of 18 (permalink) Old 05-10-2019, 08:41 PM
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I have to agree with JT as I can't believe any car constructor would "waste" money on an unnecessary part and although we may care about underside aesthetics few normal people do (let's be honest, we're not normal about these things). It's on there for a purpose, whatever it may be.
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post #15 of 18 (permalink) Old 05-10-2019, 09:27 PM
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I'm surprised no one mentioned this.

If you look at the undertray panel, it functions as ducting from side sill vents to the engine.

If you remove the undertray, you have just disabled the cooling air from the side sills.

Granted, for speeds below 30 MPH, it may not be that big a deal. But for a long trip, seems like it would be better for long term durability to keep the engine cooler.
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post #16 of 18 (permalink) Old 05-11-2019, 12:15 PM
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This is indeed the most reasonable of the arguments for and against that I have seen. I did notice that SJ sportcars has at least some Stevens car undertrays pretty reasonably priced. JAE i'm guessing probably too. Point is they are obtainable .
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post #17 of 18 (permalink) Old 05-11-2019, 06:15 PM Thread Starter
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I am going to go with engine noise (not an issue for me) I have read somewhere this was/is a big deal in europe and keeping sticks out of the timing belt. I might look at a simple screen over the timing belt area. Other than that I think the benefits outweigh the negatives.

I really appreciate everyone's thoughts. I found it very constructive. I did a brief search on the subject on this forum and did not find anything. I apologize if its been brought up before.

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post #18 of 18 (permalink) Old 05-11-2019, 11:59 PM
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Quote:
Originally Posted by Erik L View Post
I am going to go with engine noise (not an issue for me) I have read somewhere this was/is a big deal in europe and keeping sticks out of the timing belt. I might look at a simple screen over the timing belt area. Other than that I think the benefits outweigh the negatives.

I really appreciate everyone's thoughts. I found it very constructive. I did a brief search on the subject on this forum and did not find anything. I apologize if its been brought up before.
I found it very informative and I don't have an Esprit.

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