Hi I have recently come across a pukka Seat Sport kevlar and carbon front bumper for my ibiza - as used on the F2 cars - so it has prompted me to rethink fitting a flat undertray to the front of the car, to include a functional front splitter it wants to be stiff, abrasion resistant, light and cheap......not much to ask for then what are folks thoughts on materials to make this out of? My initial thoughts were plywood, but then I got to thinking about balsa with a kevlar laminate, ABS plastic, etc Ideas welcome Cheers Rob
I'm thinking of doing the same thing, engine undertray and splitter. How did you get on with your diesel van undertray? I was thinking abs for the undertray, plywood for the splitter since its stiff, light, can take some abuse and best of all is cheap! A big splitter might actually have to withstand a decent amount of high pressure if it works so it needs to be pretty substantial. I can't imagine how much I'd cry if a new kevlar splitter got smashed to pieces on the first speed hump (or circuit kerb). [:^(] If you break it and need a new one quickly then you might struggle for kevlar at B&Q. apparently sign writing shops are good supply for large polymer sheets. I think they're like sandwiched layers so technically composite
diesel undertray has worked well - but now want to extend forwards into a splitter so it will be modded or replaced by something else ply does sound good and is actually pretty light and cheap to replace - just wondering if I am missing anything though - will check out the sign writing shops
been out at lunchtime: 6mm ply is too bendy for a splitter (3-ply) 9mm ply has 5 plies and is quite a bit stiffer - probably ok - 180 x 60cm sheet 14 12mm ply has no more plies, and is too heavy boxy U-section plastic guttering for side skirts.... but is the increase in weight from all this going to negate any aero advantage?....
I dont know much about aero packages but isnt the idea to have a front air dam ie a lower front splitter and a higher floor under the engine with a fence around the back/ wheel arches to create a vortex of air creating a high pressure area forcing the front end down to increase downfore = front end grip. The flat bottom is to channel air straight along the underside of the car to a rear diffuser with coupled with a rear wing. Need both to make it work = rear end downforce = high grip levels. I work in the sign trade and we use a material called Dibond in 3mm it has .32mm ali either side sandwiched with a plastic core. Weight would same as 9mm ply ideal for flat floors. For a front splitter i would use a Black 10mm 'Foamex' Aerated PVC Strong but light weight Just a couple of ideas Rob
I made a splitter for my Nova many years ago (don't laugh, it would pull a genuine 134MPH and needed as much help to stop the nose lifting as you could give it!), using the stuff double glazing people use for the white UPVC window sills and for 'boxing' in window openings when replacing windows - a sort of sandwitched composite of smooth white, hard outer UPVC with a lower density (semi-honeycombe type) inner core. The advantage was that it was light, and fairly impact resistant. Although I only made a blade type splitter...it worked. And having a sheet of it would give the opportunity to make an undertray easily and cheaply. Impact resistance was good, although it wouldn't take hitting a rock quite as well as aluminium. I had a mate in the trade, so managed to blag some off him...not sure what it's called. It's about 10mm thick, pretty light and won't absorb water. I'm guessing it may have been the same type of material as pascal describes here, but in white:
Dibond, Alucabond, Renobond.... infact any form of the cheaper composite sheets will do the job. Dibond is the original branded product and is sold as a 3D material but in reality any of the cheaper composite sheets will work in the same way but won't have the aesthetics of Dibond and might bloom crack or distort when bent due to a thinner ali skin. Not ok for a shop sign but fine for an undertray of a car. ABS would also be good Rob, doesn't have to be a virgin grade, regrind/reprocessed would do grand. Think we covered this a while ago.
Cheers Phil - have been trying to pm you but your box is full - you were going to send me a few samples?
Hi Rob, just emptied the inbox. Unfortunately I've moved jobs and now work for Chrysler/Jeep. You're welcome to pick my brain on anything plastic related though...
thats about it from my under standing, the lower dam forces are over the car, and with the sides being fenced off and low to the floor you help smooth out the air flowing under the car, by stopping it escaping in front of the rear wheels or extra air being drawn in under the car depending how good your front splitter is. then with the air dam and sealed off side skirts you create lower air pressure under the car thus sucking the car to the floor, but for the max effect you need to smooth off the area where the low pressure from under the car meets the very low pressure aur in the dirty bubble behinde the car... by the use of venturi's on the rear bumper this can be helped which will lower the drag and help smooth the air flow from out under the car again helping to suck it down. Ill see if i can find any pics at when im at work and more awake to explain it better than my words
Have been reading this excellent book on the subject: and have some ideas now on what to actually do to the car - sketches soon Think I will use 9mm ply to begin with as its cheap, easy to work, easy to get hold of and can always be used as a template for other materials later The only partially difficult bit is to get a support made for the front of the car, like a sump guard bar, to go behind the front bumper, so will mock one up in wood and get someone to fab it in ali for me. Will also have a support bar between the wishbone pivots or maybe use the front subframe mounts for the factory plastic undertray (although they are a bit small/weedy). The bumper I have already has a bit of a splitter on the lower edge but will extend the splitter below and forwards to the max allowed by the regs. The bumper can then sit on the undertray for additional support. Its unclear if having the front floor area slope upwards into a diffuser under the engine area is actually of benefit, so will keep the whole thing flat to begin with. Planning some side skirts also to 40mm from the ground (regs limit) More pics as I start to get into this over the coming weeks.
I'd like to know how you get on Rob, I'm thinking along the same lines; fabbing a frame underneath the front panel to mount to. how about mounting to the ARB at the back with something like this...
I'm sure the owner said this was made with Marine Plywood as it a fair bit stronger and withstands the elements too. He also said that it pivots at the rear to allow it to kick up at the front if hitting something like a kerb ... His thoughts exactly on the cost as everything else was carbon or kevlar Awesome car and fast as hell Anyway back to the thread topic
thats a good idea, spose if its doing its job it only really needs to be held up not necessarily fixed rigidly. nice motor! I drive my car to events so was thinking about a 2 piece undertray with a detachable splitter I can put on when i get there. one other thing i just remembered about splitters, apparently the angle of attack makes a big difference. pointing down gives a big increase in downforce but at a cost of extra drag, and obviosly if its pointing up the front then you'll just get a load of lift.
all good stuff - the book above is pretty complicated in places but it says that just having a splitter makes a load of difference - it makes the high pressure zone at the front of the car work for you are provide downforce - it says nothing at all about the angle though - I was thinking flat to the ground and as far forward as the regs allow - for mod prod that is upto 15cm beyond the existing bodywork (excluding bumpers) so thats going to be interesting to draw out......4cm minimum ground clearance and no part of the body can touch the ground with the tyre deflated - it also reckons that for materials and strength of the system, think of it along the lines of it needs to be strong enough to stand on without snapping or coming off the car
I made a simple splitter years ago for my Nova (bear with me, it was before the image went through the floor) as the steering was going light at high speed (it would do 134 MPH genuine...and at that sort of speed it wandered about where it wanted!). I ended up with a large 'blade' sticking out about 100mm from the bumper, parallel to the floor, and tied down using a pair of stabilising brackets designed for spotlights (that shows how long ago it was!). It was made of the plastic stuff I described earier - so was light but strong. The splitter blade would break the air first, sending the air over the car...effectively stopping front end lift. It was pretty non-scientific by aproach...but it worked. At 130+ it would sit steady and you could take your hands off the wheel, whereas before you were constantly correcting the steering as it go lighter. It wasn't as dramatic as on the 935 above, but a smaller scale version of - just a flat 'plate' sticking out. I'll see if I can dig a pic off my laptop tonight.
I'm not sure looking at sports cars, single seaters etc. is necessarily the way to go, their aero is designed as a whole package and has different priorities to a hatchback. They have flat undertray, skirts and are very low, they often try and encourage underbody airflow to increase the venturi effect. On a hatchback its just not low enough or flat enough and air will just bleed in from the sides. if it doesn't and you dont have an effective diffuser then it'll just result in more drag anyway. I think on hatchbacks etc. the main aim of the splitter is to limit the amount of underbody airflow to reduce drag and lift from the wheels and messy underbody. As a nice secondary effect it acts like an airdam, increasing high pressure on the upper surface and at the same time the compression of the air flowing underneath gives low pressure. I'd have thought you'd want it more or less level but you want to make sure the leading edge is not pointing up. thats all theory though, i cant prove any of that does anybody else wish they could go a whole day without thinking about cars?!?!
Right, no laughing now (It was 1995!). Pics aren't great as they were scanned from CCC. Splitter only went as far back as the bumper would allow, and was tied at the front with the two spotlight ties as you can see...but it was stable. It didn't lift, or tuck, even above 130MPH...but it wouldn't have taken bodyweight. No undertray attached, only the splitter to try to reduce front end lift, which it did. It was approx 120mm out from the lower edge of the bumper unit, probably about 40-50mm further forward than the furthest forward point of the bumper, and maybe 25-30mm out at the sides. I'm not going to claim it was as a result of some fancy calculations - as it wasn't. It was from looking at race cars, chatting to Gerard Sauer (who used to write for CCC) and seeing what I could build from what I could scrounge. But it worked, when it came to reducing lift.
