Great insights, thank you for sharing

Quote from: AdamR28 on November 10, 2020, 09:38

Quote from: Joesson on November  7, 2020, 13:41PS. 10/10 for ugly, you've got that nailed no adjustment necessary!

That made me laugh quite a lot. Ha. Thanks.


@Petrus , at the moment I have Tein lowering springs with 1 coil cut off the front and 3/4 of a coil cut off the rear. As standard they have the first one and a bit coils completely coilbound, so I figured this is a) safe and b) doesn't affect the spring rate much, if at all.

Ride height, to the lowest part of the pinch weld on the sill, has ended up 130 rear and just over 130 front - that's with the 25mm smaller than standard radius tyres, so working all that back it is about 5mm higher than standard despite the lowering springs!

As for handling balance, I can cope with understeer at low speeds as it allows you to trail brake more, but I really cannot deal with the front end not going where I tell it to at higher speeds or corners where you don't brake. So maybe if I can get the low speed balance close enough, I'll stick a big splitter or wing on the front for a laugh.


@JB21 I'm not expecting it to be able to get much over 100mph to be honest    Top of 4th gear looks to be just under 115mph so that matches 'ok'. I will add some sort of panelling to the front and sides though I think, mainly to keep driving water out and my arms in should there be any sort of bump.


Done a few more bits this morning and over the last few days, tidying up the rear end by making a new exhaust hanger / mount, enabling me to get rid of the weird 'cage' thing, and added a rear 'bumper'.

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Also chopped the ends off the standard rear ARB and added / cut and shut some (well, one side is, the other is fixed) adjustable drop links. This has in effect stiffened the rear ARB a touch which will help with the understeer, and gives me a bit of easy adjustment at the track if required.

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The ARB clamps are my own design and have an egg shaped / shallow V at the opposite end to the clamping bolt, so they clamp 1/2" through to 3/4" bars at 3 points (the sides of the V, and the bolt itself). The standard ARB is 15mm and I have some 5/8" (15.9mm) and 11/16" (17.5mm) bar knocking about, so can always increase rear ARB stiffness in future if required.

That said, I am not a fan of this on RWD cars. I spent a couple of years with a previous Westfield doing the maths, building and testing ARBs, changing spring rates, roll centres, etc - and ended up coming to the same conclusion as Caterham did when developing their R400 (I found the document after I'd finished, d'oh!): Soft springs and stiff bar up front, stiff springs and soft bar at the rear. It seems Toyota agree. And Lotus (no rear ARB on the S2 Elise, for example).

My feelings around this are:

- The ARB acts in torsion, so (depending on mountings etc) this effectively doubles roll stiffness for the same increase in single wheel bump stiffness. The front end of the car is what you feel first when turning, so it gives good driver feedback, and the softer single wheel bump is great for kerb-hopping.

- Uncoupling the rear as much as possible aids corner exit traction. If you have a really stiff rear ARB and are leaning on the outside rear tyre on corner exit, the ARB is then trying to lift the inside rear off the ground - not ideal.

- Mismatched wheel bump frequencies front to rear (front softer) means the car settles evenly after hitting a bump. The front hits it first, but oscillates slower, so by the time both ends have settled they are back in unison again.

- All in, my preference (and Caterham's) is to end up with the front ARB contributing around 40-50% to front roll stiffness, and the rear ARB 10-15%, then front wheel frequency around 10% lower than the rear.

I think Mr Poo is the same front and rear, or perhaps higher wheel frequency at the front, but I will test this at some point and lob all the numbers into my handling calculator.

Quote from: FredyCro on November 14, 2020, 11:19Great insights, thank you for sharing

Quote from: AdamR28 on November 10, 2020, 09:38That said, I am not a fan of this on RWD cars. I spent a couple of years with a previous Westfield doing the maths, building and testing ARBs, changing spring rates, roll centres, etc - and ended up coming to the same conclusion as Caterham did when developing their R400 (I found the document after I'd finished, d'oh!): Soft springs and stiff bar up front, stiff springs and soft bar at the rear. It seems Toyota agree. And Lotus (no rear ARB on the S2 Elise, for example).

Toyota by way of TRD goes to relatively stiffer still rear springs and maintains the same softer rear ARB ration.

Well, thanks for the support guys and I also hope those who struggle / are struggling with your brains at the moment have an outlet. Always here if you need!


@JB21 thanks for the YouTube link Phil, that is interesting. I ended up in a bit of a YouTube Black Hole™ for a few days after that, doing loads of CFD and aero research. After that I exchanged a few messages with a mate who runs the wind tunnel at Southampton Uni - he's done some work with the M-Sport WRC team and he confirmed I was along the right lines, plus added a few tips.

The plan is to reduce drag as much as possible (while still applying the 80:20 rule - 80% of the function for 20% of the effort!), and have a small nod to downforce while I'm at it. The balance of the car will be significantly upset from standard, so it'll need a bit of iteration to get it set up now - figure I can add downforce where necessary as I go.

Haven't done much actual work on the car recently, more been thinking about aero, but have done a little tidying up of wiring, fitted an FIA cut-off into the rear firewall, added a few switches for lights and a cheapo reversing camera / screen as a rear view mirror (lighter and less drag!  ), plus rigged up a Koni damper adjuster as the 'key' to start her up. Because why not? I always lose these things and I figure I'll either have the engine running OR be adjusting the dampers, not both...


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Hoping to get a few more hours fettling today - though I have other cars to fix. The Bucket has a leaky rear caliper and my partner's Fabia has lost power steering. It doesn't rain...

Looking forward to (copying) your aero creations.

If you want a head start... (Bear in mind I'm mainly going for low drag, rather than downforce)

- Block up around half of the nose cone air intake, and duct this to the radiator.

- Block up the faux brake ducts on the bumper.

- Cut a big hole in the bonnet and duct radiator air out of there.

- Gurney flap at the rear to move the region of lift / negative pressure further back from the car.

- Add aerofoil shape to the roll cage. This is banned under MSA rules which indicates it probably does something! My basic calculations show I can drop the overall drag of the car by nearly 10% from doing this!

- Cut slots / fits louvres to the tops of the wheel arches front and rear.

- Fit wheel deflectors front and rear, extending right up and making some vertical air 'dams' to prevent air entering the wheel arches (see Page 10: http://publications.lib.chalmers.se/records/fulltext/250512/250512.pdf - and pages 18-19 and 23-24 for the amazing results!)

- Maybe even enclose the rear wheels like the original Honda Insight (see Page 11 of the document above) - but have concerns about brake cooling if I do this...

- Add a flat floor.

Then drive it, maybe add a rear wing, or a wing mounted to the roll bar, depending on what aero handling balance is like.


Some little snippets of info I've hoarded, uploading here for safe keeping / general interest...

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More bits of progress today...

Made a little tool to allow me to louvre the engine cover - just a bit of steel with a slot ground in it. Worked a treat!

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Tested with the heat gun - the standard side didn't lift a strip of paper when air was blown across the panel, the louvred side did. That should help suck hot air out of the engine bay, and depressurise it should any air get in there somehow (drag and lift reduction).

Had a quick look at The Bucket - it has little deflectors in front of the front wheels, screwed onto what looks like some sort of diffuser sending air towards the front brakes. Clever. Mr Poo's had obviously disappeared in the prang!

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I have a feeling that the position of the 'dam' is more to keep air out of the wheel arch than away from the tyre - I think I'll go much longer in an attempt to block both, then add brake ducting if required.

Bought a nibbler off eBay: https://www.ebay.co.uk/itm/5pc-Double-Head-Cutter-Sheet-Metal-Nibbler-Cutter-Power-Drill-Attachment-/333753702487?_trksid=p2349624.m46890.l49292

Wasn't expecting much for the money, but it made mince meat of the bonnet! Highly recommended, very handy tool to have.

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Quick tidy up with the file, aerocatches in, and the bonnet / front end is finished (apart from some extra ducting to the radiator).

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Yep, looks crap. Function over form for this one as you may have guessed by now 

Function over form every time.
Unless Rachel Riley comes calling 😳

Quote from: 1979scotte on November 20, 2020, 22:29Unless Rachel Riley comes calling 😳

...and make form functional.

@AdamR28
Iirc I have read on here that the  "little deflectors / the dam" is to aid front end stability.

Yep that makes sense looking at the pressure plots in the last PDF I linked to. They will also reduce drag / improve fuel economy.

PS: I also have a lot of time for Rachel Riley!

Quote from: AdamR28 on November 21, 2020, 08:45PS: I also have a lot of time for Rachel Riley!

Fun and smart ticks both boxes 😉

Just what I was thinking / meaning! 


Made some progress with B&Qs finest today.

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Making a rather huge flat floor!

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I think I may have overcooked this a bit, but we'll see in the real world I guess...


But for now, some maths:

Air at 100mph hitting a flat wall head on creates pressure of approximately 0.18psi. That's pounds per square inch.

This chap has a really interesting channel with some good real world data:


Which agrees with CFD info I've found:





Basically, even without a front splitter, a flat floor can create a heck of a lot of downforce!


This is rough numbers and I am cutting a few corners, and making assumptions, but bear with me...

The front of the flat floor on my car is around 70" wide for perhaps 18", tapers in to about 36", then behind the wheels is 48" wide all the way back.

Using 0.18psi at 100mph, and the data from Julian's video, you will get approx 0.125psi at the front of the floor, 0.04psi in the middle, and (with a reasonable diffuser) 0,085psi at the back. I probably won't fit a diffuser, so I'm going to halve this number.

I will also reduce the total downforce by 20% as Julian's numbers will be at the centreline of the car, and air 'bleeds' away around the sides of the floor (unless I fit some side skirts!).

So lets split the floor down:

Front = 18" x 70" = 1260 square inches.

Middle = 40" (average) x 64" = 2560 sq inch.

Rear = 48" x 64" = 3072 sq inch.


Front: 1260 sq in x 0.125 psi = 158 lbs.

Middle: 2560 sq in x 0.04 psi = 102 lbs.

Rear: 3072 sq in x 0.04 psi = 123 lbs.

Reduction of 20%

Total: 306lbs / 140kg of downforce! That would be enough to lower the car about 15mm at speed, which would be, er, interesting.

For comparison, I did the same maths based around the same assumptions for a 6" front splitter and front tray the same size as mine, with no full flat floor. Total downforce just over 100kg, but obviously all of it ahead of the front axle (not as good aero balance), and much more total drag.




Of couse the other possibility is that I've made a huge mess of it and the car will take off!


Anyway, enough theoretical stuff - more pics from today.

Made a bracket up to hang the front of the floor from the chassis. Makes it easier to get on and off, and makes sure it bolts to something solid.

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Also gives some grab handles for a very awkward piece of wood!

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The eagle-eyes will spot a plate bolted to the rear edge of the front undertray - this allows it to be hooked up on top of the rear part, so fitting and removal is still a one man task and means you don't have to balance it on your head 

More shaping. I once made the mistake of cutting both sides 'freely' rather than cutting one half then using the offcut as a template. Looked rather wonky, as you can imagine! This one still looks a bit bog eyed but I think it's just the whole front end of the car being bent.

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Chopping clearance for front wheels on full lock both ways...

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Checking exhaust and sump clearance. I'll add a NACA duct just in front of the sump to give both of these areas some airflow / cooling.

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And here's where I finished today, about 4 hours work to this point.

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Looks like a massive splitter but once the air dam is in there there won't much much sticking out at all. I want to keep it this way to make the car look a bit less 'developed'.

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Also going to add some deflectors underneath as discussed above, and some more at the very rear sides of the splitter / undertray to fire air around the sides of the wheels.

Obviously needs some paint to seal it, but total weight about 25kg. Heavier than I wanted but hopefully the trade-off will be worth it...

Awoken at 3:30am again this morning by a knee to the hip and an elbow in the shoulder (thanks Jane!  ) so decided to do some more fettling before work.

Boot lid is fitted. I cut some slots at the front edge and put stood-off countersunk bolts into the hardtop mounting bracket holes, then two push-button type catches at the back. The bonnet is fitted by clipping in at the front, pushing forward to locate the bolt heads over the slots, and pushing down at the rear to secure the on the catches. Simple, light, quick to remove (main concern given how much oil this thing burns!).

Fitted the driver's side door skin. I'll gaffer tape up the shut lines too.

Made some spreader plates / nuts for the tunnel-facing harness eye bolts. Was prepared to buy some but couldn't find M10 x 1.25 anywhere! 7/16" UNF the other side, weirdly, so the eyes I had screwed straight in.

Fitted the scuttle and made a 'windscreen'. It's really surprising how little height you need to direct air over your head effectively, when you're sat low in the car. Still need to make the passenger side, this will probably be just a plain lip of about 25-30mm, also out of lexan.

Added a bit more to the ducting out of the bonnet, that's almost completely sealed now.

It's actually starting to look half decent    I really, really hope the trackday at Oulton on 5th December goes ahead with whatever new rules the mongs in charge come up with next.

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Good progress as always.

That looks like thick plywood and 25kgs is a lot of weight in the scheme of things. Will you look at lighter options if it works?

If you are buying paint, would be rude not to do the whole car, it would probably help getting onto trackdays too!

You can use rustoleum on wood as well as metal.

https://tools-paint.com/rustoleum-combicolor-7300-gloss-metal-paint-standard-colours-25l-16925-p.asp

Ah, Rachel, Sean Locks finest moment....

https://www.youtube.com/watch?v=Nrty2XITqTE&ab_channel=SubOnPoonGoonOrEatShit

Decided to use SBR primer on the floor instead, have a few litres leftover from a roofing job which will go to waste otherwise. It'll be fine without paint, too much weight added and time wasted making it look pretty

The ply I used is 9mm. Most people use 12. I looked for lighter options but really struggled to find anything for similar cost (or even 2, 3, 4 times the cost) that was lighter for the same stiffness, or stiffer for the same weight. Perhaps I have missed something though!

Haven't seen that clip before, hilarious!!

Quote from: Topdownman on November 23, 2020, 09:59That looks like thick plywood and 25kgs is a lot of weight in the scheme of things.

For the floor thinner would be ok as long as there are enough mounting points to spread the load; see the OEM plastic underthingies.
The splitter however needs to be sturdy. The usual twin tie-rods between front edge of the splitter and the chassis are a popular way to minimalise the strength of the plate needed.

Quote from: Petrus on November 23, 2020, 11:22For the floor thinner would be ok as long as there are enough mounting points to spread the load; see the OEM plastic underthingies.
The splitter however needs to be sturdy. The usual twin tie-rods between front edge of the splitter and the chassis are a popular way to minimalise the strength of the plate needed.

Given the sorts of loads a flat floor can develop, and the locations of said loads, I went thicker to be on the safe side. As the images above show, you can actually end up with higher peak downforce over a larger area somewhere around the front axle, than at the splitter...

Why 9mm mate?
Is it rigid enough?
I suppose with enough fixing points it would work.

Yeah, I think it will be enough, based on feel, the maths above, having made similar out of 12mm before (https://www.mr2roc.org/forum/index.php?topic=70241.msg838365#msg838365), and not having overhang at the front.

There's 5 fixing points along the front at the area of most load, 2 more at the back of the front piece, then the front and rear pieces interlock, and the rear has 3 fixings along the front edge and will have a further 6 spaced pretty equally around the rest of it. With a 'tug test' the whole lift flexes and wobbles a fair amount.

I figure most of the loads will be evenly distributed, so if I can stick a couple of 10kg weight plates in any single location, it ain't coming off. Hopefully. Fingers crossed!

Quote from: AdamR28 on November 23, 2020, 11:50Given the sorts of loads a flat floor can develop, and the locations of said loads, I went thicker to be on the safe side. As the images above show, you can actually end up with higher peak downforce over a larger area somewhere around the front axle, than at the splitter...

It is either thinner with loads of fixtures to distribute the load or thicker material to do that over less.
It´s a choice you made.

The issue with the splitter is the possible tórque on the rear mountings. Hence the popular tie rods.
Again there are more roads to Rome.

You btw highlight a very interesting and little understood/known fact; that súction is a lót more significant in downforce than forces pushing down.
On a rear ailleron per exampe the angle of attack is not to maximise the direct force against it but to maximise the speed of the flow underneath it. This illustrates the function of a small deck lip under it.

Anyway, bottom line is that I lóve your aero efforts. It is véry effective at surprisingly low speeds and the lighter the car how bigger the effect.
This is the core of the myth that is doe not make much sense on road cars ´because they do not go fast enough.´ Well not exactly. Not fast enough for the forces to be large enough to have much effect on the weight of the car.
On your car the forces have almost three times the effect it would have on an SUV.
As the standard Spyder/roadtser in only 1000-1100 the argument applies too; anything aero has two times the effect it would have on a 2 tonne SUV.

Top work on the flat floor, pretty much the same that I've marked out and up using   foam backed board for a template.

Still undecided on final material though, but may give 9mm ply a shot.
We work with a lot of flat galvanised steel at Work and have loads of presses and folding machines. Just need to check the weight of 1.5mm galv sheet vs ply.

Quote from: Gaz2405 on November 23, 2020, 19:49Just need to check the weight of 1.5mm galv sheet vs ply.

Steel density is about 8 and ply 0.8, less than the 1.0 of water ;-)
So about 10 to 1.
So 1.5 mm steel is roughly 15 mm ply.

There is a véry sturdy variant of foam board with pvc outer layers. I have the 6 mm. one as side plates for the rear ailleron but is is avialeble in different thickness too.
The most dense variety is 0.4 and you could probably use thinner than 9 mm.
It is véry easy to work with and none too costly.
The stuff is widely used for shop sign boards p.e.
Imo great for this application.

Quote from: Gaz2405 on November 23, 2020, 19:49Top work on the flat floor, pretty much the same that I've marked out and up using   foam backed board for a template.

Still undecided on final material though, but may give 9mm ply a shot.
We work with a lot of flat galvanised steel at Work and have loads of presses and folding machines. Just need to check the weight of 1.5mm galv sheet vs ply.

Have a look at ABS plastic sheeting. Not to expensive and is very strong and lightweight, this is what i'm looking to use for a front splitter.

Quote from: Gaz2405 on November 23, 2020, 19:49Top work on the flat floor, pretty much the same that I've marked out and up using   foam backed board for a template.

Just need to check the weight of 1.5mm galv sheet

Cheers Gaz, good to know our ideas align.

Same size floor as mine in the stuff Petrus mentioned (0.4 density at 6mm thick) would be 22kg, 4mm ABS would be 39kg, and in 1.5mm steel would be 105kg!

I think there's a good reason many people use ply - as well as the weight not being bad, it is cheap (under £50 for two 8x4ft sheets), easy to get hold of (Wickes, B&Q), easy to work with, and pretty resilient to knocks.

Phil, just realised I have a slightly damaged (easily repairable with some wood glue) splitter that came off the front of Matts S2k MX5, you're welcome to it if you want, the shape is pretty good for the MR2. Can grab a pic and dimensions if you want.