Downforce question and information

[Daleevs]

So im currious as to know if mazda ever mentioned the down force on all the models of rx8's as some have different kits, spoilers and wheels ect, ive noticed theres a under car channel which looks like its for areodynamics ive searched for a while on google and cannot really find any information on how much down force say the 192, 231, R3 or even the jdm models have.

[SeriousSam]

I think the answer is 'enough', in standard trim at least. There are a lot of aerodynamic considerations that Mazda made when engineering these cars, and at the speeds a stock car can reach, they don't need any more downforce than they have from the factory. There are cosmetic bodykits available, and some that have a minor aerodynamic effect, but realistically they don't add much. Same thing goes for spoilers, the car doesn't go fast enough as standard to need one so if you add a big wing, it will only slow you down.

That said, if your car is running a lot more power than stock (read: boost, engine swap or Nitrous) then you might well find that aero becomes a more important consideration. But for a standard or lightly modified car, body mods and aero are purely for looks

[bigpete8]

Have you seen:
viewtopic.php?f=6&t=74494#p1095762

[Eddie_r32]

My rear wing has made a noticeable difference to the point that I have vented the bonnet for cooling as well as reducing front end lift a bit. You can feel it pushing you down when you hit a bump, you have to get a decent wind though not just a cheap thing from ebay

[PeteH]

I don't think Mazda ever quoted anything. I think the nearest was when Prodrive declared that the PZ spoiler was a genuine aid to downforce.

Very few manufacturers quote downforce. Some supercar manufacturers will state "produces 'x' kg of downforce at 'y' mph", but I don't think I've ever seen a coefficient quoted for a road car. I'm not sure if that's because they think the public would be confused, or because it's too complex to quote a reliable value.

For reference, almost all normal road cars actually produce lift, not downforce. Some cars have famously produced enough lift to get themselves into trouble (I think the first generation Audi TT had major issues, and had to be rapidly redesigned with an ugly rear spoiler).

When I fitted the aero rear wing I had to stiffen the rear anti-roll bar to rebalance the car, so I am confident that the Aero rear wing reduces the rear lift noticeably.

On a related note, it's worth watching Liam22's latest video in his build thread. It looks to me like he was taking Riches faster than almost anyone else in the field (on a wet track). That's a corner where downforce plays a huge part, so I think it's good evidence that Liam has sorted his aero really well. And to end up 3rd overall in a class C car, winning his class by a mile, also suggests the aero is spot on.

[warpc0il]

Manufactures are much more concerned with stability at high-speed, especially with cross-winds, than they are with downforce.

Downforce is actually dangerous on the road, as it reduces with reducing road speed and it disappears if you turn out of the wind direction.

Most OEM spoilers, whether an actual wing or just a lip on the boot/roof/c-pillars are exactly that, they spoiler the airflow and ensure that the centre of pressure remains behind the turning moment of the bodyshell, such that the car will fly straight, like an arrow or dart, and will tend to turn into a cross-wind rather than be pushed by it.

[delta0]

I can run some CFD models if anyone has something they want to try out. I should really revisit the one I did before to fix a few of the issues and refine the mesh some more.

[Daleevs]

Reason i ask is i find no one really knows or has a answer, im looking at doing a road/track car with the rx8 with forced induction via turbo coming next year, now theres going to be even more speed and load coming from that, so i was thinking il going to do a few track days in the car to get used to it as it is then try and improve from there, im thinking of doing a wind tunnel test before all this starts but also one towards the end phase so there'l be some nice information out there then too with proof then.

[ChrisHolmes]

Have a look at Clive's 450hp build thread as he has explored various aero options

[Dr. FrankenRex]

Reason i ask is i find no one really knows or has a answer, im looking at doing a road/track car with the rx8 with forced induction via turbo coming next year, now theres going to be even more speed and load coming from that, so i was thinking il going to do a few track days in the car to get used to it as it is then try and improve from there, im thinking of doing a wind tunnel test before all this starts but also one towards the end phase so there'l be some nice information out there then too with proof then.

Potentially daft question - but do you have any idea how much a wind tunnel costs for a full size car?

In terms of the RX8 as standard, the OEM rear spoilers are for reducing coefficient of friction and reducing lift. Supposedly the R3 spoiler (and I imagine the aero and PZ as well) reduce the coefficient of friction by ~0.01 - which is not a small amount really.

I disagree with Sam, though, in respect that an RX8 can certainly reach speeds where downforce would be beneficial - however I don't think it would be beneficial on a road. In the same respect that road cars are designed to naturally under-steer for stability, downforce would cause issues with speed and wind changes that the average driver would be caught unawares by.

[ChrisHolmes]

The lip spoiler on my car was refitted with quite thick foam tape and you can actually see witness marks on the boot surface where the spoiler has moved downward and rubbed. The force required to move the spoiler the same amount by pressing on it is considerable so it's certainly not just a cosmetic item.

[Daleevs]

Yea theres a cost but a small fee for a good figure and understanding for someones car call it research and developement, and a much better understanding for your car, also you guys will have a base line understanding of down force for your cars minus your spoilers i only have the boot lip spoiler atm just wanted a base then see what that would look like later down the line with forced induction and track use

[mrspiller]

Yea theres a cost but a small fee for a good figure and understanding for someones car call it research and developement, and a much better understanding for your car, also you guys will have a base line understanding of down force for your cars minus your spoilers i only have the boot lip spoiler atm just wanted a base then see what that would look like later down the line with forced induction and track use

I can see you want a starting point , that’s a fair comment . Personally I’d get the car set up to your liking for track driving first leaving aero out of the equation . You’d be very surprised how capable the car is as standard with updrated ARB’s etc . I have a turbo set up which I bought for the car but I’m not sure the gains will be that significant .Because of the low torque you can pretty much keep the throttle flat through majority of bends where more powerful cars can’t . Example is my cousin who runs an 265 bhp 1.6 Mx5 simply can’t keep up as he has to thread the throttle so much through bends to avoid the lag and twitch of the turbo .
And I think by doing the conversion , albeit a low boost one I would suffer from the same issue .
Take a look on some of the track day videos
Of club meets , you’ll be very surprised .
Good luck

Wayne


Sent from my iPhone using Tapatalk

[PeteH]

a small fee

As Dan was hinting at, it's not a small fee. It would run into tens of thousands of pounds for you to get reliable Clf, Clr, and Cd values.

[Dr. FrankenRex]

I mean, if you can do it and provide the data then that would be AMAZING and I would love to see the info, but I worry you haven't got any pricing back as to the potential cost of it all.

CFD exists because wind tunnels are expensive...

[Conan]

Hang on chaps
The guy may actually work at one of these facilities
Pete

[PeteH]

He might do, but he doesn't. So I think our advice is valid.

I've found this published info for the commercial rates of a small tunnel in the USA. Note that this tunnel is too small to take a full size car.
https://www.aa.washington.edu/AERL/KWT/rateguide

The basic cost starts at about $5,000 per day. On top of that you will need computing and measurement facilities (they charge $3,000 for use of either a force balance or pressure measurements, neither of which will work with a full size car). Most tunnels require two or three operators and, if you can't operate it yourself, you will also have to pay for them. So you will be looking for a bigger tunnel, with in-ground measurement load cells. And most car tunnels use a moving ground, which makes them substantially more complex and expensive. And if you do find one (and there aren't that many full size tunnels in the World....), you will be competing with major race teams and OEM car manufacturers for the time in the facility.

Seriously, it's tens of thousands. You have to be a medium sized race team before you even think of spending time in a tunnel.

[RenesisRaceBuggy]

Last time we had to put a car in a tunnel at MIRA (accident investigation, not even development work - and not our car, I might add ) it was about £8k...

[geofftl1000r]

There is a YouTube video showing a drag car being tested in a wind tunnel (USA). The car is naked so they were testing what difference body panels make. It was quite surprising what did and what didn't work. They did mention costs but I can't remember the numbers. Wasn't cheap I do remember that!

[StreetDragster]

This thread has caused me to re-read Clives and Liams build threads and inspired me to put a diffuser, front wing vents, splitter, cannards and wing on my car (eventually)

Cheers all, now it will be even more difficult to get on the trailer

Matt

[Daleevs]

Cheers mrspiller thats good advice, its a longggggg story one of which im waiting for a outcome (knows someone) kinda deal, just hope this person or persons dad is still a specialist in this field, many moons ago last i heard aome race times were in heavy use of the facility ages ago tho