Functional flat underbody and rear diffuser design

[s4mmie]

Thanks Guy, those track days look fantastic and well worth the money. I may have to bring it up with the Minister of W&F.
No doubt about it, the more practice I can get the better, it's a ball to drive.

Just to be clear, I'm not driving like an absolute lunatic and expecting modifications to make up for my lack of driving ability or judgement for putting it too hard into a corner. I've noticed that when I'm carrying speed, the rear feels very light after losing a lot of weight from the rear. The problem was nowhere near as bad before. The way I see it, if I can potentially add the amount of downforce equivalent to the weight I've removed, then at speed it should effectively be the same as fully laden and I'm back to square one. But hopefully faster being lighter..

Is that the wrong way to go about it?

I'm not trying to be argumentative in any way, I don't think anyone is, just trying to make sure everyone's on the same page.
I don't mind the tangent this thread has taken, as it seems we all have the same end goal: to be better and faster drivers.

[kaanage]

The basic problem is that the car is hugely unbalanced with all the stuff removed from the rear and the aero package needed to fix it would be dramatic and probably impractical for street use.

I'd try putting the rear seat back in and filling the tank up to see how it feels but without doing proper timed track sessions, you will never really know which setup is faster unless you can get accurate splits for that sector with a timing device.

[clicht]

Best info above is practice, practice, practice.

Track & Training Days

Any suggestions on equivalent in Melbourne....thanks

[s4mmie]

...or to lift off BEFORE the corner and then get back on the gas as you turn in.

Yep, that's the approach I take at the moment. It beats meeting the wall

Fair point about the rear diffuser not being as effective as a rear wing. The main reason I'm pursuing the diffuser is it's a little more subtle. I would like to run a wing solely for track days, but I'm still trying to come up with a mounting solution that is completely removable. Until then, I thought it would be worth pursuing or even bring up the idea of a rear diffuser/flat pan combo. The way I understand it is if you can get the air moving faster under the car then above, it effectively sucks it to the ground..
Even smoothing out the rear area so it's not acting like a damn parachute!
My thoughts were if it was cost-effective it might not be a bad way to go. Bang-for-buck seems to be in the wings favor tho.


I think there's merit in both sides of opinion, but personally I don't want to learn how to drive a skittish car fast. Putting the weight back in or removing components may help alleviate the problem, but then I lose the benefits of those in other areas. Like I mentioned in my last post, I feel that a bit-o-aero will give me the best of both worlds. At least then I can feel confident to practice and push harder. A few years ago I would just sack up, but I have a wife to come home to people! haha

[s4mmie]

Just to throw another Q out there; How low would be too low pressure in the rear with low profile tyres?
IIRC low profile tyres need higher pressures than normal to help protect the wheel itself which is why I havent ventured too low..
Currently gone from 38 to 36psi with a marked improvement.

[Guy_H]

QR is a way better track to do your driver training on, then build up to Lakeside.

Tyre pressures? - that will depend on a huge bunch of factors - that is something the driver trainers can help advise on

Clicht - I think John Bowe does similar days in VIC John Bowe Driving Defensive Driving Courses & High Performance Driving Courses

[kaanage]

Any suggestions on equivalent in Melbourne....thanks

Just get on to a track day and drive, Clint. You've done open wheelers in the past which is far more than most of us here, so don't bother with driver training unless you feel something is "missing" when you get out there.

[team_v]

Just to throw another Q out there; How low would be too low pressure in the rear with low profile tyres?
IIRC low profile tyres need higher pressures than normal to help protect the wheel itself which is why I havent ventured too low..
Currently gone from 38 to 36psi with a marked improvement.

I thought for circuit driving you wanted higher pressures as opposed to low pressures for drag racing.

[Guy_H]

I thought for circuit driving you wanted higher pressures as opposed to low pressures for drag racing.

Depends on your tyre. An "R" compound will have a sidewall 4 to 10 times stiffer than a road tyre, so will work better with lower pressures. edit: and a drag tyre will be considerably software in the sidewall over a street tyre too.

[Stan]

just a thought, but wouldnt it be better to make a series of single changes instead of a heap all at once - that way each change can be evaluated on its merits.

e.g. first try different anti sway bar settings, then put seats in, then rear wing, then splitter, etc and work out which things in your case make marked improvements, vs which things make little or no gain. An extensive process, but the end result is more informed...

[team_v]

just a thought, but wouldnt it be better to make a series of single changes instead of a heap all at once - that way each change can be evaluated on its merits.

e.g. first try different anti sway bar settings, then put seats in, then rear wing, then splitter, etc and work out which things in your case make marked improvements, vs which things make little or no gain. An extensive process, but the end result is more informed...

I think the problem is that there are so many variables (air temp and humidity, tyre wear, amount of fuel, potential boost leak from DV etc) that it is almost impossible to tell the differnece that one change will make.
You also have to bear in mind tht the more you drive the same circuit you are going to be more comfortable with it so you may end up going quicker by your own practice rather than any modification.

[Stuwey]

just a thought, but wouldnt it be better to make a series of single changes instead of a heap all at once - that way each change can be evaluated on its merits.

e.g. first try different anti sway bar settings, then put seats in, then rear wing, then splitter, etc and work out which things in your case make marked improvements, vs which things make little or no gain. An extensive process, but the end result is more informed...

And, ultimately faster. After all, isn't that what we're trying to achieve?

You all say the Mazda has heaps of aero. Don't forget the hi-tech leaf springs and recirculating ball steering!

I think you lot need to sort some things out.
-Is it a race car, or a street car?
-Can you actually afford to do this? Both monetary and emotionally (if you get it really, really wrong)
-if you can't afford to leave it in a crumpled mess at the track, you can't afford to take it there!
-Sam, there really is something incredibly satisfying about driving essentially average cars, very fast.

Change one thing at a time. Money and stick-on things won't make your car fast, developing it over time with well thought-out additions and adjustments will.

[s4mmie]

Good points Stuwey, and obviously some of the limiting factors when trying to build a street x track car.
I think that before going any further, my money would be best spent on getting a driver in the car with more experience and seeing how that goes.

Who knows, maybe I just need to learn to drive it the way it is? I like how it handles at the moment. It could maybe do with a little bit more turn in. I figure you want the car to want to rotate rather than understeer like a pig.

[Redliner]

If you don't want to soften the rear roll stiffness or increase the front, raise your front ride height or lower the rear. With a torsion beam rear end/mac strut front end, this shifts the bias of the grip slightly towards the rear.

I did this after I spun at turn 1 Phillip Island with lift off oversteer and I only lifted off for a moment at turn in. Since then, the car is much more stable under brakes too (the dive under brakes exacerbates the situation).



+100 (and kudos for being brave enough to state what I feel)

Totally agree.
When I installed my Kw coilovers the front was lower than the back.
I took the car out for a test drive and the tail was all over the place.
Played around with heights and the handling changed dramatically.

If the car is too low it could also affect how it handles. (spring pretension, roll centres etc).
I would think that fine suspension tuning would have the greatest effect on lap times
combined with testing and practice.

[Eddy]

Hoyhoy.

Folks watch this video of Warren Luff (he can drive) in Guy Hardings new Polo @ 2011 June Motor Magazine Shootout, he ended up doing
a damn good time.
You'll see what I mean in the first 1.5 minutes.
It behaves just like the Little Blue Girl, Its only after I got that sort of behaviour in the Pog that I got my fastest times.
If I go out too hard on the first lap, I'm a goner, I know, been there many times, thats why I like Wakefield Park.
It has run off everywhere, good for OLD FARTS like me, plus it lets ya go 110% & taste the dirt, but after a wash all is good.
Me started late in life with tracking, 2007 in the Dutton Rally I achieved 1'18" @ Waky in a powerfull car, now with practise
I've obtained a sub 1'10" in a wee Little (Blue) Polo.

What I'm trying to say is,,,,, things can get scary out there,,,,,PRACTICE.