Oversteer: FM Stage 2 V-Maxx kit + turbo

[Scoota]

I used this spreadsheet on the Fat Cat Motorsport page:

http://fatcatmotorsports.com/FRC_1_6NA/FCM_MSDS_1_6NA.htm

Put in your car's vital statistics (anything in orange text) and hey presto.... It gives you a bunch of info in green. Essentially it tells you about your car's handling characteristics. The front Roll Couple (FRC) is the figure to look at when considering a car's tendency for understeer or oversteer. In general terms, your car's handling will be either over-steeery, neutral or under-steery, based on your FRC (not shown on the spreadsheet anymore, but I have an old version that includes this info).

Over-steery: FRC less than 62%
Neutral: FRC = 62 to 68%
Under-steery: FRC more than 68%

I have 6 configurations to choose from, using combinations of my OEM sways and a Flyin Miata front bar. This gives me 6 different setups to choose from, ranging from FRC = 53.4% to FRC = 41.3%.

I've done three track days since the PSS-9 and FM bar install and now that I'm used to semi-slicks and the new dampers, I find the car to be a little under-steery for my liking, using the FRC = 53.4% setup. Now that I know the "order" of the different setups with regard to FRC, I can choose to go in either direction. In my opinion this is a very useful tool for making predictions about what effect your mods will have on the general handling characteristics of your car.

To go more understeery I would need to buy a harder front bar or front springs, but I have lots of options if I want more of a tendency for oversteer. That's my plan. I'm going to wind it up to FRC = 47.5% and see how that goes. I'm predicting lots of lairy skids.

And let's be honest, who doesn't like doing skids?!

Disclaimer: I have no affiliation with FCM, I just love their spreadsheet. And I always found the standard setup with FRC = 55.5% to be understeery. Maybe I'm doing it wrong?

[deviant]

Remember that driving style, tyre compound, track temperature and even the construction of the track surface all play a part.

Someone who is very smooth might find a set up neutral where someone who is a bit more rough might find the set up understeers due to them overwhelming the front grip.

Those sorts of spreadsheets are very good for getting you in the region in one hit and then you can move away from it and tweak either side of that number to suit your own needs...so you are probably not doing it wrong Scoota, just different cars with different drivers on different tracks perform differently.

[zossy1]

Update:

I had a set of KU36 fitted, and removed the rear sway bar. Oversteer is now very manageable, but understeer under power is quite noticeable. I think going to a lighter OEM sway might be the answer...

[deviant]

You could tweak that out with coilover and alignment settings?

[Jace]

So for more oversteer and less oversteer in a gutless stock car (yes I'm thread jacking), tighter rear sway bar and any other bracing (lower tie bar, rear strut brace etc) and keep the front end aligned perfectly and dampened/sprung to suit stock front sway bar?

[zossy1]

You could tweak that out with coilover and alignment settings?

The V-Maxx don't have adjustable damping. Not sure if ride height changes would do much good - besides, I'm not that keen on breaking any records in this car.

Alignment changes are doable though. Running FM specs ATM - are you suggesting more neg on the front?

[jerrah]

I think going to a lighter OEM sway might be the answer...

Did you resolve the handling issue? What changes did you make to your suspension?

[NitroDann]

Considered more rear toe out?

Dann

[zossy1]

I haven't yet had a chance to mess with this - still running no rear sway bar. I'm a lazy SOB - it takes like 5 mins to fit!

One of these days i'll get around to it.

As for toe out at the rear, I will need some additional adjustment (offset bushes or something) to get that additional toe out. I am running 100mm ride height and at that height the adjusters run out of range at 2-2.5 degrees neg and around 1-2mm toe out.

[plohl]

wouldn't toe out at the rear make the car more likely to oversteer?

[NitroDann]

Dont we want more oversteer?

i dunno, didnt read properly maybe haha

Dann

[zossy1]

My understanding was that to a point, tow out on the rear tends to straighten the rear and help keep it planted on turn-in.

Beyond a certain point, it creates excessive tyre wear and contributes to turn-in understeer and power oversteer.

But I may be talking through my a$$. Go karts can't toe on the rear and I know far more about how to make a kart go around corners than a car.

[NitroDann]

Any toe out makes the car oversteer more and be less stable in the rear.

Dann

[zossy1]

I'm not sure I agree Dann. Besides, you can't make a blanket statement about all cars behaving the same way with alignment changes - FWD/RWD/AWD all behave differently as will cars with staggered tyres, different weight distribution (especially mid-engine) etc.

With a front-engine rear-drive car like the mx5, it is weight transfer that is the key to understanding alignment changes.

When you turn in (generally under brakes), weight moves forward and onto the outside wheel. The inside rear wheel unloads and, for the moment, becomes a spectator. The outside rear is having only a minor effect on the turning action of the car (unless it is locked up or something).

By mid corner, braking is done but turning is not. Weight is still on the outside tyres but shifting backwards. The outside rear is now starting to have a real effect on the turning action of the car but the inside rear is still a passenger for the most part.

From the apex, you are getting on the power and power is shifting backwards. Here is where both rear tyres, especially the outside rear, are showing their stuff. The inside front is now the passenger.

What does this mean for alignment? Well, mid corner is where you will see it at work the most, but it impacts the entire physics of cornering. Your toe out on the rear should be creating a guiding effect, keeping the rear planted. Think about it - the rear wants to step out but the rear wheel is pointing out as it is toeing out (guiding the tyre that way and maintaining traction). With no toe, your slip angle on the outside rear is greater and so is the likelihood for oversteer. This effect is maintained under power, though by this time (on corner exit) the effect is negated somewhat by the inside rear beginning to load up.

That is the theory anyway.

[NitroDann]

Unfortunately its not the theory, go get any car and put 5-10mm toe out a side on the back. Guaranteed rear end instability and sliding.

Dann