A pre-apex, tail-happy car - suggestions?

[ninerwfo]

So we have had 2 trackdays so far in the newly built turbo NB. Struggling with pre-apex oversteer. Great fun, but also slow and scary - seems like the car is actively trying to gut us like fish! Some quick footage to see what's happening:


Any suggestions on "where to from here" would be appreciated. For context, current setup details are below:
SYMPTOMS:
Last drive: 6th Feb, 2017 Lakeside. 31 degrees. Sunny, high humidity.
(i) Significant oversteer BEFORE apex.
(ii) Some oversteer after apex.
(iii) Could not induce any understeer from the front whatsoever.

EQUIPMENT
• MCA Purples - Set at 3 clicks in from soft all round as per MCA’s starting recommendations.
• Whiteline Adjustable swaybars. Front 24mm; Rear 16mm - set to full soft F&R
• Adjustable endlinks
• Super Pro bushes throughout, eccentrics package
• 17x7 ET40 Wheels (2x old Lensos, & 2x old Rotas)
• 215/45-17 Hankook Ventus RS-3s (very old, very low tread). 27psi cold, got to 36psi hot all round. Pyrometer showed 3 degrees variance between inside and outside of tyre.

Wheel alignment
Currently using the 949 Racing “dual duty” alignment as a starting point – which is:
• Front camber: -2.5 degrees
• Front caster: - 6 degrees
• Front total toe in: 0mm
• Rear camber: -2 degrees
• Rear total toe in: 3mm (1.5mm left & right).
• Tyres appear to be wearing evenly – but have only had one track day with these settings.

Ride height (measured from pinch weld)
• Target is for 130mm on all 4 corners (zero rake).
• Actual as measured: FL = 130mm; FR = 125mm; RL = 129mm; RR = 120mm (we will try again to better meet 130mm target).

What did we change on the day?
Tried softening the rear shocks 2 clicks to 1 click in from soft, but did not make any difference to the pre-apex oversteer. Also then bottomed out in the middle of the Lakeside Kink at 180kmh - something that clarifies the mind.

Where to go from here?
Using the below cheat-sheet as a guide, do we:
• Increase stiffness of front swaybar?
• Increase front shock damping?
• Change back to the standard rear sway bar?

Any other suggestions gratefully received!

[chops]

change rear sway bar to 14mm.

I used to run a 16mm bar and had similar symptoms which were vastly improved by going back to the original 14mm rear sway bar

[MX593]

Get some good NEW tyres.

[Trackphotos]

+1 on sway bars, rear is too big. I had the same combination on my car briefly and it made it very twitchy on 11/7kg springs, MCA Blues, otherwise standard suspension. No amount of damper/tyre pressure adjustment could dial the twitchiness out. Put oem bars back in if you've got them, and I bet you'll have an almost neutrally balanced car again.

[Magpie]

27psi cold, got to 36psi hot all round. Pyrometer showed 3 degrees variance between inside and outside of tyre.

What were the temps? Was the middle higher or lower than the inside/outside? I would expect to see more than 3° variance with that alignment especially when you have done a cool down lap. The middle temp helps with over/under pressure.

• Front total toe in: 0mm
• Rear total toe in: 3mm (1.5mm left & right)

This is aggressive, however aids in keeping the car stable under brakes at the expense of a little top end speed! Toe causes drag... You may want to consider at least some toe out (3mm total) at the front to aid turn in.

Struggling with pre-apex oversteer.

This could be more driver/technique related than mechanical, however the car being a little tail happy is a good thing whereas prone to understeer is considered 'safe'.
Are you getting on the gas too early into the corner, that is washed off too much speed and start accelerating?
Are you at the limit of grip of the tyres

Also then bottomed out in the middle of the Lakeside Kink at 180kmh - something that clarifies the mind.

This could be spring related or how the shock manages the mm/sec of that 'bump'. However, more than likely not bottomed out but rather on the bump stops. Not sure if the MCA's are fitted with progressive bump stops or they are solid. You have essentially a road car setup, that is one that is not critically damped. Remember that the dampers control the rate of weight transfer and NOT weight transfer.

Any other suggestions gratefully received!

I have to say almost all of these have been said to me (many times) and I have to admit are very valid...

1. Get a notebook and record everything
2. Do one change (if possible) at a time and jot down in the notebook the impact
3. Seat time, seat time, seat time. Until you get experienced and have consistency evaluating objectively mechanical changes will be difficult as you cannot rule out driver improvement as opossed to the mechanical improvement.
4. Consider getting some coaching to avoid developing bad habits, this helps with consistency as well
5. Chat to other drivers, but understand that what works for them may not work for you. Look for drivers who are similar times to your own as opposed to the ones doing the fastest times.
6. Enjoy what you are doing and relax...
7. Delete the brake booster (just kidding)

There is general practice and street sprints at QR on 18/02 pop out and say hi or participate. General Practice is a good place to learn.

[pepejesus]

What spring rates?

Rear bar is too big, and front too small, regardless. The MX5 never needs a 16mm bar on the rear. 14mm is as big as you'll ever need.

No point changing anything until that rear bar is replaced with 14mm (probably ideal) or smaller (probably not ideal but still better than 16mm).

You'll then need a bigger front as well, depending on the rest of your setup, probably something like 1.125" OD 0.188" thickness, eg http://www.racingbeat.com/Miata-1990-2005/Sway-Bars/54103.html

Get rid of the old, worn tyres.

[pepejesus]

Whiteline Adjustable swaybars. Front 24mm; Rear 16mm

This Whiteline swaybar package is such a joke. They clearly did zero real-world testing, you're better off with stock sways than that combo.

[rossint]

TYRES, no point doing anything else suggested (although they're all good suggestions) if your tyres don't work.

[ninerwfo]

Thanks heaps folks, lots of good adice in there, and surprisingly for the internets - a degree of consensus! Seeing as we are running a sort-of-similar setup to Trackphotos, we'll start with putting both standard swaybars back on as a first move.

Magpie, thanks for all the advice, totally possible that the loose nut behind the wheel is what is causing the malfunction. Planning to be at QR at the 18th, and hoping to book in the the Stokel training day at Lakeside in a couple of months.

Is there any agreement on the best value for money driver training around the Gold Coast Brissie area?

[Magpie]

Myself, like trackphotos run stock sway bars. Consider that trackphotos runs serious aero and this is what possibly drives his setup.

Driver Training

Paul Stokell - I have done a few of these and think at the time my skill level was not adequate to make the most of what they could offer. You do get good track time and this is important, getting an instructor can be a bit hit and miss as this depends on the number of people there unless you take the one on one option (extra $385 for a full day). I have not done any of these days in a few years now.

SDT Driver Training - they normally hold about 3-4 training days at Morgan Park. Since the numbers are usually low you get a lot of instructor time as well as track time. If starting out these are very good, if you have decent skills they allow you to practice as well as can offer advanced tuition subject to availability. Normally I try and do all of these each year.

Mr Tuning - http://www.mrtuning.com.au/about/mr-driver-development/ I have done a few of these as well and best money I have ever spent. I try and attend at least 1 of these a year.

Club days - most experienced drivers are happy to provide some personal experiences and advice on racing lines. Some may even offer to review video footage, but this could depend on their availability. Again probably organise this before the day.

Cheaper track time:
General practice at both QR and Lakeside, however no tuition options. It maybe possible to have somebody review your in car footage and provide advice but no passengers allowed on the track.

Morgan Park has general practice during most weeks (check web site for actual days) but you will require a CAMS licence to attend theses.

[ninerwfo]

Yes, reckon I'll feel like a real racer with an L2S in my pocket! Didn't know about Morgan Park - the footage of it looks like great fun

[pepejesus]

Thanks heaps folks, lots of good adice in there, and surprisingly for the internets - a degree of consensus! Seeing as we are running a sort-of-similar setup to Trackphotos, we'll start with putting both standard swaybars back on as a first move.

What are your spring rates? You're running MCAs so I'm going to assume 12/7 or 11/7?

Run the Whiteline front with the stock rear, should give you better balance than stock bars all around with those rates.

See how you like that, it should be reasonably well balanced, albeit a little soft in roll. Probably slight tendency to oversteer, which you could offset by running more neg rear camber.

Next upgrade would be an RB tubular front (or similar) and 14mm (MX5 SE) rear bar.

[ninerwfo]

Thanks Pepe , yep - 12/7

[The American]

I "activated more grip" all I could in my last mx5, and at times it was like driving a shopping trolley: No body roll and propensity to slide in any direction at a whim.

This time I stuck with the factory units and have had much more success. I am tempted to increase roll stiffness a little, but when I get around to it, it will be with increased spring rates rather than ARB's.

The popular wisdom is still that the factory rear bar is fine, and a larger front bar is good.

In my set up, the camber gain that comes with the roll is a good thing.

[RS2000]

What are your spring rates? You're running MCAs so I'm going to assume 12/7 or 11/7?
Run the Whiteline front with the stock rear, should give you better balance than stock bars all around with those rates.

Mine had terrible understeer with that setup - 11/7 mca reds, Neg Camber 3F & 2.5R, Toe 0 F, 1.5 in R, plus good V70A tyres.
I put stock front arb with stock rear to make neutral. Perhaps 14mm rear with 24mm Whiteline on front would be good in my case.