NC Mk3 MX5 road/track geo setup on Meister R Clubrace coilovers

[fangio246]

Hi

After some geo advise for a Mk3 NC MX5 

Want a good starting point for a fast road (sometime track) geo set up having had Meister R Clubrace coilovers fitted. I know driver preference affects things, but want the handing fairly neutral, certainly not oversteery...

I'm a little confused as a lot of the American guys especially seem to run more negative camber on the front than the rears. Plus I've read on Suspension Secrets the following:

The rear negative camber is often much less than the front wheels due to the tractive force needing to go through them on the straights. This set up is also coupled with a slightly softer rear end to prevent the contact patch rolling over towards positive during fast cornering.

Also some people seem to suggest to start with zero toe at the front and then go anything from minus 4 to 9 mins per side on the rear.

I'm running the Meister's around 16 from hard on the front and 19 from hard on the rears - 30psi hot all round on Nankang NS-2R's

Thanks 

[Tony]

Hi

The camber difference if because the rear "on bump" has a camber curve, whereas the front camber changes as the steering lock-on-lock migration.

Did you check the pre-load on the coils?,,, Jerrick says they are factory set, trust me they are not!

Some track day stars run -1 degree 30' all round. Zero toe on the front is fine since to drive wheels are pushing the front so it will toe out dynamically.

You need some toe on the rear to keep the temperature up.

 

 

[fangio246]

Hi Tony

Thanks for your reply. The chap who fitted the Meister's supposedly corner weighted the car and checked the pre-load etc.

Interestingly he wouldn't tell me his geo settings so I took it to a place with Hunter equipment to ask them to give me a read out. It seems weird to me

Front near side -1.51 camber 0.05 toe in  -  Front off side -1.46 camber 0.22 toe in

Rear near side -1.52 camber 0.08 toe out   -  rear near side -2.26 camber 0.09 toe in

There wasn't any weight put in the car, though i'm only 60kg

Comments?

Would you say it could go to 1.5 negative camber all round?

[Tony]

The rear is a mess..

The car has already got a 50/ 50 weight distribution... Domestically corner weighting is a wast of money?.... Fill up your washer bottle then the balance has gone.

-1.5 and correct toe is a great base. Under/ over steer is determined by the rear camber/ toe.

This going to rear odd but the front toe uses the rear toe as a datum point? The front wheels don't know where forward is, so setting the rear toe symmetrically with each wheel on the rear it will set the thrust angle and then the front wheels will tell the front where forward is. 

[fangio246]

Thanks Tony for your speedy response

Think i'll get the rear to -1.50 camber on both sides, so -1.5 all round

Toe: Front 0 (zero) Rear minus 4 mins per side?

Does that sound ok to help prevent unwanted oversteer and help high speed stability?

Cheers

[fangio246]

Morning Tony

 

Can if please confirm if my settings above would be a reasonable starting point, or if you would go more or less on the rear toe?

Camber -1.5 all round : Front toe 0 : Rear toe minus 4 mins per side?

Thanks

[Tony]

Yes those numbers are fine. Be sure the rear toe is positive +

I'm about to write a topic about dynamic indexing, read that it might help to understand why the geometry holds these settings.

[fangio246]

Hi Tony

So with dynamic indexing in mind and the 'silent' wish to adjust the suspension to compliment the handling the customer wants. Then how come you've suggested positive toe on the rear if I want a more neutral handling car that if anything leans slightly more toward understeer, as I'm a novice track driver?

Quote:

Toe out on the rear wheels will make the car more nimble and faster through tight sections, making it feel as though it has a shorter wheel base. This effectively makes the car have a higher tendency to oversteer so is a set up used by smooth drivers who can be light on the throttle. Toe out will also make the car feel less stable through high speed corners due to the feeling of oversteer occurring at the rear wheels.

[Tony]

A small amount of positive rear toe heats the tyres up. this reduces the hot lap.

Every car sold is designed to understeer. This is a safe zone so if the driver gets it wrong they hit the tree arse first.

We have an enormous responsibility calculating chassis settings to compliment any modifications. Most shops use the OEM settings which in truth don't apply to the modified car.  

 

[fangio246]

Thanks Tony

If you look at the Lotus Elise settings for example they suggest: Front camber -0.3 : Toe 0   - Rear camber -1.8 : Toe - 1.5mm per side (toe in). Up to 2.5mm toe in on the Exige V6

These are semi track focused road cars all running rear toe in?

I'm very nervous about the idea of running rear toe out, are you saying that a little rear toe out (4 mins per side) won't upset the MX5 high speed stability?

I did a Donington track day with the MX5 settings as described in my second post. I noticed the front were only running 0.5 psi hotter than the rears. So to get to the 30 psi operating pressure the fronts ended up at 24.5 psi cold and the rears 25.0.

Interesting both rears were at the same 25psi cold and 30psi hot, even with the nearside slightly toeing out and the offside running 0.75 degrees more camber with slight toe in! Maybe it's due to Donington being clockwise with virtually all right hand bends??

Any comments gratefully received as I'm going to get the geo reset tomorrow?

[Tony]

Toe out on the front is twitchy at speed but great for short track and trials.

Long track and neutral has a basic law?.... the rear camber needs to be a degree more than the front. Caster needs to be as much as the adjuster will allow and even. A disparity over the axel more than 30' will make the car pull and lazy to return after a turn.

As said you need a small amount of rear tow in to heat the tyre before you hot lap. Front toe is a matter of taste but as said negative will be really twitchy at speed.

Point to note, if they are measuring toe in millimetres then they have to tell the machine what size the wheels are. I measured in degrees they don't need to tell the machine.

 

[fangio246]

Hi Tony

I've probably gone against the grain but have just returned from getting it aligned.

Readings: Front caster 6.30, camber - 1.40 Toe 0.05 : Rear camber - 2.0 Toe 0.10

This alignment company didn't adjust the caster or camber, so obviously the other Hunter machine was out of calibration! All they did was reduce the front Toe and increase the rear Toe. It was therefore at -1.4 & -2.0 camber, not the previous numbers I gave you, which makes more sense as the Meister R's had been installed and set up by a race car specialist.

[Tony]

Is there anyway you could display the end positions.

[fangio246]

 

[fangio246]

Morning Tony

I've uploaded the Hunter printout sheet. What do you think of the numbers?

Thanks in advance.

[Tony]

They are more or less fast-road i wrote for the NA/ NB. How does it feel like now.

[fangio246]

Hi There

Yep sounds like your setting with a touch more negative camber.

I'm doing Prescott Hill Climb tomorrow, so will let you know after that. 

[Tony]

If your on a short track, sprint and alike then lower the caster which will aid turn in... Fast track you would increase the caster for stability.

[fangio246]

Hi Tony

Did 11 runs up Prescott Hill yesterday. Car went really well, great balance and I would say the car felt very neutral, settled and with good turn in. 

I think for a novice track driver, like myself, the combination of Meister R coilovers and this alignment feels a very safe starting point. Not nervous, darty or wallowing about on soft suspension.

Result.....

[Tony]

Excellent..... Please note, of you feel the dampers need adjusting don't adjust the front and rear... Let's say you feel the need to adjust them, do so sequentially. if thet's say you adjust the front and it didn't help put it back then adjust the rear. Owners who adjust front and rear just migrates the problem.

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