M400 ARB - pah

[joust]

Not much 'anti' in that roll bar....

[pic]http://www.trackphoto.co.uk/events/20050829_Bed_Lot_Web/NOBEL/DSC_1381.jpg[/pic]
[pic]http://www.trackphoto.co.uk/events/20050829_Bed_Lot_Web/NOBEL/DSC_1439.jpg[/pic]
[pic]http://www.trackphoto.co.uk/events/20050829_Bed_Lot_Web/NOBEL/DSC_2502.jpg[/pic]

[V6GTO]

Justin...check to see if it's broken. The welding on my one went and caused a 180.

Martin.

[DanH]

Of course, the only way around that would require stiffer springs and a very harsh setup for the road.

You really can't have both without some kind of active suspension.

[joust]

Will do - although as people seem to be posting on the LoT forums that I gave rides to it's probably just me going around corners quicker than "one really should" - indeed one of my passengers apparently felt sick

It's off to Moley though for a brake fluid bleed and post trackday check so I'll mention it to them.

J

[joust]

DanH said:

Of course, the only way around that would require stiffer springs and a very harsh setup for the road. You really can't have both without some kind of active suspension.

Or adjustable that you could "wind up" when you got to the track....

J

[m12_nathan]

joust said:

Will do - although as people seem to be posting on the LoT forums that I gave rides to it's probably just me going around corners quicker than "one really should" - indeed one of my passengers apparently felt sick It's off to Moley though for a brake fluid bleed and post trackday check so I'll mention it to them. J

There is a great story at the moment on the 'ringers list about Hans Stuck having to pull over mid ride in the M5 'ring taxi to let a paying customer be sick at the side of the track

[joust]

Class! Bit like Damon Hill driving that Merc with the bald guy off C4 and making him throw up.... classic bit of film.

J

[m12_nathan]

Well remembered, that was excellent!

Back to the original pics - the tyres are clearly working well as your nearly lifting a rear wheel

[joust]

You should see the front offside, it's lost a good 1.5" width of tread off that outside edge - but is still legal in the middle.

It's really weird how the tyre wears - I'll take a piccy.

New fronts needed now. Hmm. Which ones shall I use from my vast collection of tyres I now have at home

J

[m12_nathan]

Back to the road compromise again - the outer edge wearing could be reduced massively with more negative camber but then the inside edges would wear more on the road and the turn in might well be too sharp for road use.

You can get adjustable top mounts for the BMW that have markings in for degrees of camber, turn up, set it to 3.5 degrees, do the day and change it back and drive home. The one advantage to cheap strut suspension Mind you, that only seems to be done by the people that have taking to running 265 slicks all round and need the extra camber so the 10" wheels clear the arches!

[joust]

m12_nathan said:

Back to the road compromise again - the outer edge wearing could be reduced massively with more negative camber but then the inside edges would wear more on the road and the turn in might well be too sharp for road use.

I'm not so sure that's just the answer.

If you look at the tyre from the front of the car, the wear looks like this


Inches in-----0--1--2--3--4--5--6--7--8--9--10
mm tread left-0--0--1--4--4--2--2--3--4--5--5

i.e. the wear is almost a "wave" effect.

I have a feeling most of the wear is down to the tyre scrubbing it off by understeer - the M400 is a bit understeery on the long left handers at Bedford and it takes a bit of a while to get things balanced again under the throttle to get it neutral again.

If it was just camber, surely you wouldn't get that nice 3-4mm "bump" about 3" in from the outside edge?

J

[m12_nathan]

What do the temps say accross the surface? Perhaps a combination of pressure, camber and scrubbing? You'll notice from my comments I'm not a chassis engineer

I didn't get the "bump" on mine so cannot really comment further - be interesting to get the temp and pressure info though.

[DanH]

joust said:

DanH said: Of course, the only way around that would require stiffer springs and a very harsh setup for the road. You really can't have both without some kind of active suspension. Or adjustable that you could "wind up" when you got to the track.... J

Doesn't really work as you need to adjust the camber settings and ride height really. Ride height you can get around if you are happy to go on track with something compromised for road usage, but wheel geometry you can't feasibly adjust just for a trackday - especially on a noble!

[DanH]

joust said:

m12_nathan said: Back to the road compromise again - the outer edge wearing could be reduced massively with more negative camber but then the inside edges would wear more on the road and the turn in might well be too sharp for road use. I'm not so sure that's just the answer. If you look at the tyre from the front of the car, the wear looks like this Inches in-----0--1--2--3--4--5--6--7--8--9--10 mm tread left-0--0--1--4--4--2--2--3--4--5--5 i.e. the wear is almost a "wave" effect. I have a feeling most of the wear is down to the tyre scrubbing it off by understeer - the M400 is a bit understeery on the long left handers at Bedford and it takes a bit of a while to get things balanced again under the throttle to get it neutral again. If it was just camber, surely you wouldn't get that nice 3-4mm "bump" about 3" in from the outside edge? J

Weird wear pattern you have there. Wonder if more negative camber wouldn't help, but then you'd probably wear away the insides with prolonged road use.

If you ignore the scrubbed edges, then the pattern does suggest some over inflation as it is crowning. Presumably you let a bit of air out on trackdays though. If it was underinflation, the wear should be on both edges.

[joust]

m12_nathan said:

What do the temps say accross the surface? Perhaps a combination of pressure, camber and scrubbing? You'll notice from my comments I'm not a chassis engineer I didn't get the "bump" on mine so cannot really comment further - be interesting to get the temp and pressure info though.

I stupily forgot my infrared thermo thingy, so I'm going to take it next time and do a bit of measurement.

J

[joust]

I've changed the pressures over the the last three trackdays.

All I've found is that past the 30/20 cold, either way (tranlates to around 33/22 hot), the handling goes to pot. However, chatting to some of the other owners that were there, they've quelled the understeer by pumping up the front tyres to nearly 30?!?

That doesn't make any sense, because, as you say, if it's crowning then pumping them up would be even worse??? Confused - you bet I am!

This on the "development" curve is where I bail out, take Lee's advice, and leave it all alone

J

[DanH]

The only pressures that really count are the hot ones though!

Perhaps adding air compensates for sidewall roll a bit, although at what cost to grip?

I still suspect that more camber would be the ticket, but probably no good for lots of road miles.

I've got similar dilemmas to work through on my RS. Its all very adjustable, but finding a decent balance is hard. On the GT3 you have to let a fair bit of air out for track usage, and some of the guys have forgotten to refill their tyres after trackdays and driven home to discover the journey just tore through the inner shoulders of their rear tyres. GT3s have a fair bit of camber as standard, let alone with track optimised geo.

[ashgaunt]

The problem at the front IMHO is that it needs more camber compensation. The static camber is ok, its the rate at which the suspension adds camber as it goes into bump.

The wave effect sounds like underinflation but its still a bit odd. The tire pressure which keeps the tires happy is more like 24psi (Hot obviously) but the pressure which best suits stability and ride is 20psi. It also depends on which tyres are being used. I'm on about the corsas here.

Also, Lowering the car has a detrimental effect on the camber compensation difference between front and rear and the roll centres meaning it tends to enlarge the understeering effect out of corners.

The roll bar itself, I designed this, and its there to enhance grip from weight distribution rather than just counter roll. If you want less roll you need harder springs, and therefore harder bar (bar cannot be more than 60% front total roll stiffness), also needs more camber comp and less bush compliance to work effectively...

[DanH]

ashgaunt said:

The roll bar itself, I designed this, and its there to enhance grip from weight distribution rather than just counter roll. If you want less roll you need harder springs, and therefore harder bar (bar cannot be more than 60% front total roll stiffness), also needs more camber comp and less bush compliance to work effectively...

All of which is going to make it less fun on the road I suspect

Ash are you still at Noble?

[ashgaunt]

No mate, I've moved on, left last november. Learned a lot from Lee mind - credit surely must go to the guy. I still miss the place a bit, especially all the cool guys there.

Freelancing now, did Farboud's new rolling chassis design and now onto other fun things. I havn't had time to come on here and help fellow enthusiasts for a while with what i kno. Been too busy but hope to get time to chat more nowadays!

just realised my posts are making no sense. Blame the beer!

ash



>> Edited by ashgaunt on Tuesday 30th August 23:42