996 Front wheel and tyre size question

Dammit · 9 Dec 2018

I originally asked for 265's, Chris from Exel convinced me that the 285 fit the wheel significantly better - see the invoice:

I'm now going to add power to counteract my tyre.

coullstar · 9 Dec 2018

265 on a 10in is very slightly stretched so I can see the 285/30 reasoning.

DynoMike · 10 Dec 2018

Fascinating thread, some good info from Crash and Martin RSR.

One other variable on the front end is caster, adding more increases the steering angle induced camber gain, meaning less static camber can be applied in the first instance, giving more braking grip in a straight line. I know mine is a Turbo but running 8' 15" with skinny camber of 55", the car simply doesn't suffer from understeer.

The guys are spot on with driving style adjustments - load the front good and proper on turn in, then use throttle to steer the car. Rear toe has an amazing affect on the front end characteristics, less toe back there tends to make the car rotate faster and grip more keenly on the front.

Will be following this thread with interest :thumb:

Jamesx19 · 10 Dec 2018

Hi Mike,

Some good info on Castor angle affecting Camber. I hadn't considered that at all.

I know my C2 castor angle is not adjustable but when it was set up at 9e it was circa 8 deg 15'.

I wanted as much front neg camber as I could, and 1deg 20' was achieved. The other value that I wanted adjusting back from the X74 settings was rear camber. It was set at around 1 deg 30'. I asked for it to be wound back to the standard 1 deg 10' as the rear tyres were wearing the inner shoulders fast, but that refused on grounds of safety! In the end we went with circa 1 deg 20' at the rear as well.

This set up feels very nice for road use. Good turn in and really only starts to push in tighter corners where perhaps I am not making best use of proper 911 driving technique.

I have been trained in mostly front wheel drive / front engined cars where the weight is at the front of the car. The safe method of road driving here being to brake in a straight line, off the brakes, then apply a small amount of throttle to balance the car and move weight to the rear and turn in. More throttle applied once through the apex.

Explained to me as "Might not the fastest method, but the fastest method to use and not crash."

Conditioning myself to either brake into the start of a bend, or lift on entering is a challenge. If the corner is sharp with a well sighted exit, its a lot of fun and I can feel the move to a rear balance. But, not as much as I'd like at the moment. The current 295/30's are perhaps preventing that? (Based on Martin996RSR and Crash7's comments)

Mike, maybe less toe might be something I try before swapping rims and tyres. Do you know what yours is for reference?

Cheers James

Martin996RSR · 10 Dec 2018

Before I did a lot of development of my car I took it on track and found it was very keen to swap ends on corner entry, leading to some pretty lurid drifts, some at pretty high speeds too. This was with 285 section rear tyres and 235 fronts. I later found the problem to be duff dampers, but I would still not recommend using a lift to get the car to rotate when you're really on it (lets not get into a debate about driving fast on the road, that's for another thread).

To be fast and safe on the road you need the car set up to behave predictably, and you need to drive smoothly, whether you prefer a little oversteer or a smidge of understeer, if you're spending too much of your time thinking about how to control the car then you'll be spending too little on what's going on further up the road.

I currently have 255 rears, which I think is ideal, and about -1.5 degrees camber and zero toe on the rear. I'll soon be fitting adjustable rear toe arms to allow me to go back to the -0.5 degrees rear camber that I used to have before I went to coilovers. My car is now faster point to point than it's ever been, but the ultra-stable rear end is just a little dull for me and I want to go back to easier-access oversteer.

BTW, you can adjust castor by making use of non-standard coffin arms with pucks in the centre that allow the dog bones bolts to be moved, which moves the outboard end of the coffin arm forward or back as desired.

crash7 · 10 Dec 2018

'The safe method of road driving here being to brake in a straight line, off the brakes, then apply a small amount of throttle to balance the car and move weight to the rear and turn in. More throttle applied once through the apex"

James, this ^ is good practise even in a RWD car and using this technique you won't go far wrong in a 911.

The challenge comes when your chasing lap times or want to drive faster, using the above technique means when turning in on a balanced throttle there is little weight on the front of the car, so when you start to pile on the power the car wants to 'push' the front end out, aka understeer, now this is not uncontrollable FWD mega understeer, but enough tyre scrub to delay you from being able to get on the power.

To help elimate the issue you need to trail brake, sometimes all of the way into the apex, sometimes not it depends on the corner, but generally I find myself carrying the brakes into most corners, even quick ones, as I find it helps settle and set the car. - This however is on track

Amongst a multitude of other things rake in your setup, car higher at the rear than the front and a softer front end, spring rate / damping, ARB, also helps eliminate understeer.

I agree with Martin in that I also would not recommend a lift to rotate the car at turn in, you naturally get a little between coming off the trail brake and back on the power, unless you left foot brake, but this is usually small as the car is set and balanced. - 996 has great mechanical grip.

Everyone's driving technique is different what works for one may not work for another and it's often trial and error, once you know what works for you, you can adjust your car to make it behave in the way you like. - My setup is fairly aggressive, happy to share, and works for me, but may not for anyone else.

If your interested this chap has some great videos that touch on various driving techniques

https://driver61.com/uni/

DynoMike · 11 Dec 2018

The post above by crash7 contains some good advice. Rake is very important on the 996, my car likes 20mm front to rear rake, when measured at the recommended Porsche measuring points, but it is a turbo...

Rear toe makes a huge difference to the playfulness of the car, as does camber. I have run as little as 1'04" on the rear camber and 5" toe per side, which made the car feel like a good BDA Escort - sideways everywhere! Not fast but huge fun on the road, bringing the 'fun speed' way down from standard levels. I would definitely not recommend this unless you are used to cars that oversteer an awful lot.

The 996 platform is so playful and sensitive to set up, it is a joy to drive when discovering the various options, see my journey here -http://911uk.com/viewtopic.php?t=115436&start=0&postdays=0&postorder=asc&highlight=suspension+journey

Suspension set ups are incredibly personal, by way of example, my own camber settings are almost a mirror image of Manic996t's, yet both of us are very happy with our respective cars. In your shoes I would ask 9e's advice again as they set yours up in the first place.

Enjoy the journey
:thumb:

Jamesx19 · 11 Dec 2018

Hi Crash,

Happy with the theory, just need more wheel time. Set up info and experience from forum members is very informative thanks.

The Fiat X1/9 I used to track, was extremely sensitive to throttle input and pre corner set up. Made it a great road car, but a tricky track machine if is was wet or you had to adjust the line mid corner. If you weren't careful then a spin would ensue as once the rear lost grip it would gain momentum v quickly!

Think I've been spoilt by such a throttle adjustable chassis that the 996 still feels a little inert. The 996 is of course far superior in every regard though.

Jamesx19 · 11 Dec 2018

Good advice Mike.

Will see where I end up! ( Set up wise, not in a hedge) :thumb:

996 Front wheel and tyre size question

Dammit

Paul Ricard

coullstar

Singapore

DynoMike

Albert Park

Jamesx19

Hockenheim

Martin996RSR

Montreal

crash7

Imola

DynoMike

Albert Park

Jamesx19

Hockenheim

Jamesx19

Hockenheim

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