Another Pedal..

[ralphmusic]

Brian,

You are right about the effect of seemingly small changes. When my old car was running one degree more front and rear camber than my GT4’s Centre Gravity setup, we started with less rear toe and increased and then decreased it. These changes were accompanied by variations in ARB stiffness and camber until I settled on a combination that worked best for me.

The settings seem to have settled the rear under hard braking from street speeds; we’ll see what it’s like on track at Castle Combe.

Ralph

 

[Twinfan]

The car was first measured with 100% fuel and 90kg driver weight and on that basis the 'as delivered' alignment was: front camber -1:25 and -1:32 (degrees:minutes) with 0:05 and 0:08 toe. Rear camber -1:18 and -1:17 and toe 0:13 and 0:12, so pretty square. ARB factory settings were middle of three, front and rear. Ride height was reduced by 11mm and 9mm front and rear, respectively and corner weights balanced, now just 1kg cross weight difference. I prefer more camber and we ended up with -2:25 front and -1:50 rear (rear OEM TCA is still the overall constraint on camber) with 0:02 and 0:24 total toe, front and rear, respectively. The rear ARB was adjusted with one side middle and the other stiff, so slightly stiffer rear. My 200 mile journey home was 190 miles of motorway so we'll see how the new settings work up Avon Rise in a couple of weeks.

Thanks for this Ralph, my car is going in for a geo tweak next week and I think I'll end up with something broadly similar to yourself.

Is the rear camber at -1:50 the maximum you could get, or have you only gone that far to keep the difference from the front? I could get up to -2:00 out of the rear of my old GTS but only -1:50 out of the front so the front was the overall limiting factor rather than the rear.

 

[ralphmusic]

Rear toe adjustment is the limiting factor

 

[Twinfan]

Thanks Ralph, so -1.5 is the best you could get?

 

[ralphmusic]

It was the most CG could get. We shall see if it is the best...

 

[Twinfan]

Thanks Ralph, I'll see how they get on with mine next week. It'll be a bit rubbish if my GTS could get more camber than my GT4!

 

[Brian_Innes]

David,

You should be able to dial-in -2.0" negative on your rear axle on the GT4 with minimum rear toe of 0.6" each side giving a total rear toe of -0.12".

With the stiff bushing of the GT4 this should not induce any rear wheel steering symptoms under braking or acceleration.

This is from my experience anyway.

Brian

 

[AndrewCS]

How do the 982`s `owners manual settings` compare with those of the 981 please ?

Front axle overall toe-in +2’ ±2’

Front axle camber -1°30’ ±3’

Rear axle toe-in per wheel +10’ ±2’

Rear axle camber -1°30’ ±5’

 

[Twinfan]

David,

You should be able to dial-in -2.0" negative on your rear axle on the GT4 with minimum rear toe of 0.6" each side giving a total rear toe of -0.12".

With the stiff bushing of the GT4 this should not induce any rear wheel steering symptoms under braking or acceleration.

This is from my experience anyway.

Brian

That's not what Ralph is saying Brian, which is why I asked how much he could get...

 

[ralphmusic]

Given toe is a limiting factor, less toe means you can get some more but not a lot more camber. Setup is a balance of settings on those components that are adjustable to get what works best for the driver’s style and usage.

 

[Brian_Innes]

Rear toe-in is always the limiting factor with rear camber settings on the Cayman. Individual cars do vary in the degree of available adjustment, as I have found out when tweaking the geo settings on all of my 5 Caymans.

In my experience, you can run less rear toe-in on the rear axle on cars that are set lower, eg the GT4 and GTS and the Cayman R. On smooth race track surfaces with no bumpy sections you can successfully run minimum rear toe such as 0.06" each side on the rear axle. The thing you have to watch out for is bump-steer when running marginal rear toe. For that reason, at Knockhill and Oulton, my favourite circuits, I used to increase the rear toe-in to 0.09" each side giving a total toe of 0.18". This worked perfectly for me as my lap times prove.

Too much, or too little rear toe-in, results in squiggly handling at the rear. It's all a case of balance and personal driving style. I have a smooth and progressive cornering style carrying pretty high corner entry speeds, so I need stability in the rear axle for the sake of confidence. Those drivers who prefer the Chris Harris approach to cornering may be less sensitive to toe and camber adjustments. They pay the penalty in tyre bills eventually.

For many people geo settings are a black art subject. I have experimented with many configurations of camber and toe on my cars and I can only relate my experiences of the different settings. I hope this is helpful.

Brian

 

[ralphmusic]

I had the oil changed earlier this week at 2k miles and prior to next Monday’s Trackday at Castle Combe. Centre price was £380 and Indy actual charge was £293 - both ridiculously high.

 

[Motorhead]

Yes it's a rip-off price Ralph, but in addition to sky-high labour rates that the Centres charge they charge top price for Mobil 1 which no doubt they buy in bulk for a huge discount. In my experience Porsche Indies have a more realistic labour rate but still charge OTT for oil.

Enjoy Castle Combe ... hope you're able to get the benefit of the optimised chassis set-up.

Jeff

 

[Nick_USA]

I had the oil changed earlier this week at 2k miles and prior to next Monday’s Trackday at Castle Combe. Centre price was £380 and Indy actual charge was £293 - both ridiculously high.

Most Porsche centres will allow you to provide your own oil if you ask. The likes of Opie Oils and others do deals on Mobil 1.

 

[ralphmusic]

At Castle Combe yesterday the track was dry after 10am albeit with some minor showers but the wind which was quite strong kept the track dry.

The suspension alignment worked well with stable braking up through Avon Rise and into Quarry. Hard acceleration out of Bobbies (a little bumpy) caused the rear to momentarily bob around but that seems to be a characteristic of the strut suspension. Change of direction was quick in terms of wheel angle and response. Tyres look good, no shoulder wear and tyre temperatures were within 4 degrees across the tread on all four corners. Engine power is good with useful torque from around 3k and it pulls strongly up to max revs.

All in all an enjoyable platform, but..

I went round in 1:22 which is a couple of seconds off my best in the old car. I had HLT working some of the time and Porsche Precision app (PPa) also some of the time. Both were a pain and neither as easy as my old VBox system which presented data analysis with video context using Circuit Tools. However VBox lacks access to the CanBus, whereas the PPa does but its video integration with GoPro footage is not automatic. I managed to get the extensive PPa data into Circuit Tools and my best lap when PPa was working was a 1:26.

Looking at the PPa data, I could see my inexperience with the car and a manual box..

- 12 gear changes took 5.6 seconds, need to be quicker and more consistent on judging best change points, although I did get to 7,943 revs and it sounded great

- 23.9 seconds on the brakes, could be shorter time and better profile

Off to Silverstone next week, a completely different track that I know well so we'll see how my gear selection, gear changing and braking skills develop.

 

[JohnCRS]

Great update Ralph, thanks. It got me wondering how much lap time was actually lost on the gear changes. I guess some were done under braking / overrun, others would be effectively a half second hesitation before drive was re-engaged.

I suspect half the benefit of PDK is that it allows more attention on positioning and braking points - is that so?

(No reason for this query really, just an interest in hearing how theory compares to the reality of the driving experience)

 

[ralphmusic]

John,

The gear change aspect is more about getting used to changing at the optimum points and not getting fifth instead of third, than the time taken but it was interesting how long I was between gears. I should check the throttle opening trace to look at time off throttle whilst changing gears. I think the major point is one you allude to, that is less capacity to apply to positioning and the sequence of change events, all in all regaining fluency.

The benefit of good and extensive data cannot for me at least be underestimated. It enables a better post-event understanding of what was going on and comparison of different laps to highlight inconsistencies. The VBox system can access the CanBus but that requires splicing in or 'sniffing' connectors and the available data is less than available from the Porsche Precision app.

 

[Twinfan]

For anyone who's interested, I had my geo adjusted today so I'll compare it to Ralph's:

Ralph from the factory:

front camber -1:25 and -1:32 (degrees:minutes) with 0:05 and 0:08 toe rear camber -1:18 and -1:17 and toe 0:13 and 0:12

Dave from the factory:

front camber -1:21 and -1:37 with -0:02 and 0:04 toe rear camber -1:29 and -1:28 and toe 0:06 and 0:11

So quite a bit different, and not consistent between cars. Typical Porsche factory tolerances really! Unlike Ralph, I've not adjusted the ride height or the ARBs as my car is not currently tracked. The best we could get without changing any parts is:

Ralph after adjustment:

ride height reduced by 11mm and 9mm front and rear

front camber -2:25 each side with 0:02 total toe rear camber -1:50 each side and 0:24 total toe

Dave after adjustment:

front camber -1:24 and -1:37 with 0:04 total toe rear camber -1:29 and -1:28 and 0:24 total toe

So Ralph can get more camber due to lowering the car, but our toe settings are pretty similar. Speaking to the guys at my place, I've ordered some shims to get more camber on the front of my car but the rear will be left alone. I'm going back next Thursday morning for fitting and we're aiming for -2:15 to -2:30 on the front which should give a nice balance for road use while retaining the stock settings for ARBs and ride height.

I still think it's a bit odd that my GTS could get -2:00 on the rear out of the box but the GT4 only 1:30 but there you go!

 

[Motorhead]

I still think it's a bit odd that my GTS could get -2:00 on the rear out of the box but the GT4 only 1:30 but there you go!

Maybe it was just the way the body, top mount and lower control arm tolerances stacked-up on the GTS Dave?

Jeff

 

[Twinfan]

Yeah, it must have been. Odd though that the GT4 has a very low max camber limit at normal ride height. I think it's bit cack for a GT product if I'm honest.

Mind you, the shims are reasonably cheap. I think they've ordered two 1mm which were a few quid each and two 5mm which were £23. 7mm shims are £64 each!