GTgears

LSDs will be available by the 1st of Dec...

TRAKCAR

Don't need it to be at BGB till Feb 1

Bill Lehman

I won't receive my GT4 for several months but the addition of a LSD on my 987.1 immediately reduced my lap times and with PSM off, significantly reduced PSM intervention. My front brake pads wear twice as fast as the rears.

jphughan

I would think that PSM being off would be primarily responsible for significantly reduced PSM intervention.

jphughan

Not related to LSDs, but since we've been talking about PTV here quite a bit, I figured I'd ask this question of those more experienced with the Cayman platform here. A few times driving my GT4 mildly spiritedly on windy roads during the break-in, I've had to tighten steering mid-corner (unfamiliar roads), and on a few of those occasions it's felt as if rather than the front tires gripping more to tighten my line (I was nowhere even close to the limits of adhesion), the rear instead felt like it was stepping out just a bit to get the car rotated. I'm fairly certain I did NOT back off the throttle in any of these instances. For a while I thought it might just be due to the mid-engine setup having a greater tendency to oversteer and my being unfamiliar with mid-engine cars, but now I'm wondering if maybe PTV was at work here rotating the car this way by braking the inside front wheel? Anyone have any expertise and/or experience to share? Whatever the cause, it's already abundantly clear that I have a lot to learn and adapt to here, even before I get into track driving, sway bars, and aero, so I'll be building carefully and systematically -- but it looks like it's going to be a lot of fun!

mooty

^ PTV wont do that.
if you are tightening steering in unfamiliar road i bet it's reducing radius.
to make the turn, you have to turn more and i am sure you let off the thorttle a tad, else turning the wheel alone wont make that turn. and stock GT4 understeers quite a bit. so rear shouldn't step out.

jphughan

Interesting... I may have let off the throttle a bit, but I'd have guessed that having more weight in the middle of the car would have reduced the amount of weight transfer (and therefore grip change) that would occur as a result of reducing throttle compared to the front-engine cars I'm used to. The rear didn't exactly step out to the point that I had to countersteer, but it just felt like a different type of rotation than I was used to, almost like the hand of God gripped the roof and rotated the car a bit almost in-place. But maybe it's just strange to me because it's such a different setup from anything I have real experience with.

vantage

Lower polar moment, the car rotates around your hips.

Weight transfer isnt less just because the car is mid engines. Still very important thing to manage, perhaps even more so than in an M3 because the cars behavior can be so heavily influenced depending on whether you are putting weight on the front or rear tires. A friend of mine who is used to driving BMWs spun a Lotus on his fourth turn at a race track. He lifted. Try swinging a hammer flipped around with the head in the back. That's a mid / rear engine car.

That said I find the Cayman platform quite forgiving.

mooty

ah... that explains it, you came from FWD.
compared to FWD, a mid engine car would fee loose and feels like it's moving around a lot.

yes and yes
but it's really hard to spin a lotus. well maybe not the 211. that's like a 911. exige elise are solid.

jphughan

Not FWD, but FR. I only tracked a FWD car once, and otherwise the only time I have a little fun with FWD is in my wife's Mini, which does indeed need to be driven differently than my M3. But you're right that the GT4 does feel loose to me, which surprised me given that its tires are both stickier and (in the rear) wider, so if anything I was expecting it to be LESS loose in the rear. But good to know it's normal, in which case I'll just enjoy getting a feel for it and figuring out how to use that behavior to my advantage.

TRAKCAR

No expert whatsoever but FWIW to me rake and LSD work together for balance once you like don't mess with it..
Toe and bar are for adjusting per track / preference.
Camber is for tire wear.

Better start with getting LSD first, sort rake now you have platform, than mess with toe and bar, then look at my tires for wear.

Sven76

Nothing easier to spin an Elise, mid-engine, no electronic gizmos, super-short wheelbase. I drove one for years and was quite active I. The local scene, we had so many "beginners" killing the car with lift-off oversteer. Surviving the first year was most critical... Still, a fascinating car...

mooty

^ i got lucky then. 97 days in elise/exige. one spin whew.

BGB Motorsports

There is a lot of information on here from which to disseminate BUT let's keep it simple:

1.) If there is any chance that you did indeed crack the throttle some and reduced throttle, then dynmanically you will have shifted weight forward and towards the nose of the car making the front more reactionary.
2.) IF there is any chance that you did indeed crack the throttle some and reduced throttle, then the diff lockup % was changing mid-corner.
3.) IF there is no chance that you reduced throttle whatsoever, you still added more steering input which increases the camber on the loaded front tire via the effect of caster and by doing so, you made the front more reactionary.
4.) By cranking the wheel and increasing the caster you're jacking weight all around so this too will have an effect.
5.) You could have been on damp pavement, pavement with loose gravel, dirt.
6.) The car's lack of rear camber could have come into play but not likely if you weren't at the limit of adhesion.

It's best to leave these experiments to the track day because when it does happen, a gravel trap or a big grassy field is way better to finish your spin!

Finally, as Mooty said, remember that you need to think of PTV as another word for an LSD. The whole ABD which all cars have regardless of PTV occurs at corner exit and is used as wheelspin control and it's part of the PSM. The idea of breaking loose the inside rear tire at entry or apex does not happen mid-corner under any activity equipped on the Cayman. Only the GT3 with its rear steer stability control cheats physics and it does so by adjusting the length of the toe link located on the front side of the rear upright. It shortens and lengthens that link to move the tire inboard and outboard.

TRAKCAR

^^ he was trying to say that you'll go fasterder...