Understeering issues with 997S
#46
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I want to agree with you, but the facts don't bear it out. If it did, then all Porsche track cars would be AWD. If I remember correctly, this is a complex situation involving the rear weight bias, rear wheel drive, weight distribution, etc. I remember some Porsche Race Team guys explaining it in one of our DE / Racing workshops that you simply can't ask a tire to do more than is possible. Braking and turning is asking for two things, so there's a balance point. Same with turning - and thus turning and acceleration. When you have 295 stickies on the rear of a rear-weight biased car (like the 911) and you are under full throttle exiting a turn, then there's just so much contact patch up front whether the wheels are driven or not.
Also, consider this. Dial in about 2-2.5 degrees of camber up front to erase what Porsche Marketing / Legal took away from Engineering, and you have Zero understeer in a RWD 911.
Also, consider this. Dial in about 2-2.5 degrees of camber up front to erase what Porsche Marketing / Legal took away from Engineering, and you have Zero understeer in a RWD 911.
http://autopedia.com/stuttgart-west/...Physics07.html
#47
Pro
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Here is my track camber set-up. I would highly recommend it for better tire wear and less understeer. Use GT3 control arms for the front with shims. Total cost about $1,300. I now have -2.5 front and -2.0 in the rear. The GT3 control arms also give a bit of a wider stance in the front making the car more stable. Front toe should be very close to 0 for very good turn in. Makes the car a bit more touchy on the highway but very good turn in. Also, before the GT3 control arms, my front outside edge of the tires were getting eaten up badly. Absolutely a waste of a good tire. Add, GT3 front brake ducts, GT3 seat, harness, harness bar, and neck restraint and I am good to go. Perfect set-up for DD and DEs (my commute to work is short so not worried about wearing my tires out with this set-up.
#48
Rennlist Member
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I'm not talking about the difference while tracking the car. The typical turns on a track are not high angle. Here is a test for you. While in your car sitting at a stop, turn the front wheels 40-45 degrees and then hit the gas. How far forward do you go and what turn rate do you estimate you have? If I do the same thing, and I have, the front wheel drive pulls the front end around with minimal scrubbing of the front tires.
Again I am talking about typical road driving situations where the 4 wheel drive gives me capabilities the 2 wheel drive does not. How about making a U-turn as quickly as possible. I can make a smaller min radius turn with the 4 wheel drive if makeing that turn power on in an agressive fashion.
Sure, if you are tracking your car, get the 2 wheel drive. But if you want incredible turning performance on the road, especially on turns greater than 90 degrees the 4 wheel drive offers much more capability.
I've had both cars and in the C4S the high angle off cornering an turn rate is eye watering.
Again I am talking about typical road driving situations where the 4 wheel drive gives me capabilities the 2 wheel drive does not. How about making a U-turn as quickly as possible. I can make a smaller min radius turn with the 4 wheel drive if makeing that turn power on in an agressive fashion.
Sure, if you are tracking your car, get the 2 wheel drive. But if you want incredible turning performance on the road, especially on turns greater than 90 degrees the 4 wheel drive offers much more capability.
I've had both cars and in the C4S the high angle off cornering an turn rate is eye watering.
#49
Moderator
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This entire thread is all about track driving and understeer... There's simply no situation where AWD is superior to RWD in a Porsche unless you are talking about traction in the snow. As to making a U-turn, the C2S can do it as well if not better than a C4S. Heck, if you want to be extreme, w/ RWD we can leave the front tires sitting pretty much still and have the rear end walk around and do a 180 in half the distance as AWD.
#50
The Penguin King
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I beg to differ on this point. Yes the cars are much more stable than the earlier models, but a lift at the wrong time will most certainly initiate oversteer very quickly. ask me how i know...
#51
Instructor
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This entire thread is all about track driving and understeer... There's simply no situation where AWD is superior to RWD in a Porsche unless you are talking about traction in the snow. As to making a U-turn, the C2S can do it as well if not better than a C4S. Heck, if you want to be extreme, w/ RWD we can leave the front tires sitting pretty much still and have the rear end walk around and do a 180 in half the distance as AWD.
Mr. B
#52
Burning Brakes
#53
Burning Brakes
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+1. I love how the rear end rotates around nicely at Summit Point (in the Karussel) when I lift just the right amount.
#54
#55
Instructor
#56
Race Director
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When I test drove a Carrera S I also drove a Turbo. Although I liked the acceleration I did not like how heavy it was. The front end felt heavy.
2wd is more fun. AWD understeers more.
RWD for me.
2wd is more fun. AWD understeers more.
RWD for me.
#57
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PASM doesn't help as it makes it harder to load up the front of the car. Understeer is a problem with the GT3 and RS too. Trail braking gets rid of what's left after optimising your geometry - just make sure you do it right!
#58
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ECS
wtih those camber settings with the gt3 control arms what is the toe and total caster? on the alignment..
thanks
thinking of getting those arms too..would get the gt3 control arms first, switch to R compounds (r888's or MPCS ) or do both at the same time?
thanks
wtih those camber settings with the gt3 control arms what is the toe and total caster? on the alignment..
thanks
thinking of getting those arms too..would get the gt3 control arms first, switch to R compounds (r888's or MPCS ) or do both at the same time?
thanks
#59
Pro
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mkk62 - can't remember the caster, but I believe my front toe was 0.02 per wheel. I will be getting a full alignment before Barber on the 8th so I will let you know then.
#60
Racer
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I had an 89 911 before and I'm telling you tire pressure made such a huge difference in handling I was amazed. I could completely change the car from under to oversteer just by adding a few pounds or taking a few pounds of pressure.