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unless you are already at full tight on the rear bar + full loose on the front bar and still getting understeer, there is really no advantage of changing to the Gt2 rear sway.
No it wasn't.
Scott had told me the same information - and he got it from Porsche directly.
Just thought I'd throw it out there.
Should have done a google search first and would have found the formula
When I got my GT2 bar, I was very surprised that it was only 25.5mm vs the stock bar at 23.9mm as it just didn't seem it could be that much stiffer given the small increase in diameter.
Live and learn.
Can someone find out what hole the factory is delivering the rear bar on the new GT2?
unless you are already at full tight on the rear bar + full loose on the front bar and still getting understeer, there is really no advantage of changing to the Gt2 rear sway.
The car is delivered full stiff rear (3 holes) and one from fully soft (5 holes) from the factory and the car still pushes like crazy at 9/10ths to 10/10ths track driving even with more aggressive front camber (this is on all 2nd gear and mid rpm 3rd gear corners)
If the tracks you drive do not have these types of corners or you keep the car below 9/10ths then the bad push does not reveal itself - in fact the car feels perfect.
Under the these types of conditions, the car needs more front tire + a rear end that will rotate slightly more under throttle to "balance" the car.
Many people that track their 997GT3s on similar types of tracks and under similar types of conditions have reported the exact same issue - so much so that I think this alone speaks to why Porsche has released an "updated" anti-sway bar for the GT2 - especially when we consider the previous GT2's "widow maker" reputation. Yes the GT2 comes with a wider rear tire but with the tremendously higher tq numbers, you would think if anything they would want to neuter the rear end even more than the GT3's but it would appear that the lawyers have let WR dial in the car further.
If the bar doesn't work then it doesn't - but I think it is worth a try to fix the only real issue that this great car was delivered with.
- both rear bars have 3 holes
- both bars are hollow
- i do not yet know what hole the GT2 arrives installed on
- the GT3 we know comes fully stiff
- is it stupid math to say that 1.6/23.9 (approx 7%) implies that the GT2's bar is 7% stiffer ( or do we use different math for twisting a hollow tube?)
- think i might give a sway bar company a phone call
paul
Paul,
Before you run off making changes you need to remember that the GT2 has a lot more weight over the rear wheels than a GT3 (100+ lbs). All the extra weight is out back in the form of wider bodywork, turbos, intercoolers and air plumming. This means the GT2 has more rear weight bias than a GT3. That 7% extra stiffness is probably there to correct the weight transfer from the extra weight.
Paul, my heavy non-adjustable 997tt pushed even more than my Gt3 in corners, but switching out the crappy tires to 245 width R6's in front made the car almost completely neutral. The stock "R" compound tires are completely inadequate for 9/10 track driving IMHO. Running R6's vs MPSC's on my 997tt my track out is about 20ft wider on the Michelins than the Hoosiers given the same steering input on a high speed turn
C.J. thanks for your words, anyone playing sports at your level certainly has mine as well!
Back on topic, I have thoroughly tested the understeer on the GT3RS 6 months ago, nothing that could not be cured with different alignment settings, different tire sizes (245s as Eclou rightly said) and pressures (almost same front and rear), and using slightly more trailbraking.
The best solution came when the suspension mounts were rotated and some shims were added to increase camber. Increase toe out in the front a little as well. There is no need for a different anti roll bar IMO, although it might help for sure.
I just got home from the mechanics- installed some new suspension goodies and getting the alignment set up for faster driving. will post pics thursday when I get it back with the cage and other safety stuff installed as well.
gmg makes solid suspension pieces for the lower control arm and new dog bone thingies with shims. also lowering the car 10mm and will asses the setting of toe/camber at the track friday and sunday...
TPC Racing is in the sway bar making business. An anti-sway bar(aka anti-roll bar or stabilizer bar, or just sway bar for short) is a torsion bar-type spring. One cannot conclude the full characteristic of a bar by the OD(Outside Diameter) alone. Other design specifications(often proprietary/unpublished info) that contribute to the full characteristic are:
1) Solid or hollow tube
2) If hollow, what's the wall thickness or ID(Inside Diameter)
3) The spring alloy and heat treatment
4) Leverage- distance of the hole(s) from center of tube
5) Does the bar end design flex before or after the tube
6) Any changes to bushing offset or the mounts
It can get very scientific or can get as simple as the test driver just want a stiffer or softer bar than what he currently has to complement the rest of car's setup to achieve the balance he wants.
Here's some example images of three different hollow front bars for 997 GT3/RS. Its a pretty neat and fun comparison to see how they stack up, literally with the tube stacked on top of one another.
I'm clueless but am told the GT2 rear sway bar is a GREAT mod for the GT3 - would appreciate thoughts on this
It depends on what you are trying to achieve. For example, some drivers feel corner entry or exit push(understeer), presuming that the push isn't tire or tire pressure related, then the single easiest way to balance out the push is with a stiffer rear sway bar regardless of the brand. But too stiff of a rear bar will then make the car loose(oversteer). At one point Porsche put out a service bulletin that states if a 997.1 GT3 customer complaints of understeer it is acceptable to install a GT2 rear sway bar. IMO, this bulletin is very general, not enough specifics. Because if this customer was an avid track driver and setting his alignment camber and toe, ride height to change rake, the rear bar change would like be unnecessary. But I guess Porsche can't have every dealer tech doing track setup on street GT3's and then have customer complaint about tire wear afterwards, and steering feeling too sensitive so perhaps in their point of view a stiffer rear sway bar is the better solution.
If you don't feel understeer, then you don't need to buy a stiffer rear bar.
If you do you feel understeer, then you have options- buy stiffer rear sway bar, or reduce front tire pressure(within reason), or increase front negative camber, or toe-out front, or lower front ride height, or raise rear ride height, or combination of all/some of the above depending on the severity of the understeer. Or you can set your stock 997.1 rear sway bar one hole stiffer(which is a bigger change than using a GT2 rear bar set at middle hole). Sometime understeer is induced by driving style.
I am a terrible saleman...if I was a good one I'd just say buy TPC bar. LOL
Last edited by Tom@TPC Racing; 11-16-2018 at 06:18 PM.
- both rear bars have 3 holes
- both bars are hollow
- i do not yet know what hole the GT2 arrives installed on
- the GT3 we know comes fully stiff
- is it stupid math to say that 1.6/23.9 (approx 7%) implies that the GT2's bar is 7% stiffer ( or do we use different math for twisting a hollow tube?)
- think i might give a sway bar company a phone call
paul
Tube strength is proportional to the radius^5. yes 5th. Bending stiffness(I know , not torsional) is proportional to the r^5 Yeah 5th power. My memory may be faulty, but I think I recall torsional stiffness is proportional to r^4th Hollow tubes use D^4 - d^4 in the equation possibly (D= outer diameter, d=inner diam)
TLDR - I think a little bit, gives you a lot more.
02-05-2008, 09:55 AM
