Black TechArt Formula 19's "Weight Watchers"
#31
05-23-2006, 04:13 AM
I read somewhere in the past that for every 10lbs of unsprung weight you lose, you 'gain' roughly the equivalent of 4-5rwhp.
As the rpm of the wheel increases, the rotating mass becomes exponentially significant due to centrifugal force; for eg, according to Motor Trend the sidewall load at 200mph is 350lbs vs only 30lbs at 60mph (June 06, page 59 "Born for Speed, Michelin Pilot Sport 2").
As the rpm of the wheel increases, the rotating mass becomes exponentially significant due to centrifugal force; for eg, according to Motor Trend the sidewall load at 200mph is 350lbs vs only 30lbs at 60mph (June 06, page 59 "Born for Speed, Michelin Pilot Sport 2").
#32
05-23-2006, 10:50 AM
I've seen people talk of such formulas, but I don't think there's any scientific basis in them.
I also think that the effect of heavy wheels is even more prominent in braking than acceleration (since that rate of deceleration under hard braking is way higher than in acceleration) and in turning (two heavy gyroscopes up front that don't want to change direction).
Also, the effect on heavy wheels on acceleration is more prominent in lower gears where rate of acceleration is higher. Similar to why ltw flywheels have notable impact in 1-2 gears, but none really in the higher gears.
I also think that the effect of heavy wheels is even more prominent in braking than acceleration (since that rate of deceleration under hard braking is way higher than in acceleration) and in turning (two heavy gyroscopes up front that don't want to change direction).
Also, the effect on heavy wheels on acceleration is more prominent in lower gears where rate of acceleration is higher. Similar to why ltw flywheels have notable impact in 1-2 gears, but none really in the higher gears.
#33
05-23-2006, 11:25 AM
"(two heavy gyroscopes up front that don't want to change direction)."
well stated Frayed!
just goes to show the impact of heavy wheels on handling - especially higher speed corner entry/braking etc.
so I guess the bottom line is consider your driving style, objectives and, as usual, personal taste will dictate the decision. IMO style and weight are important so I'm considering champion RS98 versus Kinesis F110s.
well stated Frayed!
just goes to show the impact of heavy wheels on handling - especially higher speed corner entry/braking etc.
so I guess the bottom line is consider your driving style, objectives and, as usual, personal taste will dictate the decision. IMO style and weight are important so I'm considering champion RS98 versus Kinesis F110s.
#34
05-23-2006, 12:08 PM
I like those 98's as well. Both the 98s and the Kinesis F110s are Champion wheels, should be both equally durable, and I think it really boils down to aesthetics.
I really like the 997 GT3 wheels though too, in addition to Fikse.
I really like the 997 GT3 wheels though too, in addition to Fikse.
#35
05-23-2006, 08:36 PM
Originally Posted by frayed
I've seen people talk of such formulas, but I don't think there's any scientific basis in them.
I also think that the effect of heavy wheels is even more prominent in braking than acceleration (since that rate of deceleration under hard braking is way higher than in acceleration) and in turning (two heavy gyroscopes up front that don't want to change direction).
Also, the effect on heavy wheels on acceleration is more prominent in lower gears where rate of acceleration is higher. Similar to why ltw flywheels have notable impact in 1-2 gears, but none really in the higher gears.
I also think that the effect of heavy wheels is even more prominent in braking than acceleration (since that rate of deceleration under hard braking is way higher than in acceleration) and in turning (two heavy gyroscopes up front that don't want to change direction).
Also, the effect on heavy wheels on acceleration is more prominent in lower gears where rate of acceleration is higher. Similar to why ltw flywheels have notable impact in 1-2 gears, but none really in the higher gears.
#36
05-23-2006, 10:07 PM
Originally Posted by C4Cortez
Also wondering about reading somewhere that the offsets on 997 GT3 won't work with 997 C2/4/S? I guess we'll know in a couple of months.
I haven't seen the offset numbers (maybe someone here has?). C2S is 57/67 offsets, 996 GT3 is 40/63 (I think). If 997 GT3 uses the same offsets, they won't work on our cars.
This from Excellence gives some hope, but offset can vary widely depending on hub design.
Rolling stock is a set of 19-inch alloy wheels based on the 18-inch ghost of Fuchs past design introduced on 2004 GT3s and GT2s. Now 19x8.5 and 19x12 — up from 18x8.5 and 18x11 — the rims carry “special sport tires” sized 235/35R19 and 305/30R19, front to rear. The wheels and tires fit under the same narrow-body fenders on rear-wheel-drive 997 Carreras, but are pushed out in the wells by five millimeter spacers. Asked why Porsche AG didn’t just make wheels that fill the wells, Motorsport Director Hartmut Kristen says that federalizing cars for Japan requires the wheels to sit further inboard.
#37
05-23-2006, 11:17 PM
Originally Posted by frayed
Probably so, forgot about that. The 996 GT3 wheels weren't compatible with other 996s, probably the same with the 997.
I haven't seen the offset numbers (maybe someone here has?). C2S is 57/67 offsets, 996 GT3 is 40/63 (I think). If 997 GT3 uses the same offsets, they won't work on our cars.
This from Excellence gives some hope, but offset can vary widely depending on hub design.
I haven't seen the offset numbers (maybe someone here has?). C2S is 57/67 offsets, 996 GT3 is 40/63 (I think). If 997 GT3 uses the same offsets, they won't work on our cars.
This from Excellence gives some hope, but offset can vary widely depending on hub design.
#38
05-24-2006, 08:08 AM
Originally Posted by jhbrennan
I believe the new GT3 offsets are 53 F and 68 R - very close to the Carrera Sport offsets. I don't fully understand the relationehip of width, offset, etc. to say whether or not they would be a good fit for a 997 - soneone like Wheel Enhancement would know. Also, these wheels are cast (not forged) so they're probably not the lightest available.
Front GT3 wheels will stick out more (outboard) by 4mm + 1/2 the increase in width. Width is 12.7mm wider, so 6 mm. That's a total of 10 mm outboard.
Rear GT3 wheels have about the same offset, so they'll sit inboard an extra 1/2" and outboard extra 1/2" due to the increase in width.
Given the engineering that goes into proper offsets and tire and rim width by Porsche, i'd be hesitant going with a compromised fitment.
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