sbarton

On another forum that I am on someone asked a question about the impact and effect of aditional rotating mass (ie. larger heavier wheels).

C DeVito

I picked up this info (mostly 996 vintage) on a multiple forums over the past few years. I didn't take the measurements, so not sure of accuracy but they seem reasonable.

Factory 996 Turbo Hollows
8x18" at 22 lbs 2oz
11x18" at 26 lbs 5 oz

Factory 996 Turbo Solids
8x18" at 26 lbs 2 oz
11x18" at 31 lbs 6 oz

Factory GT2 wheels (earlier years, Turbo Solids):
8.5x18" at 28lbs 11 oz
12x18" at 33 lbs 0 oz

Factory GT2 wheels (later years, GT3 style)
8.5x18" 25 lbs 2 oz
12x18" 29 lbs 0 oz

Factory GT3 wheels
8x18" 22 lbs 10 oz
11x18" 27 lbs 11 oz

Fiske Profil 13:
8.5X18 = 21 lbs.
12X18 = 22.5 lbs.

19" Dymags for 997S
16 lbs., 0 oz. front
19 lbs., 0 oz. rear

BBS RS-GT
19x8 21 lbs
19x11 24 lbs

odb812

This principle of physics isn't entirely accurate and actually the opposite. Consider the following formula dealing with different torque forces.
F1 x r1 = F2 x r2
where F1 is one force and F2 another and r1 is one radius from the fulcrum and r2 another. Now force is a product of mass times acceleration( F = m x a) and the goal here is equal acceleration under both conditions, so we can say
F1 = m1 x a1 and F2 = m2 x a2 where a1 = a2 so we will just say 'a'
this yeilds the formula
m1 x a x r1 = m2 x a x r2
since the acceleration is the same, we can divide both sides by a and get
m1 x r1 = m2 x r2
now if we say r1 to be 9.5 inches, the radius of a 19 inch wheel and r2 to be 8 inches, the radius of a 16 inch wheel, we get
m1 x 9.5 = m2 x 8
dividing 9.5 by 8 we get 1.1875, so
m1 x 1.875 = m2
so a 19 inch wheel can have 1.875 times the mass at its rim than a 16 inch wheel and still be accelerated at the same rate with the same ammount of torque.
Think about closing a door. It's much easier to close a door by the handle than it is by the inner side of the door where the hinges are.
This is one reason stepping up the diameter of your wheel is not as bad as one would excpect, since most of the mass of a wheel is in the rim. Also, you have to factor in the weight of the sidewall. A 16 inch tire of the same brand and width is going to weigh more than the equivalent 19 inch tire because it has more sidewall.
Todd

auto-xr

Good stuff here.

Here's what I collected from various sources (rennlist/6speed/vendors/friends - thanks to all)


CCW

c10 (estimated)
18x9 Front 19.4lbs
18x11 rears 20.6lbs.

T10s
18x9 front 20 lbs front
18x11 rear 21-22lbs (estimated)

C14 (estimated)
9 Front 21.5lbs
18x9.5 front 22lbs est.
18x10 front/rear 23lbs
18x11 rear 22.5lbs
18x12 rear 24lbs

BBS

The BBS Racing wheels on datax's car (aluminum centers):

18" x 8.5": 19 lbs
18" x 11": 21 lbs

The BBS Racing Magnesium centers

18" x 8.5": 20 lbs
18" x 11": 22 lbs

Champions

RG5
18x8 front 18.5lbs
18x8.5 front 19 lbs 2 oz.front
18x10 rear 19.5lbs
18x11 rear 19lbs 9 oz.

HRE Competition Series

8.5x18” 19 lbs. 5 oz.

11x18” 20 lbs. 4 oz.

Volks

TE37
18x8.5 18.5lbs (bathroom scale teseted too)
18x9 front 18.5lbs (estimated)
18x10 rear 19.5lbs
18x11 rear 20.5lbs (bathroom scale tested too)
19X8.5 20lbs
19X11 21.5lbs

Wheel Dynamics 02 5 spokes (Boxster fitment)

18x8 front 23lbs
18x9 rear 26lbs


Porsche/BBS

18" Sport Designs
7.5" Front 26.5lbs
10" Rear 30lbs

18" 02' Carrera2 5 spokes
7.5x18" 20 lbs. 9 oz.
8" Front 21lbs
9x18" 22 lbs. 13 oz.
10" Rear 23lbs


Porsche Factory 2002 996 Carrera 10-spoke
7x17" 18 lbs. 1 oz.
9x17" 20 lbs. 15 oz.

Porsche Carrera Sport
19" x 10": 27 lbs
19" x 11.5": 29 lbs

Porsche Sport Technos (hollow spoke)
Front 8x18" 20lbs, 11oz
Rears 11x18" 25lbs 8oz

993 18" Turbo Twists (solid)
18x7.5" Front (50mm) 24.5lbs
18x10" Rear (65mm) 28lbs

Another good site that matches OEM and some Aftermarket wheels with corresponding pictures and weights.

http://www.944racing.de/reload.php?u...elweights.html

MagnusB

I do think you need to check your calculation ...

C DeVito

" m1 x 1.875 = m2
so a 19 inch wheel can have 1.875 times the mass at its rim than a 16 inch wheel and still be accelerated at the same rate with the same ammount of torque. "

I was with you right up to the conclusion. The equation says M1 the mass of the 19 inch wheel is multipled by 1.1875 to get the weight of a 16 inch wheel of equal acceleration. So the 16 incher (M2) can weigh MORE than the 19 incher (M1). Substitute some numbers for M1 and M2 to verify. A 10 lb 19in wheel will be equivalent to a 11.8 lb 16 inch wheel.

odb812

Yes, you guys are absolutely right. I guess doing math on valuum is not a good idea. That's also probably why you guys drive 996s and I drive those fake front engine VW/Audi/Porsches.
I'm also thinking about this whole thing backwards. It is easier to break a tough bolt when you move further away from the fulcrum, like using a longer breaker bar, just like the closing a door example I used before. But that is the exact opposite of what we are dealing with. If you think about it like swinging your keys on a lanyard keychain. It would take more force to swing those same keys on a 5 foot long string it would take more effort.
The final verdict: I was wrong. I need to stop trying to sound smart when I take my pain medication. I basically proved the point that I was arguing against.
Hopefully this at least brought a mathmatical proof to what's going on here, even though I look like a complete jackass.
Todd

moorepower

Todd, don't be so hard on yourself. And more importantly, don't be so hard on on the front-engine VW/Audi/Porsches.
We all make mistakes, that's how we learn. At least you were smart enough to realize it, and man enough to admit it, unlike alot of people on this board (including me, sometimes).

C DeVito

Todd,

I agree with Moorepower, no worries, it's a good discussion. The 944T is the only car I ever bought twice and is still one of my favorite P-cars. Everytime one goes by I get the urge to buy another.

odb812

I just wish there was an emoticon with a foot in the smilie's mouth.

sbarton

Just to clarify, what you are talking about here is the location of the force, not the location of the mass. That would be like saying larger wheels are better b/c they are rotated by the outside of the tire (ie by the tread). The reality is that the wheels are rotated by the axels which are in the center of the wheels. Having the mass located closer to the center would make it easier to rotate.

The same goes for the door. It would be easier to close the door if most of the mass where located close to the hinges (inside part of the door), instead of the outside part.

-Scott

auto-xr

Lightweight is good but getting lighter at the price of rigidity may have some unwanted consequences. Here is an article that is a good read (I think vivid racing posted this same article as well but this site's version is a little easier to read).

http://og-made.com/archives/1904

In a nutshell the lighter wheels were faster in certain parts of the track but the more rigid wheels were able to attack the corners more aggressively. The rigid wheels were faster in the end.

The article echos my conversation with CCW when I was inquiring about the C10s. They said that they could shave the wheels to make them lighter but that they wouldn't be as strong.

911pcars

The website link: http://og-made.com/archives/1904

..... makes an oversimplification, IMHO.

Rigidity and relative lightness are not necessarily independent variables. You can have both. RE: Fuchs. And it's all relative to a reference point.

In that the the wheels in their test included those that were:
1) rigid (retail wheel)
2) less rigid, but lighter (lightened version of retail wheel)

......doesn't necessarily prove that rigid (and thus heavy) is better than light (but equally rigid). I would guess that particular wheel design doesn't lend itself to lightening modifications w/o a loss of rigidity.

Me thinks the article is an advertising plug in the guise of a technical test; "Although my company's wheels are heavier, their rigidity (and weight) is more important when it comes to track results." Nah.

Sherwood

auto-xr

In the end, I think that the article calls for a good balance of weight and rigidity.

"In summary, Kobayashi expressed that a balanced wheel with both rigidity and lightweight characteristics is important, but he never imagined that the effects of rigidity played such a large role."

They could probably stand to do more testing, but I think they still bring up some things to consider. If you have two equally lightweight wheels, the more rigid one will probably do better.

Expanding a bit to include 18" wheels vs 17" wheels, per the rennlist 996 faq, "Track drivers favor 18" for their larger contact patches and thinner sidewalls which deform less under hard cornering. Auto-X drivers favor smaller wheels for less weight and sharper turn-in."

https://rennlist.com/996_faq/b.htm

Martin Bishop

here is a good link on all the Porsche wheel weights

http://www.944racing.de/wheelweights.html