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A fellow Pelacanite
 
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While we are on the topic of weight, wheels and tyres...

I can't understand why an 18" wheel & tyre combo weighs more than a 16" wheel & tyre combo.
If the wheel is bigger and weighs more then the tyre is smaller (sidewall height) and should therefore equal out the difference so we end up with the same weight?

Please help me out here...
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 08-13-2008, 10:55 AM
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I agree Nathan, but without doing the weight scale mamba I can only surmise to the outcome. But I'd bet we are really talking onces not pounds.
But I've been wrong before.....my first wife will tell you so.
Mark
Old 08-13-2008, 11:11 AM
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Cynical Misanthrope
 
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Each inch of rim diameter = 3.14~" more metal around the circumference of the rim. Keep in mind the rim is a 3-dimensional object, and each additional circumferential increment is multiplied square by the width. Additionally, this weight is further from the axis, increasing it's moment of inertia.
Larger wheels/lower profile tires are a performance benefit ONLY for their stiffer sidewall. Heavy wheels are bad.
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 08-13-2008, 11:30 AM
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Aha! Now I see it, thanks for opening my eyes. I'm so dumb...
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 08-13-2008, 11:36 AM
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This is all true...however, old rims were thick cast material, new rims are very thin, forged, machined units. Geometry aside, I still say we need a scale here.
Mark

p.s. I know, I know...there are many different rims out there so many variables.
Old 08-13-2008, 11:46 AM
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Cynical Misanthrope
 
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I regret if I made you feel the least bit dumb!
Most people neither understand nor appreciate the importance of rotating, reciprocating or unsuspended mass. Our roadwheels are both rotating and unsuspended, and are HEAVY due to the large stresses. Wheel weight affects acceleration, deceleration, and turn-in response directly, and secondarily affects traction.
To imagine a heavy vs lighter wheel, ask yourself if it's easier to dribble a lightweight basketball vs a heavy medicine ball. It's much easier to stop and push back down the lighter ball, as well as guide it. Likewise the heavier wheel will want to continue bouncing UP when it hits a bump, rather than being held to the pavement by the suspension. Does that make sense?
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X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 08-13-2008, 11:49 AM
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I would prefer not to have 17" wheels - RUF or Fuchs. But the car came with thatn and I can't afford to change them at the moment. Would really prefer 15" for the track, but 16's would do.
As for the weight difference hobieboy - I carry a measured liter of water in my washer bottle - thinking of removing it - but one day my screen may get smeared in dirt on the track. I think the bumpers would account for most of it.
Did you strip out all the rear seating stuff and floor coverings down to the bare shell - including the side trim etc? Have you removed all the rear wiper gear?
I then recovered mine in a very light weight carpet - would weigh about a kilo.
I'll weigh the sunroof gear today. I actually put a full hood lining back in place - partly to cover the ugly hole, and partly because the class I race in requires it. Had to make up some bows for the lining. Didn't realise big difference between sunroof and non- in terms of fitting the linings.
Regards
Alan
Old 08-13-2008, 11:50 AM
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I am waiting for some new rubber to arrive - early next month. I will weigh the rims then, and with rubber after.
Alan
Old 08-13-2008, 12:01 PM
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Sunroof + all related bits weighs just over 19lb for you non metrics.
Door pockets also removed. Front and rear speakers , as well as head unit.
Alan
Old 08-13-2008, 12:41 PM
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I cut off my head and went on a diet and lost 50 lbs.
I also filled my tires with helium and drilled lightening holes in the rims and then I angled the exhaust pipe towards the ground to get a little lift.
Still waiting to flip the whale tail spoiler over to creat lift on the rear of the car to get another 50 lbs off.
Removed the battery from the luggage area and push start the car since it is a 4 speed stick.
Not sure what else to do......

Sorry about the humor above, but was in a wierd mood today.
__________________
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 08-13-2008, 04:12 PM
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Fredmeister - you could take out the engine - big weight saving.
Leave in the tranny - then you can sit in car making vroom noises while shifting gear.
Helium will make your tyres squeeky.
Alan
Old 08-13-2008, 04:24 PM
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"I wuz the liquor..."
 
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Quote:
Originally Posted by fredmeister View Post
I cut off my head and went on a diet and lost 50 lbs.
I also filled my tires with helium and drilled lightening holes in the rims and then I angled the exhaust pipe towards the ground to get a little lift.
Still waiting to flip the whale tail spoiler over to creat lift on the rear of the car to get another 50 lbs off.
Removed the battery from the luggage area and push start the car since it is a 4 speed stick.
Not sure what else to do......

Sorry about the humor above, but was in a wierd mood today.
LOL! Good stuff, Fred!
__________________
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back in the saddle: '95 993 - just another black C2
*SOLD*: '87 930 GP White - heroin would have been a cheaper addiction...
"Ladies and Gentlemen, from Boston Massachusetts, we are Morphine, at your service..." - Mark Sandman (RIP)
Old 08-13-2008, 04:42 PM
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Quote:
Originally Posted by Alan L View Post
I would prefer not to have 17" wheels - RUF or Fuchs. But the car came with thatn and I can't afford to change them at the moment. Would really prefer 15" for the track, but 16's would do.
As for the weight difference hobieboy - I carry a measured liter of water in my washer bottle - thinking of removing it - but one day my screen may get smeared in dirt on the track. I think the bumpers would account for most of it.
Did you strip out all the rear seating stuff and floor coverings down to the bare shell - including the side trim etc? Have you removed all the rear wiper gear?
I then recovered mine in a very light weight carpet - would weigh about a kilo.
I'll weigh the sunroof gear today. I actually put a full hood lining back in place - partly to cover the ugly hole, and partly because the class I race in requires it. Had to make up some bows for the lining. Didn't realise big difference between sunroof and non- in terms of fitting the linings.
Regards
Alan
Hi Alan,
I also only have the small windshield fluid tank that sits inside the trunk & it is 1/2 full (probably 500ml). With my bare rear aluminum bumper+Euro shock tube, it weighs probably 10/15lb heavier than the FG unit I have hanging on the wall.
I haven't done same for the front though. All the interior seats/lining/soundproof are gone. And I replaced the stock metal rear wing with FG unit. And RS America like door panel replaced the stock ones. The front trunk is emptied.
So, the only thing left that I can think of are heater fans behind the dash (I still need heat though ), underbody coating, then body panels (including bumpers) & glass...
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87 930 K27HFS/B&B/Twin-Plug... Megasquirted
Old 08-13-2008, 05:05 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #53 (permalink)
A fellow Pelacanite
 
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Quote:
Originally Posted by AFM744 View Post
I regret if I made you feel the least bit dumb!
Most people neither understand nor appreciate the importance of rotating, reciprocating or unsuspended mass. Our roadwheels are both rotating and unsuspended, and are HEAVY due to the large stresses. Wheel weight affects acceleration, deceleration, and turn-in response directly, and secondarily affects traction.
To imagine a heavy vs lighter wheel, ask yourself if it's easier to dribble a lightweight basketball vs a heavy medicine ball. It's much easier to stop and push back down the lighter ball, as well as guide it. Likewise the heavier wheel will want to continue bouncing UP when it hits a bump, rather than being held to the pavement by the suspension. Does that make sense?
Hey don't worry! It's just that I thought about it and didn't come up with an explanation. Maybe if I looked at wheels side by side (I have a spare set of 16" and 17" wheels in my shed) I might of saw it

I ran some 17" turbo twists on my carrera many years ago. I noticed the fronts were much heavier as the car felt like it was 4WD when cornering compared to the 16" Fuchs. What I mean is that I could actually feel the wheel not wanting to slow down when the car went tight like it did with the lighter wheels.
It was a bit like one of the toy cars I had as a kid, you pushed and it stored the energy by having a big wheel spinning inside of it.
__________________
1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg

Last edited by NathanUK; 08-14-2008 at 09:08 AM..
Old 08-14-2008, 09:06 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #54 (permalink)
Cynical Misanthrope
 
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"It was a bit like one of the toy cars I had as a kid..."
Precisely! Also, do you remember what happened when you tried to tilt and rotate that car in your hand when the flywheel was spinning? Funky gyroscopic reactions that fight your input, and make it angle off 90 degrees. These reactions are what help a motorcycle/bicycle lean and steer, but are simply undesirable in our quadrapeds.
Larger wheels (18, 19, etc) that are not forged, 3pc lightweight assemblies are more performance hindrance than folks realize, though they LOOK faster. I had a set of BBS RCs in 18x8.5 on my Audi, they were ~18lbs which was pretty light for that size. The Kenesis 17s on my car right now don't look very radical, but it'll cost a FORTUNE to find an 18" that's the same weight.
__________________
X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 08-14-2008, 09:28 AM
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