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      02-28-2011, 10:23 PM   #1
ProPedderKustom
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ZCP wheels = .1 second slower in the 1/4 mile?

I see that the ZCP 359M wheels are:

Front: 25.5lb
Rear: 28lb

Then the other 220M 19's are:

Front: 23lb
Rear: 26lb

I then read that each 1 pound of unsprung weight equals about 10 pounds of sprung weight as far as performance goes. Also, each 100 pounds of sprung weight added to the car equals .1 seconds more in the quarter mile.

So, my question is, can you feel this difference? Is it a real world difference?
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      02-28-2011, 10:26 PM   #2
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Absolutely not
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      02-28-2011, 10:27 PM   #3
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Do you mean in a perfect world, with perfect surface traction, in a vacuum, with perfect tire condition, perfect clutch and throttle application, with perfectly straight steering angle, with no head or tailwind, with a 50th percentile male driver, with a full tank of gas and fluid?

/sarcasm. Sorry, I couldn't resist.
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      02-28-2011, 10:27 PM   #4
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So your question is whether someone can "feel" a .1 second difference in an all out 1/4 mile sprint?
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      02-28-2011, 10:29 PM   #5
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They are wider. Therefore better grip. Therefore faster.
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      02-28-2011, 10:29 PM   #6
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Well,

1) Can it be felt?
2) Is this true about the slower time for ZCP wheel cars vs 220 wheel cars?
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      02-28-2011, 10:41 PM   #7
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I found ZCP wheels to be a joke... heavy and cast.. sold them within a month of getting the car... I switched to 18" APEX wheels that weigh around 19lb..
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      02-28-2011, 10:42 PM   #8
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Well the extra HP in the ZCPs should make up for that extra weight.
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      02-28-2011, 10:43 PM   #9
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      02-28-2011, 10:52 PM   #10
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      02-28-2011, 11:05 PM   #11
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      02-28-2011, 11:27 PM   #12
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Quote:
Originally Posted by ProPedderKustom View Post
I see that the ZCP 359M wheels are:

Front: 25.5lb
Rear: 28lb

Then the other 220M 19's are:

Front: 23lb
Rear: 26lb
Okay.... don't torch me here. I'm just trying to ask a question and/or make an observation.

I'm surprised the weight differences aren't more than they are comparing the forged 220's to the reportedly cast 359's, especially considering the 1/2" added width for the 359's. In fact, if you add 1 to 1.5 pounds for the added 1/2" (there's a 2.5 to 3 lb. difference for the added inch in each set), the difference becomes smaller than I would expect.

It makes me wonder if the weights listed above are accurate, and also makes me wonder why there isn't a bigger difference between the forged and cast wheel weights.

Clearly I'm no expert here, but I'm curious if anyone has thoughts?
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      02-28-2011, 11:30 PM   #13
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Good point Biggerunn
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      02-28-2011, 11:46 PM   #14
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Here's a good primer for those that are not familiar with any of the technologies, but it's by no means definitive and the be-all, end-all.

One issue is that we don't know with any certainty as to how the 359s are manufactured. If they are indeed flow formed castings, then they can have thinner walls as the composition is more dense due to the forming process, unlike a low pressure (or even gravity) castings.

However, take into consideration the size of the spokes of the 220, and I'm led to believe that there's more surface area on the 220 than on the 359. That's just my observation, not fact, so I could be way off. So the 220 is pretty light for an OEM wheel. Yes there are lighter ones, but still impressive.
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      02-28-2011, 11:55 PM   #15
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Quote:
Originally Posted by mrkhanna16 View Post
They are wider. Therefore better grip. Therefore faster.
Not necessarily. X mm more wheel width doesn't = X mm more rubber width as tires have tread with varying "block" widths of rubber, especially when comparing different tire types. Are the tires different sized in OEM applications? Plus, wider rubber could mean more grip at the point of inertia, but it turns into more rolling resistance at speed.
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      02-28-2011, 11:58 PM   #16
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Quote:
Originally Posted by Biggerunn View Post
It makes me wonder if the weights listed above are accurate, and also makes me wonder why there isn't a bigger difference between the forged and cast wheel weights.
OEM forged wheels are usually no where as light as aftermarket forged wheels, such as 1 piece BBS forged wheels as example. OEM wheels are made to be more stout as opposed to simply the lightest possible, forged or not.
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      03-01-2011, 12:24 AM   #17
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Quote:
Originally Posted by piloto View Post
Do you mean in a perfect world, with perfect surface traction, in a vacuum, with perfect tire condition, perfect clutch and throttle application, with perfectly straight steering angle, with no head or tailwind, with a 50th percentile male driver, with a full tank of gas and fluid?

/sarcasm. Sorry, I couldn't resist.
Haha you sound like my old physics professor!
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      03-01-2011, 02:29 AM   #18
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Quote:
Originally Posted by ProPedderKustom View Post
I see that the ZCP 359M wheels are:

Front: 25.5lb
Rear: 28lb

Then the other 220M 19's are:

Front: 23lb
Rear: 26lb

I then read that each 1 pound of unsprung weight equals about 10 pounds of sprung weight as far as performance goes. Also, each 100 pounds of sprung weight added to the car equals .1 seconds more in the quarter mile.

So, my question is, can you feel this difference? Is it a real world difference?
The wider rims with same 19" tire size for the ZCP (Competition Package in AUS) lowers the flex point of the tire sidewall. It results in a slightly more stable footprint/tread, however moving the flex point toward the rim sacrifices ride quality slightly (track drivers probably wouldn't notice ride; they'd notice the handling more so). I doubt the rim difference makes much difference for straight 1/4 mile if anything since the rolling resistance is almost the same. You'd notice on a twisty track.

After some research, I found the 220M 19" classic M3 twin-spoke style to be my primary choice for a number of reasons; in AUS, I actually paid the same price for the EDC/M Drive/220M options compared to the Competition Package (ZCP). The 220M is a true forged rim being light for its size; it is actually more expensive to BMW cost as well as much more expensive to replace at retail. Also, I liked the concept of the classic M3 twin-spoke wheel style and the best compromise on ride (for me). Simply 'flick' the narrow spoke of a 220M rim with your fingernail and you can hear the higher pitched ring tone of a lightweight forged wheel.
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      03-01-2011, 03:44 AM   #19
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They also claim that every 10 lbs of extra weight in the car is equivalent to 1 hp. I feverishly on a diet to get back down to my birth weight of 7 lbs. I'll reclaim about 23 hp...he he.

In the real world, it's doubtful the slight difference in wheel weights will matter in acceleration. If it made a considerable difference, people would be going back to the original 18" wheels to save weight. It's all about looking cool.
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      03-01-2011, 03:57 AM   #20
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Quote:
Originally Posted by piloto View Post
Do you mean in a perfect world, with perfect surface traction, in a vacuum, with perfect tire condition, perfect clutch and throttle application, with perfectly straight steering angle, with no head or tailwind, with a 50th percentile male driver, with a full tank of gas and fluid?

/sarcasm. Sorry, I couldn't resist.
Vacuum means no air in the atmosphere..how would start a car with no air in it for the engine to breath..
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      03-01-2011, 04:26 AM   #21
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In short no, the difference will be much smaller than 0.1 seconds.

Use this formula: ET = 6.1178 x (weight/power)^(1/3)

Units are lb and hp. The formula is not exact, however for trends, rough estimates and A-B comparisons it is pretty good.

You should also note that the 1:10 rule you have heard is not correct. The correct rule is that for every 1 lb saved in a single wheel it is like 8 lbs of total weight saved for the same change made in all 4 wheels (in other words only like a 2 for 1). See my post on this topic here. However for most street carsan M3 the 0.1 seconds per 100 lbs is very close to accurate. You certainly can not apply this rule of thumb across a really wide power to weight ratio though.

For your example if I simply round the 2.5 lb to 3. I'll use a total weight change of 24 lb (3*8) and that gives a mere 0.03 second difference.

You can also verify the rough power of the formula by looking at some actual test results from Car and Driver with a VW Gold. Article here. Comparing the smallest and largest wheel sizes you should us 8*14 lb difference. The formula for this comparison shows a 0.2 second difference. That is exactly what the testing found! Now the tires were wider and that should give an unaccounted advantage to the larger wheel. Also all inertial effects are not capatured in my rough relationship above and the higher inertia of the wheel would cause a disadvantage for acceleration. Perhaps these effects roughly cancelled. Either way you can see that the formula works pretty well, both for an absolute prediction and even more importantly for this A-B comparison.

On top of drag racing for autoX and road coarses there are other advantages in handling for having a light wheel and tire combo. The above is just the in a straight line advantage.
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      03-01-2011, 09:27 AM   #22
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Very interesting. Thanks for all of the info everyone.
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