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Old 08-06-2010, 12:27 AM   #126
juanmedina
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Quote:
Originally Posted by achavez View Post
the light wheels are the kosei k1 ts right? 14.6lbs $196 from tirerack.com
no the wheels are konig daylites 14.2 lbs in the color black
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Old 05-22-2011, 01:53 AM   #127
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Sorry for bumping 6 months old thread, but I am glad I came across this thread.

Interesting results on weight of both rotor and wheel/tire leading to increased amount of power.

I went from heavy LGT rotors/calipers, 17" Prodrive P1 and 225/45/17 RE070 (heavy tire) to:

Rotora slotted front rotors, JDM 4 pot aluminum calipers, 17" STI 5x100 BBS wheels and Michelin PS2 tires.

Total saving in weight per corner was around 30 lbs.
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Old 05-22-2011, 11:47 AM   #128
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First time I saw this thread.

Did you ever trap faster?

FWIW I always measure the tires as they can be off a lot more then .25 inch like Ron said. I have seen them off by .7 of an inch. So that could explain some of your whp. I am sure though that you gained some form the lighter set rims.
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Old 05-22-2011, 12:59 PM   #129
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So, is the claim that the lighter wheels helps the engine MAKE more power? I dont quite understand the concept, since Juan claims to have adjusted for the weight difference.

I keep going back to what maxpowr said regarding gearing, and what LittleBlueGT said about the tire diameter being off.

I do not see how wheels would play any role in engine power production.

The gains have to be merely from faster acceleration, which will show more power on airboy, similar to a dynojet, correct? Is it possible that airboy is simply not accurate enough to compensate for the small weight differences?
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Old 05-22-2011, 01:03 PM   #130
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^^simple, it's less rotating mass, it's takes less torque to make the wheels spin

you can see powerloss on the dyno from heavier wheels/bigger brake kits...etc. fyi research sprung and unsprung weight for a further read
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Old 05-22-2011, 01:08 PM   #131
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Quote:
Originally Posted by langsbr
So, is the claim that the lighter wheels helps the engine MAKE more power? I dont quite understand the concept, since Juan claims to have adjusted for the weight difference.

I keep going back to what maxpowr said regarding gearing, and what LittleBlueGT said about the tire diameter being off.

I do not see how wheels would play any role in engine power production.

The gains have to be merely from faster acceleration, which will show more power on airboy, similar to a dynojet, correct? Is it possible that airboy is simply not accurate enough to compensate for the small weight differences?
The engine makes the same power. It makes let's say X crank hp or brake hp. When the power is sent from the motor through the drivetrain and to the wheels, it will have an X % parasitic loss to put the power to the ground. Removing unsprung weight or rotational mass from the drivetrain will result in lowering the parasitic loss of power to the ground. So in turn yield a higher whp or wtq which is measured after the parasitic loss. Someone correct me if I'm wrong
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Old 05-22-2011, 01:09 PM   #132
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subscribed for future reference! Thanks for the experiment and contribution!
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Old 05-22-2011, 01:57 PM   #133
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I dont get it obviously it will be faster with lighter wheels.
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Old 05-22-2011, 03:39 PM   #134
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wastes less power to get her movin...simple as that.
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Old 05-22-2011, 03:40 PM   #135
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Originally Posted by maxpowr View Post
wastes less power to get her movin...simple as that.
Word. How do people NOT understand this concept?
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Old 05-22-2011, 07:28 PM   #136
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Originally Posted by mowgli29 View Post
Word. How do people NOT understand this concept?
The concept of lighter wheels making a car FASTER should not be debated.

However, Juan said that he input the different weight of the vehicle after swapping wheels. If that's the case, if the airboy dyno were indeed accurate, it should have demonstrated the SAME power, not an increase. Do you not agree?

I'd like to see what the "gain" would have been had he kept the weight the same on both.

FWIW, if I fudge the weight of my car on an airboy/virtual dyno run by 300lbs, it only gains 20 hp.

The wheel diameter will have a similar effect - by changing the tire diameter, the power will change nearly 25 hp.

This leads me to believe that the majority of the gain Juan was seeing was due to the overall tire diameter difference, and not necessarily the weight.
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Old 05-22-2011, 07:35 PM   #137
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Quote:
Originally Posted by langsbr

The concept of lighter wheels making a car FASTER should not be debated.

However, Juan said that he input the different weight of the vehicle after swapping wheels. If that's the case, if the airboy dyno were indeed accurate, it should have demonstrated the SAME power, not an increase. Do you not agree?

I'd like to see what the "gain" would have been had he kept the weight the same on both.

FWIW, if I fudge the weight of my car on an airboy/virtual dyno run by 300lbs, it only gains 20 hp.

The wheel diameter will have a similar effect - by changing the tire diameter, the power will change nearly 25 hp.

This leads me to believe that the majority of the gain Juan was seeing was due to the overall tire diameter difference, and not necessarily the weight.
Changing the weight of the vehicle is different vs wheel weight as wheels are rotational weight and change the drivetrain loss. He didn't gain any power, he freed it up.
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Old 05-22-2011, 07:38 PM   #138
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Quote:
However, Juan said that he input the different weight of the vehicle after swapping wheels. If that's the case, if the airboy dyno were indeed accurate, it should have demonstrated the SAME power, not an increase. Do you not agree?
Wrong and simply because your after wheel horsepower which is decided by how fast the motor can accelerate a car or specific values (weight, tire diameter...)...engine power did not change WHEEL horsepower did. The car as a whole is putting more power to the ground, not the engine.

Trey

Tey
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Old 05-22-2011, 10:43 PM   #139
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so why did a guy on the first page not see a difference on a dynojet with his Rav4? someone said dynojets cant read like a mustang for weight bearing or load or something i dont get but to me if lighter wheels are put on and the motor can move faster and build up speed then it shouldnt matter what dyno your on, gain should still be seen because its not as hard to get them up and moving.
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Old 05-22-2011, 10:58 PM   #140
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Originally Posted by synolimit View Post
so why did a guy on the first page not see a difference on a dynojet with his Rav4? someone said dynojets cant read like a mustang for weight bearing or load or something i dont get but to me if lighter wheels are put on and the motor can move faster and build up speed then it shouldnt matter what dyno your on, gain should still be seen because its not as hard to get them up and moving.
Dynojets use a drum that weighs about 3000lbs simulating a vehicles weight. It is what you call an inertia dyno. That is why you dont get great results on them. A mustang and a dyno dynamics dyno or a load cell dyno allows you to set the load electronicly. Allowing you to more acurately simulate the vehicles weight of the vehicle being tested.
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Old 05-22-2011, 11:19 PM   #141
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Originally Posted by CUNNINGHAM View Post
Dynojets use a drum that weighs about 3000lbs simulating a vehicles weight. It is what you call an inertia dyno. That is why you dont get great results on them. A mustang and a dyno dynamics dyno or a load cell dyno allows you to set the load electronicly. Allowing you to more acurately simulate the vehicles weight of the vehicle being tested.
i understand the difference in the dynos. so if the drum weighs 3000lbs and wheels/tires/rotors etc weigh 45lbs each for example, then the motor trying to moving 3180lbs. if you lose 30-40lbs off wheels and tires then the motor is now only moving 3140lbs which is nothing and wont show up on a dynojet??

this kinda blew my mind if anyone can understand it...enjoy

Originally Posted by Buffy
When we accelerate the car, we're actually accelerating two things; the car, with an essentially linear force, and the rotating parts with an angular force. This is most of what accounts for the difference between flywheel horsepower and rear wheel horse power as measured on an intertial dynomometer. Friction losses in the drive train are a much smaller factor. [quote]

HP going to friction losses are a larger factor than HP going to inertia losses for a dyno run done in 4th gear on an inertia dynamometer (there's no such thing as an "inertial" dynamometer...inertial designates a frame of reference). As the HP level goes up, the HP going to inertia losses increases but so does the the HP going to friction losses. On absorption type chassis dynos, HP going to inertia losses can be held constant no matter how much HP level increases (within reason).


Quote:
Originally Posted by Buffy
Conventional wisdom puts drivetrain loss on an intertial dyno at about 15% for a C6, and in terms of accelerating the car this is wasted power. Unfortunately, modelling how much energy goes into what rotating part is quite complicated. And to make it more complicated remember that some of these parts - the flywheel, clutch, drive shaft and half the transmission - are accelerated more than once as we shift gears during a run. [quote]

Convential wisdom is like common sense in that it's the least common of the senses. (And you're killing me with that "inertial" dyno thing.) There is no percentage loss that can be stated for every drivetrain or any one particular drivetrain. A stock LS2/M6 seems to have ~55 HP loss through the drivetrain. Also, the clutch/flywheel is included with the 400 FWHP rating and the driveshaft only has to be accelerated "once" in a 1/4 mile race. But you came close to a big factor in that the rate of acceleration is different in each gear which will make a big difference as you'll see later.


Quote:
Originally Posted by Buffy
But as a first-order estimate, let's assume that a C6 weighs 1500 kg (3360 lbs), a brake, wheel and tire assembly 32 kg (about 72 lbs) and a run ends with a terminal velocity of 51.4 m/s (115 MPH). This gives us a linear kinetic energy at the end of the run (1/2mv^2) of 1.98e+6J.

Further assuming that the brake, wheel and tire assembly approximates a uniform disc we get a momemt of intertia of about 1/2 x 32 x .334^2 or 1.78 kg m^2. At the end of the run the wheels are turning 1470 RPM, for an angular velocity of about 154 rad/s, so rotational energy per wheel at the end of the run (1/2Iw^2) is 66.8e+3J, or 267e+3J for all four. [quote]

While I know you're trying to make the calculations easy, assuming the brake (rotor), wheel, and tire assembly to approximate a uniform disc with "X" diameter introduces a huge error into the calculations. The HP to accelerate the C6 is the sum of the HP to going to translational inertia and the HP going to rotational inertia. To express HP going to rotational inertia as a percentage of total inertia, you have to know the amount going to rotational inertia. Your calculation for rotational kinetic energy is incorrect. I came up with 21.2e+3J for one or 84.4e+3J for all four using your numbers in your correct formulas.


Quote:
Originally Posted by Buffy
The rotational energy in the wheel assemblies is about 7% of the total energy, and they account for around 15% of the total mass. So reducing mass in the external rotating parts - brakes, wheels and tires - is roughly half again as effective as reducing the mass of non-rotating parts. But still, reducing the wheel weight by 1 kg (2.24 lbs) per corner by switching to, say, PS2s is only about a 0.4% gain, or the equivalent of about 1.6 more HP! [quote]

I came up with 4% for the wheel assemblies part of the total kinetic energy added to the system in a 1/4 mile run and 2% of the total mass of the car. Then all of a sudden, you pull a 1.6 HP number from somewhere. If you want to convert to HP, you have to analyze the problem from the perspective of kinetic energy added to the system. The sum of the translational kinetic energy and rotational kinetic energy from above is 2064000 J. One Joule=.737 FT-LB giving us 1522000 FT-LB of energy (not to be confused with torque which is a force). To solve for HP, you have to know the time it took to add the kinetic energy to the system...we'll say 12.5 seconds for a nice round 1/4 time for a C6 LS2 (not the best time nor the worst time). Dividing 1522000 FT-LB by 12.5 seconds gives us 121800 FT-LB/sec. One HP=550 FT-LB/sec so 121800 FT-LB/sec becomes 221 HP. Now before anyone begins to cry foul by citing the 400 FWHP of the LS2, remember this is only the HP required to add the kinetic energy to the car to get to 115 MPH in 12.5 seconds and includes the total weight of the car for translational inertia but only includes the tire/wheel/rotor for the rotational inertia. All the rest of the rotating components are not included nor is the effect of wind resistance. Now to tie in my comment above about the gear you're in and how it affects rotational kinetic energy and HP, you can see how the time factor affects HP above. The faster you get to speed (or the faster you accelerate), the higher the HP number will become. Now think of how quick you accelerate through 1st gear vs how long a 4th gear pull is...there is quite a bit of time difference there and the higher speeds in 4th mean more air resistance too. Therefore, the lower the gear you run in, the bigger the effect rotational weight has on HP. A one pound difference at each wheel would be impossible to feel 4th gear (and most likely immeasurable) while a 6 LB difference at each wheel would would be noticeable in 1st gear to the "seat of the pants" and take a very sensitive device to measure the difference in 4th. For road racing where speeds vary from 60-150 MPH, a pound or two at each wheel for bigger rotors or wheels or tires is going to affect acceleration performance only slightly while it substantially improves braking/cornering.

Last edited by synolimit; 05-22-2011 at 11:37 PM.
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Old 05-23-2011, 05:28 AM   #142
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TLDR
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Old 05-23-2011, 07:54 AM   #143
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TLDR
Me too
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Old 05-23-2011, 08:50 AM   #144
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Old 05-23-2011, 05:00 PM   #145
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^^^^^^^^^^^^^^^^Yeah im lost lol
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Old 03-30-2013, 09:35 PM   #146
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Interesting info in this old thread
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Old 01-15-2022, 10:28 AM   #147
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Over 30 lbs in rotating mass > temp difference. I love that the lighter wheels still outperformed despite the increase in ambient temperature. You can read more about it here https://gtd-review.com/
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Old 01-15-2022, 10:07 PM   #148
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Over 30 lbs in rotating mass > temp difference. I love that the lighter wheels still outperformed despite the increase in ambient temperature. You can read more about it here https://gtd-review.com/

This thread is 9 years old my friend. Look at post date before bumping ancient threads.
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Old 02-15-2022, 11:36 AM   #149
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It can be overwhelming to choose from so many options on the market. We can help you narrow down your options to the top 10 best vacuum for car detailing.

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Old 02-15-2022, 11:37 AM   #150
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Here's an overview and buying guide for the best single din head units currently on the market. https://gtd-review.com/10-best-singl...tereo-in-2022/
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