Wheel weight robbing power?
02-28-2007, 11:59 PM
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Wheel weight robbing power? hey guys... just wondering...
is there a formula or a rule of thumb out there to roughly figure how much RWHP loss per lb of a wheel it is??
my 19" c6 Z06 wheels and Kuhmo ecsta supra weighed in at a whopping 59.6 LBS a peice.. thats 119.2 lbs total for those wheels..
well my slicks (17" Y2k's and 26x11.50x17 MT et streets) only weighed in at a measily 41.3 lbs a piece... which is a total of 82.6 lbs total.
thats freaking almost 40 lbs less with these wheels!!!!! id imagine that has got to be pretty darn parasitic on the dyno results.. ive seen all sorts of "claims" is there any real hard core math behind it?
is there a formula or a rule of thumb out there to roughly figure how much RWHP loss per lb of a wheel it is??
my 19" c6 Z06 wheels and Kuhmo ecsta supra weighed in at a whopping 59.6 LBS a peice.. thats 119.2 lbs total for those wheels..
well my slicks (17" Y2k's and 26x11.50x17 MT et streets) only weighed in at a measily 41.3 lbs a piece... which is a total of 82.6 lbs total.
thats freaking almost 40 lbs less with these wheels!!!!! id imagine that has got to be pretty darn parasitic on the dyno results.. ive seen all sorts of "claims" is there any real hard core math behind it?
03-01-2007, 06:39 AM
#2
I think there was a earlier post about this be I would be more concerned with rolling resistance, in essance the car can cut a quicker ET with less weight having to be pushed from a stop.
As for the loss or gain, you may have to chk earlier posts.
As for the loss or gain, you may have to chk earlier posts.
03-01-2007, 09:51 AM
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Originally Posted by BlackScreaminMachine
I think there was a earlier post about this be I would be more concerned with rolling resistance, in essance the car can cut a quicker ET with less weight having to be pushed from a stop.
As for the loss or gain, you may have to chk earlier posts.
As for the loss or gain, you may have to chk earlier posts.
got a link by any chance??? my search always dicks up.
03-01-2007, 12:09 PM
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Originally Posted by LostCauseZ06
hey guys... just wondering...
is there a formula or a rule of thumb out there to roughly figure how much RWHP loss per lb of a wheel it is??
my 19" c6 Z06 wheels and Kuhmo ecsta supra weighed in at a whopping 59.6 LBS a peice.. thats 119.2 lbs total for those wheels..
well my slicks (17" Y2k's and 26x11.50x17 MT et streets) only weighed in at a measily 41.3 lbs a piece... which is a total of 82.6 lbs total.
thats freaking almost 40 lbs less with these wheels!!!!! id imagine that has got to be pretty darn parasitic on the dyno results.. ive seen all sorts of "claims" is there any real hard core math behind it?
is there a formula or a rule of thumb out there to roughly figure how much RWHP loss per lb of a wheel it is??
my 19" c6 Z06 wheels and Kuhmo ecsta supra weighed in at a whopping 59.6 LBS a peice.. thats 119.2 lbs total for those wheels..
well my slicks (17" Y2k's and 26x11.50x17 MT et streets) only weighed in at a measily 41.3 lbs a piece... which is a total of 82.6 lbs total.
thats freaking almost 40 lbs less with these wheels!!!!! id imagine that has got to be pretty darn parasitic on the dyno results.. ive seen all sorts of "claims" is there any real hard core math behind it?
The extra weight robs no power on a load dyno where the speed is constant. However on a inertia dyno such as your normal dynojet, the weight will register as a power loss as it takes longer to accelerate that extra weight. You also will probably feel this extra weight accelerating on the street too.
Hammer
03-01-2007, 12:29 PM
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Originally Posted by thehammer69
The extra weight robs no power on a load dyno where the speed is constant. However on a inertia dyno such as your normal dynojet, the weight will register as a power loss as it takes longer to accelerate that extra weight. You also will probably feel this extra weight accelerating on the street too.
Hammer
Hammer
i agree, my 480 RWHP numbers were on a dynojet.... just wondering how much those wheels robbed or if there is a formula. sticking it back on the dyno this weekend but i also rebuilt the heads and upgraded to ferrea valves. so i was trying to devise a way of seeing exactly how much power the headwork got me besides dynoing on the same shitty wheels again (they kept spinnin on the dyno)
03-01-2007, 12:54 PM
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The power loss is going to be VERY minimum with a 10lb increase in wheel weight, HOWEVER, the thing you want to look at is INERTIA. a 50lb 15" wheel might actually draw less power than a 30lb 18" wheel, simply because of where the weight is located around the wheel.
As an example, take a screwdriver between your fingers and roll it back and forth 360 degrees as fast as you can, the same motion a driveshaft uses. Now take the same screwdriver and spin it like a helicopter as fast as you can. Theres obviously more power required to spin up the screwdriver like a helicopter vs like a driveshaft because the location of the weight changed, even though the total weight did not.
22" wheels that weigh 40lbs will generally have more parasitic loss than say 15" wheels that weight 40lbs, simply because the rotating weight is farther out, which increases inertia. Tires also have the same effect. Bigger/taller tires eat up more power because the weight is farther out from the axles, which increases intertia.
As a rule of thumb though, you could probably say that for each 10lbs you gain, take off 1-2hp, but that's internet benchracer intelligence, which usually doesn't work out in real life.
As an example, take a screwdriver between your fingers and roll it back and forth 360 degrees as fast as you can, the same motion a driveshaft uses. Now take the same screwdriver and spin it like a helicopter as fast as you can. Theres obviously more power required to spin up the screwdriver like a helicopter vs like a driveshaft because the location of the weight changed, even though the total weight did not.
22" wheels that weigh 40lbs will generally have more parasitic loss than say 15" wheels that weight 40lbs, simply because the rotating weight is farther out, which increases inertia. Tires also have the same effect. Bigger/taller tires eat up more power because the weight is farther out from the axles, which increases intertia.
As a rule of thumb though, you could probably say that for each 10lbs you gain, take off 1-2hp, but that's internet benchracer intelligence, which usually doesn't work out in real life.
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03-01-2007, 02:55 PM
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yeah i just find it somewhat hard to believe that 40 total pounds of rotational mass, and smaller diameter wheels, is only going to be about 5 RWHP difference??
ive seen guys post on here before about guys gaining 10-15 RWHP from just changing wheels but obviously that seems to be a load of bullshit now that the facts are out on the table.
these slicks weight freakin 2/3 the weight of the 19's... that is ALOT of rotational mass off the drivetrain. Oh well guess we will jsut have to stick it on the dyno and see.
ive seen guys post on here before about guys gaining 10-15 RWHP from just changing wheels but obviously that seems to be a load of bullshit now that the facts are out on the table.
these slicks weight freakin 2/3 the weight of the 19's... that is ALOT of rotational mass off the drivetrain. Oh well guess we will jsut have to stick it on the dyno and see.
03-01-2007, 03:40 PM
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Most of the time that the wheels changing effect the dyno is due to the final drive ratio. Going to a smaller diameter wheel will rob hp #'s on a dyno but will get you to speed faster on the street or at the track (unless you are hitting the limiter in 4th when you go thru the traps).
03-02-2007, 09:50 AM
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When i bought my car. I had a lid/cutout with stock 16inch 245 tires. Then i had a ported TB that i put on the car and i felt a power difference and then put on my 17inch 275 SS rims and that extra power i felt went away, the car def slowed down.
03-02-2007, 10:44 AM
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Originally Posted by JakeFusion™
It's probably going to register as 10-15rwhp loss on the DynoJet.
oh yeah? is that just a rule of thumb or is that realistically the average?
03-02-2007, 10:52 AM
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It's about average from what I've seen. You'll probably see more because the slicks weigh less than a regular street tire. You're at 20lbs per wheel difference; most Vettes end up seeing 10-15lbs per wheels, and F-Bodies could see a big jump from 245/16s to 315/17s.
03-02-2007, 11:00 AM
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maybe Dynapack dyno users that dynoed on Dynapack dyno and then if they dynoed on Dynojet dyno same car same way be able to answer this .
Dynapack dynos bolt the axle flanges of the car to the dyno instead of the wheels ,so i always thought thats not the end user numbers as the topic is being disscused.
Dynapack dynos bolt the axle flanges of the car to the dyno instead of the wheels ,so i always thought thats not the end user numbers as the topic is being disscused.
03-02-2007, 11:03 AM
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Originally Posted by JakeFusion™
It's about average from what I've seen. You'll probably see more because the slicks weigh less than a regular street tire. You're at 20lbs per wheel difference; most Vettes end up seeing 10-15lbs per wheels, and F-Bodies could see a big jump from 245/16s to 315/17s.
hrmm.. thats very good to know!!! im super excited to see how the car does now then..
480 RWHP before with the heavy wheels and bad valve
now im running a ported FAST90, LS2 90 tb, way lighter wheels, and new fresh valves and seals in the heads.
anybody have any guesses on my new number?
