[Short Circuit]

http://www.maxima.org/shoptalk...shtml

Note the discussion re: alloy wheel weight & impact on performance. I thought it very persuasive. Thoughts?

 

[R Kelly]

Re: Performance Impact of Alloy Wheel Weight (Short Circuit)

Hence my post about how the Ultraleggeras are an AMAZING deal, 18x8" rims at 18.4 lbs a piece.

Quote, originally posted by "R" Kelly »

So, the Ultraleggera is 5 lbs lighter than the SLIII. Someone posted that rotating/unsprung mass has the effect of weighing 5x's more at the track. So, if I don't mind the looks, the Ultraleggera would have the effect of weighing 100 lbs less at the track over the SLIII, and save me $2248 over the silver, and $1016 over the light grey now on sale.

Information from the article:

So how big of a difference does a low moment of rotational inertia make? Well, the actual equations and algebra needed to show this directly get a little complex for those that are not engineers or mathematicians, so we will not do that here. However, a good approximation has been discussed and widely agreed upon that states that every single pound you add to your wheel and tire combination is equivalent to adding eight pounds to the curb weight of your car. However, you don't just have one wheel and tire. You have four of them, and all four wheels require energy to accelerate. In the above example of going from 15" to 18" rims and vice versa, that represents a difference of 480 lb of curb weight!!!! Now it's very easy to see how significant just a few extra pounds of wheel and tire mass can become.

Using 8 lbs as the effective difference in acceleration ratio... swapping from 27.8 lb 18x8" pegs, to 18.4 lb 18x8" Ultraleggeras would be equivalent to STRIPPING 300 LBS FROM THE CAR. Using the 10 lbs = 1 hp rule of thumb, you gain 30 effective hp. Quite the performance mod value at $1200, especially since you can use your 18" pegs for winter wheels or sell them to recover a good portion of the cost. And we haven't even talked about the handling advantages of losing 37.6 lbs of unsprung weight.

I had already purchased my SSWs $135 (22 lbs = 186 lbs = 17hp) when the Ultraleggeras came out, but damn, what a deal @ $295.

 

[I Roll]

Re: Performance Impact of Alloy Wheel Weight ("R" Kelly)

Your SSWs are the better performance "value" @ $7.94/hp gained vs $9.83/hp gained for the Ultraleggras. http://********************/smile/emthup.gif

 

[Johann]

Re: Performance Impact of Alloy Wheel Weight ("R" Kelly)

Pfffffff...

 

[Short Circuit]

Re: Performance Impact of Alloy Wheel Weight (I Roll)

You also want to ensure that the wheel is strong. I'd think that too-low a weight translates into less strength, increasing bending possibilities. That's my fear w/getting too low a weight wheel...

There ought to be a way to figure out if some forthought went into wheel design. Like FEA analysis...

 

[R Kelly]

Re: Performance Impact of Alloy Wheel Weight (Short Circuit)

Quote, originally posted by Johann »

Pfffffff...

You're just upset because your MAHA dyno can't disprove the benefits of lighter wheels on instanteous acceleration because it is a "load based" system.

Quote, originally posted by Short Circuit »

You also want to ensure that the wheel is strong. I'd think that too-low a weight translates into less strength, increasing bending possibilities. That's my fear w/getting too low a weight wheel... There ought to be a way to figure out if some forthought went into wheel design. Like FEA analysis...

I guess part of that is trusting the fact that the Ultraleggera is part of OZs racing line (even comes in Gold in addition to silver & graphite), and OZ is a respected supplier of race wheels.

Just ask Johann, he's running Superturismos, although possibly not for their instanteous acceleration advantages.

 

[Johann]

Re: Performance Impact of Alloy Wheel Weight ("R" Kelly)

Keep it going Mr. R"easternaerospace"Kelly!

I guess with your new rims, the DP and that great flowing exhaust of yours you must be close to 380 HP by now?

All that on a stock chip?

woow, I'm impressed...

Can't wait for that 13 flat G-Tech results.

 

[R Kelly]

Re: Performance Impact of Alloy Wheel Weight (Johann)

Quote, originally posted by Johann »

Can't wait for that 13 flat G-Tech results.

Just need a downhill section of autobahn and a 20 degree tail wind...

(btw, you forgot my CAI, BMC and Moose stickers).

 

[R_Rated]

Re: Performance Impact of Alloy Wheel Weight (Johann)

Quote, originally posted by Johann »

Can't wait for that 13 flat G-Tech results.

ha that ain't nothin! I show 500 whp on my Gtech! (don't ask how much weight i entered to get this...

)

13 flat is not that out of the wuestion for an R. Sure you need to have more than off the rack bolt ons but it can be done!

 

[[email protected] SPORTIV NA]

Re: Performance Impact of Alloy Wheel Weight (Short Circuit)

Bingo...FEA

 

[JRL]

Re: Performance Impact of Alloy Wheel Weight ("R" Kelly)

Quote, originally posted by "R" Kelly »

Just need a downhill section of autobahn and a 20 degree tail wind... (btw, you forgot my CAI, BMC and Moose stickers).

Good for at least another 5 mph http://********************/smile/emthup.gif

 

[23109VC]

i'd like to see someone take a peg, and th en a light wheel and dyno test it to see if there really is a difference.

 

[R Kelly]

Re: (23109VC)

Quote, originally posted by 23109VC »

i'd like to see someone take a peg, and th en a light wheel and dyno test it to see if there really is a difference.

I would rather see them race each other, since a dyno is just a prediction of performance and our cars behave much differently in the real world.

 

[mgotts]

Re: (23109VC)

Quote, originally posted by 23109VC »

i'd like to see someone take a peg, and th en a light wheel and dyno test it to see if there really is a difference.

Just to be clear, putting on lighter wheels will make zero difference on how much hp the engine/drivetrain produces. There is a real-world benefit, but it isn't measured on a dyno. There is no actual change in the hp at the crank or the wheels. There is simply less mass for the engine to have to accelerate.

The "rule of thumb" cited states that there is a way to approximate the acceleration performance difference of lighter wheels by assuming it as an equivalent amount of hp. The reason for this "rule of thumb" is that it is more difficult to gauge the impact of a change in rotational mass.

The benefit of a reduction in rotation mass is greater than for a reduction of "simple" mass taken from the body/chassis/frame/engine/etc of the car. Not only does the mass at the wheels have to be moved linearally (i.e. along with the rest of the car), it has to be spun up to speed as well.

Jack up your car and spin one of the wheels with your hands. Then stop it. It takes suprising amount of energy, and that energy does not contribute one wit to the vehicle moving forward. It is wasted on spinning the wheels.

Reduce the wheel/tire mass (or any rotational mass in the driveline, for that matter) and your car will accelerate quicker. But it does not produce additional steady-state hp.

 

[JRL]

Re: Performance Impact of Alloy Wheel Weight (Short Circuit)

This is THE most absolute stupidest post ever.

 

[R Kelly]

Re: Performance Impact of Alloy Wheel Weight (JRL)

Quote, originally posted by JRL »

This is THE most absolute stupidest post ever.

The whole thread or did Short Circuit say something in particular that was deleted. I think educating people on the effects of rotational mass on performance is quite a good idea, especially since we all drive performance cars with very heavy stock wheels.

 

[JRL]

Re: Performance Impact of Alloy Wheel Weight ("R" Kelly)

Tell you what.
Take a car, any car, do 3 drag strip runs.
Then, duplicate the runs, all things being equal with the weights off and then come back and post what you said

 

[24Hours]

Re: Performance Impact of Alloy Wheel Weight ("R" Kelly)

Quote, originally posted by "R" Kelly »

The whole thread or did Short Circuit say something in particular that was deleted. I think educating people on the effects of rotational mass on performance is quite a good idea, especially since we all drive performance cars with very heavy stock wheels.

He's getting closer to 20,000 posts and has to pad the count somehow. Good to see the rating back up to 100%. Well-deserved!

http://********************/smile/emcocktl.gif

 

[R Kelly]

Re: Performance Impact of Alloy Wheel Weight (JRL)

Quote, originally posted by JRL »

Tell you what. Take a car, any car, do 3 drag strip runs. Then, duplicate the runs, all things being equal with the weights off and then come back and post what you said

Well, I recently reported an improvement in 1/4 mile and 0-60 times. I attributed it to 30 degree outside temperature and the fact that my wintersport M3s would break lose and avoid bog easier.

But my 225/45x17 M3s on my 17" Pegs weigh a couple pounds less and have the weight closer to center than my 18" Pegs with 245/40x18 KDW2s. So maybe the decrease in rotational mass was helping as well for the launch, cuz damn it launched well.

Nov '05 Runs, 49 degrees, 245/40x18" on 18" Pegs

Quote, originally posted by "R" Kelly »

Run #1: 1/8 mi - 9.150 @ 81.66 1/4 mi - 14.006 @ 101.28 0-60 - 5.501 0-100 - 13.470 0-130 - 23.705 Run #2 1/8 mi - 9.118 @ 81.06 1/4 mi - 14.007 @ 100.51 0-60 - 5.463 0-100 - 13.656 0-130 - 24.207

Jan '06 runs, 32 degrees, 225/45x17 Wintersport M3s on 17" Pegs

Quote, originally posted by "R" Kelly »

Run #1 1/8 mi - 8.862 @ 82.36 1/4 mi - 13.749 @ 101.74 0-60 - 5.44 0-100 - 13.114 Run #2 1/8 mi - 8.896 @ 81.66 1/4 mi - 13.803 @ 100.92 0-60 - 5.12 0-100 - 13.37

While not a perfect comparison because of 17 degree temperature variable and rubber compound differences, the much improved 1/8 mile times could be indicative of benefits of decreased rotational mass on instantaneous acceleration.

Will post results when I put the 18" SSWs (6 lbs lighter) with 245s back on. Temps will be the same as last fall as well in a couple of weeks. Might take a little bit longer to be able to shift properly.

 

[JRL]

Re: Performance Impact of Alloy Wheel Weight ("R" Kelly)

Car has AT LEAST 12 more hp from 49 degrees to 32