Approx ET/MPH change from lighter wheels/tires? Real World?

Read all the blah blah physics about unspung weight and rotating mass.

Estimated 2950 pound ( with 250 pound me in it) car currently runs 10.84 @ 123+, dropping a total of 60 pounds, 20 from each front and 10 from each rear plus going to M/T ET fronts that are 27.5 x 4.5 from a 205/65R15 radial. Also reduced my free travel another 1.5" since the Rocky has been wheelie prone. 60' are a slow ( but controllable) 1.58 and it runs 6.90 flat in the 1/8th at just over 100.

Cant wait until spring to run it.... 'physics' calcs say about 2 tenths but im not convinced....though i Remember my Charger picked up over 2/10th going from steelies to mu first set of weld Ultralites.

I went quicker adding weight back and no way do I see .2 in that deal.............

Google "Car Craft et improvement light wheels" and you should get a link to an older (2004) article that might be of interest.

It might be more wheelie prone now with lighter front wheels.I've seen it on some short wheelbase Harleys,had to put the stock heavy wheel back on to keep the front down.The lighter rear wheels should help unless traction is a problem.

Thanks, I'm thinking by further limiting the free travel of the upper control arms by lowering the bump stops should counter the wheelie....it always helped before. I cam always add more ballast below the front bumper if i need to as well...obviously hoping i wont need to, lol.

The theory is that one pound of rotating weight reduction is roughly equivalent to removing 3+ pounds of static weight in terms of accelerating mass.

Done it, and totally hoped for the physics part of it. 1 pound of Rotational weight is Equal to 3 to 4 pounds of Dead weight.

So 60# rotational = about 180# to 240# Think the ratio was more like 1 to 3, its been awhile.

Sounds Super, doesn't it.

Real world for me, it was Pound for Pound whether it was rotational or Dead weight.

So Why was that? I know!! Its because the car has enough time to accelerate in the 1/8-1/4 that the physics effect don't have much effect combined with the acceleration rate.

Now, hang that same 60 pounds on the Crankshaft, Different story.

So with your change maybe figure .06 as in the Old rule of Thumb. .1 for every 100# and even that is just a, well old rule of thumb and not a exact science.

Here is the article BradH referred to: ( Thanks!)

http://www.hotrod.com/articles/light-vs-heavy-wheels-comparison/

With the fronts jacked up off the ground you can visualize taking something like an electric motor attached to the hub and accelerating each wheel to simulate top end speed rpm in roughly10.8 seconds taking a lot less energy amps/Kw//Hp than the massively heavy 4x4 wheels that were on it. I guess the et fronts are also about 2" taller so they'll spin a little slower too over the course of a run. 60 pounds is a little more than 2% reduction so roughly like 80 on a 4000 car.

My guess is around .15 seconds so probably worth it. Had to drastically cut down the hub register and redrill the bolt pattern to get the fronts to fit.

Time will tell tho...i tell you at least its easier to push around the garage, lol

While I do believe the advantages and would want more weight off the rotational weight vs static weight, even Brads article kind of confirms, that at the rate of witch a car accelerates in the 1/4. that it isn't even Close to the 1# to 3# difference advantage that is and was Advertised of the Physics back in the day or even today. To be accurate, It would have to be Time specific of time traveled with rotational weight differences vs static. Actually more to it then that.

As far as the article, it even shows a lessor gain from the rule of thumb .1 ET for each 100# loss from #3 test, but more, then on test #4

Test 3 shows With a 53.74# weight loss of Rotational, a .034 Gain.

Test 4 shows With a 82.08# weight loss of rotational, a .110 Gain.

Even this testing has accuracy issues. But, All can and Should conclude. No where close to the 1# to 3# advantage of rotational vs static. That I hoped for and most others, not down the 1/4 anyways.

I agree, I'm with you.....just don't know if with a much lighter car and a higher power to weight ratio it might make more of a difference than it would in a 2 ton big block chevelle.

Biggest handicap in my combo is not the wheelbase, its the lack of Aerodynamics! Lol

where's Monty??

Read all the blah blah physics about unspung weight and rotating mass

Specifically?

The tests I've read have no input for the MOI: where is the inertial center of mass of the wheel located? The OD gives nothing useful.

Read my article: http://victorylibrary.com/mopar/sprung.htm

As Poly says. In my layman's terms: If a component is a given diameter the part that has nearly all of its weight at the outer circumference (such as a tire) will have more effect than a part with the weight concentrated near its centerline (such as an axle shaft). Exactly the same as a chassis. If the weight is close to the CG it will rotate with less input than one with all the weight at the ends. How much better? Testing will tell.
Doug

Ever use a spin balancer and see how easy a 13" Honda wheel starts and stops compared to a 3/4 ton picking 16" tire?

It will change ET and MPH, but the change is different on a 10 vs15 second car, also the torque of the engine, SB vs BB.

I believe Monte is helping Chad Henderson get the Buick ready for testing. Just saw the car is repainted, and new bullet in.

http://blog.caranddriver.com/tested-quan...n-fiber-wheels/

My 69 GTX with a 493 has gone as fast as 10.84 at 123.50 with a 1.49 60 ft. 3960lbs with driver, 3.73 gear. This combo makes 494 RWHP.
I made 3 passes with my magnum 500s that had Hoosier drag radials, then switched to my centerlines with the same exact tires. I weighed the wheels and tires at the track as I swapped them. The centerlines were 38 lbs lighter.
After 3 more passes with the Center lines the improvement was.....ZERO!!!!! No change in 60 ft 1/4 mile ET or MPH.
Would it make a difference on a 3000 lbs car? maybe ...
Also tried an electric water pump and fan set up vs 5 blade clutch fan with no improvement in ET or MPH

How's your fuel supply?
Many things can hold us back with out us knowing it, I guarantee it

If the wheel weight difference were almost entirely located in the hub, the advantage would be limited to less than 1% change in the overall weight.

Cab, owned this car for over 20 years and this combo for over 16 years. 6.5 psi on dyno pull after dyno pull. Mallory comp 180 pump with 3/8 lines. Fuel/air is a tad rich at 12.5. It is not lacking fuel.
I think this car is maxed out on MY definition of a street car. Pump gas, power steering, power brakes, nice stereo, full auto valve body, 3.73 gears. I know that this combo is not to far away of failing a block. Just a bad tune up or a broken valve spring away.
Oh by the way this is a rotisserie restored car that has won 1st place 3 years in a row at Mopars with Big Daddy and in 1999 or 2000 at the Hot Rod magazine Power tour, in a sea of red Camaros, won "Best Street Machine, Non Tubbed"
I am always chasing the next tenth, but as stated, the lighter wheel combo and the electric water pump/fan and even removing the power steering belt did nothing to improve ET or MPH on this car.

Sometimes cars don't react like we think they should, just like women

Reducing the wheel OD (rim and/or tire) is very effective, except that it ruins ride quality, ground clearance, and traction, and looks too import for most people with classic musclecars.
Here are 26.5" (about average) OD tires on an import.
Front 245/40-19 on 8-1/2 X 19
Rear 275/35 on 9-1/2 X 19

We did a similar swap in my Duster years ago....also had zero change. LOL.

Hey, I resemble that remark!

^^^^ THIS ^^^^. Not specifically fuel supply, but the law of a chains weakest link. ie: If your fuel supplies limits your combo to 10.80, and you make improvements elsewhere, even if they were effective improvements in their area, the limits of your combo will most likely still be 10.80 because of the fuel supply system. Now weight improvements would seem to be the exception to this because less weight should ALWAYS be faster, but it still doesn't always seem to work. I know what I'm describing seems to be just stating the obvious, but think most of us still tend to ignore the law of the weakest link. I know I do.

It would seem to me that key to making effective changes is to continuously know WHERE your weakest link is. And that's not always easy! Again, obvious.... right?

To the OP: I made the move from steelies to lighter rims on my car and saw about a tenth improvement, but I changed tires and gearing at the same time, so....

that thing is cool.. anyway. My old 67 Coronet (3850lbs) had heavy cragars all the way around. I replaced the rears w/ 15x7 stelies and the fronts w/ 14x5.5 steelies with smaller tires. I believe the the total savings was 45lbs up front and 30something out back. The car ran 12.90 w/ the Cragars and 12.90 w/ the lighter wheels w/ the same MPH (104)

cragar ss wheels are good looking, but the 15x4's that i weighed, including center caps were just a tad over 23lbs. each ! a factory 5.5" steelie weighs in about the same at almost 24lbs.

The absolute overall weight of the wheel & tire combination should, of course, be as light as possible without losing function since it's 100% unsprung weight. However, this has no more effect on acceleration than the same weight removed from the roof or the driver.

A valid yet inexpensive test of rotational inertia (how much power is used to spin a wheel up to speed) could be a coast-down test.
Measure the actual diameter, from this calculate the speed in RPM to turn a specific MPH. Example: a 26" OD wheel = 81.68" circumference, or 6.807 feet per rotation. At 2,000 RPM that's 155 MPH.
To allow different diameter sets to be compared, the second T & W combo should also be spun at 155 MPH (not the same RPM unless it's the exact same OD) for comparo. Two sets with identical weight and OD may have different moments of inertia depending on where the weight is located: rim or hub.
Record the time in seconds to stop from speed, the one with the shortest time is the lighter MOI (duh). No, there is no easy math to say how much, just which wins.

Did I leave something out?