Re: Approx ET/MPH change from lighter wheels/tires? Real World?
[Re: Streetwize]
#2251574
02/11/17 01:45 PM
02/11/17 01:45 PM
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Joined: Oct 2007
Posts: 4,219 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,219
New York
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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
Boffin Emeritus
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Re: Approx ET/MPH change from lighter wheels/tires? Real World?
[Re: mercman1]
#2251618
02/11/17 02:33 PM
02/11/17 02:33 PM
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Joined: Sep 2004
Posts: 22,873 Chicken coop
dustergirl340
Chicken Little
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Chicken Little
Joined: Sep 2004
Posts: 22,873
Chicken coop
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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. We did a similar swap in my Duster years ago....also had zero change. LOL.
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Re: Approx ET/MPH change from lighter wheels/tires? Real World?
[Re: Cab_Burge]
#2251652
02/11/17 03:26 PM
02/11/17 03:26 PM
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Joined: Jul 2006
Posts: 4,319 Puyallup, WA
StealthWedge67
master
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master
Joined: Jul 2006
Posts: 4,319
Puyallup, WA
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How's your fuel supply? Many things can hold us back with out us knowing it, I guarantee it ^^^^ 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....
LemonWedge - Street heavy / Strip ready - 11.07 @ 120
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Re: Approx ET/MPH change from lighter wheels/tires? Real World?
[Re: Streetwize]
#2251655
02/11/17 03:30 PM
02/11/17 03:30 PM
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Joined: Jan 2003
Posts: 24,562 Brookeville, Md
Mr.Yuck
Not enough dumb comments...yet
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Not enough dumb comments...yet
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
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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. 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)
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Re: Approx ET/MPH change from lighter wheels/tires? Real World?
[Re: Streetwize]
#2252210
02/12/17 01:04 PM
02/12/17 01:04 PM
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Joined: Oct 2007
Posts: 4,219 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,219
New York
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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?
Boffin Emeritus
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