Wheel weight

[Hammer Down]

How much of a performance gain can be expected from running lighter wheels? I've been researching wheel weight for 17" wheels around the 9" width. I like the cobra r wheel which comes in at 22ish pounds and it seems most aftermarket wheels are around that also. But I saw an enkei wheel that weighs 15.9 lbs. Does a weight loss of 6 lbs per wheel give a significant performance gain? I'm planning on doing the Northeacecars 13" cobra upgrade on my 85. I guess what I really need is the proper fitment first before I shop wheels. My car is lowered 2" also.

[xctasy]

1. Wheel weight reduction reduces the unsprung weight, and reduces peak wheel pitch in road bumps, racing kerbs jounce, and it improves control.


2. Reducing wheel weight hurts the flywheel effect on drag strip vehcle launch. Having a heavy flywheel can be up to a 60 pound advantage in some bigger diameter flywheels. Wheel weight gains in one axle can be worth a (say 12 pounds increase from the 10 pound wheel to the 22 pound wheel) can be just like 24 pounds added to your flywheel. NASCAR guys found the same thing...sometimes a heavy flywheel can help you in launches, but hurt you in curves.


3. On the steered wheels, wheel mass gains are nagatives if the wheels have the same strenght in bending. Light wheels hold to the helm, and reduce yaw.


4. Weight to power. No one says no to 48 pounds less weight. Roughly for every 100 lbs reduction, it will equal 10rwhp extra for cars weighing 3000-4000 lbs


All that has been quantifed, and the race car engineers pull out or add weight depending on what goals the race teams have.

GM Research did all that kind of quantative work back in the 60's when Zora Arkus Duntov added the Salisbury Spicer IRS to the C2 Vette.

A book published in 1995 and now in its thirteenth printing, Race Car Vehicle Dynamics (RCVD) is the first in a series of books written by Bill and Doug Milliken (Author William F. Milliken, Jr. Edited Douglas L. Milliken). Those guys were influneces by air craft engineering, which dealt with all that kind stuff back in the Chaparral race car... putting air craft aerodynamics and landing gear practice into the race automobileand, eventually, the road car.

Another was the Aussie American, Arthur Bishop who worked with British and American steering gear companies. All that stuff was quantified and had numbers by the early 60's. Over the last 57 or so years, the data pickup has basically bench marked all that stuff.

Wheel weight plus or minus gains are minor in comparison with Independent Front and Rear suspensions verses Live axle weight. An IFS/ IRS often assembly weighs about 80 pounds more than the 8.5" Dana r 8.8" solid-axle setup on the F150 4X4, Jag XK-E or 2003 Mustang GT, but it allows a potentail 125-lb reduction in unsprung suspension weight over two wheels, or 60 pounds per wheel. You'll feel that in adverse conditions (horizontal and vertical curves, compond curves, switchbacks and high International Ride Index roads.

I'm a roading engineer, so use a selection of vehicles, and when you compare yaw on the same road between different vehicles, you can determine how much steering movement there is with different wheel weight and axle configuration combinations.

That kind of unsprung weight reduction totally reduces bump steer and wheel bounce and the degrees of slip angle in turns. In my 4 x 4 cars with IRS, the slip angle reduction at 65 mph in bumpy roads with tight sub 800 feet radius curves is about 1.5 degrees, and that makes a huge difference in how a car responds in panic situations.

You won't save more than 12 pounds per wheel in the 275 to 315 wide 17 or 18" Mustang wheel. The result is minor but definately measurable with equipment.




The best strength weight relationship is from the stock Explorer XLT UR 98 16 X 8 J wheel and tire combo, as little as 8 pounds with 235/60 H 16's and E36 offset wheels.

Stock P275/70 R16 is 31.1" tall, about 2 pounds heavier, 10 pounds each

RAV4 16 X 6.5 J 's were 20 pounds with 235/60 H 16's. 27.1 inch tall

The 16 x 7 J replacements were 12 pounds with 235/60 H16's

The stock 15.35 x 5.9 J TRX's with 190/65 or 200/60 series 390's were about 10 pounds IIRC.

....


Its different with my car...it runs Explorer 16 x 8's and my wife opted out of Fords because she loved those two color sooo much.


We discussed the nicests 17" rims on every red Mustang we could find, and that color just kept popping up everywhere during or discssions.

Here are the 98 UR Explorer rims on my RAV4.





Weight saving using the Ford rim on each wheel is 12 pounds per wheel, even though the Explorer rims are 16 x 8, and the G-spec Rav4 is 16 x 6.5 J. Toyota bolts fit without issue to the Explorer rim, and a 2.75" centre cap fit, the Ford cap can be made to fit. The RAV 4 automatic has a large alloy intrusion on the left hand side, so the Explorer rims help with inner gaurd clearance, and with 27 " tall in the 235/60 16's size I use, they are a neat fit.

For the Mustang, I'm planning to use redrilled stud bolts as per common GM practice. Unlike these conversions to this stud bolted wheel,


Spacers if not fitted from factory, can be black flagged as illegal down here, so I'm looking at redrilling the stock four stud Fox hub to 4.5",and that will allow me to fit transferrable Eurobien EB's or Explorer 16 x 8 JJ to the RAV4 or Mustang, total movement of 16 x 8 rims to any three cars I can use.

I told her that I could fix her danged beloved Tojo...I'll have her paint and wheels on my Fox, she could have the Ford wheels. I've been planning a Kugel Komponents, style Focus 5.0/5.8 V8 swap.....first the wheels, then a proper FoMoCo engine....

[xctasy]

The way they measured it back then was with a test ridged car, known Steering gear, known wheelbase, knowing how many degrees of wheel turn makes how many feet of turning radius. I do it the same way, stattic in a car parking lot at Bunnings, then dynamic on a known road.

As you remove unsprung weight, your steering requires less turning for the same speed in the same corner. Add unsprung weight, and it moves more.

Wheel weight reductions in bumpy environments reduce yaw, slew and movement over given bumpy surfaces.

Input sheet





The resultant wheel movement is recorded with a linear encoder, and you get the amount of wheel movement in millimeters or inches or degrees, and you just compare.



You record steering input over the same section, recording XYZ movement with a cell phone app or ball bank device, and repeat with the new wheels, IRS , or drive system. Tires have a very specific slip angle, which can be dialed in.

[Hammer Down]

So, besides negative for launch, its positive results for steering and acceleration? What about braking performance? Is a 5-6lb reduction per wheel gonna be something I notice for a street car that's run at the track on open track days a few times a year?

[xctasy]

Item 5, advatage generally to lighter, high voids (holes, flow paths etc) aluminum wheels.

Despite claims by ome very repudable wheel makers, only open air flow cools brakes. You don't see Centrelines on many competition endurance cars, but you see them on drag racers.

A flat aluminum wheel with a lot of metal and few voids cannot conduct or "heatsink" brake heat away from the disk or drum to the air very well. Lighter wheels have higher voids, less aluminum, and should cool the brakes better, but only back to back testing with a Pyrometer that reads peak and average brake heat can prove that.

[wraithracing]

Reduction in unsprung weight and rotating wheel is generally a good thing, especially in the context of a track car. In regards to a Cobra R, be careful as many of the aftermarket copies are much heavier than the original Ford Racing pieces and the actual weight seem to vary from one manufacturer to another.

Also keep in mind that there are no freebies in life and definitely not in racing. A lighter wheel generally comes either at a reduce service life or a reduced bank account or both. Lightweight track only wheels are great, but need to be checked on a regular basis for damage such as cracks, bends, etc. that might cause catastrophic damage while driving. Also plan on replacing the wheels when any damage occurs or after a certain interval to prevent failures on track.

I would be aware and take note of wheel weights when choosing, but I don't believe that shedding every possible pound for the street has the benefits that maybe a track car might see. I would keep the wheel weights down as much as the finances allow and not worry too much about it. Good Luck!