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Discussion Starter · #1 ·
Gents...

Just like to share with you some of my observations after installing my Toyo Tire / Motorsport reproduction Z06 wheels on my stock '03Z.

Lifitng them onto the rotors I had a feeling there would be a handling change since they are easily another 5-8 pounds heavier per wheel.

Off the ramps and off to the Tennessee back roads.

The tires, replacing a mismatched set of corded F1 supercars up front and balding Yokohama AVS sports in back were definetly several months past due on replacement, and the Toyos feel like Velcro in comparison. High speed cornering is predictable and the tires give plenty of feedback as you approach the limit...

However...

Everything about the car seems much heavier. The steering requires almost a 1/3 more effort. Theres no loss in precision, you can just feel the mechanism taking more effort to push.

The biggest change comes on sudden transitions, either in acceleration or braking, or sudden side-to-side as in a slalom. You can tell the car's moment of inertia (or at least is perceived to be) much more sluggish. The nose tends to wobble as the weight shifts around before finally tracking in an gaining stability. Acceleration seems to be somewhat effected but havent had a chance to eval on a track...will let you all know as soon as I do.

So all in all my Motorsport wheels are a "Show" wheel not a "Go" wheel. They look great and house some great all weather rubber (Toyo T1-S), and will serve fine on the street where I dont really have call to push the car that hard.

I've maintained my stock rims for use in the car's track "combat" configuration. I will be fitting them with Nitto RIIs as budget permits. The Toyos will have to get me through my first DE in Joliet on July 9-10 :yeadog:

Id like to powdercoat them black before then. Any reccomendations on custom wheel coating?


Joe
 

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Adding SPRUNG weight is pound for pound.

Adding UNSRUNG weight is double additive, therefore 5 #'s equal
5# + 5# = 10#'s.

However, adding ROTATIONAL weight increases to the 4th power !!, therfore 5 #'s equal 5^4 or:
5# x 5# x 5# x 5# = 755#

So adding 5#'s of UNSPRUNG AND ROTATIONAL tire and wheel weight at each wheel is like adding:

755# + 10# = 765# to each wheel !!

That's an additional 3060#'s total,

OR like towing another Corvette around the course !!!



Powder coating will add another pound or two depending on thickness and I suspect the Toyo's and Motorsport wheel combination weigh more than just 5#'s.

That's why racers spend so much to reduce unsprung and rotational weight by using light racing tires, Magnesium wheels, with Titanium hardware, and then polishing and anodizing.

IMHO buying heavy chromed wheels or powder coated wheels for show is a waste of money. But that's a racers perspective.

You would be better off and money would be better spent on the track with a lighter and stronger race wheel such as CCW's and Hoosiers or Kuhmo's race tires.
 

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you are not correct, a buddy of mine just put new 26" wheels on his escalade and they weigh somewhere close to 75 pounds a wheel. His stock wheels and tires weighed around 30. SO by what you are saying he is adding 45 pounds which you would increase to the 4th power giving you an addition 4,100,625 pounds for 1 wheel. Give me a break, I would belive you saying possibly x4 but not ^4.
 

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well i want my new Z06 rims to be black. what good options are there other than powdercoating?
 

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I've read about the unsprung weight thing before and didn't let it bother me to much until the new Hoosier tyres came out. The 04's are about 4to5 lbs more in the 18" size. Now this weight thing starts to hit home. So I find it really difficult to understand 5 lb increase in wheel/tyre weight making our car weight as much as the tow truck. Someone needs to explain this to me. My lap times didn't fall off that much. In fact the new o4's helped. Is the design of the tyre that much better, can't wait until the 05's are out in the r series.
Tony #54
 

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Just a thought but I would think it would all come down to precession of a rotating mass. A gyro being precessed. Added weight at the outer reaches of a gyro would make it more difficult to precess or turn at the center of the axle. I think that may be what our friend is feeling in the steering wheel and in the car in general. The effort to move more mass/weight and to stop it once it's moving would rank right up there with all the other issues. I'm not a professor so feel free to crush me like a bug if I'm wrong.

D.J.
 

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Rotational inertia is WR2. The radius is the squared term. W is weight. The torque to spin a wheel and tire is affected buy the weight to the first power an the location of that mass to the second power. R is the distance from the center of mas to the axis of rotation.

ie. if your wheels are 10 lb. heavier and the increase in mass is all at the hub, WR2 doesn't go up much. However if the rim portion carries all the increased mass, then the inertia will be increased much more. That is why lightweight wheels are usually multiple piece with a spun aluminum rim and either cast or CNC machined hub.

Torque to accelerate a disc (wheel and tire) is:

WR2(RPM change)/308/time to accelerate in seconds

Dunno where DJ got the 4th power from.
 

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Discussion Starter · #9 ·
Gents...

Update...well its amazing what a little retorque of your lugnuts can do. I was picking up some harmonic vibe around 50-55 mph so I decided to retorque the lugnuts to spec. I got in and instantly much of the steering precision and wobble was gone and the car feels much like her old self again. Still a bit more "planted" but not nearly to the degree it was before.

So the smile is back on my face and Im not chucking my new wheel/tire combo.

DJ worm,...had a chance to pick up wheels and tires for the price of wheels from a member and sprung for it. This will allow fitting of much more aggressive rubber on my stocker rims when the car goes into "combat config" as I call it. So I figured I got a deal since 99% of my cars time is on the street and it is my daily driver. Beleive me Im all about the go faster parts rather than the parking lot profiling parts.

On a completely different note....any good how tos on adjusting from a street alignment to a track one in your garage! Thanks for feedback fellas

Joe
 

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And beyond that, remember tire weight is more important than wheel weight, since it's farther away from the axle centerline. Ie, (all things being equal) a 25 lb wheel and a 20 lb tire is better than a 20 lb wheel and a 25 lb tire. Both weigh 45 lbs, but the former has more of it's weight closer to the axle (or hub) centerline. Easier to spin it up and slow it down.

Aren't the V710 a bit heavier (in a given size) over the Hoosier's? I know the old V700 victoracer are pretty heavy.
 

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Good info guys...some of it is a bit confusing but overall it makes alot of sense. :cheers:
 

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The force required to accelerate a rotating object to a given speed is in direct proportion to it's rotational inertia. Rotational inertia varies in direct proportion to mass. Therefore, the force required to accelerate a rotating object to a given speed varies in direct proportion to mass.

Twice the mass, twice the force to get it accelerated to the same speed in the same time.

Inertia also varies in proportion to the square of the radius of the rotating object. Twice the radius needs four times the force. But also, since the mass you add is multiplied by this number when calculating Inertia, that mass is made bigger. Each pound of additional rotating weight is actually worth more than a pound of deadweight.

For any given wheel diameter, the inertia of the wheel increases in direct proportion to the added mass of the wheel. Delta I equals m2 - m1. And the additional energy required to accelerate that added inertia to any given speed in any given time is proportional to the change in Inertia. There is no exponent in this equation.
 

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RocketSled said:
The force required to accelerate a rotating object to a given speed is in direct proportion to it's rotational inertia. Rotational inertia varies in direct proportion to mass. Therefore, the force required to accelerate a rotating object to a given speed varies in direct proportion to mass.

Twice the mass, twice the force to get it accelerated to the same speed in the same time.

Inertia also varies in proportion to the square of the radius of the rotating object. Twice the radius needs four times the force. But also, since the mass you add is multiplied by this number when calculating Inertia, that mass is made bigger. Each pound of additional rotating weight is actually worth more than a pound of deadweight.

For any given wheel diameter, the inertia of the wheel increases in direct proportion to the added mass of the wheel. Delta I equals m2 - m1. And the additional energy required to accelerate that added inertia to any given speed in any given time is proportional to the change in Inertia. There is no exponent in this equation.
Yep...just what I was thinking.
 

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drivinhard said:
Aren't the V710 a bit heavier (in a given size) over the Hoosier's? I know the old V700 victoracer are pretty heavy.
According to Tire Rack the Hoosiers R3S04's and the Kumho 710's in 315x35x17" both weight 26#'s each.
 

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Ok, you guys that know the math ...how about the anwser.

We all understand lighter is better, but how much better?, How much of our hard earned dollars should we plunk down to save a few pounds.


Stock 18" rear wheels all around with a 30lb tire
26lb tire
20lb tire

Can you calculate what the benefit would be

Example : If you drop tire weight 4 lbs each or 16lbs
What is the real effect?
It is still 16lbs, but will react like (24lbs)

Maybe something the rest of us can understand. I don't own a scientific calculator :(
 

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Anybody have an accurate weight of the stock 02-04 wheels (front and rear?)

IIRC the 01 wheels are a couple of lbs heavier than the 02-04
 

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Stock 18" rear wheels all around with a 30lb tire
26lb tire
20lb tire

Can you calculate what the benefit would be

Example : If you drop tire weight 4 lbs each or 16lbs
What is the real effect?
It is still 16lbs, but will react like (24lbs)
That is a fairly complex problem to accurately analyze. The vehicle weight, drag coefficient, rolling resistance, WR2 of the driveline components and WR2 will all figure into acceleration.

All things being equal, changing tire weights will affect acceleration and braking. How much exactly is hard to predict.

If the center of mass of all the tires in question have the same radius to centerline of rotation dimension, then it will just be in direct proportion to the weights.

If the tire weight reduction is all in the tread area then the acceleration difference will be more pronounced.

For most people, your driving abilities will have more affect on lap times. Go with the lightest tire you can afford and concentrate on driving.
 

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I posted this on another forum a while back, might be useful:

A while back I actually went through the physics and calculated the equivalent weight reduction of tires and wheels due to the added effects of rotational inertia. It wasn't as bad as what I'd been led to believe. Absolute, worst case for tires was 2x, meaning removing a pound of tire weight was equivalent to removing 2 pounds non-rotating weight. This was assuming all the mass was at the perimeter, that is, at the same radius as the rolling surface.

For wheels, it obviously depends on the type of wheel, but for a simple band + disc model of roughly stock proportions it came out to around 1.6 or so. Again, meaning that a one pound weight reduction of the wheel was worth 1.6 pounds of non-rotating weight reduction.

I'm guessing a pound removed from the rotors is equivalent to maybe 1.3 or so pounds of non-rotating weight reduction, since the mass is largely concentrated near the center (compared to the tire).

A few quick notes:

1) This is a per-wheel reduction. Multiply by 4 to truly appreciate the impact of removing, say, 10 pounds per corner.

2) The weight equivalents are from an energy analysis for acceleration and braking. Obviously, reducing unsprung weight (rotating or otherwise) pays handling dividends as well.

3) You still want to minimize rotataing weight, even if the scale factor is only 1.3 or so, and I don't mean to take away from that. I just think it's useful to have some sense of the relative impact of rotating vs. non rotating weight reduction.

Hope this helps,
-Stephen M
 
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