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Discussion Starter #1 (Edited)
Wanting to hear from different guys on how much your aftermarket wheels slow you down on the track, street, or both.

Does it feel like a big difference or barely noticable?
Track times would be great if you have them.
Post wheel dimensions, name, and weight if you have it.

I know rotational weight has alot more effect than dead weight. If you have or know of good light weight wheels for everyday use please post! Post how much your skinnys help is also fine.
 

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Baddest N/A NPI in Canada
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I have a 15" racing wheel set for my TBird. I have 15x4 wheels with 26x4.5x15 Toyo Front Drag radials and 15x8 wheels with 26x9.5x15 M&H Cheater Slicks that are DOT approved. When I ran the 12.750 with these, I ran a 13.016 with my 16x8 Borbet wheels and 245/50 R16 Bridgestone Potenza tires. The car is noticeably different with drag combo on it and even though my times do not show it, they help a lot more...
 

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Others here probably know more than me, but I would think larger diameter wheels and tires would cause the engine to require a longer distance to get to a higher RPM.

My perception is that going to larger wheels would require a gear ratio change somewhere to compensate. Otherwise it would be like going from a 3.55 gear to a 2.76 gear in the rearend.

I believe there is also more rolling resistance to overcome with the larger diameter wheels and that would have a negative impact on fuel mileage. Larger wheels cause the transmission to shift at a greater than normal distance from stop, i.e., farther down the quarter-mile.

I would think the reverse would be true if you ran on 14" wheels, but IDK. :zdunno:
 

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Back a few years ago, I was able to slow my car down to be competitive in the 14 second class of the True Street competition at the NMRA/NMCA event in Joliet. IIRC, at the time I was running mid to mid-upper 13s. With running stock wheels/tires instead of the Hoosier QTPs on light weight rims, a little heavy on the fuel level and a slightly milder tune, I was running consistent 14.0x ETs all weekend. ;)

There was approximately 15 lbs per wheel difference, which accounted for a solid 0.25 seconds in the ETs. The change in the tune accounted for about a tenth and I fine tuned the fuel level from there making sure I tracked the fuel level and the weather conditions.
 

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Baddest N/A NPI in Canada
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Others here probably know more than me, but I would think larger diameter wheels and tires would cause the engine to require a longer distance to get to a higher RPM.

My perception is that going to larger wheels would require a gear ratio change somewhere to compensate. Otherwise it would be like going from a 3.55 gear to a 2.76 gear in the rearend.

I believe there is also more rolling resistance to overcome with the larger diameter wheels and that would have a negative impact on fuel mileage. Larger wheels cause the transmission to shift at a greater than normal distance from stop, i.e., farther down the quarter-mile.

I would think the reverse would be true if you ran on 14" wheels, but IDK. :zdunno:
Larger Diameter wheels do not have a negative effect. It comes down to wheel/tire weight and overall size. A 15" wheel with a 26" tall tire that weighs the same and the same tread width as a 17" wheel with a 26" tall tire that is the same (Hoosier QTP as an example) should show exactly the same results. If you compare say a 205/70R15 vs a 225/60R16 with the weight being the same, the larger tire car should be slower. If the bigger tires/wheels weigh less than the smaller ones, hard to say what would happen.

When the 17" racing wheels hit the market for the S197 guys, people have stopped trying to make the 15" racing wheels work. In fact my 17" racing tire/wheel combo for the Mustang is lighter than the 15" racing tire wheel combo for my TBird.

That said, I need the brackets for the Cobra rears, otherwise I have everything to do the hub swap for the TBird. I am seriously considering it as I would only need one set of racing wheels/tires...
 

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The Parts Guy
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If I'm looking to slow down a little to run a class, I'll throw my 255/45R17's on 17x8" Bullitts on the front instead of the usual 165R15's on SC aluminum spares. Doing so adds ~0.2X seconds onto my E.T.'s.
 

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This article uses some rule of thumb that states every reduction of unsprung weight (weight not supported by the vehicle's acceleration) is equivalent to reducing 10x reduction in vehicle weight.
This reduction in overall vehicle weight can be equated to a reduction in 1/4 ETs
http://robrobinette.com/et.htm

Example Given:
A reduction in the weight of the rim/tire assembly of 5lbs x 4 (all around the car) is equivalent to a 200lb weight reduction in vehicle weight (thats worth 0.200 in the 1/4 mile)


http://hondaswap.com/general-tech-articles/unsprung-weight-part-2-a-29058/
http://hondaswap.com/general-tech-articles/unsprung-weight-part-1-a-29057/

I'm trying to find a more scientific analysis but the .200 gain is roughly seen with this ET calculator:
http://robrobinette.com/et.htm

Here's a post that disputes the 1:10 unsprung to spring weight rule of thumb (post #2)
http://www.audiforums.com/forum/s-car-model-line-13/wheel-weight-rotational-mass-130606/

Regards,
-g
 

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Discussion Starter #10
Hey thanks! Great read. Those articles on hondaswap.com had especially good info. I'll quote them incase the link breaks later.

Unsprung Weight - Part 1

By: Eric Albert

Introduction

Every car built today has some type of suspension on it. Whether it's a double-wishbone or a MacPherson Strut design, we, as tuners, need to know a little more about suspension that just 'dropping' the chassis down a little bit. Let's take a deeper look at what exactly the job of your car's suspension is.

Suspension on the Clock

So we all know that suspension works. It works for you, but it never gets paid. In the same way as you and I work, we probably have different jobs. Suspension is no different. There are a few different ways your suspension works.

The main job of your suspension is to suspend your car above the road. If that was the only reason for the existence of springs and shocks though, why don’t we just solidly mount the car to the axles? “That’s obvious!” you say. Of course, you’d have a lot of trouble with bumps and corners with a solid suspension. This is because a suspension is supposed to allow your wheels and tires to follow the road, irregularities and all, while the body of the vehicle travels smoothly. Turning things around, the suspension should also keep the wheels and tires in maximum contact with the road for the best performance (this is more important than ride for us driving enthusiasts). So, to continue, for a suspension to be effective, it must allow the wheels and tires to accelerate and decelerate rapidly up and down while not allowing them to make excess motions (example - axle hop). The springs prevent the wheel assembly from traveling too far, while the dampers prevent oscillation by the spring.

Sprung Weight

Sprung weight is the weight supported by the springs. For example: the vehicle's body, frame, motor, transmission, interior, fuel, and passengers would be sprung weight. A simple concept to grasp. Basically, the sprung weight of the car is the car's mass as seen to the suspension components.

Unsprung Weight

This is one of the most critical factors affecting a vehicle's road holding ability. Unsprung weight is that portion of a vehicle that is not supported by the suspension (i.e. wheels, tires and brakes) and therefore is the most susceptible to road shock and cornering forces. By reducing unsprung weight, alloy wheels provide more precise steering input and improved "turning in" characteristics. So what. SO WHAT!? This is a key concept that many people overlook. We have been telling you for a long time now to get light weight wheels and tires. Here's how it all comes together.

Every time you hit a bump, the wheel assembly is accelerated upwards, decelerates to a stop, then accelerates downward till it reaches equilibrium. If the wheel can’t accelerate fast enough, shock is transmitted to the body, which may upset the balance of the car. A s an example think of small, sharp edged speed bumps versus those gigantic, but wide, monsters in some lots. The sharp edged ones are much more annoying to traverse, aren’t they? That’s because they require the suspension to accelerate more rapidly. Now imagine going over some stutter bumps in a corner. You’ll have a very rapid series of accelerations and decelerations. If the wheel is lighter, it will accelerate upwards and downwards faster (a=F/m). This means it will follow the road better and, even more importantly, it will allow the suspension to work better. The shock and spring will have to control less unsprung weight/mass, which means they can stop and start the motion of the assembly easier and at a rapid pace.

Why Reduce Unspring Wieght?

Reducing unsprung weight minimizes the load placed on controlling the motion of the wheels and tires. This means that suspension springs and shock absorbers will have a greater reserve capacity to control body motion -- just as they were intended to! The result is better handling, which we, as tuners, are all after.

In part two of this article, we will discuss the other end of the spectrum: why it is good to have a low weight wheel/tire, but not for suspension, for acceleration.

Unsprung Weight - Part 2

By: Eric Albert

Introduction

In the first part of this series, we took a look at the effects of high unsprung weight on suspension and handeling. In this part, we will look at rotating mass. Be careful not to confuse unsprung mass with rotating mass. Reducing both is good, but they are not the same. Let's take a look.

Rotational Inertia (or Momentum)

Rotational inertia is a concept a bit more difficult to deal with than unsprung weight. Inertia can be thought of as why a car wants to keep rolling once moving, or remain in place once stopped (unless you forget to set the parking brake on that hill). I believe the terms momentum and inertia are interchangeable. The term “flywheel effect” also refers to these concepts. In a car, there are a number of rotating masses which require energy to accelerate. Up front, ignoring the internal engine components like the crankshaft, we have to worry about the flywheel, clutch assembly, gears, axles, brake rotors and wheel/tire. Out back its a little simpler (for FWD) with just the brakes and wheel/tire contributing most of the mass.

The more mass an object has, the more energy it takes to accelerate it. To accelerate a rolling object such as a wheel, you must both accelerate its mass plus overcome its rotational inertia. As for braking, you must overcome its rotational inertia plus decelerate its mass. By reducing the weight of the vehicle's rotational mass, lightweight wheels provide more responsive acceleration and braking.

Before continuing with our informal analysis here, I want to point out something very important about rotational inertia. We’ve all seen the ice skating move where the skater starts spinning. She pulls her arms in and speeds up, then extends them again and slows down. Why is this? Well, the further a mass is from the center of rotation, the faster it must travel for a given angular speed (how many degrees of an arc it traverses per time unit). The faster anything moves, the more energy it has, so when the arms are pulled in, conservation of energy says that the rotation rate must increase due to equal energy being applied to the same mass over a smaller diameter. Applying this to wheels and tires, which have most of their mass spread as far as possible from the rotation center, I think you’ll agree that it naturally takes more energy to accelerate them. Example: Take a two identical masses, but one is a solid disk of diameter D, the other is a ring of diameter 2D. The ring will require more force to accelerate it (in a rotational manner). Therefore a heavier rim with a smaller diameter could have less rotational mass than a lighter rim of a larger size, and accelerate faster with the same force applied.

The effect of rotating mass can be calculated using Moment of Inertia (MOI). MoI is related to not only the mass of the rotating object, but the distribution of that mass around the rotational center. The further from the center, the higher the MoI. The higher the MoI, the more torque required to accelerate the object. The higher the acceleration, the higher the torque required.

Because of this, the weight of rotating mass such as wheels and tires on a car have a bigger effect on acceleration than static weight such as on the chassis on a car. When purchasing new wheels and tires for a performance car, it can be useful to compare the effects of different wheel and tire combinations. This is especially true when considering upgrading to larger wheels or tires on a car.

The use of light-weight alloys in wheels reduces rotational mass. This means that less energy will be required to accelerate the wheel. Given that each pound of rotational mass lost provides an equivalent performance gain as a 10 pound reduction in vehicle weight, the benefits of light alloy wheels on vehicle performance cannot be overlooked.
For example:
A reduction in the weight of the rim/tire assembly of 5lbs x 4 (all around the car) is equivalent to a 200lb weight reduction in vehicle weight (thats worth 0.200 in the 1/4 mile)

So What's the Point?

The point of this discussion is as follows: There is a great deal of rotational mass to deal with in a car and tires and wheels may only make up half of it. Estimates for weight (o.k. for comparison since they’re all in the same gravity field, therefore the mass would be a similar ratio)
Front: Rear:
Wheel/tire: 30-35 lbs each 30-35 lbs each
Flywheel: 15-20 lbs
Clutch: 15 lbs
Halfshafts: 7-10 lbs each
Gears: 5-7 lbs
Rotors: 3-5 lbs 3-5 lbs
Misc: 3-5 lbs 3-5 lbs
------------------------------------------------------------------
Total: 115-148 lbs 76-90 lbs

So a couple pounds here and there on wheels and tires will make a difference, but that difference is magnified because that weight is placed further from the axis of rotation than any other mentioned (remember the ice skater). All these masses must be accelerated, so any reduction is a good thing. Now you know why we always say don't get those 18" rims for your civic. Not only are the heavier, they have a larger overall diameter. Even with lower profile tires, most plus sizing leaves us with a slightly larger wheel.
 
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