Wheel size

[cudabob496]

Keep hearing that the larger diameter your wheel, the slower you will be,
because you are slinging more weight (wheel and tire) farther away from the wheel hub.
I know that NASCAR only uses a 15 inch wheel.
Guess I'll see if there are some calcs out there that show that.

[RCCDrew]

Makes sense. Also I hear that every pound of rotating weight is like adding seven pounds of static weight.

[GoodysGotaCuda]

Keep hearing that the larger diameter your wheel, the slower you will be,
because you are slinging more weight (wheel and tire) farther away from the wheel hub.
I know that NASCAR only uses a 15 inch wheel.
Guess I'll see if there are some calcs out there that show that.

Slip angles will change quite a bit as the wheel gets larger. Last time I checked, NASCAR doesn't do very much changing in direction..like road course or autox. [Yes, NASCAR does run one[?] road course every year]

If we are using very simplified examples, not one current Supercar or "Fast" car has a wheel remotely close to 15" in diameter.

Just because it's 15" doesn't make the wheel assembly lighter than a 18" of similar overall diameter. Depending on the wheel construction, that's a reduction in 3" of sidewall height as well [solid rubber isn't necessarily light].

[cudabob496]

even if a 15 inch wheel and 18 inch wheel weigh the same, I think the 18 inch will make car slower, because some of the
weight is 1.5 inches farther from the center of the wheel, requiring more power to turn wheel.  Also, an 18 inch wheel
will have a bigger contact patch, which wil help handling, but represent more friction between the car and the ground, that the engine
has to overcome.

[cudabob496]

Here's a discussion I found.  The answer seems to be you are a little slower due to having to overcome rotational inertia of the larger wheel, not increased friction due to more rubber on the road, as was initially claimed.  I noticed on the Tire Rack website that the larger the wheel diameter, the more the wheel weighed, in general. So basically, if you go from 15s to 17s or 18s, etc, you will lose some quickness.

My friend and I both have a 98 GS400 and we constantly race one another. We both do not have any mod's and are running completely stock except for his rims. Here's where it gets interesting. He recently got 18'' rims with Toyo T1. I am riding on the stock 16's with the Goodyear eagle garbage. Before he went to 18's he was also on stock 16's and we use to be neck and neck all the way to 80mph which was expected. Since he went to 18's, my car launches a bit quicker and I am almost a full car length ahead of him to 80mph. We only race to 80 mph, nothing over that. We did this several times and it was the same result every time with my car on 16's ahead by a full car length. We even switched cars and he pulled ahead of me in my own car ....this was to eliminate the driver skill. His car definitely handles much better, but its the 0-60 sprint time at a traffic light which really matters to most of us.

The conclusion we came too is this: With his wider tires, he has almost 2'' of extra traction per tire multiply it by 4 and you get 8'' of extra traction and more friction. This obviously helps make a big difference in the handling department but actually slows the car down a bit from 0-80 mph. Technically, wider tires have more friction, and more power is required. But since the rear wheel HP is the same in both cars, his wider tires actually slows down the car. The only reason to go to 18's or higher in my opinion is if your car's HP increases so the tires can better handle the extra power or better handeling or purely for the looks. His car also rides much harsher which was expected. I think a good compromise would be to the optional stock 17 which I am planning on going to in a couple of months with Yoko dB's. My stock 16's are just too floaty especially at speeds over 80mph.

We are both surprised and shocked at these results. He is trying to convince me to swap my stock 16 with his 18's and race again. He is the kind of person that just doesnt take no for an answer. I probalby will end up doing this this weekend and will post a followup w/results on monday providing the weather is good.
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Old 02-14-02, 08:52 AM     #2
mooretorque
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Decreased acceleration due to greater rotational inertia of a heavier wheel and tire unit, not increased friction. However, assuming no change in circumference, top speed remains the same, just takes a little longer to get to.
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Old 02-14-02, 08:53 AM     #3
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well depending on the 18's, he has probably increased the weight over the 16 inchers. this increases unsprung weight and inertia at the rear wheels. with the increase in inertia (an object at rest tends to stay at rest) it will take more power to get them moving. and since there has been no such increase, ie mods, he will be slower of the line. that is why you see guys here that have 20s and such that are heavy complain that there car isnt as fast as it used to be. however, there really shouldnt be too much difference once the car is moving. thus ends the physics lesson for today boys and girls..........Dr. Crosthwaite at UNCC would be proud.


Read more: http://www.clublexus.com/forums/gs-2nd-gen-1998-2005/37438-can-larger-rims-and-wider-tires-can-slow-down-your-car.html#ixzz3xlVwES18

[Bullitt-]

overall diameter of the tire will come into play, many newer lower profile tires are about the same diameter as the OE sizes & no larger than the up-sized tires a lot of folks are using. Increasing the diameter of the tire would make acceleration slower given all else is equal. 

for instance a 205\70-15 has a 26.3" diameter & a 275/40-17 is 25.7 according to this calculator, notice at the bottom of calculator the "TYPICAL WEIGHT" on these came in the same. http://www.rimsntires.com/specspro.jsp 

Here is an earlier discussion of the weight difference which depending on the wheel choice can be negligible as well because the tires weigh less. .  http://www.cuda-challenger.com/cc/index.php?topic=48878.msg500978#msg500978

even if a 15 inch wheel and 18 inch wheel weigh the same, I think the 18 inch will make car slower, because some of the
weight is 1.5 inches farther from the center of the wheel, requiring more power to turn wheel.  Also, an 18 inch wheel
will have a bigger contact patch, which wil help handling, but represent more friction between the car and the ground, that the engine
has to overcome.

of course there's going to be compromise in anything but for a good mental evaluation think of a Top Fuel Dragster...
wouldn't make sense to put the front tires on the rear would it? 

[RCCDrew]

 Here's an example of a smaller diameter wheel ( even with a dedicated race slick) going slower than a bigger wheel.

http://blog.caranddriver.com/whats-the-hellcats-true-potential-we-head-to-the-drag-strip-with-various-tires-to-find-out/

[Bullitt-]

Here's an example of a smaller diameter wheel ( even with a dedicated race slick) going slower than a bigger wheel.

http://blog.caranddriver.com/whats-the-hellcats-true-potential-we-head-to-the-drag-strip-with-various-tires-to-find-out/

they blame the weight of the wheel on the slower time, not the size. & I imagine the 17" tire was heavier also based on other findings I've seen, they never give all of that info. 

"The bias-ply Hoosiers on steel wheels out-weighed the Nittos on aluminum rims, the reason we think the quarter-mile times slowed by a couple of tenths."

[YellowThumper]

CudaBob
Look forward to the swap comparison.
If possible measure the weight difference between them while you have them off.

One other thing is the sidewall height. Keeping the overall od the same sidewall is reduced. Large sidewalls will wrinkle providing a slight cushion and will also expand as acceleration starts. This has benifit of additional downward force as it is lifting car. Whereas short sidewalls don't help on acceleration they provide the flat footprint in the corners. The larger sidewall also will absorb traction inconsistencies better when you are on the edge of spinning or grabbing.

Mike