Wheel Weight and Tire Weight

I'm on the civicx forum on one of the threads about a guy with a blown Civic Type R engine and one user posted this based on this subjective experience

It's just like the wheel and tire conversation I have with Type R owners here in the South. People pay thousands of dollars for forged lightweight wheels, and then go and do someting really stupid like put wider and heavier tires on their super-lightweight wheels. So, all they do is make the wheel lighter, but then throw on a tire even heavier than stock, causing the heaviest weighting thing on the entire wheel to be towards the outter portions of the rotating mass...which is worse thing you can do for braking and acceleration. If you get a wheel that 19lbs and throw on a 27lb tire, thats horrible. You're better off keeping your 24lb stock wheel and keeping the 23lb stock tire (just an example) because your heaviest part of your entire wheel is towards the center of the rotating mass, not the outside of the wheel.

Is there any truth to this? I have a hard time believing a 10 lb carbon fiber wheel with tires for 18" wheels with an average weight of 24lbs will have worse performance even though rotational mass has decreased. 

Apparently no consideration of contact patch size. 
 

So the answer is, it depends. 

A wheel, unless it's flimsy enough to fail to maintain its geometry, is mostly defined by its weight.

A tire defines everything about the car's interaction with the ground, so weight may be a consideration, but it's certainly not the primary consideration.

I mean, would you run a 20lb rock-hard all-season with flimsy sidewalls or a 27lb high performance tire with nice stiff sidewalls and lots of grip? I would have zero interest in the the all-season. The saved weight is real, but the tradeoff is not so good.

If you determine the best tire for your application is 27lb, saving 3lbs on the wheels is still saving 3lbs. If the 2nd best tire is nearly as good functionally but significantly lighter, then maybe we're looking at a tradeoff worth making.

Also, we've failed to define performance. It kinda sounds like you guys are racing equations without concern for grip.

As far as the weight being harder to accelerate at the outer portion of the wheel/tire combo, that's true.

It's kind of a step removed, but here's a demonstration of moment of inertia and its effect on acceleration of a wheel (cylinder). In this case the acceleration is provided by gravity, but you can still see that with that equalized, concentrating the mass at the perimeter (tire) makes it harder to accelerate the cylinder. Think of the solid cylinders in the demo as a heavy wheel with a light tire, and the hollow cylinders as a light wheel and heavy tire.

Mathematically speaking he is correct that a heavy tire with light wheel is worse for rotational inertia. But obviously the benefits of the wider tires far outweigh the cons. That's also much more of a concern on cars that actually struggle to rotate the wheels. I'm pretty convinced that anyone that claims they can tell the acceleration difference from a few pounds of wheel/tire weight on a car with more than like 100hp is either lying or getting a placebo effect.

In reply to Jesse Ransom (FFS) :

Is angular momentum with the R hand rule the reason that almost all screws are "righty tighty"?

The clockwise rotation of the nut along the threads of the bolt obviously would guide it against the angular momentum of the spinning nut, but is the convention aligned that way because of the natural angular momentum?

In reply to dps214 :

When I was racing my 1987 VW GTI in ITB, I could tell the difference between my two sets of tires. The tires were all the same, but the wheels in one set were 3 pounds lighter than the other. You could feel it on acceleration and deceleration, but on a twisty track you couldn't see any consistent difference in laps times between the sets. I think the HP rating of that car was 108. On my Miata NB I can feel the weight differences between sets in the ride quality, and even that is more likely due to the different tire constructions. I'm in the camp that buys my wheels on looks, not purely on weight. Most people never drive the cars at the limits where lightweight matters a whole lot.

It is indeed possible to over tire a car.  When I was looking to possibly switch tires from the Hoosier vintage TDR to R7s the Hoosier tech guy recommended I stick with the TDR as it's lighter by 7lbs a tire. Note I have a 100hp car.

This effect is going vary based on horsepower. The wider heavier tire may increase cornering speeds at the expensive of acceleration and braking. Putting super wide tires may indeed make it slower.

Like others have said, I doubt most people would notice the difference between the two set ups.

That guy needs a reality check though. I have a Miata. Stock wheels are 15lbs. I would like to see someone find a tire that weighs equal or less than the wheels. Almost all tires are about 20lbs. 

In reply to Vajingo :

True. Even my Hoosier race tires were 17 lb a piece and they were a pretty light tire by street or autocross tire standards. My SpecMiata wheels were 13 lb per the rules.

Edit: Out of curiosity I just looked at tire weights on Tire Rack. I used 205/50/15 because that's the size the Dunlops on my Miata are. Almost everything is listed as 20/21 lb, EXCEPT the Yokohama ADVAN A052 ,which is 18 lb. I found that a little surprising.

Edit#2: I take that last part back. Still surprising , but there are 3 or 4 other tires listed at 18 or 19 lb. and a Vredestein all season tire at 17.

In reply to DeadSkunk (Warren) :

Now that is interesting. Would make for a neat tire test (nudge nudge GRM)

This is an anomaly of course; the bias ply Hoosiers I use are 11 lbs per tire (6.0-13) and the wheels are 13lbs. 

In reply to Vajingo :

I recently sold/traded a set of forged wheels (10.5 lb) in a 15x7 size. Those wheels and some four season Vredesteins are the lightweight "killer" combo 27.5 lb, I guess. Now I'll never know.

In reply to Tom1200 :

6.0-13 tires on 13x6 wheels? You need to do something about those "plump" wheels.

I looked at 15" wheels on Tire Rack, too. Weights ranged from 9.9 to 19 pounds !!! The lightest tire/wheel combo would be 26.6 and the heaviest 40. That you would notice.

In reply to DeadSkunk (Warren) :

I know right, we went crazy when replacing the stock 12 by 4 wheels.

Vajingo said:

That guy needs a reality check though. I have a Miata. Stock wheels are 15lbs. I would like to see someone find a tire that weighs equal or less than the wheels. Almost all tires are about 20lbs. 

The OEM 14" Miata wheels are in the 10-12 pound range, and the OEM 15s are around 13. :)  The 16s that showed up on NB2s got porkier though.