wheel vs. tire weight ratio

with all the discussion of wheel weights and such, i came up with an interesting question.
how do tire and wheel weights compare?

if you keep the same OD, then how would using a 1" bigger wheel change the weight versus keeping it stock?

to rephrase the question...
what is the weight of 1" section of tire versus a 1" section of wheel, and is there a certain size that is the "optimal" size...

i realize that this is not going to be easy to answe because there are so many variables, but lets start with a 28" OD, and a stock 15" STEEL wheel.

a 17" ALUMINUM wheel would probably weigh about the same as a 15" STEEL wheel, so you end up saving weight in tire size.

anyway, if anybody has any insights into this matter, i'd like to discuss....

If you are looking at this from acceleration point of view, than moment of inertia is what matters, not weight.

to me, this is a pointless question.

If you want ultimate output, then you'd go for the wheel that is the lightest.
If you just want the same wheel but bigger, then you aren't really 100% set on the lightest wheel because you probably wouldn't be looking for the same wheel. If it already is the lightest wheel on the market, you have no choice anyway and any discussion on that would be moot.

In turn, this goes back to the question of the effect of wheel size on gear ratio

a 17" ALUMINUM wheel would probably weigh about the same as a 15" STEEL wheel

very bad assumption. Not all AL rims are the same, not even close.

Same goes for tires. Just because a tire is a low-profile (thereby, less rubber) doesn't mean its lighter. The lower profile tires usually have much thicker beads and side walls.

Although I don't measure such things, I do pick up lots of tire/rims, most of the aftermarkets are quite a bit heavier than stock. The most offensive are the 20+ inch rims and tire sets. They are at least twice as heave as stockers.

ok, well look at it from an optimization point of view.
so you have a 28" OD.
you can have a wheel size ranging anywhere from say 10" to 24"
what would be the optimal size...

i'm assuming that in general, a smaller wheel weighs less, but how would a 10" wheel effect acceleration?
with that small of a wheel, the rubber weight becomes an issue...

do you see where i am going with this?

if you have taken calculus, you know what i mean when i say optimization...
for example:
what is the largest area you can enclose with 50' of fencing...
or
what is the largest volume box you can make from a 20" x 20" piece of flat cardboard.


does this make any sense?

it does make sense but there is no point in asking the question because what is available is limited due to market demands.

let's just take the hypothetical optimum for ONE particular tyre of ONE particular compound of ONE particular tread pattern for ONE particular wheel design. That optimum is only for that particular tyre/wheel combination.

LOL it's not that easy in real life. Wheel ( as any other auto part ) is a product of numerous compromises, so linear optimization does not apply.

do you understand my question?
look.
you have a brand of tires.
michelin for example.
you have a brand of wheels.
american racing series 335 wheels, which come in 15-18" diameter.

what i am thinking is that as you increase the size of the wheel, the weight increases in a nearly linear fashion.
under these circumstances, it would be possible to figure out the best size for the wheels.

however, since everybody seems to think that i am some kind of idiot for being curious about this, it dosent really matter anyway.

No, under those circumstances the weight increases not in a linear "fashion", but in square, to be more precise :)
And you need to define what is the goal for your optimization first. If you want better acceleration, you have to look at the moment of inertia, not at the weight, as I told you above.

the first question is optimum for what?
if it is grip you want then first variable to fix is the overall diameter (and width) of the wheel+tyre which you have established.
the next step is to determine what qualities each gradually thinner tyre has and which qualities you are after.
In short, the tyre determines what size wheel you have.

I don't think it is a valid question because simply looking for a so-called "optimum" tyre+wheel combo doesn't exist other than in numerical terms, which don't really relate to the tyre beyond weight, which is isn't the only aspect that matters.

incidentally, you are talking about volumes of (non-uniform object); the rates of change wouldn't be linear.

its really not that complicated.

say for a certain brand and style of wheel,
a 15" wheel weighs 10 lbs.
a 16" wheel weighs 11 lbs.
a 17" wheel weighs 14 lbs.
a 18" wheel weighs 16 lbs.

the tire for the 15" wheel weighs 6 lbs.
the tire for the 16" wheel weighs 4 lbs.
the tire for the 17" wheel weighs 3 lbs.
the tire for the 18" wheel weighs 2 lbs.

the best (lighest) combo would be the 16" wheel and tire.

i realize that its not this simple exactly, but there are trends in wheel weights.
how much weight does adding one inch of diameter add to a certain wheel, and how much is subtracted by taking one inch of sidewall out.

maybe this is a question for the wheel/tire guys...





as for the moment of inertia, i dont really think it is as big a consideration as weight because the wheels are all of the same design and the tires are all made by the same manufacturer.
its not like i am trying to compare two different wheel sizes and styles at the same time...

what if the tyre for the 16" wheel has horribly over-squishy side-walls and is a pain to work your suspension around?
what if the tyre for the 17" wheel works out to have better ride compliancy than the 16" wheel?

i mean... these things are certainly possible, but not likely if the tires are otherwise identical.

its quite easy to research yourself, you can become an expert "tire guy" with just a couple clicks of the mouse

www.tirerack.com

Assuming this:

-keeping same overall diameter and section width
-increasing wheel diameter

You almost always increase overall weight. The answer to your question (which seems to have been missed :)) is that you add weight with the larger wheel, AND you add weight with the lower aspect ratio tire. It sounds backwards, but less tire usually means more weight. In order for the tire to maintain its roundness and weight capacity, there is often times more material required in both the tread area and sidwalls.

For instance, if you compare a 275/40-17 and a 275/30-20 tire, the 20" tire will almost always be heavier, even though it is the same overall diameter.

Judicious selection of brands, styles, and tires can net you a minimal gain in weight, but among the same brands and models, bigger wheels = more weight for the same diameter.

as for the moment of inertia, i dont really think it is as big a consideration as weight because the wheels are all of the same design and the tires are all made by the same manufacturer.
its not like i am trying to compare two different wheel sizes and styles at the same time...

It is a big deal because the rotational moment of inertia is related to the wheel radius raised to the 4th power. So even modest changes in tire diameter can have large affects on MofI.

As for the optimization of the wheel and tire, I think it could certainly be done to include both weight and MofI.

However, for most cases the trend is that a smaller tire/wheel combination will yield a lighter assembly with a lower rotational moment of inertia. The leading constraint becomes clearing the brakes. So the best overall solution is the smallest tire/wheel that clears the brake calipers.

Assuming this:

-keeping same overall diameter and section width
-increasing wheel diameter

You almost always increase overall weight. The answer to your question (which seems to have been missed :)) is that you add weight with the larger wheel, AND you add weight with the lower aspect ratio tire. It sounds backwards, but less tire usually means more weight. In order for the tire to maintain its roundness and weight capacity, there is often times more material required in both the tread area and sidwalls.

For instance, if you compare a 275/40-17 and a 275/30-20 tire, the 20" tire will almost always be heavier, even though it is the same overall diameter.

Judicious selection of brands, styles, and tires can net you a minimal gain in weight, but among the same brands and models, bigger wheels = more weight for the same diameter.

now thats an answer that i like.
not telling me that i'm dumb for wanting to know...

thank you.


it does seem to make sense that a lower profile tire would weigh more now i guess.
i guess you have to find the lightest and biggest wheel you can so that brakes will fit and you can keep the light weight.

either way, anything is better than the hugely heavy stock steel wheels.

If you're set on one wheel and/or tire type, you'll have to choose a size/weight that fits your purpose, making a trade-off between looks and performance. Often times you can add size without too much penalty if you're willing to compromise on price and/or style.

I was able to lose weight on a BMW E30 when going from stock 14" to aftermarket 16". I was able to find lighter wheels and tires that weighed the same, but it wasn't cheap. $1600 for the wheels and $800 for the tires. Then I ended up selling them when I started running consistently better times on 15s.

I was able to lose weight on a BMW E30 when going from stock 14" to aftermarket 16". I was able to find lighter wheels and tires that weighed the same, but it wasn't cheap. $1600 for the wheels and $800 for the tires. Then I ended up selling them when I started running consistently better times on 15s.

and that was why i said it was a pointless question.
having the lightest wheel/tyre combo doesn't always mean having the best performing tyre/wheel.
As he also said in the previous post, to maintain the use of the tyre, there is often more mass in the tyre. This means that the behaviour of each tyre as you get a narrower sidewall is going to be very different again, affecting what is "optimum".