This question refers back to the "20 Inch Rims" post under Aftermarket Product Review section...from what was mentioned, is it true that large wheel size will hinder/reduce acceleration and/or power as compared to a smaller wheel size?...Does that mean that if i upgrade my stock 15" wheels to IROC 16" or Replica 17"s that my car in "theory" will accelerate slightly slower than it would have if i kept my 15s?

 

Im not 100% clear on the topic...but I think that yes...it would be slower due to more rotational mass.

Not 100% sure as I plan to watch this thread as well to see the correct answer.

 

It's not just a matter of size, as weight vs size and where the weight is at in the overall circumfrence.
- It all depends on overall weight, but is largely dependent on where the weight is at. The heavier the wheel/tire combo is, the more power it takes to pull, but specifically the further the weight is from the point of center (the hub) the more power/time it takes to get it moving. At the same point, it also takes more power/time to slow that weight down once it does get moving.

Simple physics. - Would you rather stop a brick that is spinning on its axis or stop it spinning from a 6' radius?

For note, my 17x11 billet rear wheels and 315/35 tires are actually the same weight as my factory GTA 16x8 and 245/50's were. The front 17x8 and 245/45's are lighter. The problem is that most of the larger wheels (19"+) tend to be cast wheels, which are much heavier, especially the "bling" chrome wheels.

 

The weight of the tires affects it alot because its the farthest from the axis of rotation. Lower profile tires have beefier sidewalls, so even if your 18" wheel weighs a bit less than the stock wheel, the heavier tire will have more affect. Perhaps evening it out a bit.

Its hard to calculate.

 

Unless you go to specific handling oriented tires that specify stiffer/thicker sidewalls or more plies, lower profile tires are usually lighter. The reason they're stiffer is because they don't have as much area to flex. Yes, low profile tires tend to be made up differently, but unless you change the over-all size, they're still lighter because there's still less material in the smaller surface area. - I've worked at a tire store. I've weighed several different tires on a digital scale. - The real tough calculations come in when trying to calculate the difference when dealing with different sized tires. Then you have to allow for the differences in the amount of surface area vs actual component weight.

I qouted myself - edit is in bold....
Not just the wheels were lighter, my entire package was lighter.

 

It’s called the radius of gyration, which is defined as the radius from the center point where you can theoretically imagine the entire mass of the rotating assembly being distributed for the purposes of calculating it’s energy, momentum…

Since the force, momentum… are all proportionate to the square of the radius, the amount of force required to accelerate your wheel assembly goes up exponentially as it’s radius of gyration increases.

Very few larger diameter wheels are worth talking about for 2 reasons… as the wheels get larger it’s harder to make a light wheel that’s strong enough, and secondly, as you make a larger diameter wheel the wheel rim and entire tire assembly is fit in a smaller band around the outside diameter of the tire/wheel assembly, meaning that even if you make the whole assembly lighter the radius of gyration will be greater and because it’s effect is exponential even a relatively small increase becomes very significant.

This is why when you take your 33” tall, 16” wheels off your full size chevy truck and replace them with a 28” tall, 20” wheel assembly you suddenly find you need to upgrade your brakes to maintain your braking and to prevent from having to replace your pads yearly or more often.

Comparing factory Pontiac rims to aftermarket rims is a bit of a waste of time. For example, the high tech 16x8” rims used on TA’s, formulas… are some of the heaviest that I’ve ever seen in that size range, with tires I’ve weighed them in the 54-59lb range depending on front or rear and what tires are mounted. Some of the lightest large diameter factory rims are the 4th gen WS6 cars, which in contrast I’ve weighed in the 42-44lb range with a 275/40 rim. This sounds pretty good, especially when you compare similar sized ‘vette wheels/tires which usually weigh in at 52-55lbs, but if you compare it to a set of 3rd gen 15’s or the larger (and lighter) 2nd gen 15’s, which with a larger 275/50 (which is usually sized way oversize) or much larger 275/60 tire usually weighs in at 35-39lbs.

BTW, those “lightweight” WS6 wheels are forged (there is a note about funny coloration as a result that was included in the glove boxes of WS6’s equipped with polished ones in ’97) and are borderline what I would consider too light weight for street use. I’ve seen them egg from what most would consider fairly mild bumps

 

I’ve never seen this in real life on a similarly constructed and rated tire, because that similar tire needs stiffer heavier construction to prevent damage and other problems with less sidewall. For example, a bfg f-force sport in 275/45/17 weighs 25lbs, and in 275/40/18 it weighs 27lbs, or with bfg DR’s, the 275/50/15 weighs 25 and the 275/40/17 weighs 26, and again, because of it’s location it would have to be lighter to have the same effect as the smaller diameter setup.