and then there's the radius too! don't forget. . . it's not JUST weight.

 

This thread is pretty helpful. I have Enkei 19's on my tC right now and I do feel a loss in power when accellerating. Larger rims are for show purposes mostly. I would rather keep 17's for daily driving and racing.

 

djct has it right. It's not necessarily a matter of increased weight (although this does come into play as well)

The thing that must be rotated here isn't mass, its called the "moment of inertia." Assuming an object with uniforma mass distribution and constant radius, this can be calculated by mass*radius^2.

So what happens when either mass or radius (or both) increase? I (moment of intertia) increases. Also, the more rubber you have on the road (like from wider tires), the more static friction that needs ot be overcome intitially to turn the wheel - also goes for higher performance tires that are "stickier." Actually, I'm not sure that mu(s) is really higher... its just that you have more rubber on the road. I'm sure you know what I'm talking abotu anyways.

someone correct me if I'm wrong, but I really don't think I am

Also, remember that true lightweight racing wheels don't really come in large sizes like 19... I think that they pretty much top out at 17 - there's a reason for that.

 

you're right paul34. . .

. . . one thing to keep in mind though: the majority of the mass in a wheel is on the out rim, thus the weight distribution is not uniform. That's why it makes such a huge impact to increase the wheel size-- not only do you increase the mass at the outer radius. . . you MOVE the entire majority of that mass to that extreme radius.

And you make a good point about width affecting performance. The ideal width of a tire is suited for the traction limits of the car (assuming you have selected the best tire compound/material). Anything larger than that is unnecessary. I.E., 315 width tires are uselss on a stock anything. . . save a torque heavy monster like a Viper or Corvette.

Also remember that the moment of inertia works both ways, in acceleration AND braking. With a loss of power you can also expect longer braking distances and more brake wear. All those cars rolling on 20"+ wheels are just accidents waiting to happen. The stupidest thing to do (performance wise) to a car since whistle "woo-woo" tips. Imagine a Yukon with 26" wheels trying to stop. . .

 

higher quality does not mean that it will provide higher efficiency in regards to gas mileage. i'm running on 19s, pretty heavy, bout 27lbs each, and i've gotten about the same gas mileage. I get around ~25mpg 50/50 on city/hwy. It's all dependant on your driving habit.

 

Also, the handling will change slightly too.

 

The quality really doesn't affect anything except durability (unless you mean high quality as in expensive and exotic alloys and materials).

Everything else is just physics. . . mass, diameter, weight distribution, etc. . . given all physical measurements are identical (which is unlikely), you would not be able to distinguish a high quality rim from a low quality rim in terms of performance. . . unless you use a butt-o-meter; the most worthless measurement of performance ever conceived.

However, you would see a difference aesthetically as well as the time it takes for the wheel to warp, damage, or fall apart.

And it is possible to upsize the rims without adversly affecting performance (if you go extreme light weight). But you will usually lose durability. However, an identically built wheel of a smaller diameter will ALWAYS out perform it.

 

I actually received a gain with my new set of wheels and tires.

Have to double check to see if this next tank of gas rings true but if anything it at least stayed the same.

I picked a stock width, offset, and height wheel purposely to preserve ride quality and MPG.

MPG is why I bought this car versus my old vehicles.

I picked a lighter weight wheel and a different set of tires and a proper alignment so I am not draging a tire down the road improperly after my drop.

The taller height tire should actually increase gas mileage but decrease acceleration since the gear is not as low any more but it is so minimal, it is not like we are low riding by using some 13 inch wheels and low pro tires like some do.

Tires do change in weight as well. Take a look at a manufactures web site and not tire rack or where ever else you might look since they just seem to put in generic weights. I was looking at some avons and compared them to some other tires and they weighed I believe 3-4 pounds more than some other tires which is a decent amount.

 

You WILL see a gain with that set up. . . just keep in mind that your speedo will be off (will indicate a slower speed than actual), as will your odometer and trip meters.

Therefore, you will have to adjust your MPG measurements (assuming you are using the trip meter) and adjust the indicated miles traveled for the actual.

The majority of mass in a wheel/tire combo is in the wheel itself. . . so with lighter wheels of the same dimensions, you will see increased HP (to the wheels), better braking, and better MPG. However, I'm not taking into account the change in gear ratios. With the increased tire height, effects in performance (acceleration) are hard to guess. It depends on driving style, rev limits, powerband, avg speeds traveled. But in general, a bigger tire height will usuallyt give you better mpg on the highway (at the same speed), but not always

 

I will figure out my exact gas mileage with the new setup and post back.

I am a bit picky on gas mileage and always check when I fill up.

I know the correct procedure to adjust for the extra tire height and will factor that in to see if the mpg goes up or down.

This is driving the same route back and forth to work everyday and I typically was getting only a 10 mile per tank difference before since I drive the same route and driving style.

See what happens, I will post back.

In terms of acceleration decrease with the increased height it seems minimal or not even noticeable but only a true time would tell but it could be offset since it does not spin the tires anymore when leaving from a stop which it would before.

Either way I am happy with the setup in terms of looks and comfort which is all that really matters I guess.

 

And despite my trash talk of super large rims (which you didn't get, thank GOD) and technobabble, your happiness is what ultimately matters. If you're happy with your purchase, then you made a good decision.