Henessey

would 18s slow the car down any?

if so would a 17 front 18 rear slow down an fd?

yes i just bought this car and no i do not want to make mistakes.

thanks

ptrhahn

iTrader: (9)

Make sure you buy very lightweight wheels (and tires!), be they 17 or 18, and you'll be fine.

Johnsrx7

17s will give you more cushion to take bumbs without damaging the rims.

aznpoopy

relatively speaking 17" will be lighter then 18" for the same type of wheel. even if you buy super expensive lightweight wheels the 17" version will be lighter then the 18". common sense.

rynberg

In most wheels, the weight increase between 17 and 18" wheels is only about 1-1.5 lbs. Many 18" tires are actually lighter than their 17" counterparts, so it is possible to end up with an 18" combo that weighs essentially the same as a 17" combo.

Pat McGroin

You should also take into account the overall diameter of the 17's and 18's with tires on.

Whalentire.com has a calculator which will tell you the diamter with different profile tires etc...

t-von

iTrader: (8)

The biggest deciding factor here is the weight that's further away from the center of rotation. I actually saw a situation on television where a car lost 5 whp while upgrading to a larger diameter wheel that was actually lighter than the original. The overall diameter between the two was exactly the same however, the position of the weight was moved further outward. I can't remember the exact explanation they gave how to explain it but this was the way "I" interpreted it.


Example: Go to the park and have a friend stand in the middle of a merry go round. Spin the merry go round and note the difficulty. Stop the merry go round. Now have that same person move to the out side edges and spin it again. It will be more difficult to get it moving. The overall weight didn't change just the position of it. Moving any weight further away from the center of rotation increases the rotational resistance(or whatever technical scientific term you wanna insert here). The laws of physics.

Henessey

thats what i figured
not in as deep as how you put it lol but yea thanks

FDNewbie

iTrader: (10)

But a lot of times when you go w/ wide wheels, the 18s are 3-piece wheels, which get pretty heavy... my 18 X 10 SSR GT3s are considered "lightweight" 3 piece wheels, weighing in at 26 lbs a pop! lol

Catharsis

you seem to have all the objective questions that cant be answered with an absoulute. maybe you should step back and read for a while.

GoodfellaFD3S

iTrader: (213)

I am very happy with my 17s, most people assume they are larger---i think some of it has to do with dialing in the ride height properly.

KevinK2

http://www.mazda6tech.com/files/wheel_inertia.xls

You can compare the inertias here. Just need wheel and tire weights and sizes. This spreadsheet uses 3 different methods to determine inertias ... they are close.

Assuming same circumfrence, you can determine wasted torque at each wheel, and the effective "bag of sand" weight penalty for the inferior combo.

For a road course, 18" allows mega brakes.

NeoTuri

iTrader: (2)

Moment of inertia

http://en.wikipedia.org/wiki/Moment_of_inertia

Mahjik

iTrader: (1)

What are you doing with the car? Road racing, autox, drag racing or just driving it on public streets?

If all you are doing is driving on the street, I wouldn't get all that worked up about wheel weights.

t-von

iTrader: (8)

Thx!

Henessey

road racing... im not some kind of street racer thogh

i just want power when wanter or needed.

a few trips to the track can be cool

rynberg

There's only a handful of people on this forum that are good enough drivers on the track to even begin to worry about a slight increase in inertia! If the wheels are 90% street use, just get some reasonably lightweight, well-made wheels that look good to you and don't worry about it...

speedfreak95

I BELIEVE IT IS CALLED ROTATING MASS. tHAT IS WHY GUYS WITH NICE DECKED OUT PRELUDES GO FROM FACTOY WHEELS TO HEAVY 20'S AND WONDER WHY THEY ARE SLOWER.

Mahjik

iTrader: (1)

IMO, probably the best bang for the buck wheel around right now (in 17's):

5Zigen Pro Racer GN+

Not too heavy, sturdy, cost effective and looks good.

connor@tirerack

What you are referring to is the effect of "rotational mass" the closer to the center the source of the weight is the less it will affect the outcome (acceleration or braking). The further out from the center that the source of the weight is the more it will affect the outcome. In other words if you take a 17" wheel that has a cast barrel section and thicker spoke towards the outside and compare it against a 17" wheel with a spun barrel and thinner spokes the first wheel would have a higher rate of rotational mass even though they are both 17".

The negative side to high rotational mass is that it take more power to start rolling as well as more braking power and longer distances to stop. Regrettably every wheel is a little different so it isn't something that can be generically figured by size. the effects of rotational mass can be different even between two wheels of the same overall weight. It simply depends on where the weight is distributed on the wheel.

To someone that is using the car as an every day driver rotational mass doesn't really mean anything. For someone that is using the car for track and especially auto cross then rotational mass can be very critical.