effects of bigger wheels-video
 

[ame="http://www.youtube.com/watch?v=r_IWa_qlt3g&feature=g-all-u"]5 Minutes to a Faster FR-S - YouTube[/ame]

Would have been nice if they had run 235/40/17s to compare the same width tires on the two different wheel sizes. They increased the gearing a fair amount with 235/40/18s also.

Good info but not the best testing IMO. I prefer 17s over the 18s regardless but hard to use the test as proof that 18s are worse because of the gearing issue and the width/weight changing.. could have been the 235 width more than the 18s, or could have been the 18s, but better testing would have revealed that.

Regardless of the absolute rigor of their scientific method, you have to admit it's food for thought. ;)

Those Advans are forged, are they not? Given that and the fact that they're not crazy wide, they should be one of the lighter 18 inch rims out there.

As for the gearing issue, I think tire rack has stats on tire diameter.


Edit: going full nerd;

Stock 17inch rim weight: 21.4lbs

Source:
http://www.ft86club.com/forums/showthread.php?t=7881

OEM tire:Michelin Primacy HP, 215/45/17
OEM tire weight: 20lbs
OEM tire diameter: apparently unknown :P

http://www.tirerack.com/tires/tires....lar=&tab=Specs


Dunlop Direzza Star Spec 215/45/17
Weight: 23lbs
Diameter: 24.6 inches

Dunlop Direzza Star Spec 235/40/18
Weight: 26lbs
Diameter: 25.4 inches

Agree that it would have been interesting for them to have tested a 235/40/17 Star Spec (especially on a lighter 17 inch rim):

Dunlop Star Spec 235/40/17
Weight: 24 lbs
Diameter: 24.4 inches

Source:
http://www.tirerack.com/tires/tires....lar=&tab=Specs




;)

Mazdaspeed 3 stock tires:

Dunlop SP Sport 2050
P225/40R18 Y-speed rated high-performance summer tires
240 AA

WRX stock tires:

Dunlop SP Sport 01 235/45R17 Summer High Performance Tires
280 AA

Star Specs:

215/45/17
200AA

While I'm impressed that a set of tires could put the BRZ in front of these two cars on the track, I'd be willing to bet that if you fit the Star Specs to the MS3 and WRX they would still be quicker than the BRZ.

In the end...we need more hp. :)

Not sure on the Advans.

Those tires are .8" larger than stock, which is a decent amount.

What they are attempting to say is that 18s are bad, but they changed more than just diameter which actually makes the statement invalid. A proper test would have been like GRM has done (same tire and wheel, just diameter of wheel changes).

And GRM has found that larger wheels CAN be faster to a point, but that's too general to say 18s are faster since there are many factors.

For this specific car a valid test, IMO, would have been:
Stock
Stock wheels with 215/45/17 good tires (like the star specs they used)
17x8 (or 17x9 pref) Brand X Model Y wheels with same good tires as above but in 235/40 or 245/40 tires.
18x8 (or 18x0..) Brand X Model Y wheels with the same tires as the above in 235/35 or 245/35 depending..

Exactly what I was thinking.. Good to watch nonetheless

The Advan RGIIs are 1-piece cast. They're lighter than stock wheels, but certainly not as light as a forged wheel can be.

Just for reference, here's a 18x10 (closest I could find).

http://farm8.staticflickr.com/7151/6...29849164_b.jpg

wish this video was a bit longer and detailed, but a good reference point for rubber and wheel shopping.

Physics, it's all physics
 

I was thinking this through last night and came to the conclusion that bigger may not mean better (but Yes they look oh so good). Take this into consideration. We will concentrate on acceleration and deceleration in this example only. Road holding will be another issue for later.

Lets compare the stock wheel tire set up with a wheel tire set up that is just 1" bigger. So lets compare the stock 17" to a set of 18". But consider that everything is the SAME. Same tire, Same wheel etc. But the only thing is that it is a 18" wheel. Lets also say that the weight of the tire is the same as the 17" and the wheel weight is also the same. I know this would be hard to compare in the real world, but lets use Physics.

So lets just look at the wheel. If we bump out the wheel from 17" to 18" this will cause the outer mass of the wheel to be a 1/2 further out from the axle.

And if you look at the tire mass. Now the decrease in series tire, to keep the overall wheel tire diameter the same, would mean the tire is thinner, but also that the overall bulk of the tire weight will also be further from the axle.

Now if you put this together it means that YES the overall weight of the tire wheel combo is the SAME, BUT the MASS of the wheel tire combo has MOVED further away from the axle. This means that it would take the car more energy to cause the wheel to turn, thus, a slower acceleration and stopping.

So in reality it is not the fact that getting BIGGER wheels is what slows down the car in acceleration and deceleration, IT IS the FACT that you are MOVING the mass into an area that is less advantageous.

Take this example, put a wheel that is 13" with a tire that makes the same overall wheel size as the stock 17". This would give you a huge increase in acceleration due to not only the wheel being lighter due to size, but all the major mass is very close to the axle.

SOOO, if you want to increase you wheel to an 18" you will have to make a change somewhere to keep your speed. Either a major reduction in wheel tire weight, or boost the horsepower.

There is your physics lesson for today. Anything else I can help with?:happy0180:

What you're saying is simple increasing the width pushes the mass further from the axle . . .
thereby decreasing acc-/de-celeration.

But what if you keep the width the same, weight the same, but simply increase the height
only. go up to 18 (or 19) and keep the width at 7.5

that may keep the gains the same.

in addition, in the video those 18s still produced a noticeable gain over the stock set-up.

Still moving mass
 

You are STILL pushing the mass further from the axle. That's still happening. Now the question is how much different does the car drive? I'm just pointing out the physics and what changes happen with tire size increase. My example before assumed the width was the same. :happy0180:

Sigh, i guess its back to the drawing board once again.

Road & Track does a test with tires on a FR-S
 

http://www.roadandtrack.com/highligh...-a-faster-fr-s

Bigger isn't always better. But then we all knew that.

-J

Very true, but damn my 8 in wide wheels look hella good on my car...https://sphotos.xx.fbcdn.net/hphotos...47869035_n.jpg