Why do you guys think Mazda opt for 18” wheels rather than 17”? Aside from an aesthetic reason, I can't think of a reason. While I don't know how much the 18” weight, I'll bet an equivalent (same material and design) 17” would weight less and have less rotational inertia. Seems to me conserving unsprung mass is a priority for a car with modest torque. I will probably switch to light weight 17” for track use.

 

It seems like car companies are putting bigger and bigger wheels on cars due to demand. It used to be that 20" wheels (dubs) were massive. Now it is not uncommon to see them come stock. I think it is due to the bigger is better concept that is sweeping the car industy.

 

I agree, the most important reason IMHO that the RX-8 will come with 18'' wheels is that most people like big wheels. The same as with pick-up's and SUV's, we like big ones. But bigger is not always better (I mean for cars anyway):p .

 

The bigger the better... that's what everyone wants these days. At the Mazda 6 unveiling @ John Hine Mazda (San Diego) awhile back, Mark from Mazda R&D brought a silver 6 with 8 rims on it. They looked a lot better with 18s. There was one person who wanted the six with the 8 rims and thought they were a dealer add on. I smiled :D and Mark laughed. He said they are not available for the 6 because they are for the new Mazda RX-8 which is due out in the spring/summer.

 

Sheylen! your avatar tsk tsk tsk

 

Not only do 18s weigh more but the longer radius means less torque at the treads.

 

In order to fit big 323mm brake rotors they have to use 18 inch wheels.

 

Actually you can fit a bare minimum of a 17" rim on there, even with the upgrade brakes.

 

The only reason imo Mazda used 18's is for the "bling" and marketing value. I would have much preferred 17's for lower unsprung weight, better inertia and cheaper tires. Especially since the bigger brakes/rotors apparently will fit with 17's. Stupid North American "bigger is better" mentality..

 

How hard would it be to adjust the speedo if you change it to 17? Is it something that can be done yourself? I too think that it's kinda contradicting to put 18in wheels on a car that is supposed to be light weight, this is not a Z06! On top of that it is rotational weight, the worst kind of all.

 

I'd assume that they are lightweight rims.

 

If you keep the overall height of the 17" tire and rim the same as the overall height of the 18" tire and rim (which is HIGHLY recommended), no adjustment to the speedo is necessary.

 

There's Herc putting a positive spin on things again.. :p You need a job in PR not IT. :D

The point is that exactly the same rims constructed with the same alloy/design in a 17" size would weigh less and have a lesser rotational resistance than an 18" size. So no matter how lightweight the 18's are, 17's would always be lighter aotbe. Not to mention the much lower cost of replacement tires. There is no positive about 18" wheels.. just the "look"

 

Well if Mazda's reading *wink wink*

Nah, I don't care one way or another.. I figure the difference in price for tires will run at most maybe ~$100 more for the set of four, so it's not a huge setback... Just a minor one.

 

If I got an RX-8 and used it for track duty I'd probably buy some lightweight 17x8s and slightly smaller tires to shorten the gearing a bit. From reading the speeds at which each gear tops out at, it seems the RX-8 is geared on the long side, and some shorter, closer-ratio gearing would help give it some extra oomph.

 

Not always true. What if the alloy was actually lighter then the rubber. Bigger rim = lower profile tire = less rubber. I think a smaller sidewall would make a run-flat tire lighter. And less sidewall usually means less flex and more performance.

 

Even assuming the metal is lighter than rubber, I think the rotational inertia is still greater. Most of the weight of the wheel is concentrated on the rim. If you are going from 17in to 18in, you are moving the radius 0.5 in from the center. The rotational inertia is mass * r^2, assuming my calculations are correct, it would increased by 12%. As for the tire, it is losing that half inch of sidewall. Doing some basic math that comes out to about 55 sq in, or .382 sq ft of less rubber, which is not very much. I think it wouldn't overcome the effect of the rim. Maybe Buger or someone can jump in and do a more precise calculation.

 

Yeah but sidewall is a percentage of the width... So for example a 215/40/17 S03 is 24lbs, 225/45/17 is 25lbs and 225/45/18 is 27lbs. No matter how you look at it an 18" tire is usually heavier. And a 17" wheel assuming identical construction is lighter than an 18" wheel. I still say that the only reason Mazda is using 18" is for looks and marketing. So then a Nissan salesman cannot say that the Z or G35 coupe come with 18's while the 8 uses "only" 17's. Too bad..

 

What is the problem?

 

Sheylen is allowed to have a VW bug in his avatar isn't he? :D

 

okay, i'll make this blunt, and easy to understand: solid metal alloy is NOT less dense than thin rubber and assorted light material lamenant filled with pressurized air. for any given wheel of the same overall diameter, it will ALWAYS be lighter with a taller side wall and smaller rim+hub assembly, all other things equal.
'nuff said.

another thing, losing area of rubber on road doesn't necessarily decrease grip. it's late, so i'll explain again later if someone asks. it does in the real world, more so at the limit than normal driving, but statically, no.

 

That's good news. I can understand why Mazda went with the 18", straight up marketing. I have seen a fair number of S2000 owners complain about the fact that the car only comes with the 16". Most people who get aftermarket wheels for the S2000 end up getting 17" or 18". I ended up getting wheels with less than ideal offsets just so I could put a lightweight 16" on mine. Personally if I end up getting an RX-8, I would put some lightweight 17" on the car and sell the 18" to someone who got an automatic and would prefer the bigger wheels.

 

What are you talking about Buger? That is clearly an Audi TT in his avatar!
:D

 

Here's the solution to all your heavy-wheel problems: just fill them with helium instead of rgular ol' air! :D

-Stephen

 

Originally posted by zoom44
Sheylen! your avatar tsk tsk tsk

Originally posted by Buger
Sheylen is allowed to have a VW bug in his avatar isn't he?

posted by WankelWannabe
What are you talking about Buger? That is clearly an Audi TT in his avatar!

I think Buger knows best (as usual) it is a bug!:o