thirdgen

iTrader: (26)

I'm sick of looking at my Motegi's...I also did a little research about size/ heights.
I'd like a set of Nickel 15x8 6UL's, but (no offense to you cause I like the 6UL's) everybody has them. They are nice, and for the price, they're a great wheel.
I asked Emilio at 949 about fitment issues on my car ('99 with FM springs) with a 225 tire. He said a 225/45/15 would fit no problem.
I asked Brian Goodwin about them also, and he replied with "Folks use a 205/50/15 or 225/45/15 on those 15x8."
The reason I want a 225 is because I want my car to hook when I launch it, and it usually works out that the wider the tire (the more surface contact) the more traction I will get on launch. (Unless I'm missing something).
The reason I want a 45 series tire as opposed to a 50 series is simple. Everybody runs a 50 and I don't know why. The 45 is a lower sidewall which means less sidewall flex, and also a lighter tire due to less material.
Let's begin the wheel debate.
I like the 6UL a lot, a real lot. If I didn't go with Nickel, I'd go with Black. I also like the spoke wheel look such as the Konig Flatout.
Then I thought about it. Why run a 15" wheel? What's the reasoning??
I remember I weighed a wheel and tire from my car on my bathroom scale and it was like 33lbs?
My wheels are 16x7 Motegi's with Toyo Proxes 205-45-16's on them. That means it has an overall diameter of about 24".
According to tire rack, one of those tires is supposed to weigh like 21 lbs? There is no way my wheels only weigh 12 lbs.

A 15" 6UL with 205/50/15's...let's use the same Toyo as mentioned above.
The tire weight is the same, but the diameter is 23".
I don't understand what is gained?? It is a wide wheel, but the sidewall is also higher, but now the car will sit 1/2 lower?
A 225/45/15 tire would end up being the same 23" overall diameter. This would make my car sit 1/2" lower than it does now. Is that the gain the everybody is talking about?
Can you explain to me what is going on that I'm not seeing?

The offset of a wheel is the distance from it's hub mounting surface to the centerline of the wheel.
The factory offset of a 90-05 miata wheel is 40mm.
The 15x8 6UL comes in a 36mm offset and weighs like 12.6 lbs.
The 15x8 konig Flatout comes in a 25mm offset and weights 12.4lbs.
Then I found the Konig Helium in Black.
Miata Performance Parts : BLACK Heliums, 40mm Offset--11.4 Pounds : 16x7
It's a 16x7 and it only weighs 11.4 lbs. I really dig these wheels, and I could be a cheap-o about it and craigslist my motegi's and put my current tires on these new rims.

I don't like how the Konig Flatout with a 50 series tires looks...it makes the car look like it's sitting on big tires, in my opinion.

Miata's with flatouts: and 50 series tires:






So what do I do? Buy the 16x7's and keep my 205/45/16 Toyo's because I drive it on the street? Or buy 225/45's and 15x8 6UL's?? Or Konig Flatouts?
This drives me nuts...I want new wheels, but I don't want to make a purchase regret.

albumleaf

iTrader: (7)

You do realize that the profile of the tire is proportional to the width right? a 225/45 will have approximately the same profile as a 205/50.

thirdgen

iTrader: (26)

But the 50 will be a higher side wall...And isn't it wheel dependent? For instance, put a 205 on a 15x8 wheel and it'll be wider than if you had the same tire on a 15x7...

viperormiata

iTrader: (24)

Sidewall height = straight line traction

curly

iTrader: (25)

No, the 205/50 is the same sidewall height of the 225/45. that's why people run those two sizes, cause it'll keep the gearing the same for the speedo, and won't rub like the larger diameter 225/50s.

The way it was explained to me was that the sidewall number is a percentage of the width so 45% of 225 is 101.25mm, and 50% of 205 is 102.5mm. The 225/50 size, which has a number of inexpensive all season tires instead of just rs-3s and nt-01s, is 112.5, a whole centimeter taller. You can imagine the "issues". And then you have the stock size of 185/55-14 (for NAs) which is 101. See how that works? It's a far from perfect system, just like tire widths always vary from manufacturer to manufacturer.

RedCarmel

iTrader: (7)

205mm is 205mm.

The overall diameter difference between the 205/50-15 and 225/45-15 tires is .01" The overall diameter of your current 16" tires is about 0.2" taller than the 205/50-15 or 225/45-15 tires

thirdgen

iTrader: (26)

Ok...now I understand. I wasn't aware that the sidewall number is a percentage. I thought it was a measurement. That clears a lot up for me.
Now my other debate.
Let's compare what is going on when using these two wheels:
1) 16x7, 205/45/16 tire.
2) 15x8, 205/50/15 tire.
How different would these 2 wheels be? Or I should say, what is being changed about the car to affect handling?

RedCarmel

iTrader: (7)

The lighter the wheel and tire package the better. 8" wide rims would give 205mm wide tires more support in cornering and put you around a track faster.

18psi

iTrader: (76)

This is a street car. In which case go with whatever you like better. The difference won't be enough for you to feel any difference between the two, because it will take good suspension, good tires, and a decent driver, on a track, to show which shaves seconds off a lap time. None of those you have, at least right now.

I went with 15x8 50 because I wanted more sidewall for the crappy roads around here. If it wasn't for that, I would have gone 16x7 because as previously mentioned that size has a few decent inexpensive tire choices and 16's still look really good on an nb.

Doppelgänger

iTrader: (12)

You over-analyze too much lol.

Yes, tire size is called aspect ratio for a reason. Height is proportional to width and vise-versa. My 215-40/17 tire is a 23.9" diameter...on a 17" wheel....that weighs 14lbs.

Don't forget that tire diamter can be as much as .3" difference between tire models and manufacturers. Not all 205/50-15 tires are the exact same width and diameter....so don't get hung up on tenths of an inch....beconcerned at 1/2"+ in difference.

So pick either a 205/50 or the 224/45 based on the tire and compound you desire. After that, pick your wheel. Unless you are looking at 0-offset wheels, most anything is going to fit with little to no problems. Use intuition on width and offset though. Pretty much any 7-8" width in the range of 20-40 offset will not be a problem. Once again, width and offset of a wheel is proportional. 0-offset on a 6" wheel will not stick out nearly as far as on 8" wide wheel (as in a 2" difference)...eventhough you are saying "0 offset".

Finally, use Wheel Offset Calculator to help you understand how changing widths and offsets will affect the wheels position.