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Discussion Starter · #1 ·
Ditched the original 195/55-15 tires as soon as they wore out, and went to 205/50-15. Fairly common mod. I've been through a few sets of 205s since then, of various makes.

That works fine. But I'd like something slightly taller to fill out the wells (which look cavernous at stock ride height on 205s), and a bit more contact patch never hurts.

There's a special on the BF Goodrich g-Force Sport right now. I've liked Goodrich tires in the past on other vehicles. And they are available in 215/50-15. If this car were lowered at all, I'd rule them out at once. It's on OEM springs, though.

I have a vague recollection that some of the JDM ITRs used the 215/50 size without rubbing or clearance issues. But they may also have had slightly different offset in the wheels.

Any thoughts, warnings, confirmations?
 

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What's the width and offset of your wheels?
 

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the 215 is the width, not the height. the 50 is the height... if you want taller tires, you have to go to a 55 or something...
 

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NO. JDM ITR '98 Spec is 215/45-16.
You can't just fill out your wheel wells. The OEM springs still use all of that suspension movement space. If you want to get rid of the gap, first get springs with a higher spring rate & shocks that can complement them.

However, 215/50-15 will still fit the car, but they are 4.168% larger diameter than stock, which is not really a good thing.
 

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Discussion Starter · #5 ·
What's the width and offset of your wheels?

6-inch, 45 offset.

If I had this suggested to me years ago, I would have said, "6 inches is not wide enough for a tire with a 215 tread width. The sidewalls will curve outward from the edge of the rim and they will flex under dynamic loading. Handling will feel squirmy. You want a rim edge that aligns pretty closely with the sidewall."

But later on, I drove a friend's vehicle with a wide tread relative to the wheel width, and a curved sidewall, and empirically, it felt and handled fine. I later did the same thing on a car of mine (not the current GSR) and had good results from it.

Warning: this may well vary with the choice of tire. Some tires would, I think, be unsuitable for that kind of fitment.

I myself specifically look for a tire with very stiff sidewalls to begin with. Some so-called "performance" tires have sidewalls so soft that I can grab them in oNE hand on the tire shop floor and bend the sidewall half over on itself with hand pressure. (example: certain Pirelli and Sumitomo tires.)

I have strong hands, but still, sheesh. Other performance tires given the same test with the same strength display almost no flex under load, and that's the sort of tire I like to buy.
 

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DoNT FORGET! it's also who makes the tire and what tire it is. you have to find out the tread width on the tire itself. for example: the 205 azenis have 7.6" tread width...but the 215 hankook ventus has tread width of 7.6" also. make sure to look at that when make your choice.
 

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cannibalsnax on Jan/31/06 said:
the 215 is the width, not the height. the 50 is the height... if you want taller tires, you have to go to a 55 or something...
50 is not the height. It is a FUNCTIoN of the height. The height of the tire is determined by both the WIDTH of the tire and the ASPECT RATIO of the tire.


Chris, do you do any auto-x-ing or tracking? As long as you fit the recommened tire width on the rim spec, you will be fine daily driving.

It is when racing that you should choose an optimum tire width for the width of the rim for best handling.
 

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Discussion Starter · #9 ·
the 215 is the width, not the height. the 50 is the height... if you want taller tires, you have to go to a 55 or something...

50 isn't the height, it's the "aspect ratio". It's not a dimensioned number as the height would be.

The first number, 215, is the width, and it is a dimensioned number (in this case, dimensioned in millimeters).

The second number, the 50, is a dimensionless ratio. You use that to compute the sidewall height as a function of the first number (the tread width).

A 215/50 tire has sidewall height 215mm * (0.5) = 107.5mm. (or 4.23 inches for those who still use Fred Flintstone units).

Let's do that same math on the current tire, the 205/50-15. Sidewall height = 205mm * (0.5) = 102.5mm sidewall height.

The 215/50 is thus in fact a taller tire than the 205/50.

Remember also that in computing overall tire height, there are two sidewalls to be taken account of, top and bottom. I've forgotten that once or twice and been left scratching my head.

For more on aspect ratio math:

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46
 

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Discussion Starter · #11 ·
RoadRacer02 on Jan/31/06 said:
DoNT FORGET! it's also who makes the tire and what tire it is. you have to find out the tread width on the tire itself. for example: the 205 azenis have 7.6" tread width...but the 215 hankook ventus has tread width of 7.6" also. make sure to look at that when make your choice.
Excellent point. There is a lot of variation between manufacturers and within individual manufacturers' lines.

I don't have the spec on the actual tread width for the 205/50 tires currently on the vehicle. Will measure that.

Per the Tire Rack, the 205/50-15 BFG g-Force has an 8.4" section width. (SW == sidewall to sidewall width)

The 215/50 in the same line has an 8.9" section width.

Assuming the current 205s and the BFG 205s are roughly comparable in section width, the move up to the 215 would mean roughly a one-half-inch increase in overall tire width, or one-quarter inch wider on both the inside and the outside.
 

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Discussion Starter · #13 ·
timpac167 on Jan/31/06 said:
Chris, do you do any auto-x-ing or tracking? As long as you fit the recommened tire width on the rim spec, you will be fine daily driving.

It is when racing that you should choose an optimum tire width for the width of the rim for best handling.
This vehicle is currently a daily driver, and is pretty much certain to stay that way, at least for the lifetime of this set of tires. Used to like to autocross, but am just too busy with the rest of my life right now to even think about it.
 

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Discussion Starter · #14 ·
Zuul on Jan/31/06 said:
NO. JDM ITR '98 Spec is 215/45-16.
You can't just fill out your wheel wells. The OEM springs still use all of that suspension movement space. If you want to get rid of the gap, first get springs with a higher spring rate & shocks that can complement them.


Here's my own reasoning and experience in the matter.

When you go to a tire with a sidewall of lower actual height (assuming constant wheel diameter) two things happen.

The first is that the car itself sits slightly lower (because the reduced height of the tire sidewall between wheel and ground causes the axis of the wheel to sit lower, and the rest of the vehicle follows that.

The second is that there is slightly more clearance between the top of the tire and the fender. The top of the wheel rim remains at roughly the same distance from the fender (both rim and fender have moved downward in response to the shorter *lower* sidewall). But the shorter actual height of the *upper* sidewall increases the distance between the top of the tire and the bottom of the fender. Thus more reveal.

A taller sidewall (in actual height terms) goes the other way. The vehicle will sit a bit higher. And the distance from tire top to fender bottom will get smaller.

Note that this analysis excludes the way in which the flexibility of the suspension slightly alters the input. A lower sidewall lowers the wheel axis x mm. But the car itself may not necessarily decrease in height by x mm precisely, because the body of the car is not fixed in a rigid relationship to the wheel (which is a good thing :).

Quote: However, 215/50-15 will still fit the car, but they are 4.168% larger diameter than stock, which is not really a good thing.
I'm too pressed for time to run the math myself, but I quickly pulled up the very convenient Tire Size Calculator which someone wrote a few years ago:

http://www.miata.net/garage/tirecalc.html

I've never had this applet disagree with my own hand calculations. Using it to compare the stock 195/55-15 to a 215/50-15 shows almost no overall diameter change.

The 215 is significantly *wider*, yes.

TireRack also show from the BFG spec tables:

215/50-15 g-Force: 23.5" overall diameter

195/55-15 g-Force: 23.4" overall diameter

Not a big change from stock diameter.
 

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It is sometimes called "sidewall height", since that is technically what it describes. But a 205/50R15 will NOT have the same sidewall as say, a 225/50R15.

The "50" means that the total height of the sidewall is 50% of the tire's width. When I say total height, you must add the sidewall height at the 12 o'clock and 6 o'clock to get the true sidewall height.
 

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i know all that, i was using it in a descriptive way. the 205 is descriptive of width, not height, and in his post he used it as a descriptive of height.
 

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Discussion Starter · #17 ·
Run the same size tires front/rear.

I'm curious as to your reasoning.

Due to vehicle dynamics and handling?

I wouldn't do it myself due to wear and economics. I've found that tire service life is at its highest (especially on hot FWD imports) with frequent rotation, both left to right and back to front.

Have never talked to an NSX driver about tires, but have talked to plenty of 911 and M3 drivers. They have different sizes front to rear as well.

It's not uncommon on those vehicles, with the highest performance tires, to spend more than $1500 for a set of tires, and have them down to the wear bars at less than 10K miles. Yikes.
 

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Discussion Starter · #18 ·
in his post he used it as a descriptive of height.

I said, "Huh? I didn't say that, did I?"

But I went back and looked at the original and sure enough, I had said that the wheel wells "look cavernous at stock ride height on 205s".

And I can see how that could get misparsed. Apologies. I should have said, "at the sidewall height of a 205/50".
 
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