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Hey guys. I'm new here.

I have the stock 195/60 R15 tires and stock rims on my ZX3 Hatch right now...I want to upgrade to 205/50 R16 with new 16" rims.

I work in a shop and one of the mechanics said it would be a bad idea to change the stock rims and tires due to gear ratios and what-not. That makes perfect sense, but will upgrade my rims by one inch really affect my performance?
 

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205/50/16 is what came stock for the Foci with 16's factory. you're not going to have a problem. . .
 

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It'll affect the gear ratios? Who's this mechanic?

It will affect the speedometer based on the fact your tire/wheel combonination is a different size, therefore rotating at a different speed. This will affect what your speedometer's reading and only varies slightly depending on the size difference between the original combination and the new one.

You will have a slightly stiffer sidewall due to a smaller tire sidewall and more rim being in the void space than a tire. You will also have more mass a little bit further from the center of the wheel which will rob you of some power. However, the tires available in the 16" size and the sidewall stiffness will improve the handling from your current 15" set up. You will most likely have less unsprung weight since you'll be going from steel wheels to a lighter alloy wheel. You'll also get a wider rim that can support a larger section width for your tire. This will lead to better braking and acceleration traction, and your lateral grip will increase tremendously (depending on the tires you choose, but definitely has the capability).

I would go with a 225/45/16 tire if you have the option. It will have a slightly lower profile, but you'll have a noticeable gain in tire width (over 15%), which will net you much better traction (think safety on top of handling performance).
 

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Discussion Starter #4
I knew the stock 16's were that tire size, and I told that to the mechanic, but he insisted that my focus and the 16" focus had different gear ratios, but he is also a chevy tech...are you sure there will be no problems?

Oh yeah...My car is lowered....I THINK 1"...but I am not sure, because I bought it like that
 

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puddins betch
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u only have to worry if the overall dia. changes and if you reprogram the car u can correct the speedometer ur self as well as go up to 18's if you want and not change much but the ride
[:)][:)][:)][:)][:)][:)] if u keep the same O.D. every inch u go up in wheels you will take a inch from the side wall of the tire and that will give u performance and take away from the comfort of the ride a little

the stock O.D. is 24.21" ( 05 ses ZX3) that has 16" wheels... falken makes a few whells for a focus and tires for them too. i have three quotes on them and they all have a O.D. btween 24.61-24.71 and they are 17's im looking at ,only a half a inch wont afect the sped. too much but it will show in the ride of the car
look in to a set of 16" al. wheels from a ses or svt or any other focus of the same year and it should swap right out w/o problems
 

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Oh yeah, I forgot one other thing. The offset of the wheel will be different, which may or may not have an affect on your handling (perceived that is) depending on how different the offset is from stock.

It will not hurt anything if that's what you are concerned about. It may change your speedometer reading slightly, but that's it (not because of gear ratios - have no idea where the hell is pulling that BS from - but because of a slightly different circumference for the new wheel/tire combo).

The biggest difference and best benefit of going from a 16" wheel from a 15" wheel is the wheel width. You can fit a wider tire, and that's always the best way to gain more traction in all directions.

If you want to see what various tire sizes you can use for the 16" wheel to keep the 15" OE setup as close to the original speedometer rating, check out this site. Keep in mind, all speedometers are inaccurate to an extent.

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

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Sückn' n Blown
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Miata is right.

1 mile = 63,360 inches
63,360 / 73.67 = 860.05

That tire size worries me. A 205/40 doesn't leave much of a sidewall for wheel protection and ride quality.
 

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OT:
I ran 205/45/17 and the ride was harsh when hitting the little bumps.
I recently changed over to 215/45/17 and the ride is much better.

And yes, my ECU has been reprogrammed to compensate for the new tire diameter.
 

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microtonal said:
OT:
I ran 205/45/17 and the ride was harsh when hitting the little bumps.
I recently changed over to 215/45/17 and the ride is much better.

And yes, my ECU has been reprogrammed to compensate for the new tire diameter.
I am looking to upgrade my wheels from the stock 16 inchers to some 17 inch wheels. When I took a look a the wheel and tire information on this site, it said that the recommended size is 205/45/17. Should I be looking at 215/45/17 instead? Also, in order to reprogram the ECU, did you have to purchase a chip or did a dealer do that for you?
 

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I recently upgraded mine from the factory 16X6.5 wheels with 205/50R16 Pirelli P6's to 225/45HR17 Yokohama AVID H4S tires on Mille Miglia 17X7 wheels, and other than the slight speedo error (which I intend to correct as soon as I get my Xcal-2) I see only improvement.....in ride quality, less noise than the stock Pirelli P6, better handling and it sure looks good. the tires are 1 inch larger in diameter than the stockers, and fill the wheel wells a LOT better. NICE!

[cheers]

Dave
 

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The 215/45/17 make the speedo a little slow so if you compensate, it's not too big of a deal.
I had mine adjusted via a reflash to the ECU but a chip or XCAL can do the same.
But beware that the larger tire you go, the more HP you rob at the wheels and also alter the gear ratio as mentioned. I believe larger tires than stock will make the car seem like it's reving up/speeding up slower due to the larger diameter.
Also, if you have a 2" or greater drop/lowering and do not have the proper wheel offset, you can run into rubbing issues as well.
 

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You can go to TrieRack.com, go to the upgrade garage, put new wheels on your current, and it'll show you the reconmmended tire size.
 

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True, but I don't notice much change, at least not in normal driving. I'm an old fart, so I'm not interested in gofast stuff anyway. SUUUURRE I'm not..... [race]

Dave
 

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Excellent information guys. I have the SVT suspension on my car, so if I do go 17's, I might just stay at the recommended 205/45/17.
 

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an easy way to get fairly close in size is use a simple method +10,-10,+1


a 195 60 15
+10-10+1
=205 50 16

This will always get you within a few millimeters of stock, and that is fine, considering a new tire verses an old tire loses over 3/4's of an inch in diameter as it wears out.

You can continue the pattern as well, for the same 195 60 15 to convert to 17"..

+20-20+2 = 215 40 17 (205 45 17 would be within that range also)
 

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Changing your overall diameter will not change the actual gearing but it will cause an "effective" gearing change. In other words, your RPMs at a given speed will be different from stock.
 
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