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Discussion Starter #1
Couple of issues, would like more rubber on the road, so dropping a series and going 10mm wider SHOULD fit on our stock rims. Question, will it affect the GPS/Nav system? I know it uses gyros and wheel speed input in addition to the GPS signal. Would this cause problems? I'm not an expert, but I believe this would give a different rotational circumfrence. It's caused speedo problems in previous vehicles I've owned with speedo accuracy. How bad would it F with the nav system? I'd like to do this before I go to Texas World Speedway in December for the Porsche club event, 215's just seem too skinny for the track! I'm considering these:

http://www.tirerack.com/tires/tires.jsp?ti...yes&place=8

Anyone done this and what is the end result???
 

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Couple of issues, would like more rubber on the road, so dropping a series and going 10mm wider SHOULD fit on our stock rims. Question, will it affect the GPS/Nav system? I know it uses gyros and wheel speed input in addition to the GPS signal. Would this cause problems? I'm not an expert, but I believe this would give a different rotational circumfrence. It's caused speedo problems in previous vehicles I've owned with speedo accuracy. How bad would it F with the nav system? I'd like to do this before I go to Texas World Speedway in December for the Porsche club event, 215's just seem too skinny for the track! I'm considering these:

http://www.tirerack.com/tires/tires.jsp?ti...yes&place=8

Anyone done this and what is the end result???
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WHAT?? Who told you that, man? The only thing using wheel speed sensors on this car is the ABS; that nav system is bought out on a contract; I bet you it doesn't even interface the ECU at all.

Anyway there's no reason it should need wheel speed information. It can detect a velocity from the GPS information alone.
 

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Do the calibration settings on the nav options. I have nav on both of my cars and you have to reset the calibration when you change the tires. You should be OK. The speed sensor should then recalibrate. By the way...there aren't any gyros...they are actually tuning forks. Sounds weird but true. Your speed will be 56.7mph when you are going 60MPH on the dash. That could add up to some excess miles pretty quick.
 

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Discussion Starter #4
WHAT?? Who told you that, man? The only thing using wheel speed sensors on this car is the ABS; that nav system is bought out on a contract; I bet you it doesn't even interface the ECU at all.

Anyway there's no reason it should need wheel speed information. It can detect a velocity from the GPS information alone.
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Hmm, then how does it keep track of my location when I'm in a 6 level parking garage and I lose the GPS signal? If you have the Nav system, you know that the GPS symbol goes disappears when your in a parking garage and it can't read the satellites, but it still can keep track of which diection you are pointed and how far you've gone, pretty damn accurately, I must say

explain that if it doesn't use wheel speed and gyro info?
 

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He's wrong.

It uses speed sensors....how do you think it cuts out all of the menu items when you go over 1mph?
 

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Discussion Starter #7
Do the calibration settings on the nav options. I have nav on both of my cars and you have to reset the calibration when you change the tires. You should be OK. The speed sensor should then recalibrate. By the way...there aren't any gyros...they are actually tuning forks. Sounds weird but true. Your speed will be 56.7mph when you are going 60MPH on the dash. That could add up to some excess miles pretty quick.
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Awesome, great info, thanks!

Obviously I've only done a cursory read of the GPS part of the manual, it's more like a book :)
 

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Discussion Starter #9
He's wrong.

It uses speed sensors....how do you think it cuts out all of the menu items when you go over 1mph?
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Figured he didn't have Nav, but didn't want to be an ass :)
 

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Yeah a steering angle sensor. No gyro....they call it that for "lay man" reasons...but it's actually a tuning fork.
 

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Discussion Starter #11
The stock wheel is too narrow for 225/35/18. http://www.tirerack.com/tires/Spec.jsp?mak...35YR8GFTAKDW2XL
Look at rim width - the minimum width you need is 7.5 inches. 225/45/18 will work w/ the stock wheels.
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really? I wonder why Mazda didn't put them on then? I also thought to up 10mm you needed to drop a series, like for 45 to 35. Again, I'm no wheel/tire expert, but in my old 240z, that's what we did to go from 225's to 235's...If so, it's actually save me some money, 35 series tires are STEEP :)


gyro in dvd unit IIRC, but there is also a sensor in the steering wheel.
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Good data, thanks. Beyond that, no adverse affect on the car?
 

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From the european shop manual, there is a GPS inside the DVD/Nav unit. The DSC unit sends wheel speed to the nav unit. Reverse switch also sends input.
 

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From the european shop manual, there is a GPS inside the DVD/Nav unit. The DSC unit sends wheel speed to the nav unit. Reverse switch also sends input.
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So, is anyone actually running 225/45/18? Do they fit without any rubbing?

There are certainly more choices in 225 than in 215! 225/40/18 has even better pricing and more choices although they will give a ridius that is 6.75 mm smaller (~1/4 inch).
 

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Discussion Starter #14
So, is anyone actually running 225/45/18? Do they fit without any rubbing?

There are certainly more choices in 225 than in 215!
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see, this is what kills me, if 225's fit the existing wheels, wouldn't it follow that Mazda would run with them? Or is it a CAFE thing for mileage?
 

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225/40/18 is better choice than 225/35/18. 225/45/18 is even safer but i don't like running taller tires as a rule of thumb. I ran a 225/40/18 on an 18x7 for 4 years with no problems. BTW i used to work at an aftermarket wheel and tire shop so i would never put something on my own car that i knew would be unsafe.
 

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225/40/18 is better choice than 225/35/18. 225/45/18 is even safer but i don't like running taller tires as a rule of thumb. I ran a 225/40/18 on an 18x7 for 4 years with no problems. BTW i used to work at an aftermarket wheel and tire shop so i would never put something on my own car that i knew would be unsafe.
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225/40/18 is not recommended for a 7" rim. Same link as above - 7.5" is the minimum recommended.
 

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So, is anyone actually running 225/45/18? Do they fit without any rubbing?

There are certainly more choices in 225 than in 215! 225/40/18 has even better pricing and more choices although they will give a ridius that is 6.75 mm smaller (~1/4 inch).
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I am running 225/45/18s - no rubbing.
 

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I am running 225/45/18s - no rubbing.
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based on the pic in your sig, you are not on stock wheels though. The poster is asking if they will work on stock rims.
 

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based on the pic in your sig, you are not on stock wheels though. The poster is asking if they will work on stock rims.
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I was going to specify that I didn't have stock wheels, but since my wheels are .5 inches wider and they have an offset of 50 vs 55 for the stocker - making my wheels that much closer to the fender, and being that I don't rub, certainly the stock wheels mounted w/ 225/45/18s shouldn't rub...I should have noted I wasn't on stock wheels.
 

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Discussion Starter #20
So, is anyone actually running 225/45/18 on stock rims? Do they fit without any rubbing?
There are certainly more choices in 225 than in 215! 225/40/18 has even better pricing and more choices although they will give a ridius that is 6.75 mm smaller (~1/4 inch).
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I don't think this was ever answered. Did anyone say they ARE running 225/45/18's on the STOCK rims? How are they working?

Trying to decide between going wider to the 225s on stock rims or lowering the rotational mass with new, lighter wheels (keeping 18x7.5) and sticking with the EOM 215 tires. With the upcoming CAI purchase, I can't afford both new wheels and tires at the same time....
 
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