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Discussion Starter #1
Hi guys,

My 2008 wears a 235 45 17, she is due for new tires..I was thinking of going smaller 225 45 17...is there any reason that this is not a good idea?

My reason for the narrower tires are for mpg and better traction is rain and light snow.
 

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I don't think you'll see much better traction. 225 vs 235 isn't a huge jump.

Your speedo will be off. One of the tire calculators will tell you what %. Just google Miata tire calculator.
 

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The difference in height and tread width of the two tire sizes, in my opinion are minor. Your probably better off selecting the best tire based upon reviews and your driving style / environment. If you live in the snow belt and above, maybe your budget can afford some snow tires on separate rims.
 

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I don't think you'll see much better traction. 225 vs 235 isn't a huge jump.

Your speedo will be off. One of the tire calculators will tell you what %. Just google Miata tire calculator.
This is a very good tire size calculator because not only can you compare 4 additional sizes (compared to stock size), it'll also show you all the brands and models of tires that 1010Tires (a Canadian retailer) sells for each alternate size:

http://www.1010tires.com/Tools/Tire-Size-Calculator
 

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Discussion Starter #6
Yeah, I kindda know I'll probably stick with OEM size but I am just wondering because smaller tires are better for fall winter condition and better on mpg too. I don't think I can afford 2 sets of tires now....plus a new set of rims.

Ok thank you ...this forum is the best ;ol;
 

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Yeah, I kindda know I'll probably stick with OEM size but I am just wondering because smaller tires are better for fall winter condition and better on mpg too. I don't think I can afford 2 sets of tires now....plus a new set of rims.

Ok thank you ...this forum is the best ;ol;
Buy a used set of winter tires (205 or 215 ?) mounted on rims on CL.

Some used rims with A/S (?) tires for $200:

http://portland.craigslist.org/clc/pts/4666453241.html

Bunch of rims:

http://portland.craigslist.org/mlt/ptd/4659023603.html

Cheap but usable winter tires (prolly good for 2-3 winters):

http://portland.craigslist.org/clk/pts/4660855263.html

http://portland.craigslist.org/mlt/pts/4655005241.html


Or also go check out Garry Small SAAB in PDX, they might have something too.
 

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Discussion Starter #8
Buy a used set of winter tires (205 or 215 ?) mounted on rims on CL.

Some used rims with A/S (?) tires for $200:

http://portland.craigslist.org/clc/pts/4666453241.html

Bunch of rims:

http://portland.craigslist.org/mlt/ptd/4659023603.html

Cheap but usable winter tires (prolly good for 2-3 winters):

http://portland.craigslist.org/clk/pts/4660855263.html

http://portland.craigslist.org/mlt/pts/4655005241.html


Or also go check out Garry Small SAAB in PDX, they might have something too.
Thank's the recommendation.....yeah used winter tires might be a way to go...but getting those metal rims...that's gonna destroy the look on my car...haha
 

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It's winter. Everyone's car is dirty anyways.
 

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Personally, I'd go with a tire that is slightly larger.

Two reasons:

1: The oem speedo has about a +2mph difference "baked" into it's readings. This is common for just about all oem speedos. This means, that typically, at 55mph, your speedo shows 57mph. A larger tire will help to negate this difference and bring the oem speedo readings closer to actual speeds.

2: Ride comfort. I know the "trend" nowadays is lower profile for looks, but I prefer something more towards the comfort side. If I want something for "looks", I'll lower my ride height a bit. Seeing as how this will also stiffen up the suspension, I'll take whatever comfort I can get out of my tire size.

possible alternatives to oem size of 235/45-17 that would get your speedo to a more accurate "actual" speed would be:

245/45-17, 225/50-17, or 235/50-17

I believe the oem 17" wheels are 7.5" wide. The 245/45-17 tires would be both wider and have a slightly larger overall diameter. If your wheels are less than 7.5" wide, then I would not go with those, as this tire size is recommended for 7.5"-9" width wheels.

225/50-17 would be a skinnier tire with a larger overall diameter for road comfort, which may be better for snow/ice conditions.

235/50-17 will be the same as oem width, but have a larger diameter for road comfort.

That's my $.02. It's a purely subjective topic, but maybe my opinion and reasonings will be of some use to someone.
 

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I agree with Roscoe. I settled for a 225-50-17 just to give me a little more sidewall with the added benefit of getting closer to the actual MPH. I run the Altimax HP during the summer. I have Firestone Winterforce 215-60-16 for my winter set on my 9-5 with no rubbing, your results may vary.
 

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Discussion Starter #12
Personally, I'd go with a tire that is slightly larger.

Two reasons:

1: The oem speedo has about a +2mph difference "baked" into it's readings. This is common for just about all oem speedos. This means, that typically, at 55mph, your speedo shows 57mph. A larger tire will help to negate this difference and bring the oem speedo readings closer to actual speeds.

2: Ride comfort. I know the "trend" nowadays is lower profile for looks, but I prefer something more towards the comfort side. If I want something for "looks", I'll lower my ride height a bit. Seeing as how this will also stiffen up the suspension, I'll take whatever comfort I can get out of my tire size.

possible alternatives to oem size of 235/45-17 that would get your speedo to a more accurate "actual" speed would be:

245/45-17, 225/50-17, or 235/50-17

I believe the oem 17" wheels are 7.5" wide. The 245/45-17 tires would be both wider and have a slightly larger overall diameter. If your wheels are less than 7.5" wide, then I would not go with those, as this tire size is recommended for 7.5"-9" width wheels.

225/50-17 would be a skinnier tire with a larger overall diameter for road comfort, which may be better for snow/ice conditions.

235/50-17 will be the same as oem width, but have a larger diameter for road comfort.

That's my $.02. It's a purely subjective topic, but maybe my opinion and reasonings will be of some use to someone.
Wow this is very helpful....I am curious if I run a larger tire 245 45 17, would it effect my mpg? maybe 0.5??

So in a summary:
look= 245 45 17
comfort = 235 50 17
winter driving + comfort = 225/50/17 ?? mpg gets better too??
 

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Wow this is very helpful....I am curious if I run a larger tire 245 45 17, would it effect my mpg? maybe 0.5??

So in a summary:
look= 245 45 17
comfort = 235 50 17
winter driving + comfort = 225/50/17 ?? mpg gets better too??
I wouldn't say any of them are for "looks" if you want a lower profile. They will all give you a slightly larger sidewall/overall diameter.

245/45-17 = wider/larger sidewall: good for comfort and maybe added traction in dry/wet conditions.

235/50-17 = larger sidewall: good for comfort.

225/50-17 = skinnier/larger sidewall: good for comfort and maybe better for snow/ice conditions.

"looks" is usually associated with a lower profile, so you'd be going with something of similar width but shorter sidewall, like 235/40-17 or smaller.

something both skinnier and shorter might also give a bit of "stretch" that would effectively reduce the sidewall even more, but it'd be a very small effect given that our wheels are only 7.5" wide.

also keep in mind that a smaller profile tire will likely increase the speedo readings, so the usual +2mph reading at the speedo may become closer to +3 or +4mph. you can either have the speedo recalibrated, or just live with it.
 

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Hi guys,

My 2008 wears a 235 45 17, she is due for new tires..I was thinking of going smaller 225 45 17...is there any reason that this is not a good idea?

My reason for the narrower tires are for mpg and better traction is rain and light snow.
You will lose some load rating by going to a smaller tire. a 235/45-17 is load rating 94, while a 224/45-17 is load rating 91. At least for a couple of tires I pulled up on tirerack. This isn't the end of the world, but you could get into possible legal issues, and some shops might not sell you undersize tires.

I agree with everyone who said "get winter tires for winter".

For better MPG, you really don't want to reduce the diameter of the tire, but you do want to reduce the width. So you're looking more at a tire like 215/50-17, which has load rating of 95 and is a touch bigger in diameter than your tire (depending on manufacturer etc.) Of course tires come in a plethora of sizes, so there are other possible sizes to consider, but the 215/50-17 is most similar to what you have, only a bit narrower.

To be honest, here's how I'd see it:

  1. Get winter tires for the winter. You can use alloys. 16" 9-3 rims are cheap and common; I got a set of stock Linear rims for $100 total in great shape. Get good quality winter tires in an appropriate size--your Owner's Manual should give suggestions. (215/55-16 as it turns out)
  2. Get the best summer/all-season tires you can find. Better traction in rain depends almost entirely on the design and quality of the tire. A small change in tread width won't be anywhere nearly as effective.
  3. If fuel economy is important, I question whether any 17" tires will do that. Again, you should go to a 16" rim and low-rolling-resistance tire in the size recommended in the Owner's Manual (which is 215/55-16 XL/Run Flat it seems).
 

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Discussion Starter #15
You will lose some load rating by going to a smaller tire. a 235/45-17 is load rating 94, while a 224/45-17 is load rating 91. At least for a couple of tires I pulled up on tirerack. This isn't the end of the world, but you could get into possible legal issues, and some shops might not sell you undersize tires.

I agree with everyone who said "get winter tires for winter".

For better MPG, you really don't want to reduce the diameter of the tire, but you do want to reduce the width. So you're looking more at a tire like 215/50-17, which has load rating of 95 and is a touch bigger in diameter than your tire (depending on manufacturer etc.) Of course tires come in a plethora of sizes, so there are other possible sizes to consider, but the 215/50-17 is most similar to what you have, only a bit narrower.

To be honest, here's how I'd see it:

  1. Get winter tires for the winter. You can use alloys. 16" 9-3 rims are cheap and common; I got a set of stock Linear rims for $100 total in great shape. Get good quality winter tires in an appropriate size--your Owner's Manual should give suggestions. (215/55-16 as it turns out)
  2. Get the best summer/all-season tires you can find. Better traction in rain depends almost entirely on the design and quality of the tire. A small change in tread width won't be anywhere nearly as effective.
  3. If fuel economy is important, I question whether any 17" tires will do that. Again, you should go to a 16" rim and low-rolling-resistance tire in the size recommended in the Owner's Manual (which is 215/55-16 XL/Run Flat it seems).
Thank you so much ...this is really helping my decision on what I need to get ;ol;

Likely I will get a 235 50 17 at this point, winter tires are still a little bit of a stretch at this point plus wheels (no steel wheels, I will want used Saab wheels) maybe the next time around I will slowly hunt for some wheels and then put some used winter tires on them...and get myself a good summer tires.
 

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Thank you so much ...this is really helping my decision on what I need to get ;ol;

Likely I will get a 235 50 17 at this point, winter tires are still a little bit of a stretch at this point plus wheels (no steel wheels, I will want used Saab wheels) maybe the next time around I will slowly hunt for some wheels and then put some used winter tires on them...and get myself a good summer tires.
If you go 50-series, the diameter variance will be +3.65% while the tire circumference will be almost 3" greater:

http://www.1010tires.com/Tools/Tire-Size-Calculator/235-45R17/235-50R17

(I used 2008 9-3 2.0T 17" option as your OEM model)
 

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Discussion Starter #17

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I don't think you'll see much better traction. 225 vs 235 isn't a huge jump.

Your speedo will be off. One of the tire calculators will tell you what %. Just google Miata tire calculator.
why would his speedo be off if he changes the width of the tire...he is staying the same 45/17 size. the width would not make a difference in the speedometer calibration.

And who are we to judge if he likes to wear a speedo? :cheesy:
 

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Also....on the subject...if i go to a smaller rim size on my viggen for winter 16" from 17" that WOULD throw my speedometer off a great deal...but like you said..easier to find rims and tires for the 16 than the 17. cheaper as well
 

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why would his speedo be off if he changes the width of the tire...he is staying the same 45/17 size.
That's not how it works. The 45 means the sidewall height is 45% of the tread width, so a wider tread will have a higher sidewall ,in this case the od is .36" bigger on the 235 tire.
 
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