I have 215/50 17 on my cls now. Can I change to 205/50 17? buying used, its a good deal if they will work. What are the pros and cons. Thanks

 

Pro is the price savings.

Con is your speedometer will be off, saying that your actually driving faster then you really are.

The choice is yours, I have nothing against buying used tires. But you just have to think about the price difference between new and used and how much longer the used tires will last you. Also look at the date at when the used tires were made (google this and you'll find out what to look for). If they are more then 5 years old then I would probably pass because tires start to become old and unsafe around 7-8 years old.

 

Tires are coming off a bmw that was totaled. Thanks for the info. I will check out the date.

 

^^
Good point. Ya they will fit just fine and I wouldn't worry about the speedo difference, minimal affect.

 

I'm running a set of tires thats about 8 years old right now and the tread is low so I'm replacing them before winter but you can see small dry rot cracks in the tread and sidewall.

 

Uh, guys... 215/205 is the width of the tire, not the diameter. Slimmer tires will cut snow better, but wider will generally give you better traction on dry roads. If you go from a 215 50 17 to a 215 65 17 then you would see a speedo difference. One full rotation of the tire would be farther than on a smaller tire.
i.e. 215=width of the tread, 50= the height of the tire from the rim to the tread, and 17= the tire diameter in inches.
Going with a slimmer tire won't be an issue as far as rubbing goes... Very different if you go wider.

 

Wrong. The series number is also called an aspect ratio number. My 215/45/18 tire has nearly the same sidewall height as my 235/40/18 tire. The middle number is simply a ratio of the width of the tire.

You can also google miata tire calculator to see what size tire is closest to the stock diameter. 1010tires also has a calculator. 215/45/18 and 235/40/18 are the cloest tire sizes to the stock Type S size of 215/50/17.

 

^ This.

A 205/50 tire is 205mm wide, and the sidewall is 50% of the width = 102.5mm tall. Changing the width without addressing the sidewall percentage will change the overall height of the tire.

 

Let me rephrase that statement... Based on the information that was required in the question by Misty...
My point was that with the sidewall height (aspect ratio) being the same and the width only marginally different; The speed offset would be pretty minimal. Given Misty wanted to go from a 215 to a 205; Which isn't a bad idea for winter tires. The size difference would be the smallest by going from a 215/50/17 to a 205/50/17 (speed dif 1.554% too fast) as opposed to:
Going to a 205/55/17- 1.604% too slow
Going to a 205/45/17- 4.945% too fast
There was only a 10mm change so at a 50 series tire the difference would be 5mm. (about this [] big. lol ) I didn't feel the need to go into a long explanation of the hows and why's, just give Misty the information that was asked. I pretty much did the math in my head as I was reading, but didn't go into heavy detail. My apologies if I sounded patronizing in my post, but a lot of people think the first set of numbers in a tire code is the diameter in millimeters.
I'll go into more detail next time.

 

But the sidewall hieght is NOT the same.

50% of 215mm = 107.5mm
50% of 205mm = 102.5mm

The speedometer would indicate 80mph when you are actually travelling at 74mph. That will effect the overall mileage on the car as well (not by a whole lot but it does add up).

 

i was fine with used tires as long as i had one tire exploded and nearly crashed my car it may save you a few bucks but what about car ? life ?

 

What was the age of the tire?

 

Really? Do I need to get a lawyer to write my posts? lol I think I explained things pretty thoroughly and did the math.

I think you carried the "9" CD. lol Maybe I messed up? On my calculations I got 60 mph will be 59.1 mph on the 205's. At 80 mph you'll really be doing 78.8 (give or take a bit for tread height left) Here's how I got that...
Revs p/mile (215 tire) 816.9/829.6 (205 tire)= .01544
.01544 x 100= 1.544%(+)
60mph x .01544=.93 (rounded down to .9)
60mph - .9mph= 59.1mph
So at 80mph, wouldn't you be going 78.8?
80 x .01544= 1.23 (rounded down) 1.2 mph
80 - 1.2= 78.8mph
I did check to see if there was a tire size closer (above), but the 205 was the closest without changing rim size. Most tire manufacturers say within a 3% difference to stock size is acceptable. Obviously the closer to zero you can get, the better.
If I messed up in my math, my bad!

 

You said the sidewall heights were the same. Thats what my post was replying to (since, ya know, they arent).

Your math is correct, Im not sure how I ended up at 74mph

The 205/50 is the closest to the stock tire size.

 

No need to do math, like I said in one of my posts, there's plenty of calculators out there where you just insert the two tire sizes.

 

 

I used to work for Goodyear, so I'm used to doing it in my head like a zillion times a day... Just wasn't sure if I had lost my touch in my old age. lol

 

Props for doing that in your head. I studied engineering and accounting and I couldn't ramble off numbers like that.