Slight Change in Tire Size

forteatwo · 08-26-2020, 12:40 PM

My current tires are the stock 225/50 R17 on my X1 S. I have an option to buy some snow tires that are 215/50 R17. The rim offsets would be the same or within 2mm of the stock. My question is, is this significant with regard to safety.

Using a tire calculator from one of the nifty online calculators the circumference of the stock tires is 81.2". The Snows, having a slightly smaller sidewall have a circumference of 80". This would create an odometer error at 70 mph on the stock tires of 68.9 mph or about 1 mph with the snows.

One of my thoughts is narrower tires are sometimes better in deeper snow so I do not mind that aspect.

Any thoughts?

Spectralus · 08-26-2020, 01:49 PM

It will work fine, you will have slightly less rim protection since the tire is more narrow.
OEM wheel size 17" x 7.5J, recommended tire width 215-225mm.

bucketfoot · 08-26-2020, 02:07 PM

If I recall the general rule of thump is to keep the circumference within 3% of stock. In this case you are at 1.5%, so it should be just fine.

forteatwo · 08-26-2020, 02:51 PM

Thanks to both of you. That is the information I was looking for.

0w40X1 · 08-28-2020, 09:54 PM

I bought my 14 X1 s28i with 8x18 and 9x18 355 wheels so I could put approx 4% lower profile Michelins on it.

Car has no way to know I geared it down since all tires are smaller.

Fronts 225/45r18 went to 225/40r18, and rears 255/40r18 went to 255/35r18.

26" rolling diameter to 25" diameter.

08-26-2020, 12:40 PM	#1
forteatwo Private 6 Rep 65 Posts Drives: 2014 X1 S-Drive Join Date: May 2013 Location: Wisconsin iTrader: (0)	Slight Change in Tire Size My current tires are the stock 225/50 R17 on my X1 S. I have an option to buy some snow tires that are 215/50 R17. The rim offsets would be the same or within 2mm of the stock. My question is, is this significant with regard to safety. Using a tire calculator from one of the nifty online calculators the circumference of the stock tires is 81.2". The Snows, having a slightly smaller sidewall have a circumference of 80". This would create an odometer error at 70 mph on the stock tires of 68.9 mph or about 1 mph with the snows. One of my thoughts is narrower tires are sometimes better in deeper snow so I do not mind that aspect. Any thoughts?
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08-26-2020, 01:49 PM	#2
Spectralus New Member 2 Rep 26 Posts Drives: E84 xDrive 23D Join Date: Jan 2019 Location: EU iTrader: (0)	It will work fine, you will have slightly less rim protection since the tire is more narrow. OEM wheel size 17" x 7.5J, recommended tire width 215-225mm.
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08-26-2020, 02:07 PM	#3
bucketfoot Captain 1064 Rep 819 Posts Drives: 2020 Toyota GT86 Join Date: Oct 2015 Location: Centennial, CO iTrader: (0)	If I recall the general rule of thump is to keep the circumference within 3% of stock. In this case you are at 1.5%, so it should be just fine. __________________ This post sent using 100% recycled electrons.
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08-26-2020, 02:51 PM	#4
forteatwo Private 6 Rep 65 Posts Drives: 2014 X1 S-Drive Join Date: May 2013 Location: Wisconsin iTrader: (0)	Thanks to both of you. That is the information I was looking for.
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08-28-2020, 09:54 PM	#5
0w40X1 Lieutenant 34 Rep 485 Posts Drives: 2014 BMW X1 s28i M Sport Join Date: Sep 2013 Location: West Texas iTrader: (0)	I bought my 14 X1 s28i with 8x18 and 9x18 355 wheels so I could put approx 4% lower profile Michelins on it. Car has no way to know I geared it down since all tires are smaller. Fronts 225/45r18 went to 225/40r18, and rears 255/40r18 went to 255/35r18. 26" rolling diameter to 25" diameter.
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