Smaller than OEM tires

November 21, 2008 7:11 AM

Can I use winter tires that are smaller than the OEM tires on my car now?

I'm looking for winter tires for my car (245/65R17) but apparently there aren't any left in Ontario due to the recent spike in demand from Quebec, where new regulation is requiring winter tires on all vehicles this winter.

The mechanic is suggesting that I get 235/65R17 tires instead. From cursory searching on the internet, it seems these tires would be narrower than OEM and have a smaller diameter as well (since the aspect ratio is the same). Will that have an adverse effect on the handling of the car? Also, here's a silly question: will the narrower tires even fit on the current rims?

posted by reformedjerk to travel & transportation (10 answers total)

They'll be fine, both for handling and going on the wheels. If anything your handling in snow may improve since narrower tires tend not to 'float' as much as wider tires. But the size difference is pretty insignificant. Your speedometer may be off by a couple of percent, but again, negligible.
posted by hungrysquirrels at 7:18 AM on November 21, 2008

They're only 1cm narrower than your existing tires. Unless you have some unusual rims (which you don't) they'll fit. Your speedometer will be high by 1-2%, because the new size has a slightly smaller circumference than the old one.

I don't have the link handy, but there are a few tire size calculators online that will show you exactly how different two tire sizes are in terms of rim fit and speedometer error.
posted by zippy at 7:40 AM on November 21, 2008

Should fit. The first number is the circumference of the tire from edge to edge. The second number is the rim size in inches. So you have 17-inch times with 245mm sidewalls. Your mechanic thinks that a 235mm tire will fit just fine. He's probably right. That's a really small difference.

Will that have an adverse effect on the handling of the car?

This is something gearheads argue about all the time. I doubt such a small difference will matter one way or another.
posted by damn dirty ape at 7:56 AM on November 21, 2008

My own snow tires, new (to me; they're used) this year due to Quebec law, are 10 mm narrower than my summer tires, on 16-inch rims. I haven't noticed a significant difference yet. The snow tires have their own rims.
posted by mcwetboy at 8:18 AM on November 21, 2008

1-2% is well within the standard error of a speedometer, anyway, mind you. I'd certainly use those tyres if I were you. Big fat snow tyres are not much good.
posted by Brockles at 8:26 AM on November 21, 2008

Thanks everyone! I'll go ahead and get them then.
posted by reformedjerk at 8:36 AM on November 21, 2008

Run the sizes through this size calculator. It will tell you just how much your speedometer will be off.
posted by Thorzdad at 8:53 AM on November 21, 2008

Here's the fun part of having slightly short tires - you'll be buzzing along, see a cop and HOLY FUCK I"M DOING 75 IN A 70 and the cops are dicks in this area...except you're only doing 72, which unless they're *really* dicks ( I got pulled over for doing exactly the speed limit - see, that's suspicious) isn't enough to get you in trouble.
posted by notsnot at 9:38 AM on November 21, 2008

Should fit. The first number is the circumference of the tire from edge to edge. The second number is the rim size in inches. So you have 17-inch times with 245mm sidewalls. Your mechanic thinks that a 235mm tire will fit just fine. He's probably right. That's a really small difference.

Correction: The first number is the tire width in millimeters, so it's 245mm wide. The second number is the sidewall height as a percentage of the width, so the sidewall is (245 * .65)mm high. The third number is the wheel diameter in inches.

No, it could not be a weirder system for describing tires.
posted by paanta at 9:59 AM on November 21, 2008

I put 235/65R17's on my car that came with 225/65R17's just fine.
posted by SirStan at 6:03 PM on November 21, 2008