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#4689796 - 03/09/18 04:53 PM Running different size on front and rear question.
pbm Offline


Registered: 04/19/04
Posts: 7605
Loc: New York
I recently picked up a 2006 Focus wagon and I'm replacing 2 tires (2 are like new). The OE size is 195/60/15. I have 2 brand new 195/65/15's (Cooper CS-5) that I bought for a different car. Would you run the slightly bigger (195/65/15) on the rear or front? (I'm thinking rear is better but I'm open to be educated differently). Anybody see a problem doing this? Thanks.
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#4689803 - 03/09/18 04:56 PM Re: Running different size on front and rear question. [Re: pbm]
Lolvoguy Offline


Registered: 02/06/14
Posts: 2336
Loc: Canada
Most tire and service shops will not mount/balance your new tires if they know the other set are a different size.
Personally I'd hold out for all 4 the same size to avoid any safety issues.
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#4689823 - 03/09/18 05:24 PM Re: Running different size on front and rear question. [Re: pbm]
d00df00d Offline


Registered: 10/20/05
Posts: 11212
Loc: PA
Don't do it. Different front and rear diameters will screw with your ABS. Stability control too, if you have it.

At a minimum, those systems won't work right. Your car might even disable them outright if it detects a chronic difference in wheel speeds between front and rear.
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#4689824 - 03/09/18 05:25 PM Re: Running different size on front and rear question. [Re: Lolvoguy]
pbm Offline


Registered: 04/19/04
Posts: 7605
Loc: New York
Originally Posted By: Lolvoguy
Most tire and service shops will not mount/balance your new tires if they know the other set are a different size.
Personally I'd hold out for all 4 the same size to avoid any safety issues.


Where I get them mounted and balanced that won't be a problem.
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#4689828 - 03/09/18 05:28 PM Re: Running different size on front and rear question. [Re: pbm]
oldhp Offline


Registered: 06/28/12
Posts: 1626
Loc: USA
3/4" taller with the 195/65R15 which would be 3/8ths" taller on the car. Wouldn't hurt a thing to me. I would put these on the rear. Go to https://tiresize.com/comparison/ to see for yourself.
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#4689829 - 03/09/18 05:30 PM Re: Running different size on front and rear question. [Re: pbm]
Dyusik Offline


Registered: 09/26/14
Posts: 1982
Loc: US-WA
Rear to not mess with the speedo. Did that on my old Cavalier, they were MUCH bigger. Improved my handling drastically, much needed as my front shocks were fubar.
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#4689831 - 03/09/18 05:30 PM Re: Running different size on front and rear question. [Re: pbm]
Traction Offline


Registered: 06/04/13
Posts: 981
Loc: iowa
It's a pretty simple answer. Sell them, and run what's supposed to be on your car.
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#4689844 - 03/09/18 05:44 PM Re: Running different size on front and rear question. [Re: pbm]
Ducked Offline


Registered: 10/25/12
Posts: 4368
Loc: Taiwan
If you follow the "best tyres on the back" mantra, and you think lower profile tyres are better, then the OEM tyres should go on the back, assuming there are no clearance issues at the front, and that you're not bothered about a slight change in gearing and speedo reading.

I wouldn't have thought a 5 point change in aspect ratio would make that much difference to handling or modern gizmology like ABS, but I'm open to being educated differently too.

Theres allegedly a rule-of-thumb limit of 2% change in rolling radius. According to this online calculator, you'd be over that at 3.17% and shouldn't do it.

http://tyrestore.in/upsizing.htm

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#4689868 - 03/09/18 06:08 PM Re: Running different size on front and rear question. [Re: pbm]
slacktide_bitog Online   content


Registered: 03/20/08
Posts: 6167
Loc: USA
Tires in those 15-inch sizes are not expensive. Get a set of 4 of the correct size 195/60-15 smile

DT/DTD often has a good sale on the CS5 Ultra, so you can always get a set when they go on sale again. It ends up being a set of 4 tires for the price of 2 anyway.

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#4689873 - 03/09/18 06:12 PM Re: Running different size on front and rear question. [Re: Ducked]
Quattro Pete Offline


Registered: 10/30/02
Posts: 35863
Loc: Great Lakes
Originally Posted By: Ducked
I wouldn't have thought a 5 point change in aspect ratio would make that much difference to handling or modern gizmology like ABS, but I'm open to being educated differently too.

The ABS sensors in my car will trigger the traction control light when my tires are only slightly under-inflated (cheap man's TPMS), so I can see how using an even slightly different tire size could do the same.

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#4689904 - 03/09/18 06:44 PM Re: Running different size on front and rear question. [Re: pbm]
supton Online   content


Registered: 11/09/08
Posts: 11971
Loc: NH
If it has ABS I probably wouldn't--although if they are on rims and you can swap on and off with ease... then why not? Could always disable ABS if you're trying to save a buck. If it didn't have ABS I wouldn't think much about it. Same width, only slightly different aspect ratio.

Not that uncommon to drop a size in width (and gain in aspect) when running snow tires, under the mantra of more narrow is better for traction. This case, it's not even that.

I'd be more concerned with running wildly different tread patterns, and upsetting the cars natural handling--but I'm guessing that, as long as the tires have tread, it's just a matter of how much it wants to understeer, not that it suddenly oversteers.
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#4689909 - 03/09/18 06:46 PM Re: Running different size on front and rear question. [Re: pbm]
pburchett Offline


Registered: 03/08/05
Posts: 26
Loc: KY
It will work just fine. Did this on a 2009 Focus. Wore the tires out and never had a problem.

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#4689985 - 03/09/18 08:18 PM Re: Running different size on front and rear question. [Re: pbm]
14Accent Offline


Registered: 08/03/17
Posts: 391
Loc: MN
It'll be fine.

I'm running completely different size than stock on my Marauder due to the factory size rear being very odd (and expensive). Stock is 235/50R18 front 245/55R18 rear. I'm running 245/40's up front and 255/34's out back. The ABS works just fine, it doesn't know the difference.

The 2004 Marauders are more picky, but there's still a wide range of sizes that work fine.
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#4690184 - 03/10/18 05:08 AM Re: Running different size on front and rear question. [Re: 14Accent]
d00df00d Offline


Registered: 10/20/05
Posts: 11212
Loc: PA
It's one thing if the ABS works -- as in, it engages and does something.

It's another thing if the ABS works "just fine" -- as in, the way it should. How have you determined that part?
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#4690270 - 03/10/18 07:43 AM Re: Running different size on front and rear question. [Re: d00df00d]
Kira Offline


Registered: 08/19/10
Posts: 5242
Loc: Champlain/Hudson Valley
To pbm: Simply explain the situation to the manager and swap 'em. Lots of cars use the 196-65-15 size so they'd move.
Keep it simple and easy. Do your new "65's" still have their stickers?

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