AWD systems and donut spare

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Colorado Springs
Ive been researching the topic at hand, and most manufacturers recommend removing a good full size tire from the back and putting it up front if you get a flat on any of the front tires. Subaru even makes you put a special fuse in to disable the AWD system. I read that some Chrysler vehicle computers have an algorithm that can sense when the donut spare is installed and it disables the AWD system so nothing gets damaged. My question, does anyone know for certain whether most modern cars will do this by disabling the AWD system when the donut spare is installed? Specifically Mazda? Thanks!
 
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Do most manufacturers that recommend you to put the good spare up front give you 2 jacks? What does your owner's manual say? What's the rolling circumference of your spare vs actual tire? Mine, 235/50r18 vs 145/80r18, the spare is only 0.4% smaller circumference
 
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Drew99GT

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Just one jack; if you have a flat in the front, you first jack up a rear, remove a good tire and install the donut spare, then put the jack under the flat, remove it and install the good full size you took off the rear! Seems like a PITA to do on the side of the road...
 
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11,194
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MA
I think that depends on the split for the AWD system. Mercedes is set up the other way, most of the power is to the rear not front and it's full time, doesn't shut off. Standard advice has always been to put the spare on the non drive wheel so for FWD, the rear, for RWD, the front. For AWD I guess whichever wheel gets the least power. Although a donut on the front means you get less braking power.
 
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For my 2017 CX5 it does not mention anything about the AWD. They are specific in requiring that the spare be installed on the rear wheel and that it be driven as few miles as possible. It is a true spare. Estimated tread life is 3000 miles max. I believe it said to be used no more than 30 miles in any situation.
 
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5,295
Originally Posted by slacktide_bitog
Originally Posted by wog
Buy full size spare,is this an option?
approved This is what I do for every car with a stupid donut, AWD or not thumbsup
That is what I did when I had my 2009 Subaru Forester. The well under the rear cargo floor plate was just large enough to accommodate a full size spare.
 
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Originally Posted by IMSA_Racing_Fan
Sounds like you would need to have a NASCAR pit crew riding in the back like in those commercials.
That's why I have my Milwaukee 2767-20 just in case, 1400 foot pounds of torque in reverse. A full won't fit in the space in the trunk. Plus a full size tire for my car is around $200 so somewhat overkill. Although I've had flats, most of them were nails that couldn't be repaired but I didn't have to use the donut.
 
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MA
Originally Posted by IMSA_Racing_Fan
Unrepairable nail punctures? I've been repairing them forever with fiber plugs and rubber cement.
Yeah, you know how it goes, nail puncture in the outer rib. No chain tire store would fix it. Would be a coin flip as to whether it'd be worth plugging. Didn't feel like gambling that much so just got a new tire. I drive fast sometimes....
 
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Originally Posted by LoneRanger
Originally Posted by slacktide_bitog
Originally Posted by wog
Buy full size spare,is this an option?
approved This is what I do for every car with a stupid donut, AWD or not thumbsup
That is what I did when I had my 2009 Subaru Forester. The well under the rear cargo floor plate was just large enough to accommodate a full size spare.
It doesn't really solve the problem, if the tire wear isn't reasonably close you create the same problem as running the spare not having the same diameter. Then you factor in variances between different brand tire diameters...
 

Drew99GT

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I got my situation figured out! Mazda specifically used a 155/90 R18 on AWD CX-7s, and that tire is listed as a specific tire for the CX-5, but in the US we got the tiny donut instead. https://www.mazdas247.com/forum/index.php?threads/2017-spare-tire-mod-for-u-s.123861462/page-2 So I found a CX-7 spare wheel and tire on Ebay for 60 bucks. Its the exact same diameter as the regular wheels and tires. It fits in the spare tire well perfectly! So no more worrying about whether I'll cook the AWD system if I get stranded with a flat. I tried putting a regular wheel and tire in the spare tire well; way too tall.
 
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14,897
Location
Central NY
I've considered getting a bigger donut spare for my Forester. Tirerack has a 17'' donut which has the exact same diameter listed as the factory size tires. I'll likely stick to a winter tire as a full sized spare. If I was on a longer trip, not sure I'd want to run hundreds of miles on a donut even if it was the ACdiameter.
 
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Location
Channahon, IL
I've put a few donuts on customer vehicles at their request. Any time it's AWD, as I'm pulling out of the shop, the dash invariably flashes a warning saying AWD is disabled, and I always make sure to tell the customer this.
 

JTK

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13,635
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Buffalo, NY
I'm probably missing the point here, but even if it's a donut spare on an AWD/4x4 equipped vehicle, it's the same diameter (with in reason) as the OEM tires. I get it though that it's only intended for very temporary use. Our 2019 Pathfinder came with a skinny donut, but it's the same diameter as the factory rubber. It's undermount and a real tire/wheel might fit, but I'd hate to hang it up on something and tear the arse-end off the car. My Ram came with a real Goodyear Wranger SRA on a steelie, yet I've seen some Ram 1500s come with a donut.
 
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