Spare tire conundrum

[dannonebr]

This week I went out and bought a new set of AT3's XLTs for my 2020 2500. The stock tires were LT275R70-18s. After quite a bit of thought I settled on a set of larger LT295R70-18s on the stock rims plus a new spare of the same size.

The new tires ride great and are super quite and fit with plenty of room, BUT the new spare does not fit into the original tire storage area under the box. With the 295 fully inflated, it will not fit between the rear sway bar and the receiver hitch.

According to the tire size data from the Cooper web site, the new 295's (34.6" dia) and are about 1.5 inch larger in diameter that the original 275 (33.2" dia I think) Firestones. I'm thinking that I will need to go back to the tire store and get my old (new) spare to fit into the hole. I don't want to have to carry the bigger spare in the box of the truck. While I have not had to use a spare tire for as long as I can remember (if ever), if I have to use the 275 spare in a pinch, am I going to cause damage to the drive train?

Or does anyone have any ideas such as an adapter that can be used under the bed of the truck in the original spare tire location to house the 295? I'm thinking about deflating the 295 to see if it will fit, I carry a Viair air compressor with me in my truck box and it inflates a tire pretty quick. Any one have any other suggestions?

 

[Wiredawg]

Don't know if it's possible or you would want to do it: Have you thought about deflating the tire to see if it will fit between the frame? Just a thought.

 

[BigPapa]

I'm thinking about deflating the 295 to see if it will fit, I carry a Viair air compressor with me in my truck box and it inflates a tire pretty quick. Any one have any other suggestions?

 

[Tuesdak]

IMO Put the OEM Tire size back on or match all 5 making the spare fit/relocate it. The difference in tire size should you need the mismatched diameter spare will cause a "pull" and spin the spider gears in the diff a lot more than normal. (This isn't NASCAR and the diff isn't designed to deal with this big of an RPM difference for extended times at speed.)

You have a risk of the traction control making this worse if it kicks in. (Say you need it a moment and then it never lets go. Or just locks in from the RPM difference made worse in a turn. )

 

[Wiredawg]

IMO Put the OEM Tire size back on or match all 5 making the spare fit/relocate it. The difference in tire size should you need the mismatched diameter spare will cause a "pull" and spin the spider gears in the diff a lot more than normal. (This isn't NASCAR and the diff isn't designed to deal with this big of an RPM difference for extended times at speed.)

You have a risk of the traction control making this worse if it kicks in. (Say you need it a moment and then it never lets go. Or just locks in from the RPM difference made worse in a turn. )

T,

I agree 100% with you IF he can't get the tire he already bought and mounted to fit.

Waiting to hear how it turns out!

 

[odinjunior]

How does it look with the bigger tire? No rubbing when turning? I put 305s on my 98.5 and had no problems.

While it's a different drive train my Subaru manual suggests if the flat is a rear tire putting the spacesaver spare on a front wheel and moving that tire to the rear.

 

[Ozymandias]

IMO Put the OEM Tire size back on or match all 5 making the spare fit/relocate it. The difference in tire size should you need the mismatched diameter spare will cause a "pull" and spin the spider gears in the diff a lot more than normal. (This isn't NASCAR and the diff isn't designed to deal with this big of an RPM difference for extended times at speed.)

You have a risk of the traction control making this worse if it kicks in. (Say you need it a moment and then it never lets go. Or just locks in from the RPM difference made worse in a turn. )

Put the mis-matching spare to the front axle if needed and you can travel from NY to LA with it.

 

[mpaulson]

Yep, put the OEM size spare on the front if a spare is needed. You have a front axle disconnect so you won’t be spinning the front diff spider gears anyway. Just an extra move if your flat is on the back. You’ll have some steering pull, but it should be fine if your only driving to the next place to get the tire fixed. I have done this and drove 350 km’s home.

 

[AH64ID]

Actually the way the front axle disconnect works the spider gears are always spinning. The short shaft is solid, so the drivers side front tire spins the spider gears. The long shaft has the disconnect and is easier to spin than than the driveshaft so the inner portion of the long shaft spins backwards as you go down the road.

I’m not sure it’s really a big deal to run one size different tire until you can get the correct size back on. I drive lots of roads where the truck doesn’t go straight for miles and miles. The difference from corners is bigger than one tire size. They are designed to allow a difference in tire rpms.

That being said I don’t like the wrong size spare and wont run a tire size I can’t carry a spare for.

 

[lpennock]

I used Toyo AT3 for the sizing info below.
LT275/70-18 is a 33.2 diameter tire.
LT295/79-18 is a 34.3 diameter tire with slightly more that 16/32 or about 1/2" of tread depth.
If you have a worn out 295 your diameter will be 34.3-(2x1/2") or 33.3 diameter.
Therefore running a brand new 275 as the spare is the same as running a worn out and new 295 on the same axle. Won't hurt anything (unless running detroit lockers which will be damn annoying) as the systems are engineered to handle that mismatch. With that said I wouldn't do it very long with a clutch type limited slip as it puts additional wear on the clutches. The torsen styles and open units won't care.

Bottom line won't hurt to run a new 275 as the spare but I wouldn't use a worn out 275 as the spare.

 

[dannonebr]

The 295's fit the truck just fine, no rubbing. They do drive better than the original Firestones, steering and smoothness wise. With my experience and looking at the various tire specs, a 285/65 would fit in back but not a 285/75. As far as the rear spare, I was originally thinking about using the 275 as a temporary front spare only and swapping with a rear one if need be. I'm going to take a look to see if a spool between the spare and bottom of the truck can be fabricated for the original mount location, but it may stick down too far, I'll have to play with it. While I have not had a blow out or damaged tire while traveling for as long as I can remember, I don't like traveling without being prepared. As Benjamin Franklin one said or wrote, "An ounce of prevention is worth a pound of cure".

 

[bcbender]

While I have not had to use a spare tire for as long as I can remember (if ever), if I have to use the 275 spare in a pinch, am I going to cause damage to the drive train?

I had that issue when a texting beach barbie hit me and broke my 18" rim!!... Just put it on the front axle and go get it fixed, I drove 100mi home on the OE 17" spare which I had to dust off and had never used..... no worries on the front axle.

 

[Badunit]

I have the same thing going on with the same size tires as you. I never bothered changing the spare from the stock size but I had read a 295 was the largest tire that would fit. Guess that wasn't true (or maybe it got tighter in 2020?). My plan has been:

1. Keep a plug kit with plenty of plugs in my truck to handle the typical nail and screw holes.It is hard to get them through these tires and I have ruined a few trying so I want to have a bunch of extras.
2. Have a capable 12V air pump with me, not a cheapo one that can barely fill a tire or can't get one to 80psi.
3. Use the 275 spare on the front if necessary.
4. Cell phone and a AAA membership if all else fails.

 

[AEdelheit]

So you actually put the spare tire up there and confirmed it did not fit? I have seen people put tires measuring about 34" in the spare tire location but sometimes need to use a ratchet strap to hold the tire up against the hitch.

 

[dannonebr]

The bigger 295 tire would not fit between the rear track bar and the back of the receiver hitch, and next to the heat shield next to the tail pipe. With the 275 stock spare there is about 1/2" clearance at best on my truck between all these parts. I did not try bleeding the air pressure off and maybe risk popping the bead. I considered the post above by ipennock and he made total sense (thanks). So the 275 went back into the hole. I figure that having a new 275 that's filled with air is better than having a 295 with no air, even with a pump on hand. The 275 is a bit lighter than the AT3 XLT 295's if I should ever have to change it.

 

[BigPapa]

Not saying you did the wrong thing at all, but just so you know, it would take purposeful force for the bead to “pop off” the rim.

 

[MRFost]

And always remember that tires, including the spare, are good for 7 years. An old spare can be as bad as no spare as a blowout with that on your steering axle can be no bueno. Just saying.

 

[Ozymandias]

Nope, blow out on the steering axle is easy peasy if you are an alert driver. On the rear axle it is challenging as you have no way to correct that one if it starts to go sideways.

 

[MRFost]

A N D you completely missed the point.

You do not want to have an aged spare. For completely missing the point, Oxyman gets a -1.

I've had two blowouts at speed over the years, one in front and one on back . Both were in front wheel drive cars. I assure you the blowout on the front of a FWD car *was* far more exciting. I intend to never have a blowout in the truck.

Anyway, keep your spare in good repair else it might not be a spare...or even worse.

 

[BigPapa]

Don’t think Ozy missed the point, and we don’t talk about front wheel drive cars here…