Largest spare tire diameter

6780 Views 15 Replies 8 Participants Last post by Saxis, Jun 13, 2009

bfrench

Discussion Starter · May 18, 2009

Hi, Folks,

I've done a search on the spare tire size and couldn't find anything on the maximum tire diameter we can put in the spare tire location.

What I've done is put four Goodyear Wrangler Silent Armor tires on and left the factory spare as is.

The upgrade tires are 255 70R17 with a diameter of 31.06" and the factory spare is the 245 65R17 with a diameter of 29.54" as per the Tire Size Comparator program that I use for a 1.52" increase in diameter.

If it is acceptable, I'll leave the factory spare as is but I'm wondering what effects there are with an two size difference between the mains and the spare.

For instance could I drive 100 miles to a service station with that kind of tire size imbalance and how fast would be safe and prudent considering it might be on gravel roads or wet and slippery paved roads?

Oh,yeah - the choice of the Goodyear Wrangler Silent Armor - most of the driving is paved highway and gravel side roads with an occasional trip to the back forties on the brother's-in-law farm - so after looking at the punishment The Roadie had given his and how long he got out of them, I figured they'd be more than adequate for my needs - thanks, Roadie.

Thanks,
Bill

1 - 16 of 16 Posts

bubster020

· #2 · May 18, 2009

Im not positive but i dont think you can fit anything bigger under there. There is a heat shield and it is pretty close the spare on mine already. Yes you can drive it with a different size tire but probably dont want make to long of a trip on it though.

WOOLUF1952

· #3 · May 18, 2009 (Edited)

All you really need is 0.75". Half of the total diameter increase. Just look under your TB. Is there at least 3/4" from exhaust pipes? From the heat shield? If so then you are good to go. If you have to run a smaller tire on one axle, the least amount of wear/damage would be on the front axle. Specially if you have the G80 option.:m2:

bikingguy1

· #4 · May 18, 2009

WOOLUF1952 said:
All you really need is 0.75". Half of the total diameter increase. Just look under your TB. Is there at least 3/4" from exhaust pipes? From the heat shield? If so then you are good to go. If you have to run a smaller tire on one axle, the least amount of wear/damage would be on the front axle. Specially if you have the G80 option.:m2:

:iagree: with the different wheel sizes on each side the wheel speed would be different on each side of the axle and would mess with the g80

the roadie

· #5 · May 18, 2009

bfrench said:
... after looking at the punishment The Roadie had given his and how long he got out of them, I figured they'd be more than adequate for my needs - thanks, Roadie.

Glad my abuse test can serve as an adequate testimonial. You're quite welcome.

WOOLUF1952 said:
If you have to run a smaller tire on one axle, the least amount of wear/damage would be on the front axle. Specially if you have the G80 option.:m2:

The presence of the G80 is almost irrelevant since you would never get the RPM difference required for a lock-up. The G80 *does* contain clutch plates that will see increased friction if there's a tire size difference. But in the oil bath they're in, I doubt it would amount to anything. I'll have to look at its construction more to see if they would notice a few RPM difference for an hour or two or running.

A difference in tire size on the front might be enough to trip the ABS fault monitor, or the same thing on a new style rear with the 4-channel ABS controller. Hmmmmmm. I don't think I have enough data yet to recommend either axle over the other. I'm so conflicted.

WOOLUF1952

· #6 · May 18, 2009

the roadie said:
Glad my abuse test can serve as an adequate testimonial. You're quite welcome.
The presence of the G80 is almost irrelevant since you would never get the RPM difference required for a lock-up. The G80 *does* contain clutch plates that will see increased friction if there's a tire size difference. But in the oil bath they're in, I doubt it would amount to anything. I'll have to look at its construction more to see if they would notice a few RPM difference for an hour or two or running.

A difference in tire size on the front might be enough to trip the ABS fault monitor, or the same thing on a new style rear with the 4-channel ABS controller. Hmmmmmm. I don't think I have enough data yet to recommend either axle over the other. I'm so conflicted.

I was thinking more about the extra wear, of basically turning in a circle for 100 miles, on the rear diff. According to the calculator there is only approx. 36 revolutions per mile difference between the two tires. Definitely not enough to cause the G80 to lock-up. It's just more expensive to replace the G80.

N467RX

· #7 · May 18, 2009

Have you thought about just swapping the tires in your driveway and see if one of the SilentArmors fits in there?

bfrench

Discussion Starter · #8 · May 18, 2009

N467RX said:
Have you thought about just swapping the tires in your driveway and see if one of the SilentArmors fits in there?

Yes, I have thought about doing that.

But with the left knee replaced about 3 momths ago and the right knee to be replaced on 2 June - for once I let my top head do the thinking and decided against it.

Btw - thanks to all of you for your answers.

Bill

DZP

· #9 · May 19, 2009

I have my 265/70-16 under mine with no problems found. As far as using different sizes on same axles that is something that I would avoid. I know that in the past Jeep had a recall on their spare tires that was approximately 5mm taller. Even with minimal use for emergency purposes they destroyed the viscous coupler in their all-wheel drive platforms. There was a lot of warranty money paid out due to this problem.

N467RX

· #10 · May 19, 2009

bfrench said:
Yes, I have thought about doing that.

But with the left knee replaced about 3 momths ago and the right knee to be replaced on 2 June - for once I let my top head do the thinking and decided against it.

Btw - thanks to all of you for your answers.

Bill

Hmmm yeah... that's a good decision

DZP said:
I have my 265/70-16 under mine with no problems found. As far as using different sizes on same axles that is something that I would avoid. I know that in the past Jeep had a recall on their spare tires that was approximately 5mm taller. Even with minimal use for emergency purposes they destroyed the viscous coupler in their all-wheel drive platforms. There was a lot of warranty money paid out due to this problem.

Tell that to all those who drive with 4 mismatched tires. Although it's kind of interesting, because a lot of car manufacturers are now using the space saver spare, including in AWD cars and even some small crossovers.

Saxis

· #11 · Jun 12, 2009

I'm a bit late chiming in, but this is also an interest to me as I've been looking at bigger tires when the time comes. I'd really like to stick a full-sized spare under there, so I was going to stick with ~30.5" tires. That was the size I initially read should fit under there. Upon crawling under and inspecting though, I found that my Denali only has about 1/4" between the current 29.5" spare and the backside of the hitch. Pretty much smashed my dreams of getting bigger tires with a full-sized spare. I'm just not into the roof rack or hitch-mounts. I see a lot of TrailVoys running around on here with 32"+ tires and no visible spare. Are they just wheelin' and prayin', keeping a spare in the back, or just going without? :undecided

DZP

· #12 · Jun 12, 2009

N467RX said:
Tell that to all those who drive with 4 mismatched tires. Although it's kind of interesting, because a lot of car manufacturers are now using the space saver spare, including in AWD cars and even some small crossovers.

The space saver spares are thinner on the tread width but rotationally the same height. A 235/85-16 can be used in the place of a 265/75-16 for an emergency on a roadway. But I would not recommend using that size as a spare off road since you never know where the problem can occur. On the other hand it would be better than no spare at all.

N467RX

· #13 · Jun 12, 2009

Saxis,

If you want a full sized spare for offroading but don't mind a smaller spare for highways, you can get the spare and then just carry it in the trunk (a la Jeep). Or you can carry it in the trunk all the time, but it'll take a lot of space. Old Blazers were like that.

DZP,

Are you serious? the space savers always looked way smaller to me, but the last time I used one was back in 97 or so. And they are rated for only 50MPH, at least ours was (my dad wasn't too happy about driving the remaining 2 hours of the trip doing 50MPH, which of course got extended to 2.5 or so).

I wonder what GM did with the Acadia/Traverse/Outlook/Enclave in terms of spare tires. A friend said that 2010 Escalades come with a fix a flat instead of a spare, which is a really stupid idea. hopefully that got ditched in favour of a real tire.

Saxis

· #14 · Jun 12, 2009 (Edited)

N467RX said:
Saxis,

If you want a full sized spare for offroading but don't mind a smaller spare for highways, you can get the spare and then just carry it in the trunk (a la Jeep). Or you can carry it in the trunk all the time, but it'll take a lot of space. Old Blazers were like that.

I've got quite a while before I'm ready for new tires, probably a year or so, which is fine. I'm still pretty hesitant about taking the brand new Denali out in the sticks and beating her up. :hopeless Less than 14,000 miles still! Gives me time to spread out the costs of upgrading. I'll get the spacers, Bilsteins and lift this year, tires next year.

The ultimate goal will be around 285/60R18, but I'll probably try to get a test fit. Someone here got a similar size Nitto Terra Grappler (285/50R20) without a lift and only hammering. More than likely I'll end up going with a 265/60R18...

N467RX

· #15 · Jun 12, 2009

I'd see that as very hard unless you have decent spacers, the upper ball joint puts enormous limits on everything.

I'm definitely not going into the extremes and staying around 265/65/17 or so, probably the biggest size w/o spacers or the next one up (and the spacers). And either Dueler A/T Revos or Silent Armors. I'm sticking with my current tires until the first one gets damaged beyond repair, then I'll replace all 4. I might just keep the original spare for general use. Maybe at some point get an extra wheel and full size tire just for off road trips (having 2 spares would. be awesome).

And I haven't done any real mods. The first one will be the tires and possibly spacers. Then I'll consider a small brushguard. I've focused mostly on interior accesories (CB, 2M, nav GPS. In a few months I'm chaging the power distribution for my radios and possibly getting a 12V deep cycle battery for powering my radios w/o the car battery).

Saxis

· #16 · Jun 13, 2009

N467RX said:
I'd see that as very hard unless you have decent spacers, the upper ball joint puts enormous limits on everything.

Not worried about the ball joint as much as the rubbing. Tires are about 1.75" wider (.86" on each side), so with 1.5" spacer it should be fine. I've got about 1" clearance stock. Looking at my plastic fender liner, only about 1.25" to spare. Not sure how a lift will effect that, but by the looks of it, not much. The trim is easily pushed back a good inch by hand, so I might be able to hammer it a bit.

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