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Old 08-20-2018, 12:16 PM   #1
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Full size spare tire?

I recently switched my 1993 E250 over to 265/75/16 tires. My spare is still a 245/75/16. The outer diameter differs by at least an inch.

I've been outfitting my van to be as foolproof as possible and also as prepared as possible in terms of field repairs/ability to get out of a jam.

So, my question: How critical is it to upgrade my spare to 265/75/16? It's 2wd with a mild lift. I'd rather upgrade the spare than have to swap front/rear wheels in the event of a flat.

Thanks,

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Old 08-20-2018, 12:43 PM   #2
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If you have an open differential, it's not that big of a deal, but you'll feel a hard pull under braking up front.

If you have limited slip diameter does matter.
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Old 08-21-2018, 11:53 AM   #3
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Naturally my van doesn't have the door sticker to help me out here......the only stickers are from SMB and don't mention the axle.

What's the easiest way for me to determine what I've got in terms of gearing and diff type?

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Old 08-21-2018, 12:26 PM   #4
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Should be a sticker on the b-pillar inside drivers side. Is your spare still mounted up underneath the rear of the van? Anyone know if a 265 will fit under there?
As mentioned, depends on your diff, you could just swap the tires around so youíve got 2 of the same in the rear and wait until you need new tires and use one of the 265ís to replace your old spare.
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Old 08-21-2018, 12:51 PM   #5
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Quote:
Originally Posted by REF View Post
Should be a sticker on the b-pillar inside drivers side. Is your spare still mounted up underneath the rear of the van? Anyone know if a 265 will fit under there?
As mentioned, depends on your diff, you could just swap the tires around so youíve got 2 of the same in the rear and wait until you need new tires and use one of the 265ís to replace your old spare.
Unfortunately my van does not have the door sticker, just a few Sportsmobile stickers with paint codes/tire size/etc.

My spare is mounted on an Aluminess swing away. It should handle a 265 just fine.

My 265 tires are fairly new, as is the 245 spare. I just want to make sure I can use the 245 spare on the rear end of the van without causing an issue with the diff.

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Old 08-21-2018, 12:55 PM   #6
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If you dont want to spend the money on a new tire for the spare, see if one of the tire shops near you will sell a used tire. The local shop here will charge $25 for a used tire, mounted and balanced. Then you don't have to worry about it.
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Old 08-21-2018, 01:07 PM   #7
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I too bought a used tire for a spare. No sense in spending the full monty on a tire you wont use. Too bad mine was $75 mounted and balanced.
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Old 08-21-2018, 02:23 PM   #8
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Quote:
Originally Posted by BrianBlair View Post
Naturally my van doesn't have the door sticker to help me out here......the only stickers are from SMB and don't mention the axle.

What's the easiest way for me to determine what I've got in terms of gearing and diff type?

BB
Gearing can be calculated this way:

How To: Determine the Rear Axle Ratio
https://shiftsst.com/articles/how-to...ar-axle-ratio/

NEXT: (and most importantly for your question): Differential Type

On a van of your's age (1993), it won't have any sort of sophisticated electronic limited-slip rear axle. But it might have an old-school clutch-pack type rear limited slip. (I think.)

That being the case --- you rear diff type can be likely determined THIS way:

1) SAFETY FIRST --- Van OFF. Key OUT OF IGNITION.
2) ALSO SAFETY FIRST --- chock the two front wheels of the van (in both the front and rear of each tire). Do this ONLY on a level surface.
2) Lift up both rear wheels on jacks and also jack stands.
3) Try to spin one rear wheel with your hand. (May take a little bit of effort.)

If:
A) The other wheel spins in the **opposite direction** fairly easily --- you have an "open" rear differential (no limited slip.)
B) You can't get the wheel to turn AT ALL --- you've got some sort of rear limited slip axle (with a clutch pack in the differential that prevents/resists differential action.)

If you've got a rear limited-slip axle of any sort, then as others have already mentioned you can't get away with driving any significant distance on pavement with different-sized (left-to-right) rear tires. Will overheat the differential/clutch packs and probably grenade itself within several miles, IMHO.

FWIW, my '95 E250 did not come with a limited-slip rear axle.

(You can also look on your rear axle for the Dana BOM (Bill of Materials) number (either on a tag bolted to the rear diff cover, or stamped on the axle tube.....somewhere......) and utilize that to scour the web for the official Dana spec sheets....and then find your match to list what your axle's specs are.

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Old 08-21-2018, 05:34 PM   #9
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[QUOTE=MountainBikeRoamer;
If:
A) The other wheel spins in the **opposite direction** fairly easily --- you have an "open" rear differential (no limited slip.)
B) You can't get the wheel to turn AT ALL --- you've got some sort of rear limited slip axle (with a clutch pack in the differential that prevents/resists differential action.)[/QUOTE]

With both wheels off the ground, shouldn't a L/S should turn both wheels the same direction?
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Old 08-21-2018, 06:27 PM   #10
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With both wheels off the ground, shouldn't a L/S should turn both wheels the same direction?
Not unless you've got the van in Neutral!
(The drive shaft would have to be allowed to spin for what you're describing.)

To keep things as simple (and as safe) as possible, I've described how to sleuth this out with the van in "Park" and key out of the ignition.

But if the van were put in Neutral, yes --- both wheels would spin together in same direction. (And would also spin the driveshaft.)
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