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Anyone know why a WK2 spare tyre is bigger???

279 Views 10 Replies 4 Participants Last post by  ColdCase, 
J
Hey 👋

Does anybody know why the Jeep cherokee 2011 has a bigger spare tyre?

The spare is 245/65/ R18 and the standard tyres are 265/60/ R18 so as you can see the spare is clearly bigger (smaller width (245 vs 265) but bigger diameter (65 vs 60)).

According to the "Car Wizard" on this video
(skip to the 8:30 mark) he clearly explains that the main reason for Cherokee transfer case failure is mismatched tyres as the computer thinks your off road and over engages the transfer case clutches which burns them out.

I thought somebody had put the wrong sized tyre on the spare but the tyre info sticker states the spare is 245/65/ R18 - go figure???? 🤷‍♂️
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ColdCase
a 65 or 60 indicates the ratio of sidewall to tread, not overall tire diameter.

A 245/65/18 has a 30.5 inch diameter, a 265/60/18 tire has the same 30.5 inch diameter, so they are the same size from a transfercase perspective.

They use a narrower tire for the spare to save a few bucks and they do fit the spare tire well better.

By the way, the WK2 has two different transfercases, one has clutches one doesn't.
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J
Cheers ColdCase, :)

A wealth of info as always 👍 you live and learn.

I've just replaced all 4 of the tyres with Goodyear Wranglers(old tyres looked good with lots of tread and no cracking but 11 years old(!) so had to go), I'm super glad I asked on here because the spare looks new and after buying 4 new tyres I didn't want to fork out some more for a new spare.

I'm not sure which transfer case mine has but I will snap a pic of it when I change the fluids - AFAIK it takes ATF+4.
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ColdCase
If you have a center console knob to select traction modes then you have QTII which has clutches. If not, you have the base QTI which has an open diff.

By the way, the YouTube video presents some good info, but much of the guesses on detail is way off. The QTII clutches are always engaged a little and slip when the rear and front driveshafts spin at a different speed, like when turning. When you have different size tires, its likely that the drive shafts are always spinning at a different rate so the clutches are always slipping... which adds wear and tear and may heat them up enough to warp.
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J
It imust be QTII as it has all the modes also has air suspension.
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J
Seeing as your the man to ask what is the difference between placing the stick in neutral and turning the QTII transfer case switch to 'N'?

Im asking as my air suspension blew out both front bags some weeks back (compressor overpressurissed system) and the recovery truck winched it up on the flat bed with it in the standard Neutral position and I did wonder with it being a somewhat complex car if this was correct?
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Mr. Bitey
OD is the the same, only the latter is wider....

I reference this site frequently. Bookmark it!
tiresize.com

Tire Size Calculator

The best tire size calculator. Use our tire size calculator to find tire size specs and suggested tire sizes. Then check prices for all available tire sizes.
tiresize.com tiresize.com

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J
Yay, good site I found it last night, I thought I knew about tyres until ColdCase schooled me lol 😅
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R
jeep_lover_brazil said:
Seeing as your the man to ask what is the difference between placing the stick in neutral and turning the QTII transfer case switch to 'N'?

Im asking as my air suspension blew out both front bags some weeks back (compressor overpressurissed system) and the recovery truck winched it up on the flat bed with it in the standard Neutral position and I did wonder with it being a somewhat complex car if this was correct?
Click to expand...
With the transmission in NEUTRAL the engine is disconnected from the drive train. With the transfer case in NEUTRAL the two drive shafts (front and rear) are disconnected from each other and the transmission.

The transfer case NEUTRAL is needed for flat towing. If you're just dragging the Jeep onto a flatbed then transmission in neutral is fine.
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J
👍 Cheers for all the replies

Just a heads up regarding this transfer case issue with QTII is before I got my new tyres(old tyres were nearly 12 years old + stiff as hell) the car used to get extremely hot - you would really notice the heat standing by the drivers or front passenger door now once I got my new tyres it was noticeably cooler and then after I changed my transfer case fluid with ATF+4 I no longer noticed the excess heat. Worth remembering if your 4WD has limited slip type clutches and you notice excess heat coming from underneath the car.

A good article I found on the QT II transfer case is here - Exploring Some of the Mystery in the MP3023 Transfer Case - Transmission Digest

It says that all wheels have to be within 1/4 diameter maximum of each other with identical tyre pressure or else the clutches will over engage.

I hope I managed to save my transfer case just in time 🤞
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ColdCase
Yes, pretty good article, better before all the marketing nannies. I think we have links to it it and a couple others indexed in the FAQ. GM used the same transfer case with different control software in many of its light trucks. There has been much published in GM articles that is directly applicable to the WK2.
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