Author Topic: odd sized spare tire on K10 with 203 case  (Read 3165 times)

Offline FlatBlack77

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odd sized spare tire on K10 with 203 case
« on: November 13, 2014, 10:46:33 PM »
Hi all i have a 79 K10 with a 203(non part time conversion) transfer case. im running 33/12.50/15s right now and i dont have a spare at all. however i do have a spare wheel and 2 different sized tires i could put on the wheel. one is a 31/10.50 and the other is a 235/75.

say i would mount one on the wheel, throw it in the bed of the truck, and get a flat one day. would it be okay to put on the truck and drive to wherever i needed to go?

i only ask because im not sure if it would hurt the transfer case. ive heard of people with AWD cars doing this and it messing things up. even though i dont know if its true or not.

thanks in advance
"When you are a hammer, everything looks like a nail"
'77 C/10 - 350/350 mild street motor

Offline AlanR

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Re: odd sized spare tire on K10 with 203 case
« Reply #1 on: November 14, 2014, 07:29:58 PM »
It really depends on how far you would need to drive.  The diameter of the 235/75 is about 4" less than the 33's you are running.  I'd use the 31/10.5/15 as it's only 2" less and then use it only as a limited emergency spare.  You can take the truck around town, but limit as much as possible highway speeds and distances.  Most of the speed difference will get absorbed by the differential, assuming you don't have a limited slip setup.  If you do have a limited slip setup on the affected diff, that's where you'll potentially ruin things quickly.

AWD cars typically run into issues because those have fancy electronics and ABS systems that get confused if a tire is going a different speed.  Plus, there is often a clutch or other torque vectoring system that can get hot and destroyed in newer AWD systems.   The 203's are pretty tough, the chain/gears may get worked a little so just take it easy and get the right size tire on asap! :)

Finally, it's really not hard to convert the NP203 to part time and put lockouts on the front hubs.  You'll get better fuel mileage, reduce wear on front drivetrain, less harmonic vibrations in the cab, and not have to worry about mismatched tires up front if you had to mount a spare!  Of course you loose the AWD, and some people really like/need/want that.  Just my $.02.

Have a great one,
Alan

'76 K10 Silverado.  All non-original powertrain. 350/350C/203

Offline roundhouse

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Re: odd sized spare tire on K10 with 203 case
« Reply #2 on: November 14, 2014, 10:49:24 PM »
If you're gonna throw it in the bed and not mount it underneath.   Why not find a used 33?

I dont think a 33 will fit underneath

Offline Irish_Alley

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Re: odd sized spare tire on K10 with 203 case
« Reply #3 on: November 14, 2014, 10:53:09 PM »
or you could lock the t case and remove the drive shaft. its a pain but you will be safe doing this.
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline FlatBlack77

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Re: odd sized spare tire on K10 with 203 case
« Reply #4 on: November 15, 2014, 06:39:50 AM »
Thanks for the input guys!

ive been looking for a full size spare but i havent found a single 33 yet. my trucks got a flatbed so i cant found it underneath without making a bracket setup im happy just throwin it in the bed

my truck actually had lockouts already. someone in the past put them on but didnt convert the case(i know for a fact). im happy with the truck the way it is for the time being

and i didnt think about it but i guess i could just put the spare on the front, unlock the hubs, and lock the case. it would only be a worst case scenario thing.

thanks again!

"When you are a hammer, everything looks like a nail"
'77 C/10 - 350/350 mild street motor