How Bad is it if Spares Not Exactly Same Size? - CorvetteForum - Chevrolet Corvette Forum Discussion

Notices
C1 & C2 Corvettes General C1 Corvette & C2 Corvette Discussion, Technical Info, Performance Upgrades, Project Builds, Restorations

How Bad is it if Spares Not Exactly Same Size?

Old 11-08-2018, 04:59 PM
  #1  
Lotsacubes
CF Senior Member
Thread Starter
 
Member Since: Feb 2015
Location: Huntsville AL & TN
Posts: 647
Thanked 133 Times in 103 Posts
Default How Bad is it if Spares Not Exactly Same Size?

My rears are 26.3" and it appears a matching 15" diameter is a 205/70R15. But that's too wide for the spare carrier. I may be going with a trailer tire to match diameter for a spare, unless 185/65R15 at 25.7" diameter would be ok for short distances. I don't know how much diameter mismatch could damage the posi rear end for short distances. If the spare was 1/2" smaller and limited to.... say 20-30 miles would that hurt the posi? Thanks

Last edited by Lotsacubes; 11-08-2018 at 05:05 PM.
Lotsacubes is offline  
Old 11-08-2018, 05:12 PM
  #2  
Tampa Jerry
CF Senior Member
 
Member Since: Aug 2005
Location: Temple Terrace Florida
Posts: 2,810
Thanks: 0
Thanked 128 Times in 119 Posts
Default

I know what you mean. I bought a 16" S-10 spare tire and rim at a junk yard. It fits in the carrier with no problem. If I get a flat in the rear, I can put the S-10 tire on the front and the front tire on the back. It sounds like a pain, but easier to change than a posi unit. No flats as of yet. Jerry
Tampa Jerry is online now  
Old 11-08-2018, 05:32 PM
  #3  
firstgear
CF Senior Member
Support Corvetteforum!
 
firstgear's Avatar
 
Member Since: Sep 2003
Location: Norwalk ohio
Posts: 8,369
Thanked 216 Times in 165 Posts
2019 Corvette of the Year Winner
St. Jude Donor '15
Default

Originally Posted by Lotsacubes View Post
My rears are 26.3" and it appears a matching 15" diameter is a 205/70R15. But that's too wide for the spare carrier. I may be going with a trailer tire to match diameter for a spare, unless 185/65R15 at 25.7" diameter would be ok for short distances. I don't know how much diameter mismatch could damage the posi rear end for short distances. If the spare was 1/2" smaller and limited to.... say 20-30 miles would that hurt the posi? Thanks
thats what insurance is for.....flat bed tow service....
firstgear is offline  
The Following User Says Thank You to firstgear For This Useful Post:
ZERRY 316 (11-10-2018)
Old 11-08-2018, 06:40 PM
  #4  
dr914
Junior Member
 
Member Since: Oct 2013
Location: Marietta Georgia
Posts: 33
Thanks: 0
Thanked 1 Time in 1 Post
Default

the spare tire carrier was actually made for a conventional tire, the radial needs to be really jammed in there
dr914 is offline  
Old 11-08-2018, 06:52 PM
  #5  
wmf62
CF Senior Member
 
wmf62's Avatar
 
Member Since: Jun 2006
Location: Inverness FL
Posts: 17,896
Thanked 680 Times in 581 Posts
St. Jude Donor '07
Default

this is a very good question, I hope someone provides a definitive answer

Bill
wmf62 is offline  
The Following User Says Thank You to wmf62 For This Useful Post:
Lotsacubes (11-08-2018)
Old 11-08-2018, 07:22 PM
  #6  
4 Speed Dave
CF Senior Member
 
4 Speed Dave's Avatar
 
Member Since: Dec 2010
Location: Southington CT
Posts: 872
Thanked 110 Times in 70 Posts
Default

Just do the math. The tire with the 26.3" OD travels 766.8 revolutions per mile. The tire with the 25.7" OD travels 784.7 revolutions per mile. Or 21.9 more revolutions per mile. If you go 20 miles the shorter tire will have to turn 438 more times than the taller tire. This will create lots of heat in the posi unit.
4 Speed Dave is offline  
The Following User Says Thank You to 4 Speed Dave For This Useful Post:
Lotsacubes (11-08-2018)
Old 11-08-2018, 07:27 PM
  #7  
68hemi
CF Senior Member
 
68hemi's Avatar
 
Member Since: Nov 2003
Location: Cottonwood AZ
Posts: 3,351
Thanked 394 Times in 309 Posts
Default

Originally Posted by Lotsacubes View Post
My rears are 26.3" and it appears a matching 15" diameter is a 205/70R15. But that's too wide for the spare carrier. I may be going with a trailer tire to match diameter for a spare, unless 185/65R15 at 25.7" diameter would be ok for short distances. I don't know how much diameter mismatch could damage the posi rear end for short distances. If the spare was 1/2" smaller and limited to.... say 20-30 miles would that hurt the posi? Thanks
Don't worry about it if you use it like a spare should be used. Get home or to a tire shop to fix the other tire or replace it.
68hemi is online now  
The Following User Says Thank You to 68hemi For This Useful Post:
Lotsacubes (11-08-2018)
Old 11-08-2018, 07:37 PM
  #8  
DAN70
CF Senior Member
Support Corvetteforum!
 
DAN70's Avatar
 
Member Since: Dec 2008
Location: PURCELLVILLE VA
Posts: 728
Thanked 82 Times in 71 Posts
2017 C1 of Year Finalist
Default

I purchased a used correct size BiasPly as a spare for my ‘54. It’ll work as a spare and fits perfectly in the spare tire tub.

Last edited by DAN70; 11-08-2018 at 07:39 PM.
DAN70 is online now  
The Following User Says Thank You to DAN70 For This Useful Post:
Lotsacubes (11-08-2018)
Old 11-08-2018, 07:40 PM
  #9  
Brian VH McHale
CF Senior Member
 
Brian VH McHale's Avatar
 
Member Since: Dec 2001
Location: LI NY NY
Posts: 1,596
Thanked 59 Times in 50 Posts
Default

Who is getting all these flat tires?
Brian VH McHale is offline  
Old 11-08-2018, 07:52 PM
  #10  
65GGvert
CF Senior Member
 
65GGvert's Avatar
 
Member Since: Jul 2006
Location: Kannapolis NC
Posts: 15,100
Thanked 973 Times in 858 Posts
Default

if you have to drive it more than a few miles on the spare, move a front tire to the rear and put the spare on the front. I personally don't think it'll hurt the posi but that's up to you.
65GGvert is offline  
Old 11-08-2018, 08:02 PM
  #11  
6D2148
CF Senior Member
 
6D2148's Avatar
 
Member Since: Jan 2012
Location: Limerick Pa
Posts: 1,055
Thanked 53 Times in 48 Posts
Default

I hate to make a jinx on myself, but I will go out on a limb and say, I'm 63 and only ever had to put the spare on one time out on the road. Keep good tires on your car, avoid large pot holes, am I just lucky or is it not the 1920 or 40's when road side tire changes were common, a part of life. If you get a lot of flats be prepared, have two spares, and the perfect second car(towtruck). Chip
6D2148 is offline  
The Following User Says Thank You to 6D2148 For This Useful Post:
Lotsacubes (11-08-2018)
Old 11-08-2018, 08:13 PM
  #12  
Frankie the Fink
CF Senior Member
Support Corvetteforum!
 
Frankie the Fink's Avatar
 
Member Since: Aug 2007
Location: Orlando Metro Area Florida
Posts: 45,119
Thanked 2,831 Times in 2,308 Posts
Default

Originally Posted by 4 Speed Dave View Post
Just do the math. The tire with the 26.3" OD travels 766.8 revolutions per mile. The tire with the 25.7" OD travels 784.7 revolutions per mile. Or 21.9 more revolutions per mile. If you go 20 miles the shorter tire will have to turn 438 more times than the taller tire. This will create lots of heat in the posi unit.
Yes, the differential thinks its in a LONG turn and acts accordingly...

Frankie the Fink is offline  
The Following User Says Thank You to Frankie the Fink For This Useful Post:
Lotsacubes (11-08-2018)
Old 11-08-2018, 08:18 PM
  #13  
wmf62
CF Senior Member
 
wmf62's Avatar
 
Member Since: Jun 2006
Location: Inverness FL
Posts: 17,896
Thanked 680 Times in 581 Posts
St. Jude Donor '07
Default

these are all good workarounds, but no one has answered the question
Bill
wmf62 is offline  
Old 11-08-2018, 08:30 PM
  #14  
6D2148
CF Senior Member
 
6D2148's Avatar
 
Member Since: Jan 2012
Location: Limerick Pa
Posts: 1,055
Thanked 53 Times in 48 Posts
Default

Minimum, need spare to limp to where ever, or a same same spare to continue on your journey. Chip
6D2148 is offline  
Old 11-08-2018, 09:21 PM
  #15  
68hemi
CF Senior Member
 
68hemi's Avatar
 
Member Since: Nov 2003
Location: Cottonwood AZ
Posts: 3,351
Thanked 394 Times in 309 Posts
Default

Originally Posted by wmf62 View Post
these are all good workarounds, but no one has answered the question
Bill
I did in post #7
68hemi is online now  
The Following User Says Thank You to 68hemi For This Useful Post:
Lotsacubes (11-08-2018)
Old 11-08-2018, 09:38 PM
  #16  
Lotsacubes
CF Senior Member
Thread Starter
 
Member Since: Feb 2015
Location: Huntsville AL & TN
Posts: 647
Thanked 133 Times in 103 Posts
Default

Originally Posted by 6D2148 View Post
Minimum, need spare to limp to where ever, or a same same spare to continue on your journey. Chip
Yes exactly. This is only for limp short distance use. At the moment my fronts are not the same size as my rears to clear fender. Hate to even mention itís been a long time since I needed a spare.

Maybe the bigger problem is where to put the big, flat tire. Sure wonít fit in the carrier. I like the big slow turn example FTF. Thanks all. I think Iíve found a skinny trailer tire.
Lotsacubes is offline  
Old 11-08-2018, 09:50 PM
  #17  
wmf62
CF Senior Member
 
wmf62's Avatar
 
Member Since: Jun 2006
Location: Inverness FL
Posts: 17,896
Thanked 680 Times in 581 Posts
St. Jude Donor '07
Default

Originally Posted by 68hemi View Post
I did in post #7
nope, a 'normal' spare is the same size as all 4 tires and can be used for as short or long a distance as needed

Bill
wmf62 is offline  
Old 11-08-2018, 09:54 PM
  #18  
Easy Rhino
CF Senior Member
 
Easy Rhino's Avatar
 
Member Since: Apr 2008
Location: Chesapeake Virginia
Posts: 18,577
Thanked 552 Times in 458 Posts
Default

I think the answer to the OP's concern is: you'll be fine. These old non-electronic non- nannified systems are far, far more resilient to differences like 1/2" differences in tire measurements. Seriously. That's not to say that one should drive hundreds of miles with such a difference, but for spare tire use, you'll be just fine. Enjoy!
Easy Rhino is offline  
The Following User Says Thank You to Easy Rhino For This Useful Post:
Lotsacubes (11-08-2018)
Old 11-08-2018, 10:36 PM
  #19  
65GGvert
CF Senior Member
 
65GGvert's Avatar
 
Member Since: Jul 2006
Location: Kannapolis NC
Posts: 15,100
Thanked 973 Times in 858 Posts
Default

Originally Posted by Frankie the Fink View Post
Yes, the differential thinks its in a LONG turn and acts accordingly...
That's why I only drive mine on straight roads.
65GGvert is offline  
Old 11-08-2018, 11:09 PM
  #20  
Easy Rhino
CF Senior Member
 
Easy Rhino's Avatar
 
Member Since: Apr 2008
Location: Chesapeake Virginia
Posts: 18,577
Thanked 552 Times in 458 Posts
Default

Originally Posted by 65GGvert View Post
That's why I only drive mine on straight roads.
LOL, I avoid going into long sweeping turns to prevent excessive wear to my differential over its life.
Easy Rhino is offline  

Thread Tools
Search this Thread
Sponsored Ads
Vendor Directory

Contact Us About Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: