Spare tire different size question? (1 Viewer)
- Thread starter jditom
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
Short period of time being?? 2 blocks? 2 days? 2 years?
- Thread starter
- #3
20-40 miles to fix the flat.
How bad is it for the cruiser to run a spare tire that is 3-5% smaller in an emergency for a short period of time?
I take it that you only do a four tire rotation vs. a five. I would think you have no choice other than using a different size tire.(when you get a flat) The owners manual says you should not run different size tires. not sure if 20-40 miles would be a real harm?
I think it would be wise to limit your speed and distance. I agree that unused spare tires are always a different size compared to used road tires. If the circumference of a 32 in tire is 100.5, then a 3% difference greater is a 33 in tire and I think that's quite a difference. So, a spare of the same size with a 1/4" height difference (reasonable assumption) would be a variance of less than 1%. Just speculating that a 1% difference would be an allowable tire difference to drive the truck without limit. I think you just tossed out 3-5%, but I don't think that would be allowable. More like 1% or therabouts. Subaru allows only 1/4 inch in circumference IIRC, on their AWD models.
So, a worn spare would be fine, but I'm thinking a truck with 33s on the ground and a 32 as a spare would not be good for very long, nor for highway speeds. BTW, I think it's the high speeds that cause the issue - I think you could run a different size on the trail as long as you wanted to.
Did the quick and dirty math here - someone check me?
So, a worn spare would be fine, but I'm thinking a truck with 33s on the ground and a 32 as a spare would not be good for very long, nor for highway speeds. BTW, I think it's the high speeds that cause the issue - I think you could run a different size on the trail as long as you wanted to.
Did the quick and dirty math here - someone check me?
- Joined
- Jul 30, 2003
- Threads
- 72
- Messages
- 2,931
- Location
- Broomfield, Colorado
- Website
- www.gamiviti.com
I think 20 miles to get it fixed is no big deal, and agree with the slow speeds. You got differentials after all that are designed to allow one tire to spin at another rate compared to the other.. that's what's happening when you put a smaller tire on. you could offset this if your journey home was one big arc and you put the small tire on the outside...
If you were REALLY worried about it, or had to go a longer distance, then you could drop the front shaft, lock the CDL then pretend it's 2WD.. putting the small tire in front. but all that said, I rotate 5.
If you were REALLY worried about it, or had to go a longer distance, then you could drop the front shaft, lock the CDL then pretend it's 2WD.. putting the small tire in front. but all that said, I rotate 5.
I disagree.
It's either enough of a size difference to screw up the VC due to overheating and seizing, or it's not. If it is, then 20 miles certainly seems to me like enough time to do it.
Curtis
I ran a wornout 35" M/T with my other 3 285/75R16 M/Ts for almost 4 months.
Never had a problem, VC still works.
Never had a problem, VC still works.
These aren't made from paper....20 miles to fix a flat is fine. Running it for 4 months like Bailey is just plain CRAZY!!! hehe
hehe
I like to push the envelope... 
I also knew I had a part time 4wd kit on the way...
I also knew I had a part time 4wd kit on the way...
- Joined
- Jul 30, 2003
- Threads
- 72
- Messages
- 2,931
- Location
- Broomfield, Colorado
- Website
- www.gamiviti.com
for the sake of my own education, how is your viscous coupler even going to know the difference? The different tire "spin rates" go into the spider gears of the diff, and are allowed to spin at different rates. That's then united into the rotation of a single ring gear, which is then transferred to the rotation of the pinion, then driveshaft, then VC. That would be while coasting.. when applying power the chain is in reverse.
so then the rotational rate of one DS would be off by 1/2 the difference of the OD difference of those two tires on that axle, since what it relays back to the VC is the average spin rate of the two tires, after their rates have made it through the diff, right? Then a straight line becomes a long, gentle corner where one DS is spinning just a little faster than the other.
Having 4 tires the same size will remain my first choice for handling and safety purposes, but IMO if you're worried about a slightly smaller spare you should always only drive in straight lines too, since what you're saying is you should never allow your driveshafts to spin at different rates. But of course I'd be happy to be proven wrong if you know different.
so then the rotational rate of one DS would be off by 1/2 the difference of the OD difference of those two tires on that axle, since what it relays back to the VC is the average spin rate of the two tires, after their rates have made it through the diff, right? Then a straight line becomes a long, gentle corner where one DS is spinning just a little faster than the other.
Having 4 tires the same size will remain my first choice for handling and safety purposes, but IMO if you're worried about a slightly smaller spare you should always only drive in straight lines too, since what you're saying is you should never allow your driveshafts to spin at different rates. But of course I'd be happy to be proven wrong if you know different.
Or at least not in an endless circle for 20 miles...
That dang VC sure is a mystery box, isn't it?
I think there's agreement that at some point, too much difference in tire size would indeed damage the VC. Given that, my point was/is that once you've passed that size difference, it seems to me that 20 miles of highway driving would certainly be enough time to realize said damage.
Is a slightly smaller spare enough size difference to worry about? I admit I don't know.
Cheers back at ya,
Curtis
- Joined
- Jul 30, 2003
- Threads
- 72
- Messages
- 2,931
- Location
- Broomfield, Colorado
- Website
- www.gamiviti.com
Isn't that a Stephen Wright joke? my neighbor's got a circular driveway.. he's still trying to get out.
Bringing back an old post
What if you have 33" tires and your spare is a 31"?
On a 2003+ where you have would you have to turn off your VSC?
Would having the steering wheel sensor know that you are headed straight down the road and the car computer sees that and that one wheel is spinning faster that the others cause Atrac to kick in?
What if you have 33" tires and your spare is a 31"?
On a 2003+ where you have would you have to turn off your VSC?
Would having the steering wheel sensor know that you are headed straight down the road and the car computer sees that and that one wheel is spinning faster that the others cause Atrac to kick in?
- Joined
- Jul 20, 2004
- Threads
- 274
- Messages
- 23,205
- Location
- Chandler, AZ
- Website
- www.tontorecreationalliance.org
Bringing back an old post
What if you have 33" tires and your spare is a 31"?
On a 2003+ where you have would you have to turn off your VSC?
Would having the steering wheel sensor know that you are headed straight down the road and the car computer sees that and that one wheel is spinning faster that the others cause Atrac to kick in?
The '80 doesn't have a steering sensor or other driver aids mentioned. The main "concern" would be the VC, but at this age, it's likely that most or all of them are on the way out, so.
Oh, this is in the 80 section. I got a 100. I'm sorry:/ I should pay more attention.The '80 doesn't have a steering sensor or other driver aids mentioned. The main "concern" would be the VC, but at this age, it's likely that most or all of them are on the way out, so.
