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mismatched tires


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jackx
User

Sep 9, 2015, 8:36 AM

Post #1 of 13 (1006 views)
mismatched tires Sign In

I have a 1989 gmc jimmy 4wd s15. It has 4wd but I never use 4wd.
I have 235/75r/15 tires on both rear wheels.
One front tire has 235/75r/15 and the other has a 235/70r/15.

The 235/75r/15 has a circumference of 90.72 and the 235/70r/155 has a
circumference of 87.82

As long as I don't use 4wd is it ok to run the mismatched tires on the
front of the vehicle.

I hate to buy another tire unless I really need to.


(This post was edited by jackx on Sep 9, 2015, 8:39 AM)


Tom Greenleaf
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Sep 9, 2015, 8:46 AM

Post #2 of 13 (1001 views)
Re: mismatched tires Sign In

? It's OK, IMO if just a local vehicle, slower speeds and you don't care that much about tires wearing a bit more and really can't align it that way. 4X4 on all I know of for about then wasn't for any real speed OR not when really needed unlike an AWD which would matter totally.


Preferred of course is matching tires all around if you can swap out for part credit or some deal I would. Right brand too helps.


If nicer and drive more and at speeds change it to the right/matching size,


T



(This post was edited by Tom Greenleaf on Sep 9, 2015, 8:48 AM)


Hammer Time
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Sep 9, 2015, 9:28 AM

Post #3 of 13 (996 views)
Re: mismatched tires Sign In

No, it's not OK, You are going to tear up the front differential and also have ABS problems.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Sep 9, 2015, 9:50 AM

Post #4 of 13 (992 views)
Re: mismatched tires Sign In

? Can't find ABS on this for front anyway. Matters if a farm vehicle now or really driven anywhere? How is it you got the mismatched tire to begin with if new? If used AYOR totally or different brands on an axle.


All thing preferably don't do this as HT said. Matters what you now use this for and would be harder on front diff. with wheels never turning the same speed,


T



jackx
User

Sep 9, 2015, 10:18 AM

Post #5 of 13 (987 views)
Re: mismatched tires Sign In

I understand why you have to run the same size on front and back if you use 4wd. So I put the
offsize tires on the front even though the rear end is not posi. I still wanted the same size tires on
both sides because I figured even though it might work now long term it might be a problem. I know you
aren't supposed to run donut tires very long. So I decided having mismatched tires on the back would
not be a good idea.

Since I can jack up the front and turn one wheel way and the other the oppposite way I have
a hard time understanding why I having slightly different size tires on those wheels matter. Even
though the cv shafts attach to the front transfer case they apparantly aren't engaged with each
other in any way or you could not turn them in opposite directions.

I really did not know the truck had abs. I know it doesn't have it on the back. I guess it may
have abs on the front.

I got the tires from my son. He had a blow out and the service station put the 235/70/15
on the truck. His truck was a 97 blazer. I have since pulled those tires off his truck and put new ones
on and I decided to put the tires on that truck on this one just to get it back on the road.
The old tires were bald and the tires I pulled off his truck have great tread and I needed to do something with them.

I'll try to find a replacement tire. I only drive this truck about 3k a year. Its a spare truck I keep around.

Thanks


Tom Greenleaf
Ultimate Carjunky / Moderator
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Sep 9, 2015, 10:53 AM

Post #6 of 13 (983 views)
Re: mismatched tires Sign In

It's always best for it to match exactly - no argument. This (if I'm right) you should only be using 4X4 just for the time needed to get out of trouble and back to 2WD like two like it I've owned. Forget and plain wet roads over 30 MPH or turns you feel it bind so mismatched is always binding a bit in this case.
If this has ABS at all you should see it under hood and a light should light while starting the truck and go out as in OFF.
In short to suggest as I should have, have matching tires for each axle. Unless this one is different front and rear would matter and wreck it's behavior if using 4X4 on non totally needed situations like stuck.


Even now if the type I think put in 4X4 on dry road/surface and turn sharp and go just walking speed. It will bind like nuts almost hop on you.
If this vehicle is worth a damn get a matching tire and be done with the issue.


What messes me up is why so many people get four wheel drive and don't need it at all or near never. It's a lot of expense and extra stuff to go wrong IMO for the "real truck" type use fine, for everyday a waste,


T



Hammer Time
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Sep 9, 2015, 11:33 AM

Post #7 of 13 (980 views)
Re: mismatched tires Sign In

What you don't understand is the differential has side (spider) gears to allow it to make turns. When both wheels travel at the same speed those side gears are not moving or engaged at all. As soon as one wheel turns faster than the other. the side gears engage and will wear them out in no time and the metal worn off of them will destroy the rest of the differential.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



jackx
User

Sep 9, 2015, 12:14 PM

Post #8 of 13 (975 views)
Re: mismatched tires Sign In

I bought a used 235/75/14 for 50 bucks that I will put on the front tomorrow and replace the 235/70/15.
Supposedly its in good shape with about 80% of the tread left. We will see tomorrow I guess.

Back when I got that Jimmy it seems like I needed it every year in the winter because back then it snowed every year.
That was 24 years ago. Since I turned 65 I stay home when it snows and it doesn't snow as much now.

I still have bad winter in Texas tough A couple years ago we had a ice storm and the ice was thick on my trucks cab.
When it slide off it took all the paint with it. That's why I had to paint it last week when I decided to put it back on the road. I didn't have the truck operational during that ice storm and I spun my Blazer around 3 times just going to the store.

Now I guess I can use 4wd if I need it this winter if it snows.


(This post was edited by jackx on Sep 9, 2015, 12:28 PM)


Hammer Time
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Sep 9, 2015, 1:04 PM

Post #9 of 13 (968 views)
Re: mismatched tires Sign In

How do you propose you are going to put a 14" tire on a 15" rim?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Sep 9, 2015, 1:18 PM

Post #10 of 13 (966 views)
Re: mismatched tires Sign In

Spring for the right tire! You can't put a 14" tire on a 15" rim anyway at all no matter what.


The middle # is % high as it is wide for same numbers which is why a 75 means % is taller hence the circumference difference.


NO. I don't care if the next 14" is on a rim that might fit and bet not. There's more to it than you think. Tires really should be of the suggested size the vehicle maker lists and at least even on most per axle - type, wear and size. If you put ONE brand new tire on a vehicle with 1/2 worn tires it's trouble enough even if you find he exact one new.


OK - now you said Texas and assorted weather of course the state's so big. Got it. TMK almost all has tons of long straight driving and that's when the differential will always think it's slightly turning and mess with it.


Other - 4X4 isn't magic by itself for ice. There's some that nothing is going anywhere for a while and shouldn't.
Wasting time with this - get the right matching tire,


T



jackx
User

Sep 9, 2015, 1:59 PM

Post #11 of 13 (962 views)
Re: mismatched tires Sign In

just like the gop debates guess you got me. I meant 15


Discretesignals
Ultimate Carjunky / Moderator
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Sep 9, 2015, 4:05 PM

Post #12 of 13 (954 views)
Re: mismatched tires Sign In

It won't hurt it on that design because it has a center disconnect that basically disconnects one axle (right axle) from the differential carrier. On that design the front differential pinion and side gears always spin while driving in 2wd because the left axle doesn't disconnect from the differential. It probably wouldn't be a good idea to put it into 4wd with two different matching tires though or have two different tires in the rear.






Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 9, 2015, 4:26 PM)


jackx
User

Sep 10, 2015, 8:17 AM

Post #13 of 13 (933 views)
Re: mismatched tires Sign In

Thanks Descrete. I guess your post settles this issue. I got worried after reading the other posts
and was afraid to drive down to get the mismatched tire replaced and I jacked it up and have it
in my Blazer now to take down.

You confirmed my suspicions when I saw that the front wheels are not engaged in any way to each
other.

I guess having the two tires the same will make it possible to nail the alignment. I just used a
sheet rock square to align it so far. I slid it up to both the front and rear side of each front tire and
both tires are perpendicular to the ground now after I adjusted the control adjusting bolts. I only wanted to
make sure the wheels were 90 degrees to the ground. I just put new ball joints and upper control
arms on it. It drives great down the road now. I did not change out the tie rods so I figure the toe is ok.

I'll watch the front tires to see how they are wearing and I may even take it down and have a shop
check the alignment after I get the tires back on it.

I was going to replace another of the tires anyway. I believe it took 4 or 5 weights to get it to balance out.
It was on the front end of the truck and I drove it with the ball joints and control arm bushing worn out
for a long time. The tire reflects this in that it has scallops on it so bad the truck starts to have a slight
vibration once you get up to 70 mph. I put that tire on the back but I believe it is the root of the problem and
I'll move it to being a spare and replace it with another 50 dollar tire. Hopefully after today everything will be
copacetic.






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