Different tire sizes cause problems?

[SteveandTracyinKY]

I just recently bought a 98 Chevy Blazer 4x4 with 170,000 miles. 4.6L V6

Today while looking thing over I noticed that the front right tire is a different size. The rest are 235 75 R15, but the front left is 225 70R 15. I know this is not optimum, but is it a "Don't drive it any more" kinda of problem. I really don't have the cash to fix this before at least Friday, or 5 days away.

Also discovered that I have no spare tire or jack. Can I use this tire as my spare when I get a new one? Buy a doughnut? Do I need a full size spare since its a 4x4?

Since I started driving it on the interstate, I have noticed at speeds above 65 it tends to have a small shake in it. Could that be caused by the smaller tire?

[Donnie]

I was told different size tires front and back is a no no for 4 wheel drive. Puts the transfer case in a bind. If you leave it out of 4 wheel drive, should be ok, I would think

[TLBones]

I'm no mechanic, but you should be OK for a few days if no 4wheeling.   Make sure the tires are the same left to right!   I think that's more critical than front to back.   I've heard even with the same size tires you want to make sure they have about even tire wear left to right.

[SteveandTracyinKY]

Well that is the difference. The right front has a 235 75 and the left front is 225 70. Talked to my tire guy a little bit ago and he said as long as I don't put it into 4x4 its should be ok for a little while.

[slingblade]

Since it is left to right it will stress the diff even when not in 4x4.  More importantly, it will screw with the speed sensors for the ABS causing uneven braking when the ABS releases (at the point of wheel lock up) brake pressure.  The smaller diameter tires will look like they are locking up vs the larger one.  Handle this ASAP.  That extra few inches of stopping distance may be the difference between a close call and the funeral home.

[bdhutier]

Agree with the above.  To sum up, here's some rules of thumb:

1. All normal-use tires the same size (eg. not a race car).

2. Each axle set the same size, especially a drive axle.  This includes a 4x4 axle.

3. Replace, as a minimum, in pairs.

[hillclimber]

I agree, It will be hard on the spider gears because your front end now thinks you're going around a corner, even when you're not.
One of your front shafts is spinning faster than the other, and the slip is being compensated by your front end.
If you happen to have manual hubs, unlock them so your front axles won't spin. Other than that, buy atleast one 235, even if it's used. Even that would be better than what you have now.
I wouldn't drive it very far that way. A hundred bucks for a tire may sound steep, but a grand for a front end would really suck.

[idelphic]

Dissimilar tires front and back isn't as big of a deal as on the same axle.  But since you are talking about a 4x4, you'll need to look into getting them the same size.  One thing you might listen for is a bumping or 'knocking' noise in the front end when you turn.  Could be a sign of binding in the transfer case.  Might also have someone drop the pan and check for bits of metal as soon as you are able, and before you depend on the 4x4...

Some old muscle cars would use larger tires in the rear and smaller in the front...  On a truck, that doesn't make sense.

You may find some tire stores willing to trade you out for a set of used tires for the mismatched tires if they are still pretty decent.

[JerseyVince]

Many sports cars have different size Tires/Wheels front and back (Corvette/lambo/Porsche) But its a NO-NO on a 4WD especially new style AWD Vehicles and QuadraDrive Jeeps, AWD Minivans. Left to Right is a problem with anything with a posi or Limited slip axle and will fry clutches at highway speeds after a while. Front to back will cook the fluid clutch pack in a Transfer case like the 247NPG-249NPG. forget cause problems with twitchy ABS, Antilock/skid/traction control detects differences in wheel speed then applies the brakes to each wheel as needed. If the wheel speeds are already out of sync ABS can apply too early or not at all. and on most vehicles transmission shift point speeds are take from the vehicle wheel speeds, so erratic shifting or banging into gear can happen too

Short answer look for a set of matched tires/wheel. try a local dealer/bodyshop/tire dealer most of them have wheels with tires (Takeoffs) laying around and want to get rid of them

[TLBones]

Jerseyvince is right.   235/75R15 is a very common size... should be plenty around if you are on a budget.

[Saint]

Folks,
need some advice on tires and since this perfectly named thread fits my "different" problem, I'm going to try here.

Have an old Jeep CJ-7 with a 3" leaf spring lift.
have always had 32" tires on it.
got a good deal on Craigslist for 35" tires.
other than the speed-o-meter probably being off (and turn radius limited due to internal clearance) are there any reasons (mechanically) I shouldn't put the tires on without some other mod? Like, mis aligning some drive shaft component or something?

Saint

[endurance]

Folks,
need some advice on tires and since this perfectly named thread fits my "different" problem, I'm going to try here.

Have an old Jeep CJ-7 with a 3" leaf spring lift.
have always had 32" tires on it.
got a good deal on Craigslist for 35" tires.
other than the speed-o-meter probably being off (and turn radius limited due to internal clearance) are there any reasons (mechanically) I shouldn't put the tires on without some other mod? Like, mis aligning some drive shaft component or something?

Saint

My only concern is the loss of power you're going to experience.  You're essentially changing the gear ratio.  I had a 4x4 truck I bought with 35" tires on it and when I finally put 31.5" tires on it, it felt like I gained a hundred horsepower.  It was a totally different truck with the smaller tires on it.

[Saint]

Thanks End - never even considered that angle.
I don't do any towing or off-roading, but that's a great point.

[hillclimber]

Your gear ratio will be important. Does it still have the original running gear?? If it's reasonably stock, (other than the 32s and the mild lift) You won't want that big of a tire.

[Saint]

yes, its stock - and that's more the angle I was thinking - just not savvy enough yet to know, but my Chilton's manual is helping

[nkawtg]

This is even a bigger problem with "all wheel drive" vehicles. Even having different brands of the same size can be a problem for some fine German engineered vehicles because of slight differences in circumference.
So for those with all wheel drive and a full size spare, you will need to include your spare in your tire rotations.

[SteveandTracyinKY]

You may want to talk to someone about the integrity of the shocks, ball joints, and brakes. It will also hurt you MPG. I am getting ready to go bigger on my tires, and this is what I have collectively been told by all the off roaders around here. I have had several people tell me that the shocks are the most over looked part during a partial build. Not sure why.

[Cacinok]

You may want to talk to someone about the integrity of the shocks, ball joints, and brakes. It will also hurt you MPG. I am getting ready to go bigger on my tires, and this is what I have collectively been told by all the off roaders around here. I have had several people tell me that the shocks are the most over looked part during a partial build. Not sure why.

It's not really intuitive to think about, but I'll try to explain.  Shocks aren't just affected by the vehicle above them, they are affected by the wheel/tire combo as well.  The shocks are are generally sized not just for the type of vehicle, but also for your stock tire/wheel combo, specifically the rolling weight of that combo.  Larger wheels and tires weigh more, often a lot more.  When you hit a bump, the shock tries to dampen/resist the upward movement of the wheel/tire.  Bigger wheel/tire means more upward force into the shock.  Also, when you crest a hill or bump, the tire begins dropping before the actual vehicle.  The shock slows the tire/wheel dropping.  B/c the tire/wheel are heavier than stock, the shock is worked harder than it is designed.  Now it may only be worked a couple percentage points more than it was designed, but it heats up more and faster than normal which will mean premature failure. 


OP, the vibration you are feeling is most likely the tire being out of balance.    Also, if you have an independent front suspension, different tire sizes will be less critical, still not ideal, than if you had a straight axle front end. 

[nkawtg]

Good point you made on brakes SteveandTracyinKY. Bigger tires mean greater rotational inertia. If your going from say 31's to 33's a pad/shoe upgrade may be all that's needed to overcome the rotational inertia of bigger wheels. Any bigger than that and you will most likely need bigger brakes.

[hillclimber]

All that stuff is true enough, especially with a more "modern" vehicle, but that old CJ7 isn't gonna be as much of a problem. We're talking straight axle both front and rear, with leafsprings all the way around.
Also, it probably still has the old straight 6 engine. If it has 4:10s in it, it should go fine with 32s or 33s.
35s are too big (for me)

Old stock jeeps like their tires tall and skinny anyway

[Saint]

I'm with you Hill,
I think this was a case of my eyes being bigger than my stomach and a "good deal" on Craigslist getting the better of me.
Going back to my 32"

[Vin-britt7989]

We had two bigger tires on the back and smaller on the front of my 05 Chevy trailblazer. It's fully loaded, I love my car... but my fiance told my it was OK to have 16's on front and 17's on the back, and I had to use 4wheel high to travel for work. Nothing seemed to work right with my 4wd, but I had no choice but to travel using it with the horrible storm. We ended up buying another set of 17's but it hums horribly when speeding up and it does it anytime I go above 15 mph. It's constant, and a deep hum, but it is engaged. ANY idea's about  what the problem is?

[CarbideAndIron]

Folks,
need some advice on tires and since this perfectly named thread fits my "different" problem, I'm going to try here.

Have an old Jeep CJ-7 with a 3" leaf spring lift.
have always had 32" tires on it.
got a good deal on Craigslist for 35" tires.
other than the speed-o-meter probably being off (and turn radius limited due to internal clearance) are there any reasons (mechanically) I shouldn't put the tires on without some other mod? Like, mis aligning some drive shaft component or something?

Saint

CJ7's most commonly are Dana 30 front, and AMC 20 rear axle. 35's are what most consider max size for those axles. I think 3.55 gears is common for stock. Some chromoly axles would help. But if you aren't wheeling it hard, those axles will be totally fine with 35's.
Now if you're lucky, one year (86?), had the Dana 44 rear axle, which will handle 35's, no problem.
If you are really unlucky, you have the Dana 35. Don't put bigger tires on if you do, or waste any money on that axle.
Also, if you have a locker, that is great, but it also adds to the stress on your axles. So that combined with the 35's might be enough to due them in.

[scoop]

Here is a site where you can compare different tire sizes:
https://www.tacomaworld.com/tirecalc?tires=225-70r15-235-75r15