Two Different Tire Sizes on Same Vehicle

If the "transfer" case is not locked, I don't see why not.

My buddy ran huge tires on the back of his Jeep PU and stock tires on the front.

He never had any problems. He never locked in this front axle until on slippery surfaces.

Thank you Lyn, when I do put in 4 wheel I am going slow. Brian

ablsolutely not. different tire sizes have a different diamaters and will spin at different speeds. it will junk you transfer case or rear ends.

I get slightly different values for the rev's per mile (721 and 698), but the spread is very similar to that calculated by lyn.

What size spare will you carry?

Thats a good ? I doubt one of each

I have had a number of four wheel drive outfits and have always run the same size tires on all corners, so I haven't had to worry about it. All four the same size really is the best way to go.

But faced with your situation, I would carry a spare the size of the rear, and hope like crazy I didn't have a flat on the steering axle when I was in the woods and needed to engage the 4WD. That would chew up the axles/drivelines/tires in a hurry.

I wasn't in a hurry, so I drove slower than you did, and my tires stayed smaller.

I'm with you, the difference will be seen by the differential and it will be whirring around like a crazy thing. They are not usually designed for such differences.

Now if the OP unlocks the front hubs, all the time except when 4 wheel drive is needed, that would be OK.

But aren't most hubs automatic nowadays? Does he have the chance to unlock them.

The only other way is to unlock the center differential, if that is at all possible.....

I have to admit I am not up to speed with modern 4 wheel drives.......

I am assuming that there is a central diff by the way, as all good 4WD have......but I don't know the vehicle being discussed.......also the problems will ONLY be there in 4WD, not in 2WD....

In the OP he posts it is a 1990 so it is unlikely that they are constant lock, probably manual of vacuum assisted.

When you engage the transfer case on a 4-wheel drive truck such as this, that is locking the front drivetrain to the rear. The Toyota trucks use gear or chain driven transfer cases, depending on the vehicle model and engine type. The geartrain separating the front and rear ouptut shafts run through a synchro only for shifting into 4WD. The purpose of the synchro in the transfer case is to ensure the speed of the front drive train matches that of the rear before engaging.

Your truck will encounter permanent slip with mismatched tires when 4WD is engaged, therefore negating any traction on hard slippery surfaces such as snow or ice because your tires will be constantly breaking traction as they spin at different speeds. In sand or mud the different speeds may be detrimental or helpful, depending on the conditions and traction needs. You will either be dragging the rear tires or pushing the front tires, depending on how you arrange the different sizes and which axle has better traction. Breaking traction with the rear on a slippery surface usually results in a 180 tail spin. Pushing the front tires results in loss of directional control and an unusual amount of stress on the CV joints.

Unless you have a system which incorporates a center differential (in concert with the front and rear differentials, and a transfer case such as the Four-Trac system) you will eventually break something due the added strain between the front and rear.

At best it will just wear out faster.

I didn't make this up. His was a 70's Jeep with manual transmission. He NEVER had a handling or traction problem!

"My buddy ran huge tires on the back of his Jeep PU and stock tires on the front.

He never had any problems. He never locked in this front axle until on slippery surfaces."

I'm not saying it couldn't cause problems on dry pavement. I am saying I rode in the thing many times with no problems.

You are being an alarmist. The difference in diameter is insignificant here.

No, not alarmist. But in an engineering forum such as this, I wouldn't refer to what my buddy did and never having a problem. I wouldn't want to be thinking about the possible problems I might have due to mis-matched wheel diameters, but actually concentrating on my driving.

I did not mention dry pavement in my response, but the different types of surfaces one might use 4WD drive upon. Leaving the vehicle in 2WD mode would not produce any noticeable effects, in my opinion.

If the OP were to query the manufacturer of the vehicle, he might get an alarmist response.

Just relaying the fact that I had real world experience with one vehicle.

I'm sure the dealer would advise against it, too.

Maybe naturaledge will give us some more real world info.

You can, at your own risk, but honestly, why would you?

Providing you have 2 tyres the same on the front, 2 the same on the back, your in 2WD and your front hubs are freewheeling, it wont matter. But i wouldnt put it in 4WD though, or you will go loading things up that arnt meant to be loaded.

I have a 90 model cruiser and I once ran an imperial trye in place of a metric tyre of very close comparible size on the rear because thats all i had when i got a flat out in the sticks. It was fine for the first 250kms on dirt, cause it was bouncing around so much and relieving the load i guess. But once i made it another 100kms on the bitumen, she must of got to wound up, cause all my axle studs snapped off on the drive side off the diff......pulled it out, threw it in the back, jammed a rag in there, and limped the other 250kms home on the front diff.

The moral of the story?...just stick to one size tyre.

No fourwheel drive with that kind of mismatch. In an emergency, on dirt or mud or sand, you can deflate the pair with the largest diameter (measure ahead of time to the center of the axle from the ground, and deflate the higher until heights are equal. Record the pressures, keep in glove box with tire pressure gage.) Get out of fourwheel drive as soon as possible. No need for 4wheel on hard pavement. The stresses developed on high traction pavement are the same level as dragging the car with a tow truck and the engine off with transmission in low low range. You get the picture?

The 235/75/15 tyres will have a slightly larger diameter than the other size. Always put the larger tyres on the front. It won't make any difference while you are in 2wd but when in 4wd it will give you much better control as the front wheels will tend to drag the rear wheels a little which is always preferable to having the rear trying to push the front. As far as tyre and diff wear is concerned it won't make a lot of difference unless you are operating on a hard dry surface at speeds over 20mph or if you're pulling a lot of weight, in which case you will get a bit of tyre scuff and transmission pre-load.

Enjoy.

Pete.

The world's cheapest car "NANO" of India, uses different tyres for front and rear:

	Front Tyre size 135/70 R12 Rear Tyre size 155/65 R12 I do not know the reasons why the do so. See the specs at http://tatanano.inservices.tatamotors.com/tatamotors/index.php?option=com_whynano&task=experience&Itemid=303

2WD???????????????????

I coluldnt help but notice they are made by Tata motors.

Did they name the motor company that so when you see them go down the street you can say hey....Nice TATA's.....

and is the susspension soft so they are bouncy.................

G'day,

If the vehicle is registered, just check with the relevant authority about the legallity.

Royce

If possible, don't mix tyre size!

If you just MUST do it; Put the mismatched tyres on each axle....one small and one bigger per axle. Say smaller on the left and bigger on the right. The two axle differentials will then always be "working" a little with no harm done to the transfer box BUT when braking the smaller wheels will lock a bit easier than the bigger wheels.

If any of the diff's is a limitted slip diff........DO NOT MIX sizes.

Still why mix'em. Rather sell the odd tires an fit the same size.

I do not know the jurisdiction, if it is registered, the drive train configuration or the intended usage, but for road use, it is illegal to mix tyre sizes or types on the same axle. This is for a bloody good reason so I think most jurisdictions would have similar rules. Besides, mixing sizes or types (radial, cross or bias ply) on the same axle is dangerous.

RRV

"... it is illegal to mix tyre sizes or types on the same axle."

Huh? Where at, as in under the jurisdiction of whom?

Can you provide documentation to support this, please? Thanks.

All states in Australia have had this rule since 1970. It is common knowledge, like putting radials on the rear.

So, you cannot provide documentation of your comment. Fair enough. I will consider your comment in the rubbish bin.

are you saying that's illlegal to put radial tires on the rear in the "down under"?

I agree with those that say as long as your not in 4WD mode your OK. Your front hubs won't be locked (even if there automatic hubs) so the front wheels will be free wheeling. Don't lock the hubs as then it will become pretty "squirrely" as it tries to turn all 4 wheels at the same speed.

The one thing I would look at would be if you have some sort of stability or traction control. Some of them use wheel speed sensors and might get a little confused if the front wheels are turning faster then the rears and might try to compensate somehow.

Shawn

Shawn, really good point about the sensors, won't ABS and ESP also get some problems from the speed differences if fitted....?

I had 2 different sizes on my truck. I used 4WD high for better traction on the dirt roads and it screwed up my transfer case. I learnt the hard way, rather keep the same sizes.

One thing that hasn't been mentioned. If you put a non stock tire size on wherever you get your speedometer reading from, it's going to throw off your speedometer.

I, unknowingly, had undersized tires on the back of my 2WD pickup when I bought it. It caused my speedometer to run about 6 MPH higher than my actual speed.

While I didn't notice a difference in driving, I would imagine that it put extra wear on the differential.

I've found that overall, it's best to go with the manufacturer's specifications. Everything is designed to work together in the best way possible.

Smaller or bigger tires will do no harm to a 2WD diff.

Different size as specs on front wheels is a much different story.....it has a big influence

on steering and road holding {Scrub-offset is then altered]

It will damage the diff if two different sized tyres are mounted on that one axle/diff.

I guess you probably did not mean that......you meant on any one driven axle, the tyres must be the same size.

You may get away with various diameters on older 4x4 as mentioned but on anything into the middle 80's to current you may be causing a lot of damage. I am not 100% up on all the new 4x4 designs but my associates ran into huge problems with minor variance in tire sizes. Check the owners manual or on line some of the 4x4 groups can shed some light. I was not aware of the problems until my buddies experienced them and all were caused by mismatched tire diameters. It appears to be an important fact in proper operation.

G'day,

What is the transfer case on the Toyota? If it has a centre dif, no problems. If the front wheels can overrun to minor eliminate axle wind up it should be okay on smooth dirt etc. Regardless, it should be okay off road where you need 4WD.

DO NOT in any circumstance, other that an emergency, mix tyre sizes or construction (radial, cross or bias ply) on the same axle. If you must mix construction types, always make sure the radial's are on the rear. This is usually a legal requirement on public roads.

Royce

Something else I remember from one case some vehicles have a rev counter on either the wheels or the differentials and if they are out of synch a certain amount the feed back to the computer ECM or ??? causes the engine to vary output plus other rare conditions. . Not knowledgeable 100% but these are the results of several conditions.

Toyota has yet to produce a truck with a center differential for the consumer market. The various transfer cases include the RF1A, VF1A, VF2A, and A340H depending on the model of truck. Each of those transfer cases uses either gear or chain drive, which is un-relenting to ratio changes front-to-rear.

Any preloading on the front end will ultimately result in damaged/failed components.

Center diffs are there to iron out changes between the front and back axles as you go round corners, not to change between tyres of different sizes. The diff will be rotating at a very high rate, even when driving in a straight line, I am sure the bearings won't stand for it over a long period.

Someone else who posted here has already had this experience.....LeonF in post#24.

Well I suppose I was assuming that the size difference would be "reasonable". without huge differences in the dist per rev. Then again, if someone wanted to put vastly different wheel and tyre sizes front to rear on their vehicle, no matter what the drive train, I do not think they would be on this site.

Royce

Even quite small differences will cause unaccustomed extra work/wear on the central differential, or what we called "Axle windup" if there is no central differential....Both are not good.

Not to mention reduced road holding on roads and extra tyre wear.

I disagree. Differentials are designed to cope with varying rotational speeds, that is what they do. AS far as a locked diff is concerned, axle windup is only of concern on surfaces where 4WD is NOT engaged or the front hubs are set to free wheel at the least.

Your biggest worry is the change in geometry made to the suspension, primarily the front and rear roll centres and the resulting roll axis. There are also changes to the mass axis and the distribution of said mass.

Then again, many 4WD's will become pig handlers with a change in tyre size. Even early Rangies good handling was downgraded with the fitment of wider tyres.

RRV

Differentials were never designed for the "amount" of re-adjustment that would be needed.....t5hey are designed to swing backwards and forwards as a vehicle goes around corners only...

See post #24, he has already had the problems I describe.....

I must laugh at your comment (you did intend it to be funny I trust!!).

Part of helping an OP in such a situation is to make him aware that he might save the cost of two extra tyres, but he may have to replace the center diff within a few thousand miles or less. Look at Post #24.....

My bet is a center diff will cost far far more......assuming he has one.....

I do not personally feel that such help is "Off Topic", but let the OP decide for himself...he can also vote on or off topic!!!

Andy, 25 said he had smaller tires on the back-axle.........I am not joking.......it WIL not harm the diff.

The only time that the axle diff is not working is when driving absolutely straight and the road surface is very smooth and the driven tires are evenly worn and at the same pressure.

With tire height difference between 75mm and 70mm on the same axle and driven as above, the dif will work very slowly and no harm will be done to the driven diff. As both front and rear propshafts will turn freely if tires are fitted as said in 25 so the transferbox will be OK too!

If the transfer box had a one-way clutch on the front prop drive like some old 4x4 trucks, you could run smaller wheels in front as the trucks had.

Your idea has been tested and found to be bad for the central diff, or did you not read and understand post #24? (which was not posted by myself by the way...!)

Here it is again:-

From LeonF by the way:-

I had 2 different sizes on my truck. I used 4WD high for better traction on the dirt roads and it screwed up my transfer case. I learnt the hard way, rather keep the same sizes.

Diffs in most vehicles only "bath" in oil, no pressure feed.

As a car is driven, either two or four wheel drive, ANY diff on that vehicle, the insides move maybe a half a revolution in one direction, then in the other and as you say, do not move when driving in a straight line when on tarmac.....BUT, if in 4 wheel drive, even on a straight road, the central diff will be spinning at a rate decided by the difference in speed of the front to rear axles......an amount of work they were never designed to handle.

I found a good diff animation here, you can see a "turn" or straight ahead driving.-

http://auto.howstuffworks.com/differential2.htm

That may help you to see why a diff can fail when abused. The drive shafts run in big ball bearings, but the middle of the diff only uses plain bearings in most cars....

It would be great if Leon would tell us just how long his transfer case "lived" with different sized tyres.......

Naturally load, inclines and driving style play a role as well, but you are already operating outside of the envelope by adding tyre size differences to it!!

I looked around on the web for additional information and found the following:-

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18

Where a paragraph was written with this:-

Four-wheel drive and all-wheel drive vehicles are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.

(The underlining is from me.)

The rest of the article explains why, you should read it!!! You would then support me once you fully understand everything......

Read on here:-

http://askville.amazon.com/replace-tires-AWD-car/AnswerViewer.do?requestId=2651049

The first part of the text was (but you need to read it all really!):-

Dear Tom and Ray: I recently had four half-worn snow tires on my '04 Honda CR-V with all-wheel drive. Living in upstate New York, I was driving in snow on back roads much of the time (as a rural letter carrier for the U.S. Postal Service). I had the bright idea to buy two new snow tires this year for the front wheels and use the worn tires for the rear, and then next season reinstall the newer tires on the rear and buy new tires for the front. That would eliminate having to buy four new snow tires at one time. However, the local Honda service manager advised against my plan, saying that the newer tires would have a slightly larger radius than the older tires on the rear (even though the actual tire sizes are identical), and this could cause problems with the all-wheel-drive system. Is he correct? -- Bruce

Ray: Sadly for you, Bruce, we have to say yes. However, think of all the tire dealers who are clicking their heels while reading this!

On this website:-

http://www.thedieselstop.com/forums/f27/4-wheel-drive-different-size-tires-front-back-129517/

they ask the same question as here. The first answer was:-

wear is fine as long as it is reasonable, different size tires is going to shred your TC and maybe more. This is a huge no/no with a 4x4.

You can also read here:-

http://autos.yahoo.com/maintain/repairqa/tires_wheels/ques140_1.html

The following:-

Vehicles with all-wheel drive or full-time four-wheel drive must also run the same sized tires front and rear to maintain the proper drive relationship between axles. If one set of tires is larger or smaller than the others, it will create slippage between the front and rear axles that will accelerate tire wear and adversely affect handling.

If you read here:-

http://www.ehow.com/how_4867056_replace-tires-awd-cars.html

You will find the following:-

How to replace the tires on an all-wheel-drive car is easy. Having to replace them is going to be painful. Any reputable tire company or dealership is going to strongly recommend or require that you replace all four tires. Why? It gets a little complicated, but it has to do with a part called a center differential. To try and simplify the matter, this part tries to calibrate the front and rear axle to work together. If they do not, problems in the drive train can result. As tires lose tread wear, they begin to become different sizes. The front tires will wear on the edges more because they're on the axle that controls the steering. The reason the tires wear more is due to lack of proper rotation. But whether you have two or four bad tires on your AWD vehicle, any reputable tire dealer is going to require you to purchase all four.

I was unable to find a website that recommends different sized tyres on 4WD vehicles, I expect there to be one, but not a serious one, as serious as the weblinks I publish here!!

Andy, Thanks for "teaching" me. I replied to Kramarat [25] having on his 2WD both smaller tires.

The question was about a Toyota= [no centre diff]. As I said in [20] the transfer box will be OK if the front and rear propshafts run at the same speed......therefore if he then must use the slightly different size tires...he should use one bigger and one smaller tire per axle {to save the transfer box}.......Because I know from experience that the diff is about the strongest mechanical part. I had to replace many a crownwheel and pinion and never a diff except when it was run dry or with bad lubricant.

Farm vehicles run to 500 000km without any diff problems while used with heavy loads on winding corregated dirt roads= The diff is constantly working even with both driving wheels the right size. As I said it would be best if he sells two tires and buy the right size!

I once had a DKW constant 4WD with no transfer box or centre diff which had been used on tar by previous owner with all different size tires.The front crownwheel and pinion got chewed up but the diff was OK. If I forget to shift my Steyr Daimler Puch to 2WD it is almost unsteerable.[Jurie....oldtimer mechanic/ motormechanics teacher etc.]

Again the Propshaft Comment.

It is a truck with Drive Shafts, not a boat or plane.

hugh

The Toyota Tacoma and Tundra owner's manuals refers to them as propeller shafts. How's that for a rough translation?

A drive shaft, driveshaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical component for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement between them. (Compliments of Wiki)

Refering to it as a Propshaft is completely correct. I usually call it a driveline... but I don't see that on the list.

I'd expect that from a Seppo.

Replacing the crown wheel and pinion is replacing parts of a diff.....

On many 4WD vehicles there are 3 "diffs", one on each axle and one between the two.....sometimes there is a hydraulic unit in the middle that can overheat the oil when running on incorrectly sized tyres.....it can still get wrecked!!

Sometimes the middle one has a different name, but is still a differential.......its variable...

Andy,

The crown wheel and pinion is the final drive; The crown wheel is bolted or riveted to the differential casing.

Yeah, I don't know what these guys are thinking...try my #9 on this thread. Lyn argued the point, but that's what makes him so cute.

It made sense when you wrote it, it still makes sense now.

great efforts andy to collect this big important data

Yur nutz

LOL!

And yur right!!

AS far as a locked diff is concerned, axle windup is only of concern on surfaces where 4WD is NOT engaged or the front hubs are set to free wheel at the least.

Please explain what you mean by the above. Also how do you think a roll centre of 5mm higher or lower will influence the driveability of the said truck?

If you have no center dif and 4WD is engaged, on a tarmac road, you get "strange" steering.

Just ask anyone who has driven an old Landrover with 4 wheel drive engaged on the tarmac road, thats how you find out (if you cannot read the label posted in the cab) just why its ONLY for Off Road......it throws you out of the corner when cornering, it can cause a serious accident.....now THAT is axle windup!!!

(It gives me the "Wind Up"!!!)

As far as traction control, stability control, etc are concerned, the owners manual might give direction. On cars with a donut spare (smaller diameter), it will instruct you to disable the system with spare in place. With 4WD I imagine there would be a similar instruction.

Are you mixing because you have the tires and your controlling costs?

Why not just buy two tires of one or the other size and have four tires equal. Then use one of the remaining tires as your spare for emergencies.

How about the more likely problem that will come up with ABS brakes and traction control most newer vehicles have. Mismatched tires will be seen as tire slippage or traction issues.

its old a 1990

When I was in High School, a guy in town resurrected a junk car that he was given. He had 3 different tire sizes on it. I told him he needed 3 spares, but he was too busy building wooden seats to respond.

So, I am driving my 4wd truck and everything is fine, until my tires become worn, and I finally have to replace the worn tire with a brand new one. How much roll out difference is there between a new and worn tire?

If I had to get the value out of the tires of different sizes, I would do like the one poster said, just run the smaller tires on the high side of acceptable, and the larger ones lower.

The only concern I see is the load capacity of the smaller tires. If they do not the load rating, he will need to limit his cargo weights.

What - and still operate the vehicle on public roads? There's an easy way to find out:

• Do the change
• Send the vehicle for an MoT Test
• Assess the test report