Do you change all four of your tires?

[tom999w]

At the tire place today, the tire sign said if one tire is bad to replace all four tires at once, because one uneven tire can throw off the computers. That really sounds like a racket, since there is no road on the planet that is absolutely even and flat. Even a pebble on the road would throw off the equal-ness of the tires, so the computers are always calculating for uneven-ness... So one grain of sand of tread difference from one tire to the other sounds like a scam to sell tires...

My not the smartest sister got a flat on her new Audi. So a few days later a 48' air conditioned enclosed trailer showed up from Audi and transported her car three hours away to the dealership to replace all four tires, and then three hours back to her house a few days later for $2000. It just doesn't makes sense..

 

[harrisonm]

It's a racket.
Now if you have six or eight year old tires and one goes bad, then it would probably be a good idea to have all new tires.

 

[RustyRatRod]

Tires are replaced in pairs or sets of four UNLESS you have an AWD vehicle that utilizes a viscous coupling connecting the front and rear drive axles together. Because if this, it is imperative all four tires are as close to the exact same diameter as possible, otherwise, the drive axles will turn at slightly different speeds and burn the coupling up. I assume we're not talking about AWD, though. lol So in pairs or sets of four is correct.

 

[Princess Valiant]

Some places (mercedes dealers) will try to hold your car hostage if you dont replace the whole set if one is bad for any reason. Or if they don't like your date codes. They keep saying it's liability, its liability

That's why I go to Mexican tire places where they will put whatever f*&in tire I tell them, wherever on the car I want it.

I don't need a snooty service writer to tell me what I need and what to do with my car, I'll tell them.

 

[72bluNblu]

Tires are replaced in pairs or sets of four UNLESS you have an AWD vehicle that utilizes a viscous coupling connecting the front and rear drive axles together. Because if this, it is imperative all four tires are as close to the exact same diameter as possible, otherwise, the drive axles will turn at slightly different speeds and burn the coupling up. I assume we're not talking about AWD, though. lol So in pairs or sets of four is correct.

What he said.

Many cars now are AWD or have some kind of differential in the driveline. Plus all the traction control stuff.

Needless to say if it’s a modern shop servicing mostly modern cars there are a lot of vehicles out there that can’t have a single tire, or even a pair of tires changed out anymore.

And I’m sure they all deal with plenty of people that don’t know crap about their own cars and argue about needing all 4 when they in fact do need all 4.

 

[72bluNblu]

Some places (mercedes dealers) will try to hold your car hostage if you dont replace the whole set if one is bad for any reason. Or if they don't like your date codes. They keep saying it's liability, its liability

That's why I go to Mexican tire places where they will put whatever f*&in tire I tell them, wherever on the car I want it.

I don't need a snooty service writer to tell me what I need and what to do with my car, I'll tell them.

You do you, but if you have a modern car and don’t know how the computer on your car is reading data from each tire you may not know enough to be making a good decision.

 

[Princess Valiant]

You do you, but if you have a modern car and don’t know how the computer on your car is reading data from each tire you may not know enough to be making a good decision.

And i may know.

A service writer may not know more than the person driving the car. Anyone who has been around cars for a good length of time should be able to read a tire as some of us read spark plugs and many things of that nature.

I'm not saying to match 3 tires with a totally mismatched tire size or anything like that.

A little common sense and taking a good look at the tires and considering where they were on the car and how the car was handling, can tell a lot.

It is a "modern" car, 2019 mercedes S560 coupe and it's been fine with my care.

I just choose not to feed into the racket. If the tires read that they need replaced then by all means, tire rack here i come. But just to feed into "its a liability" when it's clearly fine, doesnt work.

 

[71GSSDemon]

Its a money grab that prays on fear and ignorance. The MM difference in a semi worn tire vs new is so negligible, especially the low profile sport tires, there is likely not much for computers to see the difference. My 2 cents

 

[72bluNblu]

And i may know.

A service writer may not know more than the person driving the car. Anyone who has been around cars for a good length of time should be able to read a tire as some of us read spark plugs and many things of that nature.

I'm not saying to match 3 tires with a totally mismatched tire size or anything like that.

A little common sense and taking a good look at the tires and considering where they were on the car and how the car was handling, can tell a lot.

It is a "modern" car, 2019 mercedes S560 coupe and it's been fine with my care.

I just choose not to feed into the racket. If the tires read that they need replaced then by all means, tire rack here i come. But just to feed into "its a liability" when it's clearly fine, doesnt work.

So, that car in particular typically has a staggered set up so switching a pair shouldn't be an issue. Depending on trim level and options of course. But typically 245 fronts and 275 rears, so, yeah unless the tires are 5 years old or more a pair shouldn't matter. Most manufacturers have gone to 5 years now for a tire age recommendation, that's pretty standard. And yes, that's down from 6 which was down from 7 which was down from 10. The compounds keep changing, so does the expected life.

For the rest of it, previous tire wear doesn't mean a single blinking thing. Yes, it could indicate a problem with the car or suspension. But it doesn't change anything with how the sensors are reading the tire. "Good sense" works fine on an A-body, it doesn't mean a thing for a modern car with multiple sensors feeding information back to an ECU that is doing real time adjustments to the ABS braking and traction control.

If you don't know the sensors that are present, the information they're sending to the ECU and the way that the ECU is using that information you may not have all the information you need to make a good decision, regardless of what you're seeing at the tire.

That said, the service writer may not have a clue EITHER. So, you actually have to know as the owner. The service writer may be wrong, and might be trying to sell you a couple more tires. Or they may be right, it literally depends on the make and model of car and its options.

Its a money grab that prays on fear and ignorance. The MM difference in a semi worn tire vs new is so negligible, especially the low profile sport tires, there is likely not much for computers to see the difference. My 2 cents

Just say you don't know. You said it already.

 

[71GSSDemon]

So, that car in particular typically has a staggered set up so switching a pair shouldn't be an issue. Depending on trim level and options of course. But typically 245 fronts and 275 rears, so, yeah unless the tires are 5 years old or more a pair shouldn't matter. Most manufacturers have gone to 5 years now for a tire age recommendation, that's pretty standard. And yes, that's down from 6 which was down from 7 which was down from 10. The compounds keep changing, so does the expected life.

For the rest of it, previous tire wear doesn't mean a single blinking thing. Yes, it could indicate a problem with the car or suspension. But it doesn't change anything with how the sensors are reading the tire. "Good sense" works fine on an A-body, it doesn't mean a thing for a modern car with multiple sensors feeding information back to an ECU that is doing real time adjustments to the ABS braking and traction control.

If you don't know the sensors that are present, the information they're sending to the ECU and the way that the ECU is using that information you may not have all the information you need to make a good decision, regardless of what you're seeing at the tire.

That said, the service writer may not have a clue EITHER. So, you actually have to know as the owner. The service writer may be wrong, and might be trying to sell you a couple more tires. Or they may be right, it literally depends on the make and model of car and its options.



Just say you don't know. You said it already.

So you are saying these sophisticated computer systems can tell of there is a few mm of wear in an inflated tire? Full tread delth vs 1/2? We aren't talking truck tires.

Traction control and ABS are speed sensors. They dont know if one tire is 25" and the other is 25.1" at some discrepancy it can sense a rotational difference, but thats not this thread is discussing.

Tire manufacturers now recommend 5 years vs 10 years? Crazy. They sell 2x as many tires now. Some how 20yr old land speed tires are still ok. Wierd. Oh and when MT made a cost effective race front runner, they now are owned by Good Year. Now they wont sell them to you if they know it is for Bonneville. You have to get the land speed tires at $700 each despite SCTA approval on the old ones. Follow the money

 

[72bluNblu]

So you are saying these sophisticated computer systems can tell of there is a few mm of wear in an inflated tire? Full tread delth vs 1/2? We aren't talking truck tires.

Full tread depth vs half? Absolutely.

Try running a set of mismatched wear tires on a true AWD and see how long the differentials last. It's not bullshit.

Like I said, it depends on the car, the model, the options. If I had to replace a tire on my wife's AWD Subaru and they had 20k miles on them, I'm buying 4. Sucks. But better than burning up one of the 3 different differentials on that car, because you absolutely can do that.

If you don't know the specific workings of the sensors and ECU on your particular car telling the service writer to shove off might not be the best idea. Absolutely some of them will bullshit you, I'm not saying they're all right. But there are plenty of cars out there where you can cause yourself thousands of dollars of pain by not swapping all 4 tires if they're much past brand new.

So is it a scam? Could be! But in some cases it is not. And if you don't know what the sensors are reading, how they're reading it and what the ECU is doing with that info, you don't know enough to make that decision unless you're just depending on dumb luck.

 

[RustyRatRod]

So you are saying these sophisticated computer systems can tell of there is a few mm of wear in an inflated tire? Full tread delth vs 1/2? We aren't talking truck tires.

Traction control and ABS are speed sensors. They dont know if one tire is 25" and the other is 25.1" at some discrepancy it can sense a rotational difference, but thats not this thread is discussing.

Tire manufacturers now recommend 5 years vs 10 years? Crazy. They sell 2x as many tires now. Some how 20yr old land speed tires are still ok. Wierd. Oh and when MT made a cost effective race front runner, they now are owned by Good Year. Now they wont sell them to you if they know it is for Bonneville. You have to get the land speed tires at $700 each despite SCTA approval on the old ones. Follow the money

We had an AWD Durango in the transmission shop where I worked. They ran two different size tires on it. Burnt up the viscous coupling. We replaced the coupling. Told them they needed 4 tires exactly the same size, preferably sequential serial numbers AS DODGE RECOMMENDS. Yup, they went out like idiots, put 4 used "same size" tires on it and burnt up the coupling AGAIN. We ended up buying that thing fixing it again, putting the right size tires on it and selling it. You're damn right the computer can tell. They're called speed sensors. No, it's not bullshit.

 

[72bluNblu]

We had an AWD Durango in the transmission shop where I worked. They ran two different size tires on it. Burnt up the viscous coupling. We replaced the coupling. Told them they needed 4 tires exactly the same size, preferably sequential serial numbers AS DODGE RECOMMENDS. Yup, they went out like idiots, put 4 used "same size" tires on it and burnt up the coupling AGAIN. We ended up buying that thing fixing it again, putting the right size tires on it and selling it. You're damn right the computer can tell. They're called speed sensors. No, it's not bullshit.

And this gets into a couple things.

First off, how the sensors measure stuff. The VSS stuff usually works off of revolutions per unit of time, or angular change per unit of time. So, a small change in tire diameter has a bigger effect on that than it does on the actual tire diameter. You're not measuring tire height directly, but rather something like revolutions per mile. Well a 1 mm change in diameter makes a bigger difference in revolutions per mile than it does in relative tire height. So that's why I say stuff like you have to know how the sensors are measuring things, and what the ECU is actually doing with that data. Because if it's taking a revolutions per mile kind of number and feeding that into an equation, a small difference in tire diameter is being amplified by the math being done by the ECU. For a 26" tall tire, a 1mm change in diameter is ~1.2 revolutions per mile. I mean, that's not a lot, but a 1mm change is nothing. Like a smidge more than 1/32", and we all know tires wear more than a few 32's right?

The other thing then the actual mechanical parts and their limitations. If Dodge is recommending sequential serial numbers for tires you can be sure of a couple of things. One, they really don't want to cover those viscous couplings under warranty!!! And two, if someone thought to get all the way down to recommending sequential tire serial numbers, the tire height difference to create an issue with that viscous coupling has to be pretty darn small! Because the engineers and bean counters at Dodge don't even want to trust the tire manufacturers' production tolerances across the board, they want to keep the tires right next to each other on the production line. And that's not even an ECU thing, that's down to the mechanical limits on the design of those couplings and how much they can slip for how long.

And again, I have no love for service writers or dealer service departments. There are plenty of terrible service departments and shops out there looking to take advantage of people, that is a 100% certainty. But the flip side of that is that on modern cars there is in fact something to the whole 4 wheel tire change. And it depends on the car, the make, model and options, and how the hell that particular ECU is processing data from whatever sensors that particular car has. On one car it might not make a difference at all, and on the next it could mean smoking thousands of dollars of parts. So, buyer beware.

 

[junkyardhero]

My not the smartest sister got a flat on her new Audi. So a few days later a 48' air conditioned enclosed trailer showed up from Audi and transported her car three hours away to the dealership to replace all four tires, and then three hours back to her house a few days later for $2000.

that's honestly not a bad deal.

i put nearly 1K worth of rubber on my dart and i changed the damn things myself. 2K for white glove service on a luxury automobile? not totally out of line price wise.

 

[72bluNblu]

that's honestly not a bad deal.

i put nearly 1K worth of rubber on my dart and i changed the damn things myself. 2K for white glove service on a luxury automobile? not totally out of line price wise.

Heck depending on which "new Audi" we're talking about the tires alone could have been close to $2k just by themselves!

 

[RustyRatRod]

We have a local BMW dealer. "At one time" they included FREE transport to and from the dealership anywhere in the state to service their cars. I'm unsure if they still offer that. I always thought that was a money burning proposition. Maybe their service charges were enough to cover the cost.

 

[junkyardhero]

We have a local BMW dealer. "At one time" they included FREE transport to and from the dealership anywhere in the state to service their cars. I'm unsure if they still offer that. I always thought that was a money burning proposition. Maybe their service charges were enough to cover the cost.

labor has the single highest margin on a line item repair bill, so it's all about getting the customers to bring their cars in. when i was at the dealer, they would hammer us about "service absorption rate"

that 2K on tires? they could've easily made 1K on the job. or, they could've just as easily lost money-- however, they've now got a relationship with the client, so when it's time for the big, big service they're banking on them coming in for that.

 

[Ozyduster]

Wife has a vw arteon thats awd with a tune and few other bits. For a kiddy hauler it is lively, chews through rubber. It runs Pirelli P-zero on all fours, we always change in pairs. (Expensive exercise as about 550 a corner lol) Many shops will refuse to change a single as by rights they are not meant to due to manufacturer clauses and the way the diffs etc work

 

[Ozyduster]

Heck depending on which "new Audi" we're talking about the tires alone could have been close to $2k just by themselves!

Exactly as above wife's arteon runs PZero Pirellis lol over 500 a corner and soft as hell and get f all miles out of them haha. Makes the dirty old ET's look cheap

 

[tom999w]

Its a money grab that prays on fear and ignorance. The MM difference in a semi worn tire vs new is so negligible, especially the low profile sport tires, there is likely not much for computers to see the difference. My 2 cents

I agree. The job of the on board computers is to send traction to this or that tire, etc... The on board computer is always computing uneven-ness, that's it's job... So 2MM of tire difference from one tire to the other on an uneven, bumpy, gravely, sandy road with potholes is rediculous....

 

[CFD244]

We had an AWD Durango in the transmission shop where I worked. They ran two different size tires on it. Burnt up the viscous coupling. We replaced the coupling. Told them they needed 4 tires exactly the same size, preferably sequential serial numbers AS DODGE RECOMMENDS. Yup, they went out like idiots, put 4 used "same size" tires on it and burnt up the coupling AGAIN. We ended up buying that thing fixing it again, putting the right size tires on it and selling it. You're damn right the computer can tell. They're called speed sensors. No, it's not bullshit.

Do they throw a code once the tire sizes differ significantly to matter, or do they just start burning up the viscous coupling?

 

[toolmanmike]

At the tire place today, the tire sign said if one tire is bad to replace all four tires at once, because one uneven tire can throw off the computers. That really sounds like a racket, since there is no road on the planet that is absolutely even and flat. Even a pebble on the road would throw off the equal-ness of the tires, so the computers are always calculating for uneven-ness... So one grain of sand of tread difference from one tire to the other sounds like a scam to sell tires...

My not the smartest sister got a flat on her new Audi. So a few days later a 48' air conditioned enclosed trailer showed up from Audi and transported her car three hours away to the dealership to replace all four tires, and then three hours back to her house a few days later for $2000. It just doesn't makes sense..

View attachment 1716480663

All wheel drive? Yes if there is uneven wear between all 4.

 

[tom999w]

I call B.S. on the whole tire thing. Traction this, tire computers that.... There are the same amount of cars in the ditches on the roads here in the rain and snow than there were in the 1970's, 1980's, 1990's, and 2000's; it just cost the drivers alot more to get there.

 

[junkyardhero]

I call B.S. on the whole tire thing. Traction this, tire computers that.... There are the same amount of cars in the ditches on the roads here in the rain and snow than there were in the 1970's, 1980's, 1990's, and 2000's; it just cost the drivers alot more to get there.

yes.... but... data shows the total number of registered vehicles on the road has nearly doubled since 1979.

so by statistics there should be more cars in the ditches...

 

[toolmanmike]

yes.... but... data shows the total number of registered vehicles on the road has nearly doubled since 1979.

so by statistics there should be more cars in the ditches...

Also, there is a false sense of security now days. We used to drive like we had a brain. Many now days don't. Front wheel drive, anti lock brakes, traction control. all wheel drive, lane alert, and self driving features and all to blame.