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View Full Version : Ok to replace just one tire?



motionneon
07-23-2012, 07:26 PM
I've read all posts and have heard opinions. My service advisor says it will be fine. Anyone with B8 S4 experience changing just one tire? 15k miles. One tire has nail close to sidewall. Sucks.

Leor604
07-23-2012, 07:34 PM
I am sure there is some acceptable tolerance in the overall diameter of the tires. How much tolerance, I don't know. If it was my car, I would want a more definitive answer rather than the word of a service advisor. If in doubt, I would have the new tire shaved to match the other three.

Maybe someone else here can chime in with an actual tolerance as defined by Audi engineers.

lmwisler
07-23-2012, 07:39 PM
2-3/32nds would be the limit. Anymore than that and I would get it shaved or replace the set.

helix139
07-23-2012, 07:53 PM
at 15k I would say you need to replace at least 2 or have the new one shaved down to match the old one on the same axle

Stereodude
07-23-2012, 07:55 PM
2-3/32nds would be the limit. Anymore than that and I would get it shaved or replace the set.Not exactly...

These are the current guidelines:
http://img834.imageshack.us/img834/5737/tiretreadguidelinesquat.jpg

motionneon
07-23-2012, 07:56 PM
Thanks guys

helix139
07-23-2012, 08:06 PM
Hey if you're interested I have 3 OEM Dunlops with about the same mileage on them. 5-6/32" tread depth. I'm in Polk County and I'll be in Tampa for work tomorrow. PM me an offer if you're interested.

Alex@TAG
07-24-2012, 12:17 AM
Shouldnt be an issue to change just one tire... ;)

Wah
07-24-2012, 04:35 AM
It depends but I would more likely than not replace two fronts or two rears.

Killaapp
07-24-2012, 06:22 AM
This happened to me at 9k miles and it was a disaster. I replaced front left tire (1/32 delta between other 3) and the car drove horribly. Literally shook side to side and pulled on the highway. It was making my passengers sick. I had all 4 wheels and tires rebalanced (twice), got a 4 wheel alignment, and had the new tire checked to make sure there were no problems. tire store and Audi said it had nothing to do with only replacing 1 tire, yet the user manual on rear-dif suggested that was the cause. Problem only went away when I had both front tires replaced.

motionneon
07-24-2012, 09:50 AM
Hey if you're interested I have 3 OEM Dunlops with about the same mileage on them. 5-6/32" tread depth. I'm in Polk County and I'll be in Tampa for work tomorrow. PM me an offer if you're interested.

Thanks for going out of your way to help a fellow Audizine member! Your 2 tires had almost identical wear to my remaining. I may be able to go another 10k-15k before changing all 4.

helix139
07-24-2012, 11:06 AM
Thanks for going out of your way to help a fellow Audizine member! Your 2 tires had almost identical wear to my remaining. I may be able to go another 10k-15k before changing all 4.

Glad I could help. They certainly were doing me no good sitting in my storage shed.

westwest888
07-24-2012, 09:00 PM
It is completely OK to change a single tire. Don't even worry about tread depth. Whenever I ruin a tire I just get a used one here for $90. Free shipping. They have between 50% and 60% life.

http://www.baytires.com/

motionneon
07-25-2012, 02:07 AM
That's a great place to get used tires!

Stereodude
07-25-2012, 05:08 AM
It is completely OK to change a single tire. Don't even worry about tread depth.Oh sure, Audi is in a grand conspiracy with the tire makers and is provides tread depth restrictions as a result. The whole idea of damaging the differentials is nonsense!

Dr GP
07-25-2012, 09:10 AM
I don't know how you guys drive, but you are definitely getting a lot more mileage on your tires that I do. Just replaced the OEM 19' Dunlop Maxx tires at 20K and they were almost down to the treadwear bars. Wore evently though. In fact I was happy to get 20K out of the soft UHP summer tires. I'm 62 yrs old and not burning up the roads. Also ran the tires @39psi and rotated at 5k. BTW, I never had any UHP tires that lasted more than 20K. Repalced the tires with Geneal G-Max As 03 All season tires basically to get better mileage out of the tires. What gives?

2011_S4
07-25-2012, 09:16 AM
I don't know how you guys drive, but you are definitely getting a lot more mileage on your tires that I do. Just replaced the OEM 19' Dunlop Maxx tires at 20K and they were almost down to the treadwear bars. Wore evently though. In fact I was happy to get 20K out of the soft UHP summer tires. I'm 62 yrs old and not burning up the roads. Also ran the tires @39psi and rotated at 5k. BTW, I never had any UHP tires that lasted more than 20K. Repalced the tires with Geneal G-Max As 03 All season tires basically to get better mileage out of the tires. What gives?

Can't speak to the Dunlops but the Pirelli P-Zeros that came on my car are in horrible shape after about 12K of use. VERY uneven treadwear and worn right down to the treadwear bars on two out of four tires. Same scenerio as Dr GP - no track use, no hooning, just regular city driving for the most part.

yss
07-25-2012, 09:47 AM
Interesting ... I recently got a big gash on my rear left tire with 15K on the tires (or the car for that matter) and I put the spare on which was brand new. I did not notice any difference in the way my car drives and I am sure there was more than 2 to 3 mm difference between the new tire. I 've been driving like this for about two months now. I drove about 3500 miles so far like this. Do I need to do something about this? There's plenty of life left on the tires which are ContiPro Contacts.

westwest888
07-25-2012, 07:00 PM
Oh sure, Audi is in a grand conspiracy with the tire makers and is provides tread depth restrictions as a result. The whole idea of damaging the differentials is nonsense!

If you believe that, well, I don't imagine you're getting out of Detroit any time soon. This isn't a particle accelerator doing the Higgs-boson experiment. It's a car. Fun fact: the outside wheels travel a farther distance than the inside wheels every time the wheel isn't pointed 100% straight! The contact patch of the tires doubles in size front to back and side to side on braking, accelerating and turning. The rear wheels point slightly inward because of the toe adjustment. The front and rear wheels lean slightly inward because of the camber.

The differentials have shims, ramps and clutches in some cases to accommodate all of this. You can't damage them with a few millimeters of tire difference. The front differential is open, for starters. You could put a 25" tall tire on the front and a 26" tire on the rear like a Corvette or a Mustang does. Side to side on the rear, a fraction of an inch is FINE. We're talking about a 10,000 mile fix. It's a differential that should be good for 200,000, unless you're racing it. In that case I imagine you'd break one of the half shafts and have to rebuild the diff while you were in there.

Stereodude
07-25-2012, 07:18 PM
Hey, you're free to do what you want and disregard Audi's recommendations. If you want to damage your car go for it. But don't come on here spreading nonsense and misleading other people who might not be interested in damaging their car.

Do you have equal suspicions about using VW 502 certified oil? How about premium unleaded? G12+ coolant?

helix139
07-25-2012, 07:53 PM
If you believe that, well, I don't imagine you're getting out of Detroit any time soon. This isn't a particle accelerator doing the Higgs-boson experiment. It's a car. Fun fact: the outside wheels travel a farther distance than the inside wheels every time the wheel isn't pointed 100% straight! The contact patch of the tires doubles in size front to back and side to side on braking, accelerating and turning. The rear wheels point slightly inward because of the toe adjustment. The front and rear wheels lean slightly inward because of the camber.

The differentials have shims, ramps and clutches in some cases to accommodate all of this. You can't damage them with a few millimeters of tire difference. The front differential is open, for starters. You could put a 25" tall tire on the front and a 26" tire on the rear like a Corvette or a Mustang does. Side to side on the rear, a fraction of an inch is FINE. We're talking about a 10,000 mile fix. It's a differential that should be good for 200,000, unless you're racing it. In that case I imagine you'd break one of the half shafts and have to rebuild the diff while you were in there.

Unless the differential is open (and ours are not), then running a smaller tire on one side will cause the clutch plates, fluid, etc. to be in a constant state of friction and therefore generate heat, as opposed to momentary wear states when you are driving normally. The difrerential internals get hot and never have a chance to cool off. This is bad for mechanical parts. The greater the difference, the greater the amount of heat/friction/wear. Your comparison of tire size between front and rear on a mustang or corvette doesn't really mean anything as they are rear wheel drive and thus have no center differential.

Will you destroy your differential right away? No. Will you cause additional unnecessary wear? Yep. It's like driving with the clutch always slightly depressed, or holding the clutch in when you stop as opposed to taking the car out of gear. Eventually, that wear on the clutch friction materials or throwout bearing will catch up with you if you keep doing it for an extended period of time.

ayz
07-25-2012, 07:56 PM
Fun fact: the outside wheels travel a farther distance than the inside wheels every time the wheel isn't pointed 100% straight! The contact patch of the tires doubles in size front to back and side to side on braking, accelerating and turning. The rear wheels point slightly inward because of the toe adjustment. The front and rear wheels lean slightly inward because of the camber.
.
Right, but now you throw on mismatched tires and exacerbate that effect, to the point of maybe beyond normally allowed/expected variation.

Conventional wisdom is that front to back matters less than left to right. Swap out both sides of the tire and you should be fine.

Sure you can try to save 200 bucks on another tire, but do you really want to risk screwing up a 55k car because you were too cheap to buy a 2nd tire?

When buying a car make sure you can afford to purchase it AND maintain it.

Vinchenzo51
07-25-2012, 07:59 PM
I feel like I need to chime in... Take my experience for what it is.

I'm running a tire difference of 2.6% from front to rear (215 front and 235 rear) and have been running this setup quite aggressively for almost 3 years and roughly 40k (and I purchased my car with nearly 100k, so this extra 40k of "excessive wear" is on an already 100k old diff). Issues? Vibrations? Noises?... None

helix139
07-25-2012, 08:58 PM
I feel like I need to chime in... Take my experience for what it is.

I'm running a tire difference of 2.6% from front to rear (215 front and 235 rear) and have been running this setup quite aggressively for almost 3 years and roughly 40k (and I purchased my car with nearly 100k, so this extra 40k of "excessive wear" is on an already 100k old diff). Issues? Vibrations? Noises?... None

As was said, front to rear is different than side to side from a mechanical standpoint.

Leo
07-25-2012, 09:21 PM
Not exactly...

These are the current guidelines:
http://img834.imageshack.us/img834/5737/tiretreadguidelinesquat.jpg


I always thought that tires with the greatest thread depth (ie. new tires) should go in the rear. Am I wrong?

westwest888
07-26-2012, 04:18 PM
Right, but now you throw on mismatched tires and exacerbate that effect, to the point of maybe beyond normally allowed/expected variation.

Conventional wisdom is that front to back matters less than left to right. Swap out both sides of the tire and you should be fine.

Sure you can try to save 200 bucks on another tire, but do you really want to risk screwing up a 55k car because you were too cheap to buy a 2nd tire?

When buying a car make sure you can afford to purchase it AND maintain it.

It's about doing what's required and doing what's smart. Buying a new tire and shaving it is the dumbest thing I've ever heard of. A used tire is fine because the other 3 tires on the car are - wait for it - used! Another brand of tire is fine too. These things have zero bearing on performance. Trust me as a guy who goes out on track I like performance. I'd also rather spend $400 on a nice dinner than a tire.

@helix319 How exactly does it produce a "constant state of friction" to have a smaller tire on one side by a few mm? It's a different number of rotations per mile. So you may have 809 rotations versus 815. But guess what - if you make slightly more right turns than left turns you're also skewing the aggregate number of lifetime rotations on the left versus the right side. The differential only actually "slips" when there's wheel slip. If the tires are planted on dry pavement, the clutches spin free. You're not ruining them in any way. It is in no way analogous to letting the transmission clutch slip. It is not even like holding the clutch in at a stop light and unnecessarily exercising the throwout bearing. You have to think before you write.

@Stereodude Mobil1 or any climate appropriate oil is fine. This is also going to sound shocking to you, but the only coolant required is water! Anti-freeze is only necessary in cold climates. It's a good idea to add Water Wetter or an anti corrosive if you're running water. Water has a higher thermal capacity than anti freeze and protects your engine better by removing heat.

Stop reading. Start thinking.

Stereodude
07-26-2012, 05:22 PM
Stop reading. Start thinking.This is the best advice I could give someone regarding your posts.

helix139
07-26-2012, 05:39 PM
@helix319 How exactly does it produce a "constant state of friction" to have a smaller tire on one side by a few mm? It's a different number of rotations per mile. So you may have 809 rotations versus 815. But guess what - if you make slightly more right turns than left turns you're also skewing the aggregate number of lifetime rotations on the left versus the right side. The differential only actually "slips" when there's wheel slip. If the tires are planted on dry pavement, the clutches spin free. You're not ruining them in any way. It is in no way analogous to letting the transmission clutch slip. It is not even like holding the clutch in at a stop light and unnecessarily exercising the throwout bearing. You have to think before you write.

Wake up on the wrong side of the bed this morning? I stand by what I said. Either you're not getting what I'm saying or you don't understand how non-open differentials function. Start thinking about this:

Our sport differentials have clutch packs in each half shaft. When your tires are a different size, the half shafts have to travel at different speeds. How do you think the sport differential gets the half shafts to spin at different speeds? Yep, those clutch packs. Producing that thing called friction, which produces heat, which is bad. Like I said, they're going to be in a relatively constant state of use, especially during straight driving such as on the highway, etc.

westwest888
07-27-2012, 02:22 AM
You have no idea how a car works. The half shafts spin at different speeds every time you turn the wheel. The clutch DOES NOT ENGAGE when you turn the wheel.

RecklessactN
07-27-2012, 06:35 AM
Blew out both right side tires on a pothole at about 12k miles, replaced and havent seen any issues with this swap out. Looking to replace the set at 25k though becuase one tire does have some more wear than the others.

helix139
07-27-2012, 06:53 AM
You have no idea how a car works. The half shafts spin at different speeds every time you turn the wheel. The clutch DOES NOT ENGAGE when you turn the wheel.

You know, it's possible to disagree without being a dick about it. We'll agree to disagree.

Riu
07-27-2012, 12:48 PM
Never got why people get aggressive and mean on message boards.

premek
07-27-2012, 10:58 PM
anybody experiencing tires getting bumpy? when you slide with your hand over the surface , you can feel little bumps....tires have only 700 miles on them.. I play around a lot though.. little drifing here and there :)

Leor604
07-28-2012, 12:00 AM
You have no idea how a car works. The half shafts spin at different speeds every time you turn the wheel. The clutch DOES NOT ENGAGE when you turn the wheel.

I think what we have here is a lack of clear communication.

West, you are absolutely correct that the halfshafts spin at different speeds when you turn the wheel. No disputing this fact.

Helix, you are also correct. If the diameter of the two rear wheels is the same, the halfshafts will turn at exactly the same speed in a straight line and will turn at different speeds during cornering, thus generating heat and wear of the clutch packs only while cornering.

West, I believe the point Helix is trying to make is that with different diameter tires, you will be generating some heat and wear even while travelling in a perfectly straight line. As most people will spend the majority of their miles driving in relatively straight lines, you would not want to be generating heat/wear during the majority of your driving, but try to limit it to the times you are actually turning the steering wheel off center. It may be very minor, but wear is wear. Will it make any difference in the long term? Who knows? If it was my car, I would do my best to minimize unnecessary wear by keeping the tires as close to the same diameter as possible.

Now kiss and make up!

socfan12
07-28-2012, 05:55 AM
I think what we have here is a lack of clear communication.

West, you are absolutely correct that the halfshafts spin at different speeds when you turn the wheel. No disputing this fact.

Helix, you are also correct. If the diameter of the two rear wheels is the same, the halfshafts will turn at exactly the same speed in a straight line and will turn at different speeds during cornering, thus generating heat and wear of the clutch packs only while cornering.

West, I believe the point Helix is trying to make is that with different diameter tires, you will be generating some heat and wear even while travelling in a perfectly straight line. As most people will spend the majority of their miles driving in relatively straight lines, you would not want to be generating heat/wear during the majority of your driving, but try to limit it to the times you are actually turning the steering wheel off center. It may be very minor, but wear is wear. Will it make any difference in the long term? Who knows? If it was my car, I would do my best to minimize unnecessary wear by keeping the tires as close to the same diameter as possible.

Now kiss and make up!

Good summary, Leor604. This is why when one tire went bad on my car, I replaced the pair.

westwest888
07-28-2012, 12:42 PM
If we're going to be this anal about it, we should all corner balance our cars and carry a 150 pounds of sand bags in the passenger seat to even out the contact patches left to right. By sitting in the driver's side, the left side of the car makes slightly more contact and will actually spin a different number of times per journey.

A 26.0" tire does 799 revolutions per mile. A 25.9" tire does 802 revolutions per mile. The difference in revolutions is 0.37%. Knowing this crazy risk, be careful what you do in the rear of the car. If the differential is as sensitive as a Tag Heuer Calibre 12 automatic watch movement, well, you're got other problems.

Maybe we can all agree that since the front differential is open, that you can do whatever you want on the fronts?

I'm not going to tolerate discussion not based on facts. If we're spending money we should know what we're (not) getting. You have 4 options when you replace a tire: get 1 new one, get 2 new ones, get 4 new ones, or buy 1 used tire that's approximately the same wear as the others. I'm actually the most compliant per your ridiculous rule because I purchase a used tire when I damage one. A new tire is tall and squishy. They actually perform better when they're past the initial wear period and down to 5/10ths.

helix139
07-28-2012, 01:03 PM
If we're going to be this anal about it, we should all corner balance our cars and carry a 150 pounds of sand bags in the passenger seat to even out the contact patches left to right. By sitting in the driver's side, the left side of the car makes slightly more contact and will actually spin a different number of times per journey.

A 26.0" tire does 799 revolutions per mile. A 25.9" tire does 802 revolutions per mile. The difference in revolutions is 0.37%. Knowing this crazy risk, be careful what you do in the rear of the car. If the differential is as sensitive as a Tag Heuer Calibre 12 automatic watch movement, well, you're got other problems.

Maybe we can all agree that since the front differential is open, that you can do whatever you want on the fronts?

I'm not going to tolerate discussion not based on facts. If we're spending money we should know what we're (not) getting. You have 4 options when you replace a tire: get 1 new one, get 2 new ones, get 4 new ones, or buy 1 used tire that's approximately the same wear as the others. I'm actually the most compliant per your ridiculous rule because I purchase a used tire when I damage one. A new tire is tall and squishy. They actually perform better when they're past the initial wear period and down to 5/10ths.

It's Audi's "ridiculous" rule. Not ours. The fact is, the engineers who designed our cars do not recommend replacing a single tire in the rear with the sport differential, or more than 2mm mean difference front to rear due to thermal load on the gear oil. If you did happen to have a problem with your differentials and were not following this rule, you would probably be paying out of pocket with the way Audi is being about warranty work right now.

westwest888
07-29-2012, 01:45 PM
So following that line of logic, do we think that turning left or right adds a thermal load to the gear oil? I was under the impression that the car is designed to do this. It's not a fully locking differential. The gears meet each other at an angle and each end can move at different speeds. Wear only occurs when the clutch pack engages.

helix139
07-29-2012, 02:14 PM
So following that line of logic, do we think that turning left or right adds a thermal load to the gear oil? I was under the impression that the car is designed to do this. It's not a fully locking differential. The gears meet each other at an angle and each end can move at different speeds. Wear only occurs when the clutch pack engages.

Temporarily, yes it does, at least when under power as the clutches are engaging to send more power to the outside wheel to rotate the rear. The key is that the thermal load isn't sustained and the fluid will likely never get up to a critical temperature during normal turns.