Tire Pressure - follow car or tire manufacturer's recommendation

[Fourcircle]

My Audi manual says to run 32 psi cold on all four tires but the tech guys at Tire Rack say I should be running 42 psi cold. Tire Rack says my RE970s are "extra load"' but so too were the Dunlop Sport Maxx GTs that came OEM. Not sure which mandate to follow. Anyone know?


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[shonseb]

follow the tire. If you run low profile, the required pressures would be different from your manufacturers rec. My cousin who works in the tire and wheel industry gave me a good rule of thumb: fill the air to 20% less than Max psi. And always fill it cold. so for example with normal passenger tires max = 40psi - 20% = 32 psi, with low profile max 50ps - 20% = 40 psi. I tend to run 2 psi higher because of bad roads in NYC and I want to protect my wheels.

[Fourcircle]

follow the tire. If you run low profile, the required pressures would be different from your manufacturers rec.

Thanks shonseb. Please see the attached picture of page 230 from my car's manual. Per the table, Audi is recommending 32 front and 32 back for low profile tires measuring 255/35R19 on my A5 coupe 2.0 liter 4 cyl under normal load (2 occupants). This is exactly the size I have now and exactly the size that came as original equipment on the car. Even if I loaded up the car with 4 occupants, the table from the car manual suggests just 33/33.

So, I'm just not understanding why the recommendations from Audi (32 psi) and Tire Rack (42 psi) are so different when they are both speaking to the same size tire and load, and not sure which recommendation to follow.






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[shonseb]

Usually manufacturers run just a bit low for comfort, not sure why tire rack recommended 42. I ran at 40 psi on my Dunlop GTs (A5) and they last well over 30k miles with no uneven wear (maybe even 35k, but I swapped for winters in between). I'd take out 1 or 2 psi when I wanted a little more grip and comfort and put in an extra 1 or 2 psi if I knew I was going to be around the city to protect my wheels from potholes, but I always kept it at/around 40


That rule of thumb has worked well for me for many many years on different cars

[Fourcircle]

To test the waters, I raised the tire's cold psi 10 each tire to 42 on all corners. The car feels much more nimble now, steering lighter, rolling resistance improved considerably, and even tread noise diminished just a bit. There is a downside, however, in that the ride is a bit harder, but certainly not harsh, and a bit more drone sound coming from the tires. Given that, all I can say is the car is more fun to drive now. Will ride this a bit more, then experiment with dropping a pound or two till I find the sweet spot.

As info, I dropped by a nearby tire dealer and asked them what to follow, tire manufacturer or car manufacturer, and their understanding was that the label on the b pillar was to be followed, citing the car"s suspension is engineered and optimized to work with tires set at a particular pressure.


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[mmaturo]

For street I follow the door sticker. All my recent Audi's have higher pressures than what I am used to from past cars. They clearly have a reason. The RS5 is higher numbers and the R8 is really high (45 and 41). Track use however I have gone the other way and do in the 30s since the tires will hit the max pressure immediately never mind less grip.

[Runge]

Thanks shonseb. Please see the attached picture of page 230 from my car's manual. Per the table, Audi is recommending 32 front and 32 back for low profile tires measuring 255/35R19 on my A5 coupe 2.0 liter 4 cyl under normal load (2 occupants). This is exactly the size I have now and exactly the size that came as original equipment on the car. Even if I loaded up the car with 4 occupants, the table from the car manual suggests just 33/33.

So, I'm just not understanding why the recommendations from Audi (32 psi) and Tire Rack (42 psi) are so different when they are both speaking to the same size tire and load, and not sure which recommendation to follow.

[IMG]http://img.tapatalk.com/d/13/12/16/y2ymysut.jpg[/IM

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Interesting why the 255/35/19 on A5 is 32PSI and 255/35/19 on S5 is 38PSI. Same tire, different car, different PSI.. Assuming the S5 weights a lot more to ask for the 6PSI increase?

[fasteddy91]

I had around 31-32 PSI on my 2.0T A5 quattro and changed it to 38-39 PSI like the S5 recommendations and my average mileage went up from 18-19 mpg to 21-22 city driving. My 5 mile commute to work this morning in city streets going 45mph in 5th gear (manual tranny) netted me 31 mpg.

[NuVega]

I run 40 PSI front, 39 PSI rear, and I have Michelin Pilot Super Sport tires on my 3.2L V6 A5, 245/35R19s...I got about 40K miles on these tires and surprisingly they are at 6/32nd tread, and I think the higher than normal PSI has something to do with it...and I avg about 18/28mpg.

[Hy Octane]

I do believe those numbers are the minimum PSI not the optimum ones..

[Fourcircle]

Called Tire Rack and asked them to recheck their figures and told them what my B pillar sticker recommended. They asked me to read them the front and rear axle weights of my car and their tech guy did some calculations while I waited. Turned out they concur with the Audi sticker, but advised adding maybe 1 to 2 lbs to be on the safe side and to help avoid damage. So looks I'll be running 34 or 35 psi, not 42. Whew, 'cause 42 was damn HARD.


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[rlarsen462]

I think the RS5 door sticker is 40 and 41 from Audi...heavier car I guess or lower profile?

[GotRS?]

RS5 is 44/41 F/R and that works well. If it gets too far into the 30's it get's a little squirrely.

[litigator]

Running around 38-39 on my all season 19" setup with nice results.

[ChipB]

I believe the reason for higher pressure recommended for the S5 compared to the A5 using the same width and profile tire is that the S5 has a stiffer suspension. Hence on the S5 more shock from potholes and such is absorbed by the sidewall of the tire, and if you ran with lower pressures you'd overflex the sidewall possibly damaging the rims.

In general you should follow the manufacturer's recommendation for pressures, as long as you're using stock wheel and tire sizes. It's OK to go a bit higher, but be aware that you are deviating from what the engineers intended as the tradeoff between comfort, grip, handling performance, and tire wear.

[staticuxo]

follow the tire. If you run low profile, the required pressures would be different from your manufacturers rec. My cousin who works in the tire and wheel industry gave me a good rule of thumb: fill the air to 20% less than Max psi. And always fill it cold. so for example with normal passenger tires max = 40psi - 20% = 32 psi, with low profile max 50ps - 20% = 40 psi. I tend to run 2 psi higher because of bad roads in NYC and I want to protect my wheels.

i concur with this and always ran ~40psi

[litigator]

Anyone in NYC metro area have trouble running the 255 35 19 with the PSI close to 40 regarding bent wheels, etc.? Just want to make sure my wheels are protected the best they can be despite the current road conditions

[jasontaylor7]

My Audi manual says to run 32 psi cold on all four tires but the tech guys at Tire Rack say I should be running 42 psi cold. Tire Rack says my RE970s are "extra load"' but so too were the Dunlop Sport Maxx GTs that came OEM. Not sure which mandate to follow. Anyone know?


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There are many variables, but inbetween is best. If you ever drive at very high speed you'll want extra pressure, perhaps 8 psi, not sure, to hold in the sidewall though as the centripetal force exceeds the load and can cause a tire to squish inwards from the wheel lip and lose all pressure, leading to a catastrophic failure. The reason tire rack fills to 40 psi is pretty simple. 1. Some tires leak slowly, and they want to minimize the number of reviews from customers saying the tires do not even hold air. 2. Many people know nothing about engineering, and think more pressure translates to a better, more powerful tire.

I agree with the theory here that low tire pressures give a more luxurious feel for brand new cars in the first year of driving when a customer is likely to complain if the ride is too harsh.

It's surprising to me your manual sets them identically. I think my manual has nothing, and says to go to my B-pillar. I explained why I am surprised in a long article about this with lots of history (which I won't link to as it in the past when I did that the mods attacked me), but the short version is that the contact patch with the road is bad at low pressure. This is good for front tires if they want to reduce oversteer since they cannot grip the road. Auto manufacturers like this because oversteer is a contributing factor in many accidents, and they mostly care about legal liability, not stopping distance. So BMW and many car makers like their owners to run extra low tire pressures on the front wheels. An extra benefit to them is that if they are hit with a wrongful death lawsuit this requirement can get them off of the hook since places like tire rack will almost always set them all at the same psi.

But, in terms of physics, you normally will want more pressure in the front because during emergency breaking the normal force on the front wheels could be like 80% or something, especially if your engine is in the front.

[papadelogan]

There are many variables, but inbetween is best. If you ever drive at very high speed you'll want extra pressure, perhaps 8 psi, not sure, to hold in the sidewall though as the centripetal force exceeds the load and can cause a tire to squish inwards from the wheel lip and lose all pressure, leading to a catastrophic failure. The reason tire rack fills to 40 psi is pretty simple. 1. Some tires leak slowly, and they want to minimize the number of reviews from customers saying the tires do not even hold air. 2. Many people know nothing about engineering, and think more pressure translates to a better, more powerful tire.

I agree with the theory here that low tire pressures give a more luxurious feel for brand new cars in the first year of driving when a customer is likely to complain if the ride is too harsh.

It's surprising to me your manual sets them identically. I think my manual has nothing, and says to go to my B-pillar. I explained why I am surprised in a long article about this with lots of history (which I won't link to as it in the past when I did that the mods attacked me), but the short version is that the contact patch with the road is bad at low pressure. This is good for front tires if they want to reduce oversteer since they cannot grip the road. Auto manufacturers like this because oversteer is a contributing factor in many accidents, and they mostly care about legal liability, not stopping distance. So BMW and many car makers like their owners to run extra low tire pressures on the front wheels. An extra benefit to them is that if they are hit with a wrongful death lawsuit this requirement can get them off of the hook since places like tire rack will almost always set them all at the same psi.

But, in terms of physics, you normally will want more pressure in the front because during emergency breaking the normal force on the front wheels could be like 80% or something, especially if your engine is in the front.

You replied to a thread that hasn't been active in nearly 9 years.... this is known as a necro-bump. Not the best habit, as it dredges up really old threads, but there's worse things as well. You may want to check the date of the last post before replying next time. Just a suggestion.

[jasontaylor7]

I have the opposite view of you. The internet is a repository for sharing knowledge. The old posts are used by people with similar questions. The questions here are very general and applicable to all car owners. Indeed, I was searching on this because of my own situation with tires and I learned something I didn't know. The longer the spacing between replies the more thought that is there in each one. Otherwise, it's a few people in a thread-less chatbox discussing things casually with little detail or concern of accuracy. Some of them have sold their cars and some of them have thought for years about these questions and gotten new information they didn't share yet. Indeed, there is actual testing of different tire pressures going on. This thread contains first-hand research, and I want more of it as my ride is too harsh. Perhaps they or other readers will now share more.

Also, I've made falsifiable claims here, and if I'm wrong well I'd want to know so I can learn what I am wrong about, too.

But the idea of closing older threads of research? That leads to duplicated threads in which neither is better than a single one that nails it.

It's also censorship.

[Neil F]

You replied to a thread that hasn't been active in nearly 9 years.... this is known as a necro-bump. Not the best habit, as it dredges up really old threads, but there's worse things as well. You may want to check the date of the last post before replying next time. Just a suggestion.

For this type of thread, there is no "expiration date". This is tech info.

Answering a thread where the OP asks a question that has long since been answered...............(or the person has long since died)............those bumps are not necessary

[jasontaylor7]

"Answering a thread where the OP asks a question that has long since been answered." IMO I gave the first actual answer to explain the huge discrepancy. The call by the op just showed that if they are proven wrong, they will consent. And besides, this thread isn't about tire rack. I went to jiffy lube two days ago and they also "topped off" (i.e., over-pressurized) the tires. I'd guess it has gotten a little better, but most tire shops are still filling to notably higher pressures than what is on B pillars.

[Neil F]

"Answering a thread where the OP asks a question that has long since been answered." IMO I gave the first actual answer to explain the huge discrepancy. The call by the op just showed that if they are proven wrong, they will consent. And besides, this thread isn't about tire rack. I went to jiffy lube two days ago and they also "topped off" (i.e., over-pressurized) the tires. I'd guess it has gotten a little better, but most tire shops are still filling to notably higher pressures than what is on B pillars.

I was NOT indicating you were replying to an old answered thread. I said "For this type of thread, there is no "expiration date". This is tech info.

I quoted papadelogan

You replied to a thread that hasn't been active in nearly 9 years.... this is known as a necro-bump. Not the best habit, as it dredges up really old threads, but there's worse things as well. You may want to check the date of the last post before replying next time. Just a suggestion.

[Neil F]

.........To add to this old thread........

The US door stickers only have one set of pressures. European door stickers have indications for number of passengers and the recommended pressures.

papadelogan: Seeing that you have a Cab, as do I, because of the heavier weight, my door sticker is 42/44

[jasontaylor7]

Thanks for clarifying Neil. Sorry for not understanding what you wrote the first time.

Are Cabriolet 2.0L's really so heavy? I think the 44 psi in the front tires (which is very interestingly high to me) is because they have a very low profile. Is the ride harsh?

[Neil F]

I have a 3.0 S5. 42 front, 44 rear is the sticker. Harsh, I never thought so. I've had the car 5 years. Currently I am running oversize 275/35/19 for increased sidewall as I have bent enough rims from potholes. Before /after ride.....I don't know if I really noticed. Plus I have lowered it on K&W HAS springs so I have no idea what "stock" was like.