Tire Pressure VS MPG VS Ride Comfort

jmarshall

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2011 Jetta 6MT
Anyone have any input on tire pressure vs fuel economy? Currently running 33 PSI as per the man. specs...... Was wondering how much the economy might improve if I raised the pressure a few lbs.... but don't want to take it up so much that it causes a rough ride or premature tire wear....
 

Dozenspeed

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May 1, 2012
33? Wow. Do you have 17"s? I have 16 inch wheels, thought the suggestion was 35. Tires say max 51, and I know 42 is popular. I commonly have to load mine up with 5 people and their luggage, so I like 40. Ride is still good, it handles much better in rain and I really have noticed less rolling resistance and higher mpg.
 

under dog

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I saw an increase of mpg on my lie-o-meter when i went up from the dealer installed 32psi to 38psi. Haven't finished the tank yet, but I'm pretty sure it will work out higher. Ride comfort is no different. I might try over 40psi next tank.
 

rob6188

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I keep mine at 33. I tried 38, and I did notice the ride was harsher, so much so I went back to 33. You can check my fuelly - I make lots of notes including psi.

Hard to say if mpg would be different without running a controlled test. There are tests and articles on the web that discuss this to great length. However, none of them specifically on the Jetta TDI.

Mythbusters did a test and it didn't make much difference on the mpg unless you went extreme in either direction. Like running at 8psi or 80psi.
 

hskrdu

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Mythbusters did a test and it didn't make much difference on the mpg unless you went extreme in either direction. Like running at 8psi or 80psi.
I wouldn't put too much stock in Mythbusters when it comes to automotive issues. That being said, I also believe the ecomodder review of their show reported a different result than rob stated.

IME, tire pressure can have notable and not insignificant impact on FE, even just increments of 5 PSI. Not that it helps the OP much, I run Nokians at 40, and anything much under that feels too soft for me. There are quite a few good threads already on tire pressure and FE, but as to driver comfort- that might be best revealed through T&E.
 

jtdi15

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Does anyone know at what psi the tire pressure sensor is set off? Mine went off on the way home today from work/school. Im gonna fill up the tires later tonight was gonna put around 36 to 38 in them. Tires were at 28, 31, 31, and like 34. According to tire pressure gauge.
 

jtdi15

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Well the sensor went off on the dash, but the gauge is just one of the things you put on the nipple and the white stick shoots out of the bottom lol
 

jmarshall

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2011 Jetta 6MT
The TPMS system on our jetta uses indirect monitoring. Rather than using sensors in the tires that pick up the pressure, it uses sensors that measure the speed of each wheel. When one is low, the diameter of the tire gets smaller, and it rotates faster. This is what trips the sensor. It's not at a set pressure, its when one is significantly different from the other
 

jnmarshall

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Over inflating isn't good for handling. You will be riding on the center of the tire and will experience less taction on wet road surfaces. The max PSI on the tire is the maximum load rating per the maker of the tire. The recommended PSI for your car is determined by the car maker as being ideal for handling, load, suspension, etc... You can make a whole scientific study out of it. All my cars are set for 1psi over car makers recommended. I usually will put an extra pound or two on the driver front for my fata$$:)
As for the TPMS, you can set or recalibrate it by pushing the button in the glove box. I haven't seen it go off if over inflated, just when it's under inflated and usually somewhere around 20-25psi, REALLY low!
 

Joe_Meehan

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I suggest doing your own testing. Ride is a matter of personal preference. So If you like the ride and you are keeping the pressure in the range recommended by VW you should be fine.

Of course there is more to the story if you want to look into it. There have been many many many threads on this.

I do recommend following the recommendations that come from someone who has done in depth testing. Remember to test under the conditions you drive under may not apply to your brother-in-law who may live in an area with totally different conditions.
 

erose

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Chicago, IL
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2011 Golf TDI
i actually just went up to 42psi up from the dealer who put them at ~32psi when i noticed that my mpg was starting to go down. i noticed the rolling resistance was significantly less and the ride really isn't too harsh. of course i avoid every crack on the road as much as possible. but i think i'm going to stick with 42psi
 

rob6188

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2012 Jetta
Remember to check tire pressure every couple of weeks as temperatures drop. I think it's 1psi for every 10 degrees, but just check often.
 

R-1150-RS

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Richmond Hill ON
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Over inflating isn't good for handling. You will be riding on the center of the tire and will experience less taction on wet road surfaces. The max PSI on the tire is the maximum load rating per the maker of the tire. The recommended PSI for your car is determined by the car maker as being ideal for handling, load, suspension, etc... You can make a whole scientific study out of it. All my cars are set for 1psi over car makers recommended. I usually will put an extra pound or two on the driver front for my fata$$:)
^^^This is the way to go.^^^

The minuscule difference you save in fuel economy is more than lost by the reduced traction your over-inflated tires have for both cornering and braking, especially in emergency situations.

As temperatures drop the reduction in traction is even greater as the cold rubber flexes less and the tires' treads do not come close to proper operating temperature.

Add a film of water, or worse ice and snow, and over-inflated tires are a formula for disaster.

There are perfectly good reasons why the manufacturers specify the pressures they do, and none of them are because they want you to burn more fuel than necessary, but rather because they have years of testing to support those specifications.

Gary
:) :)
 

hskrdu

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^^^This is the way to go.^^^

The minuscule difference you save in fuel economy is more than lost by the reduced traction your over-inflated tires have for both cornering and braking, especially in emergency situations.

As temperatures drop the reduction in traction is even greater as the cold rubber flexes less and the tires' treads do not come close to proper operating temperature.
At the risk of bumping (and continuing this thread), which is now, unofficially, thread number 302 on tire pressure....

1) Please define "miniscule."
2) Please define "over-inflated."
3) Please explain at what PSI percentage (of maximum PSI allowed) will a tire have reduced traction in cornering and braking.
4) Please explain at what PSI percentage (of maximum PSI allowed) will a tire fail to reach it's "proper operating temperature."
5) Please explain the first sentance: "The minuscule difference you save in fuel economy is more than lost by the reduced traction..." Are you making a subjective (and odd) comparison between fuel economy savings and tire traction?

Add a film of water, or worse ice and snow, and over-inflated tires are a formula for disaster.

There are perfectly good reasons why the manufacturers specify the pressures they do, and none of them are because they want you to burn more fuel than necessary, but rather because they have years of testing to support those specifications.
Gary
:) :)
6) Please explain at what PSI percentage (of maximum PSI allowed) we arrive at the recipe for disaster (and how does it taste with coffee)?
7) The manufacturer picks a PSI, generally in the middle of a range, that, for an original suspension, drivetrain, engine, platform, country, and intended tire, provides what they believe will be a compromise between comfort, handling, and fuel economy. They used to provide a range at which you could run your tires, and Germans may still be given a highway rec for the Autobahn (TDIMeister?). You might, in fact, eventually use different tires than originally came with your car, and these might offer advantages, disadvantages, and differences from your OE equipment, all without becoming a recipe for disaster.
8) If anyone wants to attempt to stick to exactly what the sticker on the door jam says, that's great- more power to them. For any others, we've got millions of miles, lots of tests, (and hundreds of posts), that reveal higher PSI's producing notable % gains in FE, all without too much hyperbole.
 

R-1150-RS

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Richmond Hill ON
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2012 Jetta TDI
At the risk of bumping (and continuing this thread), which is now, unofficially, thread number 302 on tire pressure....

1) Please define "miniscule."
Let me predicate my comments with another comment.

The opinions I expressed are the result of reading and hearing comments from others involved with the automotive industry, including those with direct experience with tire and vehicle performance.

If you can provide credible opinions from others experienced in the industry that disagree with my comments I would like to see them.

As to "Miniscule", I would define that as comparable the ratio between the few dollars saved in fuel vs the cost of an insurance claim from an accident that is the result of reduced traction.


2) Please define "over-inflated."
Tire pressure above that recommended by the manufacturer that is sufficient to reduce traction and affect wear patterns


3) Please explain at what PSI percentage (of maximum PSI allowed) will a tire have reduced traction in cornering and braking.
That effect is cumulative. Typically the larger the difference above what is rated by the manufacturer as optimal the greater the reduction.

Have your doubts? Ask ANY experienced professional racing team whether even small changes in air pressure can have a noticeable effect on traction......


4) Please explain at what PSI percentage (of maximum PSI allowed) will a tire fail to reach it's "proper operating temperature."
Any tire that is at their rated pressure will build temperature due to flexing. Tire compounds are designed such that warmer rubber tends to give better traction than colder. (Within limits - too hot and the traction decreases...)

If the need is to run in cold temps the tread compound is designed differently for Winter tires than Summer or All-Season.

They also account for the heat-build-up from tire flex when compounding the tread formula and sidewall design.

Given any one tire, if you run one at the recommended pressure and another at several pounds pressure above it, there will be less flex. (This lack of flex and the heat it creates is exactly what increasing tire pressures reduces. The lower rolling resistance means less energy is used, and more fuel is saved, to heat the tire tread.)

If you think tire tread temps do not matter, try saying that to the tire engineers who regularly check tire tread temps under racing conditions to determine if the temps are 'optimum" and whether the pressures need to be adjusted......

Or better yet, as any race driver if his traction on 'cold tires' is anywhere near that of after they warm-up......

5) Please explain the first sentance: "The minuscule difference you save in fuel economy is more than lost by the reduced traction..." Are you making a subjective (and odd) comparison between fuel economy savings and tire traction?
It is only 'odd' to those who don't understand the relationship between reduced rolling resistance being at the expense of reduced tire flex, and lower temperature build-up in the treads.....

That reduced rolling resistance is energy saved (and increased fuel economy) that would normally go to raising tire tread temps....

6) Please explain at what PSI percentage (of maximum PSI allowed) we arrive at the recipe for disaster (and how does it taste with coffee)?
It is an inverse scale. Traction is reduced as pressure increases.

How much less traction are you prepared to give up?

You may decide you are willing to take that risk, but there is no question your traction does decrease as pressure rises..........

(A style comment: - Please hold the sarcasm. You obviously are not well-informed in these topics. If you really want to get information, ad-hominems towards others typically reflects worse on those giving them...)

7) The manufacturer picks a PSI, generally in the middle of a range, that, for an original suspension, drivetrain, engine, platform, country, and intended tire, provides what they believe will be a compromise between comfort, handling, and fuel economy. They used to provide a range at which you could run your tires, and Germans may still be given a highway rec for the Autobahn (TDIMeister?). You might, in fact, eventually use different tires than originally came with your car, and these might offer advantages, disadvantages, and differences from your OE equipment, all without becoming a recipe for disaster.
Agreed.

But the recommendations are certainly NOT arbitrary, and typically have to do with intended use.

Anyone who spends much time at high speeds on the autobaun will require a higher pressure to reduce the heat build-up, and to maintain sidewall rigidity under high cornering loads, than cars that rarely go above 100 KPH.

Again, look at the racers. There is no one temperature or pressure that is always optimal for all types of racing conditions. Same too for driving.

But what you can be sure of, if you go significantly above the pressures recommended you will more likely not optimize performance within 'average driving' conditions we will typically encounter on the road.

8) If anyone wants to attempt to stick to exactly what the sticker on the door jam says, that's great- more power to them. For any others, we've got millions of miles, lots of tests, (and hundreds of posts), that reveal higher PSI's producing notable % gains in FE, all without too much hyperbole.
I never denied you will save on FE with higher pressures.

But if you think that raising pressures has minimal effect on traction and potentially on your safety as a result, you are certainly mistaken.....

But if you really have 'evidence' that demonstrates the principles I have referred to are wrong, let's see them......

Gary
:) :)
 
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hskrdu

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R-1150 / Gary:

Whoa, buddy, slow down there on the attitude. If you are going to take offense or get a bit testy when other members either ask you questions to define, explain, or ask you for clarification, it's gonna be a bumpy road. Fred's is well known for its civility, humor, technical knowledge, but also for the good natured but fairly zealous commitment to challenge posts that make, let's say, unreasonable or hyperbolic claims.

The statement "over-inflated tires are a formula for disaster" is, for me, a bit too vague, if not an exaggeration, so I asked you to define, explain, and clarify. In fact, I asked you to please do so, and you'll find from a search that I am rarely impolite. I apologize if you took my humor the wrong way- it was certainly not sarcasm. I did have to chuckle at the "recipe for disaster," but gave you lots of room to clarify, amplify, and qualify your statement, lest I was misunderstanding.

As for my being "obviously not well informed," I hope that remains to be determined. I do hope, though, that when members lacking information (in your view, at least) ask questions, your answers will be void of poor attitude towards their post.

Lastly, (for now at least), my hope was to have you provide some more exacting parameters so your strong caution to others could be better understood. That did not happen. IMO, and not to offend you, you crafted a carefully worded statement that largely says something akin to "your tires are dangerously overinflated at the point at which they are dangerously overinflated." In that case, I agree. My point, which was made previously, but may have been incomplete, is not that drivers should exceed the max sidewall to improve FE, but that TDIClub members interested in these topics, have for the past 13 years, been testing/observing their tires under a variety of real-world conditions, and documenting their results in threads here. We have many ardent proponents of "sticking to what the door jam/fuel door says," (thinking of you many years back, Joe_Meehan) but we also have -literally- hundreds of posts, in over 300 threads, with millions of miles, where drivers have seen a notable increased % in FE, without crashing or other mishap caused by tires being run above what "the sticker" says.

For others reading, there are numerous outstanding threads on FE, tires, PSI, etc., which are not only fun to read, but full of great information, and spirited give and take. Most of these are from the years prior to the Mark VI, but are likely applicable. The focus in not racing, autox, or rally, but simply how members have charted their FE and handling with a variety of tires and PSI variations. Search is your friend.:)
 

R-1150-RS

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Mar 31, 2012
Location
Richmond Hill ON
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2012 Jetta TDI
R-1150 / Gary:
Whoa, buddy, slow down there on the attitude. If you are going to take offense or get a bit testy when other members either ask you questions to define, explain, or ask you for clarification, it's gonna be a bumpy road. Fred's is well known for its civility, humor, technical knowledge, but also for the good natured but fairly zealous commitment to challenge posts that make, let's say, unreasonable or hyperbolic claims.
I have responded with explanations of what I meant by my comments.

All of which support my position. Yet you still label them as 'unreasonable or hyperbolic'.

That characterization would have a thread of credibility if you had actually refuted any of my claims.

You seem to confuse your 'challenge' with something that approaches a 'refutation'.

You have not done that yet.


The statement "over-inflated tires are a formula for disaster" is, for me, a bit too vague, if not an exaggeration, so I asked you to define, explain, and clarify. In fact, I asked you to please do so, and you'll find from a search that I am rarely impolite. I apologize if you took my humor the wrong way- it was certainly not sarcasm. I did have to chuckle at the "recipe for disaster," but gave you lots of room to clarify, amplify, and qualify your statement, lest I was misunderstanding.
Tires that have had their traction reduced to the point where braking distances are increased or their ability to hold a corner lessened, are also more likely to be involved in a collision.

I acknowledge only that the expression 'formula for disaster' is subjective.

The degree of the 'disaster' is dependent on how serious any resultant accident is.....


As for my being "obviously not well informed," I hope that remains to be determined. I do hope, though, that when members lacking information (in your view, at least) ask questions, your answers will be void of poor attitude towards their post.
The previous post of mine that you originally responded to reflects what I believe to be the basic principles of tire performance.

When you chose to challenge my post it appeared to be less a sincere request for clarification, but rather a characterization of the claims as being in your words 'subjective (and odd)'.

Yet, you have yet to provide anything that actually refutes what I have said, other than point to many others who have "got millions of miles, lots of tests, (and hundreds of posts), that reveal higher PSI's producing notable % gains in FE."

Again, I never denied higher tire pressures result in fuel saving.

I only pointed to the reality that reduced rolling resistance caused by harder tires also brings with it a reduction in traction and uneven tread wear.

Yet there still are members here who advocate running tires at pressures above 40-psi when VW recommends pressures closer to 33-psi.

It is irresponsible and incompetent to promote pressures so much higher than recommended without addressing the effects on tire traction, and safety, that also results from such practices.

Yet your response neither denies nor refutes my claim that traction reduction is a by-product of that practice.......


Lastly, (for now at least), my hope was to have you provide some more exacting parameters so your strong caution to others could be better understood. That did not happen. IMO, and not to offend you, you crafted a carefully worded statement that largely says something akin to "your tires are dangerously overinflated at the point at which they are dangerously overinflated." In that case, I agree.
Sorry to hear that you would misinterpret my statement that "Typically the larger the difference (in pressure) above what is rated by the manufacturer as optimal the greater the reduction (in traction).......

I thought the concept was clearly stated and explained for exactly what it is.

I did not supply support documentation for the simple reason that every tire manufacturer I have seen recommends that you follow the manufacturer's recommendations for tire inflation to get the maximum traction and tread life from their tires.

You have yet to demonstrate how they are ALL wrong.......


My point, which was made previously, but may have been incomplete, is not that drivers should exceed the max sidewall to improve FE, but that TDIClub members interested in these topics, have for the past 13 years, been testing/observing their tires under a variety of real-world conditions, and documenting their results in threads here. We have many ardent proponents of "sticking to what the door jam/fuel door says," (thinking of you many years back, Joe_Meehan) but we also have -literally- hundreds of posts, in over 300 threads, with millions of miles, where drivers have seen a notable increased % in FE, without crashing or other mishap caused by tires being run above what "the sticker" says.
First: - There is typically a large difference in the max pressure rating on a tire, and the pressure recommended by the manufacturer. (Tires on most vehicles are 'over rated' for the typical use and load they are intended for. If the same tire was on a heavier vehicle the recommended pressure would be closer to the maximum rated pressure on the sidewall.)

Second: - There certainly are many posts by members on this topic. There are many who even have documented the effect of the change on fuel economy. You also acknowledged that there are differing opinions on which approach is best.

My response is that none of these are controlled scientific studies that conclude anything different from what the tests conducted by the manufacturers have found.

Third: - Your statement "where drivers have seen a notable increased % in FE, without crashing or other mishap caused by tires being run above what "the sticker" says." is one that you will have difficulty supporting.

There have been many posts on this forum by members who have been in accidents. Who here can say with any certainty that at least some of them might have been avoided or the damage minimized by tires with better traction by not being over-inflated?

Without a proper controlled study that analyses the contributing factors of accidents with members tires that were run at various pressures above what is recommended, vs those at the recommended pressures, you are merely guessing that none of the many accidents mentioned have resulted from the reduced traction higher pressures provide.........

Tire companies have invested much research, and multi-millions in testing, to get the significant knowledge they have about optimum tire construction and how to get the best performance out of them.......

But again, if you actually have anything that approaches a study that refutes their findings lets see it......


For others reading, there are numerous outstanding threads on FE, tires, PSI, etc., which are not only fun to read, but full of great information, and spirited give and take. Most of these are from the years prior to the Mark VI, but are likely applicable. The focus in not racing, autox, or rally, but simply how members have charted their FE and handling with a variety of tires and PSI variations. Search is your friend.:)
Not to denigrate anyone here, but I remind you of the limits inherent to an enthusiasts' site.

You can pick a side to support that reflects your opinion, but unless you can back that with something better than anecdotal experience, that is as good as it gets.....

The main reason I challenged the practice of raising tire pressures to increase FE in the first place is because it ignored the universal recommendations of the tire and vehicle manufacturers.

The results of over-inflation are widely recognized throughout the industry as adversely affecting traction.

To promote such a practice without acknowledging this potentially significant safety risk is either ignorance or incompetence.

Members should have the knowledge of the risks involved before making their choice.

Gary
:) :)
 
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40X40

Experienced
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Kansas City area, MO
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2013 Passat SEL Premium
Somehow I and other members have been running our standard issue/equivalent tires at +/- 85% of max sidewall pressure for years without encountering problems with handling or braking and yet our tires wear evenly across the tread width and we even enjoy good snow traction....

How can this be??

I suppose my tires are just too stupid to know better.

LOL

Bill
 

hskrdu

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Watch out Bill, he hasn't yet read many of the years of good tire/psi/mpg posts. After all those years, we still don't know what we are talking about. Of course, this is just an enthusiast's site.
 

Joe_Meehan

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Ohio USA
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Just remember that the recommended pressure, is there as a safety. While there is a good range when it comes to tyre pressure on modern cars, but if you are going outside the recommended pressure. (either too high or too low)

Unless you have checked it out on a test track under various conditions (like rain or gravel etc.) you would be well advised to follow the recommended values.
 

nicklockard

Torque Dorque
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Aug 15, 2004
Location
Arizona
TDI
SOLD 2010 Touareg Tdi w/factory Tow PCKG
Anyone have any input on tire pressure vs fuel economy? Currently running 33 PSI as per the man. specs...... Was wondering how much the economy might improve if I raised the pressure a few lbs.... but don't want to take it up so much that it causes a rough ride or premature tire wear....
My experience:
 

R-1150-RS

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Location
Richmond Hill ON
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2012 Jetta TDI
Watch out Bill, he hasn't yet read many of the years of good tire/psi/mpg posts. After all those years, we still don't know what we are talking about. Of course, this is just an enthusiast's site.
More sarcasm I see....

I have read enough to have learned that, as you have previously acknowledged, there remains many members with differing "Opinions" on this topic.

Everyone is welcome to their own opinion.

But when you claim your own opinion isn't be wrong, even if it differs with every manufacturers' recommendations out there, you have to do more than merely express your opinion to be taken seriously........

Until you can demonstrate with actual evidence the manufacturers are wrong, I don't think your opinion has a credible leg to stand on.....

Gary
:) :)
 

nicklockard

Torque Dorque
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Location
Arizona
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SOLD 2010 Touareg Tdi w/factory Tow PCKG
Likely not too far off from others who have taken the time to actually check it out...

Thanks!!

Gary
:) :)
NP. That chart is my qualitative opinion(s)-experiential only. I like to ride around 44-47 for summer, 44ish for fall, 38-40 for most winter conditions (28-33 for going over mountain passes), 40ish for spring. Oh, and when it's dry and I've got a bug to break a personal mpg record, I've been known to ride 49 if there's no traffic around. Edit: the wet/icy grip ranking is highly dependent on tire quality.

YWMV & YTMV.
 
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