Is my mechanic stupid?

[Zenmervolt]

Originally posted by: bernse

Originally posted by: flyfish
Take a piece of chalk and draw a line across the tire tread. Drive a SHORT distance down a dry straight road. If the chalk is line is rubbed off evenly, the tire pressure is correct for the vehicle. If it is rubbed off only on the edges, add air. If it is rubbed off only in the middle, let out some air.

I understand what you are getting at, but thats a new one one me.

Do you realize how much pressure you'd need to add to your tires to make them noticeably "bulge" in the middle? Or how low they'd have to be to only wear on the outsides?

Don't trust this measurement technique. For cripes sakes, buy a $1 pressure gauge!

Not a whole lot of difference in pressure is needed actually. Running your tires 2-3 PSI low or high can have a noticeable effect on treadwear.

ZV

 

[Pacfanweb]

So to answer your original question, yes, your mechanic is stupid.

 

[NutBucket]

Originally posted by: NutBucket

Originally posted by: isekii
I think the 44 psi is under max load ?

44 is max pressure. Follow the car door. For example, my 17's say max pressure is 44psi. I run them at about 32 or so.

Forgot to add my car came from the factory with 14's and I also ran those at about 30 to 32.

 

[PlatinumGold]

wait a minute.


so, the OPer THINKS he knows more about cars than his "stupid" mechanic and yet he STILL takes his car there??

who is the really stupid one?? hmmmmm.

carry on.

 

[Jeff7181]

You could do it the redneck way and just ad air until the sidewall is no longer "bubbled" at the bottom

*EDIT* Oh yeah, and make sure you check the tire pressure with the car up on a jack, otherwise the weight of the car will give you an artificially high number

 

[NutBucket]

Originally posted by: PlatinumGold
wait a minute.


so, the OPer THINKS he knows more about cars than his "stupid" mechanic and yet he STILL takes his car there??

who is the really stupid one?? hmmmmm.

carry on.

HAHAH!! I completely missed that one! Nice:beer:

 

[PlatinumGold]

Originally posted by: NutBucket

Originally posted by: PlatinumGold
wait a minute.


so, the OPer THINKS he knows more about cars than his "stupid" mechanic and yet he STILL takes his car there??

who is the really stupid one?? hmmmmm.

carry on.

HAHAH!! I completely missed that one! Nice:beer:

:beer:

 

[bernse]

Originally posted by: Zenmervolt Not a whole lot of difference in pressure is needed actually. Running your tires 2-3 PSI low or high can have a noticeable effect on treadwear.
ZV

2-3# will have a noticable effect on treadware on either extreme end of the spectrum (high or low end) but absolutely negligable in the middle. You will have virtually no difference in treadware on a tire at 30# or 33# on a modern radial P class tire. If you're running it at super high loads though, this goes out the window (IE - Using a P tire on a truck with a load meant for an LT tire)

However, if a car is at 17 and you boost it to 20, yes, there will be a noticeable difference.

 

[Pacfanweb]

Originally posted by: Jeff7181
You could do it the redneck way and just ad air until the sidewall is no longer "bubbled" at the bottom

*EDIT* Oh yeah, and make sure you check the tire pressure with the car up on a jack, otherwise the weight of the car will give you an artificially high number

Hopefully you added that last comment as a joke.

 

[Vette73]

OK, like most have said, the rating on the tire is MAX. BUT a common mistake, even listed here is to set your tires by the rating in the car. 9 times out of ten tires are under inflated. The PSI rating on the door is for COLD tires. So if oyu drive up to the gas and go and put your tires at what it says on the door you are anywhere from 2-4 PSI off what they SHOULD be. Like the new corvettes call for 30 Psi, but they did add a note that says if the tires are warm add 4psi to the rating. So if you have a C5 vette and drive it to the air tank, then it should eb 34psi, NOT 30 as the door has listed.

I run my cars, trucks, etc... at 34-36 front and 33-34 rear, warm. Wears very even all across.

 

[Zenmervolt]

Originally posted by: bernse

Originally posted by: Zenmervolt Not a whole lot of difference in pressure is needed actually. Running your tires 2-3 PSI low or high can have a noticeable effect on treadwear.
ZV

2-3# will have a noticable effect on treadware on either extreme end of the spectrum (high or low end) but absolutely negligable in the middle. You will have virtually no difference in treadware on a tire at 30# or 33# on a modern radial P class tire. If you're running it at super high loads though, this goes out the window (IE - Using a P tire on a truck with a load meant for an LT tire)

However, if a car is at 17 and you boost it to 20, yes, there will be a noticeable difference.

It does not need to be a great difference in order for chalk to wear a little more on the sides or in the middle. Regardless of where within the range the 2-3 PSI difference is, it will make the same amount of difference. Linear scale.

ZV

 

[v3rrv3]

Out of curiosity, what do you do if they aren't stock tires or anything of the sort, still stock PSI?

- Kevin

 

[bernse]

Originally posted by: Zenmervolt

Originally posted by: bernse

Originally posted by: Zenmervolt Not a whole lot of difference in pressure is needed actually. Running your tires 2-3 PSI low or high can have a noticeable effect on treadwear.
ZV

2-3# will have a noticable effect on treadware on either extreme end of the spectrum (high or low end) but absolutely negligable in the middle. You will have virtually no difference in treadware on a tire at 30# or 33# on a modern radial P class tire. If you're running it at super high loads though, this goes out the window (IE - Using a P tire on a truck with a load meant for an LT tire)

However, if a car is at 17 and you boost it to 20, yes, there will be a noticeable difference.

It does not need to be a great difference in order for chalk to wear a little more on the sides or in the middle. Regardless of where within the range the 2-3 PSI difference is, it will make the same amount of difference. Linear scale.

ZV

No. It isn't linear.. not even close. This is visible with the naked eye. See the difference a tire makes from flat to 5lbs? 5#is almost driveable (albeit very low). Flat isn't. See the difference between 25 and 30#? Virtually indisiguishable to the eye unless you had two tires beside eachother to compare.

 

[NutBucket]

Originally posted by: v3rrv3
Out of curiosity, what do you do if they aren't stock tires or anything of the sort, still stock PSI?

- Kevin

Yes, see my post above I went from 185/70 R14 to 205/45 R17 and kept the same pressure. At least I think that was the stock size. I choose not to keep it fresh in my memory

 

[Zenmervolt]

Originally posted by: bernse
No. It isn't linear.. not even close. This is visible with the naked eye. See the difference a tire makes from flat to 5lbs? 5#is almost driveable (albeit very low). Flat isn't. See the difference between 25 and 30#? Virtually indisiguishable to the eye unless you had two tires beside eachother to compare.

You'd have to be friggin' blind to think that 5 PSI looks "driveable". I'm sorry, but it is visually VERY clear when a tire is off by 5 PSI ANYWHERE in the inflation range.

ZV

 

[zixxer]

depends on if you have stock wheels too

 

[NutBucket]

Originally posted by: se7enty7
depends on if you have stock wheels too

No it doesn't.

 

[bernse]

Originally posted by: Zenmervolt You'd have to be friggin' blind to think that 5 PSI looks "driveable. I'm sorry, but it is visually VERY clear when a tire is off by 5 PSI ANYWHERE in the inflation range.

Compared to flat, 5psi looks great.

5psi? We were talking 2-3 earlier. Either way, as I mentioned, on the extremes of the ranges it is very apparent. However, in the mids (say 20-35) no, it isn't VERY clear. As I said, if you had them right next to each other you might see the difference.

Why do you think they even have pressure gauges? If it was so apparant if you're only out a couple of #, why bother with them?


This is getting stupid.

 

[Wingznut]

Originally posted by: Zenmervolt
I'm sorry, but it is visually VERY clear when a tire is off by 5 PSI ANYWHERE in the inflation range.

I guess I sucked as a mechanic then... Because I certainly couldn't tell a 5lb difference with my naked eye. And I'd check tire pressures several times a day. *shrugs*

Originally posted by: bernse
This is getting stupid.

I'll have to agree with you there.

 

[Lithium381]

the car door only works if you're running stock.......my tires say around 44 i think too, max, so i've got them all at 40 or so......

 

[Wingznut]

Originally posted by: Lithium381
the car door only works if you're running stock.......my tires say around 44 i think too, max, so i've got them all at 40 or so......

Not really... Your "stock" tires will also give a "Max Pressure" rating, but this is irrelevant to the CORRECT tire pressure.