tire presure
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
Actually, Mr. Kacyc3, the interesting point of my investigation was that GM recommended 20/20 tire pressure for the first-year application of their RADIAL tire. I do not know why.
In later years (from 1974 to 1982), the recommended tire pressure increased incrementally as the tire width also ultimately increased from 225 to 255. This culminated in the 1982 recommended tire pressure of 35/35 for the widest tire they had yet fitted to the car.
This is an interesting counterpoint to Mr. TooBroke's assertion that the tire width is instrumental in his ability to run lower tire pressures.
As I said a couple of times earlier, I suspect that as Radial Tires continued their development over the 'early' years, the structural adjustments required that more and more pressure be run for the contact patch to maintain its shape. It is very difficult to find historical information on this hypothesis.
The "most modern" data point we have is that of the 1982 Corvette. And the recommended tire pressures are exceedingly similar to those found on other period, and later, cars.
I'll say it this way:
If I take my BFG tire and put it on a 1982, the door sill says I should run 35 PSI. So I start with 35 PSI. I take THAT SAME TIRE on THAT SAME RIM and put it on a 1974. The door sill NOW says I can run 20 PSI. So I deflate my tire to 20 PSI and go on my merry way.
Makes sense, right?
I'm sorry, but it does not to me.
From 1970 to 1982 to NOW, we had different gas, different brake fluid, different oil, different lots of stuff. Why is it such a stretch that tire technology also changed in a way that requires a different approach to pressure?
In later years (from 1974 to 1982), the recommended tire pressure increased incrementally as the tire width also ultimately increased from 225 to 255. This culminated in the 1982 recommended tire pressure of 35/35 for the widest tire they had yet fitted to the car.
This is an interesting counterpoint to Mr. TooBroke's assertion that the tire width is instrumental in his ability to run lower tire pressures.
As I said a couple of times earlier, I suspect that as Radial Tires continued their development over the 'early' years, the structural adjustments required that more and more pressure be run for the contact patch to maintain its shape. It is very difficult to find historical information on this hypothesis.
The "most modern" data point we have is that of the 1982 Corvette. And the recommended tire pressures are exceedingly similar to those found on other period, and later, cars.
I'll say it this way:
If I take my BFG tire and put it on a 1982, the door sill says I should run 35 PSI. So I start with 35 PSI. I take THAT SAME TIRE on THAT SAME RIM and put it on a 1974. The door sill NOW says I can run 20 PSI. So I deflate my tire to 20 PSI and go on my merry way.
Makes sense, right?
I'm sorry, but it does not to me.
From 1970 to 1982 to NOW, we had different gas, different brake fluid, different oil, different lots of stuff. Why is it such a stretch that tire technology also changed in a way that requires a different approach to pressure?
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
Racer
Joined: Nov 2008
Posts: 366
Likes: 7
From: Mobile Al
Just about everyone on this site has the ability to look at and read what the pressure should be on the tire. Why -because it's written on them. If you want to run something else go ahead, just don't try and convince people that what you say is right. If you get such great mileage running a lower pressure that's great for you but I bet if you took the time to go out and look and read the stated pressure you would find out your wrong. There are alot of people that maintain their cars as they see fit and have fun with them while changing what they came from the factory with.
Go clean your headlights.
Go clean your headlights.
Last edited by Doug Kraft; Dec 4, 2015 at 12:30 PM.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
First, I completely disagree with the linear relationship between rated tire capacity and weight bore by said tire. There is zero merit in the argument that "because a tire rated at 2,000# only carries 500#, so I can run 1/4 the pressure required for it to carry 2,000#". Zero merit.
I've posted MULTIPLE times to produce a single reputable source to back up that ridiculous claim. Response = cricket....cricket....cricket..... Contact patch pressure is the key. Measuring sidewall bulge is meaningless and just shows how little some mechanical engineers really know.Most? It's all except one. You've given great information without making stupid claims because "I'm an engineer so I know better".
Race Director
Joined: Dec 1999
Posts: 11,094
Likes: 990
From: Sierra Foothills CA
one of the many articles I found.
http://content.time.com/time/busines...128198,00.html
http://content.time.com/time/busines...128198,00.html
As you have done on other topics here in the past, you fail to respond to posts that ask relevant questions or contain research info (in this case done by Tire Rack, which has no motivation to publish such data other than to inform the public) that doesn't support your opinion. For once, man up and answer to the link above- with actual research data, not just a regurgitation of your simple minded opinions.
Then answer the question asked by Kacyc3- asked for the third time in this thread- exactly what tires are you running?
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
They're BF Goodrich T/A radials but in the past I ran several sets of Dunlops (before they got discontinued) and several sets of Coopers.
When the centers of tires are worn out and they still have 3/8" of tread on the sides the tires are over inflated. What is it about that you can't understand? Over inflation wears out centers.
Race Director
Joined: Dec 1999
Posts: 11,094
Likes: 990
From: Sierra Foothills CA
They're BF Goodrich T/A radials but in the past I ran several sets of Dunlops (before they got discontinued) and several sets of Coopers.
When the centers of tires are worn out and they still have 3/8" of tread on the sides the tires are over inflated. What is it about that you can't understand? Over inflation wears out centers.
When the centers of tires are worn out and they still have 3/8" of tread on the sides the tires are over inflated. What is it about that you can't understand? Over inflation wears out centers.
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Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
They're BF Goodrich T/A radials but in the past I ran several sets of Dunlops (before they got discontinued) and several sets of Coopers.
When the centers of tires are worn out and they still have 3/8" of tread on the sides the tires are over inflated. What is it about that you can't understand? Over inflation wears out centers.
When the centers of tires are worn out and they still have 3/8" of tread on the sides the tires are over inflated. What is it about that you can't understand? Over inflation wears out centers.
I think I figured out the miscommunication between everyone. Your tires are rated a max of 35 psi, if we use the same formula that new tires use (max pressure 44 psi)= (32 recommended psi) 32/44 = .72%
(%) x 35 (PSI) = 25.5 PSI. (This is just a theory and you should contact your tire manufacturer to confirm this pressure is correct.)
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
We all agree that overinflation will wear out the centers but, telling someone to run 20 psi in their tires if they aren't built for that is dangerous.
I think I figured out the miscommunication between everyone. Your tires are rated a max of 35 psi, if we use the same formula that new tires use (max pressure 44 psi)= (32 recommended psi) 32/44 = .72%
(%) x 35 (PSI) = 25.5 PSI. (This is just a theory and you should contact your tire manufacturer to confirm this pressure is correct.)
I think I figured out the miscommunication between everyone. Your tires are rated a max of 35 psi, if we use the same formula that new tires use (max pressure 44 psi)= (32 recommended psi) 32/44 = .72%
(%) x 35 (PSI) = 25.5 PSI. (This is just a theory and you should contact your tire manufacturer to confirm this pressure is correct.)
Where does that 44 psi come from? I bought these latest tires in the summer of last year and they have a maximum pressure rating of 35 psi just like all of the other 255X60R15's I bought in the past 27 years had. The recommended RUNNING pressure of a tire is a lot different from the maximum pressure printed on the side wall. The tire manufacturer doesn't determine what pressure a tire is to be run at; the vehicle manufacturer does that based on the weight the tire will be supporting.
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
The recommended RUNNING pressure of a tire is a lot different from the maximum pressure printed on the side wall. The tire manufacturer doesn't determine what pressure a tire is to be run at; the vehicle manufacturer does that based on the weight the tire will be supporting.
The recommended running pressure is set by the manufacturer, not the tire company.
And it was incrementally adjusted upward by General Motors for radial tires on the Chevrolet Corvette from 1974 to 1982.
By golly, I think you hit the nail on the head!!! I TOTALLY AGREE WITH YOU!!! THIS IS AWESOME!!!
Sorry. I said I was done, but I had to jump in as soon as saw that we had finally resolved this issue.
Last edited by keithinspace; Dec 4, 2015 at 03:39 PM.
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
I'd like to ask a question that is a little off the subject, but also relevant to the discussion relative to being able to see true wear in a tire.
Who has replaced a set of tires on their car due to road wear (not burnouts, not track use...I'm talking around-town and interstate miles) and not due to age?
I don't want to turn this into a "how many miles do you drive in a year" thread, but honestly...I just replaced my two rear tires that dated from 1982. They still had A TON of tread on them. And based on my driving habits, it will take me well over 15 years to "wear out" a set of tires.
Point being, my tires will be long replaced before I actually have the opportunity to "see" the true wear pattern in the tread.
Who has replaced a set of tires on their car due to road wear (not burnouts, not track use...I'm talking around-town and interstate miles) and not due to age?
I don't want to turn this into a "how many miles do you drive in a year" thread, but honestly...I just replaced my two rear tires that dated from 1982. They still had A TON of tread on them. And based on my driving habits, it will take me well over 15 years to "wear out" a set of tires.
Point being, my tires will be long replaced before I actually have the opportunity to "see" the true wear pattern in the tread.
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
Where does that 44 psi come from? I bought these latest tires in the summer of last year and they have a maximum pressure rating of 35 psi just like all of the other 255X60R15's I bought in the past 27 years had. The recommended RUNNING pressure of a tire is a lot different from the maximum pressure printed on the side wall. The tire manufacturer doesn't determine what pressure a tire is to be run at; the vehicle manufacturer does that based on the weight the tire will be supporting.
A car manufacturer not using recommended pressure that a tire manufacturer told them to use is what Ford did that caused so many problem in 2000-2002. I worked at a Firestone dealer after this and they still maintain it was Fords fault (I was reluctant to believe, ya know blame someone else). Google it and go to reputable sites and read, first I found was Wiki, didn't believe that as users upload/upate and change that info. Second was something else followed suit with Wiki, then I cam across that link for time that I posted earlier that confirmed Ford went against Firestone recommendations. This only leads to 1 question, you dont use the same tires the car came with model or size so, why would you believe a 20PSI rating from 46 years ago?
Race Director
Joined: Dec 1999
Posts: 11,094
Likes: 990
From: Sierra Foothills CA
Well, I just got off the phone with my closest America's Tire store. They have a program that allows you to enter a specific vehicle along with a specific tire and, based upon the weight of the vehicle, give the correct PSI for that tire. I had the guy query the system for a '69 Vette and the BFG Radial T/A tire in 255/60/15. I chose the '69 because it's the lightest C3 other than possibly the '68, and therefore it would tolerate the lowest PSI for C3s. I explained that we were having a discussion on the subject and that somebody was recommending PSI of 24/20 and, without knowing if I agreed with that or not, he said "Oh, that sounds low."
The results- their system recommends a minimum cold PSI of 26 for that tire on all 4 corners. Of course, hot PSI goes up by a few- and the weight in their system for C3s would be for the base car. The big blocks and other options would add weight and therefore make additional PSI a reasonable route to take. Additionally, as we all know, C3s gained weight throughout the years.
What say you, toobroke?
The results- their system recommends a minimum cold PSI of 26 for that tire on all 4 corners. Of course, hot PSI goes up by a few- and the weight in their system for C3s would be for the base car. The big blocks and other options would add weight and therefore make additional PSI a reasonable route to take. Additionally, as we all know, C3s gained weight throughout the years.
What say you, toobroke?
Race Director
Joined: May 2006
Posts: 18,658
Likes: 2,561
Answer
I'd like to ask a question that is a little off the subject, but also relevant to the discussion relative to being able to see true wear in a tire.
Who has replaced a set of tires on their car due to road wear (not burnouts, not track use...I'm talking around-town and interstate miles) and not due to age?
I don't want to turn this into a "how many miles do you drive in a year" thread, but honestly...I just replaced my two rear tires that dated from 1982. They still had A TON of tread on them. And based on my driving habits, it will take me well over 15 years to "wear out" a set of tires.
Point being, my tires will be long replaced before I actually have the opportunity to "see" the true wear pattern in the tread.
Who has replaced a set of tires on their car due to road wear (not burnouts, not track use...I'm talking around-town and interstate miles) and not due to age?
I don't want to turn this into a "how many miles do you drive in a year" thread, but honestly...I just replaced my two rear tires that dated from 1982. They still had A TON of tread on them. And based on my driving habits, it will take me well over 15 years to "wear out" a set of tires.
Point being, my tires will be long replaced before I actually have the opportunity to "see" the true wear pattern in the tread.
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
Well, I just got off the phone with my closest America's Tire store. They have a program that allows you to enter a specific vehicle along with a specific tire and, based upon the weight of the vehicle, give the correct PSI for that tire. I had the guy query the system for a '69 Vette and the BFG Radial T/A tire in 255/60/15. I chose the '69 because it's the lightest C3 other than possibly the '68, and therefore it would tolerate the lowest PSI for C3s. I explained that we were having a discussion on the subject and that somebody was recommending PSI of 24/20 and, without knowing if I agreed with that or not, he said "Oh, that sounds low."
The results- their system recommends a minimum cold PSI of 26 for that tire on all 4 corners. Of course, hot PSI goes up by a few- and the weight in their system for C3s would be for the base car. The big blocks and other options would add weight and therefore make additional PSI a reasonable route to take. Additionally, as we all know, C3s gained weight throughout the years.
What say you, toobroke?
The results- their system recommends a minimum cold PSI of 26 for that tire on all 4 corners. Of course, hot PSI goes up by a few- and the weight in their system for C3s would be for the base car. The big blocks and other options would add weight and therefore make additional PSI a reasonable route to take. Additionally, as we all know, C3s gained weight throughout the years.
What say you, toobroke?
Race Director
Joined: Dec 1999
Posts: 11,094
Likes: 990
From: Sierra Foothills CA
I actually called them first and spoke to a nice gal who wanted to help. Unfortunately their system only goes as far back as '83 for car model years.
Burning Brakes
Joined: Feb 2014
Posts: 1,045
Likes: 226
From: Cape Neddick Maine
2020 C3 of the Year Finalist - Modified
Good god!!
can we still say that or do we need to use a more politically correct term??
I always thought the tire manufacturer always out trumped the car manufactures data plate on tire pressure.
At least that's what I was taught even in the service.....Are you telling us even our government is lying??? lol
come-on now we all know that 20 psi is wrong it should be 17.5 psi
can we still say that or do we need to use a more politically correct term??
I always thought the tire manufacturer always out trumped the car manufactures data plate on tire pressure.
At least that's what I was taught even in the service.....Are you telling us even our government is lying??? lol
come-on now we all know that 20 psi is wrong it should be 17.5 psi
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
Good god!!
can we still say that or do we need to use a more politically correct term??
I always thought the tire manufacturer always out trumped the car manufactures data plate on tire pressure.
At least that's what I was taught even in the service.....Are you telling us even our government is lying??? lol
come-on now we all know that 20 psi is wrong it should be 17.5 psi
can we still say that or do we need to use a more politically correct term??
I always thought the tire manufacturer always out trumped the car manufactures data plate on tire pressure.
At least that's what I was taught even in the service.....Are you telling us even our government is lying??? lol
come-on now we all know that 20 psi is wrong it should be 17.5 psi
Burning Brakes
Joined: Feb 2014
Posts: 1,045
Likes: 226
From: Cape Neddick Maine
2020 C3 of the Year Finalist - Modified