27psi or 30psi ???
Racer
Joined: Dec 2003
Posts: 368
Likes: 0
From: Atlanta Georgia
St. Jude Donor '03-'04-'05
Originally Posted by Evil-Twin
30 psi is not correct.
although it is acceptable..
People spend thousands on tuning their car, yet they let the one thing that connects HP to the road ( the tires ) to a sticker that was designed to protect against product liability, not performance , gas mileage or tire longevity. Early on there were issues about customers putting 44 psi as stated on the sidewall and having liability issues. Thus the very generic 30 psi sticker on the door.
1 or two psi can add or subtract hundreds of tire miles, 1 to 3 miles per gallon. This is so important that road surface temps are monitored BY every racing institution on the planet. I can't believe all these people have no clue about setting tires in the winter at 30 and setting them in the summer at 30, and no one seems to think that there is no benefit by tuning the tires for your driving conditions..
30 cold could easily equate to 34/36 psi, which is way too high, causes a center high condition, less contact patch, poor traction, loss of performance and gas milage. THat sticker goes on every car made, whether its in a -25 degree winter Minisota or a 115 degree day in Texas where black top roads can reach 160F, and tires swell to 36/38 psi..
If you think these tires perform the same at 27 as they do a 37 psi, then your just throwing your money away modding your car.
43000 miles on my tires and 33 mpg speaks for itself.
although it is acceptable..
People spend thousands on tuning their car, yet they let the one thing that connects HP to the road ( the tires ) to a sticker that was designed to protect against product liability, not performance , gas mileage or tire longevity. Early on there were issues about customers putting 44 psi as stated on the sidewall and having liability issues. Thus the very generic 30 psi sticker on the door.
1 or two psi can add or subtract hundreds of tire miles, 1 to 3 miles per gallon. This is so important that road surface temps are monitored BY every racing institution on the planet. I can't believe all these people have no clue about setting tires in the winter at 30 and setting them in the summer at 30, and no one seems to think that there is no benefit by tuning the tires for your driving conditions..
30 cold could easily equate to 34/36 psi, which is way too high, causes a center high condition, less contact patch, poor traction, loss of performance and gas milage. THat sticker goes on every car made, whether its in a -25 degree winter Minisota or a 115 degree day in Texas where black top roads can reach 160F, and tires swell to 36/38 psi..
If you think these tires perform the same at 27 as they do a 37 psi, then your just throwing your money away modding your car.
43000 miles on my tires and 33 mpg speaks for itself.
Racer
Joined: Dec 2003
Posts: 368
Likes: 0
From: Atlanta Georgia
St. Jude Donor '03-'04-'05
Originally Posted by C5 Curmudgeon
Care to elaborate? 
I find 33 MPG very hard to believe, unless it was at 55 MPH and without AC and for a very short trip....
With a fresh tune and new plugs/wires...the best I have seen on my '99 is around 27.5......
Just don't believe a consistant 33 MPG is possible....
Safety Car
Joined: Jan 2005
Posts: 4,799
Likes: 0
From: Lake Ridge VA
Originally Posted by 99quicksilver
Just don't believe a consistant 33 MPG is possible....
hereI know EvilTwin knows a sh%tload about the C5, as well as automobiles in general.
However, if you drive anywhere near the way I drive (1/2-3/4 WOT numerous times an outing) there is no way you are averaging 33 MPG. Mix of 3/4 highway, 1/4 city maybe, but not with a majority of stop-and-go and rushhour traffic like there is here in the DC/Metro area.
EvilTwin, you said specifically, in your post, that incorrect tire pressure could amount to 1-3 MPG difference. This is believable and I also stand by that statement. However, that means you would still be averaging 30 MPG if your tire pressure was incorrect.
On a 250 mile trip up and down I81 (65 mph speed limit for the most part) I have averaged 33 MPG, but that was over the entire distance; cruising in 6th at 65-75. Right now on my C5 for the past 3/4 of my gas tank I have averaged ~20 MPG.
So if ET is indeed averaging 33 MPG, it has nothing to do with the tire pressure...it's his driving style (as well as where/when he drives).
Last edited by AdamC5; Jun 21, 2005 at 03:36 PM.
Race Director
Joined: Jun 2004
Posts: 18,322
Likes: 0
From: ̿’ ̿’\̵͇̿̿\з=(•̪●)=ε/̵͇̿̿/’&
Cruise-In X Veteran
St. Jude Donor '09-'10
Originally Posted by 99quicksilver
Absolutely.....
I find 33 MPG very hard to believe, unless it was at 55 MPH and without AC and for a very short trip....
With a fresh tune and new plugs/wires...the best I have seen on my '99 is around 27.5......
Just don't believe a consistant 33 MPG is possible....
I find 33 MPG very hard to believe, unless it was at 55 MPH and without AC and for a very short trip....
With a fresh tune and new plugs/wires...the best I have seen on my '99 is around 27.5......
Just don't believe a consistant 33 MPG is possible....
I have to agree w/ 99quicksilver. 33 MPG by merely changing tire pressure, I don't think so. Just my .02.................later
☠☣☢ Semper Ebrius ☢☣☠
Joined: Jun 2001
Posts: 83,301
Likes: 4
From: Virginia
Cruise-In IV-V-VI-VII Veteran
St. Jude's Donor '06
Originally Posted by AdamC5
The recommendations for PSI by the tire companies are usually what is referred to as cold. That means if they recommend 30 PSI, that's what your tires should read when they are stone cold (what they read first thing in the morning, not having been driven on, etc). The companies don't expect you to do the math and compensate for driving.
The factory recommendation is 30 PSI cold, which means just that; not 27.
However, it's all personal choice...some people like to run their tires a bit lower or higher.
The factory recommendation is 30 PSI cold, which means just that; not 27.
However, it's all personal choice...some people like to run their tires a bit lower or higher.
Race Director
Joined: Jun 2004
Posts: 18,322
Likes: 0
From: ̿’ ̿’\̵͇̿̿\з=(•̪●)=ε/̵͇̿̿/’&
Cruise-In X Veteran
St. Jude Donor '09-'10
If you want to get reallly technical,you also have to consider the moisture content in the air. That's one reason people use nitrogen.
I still say 30# cold pressure w/ nitrogen, but what do I know about moisture content and the relation to pressure.
...........later
I still say 30# cold pressure w/ nitrogen, but what do I know about moisture content and the relation to pressure.
...........later
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Drifting
Joined: Nov 2001
Posts: 1,684
Likes: 0
From: Jacksonville Florida
- the tire pressure guidelines aside (30 cold and 35 hot is about right IMHO, deviation using MPG as a measure of roll resistance assumes a level nof science that does not exist without equipment not available to the normal human being. That said I agree 100% that paying attention to tire pressure, on the tack and off, can pay huge dividents in tire wear and performance.), I too have a hard time believing 33 MPG average - but it didn't look to my like he said under what conditions. I have done a number of caravans with a large number of fellow C5 owners, and on the open road running 70-75 MPH in 6th gear with cruise on, flat roads and a light tailwind a number of us got 30 MPG, a few got 31. And yes, I am careful about tire pressures - as most who track their car would be ... 33 MPG attributed to tire pressure? Not likely, driver, road and weather conditions ... downhill .. maybe. BTW drag races put 50+ PSI in their front tires to REDUCE roll resistance, which in theory would mean that higher pressure would increase MPG, not decrease, but that is a whole different thread 
Les
Originally Posted by 99quicksilver
Absolutely.....
I find 33 MPG very hard to believe, unless it was at 55 MPH and without AC and for a very short trip....
With a fresh tune and new plugs/wires...the best I have seen on my '99 is around 27.5......
Just don't believe a consistant 33 MPG is possible....
I find 33 MPG very hard to believe, unless it was at 55 MPH and without AC and for a very short trip....
With a fresh tune and new plugs/wires...the best I have seen on my '99 is around 27.5......
Just don't believe a consistant 33 MPG is possible....
Melting Slicks
Joined: Dec 2004
Posts: 3,049
Likes: 0
From: The second childhood is the best one of all.
Originally Posted by Evil-Twin
30 psi is not correct.
although it is acceptable..
People spend thousands on tuning their car, yet they let the one thing that connects HP to the road ( the tires ) to a sticker that was designed to protect against product liability, not performance , gas mileage or tire longevity. Early on there were issues about customers putting 44 psi as stated on the sidewall and having liability issues. Thus the very generic 30 psi sticker on the door.
1 or two psi can add or subtract hundreds of tire miles, 1 to 3 miles per gallon. This is so important that road surface temps are monitored BY every racing institution on the planet. I can't believe all these people have no clue about setting tires in the winter at 30 and setting them in the summer at 30, and no one seems to think that there is no benefit by tuning the tires for your driving conditions..
30 cold could easily equate to 34/36 psi, which is way too high, causes a center high condition, less contact patch, poor traction, loss of performance and gas milage. THat sticker goes on every car made, whether its in a -25 degree winter Minisota or a 115 degree day in Texas where black top roads can reach 160F, and tires swell to 36/38 psi..
If you think these tires perform the same at 27 as they do a 37 psi, then your just throwing your money away modding your car.
43000 miles on my tires and 33 mpg speaks for itself.
although it is acceptable..
People spend thousands on tuning their car, yet they let the one thing that connects HP to the road ( the tires ) to a sticker that was designed to protect against product liability, not performance , gas mileage or tire longevity. Early on there were issues about customers putting 44 psi as stated on the sidewall and having liability issues. Thus the very generic 30 psi sticker on the door.
1 or two psi can add or subtract hundreds of tire miles, 1 to 3 miles per gallon. This is so important that road surface temps are monitored BY every racing institution on the planet. I can't believe all these people have no clue about setting tires in the winter at 30 and setting them in the summer at 30, and no one seems to think that there is no benefit by tuning the tires for your driving conditions..
30 cold could easily equate to 34/36 psi, which is way too high, causes a center high condition, less contact patch, poor traction, loss of performance and gas milage. THat sticker goes on every car made, whether its in a -25 degree winter Minisota or a 115 degree day in Texas where black top roads can reach 160F, and tires swell to 36/38 psi..
If you think these tires perform the same at 27 as they do a 37 psi, then your just throwing your money away modding your car.
43000 miles on my tires and 33 mpg speaks for itself.
Team Owner
Joined: Mar 2001
Posts: 21,325
Likes: 3,841
From: small town in S.E Pa. PA
St. Jude Donor '03-'04
I never said I get an average of 33 mpg... I drive to Atlantic city every week it's 130 miles round trip... The AC expressway is very flat, it is a great place to get optimum mileage data. I get 33 mpg every week on this trip.. I have #28 pound injectors
Wait !!!! what an I doing here... , I don't have to explain a thing... OH yeah It's all bullsh|t.....This is the reason I don't post much here anymore... my 18 years with GM and My 35 years of automotive engineering means nothing. Use the Generic label.... It no skin off my nose.. I don't know what I am doing on this forum.
after spending three years prototyping this Car, and being a member of the original C5 prototype team, and following this car through launch in 97 and two years of field debugging, I retired.I came to this forum to help hundreds of people on this form and find it less and less attractive every day.
.
Wait !!!! what an I doing here... , I don't have to explain a thing... OH yeah It's all bullsh|t.....This is the reason I don't post much here anymore... my 18 years with GM and My 35 years of automotive engineering means nothing. Use the Generic label.... It no skin off my nose.. I don't know what I am doing on this forum.
after spending three years prototyping this Car, and being a member of the original C5 prototype team, and following this car through launch in 97 and two years of field debugging, I retired.I came to this forum to help hundreds of people on this form and find it less and less attractive every day.
.
Safety Car
Joined: Jan 2005
Posts: 4,799
Likes: 0
From: Lake Ridge VA
Originally Posted by Evil-Twin
43000 miles on my tires and 33 mpg speaks for itself.
Originally Posted by Evil-Twin
I never said I get an average of 33 mpg... I drive to Atlantic city every week it's 130 miles round trip... The AC expressway is very flat, it is a great place to get optimum mileage data. I get 33 mpg every week on this trip..
Regarding the information you posted:
No on here is saying that you don't know what you're talking about. We all know tire pressure changes can have noticeable effects. We also know that each circumstance (location, outside temperatutes, auto-xing, etc) would benefit from custom application for tire pressure.
However, you need to realize that 99% of the people that ask this question are just looking for the generic answer. I can tell you, I don't custom tailor my tire pressure for each trip (even long ones). Why? Because it doesn't matter to me that much. I don't care if I lose a MPG or two or my tires will wear out a little faster. I'm not so broke that I can't buy new ones. And I'm afraid that is the case for 99% of the people here.
So yes, you are correct in saying that each situation demands a custom PSI amount. But for us, just average drivers, 30 PSI gets the job done.
Racer
Joined: Dec 2003
Posts: 368
Likes: 0
From: Atlanta Georgia
St. Jude Donor '03-'04-'05
Originally Posted by AdamC5
I understand your frustration, but from what you wrote it does indeed look like you are claiming that over the 43k miles on your tires you have averaged 33 MPG.
Regarding the information you posted:
No on here is saying that you don't know what you're talking about. We all know tire pressure changes can have noticeable effects. We also know that each circumstance (location, outside temperatutes, auto-xing, etc) would benefit from custom application for tire pressure.
However, you need to realize that 99% of the people that ask this question are just looking for the generic answer. I can tell you, I don't custom tailor my tire pressure for each trip (even long ones). Why? Because it doesn't matter to me that much. I don't care if I lose a MPG or two or my tires will wear out a little faster. I'm not so broke that I can't buy new ones. And I'm afraid that is the case for 99% of the people here.
So yes, you are correct in saying that each situation demands a custom PSI amount. But for us, just average drivers, 30 PSI gets the job done.
Regarding the information you posted:
No on here is saying that you don't know what you're talking about. We all know tire pressure changes can have noticeable effects. We also know that each circumstance (location, outside temperatutes, auto-xing, etc) would benefit from custom application for tire pressure.
However, you need to realize that 99% of the people that ask this question are just looking for the generic answer. I can tell you, I don't custom tailor my tire pressure for each trip (even long ones). Why? Because it doesn't matter to me that much. I don't care if I lose a MPG or two or my tires will wear out a little faster. I'm not so broke that I can't buy new ones. And I'm afraid that is the case for 99% of the people here.
So yes, you are correct in saying that each situation demands a custom PSI amount. But for us, just average drivers, 30 PSI gets the job done.
Racer
Joined: Dec 2003
Posts: 368
Likes: 0
From: Atlanta Georgia
St. Jude Donor '03-'04-'05
Originally Posted by Evil-Twin
I never said I get an average of 33 mpg... I drive to Atlantic city every week it's 130 miles round trip... The AC expressway is very flat, it is a great place to get optimum mileage data. I get 33 mpg every week on this trip.. I have #28 pound injectors
Wait !!!! what an I doing here... , I don't have to explain a thing... OH yeah It's all bullsh|t.....This is the reason I don't post much here anymore... my 18 years with GM and My 35 years of automotive engineering means nothing. Use the Generic label.... It no skin off my nose.. I don't know what I am doing on this forum.
after spending three years prototyping this Car, and being a member of the original C5 prototype team, and following this car through launch in 97 and two years of field debugging, I retired.I came to this forum to help hundreds of people on this form and find it less and less attractive every day.
.
Wait !!!! what an I doing here... , I don't have to explain a thing... OH yeah It's all bullsh|t.....This is the reason I don't post much here anymore... my 18 years with GM and My 35 years of automotive engineering means nothing. Use the Generic label.... It no skin off my nose.. I don't know what I am doing on this forum.
after spending three years prototyping this Car, and being a member of the original C5 prototype team, and following this car through launch in 97 and two years of field debugging, I retired.I came to this forum to help hundreds of people on this form and find it less and less attractive every day.
.
Cruising
Joined: Jun 2005
Posts: 12
Likes: 0
From: Aurora CO
I know it is beating the dead dog, but has anyone thought of using a temp reader to check tire temp readings across the cross section of the tire? This way, you know where the hot and cold spots are and can adjust pressure to get the most even read possible. This only should be done after tires are warmed up after normal driving. The factory has probably done this during testing and came up with the 30lbs cold pressure. Just a thought as this is the way the racers do it.
Racer
Joined: Dec 2003
Posts: 368
Likes: 0
From: Atlanta Georgia
St. Jude Donor '03-'04-'05
Originally Posted by coskierken
I know it is beating the dead dog, but has anyone thought of using a temp reader to check tire temp readings across the cross section of the tire? This way, you know where the hot and cold spots are and can adjust pressure to get the most even read possible. This only should be done after tires are warmed up after normal driving. The factory has probably done this during testing and came up with the 30lbs cold pressure. Just a thought as this is the way the racers do it.
