Tire Pressure ?

[bouncytruck]

I noticed the tires looked a little low on my Blazer so I checked the pressure. The tires say the PSI should be at 80. That seems awefully high to me. I've never run more than 35 in any of my car/truck tires. They are LT235/85R16 with an E load rating. Are light truck tires usually higher PSI? Should I fill them to 80 even though my Blazer is probably lighter than a lot of trucks these are designed to be run on?

[aesj2]

The pressure is for the max load rating. Your Blazer will bounce all over the place at 80 psi. 32-38 psi would be about it.

[67ChevyC10Stepside]

80 PSI is cause of the load range e for hauling heavy shiste just run whatever you feel like.

[Longhorn Man]

You need to test out different tire pressures to find the right one for your ride.
You want to have even temperature all the way across the tread. You can do this with a durometer, a lazer non contact thermometer, or with the palm of your hand.
I have found in about 90 - 95% of the time, max air pressure listed on the tire is about right.
If the tire is designed to hold 80 PSI, then 30 is less than 1/2 filled. This will create WAY too much heat, and the tire can fall apart...think, tractor trailer throwing a re-cap....or picture the Ford Explorers that rolled when the right rear blew out. (they had moronicly low tire pressure becous soccer moms were complaining of the "truck like ride")
I would say if you want to fill them up and don't want to bother testing the temperatures across the tread of your tire, go with AT LEAST 75% of the max PSI listed on the tire.

[bouncytruck]

Thanks guys. I'm thinking that at max PSI, the tires would be hard as a rock, but on the other hand, I'm concerned about the issues Lonhorn brought up - especially since I take the freeway at 70 mph every day with my baby girl in the back seat. I'll try some different tire pressures, starting around 75% and see how it works. There isn't any noticable wear pattern typical of an under-inflated tire.

[LONGHAIR]

The real thing to look at here is the tire situation. Why an E rated tire on a Blazer??? WAAY too much tire for it. Longhorn Man is right, they should be inflated properly........but they will ride very hard on that truck.
You wouldn't notice the tire stiffness as much on a vehicle equipped for them.
The true cure here is to replace those tires with something more appropriate.

[aesj2]

Don't run whaterever you like or fill to 75% of the max. If you own a newer car or truck go out to it and look inside the drivers door for the tire label. It will give the correct pressures for the size of tire used on the vehicle. Then look at the tire and see that the pressure rating is much higher. Just because you can fill a tire to 80 psi, doesn't mean that it will work at that pressure. More air can mean more heat which will mean more pressure. Be careful.

[67ChevyC10Stepside]

do what you want....we tow a 18000 pound gooseneck trailer and have e range tires for that reason on a big 4wd chevy....we have run next to no air and have hit the 85 max....dont make much difference in ride cause it has 2.5 ton springs on it. get more conventional tires and dont have to worry.

[Longhorn Man]

Originally Posted by aesj2

Don't run whaterever you like or fill to 75% of the max. If you own a newer car or truck go out to it and look inside the drivers door for the tire label. It will give the correct pressures for the size of tire used on the vehicle. Then look at the tire and see that the pressure rating is much higher. Just because you can fill a tire to 80 psi, doesn't mean that it will work at that pressure. More air can mean more heat which will mean more pressure. Be careful.

This is inacurate info, and is a common (misguided) opinion.



Again, we can look as the ford explorer. The tires are rated at 40 to 50 or so max. (I am guessing on that) When ford said run the tires at 24 (!!!!) people died.

Low tire presure creates heat, and the glue holding the tire together can only handle so much heat.

Originally Posted by 67ChevyC10Stepside

do what you want....we tow a 18000 pound gooseneck trailer and have e range tires for that reason on a big 4wd chevy....we have run next to no air and have hit the 85 max....dont make much difference in ride cause it has 2.5 ton springs on it. get more conventional tires and dont have to worry.

Again, bad advice. ESPECIALLY if you are towing/hauling loads. The side wall supports the weight of your vehicle. The pressure inside the tire supports the side wall of the tire. If the air pressure is low, then the sidewalls can not be supported properly. You then get non rigid sidewalls that will let the tire flex and squirm. Zou can frequently feel it in the steering, the vehicle feels loose...or even like a boat. Wandering is another problem, not to mention odd tire wear. Plus there is the whole blow out issue like I mentioned before.

[bouncytruck]

Not sure why it has E rated tires. Definately overkill for the truck. My understanding is that the tires are the stock spec. It has optional (maybe dealer installed) 16" wheels. A PO must have done some hauling with it, because it has a dealer installed step bumper with a hitch, a classIII receiver (valley brand) and trailer brakes.

[687980chevy]

I would change out those tires. Stock rims for a blazer aren't made to handle 80psi.The rubber compound is awfully hard=low traction.Look for tires in load range C. I think you'll be alot happier with the handling & ride.

[bouncytruck]

Ok, I just called Les Scwab to see what they say. Although he agreed the E rating was a bit overkill, he said they should be just fine. He recommended running in the 40 psi range for everyday driving.

He said there is a formula to figure out the proper psi.

Weight of the vehicle/4=X

X/max pounds per tire = Z

Z /max tire presure = % of actual PSI.

I hope I didn't miss a step, but this sounds reasonable.

[aesj2]

The only bad advice is from Longhorn Man. As far as the Ford issue, can you say TIRE DEFECT. AAA estimates 15% of drivers have improper tire inflation and the NHTSA recommends using the vehicle tire label pressures.

[Longhorn Man]

Originally Posted by aesj2

The only bad advice is from Longhorn Man. As far as the Ford issue, can you say TIRE DEFECT. AAA estimates 15% of drivers have improper tire inflation and the NHTSA recommends using the vehicle tire label pressures.

The ford deal was not a tire defect, it was the low tire pressure. If you were to go to australia, you would find the Explorers were doing the exact same thing...however, they had good years on them from the factory. After all the news and everything on the roll overs, Ford sent out letters to Explorer owners telling them to bump up the tire pressure to 35 or so. (exact details have escaped me)

As far as NHTSA goes, I'll believe the tire companies, and indy car pit crews before I'd listen to them.
And yes, I have spoken to reps from BFG, good year and michilin when i did a report in high school.
And also, as far as the indy car pit crews, My boss is the tire guy for one of the teams, I have met Mario Andreti, and some other indy yahoos. We (my boss and I) spent hrs just talkin to the pit guys as they showed us all the stuff they do, torn down motors, trannys in a million pieces, and there shop was spotless too. Totally awsome.
Team andreti spend about 1/2 a million in tire research alone last year.
Untill the desk jockeys at NHTSA can match any of this, I could care less than what they say.


More proof? Look at LUV2XCLR8's post...just shy of 100K on OE tires!
I knew a guy in Tx who had done the same thing. He removed the OE tires off his 82 ram charger at 110K becouse they were dry roted so bad it was scarey. Still had plenty of tread left too.

Originally Posted by 68C30Flatbed

Great thread. My 2 cents: The heat comes from the flexing of the sidewalls. More pressure reduces the flexing and so reduces the heat buildup. More pressure also reduces rolling resistance which improves gas mileage.

Very well put. You put this into words I was unable to find last night. Thank you.

[LONGHAIR]

More pressure reduces the flexing and so reduces the heat buildup. More pressure also reduces rolling resistance which improves gas mileage.

Only up to the point of Max pressure. Over pressurizing a tire is hard on them too. You lose tread contact with the road. You prematurely wear the center tread area.

You don't necessarily need to run a max pressure at all times but I wouldn't go more than 10-15% below that though.

aesj2....When you call someone out like that

The only bad advice is from Longhorn Man.

You had better be 100% correct in your statements...And to be blunt about it You are NOT.

If you own a newer car or truck go out to it and look inside the drivers door for the tire label.

It is well known the the Explorer thing is a Ford (underinflation recommendation) problem, not the tire's fault.

More air can mean more heat which will mean more pressure.

Again, not so.......LOW pressure causes higher temperatures.

I stand by my original statement "Too much tire" the is no need for an E rated tire and I wouldn't run it underinflated to soften the ride. It's a band-aid on a broken arm.

[cableguy0]

aejs to call someone out like that is wrong especially someone who is right the tire problem was fords fault they just happen to have more money than firestone. every tire that blew was underinflated not a tired problem. there are still 10's of thousands of firestone tires on the road that havent had a problem. the sticker in the door dont mean sh!t you need to look at the tire. the rating in the door are for the tires that came on the vehicle from the factory and sometimes they arent accurate

[Longhorn Man]

You know, i didn't even read his responce 100% correctly. I read it as me being wrong about the ford and then a statistic thrown in. (remeber, 85% of statistics thrown out there to prove a point, are made up on the spot)
I did not realize he was saying that everything I said was bad advice.
Thank you longhair and cableguy...2 mechanics who know whats up....unlike the Engineers who always THINK they are right (click on his profile), but in reality, just have problems with over thinking things.
AAA is insurance, they don't test tires.
NHTSA comes up with rediculousely low speeds in off ramps and other stupid 'safety' items...they don't spend any money on testing tires.
Without getting cockey, I have been involved in (personal) tire testing per the advice of three of the biggest (US) tire makers, and a few of the Indy pit crews...again...I'll listen to what has been proven, not just what has been recomended.

[Josh]

Originally Posted by aesj2

The only bad advice is from Longhorn Man. As far as the Ford issue, can you say TIRE DEFECT. AAA estimates 15% of drivers have improper tire inflation and the NHTSA recommends using the vehicle tire label pressures.

Manufacturer specs. are for tire ride, and generally for the OEM tires ONLY. An 80 PSI tire needs to be run at a high pressure to prevent sidewall flexing and heat, and premature wear, it's designed to even out the tread at 70-80 PSI, less will wear the edges prematurely, more will wear the middle prematurely. it also varies base on vehicle weight etc. being that we are driving 30+ yr old trucks originally equipped with bias ply tires, any factory specs are POINTLESS as we run entirely different tire technology now. So why don't you stop your bashing without the proof to back anything up, and quietly leave this thread/board if you have nothing positive to contribute.

[68C30Flatbed]

Great thread. My 2 cents: The heat comes from the flexing of the sidewalls. More pressure reduces the flexing and so reduces the heat buildup. More pressure also reduces rolling resistance which improves gas mileage. I have a 1-ton C30 with duallies. They are rated for 60 p.s.i. I have 42 psi in them now but after reading this thread will boost each to 60.

[LUV2XCLR8]

For what it is worth, here is my experiance with the wife's ride.

99 Trailblazer - Factory tires - Goodyear wrangler a/t's I think

Max pressure was listed at 44 psi, I ran 40, everyone told me
that it was to much, pulled them off at 95,000 miles and still
had a ways to go on the thread indicaters, replaced with set
of Michelan cross terrain suv's, Max pressure is listed 36 psi,
running 30, and I hope they outlast the darn blazer. My $.02

P.S. - at 118,000 miles now & brakes are OE & still look new.

[Robert1970C20rstbukt]

I keep my tires at 40, and the spare is at 50. All the tires are 4 ply tread, except the spare which is a 6 ply so it can handle more air.

[68 Stepside]

I'm with Andy on this one, and most others. When you underinflate a tire drastically, you increase the heat BIG TIME. But then again, I don't get paid 6 figures a year, so I know nothing

At any point, this thread turned into a pissing match of sorts.....sorry to ramble like that.

If it were me, I'd run the tires at or just below the max. inflation specs. My friends dad had an original honda civic (early 70's), and got 89,000 miles out of the tires, and they were still on it when he sold the car....all he did was check the tires at every fillup (he's really anal), and kept them filled to spec. The heavy rated tire is gonna mess your ride up some, but I wouldn't underinflate it to compensate, I think it'd be a really bad idea.

[aesj2]

NOTHING I have stated is made up. Check the web for the info. Firestone still has problems - check the GM tire recall. Again, the deal is for MAX LOAD.
See reply #11 - let's not tell people to go away because they respond.
As for me, I'm a mechanic (ASE and State of MI)for 21 years, engineering test techinican for 12 of those and full time crew for a SCCA race team for 7.
Have a nice day.

[Josh]

Originally Posted by aesj2

NOTHING I have stated is made up. Check the web for the info. Firestone still has problems - check the GM tire recall. Again, the deal is for MAX LOAD.
See reply #11 - let's not tell people to go away because they respond.
As for me, I'm a mechanic (ASE and State of MI)for 21 years, engineering test techinican for 12 of those and full time crew for a SCCA race team for 7.
Have a nice day.

Looking at the information online, backs up my point that you must inflate the tires above the standard specs when goign from a P series tire to a LT tire. There is lots of information out there, such as: http://www.yokohamatire.com/pdf/tsb-070302.pdf. Going with an LT tire of different design, you must up the pressure above the normal 30-35 for a P tire. GM on its 2500HD trucks and a load range E tire suggests 55 front, and 80 rear. My entire point is that load range E tires operate at higher pressures even unloaded. Since you are changing from manufacturers specs, you must use different tire pressures.

[bouncytruck]

Hum, I didn't mean to start a war here guys. I just wanted to know if I should be running 80 PSI or less.



Is everyone saying that the guy at the tire store was incorrect?