Quick tire pressure question. My dealer sets the pressures to 50 psi after I get my oil changed as part of the service. I asked the service guy why they dont set the back tires to 80 psi like the tires state.(I tow alot). They said 50 psi all the way around is best. Am I wrong about setting the backs to 80 psi or are they wrong. The trailer weighs anywhere between 8000-10000 lbs. What do you guys set yours at? Thanks in advance.
I played around with tire pressures like some discussion on this site..when I was not towing. I still went back to the reccomended 80 psi rear and 60 front for all driving.
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Am I wrong about setting the backs to 80 psi or are they wrong.
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You're both wrong. [img]/ubbthreads/images/graemlins/shocked.gif[/img]
Proper air pressure in your tires depends on the amount of load on the tire. Not much load, then not much air pressure. 35 PSI is fine and dandy. When loaded for bear, probably 65 PSI is all you need. You need all 80 PSI only if you are severely overloaded.
Load up for a long trip with the trailer, then go to a truck stop with a CAT scale and fill up with fuel. Then weigh the truck and trailer. You'll get front axle weight, rear axle weight, and trailer axles weight.
Divide the front axle weight by two to get the load on each front tire. Divide the rear axle weight by 2 to get the load on each rear tire. Then apply the following load/inflation table:
Loaded for bear, my front tires had 2,220 pounds on each tire. So if I had those tires, I'd need 45 PSI in the front tires.
My rear tires had 2,590 pounds on each tire. So with those tires I'd need 55 PSI in the rear tires.
My GVW was 9,620, so if I had an F-350 SRW, I'd be just under the GVWR of my tow vehicle.
I don't tow over 70 MPH, but if I did, then I should increase the PSI per the above table by 10 PSI. So then I'd have 55 front and 65 rear. Because the fine print in the load/inflation table says to increase inflation by 10 PSI for sustained high-speed cruising over 70 MPH.
You can find the load/inflation tables for any brand of tire and it will apply to all other brands of tires that are the same size.
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My Sierra Blanca is a '99.5 PSD CrewCab hot-rod Towing Machine! BTS tranny; TurboRamAir intake and 4" stainless turbo-back exhaust; DP-Tuner tunes flashed into an Edge Evolution tuner; ISSPRO EV gauges and TTM; AIC; SP-Diesel exhaust brake and torque converter controller. I special-ordered it new and plan to drive it until it quits.
I've been inflating my tires to 55-front & 80-rear ... as stated on the door post. (Tires are LT265/75R16 ... Pirelli)
So it looks like those numbers are for GAWR. My front axle is rated at 5200 and the rear is rated at 6830. That works out to 55-front & 80-rear on the Goodyear chart.
When towing and fully loaded ... the CAT scale indicates that I have 2430 on each front tire and 2350 on each rear tire. So I should be running 50 PSI on the front and rear tires.
Is this correct, Smokey?
Also, am I doing any harm running the 55-front & 80-rear setup? [img]/ubbthreads/images/graemlins/shrug.gif[/img]
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When towing and fully loaded ... the CAT scale indicates that I have 2430 on each front tire and 2350 on each rear tire. So I should be running 50 PSI on the front and rear tires. (Tires are LT265/75R16 - same as those in the chart above.)
Is this correct, Smokey?
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Yes. As long as you don't cruise at over 70 MPH when towing. But when crossing New Mexico on I-10 and cruising at 79 MPH to keep from getting run over by the 18-wheelers, then pump them up an additional 10 PSI.
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Also, am I doing any harm running the 55-front & 80-rear setup? [img]/ubbthreads/images/graemlins/shrug.gif[/img]
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Anything up to 10 PSI more than the chart shows is probably okay. So 55 front should be fine and dandy.
80 rear is probably wearing out the center of the tire tread faster than the outside edges of the tire tread. Use a tire-tread-depth gauge to keep a check on it.
Plus over-inflation results in a harsher ride. Air them down to 55 or 60 and you'll probably get a better ride, as well as have more than enough air pressure to support the load.
You're right. The tire pressure on the Federal certification sticker is for when the axle is loaded to the GAWR. Not real world - especially on a SuperDuty SRW with it's limited GVWR but a bunch of rear GAWR.
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My Sierra Blanca is a '99.5 PSD CrewCab hot-rod Towing Machine! BTS tranny; TurboRamAir intake and 4" stainless turbo-back exhaust; DP-Tuner tunes flashed into an Edge Evolution tuner; ISSPRO EV gauges and TTM; AIC; SP-Diesel exhaust brake and torque converter controller. I special-ordered it new and plan to drive it until it quits.
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Where can I obtain a chart for the Pirellis that are on the 05?
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I've looked, but haven't found one exactly like you're looking for. That tire size is too new for the Tire&Rim Association to have published the new tables that include that size, plus give the tire companies enough time to include those new tire sizes in their tables. Give it another year or so.
However, there is a workaround. Look at the sidewall of your tires and determine the max weight capacity at 80 PSI. Then find any load/inflation table with a tire that has about that weight capacity (or a bit lower) at 80 PSI. Use that table, because the one with your tire's name and size on it will be close to that table.
For example, Pirelli LT265/70R17E tires on an F-250 are rated 3,195 pounds @ 80 PSI.
The closest to that on the Goodyear load/inflation table is 3,042 pounds @ 80 PSI. Close enough for Government work!
So at 60 PSI, the LT235/85R16 could haul 2485. Your LT265/70R17E can haul a bit more than 2485, but the exact amount of the small difference is not worth worrying about. So use this table until one for your tire size is available.
Hi guys, here's something that I just don't 'comprende'(Old Timers?), why is the max load for tires on a dually LESS than for SRW? Also, when I weigh the rear axle I should divide the weight by 4 and could run the air pressure much lower than SWRs? Correct or not? [img]/ubbthreads/images/graemlins/shrug.gif[/img] [img]/ubbthreads/images/graemlins/crazy.gif[/img]Baja
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Hi guys, here's something that I just don't 'comprende'(Old Timers?), why is the max load for tires on a dually LESS than for SRW? Also, when I weigh the rear axle I should divide the weight by 4 and could run the air pressure much lower than SWRs? Correct or not? [img]/ubbthreads/images/graemlins/shrug.gif[/img] [img]/ubbthreads/images/graemlins/crazy.gif[/img]Baja
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Tires are rated lower in dual applications because from time to time you will have a flat or an underinflated tire and one will have to carry the load by itself. The tire has the same ultimate rating, they just use a larger safety factor when installed as a single.
I've never owned a dually, but I think you're right about the inflation pressure. You can run much less than a single wheel application. Just be sure there's enough pressure that the sidewalls don't hit (I almost said rub) each other when you are driving. Little bumps and such along the way do tend to bounce tires and increase sidewall bulge.
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'00 F250 CC SWB 4x2 XLT V-10 Auto 3.73LS Silver/Graphite
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Hi guys, here's something that I just don't 'comprende'(Old Timers?), why is the max load for tires on a dually LESS than for SRW? Also, when I weigh the rear axle I should divide the weight by 4 and could run the air pressure much lower than SWRs? Correct or not? [img]/ubbthreads/images/graemlins/shrug.gif[/img] [img]/ubbthreads/images/graemlins/crazy.gif[/img]Baja
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Tires are rated lower in dual applications <font color="red">because from time to time you will have a flat or an underinflated tire and one will have to carry the load by itself.</font> The tire has the same ultimate rating, they just use a larger safety factor when installed as a single.
I've never owned a dually, but I think you're right about the inflation pressure. You can run much less than a single wheel application. Just be sure there's enough pressure that the sidewalls don't hit (I almost said rub) each other when you are driving. Little bumps and such along the way do tend to bounce tires and increase sidewall bulge.
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I'm sorry, but that just doesn't compute for me. If one got a flat and the other had to 'carry the load', wouldn't it need MORE AIR pressure? Maybe I'm just 'dense'? Oh, and I do know about not letting the duals RUB (nanner [img]/ubbthreads/images/graemlins/grin.gif[/img]). You should hear it when a rock comes out from between them as you're pulling onto the hiway(HOLY AUTOLITE, BATMAN!!!!). [img]/ubbthreads/images/graemlins/crazy.gif[/img] BajaGringo
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Hi guys, here's something that I just don't 'comprende'(Old Timers?), why is the max load for tires on a dually LESS than for SRW? Also, when I weigh the rear axle I should divide the weight by 4 and could run the air pressure much lower than SWRs? Correct or not? [img]/ubbthreads/images/graemlins/shrug.gif[/img] [img]/ubbthreads/images/graemlins/crazy.gif[/img]Baja
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Tires are rated lower in dual applications <font color="red">because from time to time you will have a flat or an underinflated tire and one will have to carry the load by itself.</font> The tire has the same ultimate rating, they just use a larger safety factor when installed as a single.
I've never owned a dually, but I think you're right about the inflation pressure. You can run much less than a single wheel application. Just be sure there's enough pressure that the sidewalls don't hit (I almost said rub) each other when you are driving. Little bumps and such along the way do tend to bounce tires and increase sidewall bulge.
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I'm sorry, but that just doesn't compute for me. If one got a flat and the other had to 'carry the load', wouldn't it need MORE AIR pressure? Maybe I'm just 'dense'? Oh, and I do know about not letting the duals RUB (nanner [img]/ubbthreads/images/graemlins/grin.gif[/img]). You should hear it when a rock comes out from between them as you're pulling onto the hiway(HOLY AUTOLITE, BATMAN!!!!). [img]/ubbthreads/images/graemlins/crazy.gif[/img] BajaGringo
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Ok, I think [img]/ubbthreads/images/graemlins/eek.gif[/img] I got it now. The lower "Rating" of a tire used on a DRW is not a 'upper limit', but a recommendation as to how much weight should be loaded on IN CASE it needs to 'carry all the load'. This is probably done because people think "more tires=more load". Moral = don't put a 3000lb camper on a dually and use tires rated less than 3200lb @ 80psi and then air them to 60psi? [img]/ubbthreads/images/graemlins/shrug.gif[/img] [img]/ubbthreads/images/graemlins/crazy.gif[/img]Baja
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why is the max load for tires on a dually LESS than for SRW?
[/ QUOTE ] Roads are not perfectly flat. With crowns and other leaning pavment conditions on some roads, one tire can often be carrying more than half of the load. So by initially giving it a lower load rating when used in that application there is a greater margin of error for those times when one tire will be subjected to WAY more than it's share the load. [ QUOTE ]
Also, when I weigh the rear axle I should divide the weight by 4 and could run the air pressure much lower than SWRs? Correct or not? Baja
[/ QUOTE ] Basicly correct, use the "D" (dual) rating rather than the "S" (single) rating in the tables. Many will find they are "off the chart" with duals. Some people won't go below 35 while others will while monitoring temps and contact issues.
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