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03-13-2014, 10:27 AM
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#1
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Senior Member
Join Date: May 2012
Posts: 163
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SMB Tire Pressure ???
I've read some of the other posts for tire pressure, in fact, I'm using someone's answer for my equation, but his weight was even front back.
Quadvan door sticker for my tires LT285/70R17 126S E/10 is:
Front 60psi Rear 80psi
Front:
2070/3070@60psi = 0.674267 x 60psi = 40.45 psi
(2070/tire scale weight, 3070 based on table and Quadvan 60psi front sticker)
but if I just go with the 80psi
2070/3750@80psi = 0.552 x 80psi = 44.16 psi
Rear:
2915/3750@80psi = .7773333 x 80psi = 62.19 psi
(2915/tire scale weight, 3750 based on table and Quadvan 80psi front sticker)
So.. I’m thinking on running Front=50psi, Rear=70psi (10psi under what the door max sticker is). But if the Front wheel equation should be the 44.16 psi I would do Front=55psi and Rear=70psi. Recommendations are welcome.
I’m just a little bummed that I’m not suppose to exceed 112 mph. I’ll have to slow down. (for the record the max I like is 67 on 65 speed limit)
Toyo’s Table
LT285/70R17 126S E/10 33X11.5R17
PSI Single Tire load limit
35 2105
40 2315
45 2510
50 2755 (C)
55 2890
60 3070
65 3195 (D)
70 3415
75 3525
80 3750 (E)
When an R or S appears in the service description, maximum speed capability is as follows: R=106 mph and S=112 mph.
__________________
Steven McKenzie
Madison, WI
2013 E350 EB-44, V10 6.8ltr
Toyo LT285/70 R17
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03-13-2014, 10:57 PM
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#2
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Senior Member
Join Date: Jun 2010
Location: San Diego
Posts: 887
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Re: SMB Tire Pressure ???
Seems resonable for your specs. I use a similar chart for my BFGs and the van rides much better at the recommend pressures based on weight.
This last Baja trip I used the digital thermometer on the tires a lot while at different pressures. In some case we did 20-30 miles on pavement with dirt pressures but kept the speeds down. Never exceeded 113F on the pavement. Had similar temps at 20 mph in the dirt.
Also interesting to note the 10F difference between the front and back tires based on pressure and weight.
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03-13-2014, 11:38 PM
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#3
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Senior Member
Join Date: Jan 2009
Location: Corvallis, OR
Posts: 5,300
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Re: SMB Tire Pressure ???
50/70 sounds very reasonable to me.
I run 50 front 45 rear since I have twice as many rear tires.
__________________
2000 E450 dually V10 wagon
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03-14-2014, 12:03 PM
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#4
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Senior Member
Join Date: May 2007
Location: East Bay CA
Posts: 1,078
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Re: SMB Tire Pressure ???
You'd wanna go with the max pressure of the tire, not necessarily what's on the door. If that's 80 in front, then the 44 figure is it.
I think you're a tad high, unless you plan on adding more weight, but it is easier to dump some air than add it. So see how it feels. You need a NASCAR crew to do those ½ lb adjustments to get not only the best performance but the best ride.
Rob
__________________
2001 Ford E250 Sportsmobile with Salem-Kroger 4x4 conversion
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03-16-2014, 08:28 PM
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#5
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Senior Member
Join Date: May 2011
Posts: 1,005
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Re: SMB Tire Pressure ???
You can't multiple pressures out. Use the Load tables. You also don't want to use the max cold pressure on the tire.
__________________
Sportsmobile-less.
"A job worth doing is worth doing at least twice."
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03-18-2014, 05:23 AM
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#6
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Senior Member
Join Date: May 2012
Posts: 163
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Re: SMB Tire Pressure ???
Quote:
You can't multiple pressures out. Use the Load tables. You also don't want to use the max cold pressure on the tire.
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You lost me Anzac, multiple pressures out?
--------------------------------------------------------------
So it seems I should be looking at it like this:
Front:
2070/3750@80psi = 0.552 x 80psi = 44.16 psi ~ 45
(2070/tire scale weight, 3070 based on table and Quadvan 60psi front sticker)
Rear:
2915/3750@80psi = .7773333 x 80psi = 62.19 psi ~ 63
(2915/tire scale weight, 3750 based on table and Quadvan 80psi front sticker)
Front 45, Rear 63, and then add some extra psi for safety?
__________________
Steven McKenzie
Madison, WI
2013 E350 EB-44, V10 6.8ltr
Toyo LT285/70 R17
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03-18-2014, 09:42 AM
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#7
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Senior Member
Join Date: May 2011
Posts: 1,005
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Re: SMB Tire Pressure ???
You cannot scale tire pressures that way using percentages of weight or multiplying. You need to use the tire sizes, and the load tables.
__________________
Sportsmobile-less.
"A job worth doing is worth doing at least twice."
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03-18-2014, 10:18 AM
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#8
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Site Team
Join Date: May 2007
Location: Turlock Ca
Posts: 10,409
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Re: SMB Tire Pressure ???
Have you seen this thread?
Covers a bit:
viewtopic.php?f=39&t=11143
__________________
2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer
Sportsmobile 4X4 Adventures.......... On and off road adventures
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03-18-2014, 10:36 AM
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#9
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Senior Member
Join Date: Apr 2007
Location: Seattle, WA
Posts: 1,061
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Re: SMB Tire Pressure ???
Here's a load table I just compiled for 16" and 17" LT tires -- to help with my current new tire decision. My data was taken from the Tire and Rim Association Load Tables, and merged with some extra data from the Toyo Load Tables. This extra data includes the new "E" load-rated option for the LT285/75R16 size. These two tables otherwise match for 99% of the data. I also found the Firestone and Goodyear tables to be apparently identical (though I didn't import them into Excel and compare like I did with Toyo). So, it seems that the following table can be used for any brand of LT tires. The "%" column I have below compares the given tire overall diameter with that of my current tires -- LT285/75R16.
Code:
Tire | W A R | diam(") % | 35 LR| 40 45 50 LR| 55 60 65 LR| 70 75 80 LR| 95 LR
---------------------------------------------------------------------------------------------------------------------------
LT215/70R16 | 215 70 16 | 27.9 -15% | 1340 | 1475 1600 1765 C | | |
LT225/70R16 | 225 70 16 | 28.4 -13% | 1435 | 1575 1710 1875 C | | |
LT235/70R16 | 235 70 16 | 29.0 -12% | 1525 | 1675 1820 1985 C | 2095 2230 2335 D | |
LT225/75R16 | 225 75 16 | 29.3 -11% | 1500 | 1650 1790 1940 C | 2060 2190 2335 D | 2440 2560 2680 E | 3000 F
LT285/60R16 | 285 60 16 | 29.5 -10% | 1750 | 1920 2085 2270 C | | |
LT245/70R16 | 245 70 16 | 29.5 -10% | 1620 | 1780 1935 2095 C | 2225 2365 2535 D | |
LT315/55R16 | 315 55 16 | 29.6 -10% | 1875 | 2020 2195 2405 D | | |
LT255/70R16 | 255 70 16 | 30.1 -8% | 1720 | 1890 2050 2205 C | 2360 2510 2680 D | |
LT215/85R16 | 215 85 16 | 30.4 -7% | 1495 | 1640 1785 1940 C | 2050 2180 2335 D | 2430 2550 2680 E | 3000 F
LT245/75R16 | 245 75 16 | 30.5 -7% | 1700 | 1865 2030 2205 C | 2335 2480 2623 D | 2765 2900 3042 E | 3415 F
LT265/70R16 | 265 70 16 | 30.6 -7% | 1820 | 2000 2170 2335 C | 2500 2655 2835 D | |
LT345/55R16 | 345 55 16 | 30.9 -6% | 2150 | 2325 2525 2755 D | | |
LT275/70R16 | 275 70 16 | 31.2 -5% | 1925 | 2110 2295 2470 C | 2640 2805 3000 D | |
LT265/75R16 | 265 75 16 | 31.6 -4% | 1910 | 2100 2280 2470 C | 2625 2790 3000 D | 3105 3260 3415 E |
LT235/85R16 | 235 85 16 | 31.7 -3% | 1700 | 1870 2030 2205 C | 2335 2485 2623 D | 2765 2905 3042 E | 3415 F
LT375/55R16 | 375 55 16 | 32.2 -2% | 2470 | 2630 2855 3085 D | 3285 3490 3750 E | |
LT305/70R16 | 305 70 16 | 32.8 0% | 2270 | 2465 2680 2910 D | 3085 3275 3525 E | 3670 3830 3970 F |
LT285/75R16 | 285 75 16 | 32.8 0% | 2130 | 2340 2540 2755 C | 2925 3110 3305 D | 3465 3635 3750 E |
LT255/85R16 | 255 85 16 | 33.1 1% | 1920 | 2110 2290 2470 C | 2635 2800 3000 D | 3120 3275 3415 E |
LT315/70R16 | 315 70 16 | 33.4 2% | 2405 | 2590 2815 3085 D | | |
LT295/75R16 | 295 75 16 | 33.4 2% | 2240 | 2460 2670 2910 C | 3070 3260 3415 D | |
LT315/75R16 | 315 75 16 | 34.6 5% | 2535 C | 2715 2950 3195 D | | |
LT375/65R16 | 375 65 16 | 35.2 7% | 2910 | 3165 3435 3750 D | | |
LT355/70R16 | 355 70 16 | 35.6 8% | 2910 | 3115 3380 3640 D | | |
LT365/70R16 | 365 70 16 | 36.1 10% | 3000 | 3250 3530 3860 D | | |
LT325/80R16 | 325 80 16 | 36.5 11% | 2755 | 2970 3225 3525 D | | |
LT395/70R16 | 395 70 16 | 37.8 15% | 3415 C | | | |
---------------------------------------------------------------------------------------------------------------------------
LT235/60R17 | 235 60 17 | 28.1 -14% | 1375 | 1510 1640 1765 C | 1890 2005 2150 D | 2235 2345 2470 E |
LT245/65R17 | 245 65 17 | 29.5 -10% | 1575 | 1730 1875 2040 C | | |
LT285/60R17 | 285 60 17 | 30.5 -7% | 1820 | 1995 2170 2335 C | | |
LT245/70R17 | 245 70 17 | 30.5 -7% | 1690 | 1855 2010 2205 C | 2315 2460 2600 D | 2740 2875 3000 E |
LT245/75R17 | 245 75 17 | 31.5 -4% | 1770 | 1945 2110 2270 C | 2430 2595 2755 D | 2900 3050 3195 E |
LT265/70R17 | 265 70 17 | 31.6 -4% | 1890 | 2075 2255 2470 C | 2595 2760 2910 D | 3005 3100 3195 E |
LT265/70R17 | 265 70 17 | 31.6 -4% | 1890 | 2075 2255 2470 C | 2595 2760 2910 D | 3005 3100 3195 E |
LT235/80R17 | 235 80 17 | 31.8 -3% | 1725 | 1895 2055 2270 C | 2405 2545 2680 D | 2815 2950 3085 E |
LT345/55R17 | 345 55 17 | 31.9 -3% | 2270 | 2410 2620 2835 D | | |
LT255/75R17 | 255 75 17 | 32.1 -2% | 1870 | 2055 2230 2405 C | | |
LT275/70R17 | 275 70 17 | 32.2 -2% | 2000 | 2195 2380 2600 C | 2760 2925 3085 D | 3120 3160 3195 E |
LT305/65R17 | 305 65 17 | 32.6 -1% | 2205 | 2385 2590 2835 D | 2955 3075 3195 E | |
LT285/70R17 | 285 70 17 | 32.7 0% | 2105 | 2315 2510 2755 C | 2890 3070 3195 D | |
LT305/70R17 | 305 70 17 | 33.8 3% | 2405 | 2605 2780 3000 D | | |
LT285/75R17 | 285 75 17 | 33.8 3% | 2210 | 2430 2640 2835 C | 2955 3075 3195 D | |
LT315/70R17 | 315 70 17 | 34.4 5% | 2535 | 2685 2915 3195 D | | |
LT315/70R17 | 315 70 17 | 34.4 5% | 2535 | 2685 2915 3195 D | | |
LT355/70R17 | 355 70 17 | 36.6 11% | 3000 | 3065 3130 3195 D | | |
So, using the table above, I see that for a 2800 lb loaded tire, I should be using at least the following PSI for the given tire size. The pressure values below are the absolute minimums, so realistically I'd be adding some margin of error: - LT285/75R16: 51 PSI[/*:m:2v6nfm5y]
- LT295/75R16: 48 PSI[/*:m:2v6nfm5y]
- LT305/70R16: 48 PSI[/*:m:2v6nfm5y]
- LT315/70R16: 45 PSI[/*:m:2v6nfm5y]
- LT315/75R16: 42 PSI[/*:m:2v6nfm5y]
-- Geoff
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03-18-2014, 11:00 AM
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#10
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Senior Member
Join Date: May 2007
Location: East Bay CA
Posts: 1,078
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Re: SMB Tire Pressure ???
Thanks geoffff.
While I agree with anzac that's it best and easy to use load tables, not every manufacturer publishes them. BFG doesn't for KOs. I used the manufacturer association ones from the octopup site geoffff linked. The relationship is not necessarily linear, but every other LT tire I looked at seems to be very, very close, usually within the margin of what I can measure with a consumer pressure gauge.
And even tire rack can be idiotic. Their first response to my query was that no one published load tables for modified vehicles. You can find more info on setting pressure based on load and weighing for the RV and big truck tires, but squat on LT tires. BFG had me call them; sorta got the impression they couldn't point me to any published load tables. Guy there said my pressures were fine for the weight given.
__________________
2001 Ford E250 Sportsmobile with Salem-Kroger 4x4 conversion
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