Interesting find on tire pressure

[ThatSickRIp]

So, there was a post here a while back that had an online calculator for setting your tire pressure for the tires size and load rating. It recommended 27 PSI for my 285 70 17. I have them at about 32.

Just now I was looking at my receipts folder for the 4R, and I noticed the tire installer receipt list 26 PSI as recommended pressure, so very close to the online calculator above.

Has anyone gone this low on their tire pressure, and if so how were the results?

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[josiahg52]

The required tire pressure is determined by the size and expected load per the Tire Load and Inflation Tables published by the TRA. Or you can just use what the door sticker says. Instead of running 80 psi in the rear tires on my Ram 2500, I found that there is really no need for more than 60 psi, IIRC, based on the rear axle and payload rating. I reprogrammed the TPMS set points to 60psi front and 40psi rear. If the weight of your vehicle and tire size supports it, 26 or 27psi wouldn't phase me as long as it falls within the tire manufacturer's pressure range.

 

[Dr_Al]

Back in the day radial tires were suppose to be at 28 psi. Bias tires needed to be at 32 psi. Then the whole Firestone Ford Explorer thing happened. Lots of fingers got pointed and suddenly they changed it to 32 psi. Fuel economy improved and suddenly 28 psi went away. There was some nonsense about other reasons (vehicles being heavier) but in the end nobody wanted to take the blame for a tire failure because it got too hot from running at a low pressure.

The real reason for the Firestone problem was a manufacturing problem. I think it was compounded by tires that were unusually old for a new tire. Ford made it worse by recommending 26 psi to improve the ride. I always set my tire pressure after the garage swaps the summer/winter tires. I've seen them as high as 38 psi (which will wear the center of the tire quicker than the edges). I usually set them to around 30 psi. If I was to go lower I would check them after about 5k miles to make sure the edges aren't wearing faster than the center.

If I was going on a trip pulling a trailer or loaded down I would air them up to at least 32 to handle the extra weight. But for normal use 27 psi wouldn't bother me.

 

[ThatSickRIp]

Thanks fellas

I think Ill give it a shot and see how it rides. When we load up for trips/vacations, I can always put a few PSI in to be safe, though we never pull a trailer so should still be good to go.

 

[morsk]

Sorta tangential, but I was looking at my stock 245/70/17 Yokohamas yesterday inflated to ~33 and they looked kinda flat. Rides well though, but was wondering if I should pump them up to 36

 

[bakutheleo]

I have seen that "kinda flat" look on quite a few vehicles, including others I have had (so I know the pressure was to spec). My guess is that going by looks is not a good idea--just go by the recommended pressure and it should be good.

 

[Skrr1225]

So, there was a post here a while back that had an online calculator for setting your tire pressure for the tires size and load rating. It recommended 27 PSI for my 285 70 17. I have them at about 32.

Just now I was looking at my receipts folder for the 4R, and I noticed the tire installer receipt list 26 PSI as recommended pressure, so very close to the online calculator above.

Has anyone gone this low on their tire pressure, and if so how were the results?

If your 285s are SL tires, online load calculators commonly output roughly 26–27 PSI to match the original factory load capability. Running them at 32 PSI may feel noticeably stiffer or slightly over-inflated for daily pavement use.

 

[ThatSickRIp]

If your 285s are SL tires, online load calculators commonly output roughly 26–27 PSI to match the original factory load capability. Running them at 32 PSI may feel noticeably stiffer or slightly over-inflated for daily pavement use.

I think I'll drop to 28 and see how it feels and go from there.

 

[Skrr1225]

I think I'll drop to 28 and see how it feels and go from there.

Great choice

 

[Joey_Midnight]

Been running my nitto g3 285s at 30 psi, ride was smoother and the mpg almost seemed to improve. Considering the outter edge blocks are closer and more stable then the center tread blocks on this tire, putting the load the edge may improve economy at a lower pressure

 

[LP4Runner]

Instead of guessing or wondering what psi you should be running day to day, get yourself a tire tread depth gauge. Check the depth across the tire, maybe on a monthly basis. Of course, going off road will often require lowering the psi, but that is temporary. For me, the factory recommended pressure on the door frame works with stock tires.

 

[Virtual-Chris]

The best way I’ve found to get tire pressures optimized is the chalk test. You can find lots of videos on YouTube but the jist is to start at what you know is probably a bit over pressure so only the center of the tread is making contact with the road, cover a cross-section of your tread with chalk, drive a bit and check if the tire is making full contact with the road, and then deflate slightly and reassess… deflate a bit more if necessary, repeat until your full tread is making contact with the road… (all the chalk is gone)… that’s your ideal pressure.

 

[Nodak]

this is more revelent as you go up in tire load range. as you get into "C" and "E" load tires, chalk test is a better measure than just going by the psi on the door jam.

but do take into account summer temps vs winter temps, especially in northern tier states.

i had mine set at 35 psi at 70F but this morning they are 31 psi at 37F and nothing has changed except ambient temp.

i 99% of the time only run SL tires, never had a need for "C/D/E" load tires since i started driving in '83

right now i run defender ltx ms2 in XL load but that is the standard for those tires, you cant find a SL load in that model of tire.

SL load tire are usually rated for max psi of 36 where as XL is rated up to 42 psi (usually)

Load Range and Ply Rating
Load Range	Ply Rating	Max Load Carrying Air Pressure
Standard Load (SL)	4	@ 36 PSI
Extra Load (XL)	4	@ 42 PSI
C1	6	@ 50 PSI
C2	6	@ 35 PSI
D1	8	@ 65 PSI
D2	8	@ 50 PSI
E1	10	@ 80 PSI
E2	10	@ 65 PSI
F1	12	@ 95 PSI
G	14	@ 110 PSI

Load Index and Carrying Capacity Table

Load Index	Carrying Capacity (lbs)
0	99
1	102
2	105
3	107
4	110
5	114
6	117
7	120
8	123
9	128
10	132
11	136
12	139
13	143
14	148
15	152
16	157
17	161
18	165
19	171
20	176
21	182
22	187
23	193
24	198
25	204
26	209
27	215
28	220
29	227
30	234
31	240
32	247
33	254
34	260
35	267
36	276
37	282
38	291
39	300
40	309
41	320
42	331
43	342
44	353
45	364
46	375
47	386
48	397
49	408

Load Index	Carrying Capacity (lbs)
50	419
51	430
52	441
53	454
54	467
55	481
56	494
57	507
58	520
59	536
60	551
61	567
62	584
63	600
64	617
65	639
66	639
67	677
68	694
69	716
70	739
71	761
72	783
73	805
74	827
75	852
76	882
77	908
78	937
79	963
80	992
81	1019
82	1047
83	1074
84	1102
85	1135
86	1168
87	1201
88	1235
89	1279
90	1323
91	1356
92	1389
93	1433
94	1477
95	1521
96	1565
97	1609
98	1653
99	1709

Load Index	Carrying Capacity (lbs)
100	1764
101	1819
102	1874
103	1929
104	1984
105	2039
106	2094
107	2149
108	2205
109	2271
110	2337
111	2403
112	2469
113	2535
114	2601
115	2679
116	2756
117	2833
118	2910
119	2998
120	3086
121	3197
122	3307
123	3417
124	3527
125	3638
126	3748
127	3858
128	3968
129	4079
130	4189
131	4289
132	4409
133	4541
134	4674
135	4806
136	4938
137	5071
138	5203
139	5357
140	5512
141	5677
142	5842
143	6008
144	6173
145	6393
146	6614
147	6779
148	6844
149	7165
150	7385

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