GFiveFifty

I’m running 305/65/18 BFG K02s. What’s the best cold PSI for city driving?

It seems the optimal PSI may trigger the low tire pressure light on the dash, but I don’t mind if it smoothens my ride.

jadatis

Needed tirepressure is all about load on tire, and max speed used.

​​Main goal is to not overheat any part of tire-material, when driving the speed its determined for.

I am able to make a cold pressure/axleloadcapacity - list for your tire, with build in maximum reserve, at wich comfort and gripp is still acceptable.

For that I give 90% of calculated axleload for the pressure for 160kmph/99mph.

Then you "ONLY" have to determine the axleloads 99 % acurate, the most tricky part, and your resoncibility.

Need next from tires.
1. Maximum load or loadindex.
2. Kind of tire to determine the referencepressure.
P-tire SL AT 36 or 35 psi.
XL/reinforced/extraload AT 42 or 41 psi.
On sidewall only maxcold of between 44 and 51 psi, and an ocacional XL// 60 psi given

Lt (lighttruck) or european equivalent C-tyre( comercial) give referencepressure on sidewall. And ocacional also 10 psi higher max inflation pressure, is maxcold.
C-LOAD 50 PSI
6PR AT 55 psi/3.75 bar
8PR / D-load AT 65 psi.

3. Speedcode, less important, shall be Q or above, for wich maxload is calculated for 160kmph/99mph.

Also give if you want list in psi or bar/kPa, Kg or LBS.
And if you want for other max speed or other reserves, we can discuss about that.
If speed is not to high, like only city use, lower pressure is enaugh, and comfort is better, but more energy use. Its yust what you want.

Mind max speed is you wont go over for even a minute.


​​​

GFiveFifty

jadatis

Assuming you dont have dualload rear axle, I will make list for next
Using lbs and psi
124 loadindex (121 is for dualload)
AT 65 psi, written on sidewall small, also E-load wich suspects AT 80 psi, but this section width lower.

So using maxload 1600kg/3527 lbs AT 65 psi upto 160 kmph/99 mph.

Then giving 90% of calculated axleload with an even tighter formula then official, close to lineair calculation. Determined that to give maximum reserve, with still acceptable comfort and gripp.

So dont do pre or aftercalculations yourselfes, all done for you.
As long as you cant determine the real axleloads ( by weighing per axle) you could look back the GAWR's (gross axle weight rating).
Then assuming you dont overload ( when towing overloading rear axle happens often) this gives maximum needed in every situation and max 99mph.

Carmakers give recomended pressures mostly for GAWR's and max technical carspeed, with no reserve.
If they calculate, nowadays more often reference pressure of OEM tires, so 35,36,41 or 42 psi.
If you see that, calculated could come much lower.
But if you chanched from OEM P-tire to this AT 65 psi LT tire, it needs higher pressure for same load calculated, about 10 psi, so in the end it can be that not calculated 35 psi for instance.


Gives next.
Cold psi/ axleload
21 psi / 2286 lbs
22 psi / 2381 lbs
23 psi / 2476 lbs
24 psi / 2571 lbs
25 psi / 2666 lbs
26 psi / 2760 lbs
27 psi / 2855 lbs
28 psi / 2949 lbs
29 psi / 3043 lbs
30 psi / 3137 lbs
31 psi / 3230 lbs
32 psi / 3324 lbs
33 psi / 3417 lbs
34 psi / 3510 lbs
35 psi / 3604 lbs
36 psi / 3697 lbs
37 psi / 3789 lbs
38 psi / 3882 lbs
39 psi / 3975 lbs
40 psi / 4067 lbs
41 psi / 4160 lbs
42 psi / 4252 lbs
43 psi / 4344 lbs
44 psi / 4436 lbs
45 psi / 4528 lbs
46 psi / 4620 lbs
47 psi / 4712 lbs
48 psi / 4803 lbs
49 psi / 4895 lbs
50 psi / 4986 lbs
51 psi / 5078 lbs
52 psi / 5169 lbs
53 psi / 5260 lbs
54 psi / 5351 lbs
55 psi / 5442 lbs
56 psi / 5533 lbs
57 psi / 5624 lbs
58 psi / 5715 lbs
59 psi / 5806 lbs
60 psi / 5896 lbs
61 psi / 5987 lbs
62 psi / 6077 lbs
63 psi / 6168 lbs
64 psi / 6258 lbs
65 psi / 6348 lbs/ reference-pressure
66 psi / 6438 lbs
67 psi / 6528 lbs
68 psi / 6618 lbs
69 psi / 6708 lbs
70 psi / 6798 lbs
71 psi / 6888 lbs
72 psi / 6978 lbs
73 psi / 7068 lbs
74 psi / 7157 lbs
75 psi / 7247 lbs/sometimes also given maxcold

shiann

My tires are a bit smaller than yours at 285/60R18 KO2's, but I run them at 35-40 for normal around town driving and pump them up to 45 when going on long roadtrips.

They're wearing very evenly being at 50k miles now and I only end up rotating once a year.

I also rarely load my G up in terms of weight but your sitution may be different.

jadatis

Reaction to post #5.

Your 285 size if E-load is most likely AT 80 psi, and lower loadindex-maxload, and the axleweights can be different.
Can make you a list too, if you like, to comfirm your in practice determined 40 psi to be right. Must be, because the milage you made with them.

shiann

My LT285/60R18's are D-load tires, max 65psi @ 2910lb. I went for the D-load tires as I never was planning on heavy loading the G, nor do I plan to tow anyting meaningful in size. The slightly softer D-load tire vs the E-load tires was more of a comfort choice.

Next go around I'll probably upsize slightly from the 285/60R18 (31.5") to a 285/65R18 (32.6") which will be E-load tires.

Not sure how you calculated your list or I would do one for my tire and the G also.

jadatis

Then I made you a list too.
Assuming maxload 2910 lbs AT 65 psi upto 99mph.

Again giving 90% of calculated axleloadcapacity.
Then you can still drive only 60 mph, but upto 99mph with still acceptable comfort and gripp.

Only have to determine the axleloads in both uses (towing and not towing) 99% acurate, the most tricky part and your responcibility.

For towing you only have to highen up the rear pressure, front axle is even lifted up a bit, so lesser weight, even with wdh used, so most likely can stay at 40 psi.

21 psi / 1886 lbs
22 psi / 1964 lbs
23 psi / 2043 lbs
24 psi / 2121 lbs
25 psi / 2199 lbs
26 psi / 2277 lbs
27 psi / 2355 lbs
28 psi / 2433 lbs
29 psi / 2510 lbs
30 psi / 2588 lbs
31 psi / 2665 lbs
32 psi / 2742 lbs
33 psi / 2819 lbs
34 psi / 2896 lbs
35 psi / 2973 lbs
36 psi / 3050 lbs
37 psi / 3126 lbs
38 psi / 3203 lbs
39 psi / 3279 lbs
40 psi / 3356 lbs/ your normal use
41 psi / 3432 lbs
42 psi / 3508 lbs
43 psi / 3584 lbs
44 psi / 3660 lbs
45 psi / 3736 lbs/ your towing use.
​​​​​46 psi / 3812 lbs
47 psi / 3887 lbs
48 psi / 3963 lbs
49 psi / 4038 lbs
50 psi / 4114 lbs
51 psi / 4189 lbs
52 psi / 4265 lbs
53 psi / 4340 lbs
54 psi / 4415 lbs
55 psi / 4490 lbs
56 psi / 4565 lbs
57 psi / 4640 lbs
58 psi / 4715 lbs
59 psi / 4790 lbs
60 psi / 4865 lbs
61 psi / 4939 lbs
62 psi / 5014 lbs
63 psi / 5089 lbs
64 psi / 5163 lbs
65 psi / 5238 lbs/ referencepressure D-load
66 psi / 5312 lbs
67 psi / 5386 lbs
68 psi / 5461 lbs
69 psi / 5535 lbs
70 psi / 5609 lbs
71 psi / 5683 lbs
72 psi / 5757 lbs
73 psi / 5831 lbs
74 psi / 5905 lbs
75 psi / 5979 lbs