What do you run for a cold tire pressure on the street for 35s?

[CharlieS]

I know there are formulas used by people smarter than I am to calculate cold tire pressure (gajin on the 200 forum is a guru), but I'm just looking for a ballpark to start from.

I am running Cooper Discoverer STT Pros in an LT315/70R17 - roughly 35".

I don't normally do much highway with the 80, but I need to make a long trip to get to an event, so I'm looking for a good highway pressure.

What are you all running for pressure in your 35s?

 

[REKCUT]

I used to run 35 but jumped it to 40 an it rolls much nicer down the highway.

 

[mudgudgeon]

I'd start at around 35 and see how it rides.
If you feel every bump, lower it. If steering feels vague, raise it.
When your happy, so a chalk test and adjust if you feel it needs it.
Chalk test helps minimise wear.

I seem to end up rocking 32psi with my cruisers.

 

[BILT4ME]

I prefer comfortable at 32 around town.

On the road I'm at 40-45 to make it roll easier and try to squeak out that extra 0.5 mpg.

 

[devo]

35-40 empty
40-50 fully loaded
When on the tarmac

 

[JoeCova]

~35

 

[COYS]

31-2 cold

 

[CharlieS]

Thanks everyone. I'm going to start with 35 and adjust as needed. On board air makes that easy!

 

[leonard_nemoy]

E rated tire I would run 30 - 35 psi
C rated 35 - 40 psi

If you really want to know run a chalk test.....

 

[family80]

I run around 40

 

[Marvelicious]

40 for highway/street.

 

[Rusty Marlin]

Conduct a chalk test and run what it tells you.

 

[77mustard40]

32 lbs gets me the best contact patch and comfort.

 

[jadatis]

On road below 99mph, you can probably do with even as low as 25 psi.
This because of the still oversised tires for the GAWR's.
This "pigheaded Dutch selfdeclared tyrepressure specialist" can make a cold pressure /axleloadcapacity list for your tire, with build in reserve, at wich comfort and gripp is still acceptable.
For that I give 90% of calculated axleloadcapacity for the pressure.

Need next from tires
1. Maximum load or loadindex
2. Kind of tire to determine referencepressure ( SL, XL, LRC, LRD, LRE)
3. speedcode, les important, shall be Q or above, for wich maxload is given for 160kmph/99mph.

 

[OffRoadScott]

Every truck is different and tires react differently to weights and air pressure.

@Rusty Marlin talked about the chalk test. That is really the only and best way to figure out what your trucks ideal tire pressure should be.

Chalk Test



The above link is a video showing how to do the chalk test.

 

[CharlieS]

Thanks again all. I appreciate the advice and the education about the chalk test.

 

[jadatis]

Found this tire googling to be 121/118 S
Is maxload for single load axle 1450kg/ 3197 lbs maxload AT 65 psi, upto 160kmph/99mph.

Check that especially the AT65 psi, but E-load in this wide size has not 80 psi, but 65 psi referencepressure, to my knowledge.
Then the 25 psi I estimated would cover a good 2400 lbs axleload.


For this I made list with that build in reserve, so now you "ONLY" have to determine the axleloads 99% acurate, the most tricky part and your responcibility.
For max speed 160kmph/99mph onroad, and with that build in max reserve, but still acceptable comfort and gripp.
So you dont need to do pre- or after-calculations yourselfes.

Axleload lbs/ cold psi/ Axleload kg
2072 lbs/ 21,0 psi / 939 kg
2158 lbs/ 22,0 psi / 979 kg
2244 lbs/ 23,0 psi / 1018 kg
2330 lbs/ 24,0 psi / 1057 kg
2416 lbs/ 25,0 psi / 1096 kg
2502 lbs/ 26,0 psi / 1134 kg
2587 lbs/ 27,0 psi / 1173 kg
2673 lbs/ 28,0 psi / 1212 kg
2758 lbs/ 29,0 psi / 1251 kg
2843 lbs/ 30,0 psi / 1289 kg
2928 lbs/ 31,0 psi / 1328 kg
3013 lbs/ 32,0 psi / 1366 kg
3097 lbs/ 33,0 psi / 1405 kg
3182 lbs/ 34,0 psi / 1443 kg
3266 lbs/ 35,0 psi / 1481 kg
3351 lbs/ 36,0 psi / 1519 kg
3435 lbs/ 37,0 psi / 1558 kg
3519 lbs/ 38,0 psi / 1596 kg
3603 lbs/ 39,0 psi / 1634 kg
3687 lbs/ 40,0 psi / 1672 kg
3770 lbs/ 41,0 psi / 1710 kg
3854 lbs/ 42,0 psi / 1748 kg
3938 lbs/ 43,0 psi / 1786 kg
4021 lbs/ 44,0 psi / 1823 kg
4104 lbs/ 45,0 psi / 1861 kg
4188 lbs/ 46,0 psi / 1899 kg
4271 lbs/ 47,0 psi / 1937 kg
4354 lbs/ 48,0 psi / 1974 kg
4437 lbs/ 49,0 psi / 2012 kg
4520 lbs/ 50,0 psi / 2050 kg
4603 lbs/ 51,0 psi / 2087 kg
4685 lbs/ 52,0 psi / 2125 kg
4768 lbs/ 53,0 psi / 2162 kg
4851 lbs/ 54,0 psi / 2200 kg
4933 lbs/ 55,0 psi / 2237 kg
5015 lbs/ 56,0 psi / 2274 kg
5098 lbs/ 57,0 psi / 2312 kg
5180 lbs/ 58,0 psi / 2349 kg
5262 lbs/ 59,0 psi / 2386 kg
5344 lbs/ 60,0 psi / 2424 kg
5426 lbs/ 61,0 psi / 2461 kg
5508 lbs/ 62,0 psi / 2498 kg
5590 lbs/ 63,0 psi / 2535 kg
5672 lbs/ 64,0 psi / 2572 kg
5754 lbs/ 65,0 psi / 2610 kg/referencepress
5836 lbs/ 66,0 psi / 2647 kg
5918 lbs/ 67,0 psi / 2684 kg
5999 lbs/ 68,0 psi / 2721 kg
6081 lbs/ 69,0 psi / 2758 kg
6162 lbs/ 70,0 psi / 2795 kg
6244 lbs/ 71,0 psi / 2832 kg
6325 lbs/ 72,0 psi / 2868 kg
6406 lbs/ 73,0 psi / 2905 kg
6488 lbs/ 74,0 psi / 2942 kg
6569 lbs/ 75,0 psi / 2979 kg
6650 lbs/ 76,0 psi / 3016 kg

 

[Rusty Marlin]

99mph in an 80 LC?! I'm resonably sure mine wouln't do 99MPH if I threw it out of an airplane.

 

[jadatis]

Its only for detetmining the highest pressure at wich comfort and gripp is still acceptable, even if you drive only 40mph.

Rule of tumb system for onroad is every 10kmph/6.2 mph different max speed used ( and wont go over for even a minute) 1 loadindex step different.
Lower speed/ higher loadindex, higher speed/ lower loadindex.
So 120kmph/75mph used max speed is 4x10km lower then 160kmph, so you could add 4 LI steps so 121+4=125 loadindex to use in the formula.

 

[Marco Lau]

long highway trip- fully loaded - 32-35 psi cold 38-42 warm
5-10 psi on rocks.