Hi everyone, i just brougt a 92 fj80 and replace the tires with 15" steel wheels and A/T tires. What tire pressur should i run them on the street? Mud? Sand?
Thanks
Thanks
Air Pressure on 31" A/T
- Thread starter doublebuck
- Start date
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What size did you replace your tires with and are they P-metric or LT rated tires? Generally p-metrics would have a lower max tire pressure then LT. I have P265/70/16 and run 38 psi on the streets and 20-25 psi off road ( dirt, gravel, flooded roads). No sand near me, some mud but i don't usually go off road.
gaijin
GOLD Star
If you can provide the following information, I can tell you exactly what pressure to run on the street and recommend pressures for off-road use:
1. Recommended tire pressure on your door jamb sticker Front/Rear
2. Recommended tire size on your door jamb sticker including whether P-Metric or LT (Light Truck) size and Load INdex (e.g. 112, 114, etc.) if known
3. Size, Load Range (e.g. D, E, etc.), and Load Index (e.g. 114, 121, etc.) of your new tires and whether P-Metric or LT size
4. Front axle GAWR from the sticker on your door jamb
5. Rear axle GAWR from the sticker on your door jamb
An added bit of info would be a picture of your door jamb sticker that corresponds to this one:
HTH
What math are you using to figure out the right pressure? Curious to see if I've been pretty close on the M/Ts I've been running and figure the best pressure for the A/Ts that are on the Tacoma wheels I'm wanting to use.
gaijin
GOLD Star
I'm using the Load Limit/Tire Pressure tables and guidelines published by the Tire and Rim Association, Inc.
Using these tables one can determine the factory recommended Load Limit for the stock tires at stock pressure. From there, it is easy to calculate the pressure required to have the same Load Limit for a tire of a different size. There is even an easy calculation for substituting a LT tire for a P tire.
For example, my 2013 LC200 has a recommended tire pressure F/R of 33/33 psi.
The stock tires are P285/60R18 114V. The Load Limit @ 33psi for those tires is 2,520 pounds. Since these are P-Metric tires used on an SUV, the Load Limit was increased by 10%. The "raw" Load Limit is therefore 2,520/1.1 = 2,291 pounds.
The larger of 1/2 the GAWR (Front or Rear) can be no more than 94% of this "raw" Load Limit. My Rear GAWR is 4,300 pounds, so 4,300/2 = 2,150 pounds which is 93.8% of the "raw" Load Limit.
OK so far?
So if you want to substitute a different size P-Metric tire, you must find the Load Limit/Pressure that results in 2,520 pounds.
Since LT tires do not have to have their Load Limits increased by 10%, if you want to substitute an LT tire, you must find the Load Limit/Pressure that results in 2,291 pounds.
In my case, this resulted in going from a P285/60R18 114V tire @33 psi (Factory recommended size and pressure) to a LT285/70R17E 121R tire @ 40 psi.
So ... if I have the information I requested in my previous post, I can look up the values on the Tables and give the recommended tire pressure for the new tire.
Clear as (IH8)mud, right?
- Thread starter
- #8
Forget the 31" tires, i just got some BF Goodrich KM2 33x10.50R15.
The LC weighs 6650 lb, front tire is 29psi, Rear tire is 41psi. Original tire is 29".
I called BFGoodrich but they couldn't help me out because if the front being so low. I put 38psi in all 4 tires now.
The LC weighs 6650 lb, front tire is 29psi, Rear tire is 41psi. Original tire is 29".
I called BFGoodrich but they couldn't help me out because if the front being so low. I put 38psi in all 4 tires now.
gaijin
GOLD Star
What I need is the factory recommended tire size - for example, 275/60-16. 29" doesn't tell me what I need to know.
Then I need the factory recommended inflation pressure from the sticker on your door jamb.
Then I can tell you the correct pressure for your KM2's.
- Thread starter
- #10
Here's the factory info on my 92 LC
6525 lb
Cold 29psi front (weight 3305 lb)
Cold 41psi Rear (weight 3970 lb)
Tire: 15x6 (rim)
P235/75R15
Please help me figure out PSI for my 33x10.50R15.
Thanks
6525 lb
Cold 29psi front (weight 3305 lb)
Cold 41psi Rear (weight 3970 lb)
Tire: 15x6 (rim)
P235/75R15
Please help me figure out PSI for my 33x10.50R15.
Thanks
- Thread starter
- #11
Factory info on my toyota fj80 landcruiser
Weight 6525 lb
Tire P235/75R15
Cold PSI 29 front (3305 lb)
Cold PSI 41 Rear (3970 lb)
I have km2 33x10.50R15 on the lancdruiser now
Thanks
Weight 6525 lb
Tire P235/75R15
Cold PSI 29 front (3305 lb)
Cold PSI 41 Rear (3970 lb)
I have km2 33x10.50R15 on the lancdruiser now
Thanks
gaijin
GOLD Star
I can understand why BFG was reluctant to make a recommendation based on the factory recommended pressures you state - not that the Front (29psi) is so low, but that the Rear is so high (41psi).
But let's assume that you are correct and that is indeed what the sticker on your door jamb recommends.
The recommended pressures, 29F/41R psi, require an "XL" rated P235/75R15 with a Load Index of 108.
Load Rating for this stock tire:
Front = 1,852 pounds @29psi
Rear = 2,183 pounds @41psi NOTE: This is the MAXIMUM LOAD @ MAXIMUM PRESSURE for this size tire.
In order to maintain the same factory recommended Load Ratings for the BFGoodrich Mud-Terrain T/A KM2 tires in size 33X10.50R15LT:
Front = 1,855 pounds @ 30psi
Rear = 2,170 pounds @ 38psi
So, if you were running 29F/41R with P235/75R15 XL stock size tires, then you should run 30F/38R with the BFGoodrich Mud-Terrain T/A KM2 tires in size 33X10.50R15LT.
These pressures result in the GAWR F/R being only about 90% of the Load Rating for the two tires on the axle - a very comfortable ratio.
Airing down for offroad use on sand, rocks, etc. is more an art than a science, so specific recommendations are a little more "fuzzy" and based a lot on personal experience and preference. For me, I do not air down more than 1/2 the on-road pressure in order to avoid tires coming off the rims, etc. In your case, that would be 15F/19R. Lots of folks recommend lower pressures than that, but I will let them make their own cases for lower pressures.
Hope you find the info helpful.
- Thread starter
- #13
What if the tires have belly look alike on the sidewall? Is that still okay? With 38 psi the tires have a little belly on the sidewall already? Thanks for your help i will try it out.
gaijin
GOLD Star
All I can tell you is the science dictates the pressures I gave you. Although I have run into a few analytical chemists in my time who swear they have a "calibrated eyeball," science wins every time.
- Thread starter
- #15
I'll give it a try thanks for your help
I'm using the Load Limit/Tire Pressure tables and guidelines published by the Tire and Rim Association, Inc.
Using these tables one can determine the factory recommended Load Limit for the stock tires at stock pressure. From there, it is easy to calculate the pressure required to have the same Load Limit for a tire of a different size. There is even an easy calculation for substituting a LT tire for a P tire.
For example, my 2013 LC200 has a recommended tire pressure F/R of 33/33 psi.
The stock tires are P285/60R18 114V. The Load Limit @ 33psi for those tires is 2,520 pounds. Since these are P-Metric tires used on an SUV, the Load Limit was increased by 10%. The "raw" Load Limit is therefore 2,520/1.1 = 2,291 pounds.
The larger of 1/2 the GAWR (Front or Rear) can be no more than 94% of this "raw" Load Limit. My Rear GAWR is 4,300 pounds, so 4,300/2 = 2,150 pounds which is 93.8% of the "raw" Load Limit.
OK so far?
So if you want to substitute a different size P-Metric tire, you must find the Load Limit/Pressure that results in 2,520 pounds.
Since LT tires do not have to have their Load Limits increased by 10%, if you want to substitute an LT tire, you must find the Load Limit/Pressure that results in 2,291 pounds.
In my case, this resulted in going from a P285/60R18 114V tire @33 psi (Factory recommended size and pressure) to a LT285/70R17E 121R tire @ 40 psi.
So ... if I have the information I requested in my previous post, I can look up the values on the Tables and give the recommended tire pressure for the new tire.
Clear as (IH8)mud, right?
Holy schnikes man I think I went cross-eyed trying to figure that out
Trying to see if I'm doing the math right for these "new" Wintercats I've got.
Last set of stock sized tires I had were P225/75r15 XL, which had a max load per tire of 2094lbs @ 50 PSI (spec'd on the tires)
Door sticker shows GAWR for the front of 2785 lbs @ 26 PSI, GAWR for the rear of 3685 lbs @ 41 PSI
So since the originals were P-metric tires, the "raw" load limits would be
2785/1.1 = 2532 front (rounded to nearest whole number) and 3685/1.1 = 3350 rear
(2532/2)/2094 = 60.5% the original tire's load limit for the front
(3350/2)/2094 = 80% of the originals' load limit for the rear; well under 94%. I assume these checks are to ensure that the load limits set by the manufacturer aren't too close to the tires' maximum load limits.
So I want to find the pressure for my Wintercats that puts the front pair at a 2532 lb load limit and the rear at a 3350 lb load limit.
The Wintercats I have are E rated and have a max load rating of 3195 lbs @ 80 PSI
(2532/2)/3195 = 40% (rounded)
(3350/2)/3195 = 52%
So based on this I want the fronts at 40% of the max PSI and the rears at 52% of the max PSI.
80 * 0.4 = 32 PSI front
80 * 0.52 = 42 PSI rear
This is based on what the factory would recommend for these tires, but given how low the PSI of the front tires is, that just doesn't sound right. 42 PSI sounds like a good pressure though, given the max ratings for these tires.
And did I even do the math right?
Last set of stock sized tires I had were P225/75r15 XL, which had a max load per tire of 2094lbs @ 50 PSI (spec'd on the tires)
Door sticker shows GAWR for the front of 2785 lbs @ 26 PSI, GAWR for the rear of 3685 lbs @ 41 PSI
So since the originals were P-metric tires, the "raw" load limits would be
2785/1.1 = 2532 front (rounded to nearest whole number) and 3685/1.1 = 3350 rear
(2532/2)/2094 = 60.5% the original tire's load limit for the front
(3350/2)/2094 = 80% of the originals' load limit for the rear; well under 94%. I assume these checks are to ensure that the load limits set by the manufacturer aren't too close to the tires' maximum load limits.
So I want to find the pressure for my Wintercats that puts the front pair at a 2532 lb load limit and the rear at a 3350 lb load limit.
The Wintercats I have are E rated and have a max load rating of 3195 lbs @ 80 PSI
(2532/2)/3195 = 40% (rounded)
(3350/2)/3195 = 52%
So based on this I want the fronts at 40% of the max PSI and the rears at 52% of the max PSI.
80 * 0.4 = 32 PSI front
80 * 0.52 = 42 PSI rear
This is based on what the factory would recommend for these tires, but given how low the PSI of the front tires is, that just doesn't sound right. 42 PSI sounds like a good pressure though, given the max ratings for these tires.
And did I even do the math right?
gaijin
GOLD Star
Trying to see if I'm doing the math right for these "new" Wintercats I've got.
Last set of stock sized tires I had were P225/75r15 XL, which had a max load per tire of 2094lbs @ 50 PSI (spec'd on the tires)
Door sticker shows GAWR for the front of 2785 lbs @ 26 PSI, GAWR for the rear of 3685 lbs @ 41 PSI
So since the originals were P-metric tires, the "raw" load limits would be
2785/1.1 = 2532 front (rounded to nearest whole number) and 3685/1.1 = 3350 rear
(2532/2)/2094 = 60.5% the original tire's load limit for the front
(3350/2)/2094 = 80% of the originals' load limit for the rear; well under 94%. I assume these checks are to ensure that the load limits set by the manufacturer aren't too close to the tires' maximum load limits.
So I want to find the pressure for my Wintercats that puts the front pair at a 2532 lb load limit and the rear at a 3350 lb load limit.
The Wintercats I have are E rated and have a max load rating of 3195 lbs @ 80 PSI
(2532/2)/3195 = 40% (rounded)
(3350/2)/3195 = 52%
So based on this I want the fronts at 40% of the max PSI and the rears at 52% of the max PSI.
80 * 0.4 = 32 PSI front
80 * 0.52 = 42 PSI rear
This is based on what the factory would recommend for these tires, but given how low the PSI of the front tires is, that just doesn't sound right. 42 PSI sounds like a good pressure though, given the max ratings for these tires.
And did I even do the math right?
Well ... you're kind of on the right track, but you went terribly wrong when you assumed Load Limits are linear and that they are based on the Max Load/Pressure ratings.
Your stock P225/75R15 XL tires have the following Load Limits:
Front: 1,631 pounds @ 26psi
Rear: 2,028 pounds @ 41psi
If you are replacing this tire with an LT tire, then we need to find the pressure that yields the following Load Limits:
Front: 1,631/1.1=1,483 pounds
Rear: 2,028/1.1=1,844 pounds
To determine this, I need the size of your LT tires.
All of these Load Limits are derived from the Load Limit / Pressure tables published by the Tire and Rim Manufacturer's Association and are not calculated.
So give me the size of your LT tires, I'll look them up in the tables, and will let you know the recommended pressures.
HTH
Had a feeling I went off track somewhere. The new tires are LT245/75r17
