Increased tire size, same psi?

I don't think the volume changes significantly. The flat spot on the bottom would get smaller, making it sit higher.

You could be right, though. They might stretch a tiny bit. That's why the middle tread would wear prematurely when overinflated.

But, why is the pressure the same for load range C and E then? You would think 10 ply would be harder to stretch than 6 ply.

I have thought it had something to do with the stiffness, though. I'm going to have to look it up.

 

You are correct in regards to C vs E.
Given equal size and pressure, the E will have slightly less deflection and contact patch. So slight, it's trivial.
This is a level of minutia even I shy away from; congratulations. Lol

Load capacity is unaffected, which is what the charts are concerned about.

 

My thread has been hijacked

 

Thanks for the answers. I’ll be towing a camper for the first time this weekend so I wanted to make sure the PSI was correct with the increased tire size

 

Good info, thanks!

OP, I'm settled on about 2+/- psi over decal pressure on my OEM tires for feedback and feel.

 

Old thread revival, I used the Toyo tires chart and according to the standard load inflation table for my 315/70R17 (121) E load tires I am supposed to be running 23psi (2238lbs) which is the closest I can get to the factory load rating of 2149lbs. I have sliders, full skids, roof rack and a 35” spare plus tonneau cover so not much extra weight unless the dirt bikes are in the bed. I’m wondering once I get bumpers and winch if I should increase the pressure to compensate for the additional weight?

The tire shop inflated them at 35psi which felt like driving on bricks. 23psi feels so nice and plush but my mpg has definitely taken a hit and my TPMS light is constantly on since anything under 25psi triggers it, trying to figure out a way to reset the TPMS to a lower value but I don’t think there is a way unless I have access Techstream?

 

30 in summer, 32 in winter with my awesome upsized Duratracs!!!

 

When you go with LT tires, it's 1,954 lbs...
I'm guessing you extrapolated a value for 1psi from the chart between 35-40 psi; since the charts do not go below 35 psi... I would caution taking this practice below 30 psi as the charts are non-linear and your load capacity could really drop off going all the way down to 23 psi.

It's hard to answer the weight compensation question, as we do not know exactly what weight you are supporting at 23 psi.

As much as I dislike the chalk method, you are probably a good candidate for it. The large increase in volume of your tire makes it very difficult to use the charts accurately.

This is the correct procedure if the chalk method is to be used:

"You can also “calculate” your tire pressure with the chalk method. This involves coloring a section of your tire with chalk to see how much tread is making contact with the ground. Start by finding a flat road surface. Concrete is actually the best choice, but you can also do this on asphalt. Make a mark with soft chalk that goes all the way across your tread. Then, gradually drive your truck forward about 50 feet and then backwards 50 feet.

Analyze the chalk on the tire. If the chalk is only worn off on the center of the tire, reduce the tire pressure slightly and go through the process again. With the adjustment, you should see the chalk wear off more broadly. Keep making tiny adjustments in the tire pressure until the chalk wears off evenly and all the way across the tread.

You will have to complete this process for each of your four tires. Once you’ve found the right street pressure, add 10% to all four tires. Then, measure the tires and add pressure to balance them. As explained above, you need to measure from the wheel to the ground. Start by balancing the profiles of the front tires with each other. Then, balance the front tires again with the rear tires. Always adjust the tires with the smaller profiles by adding air."

You should be able to reset your threshold psi with the TPMS reset button.

 

Doesn't matter how big a compressor I use, I can never get my tires to 100% full.

My dash always says their 65-75%.











Is it Friday yet?

 

Thanks for the thorough response, I will definitely try the chalk method and follow the procedure you mentioned.

I was running 30 psi before airing down but I could feel the paint lines in the road it was so stiff. I know part of that stiffness contribution is due to the E load tires and for reference I am running Bilstein 6112/5160 with ICON RXT leafs. Not the most plush setup compared to kings but my teeth shouldn’t be rattling driving around town. At 23-25psi it finally feels more factory.

Furthermore, do you run higher pressure in the front due to most of the weight of the truck being in the front? Reason I ask is if I drive in the wet with the same pressure front/rear even though the front will make full contact the rear will have about an inch that does not (dry edges).

 

Most who do the chalk method seem to end up with a front to rear bias; without a constant rear load.

 

Do people really run tires at low 20’s on the street? I did that with my last set and blew through a 60k set of tires in maybe 20. I’m currently running my 38’s at door pressure level which I think is 32.

Running them at 23 would be nice. Holy squishy.

 

If adhering to recommended psi on the door placard...
You only need enough psi to get a 1,954 lbs of load capacity out of an LT tire and 2,149 lbs out of a euro-metric or P-metric.

In the case of @Fullsend 604, with a LT315/70/17 @ 35 psi, you get 2,335 lbs. Where 1,954 lbs of load capacity actually occurs on an LT315/70/17, is a big unknown; and why I recommended the chalk test for him.

When one has a tire with so much volume, less psi is generally required to end up with a comparable total amount of air...all other things being equal. It doesn't hold true when comparing LTs to euro-netric or P-metric or vice-versa.

Big, voluminous LT tires on our trucks, in a way, really are overkill.

Technically, one could argue, LT-metric tires have a minimum inflation of 35 psi...

As I've said many times on this forum, psi is just a means to an end; 'inflated load capacity'.
My oem 265/70/16/112 tires were 30 psi.
My current LT265/75/16 are 37 psi.
The 265/75/16/116 I'm having put on Friday, will be 27 psi.
Quite a range, right? ...and that's without increasing volume much from the stock tire.
It still gives me 2,149 lbs load capacity on the oem tires, 1,954 lbs on the LT tires and 2,178 lbs on the the new tires.

 

After doing the chalk test I settled on 33psi upfront and 29psi in the rear. This was the closest I can get to the chalk wearing off on the whole tread evenly after doing it 5-6 times. Only had about 150lb of weight in the bed during the test so I may bump the rears up a bit for when I have the bikes in the bed on the weekends.

Looking back at my previous 23psi, good thing I only drove on that low of pressure for less than 100 miles because it’s not good for the tires on the street. I think I will still go down to 23psi for the trails though.

As for the stiff ride, I think my shocks may play a big role since I have my Bilstein 6112s set at max height/preload. I will probably upgrade to Kings or Fox next for a better feeling ride or go with C load for my next tires. I think E load is better suited for a Tundra anyway.

 

I recommend consulting and purchasing from Accutune for shocks valved specific to your truck.
Tires are the first line in high-speed compression; E-rated tires do not help with this. Off the shelf 6112s probably have a hard time managing the increased unsprung mass.

Out of curiosity, how much do your tires and wheels weigh?

 

Isn't there more to tire inflation than just load carrying capacity? Handling, tire wear, gas mileage?

I’ve only really cared about pressures on motorcycles. So I’m new to messing around with it on road. Just surprising people are running low-mid pressures. I’d love to run my 38’s mid-20’s but I don’t want to have to replace them every year.

Maybe a better pressure recommendation is a balance between load, handling, and tire wear. Not just look at this chart and make sure the load is good then call it a day.

I run milestars that suggest running door pressure because they are crowned but maybe now that the crown is gone I can drop the pressures.

 

I will definitely look into shocks valved specifically for the Tacoma.

Falken Wildpeak AT3W 315/70R17 weigh in at 73lb and 21lb for the wheels, quite heavy which makes ride quality worse.

 

Yes I go 4psi higher for better gas mileage

 

Yes...and partly why I said, "If adhering to the recommended psi on the door placard".

The recommended psi attains a total inflated load capacity about 150% that of GVWR .

It's also why I post the full version of the chalk test, instead of the abbreviated version most people use. After the initial chalk test, it requires adding 10% psi and then equalizing deflection by increasing psi again.

 

My results with 265/75-16 (SL load range 116t) Michelin Defenders with the Bilstein 6112/5160 kit on a AC TRD off-road..

I have 38,000 miles on the tires and have run them at ~ 27 psi since purchase for pavement. Off-road which has been 2000-2500 miles in the mountains of CO and WY at 14-15 psi. Tires are still near 10/32 tread depth with no abnormal wear. Having a good alignment done is critical also for tire wear. The only time I've aired up beyond 27 psi is when doing 1000 mile drives cross country on the freeway at higher speed with additional weight in the box. I'll run 31/32 psi cold for those drives.

The only slightly odd wear I've seen is on the outer edge of the fronts (feathering) if I'm hitting the cloverleafs on freeways like I'm driving my sports car. Simple rotation (front to back) minimizes the impact of that driving style.