New tires on stock rims...tire pressure?

Anything relating to Wheels, Tires, and Brake options and upgrades...

Moderator: volvite

mikecfry
Posts: 7
Joined: Thu Jan 23, 2014 8:10 pm
Location: South Jersey

New tires on stock rims...tire pressure?

Postby mikecfry » Thu Jan 23, 2014 8:21 pm

Hi everyone,

New to the site, but already enjoying the tons of great information here!

I purchased a 2011 SV back in July, and after pulling into the driveway to the hissing sounds of a seriously punctured tire (stook BFG Long Trails) yesterday, I bit the bullet and upgraded to BFG KOs in the stock size 265/65R17. I previously drove a lifted Jeep on Mickey Thompson MTZs, but with 2 kids in tow now I needed something a bit more family friendly. That said, I still need to be able to get 10-15 miles deep in the woods especially during hunting season, so KOs seemed like a good option.

I have them mounted on the stock rims and currently at around 38 PSI, but with the E rating I decided to call BFG and get a recommended pressure from them. I was pretty shocked when they suggested 55 PSI! I'll definitely be airing down from that come woods time, but for the highway does that seem right for what everyone else is running? Also, is anyone aware of the max PSI the stock 17" rims can handle?

Looking forward to contributing and learning.

Mike


User avatar
leadpig
Posts: 100
Joined: Thu Jan 26, 2012 1:27 pm
Location: Mississippi

Postby leadpig » Thu Jan 23, 2014 8:39 pm

I looked into this a bit a couple of months back (see LT vs P thread somewhere in here). Fom what I understand, the LT has the higher load rating based on its stronger construction that allows it to run at higher pressure than the stock p rated long trails. Running at lower pressure can cause it to overheat, not a problem off road but maybe on the highway if you also had a heavy load up. That's why they said 55, because that would allow the max load support, but it also means the ride would be harsher by quite a bit I would think. I thought about it and for my use I just went with P rated silent armors I could run in the high 30s, which I've been very happy with. I'm not surprised they gave you that advice, whether you actually need to run that high all the time, I don't know. I'm sure you'll get some feedback here from folks with similar equipment.

mikecfry
Posts: 7
Joined: Thu Jan 23, 2014 8:10 pm
Location: South Jersey

Postby mikecfry » Thu Jan 23, 2014 8:54 pm

Thanks for the quick reply! Due to the nature of my driving I was pretty set on LT tires - way too many rocks through P tires. I'm going to try the 55 PSI and do a chalk test from there to fine tune. Just hoping to hear someone else running pressures that high with the OE wheels. Seems like that should be documented somewhere but I can't find it for the life of me.

User avatar
doctahjones
Posts: 844
Joined: Tue Nov 16, 2010 11:08 am
Location: aurora, co

Postby doctahjones » Thu Jan 23, 2014 8:59 pm

i run about 40-45psi in mine. any lower and i get outer tire wear. i take frequent depth measurements, and when the outside starts getting lower than the center, i air up more towards the 45 side.

if i go any higher it rattles my teeth out when i go over bumps....

User avatar
NmexMAX
Posts: 796
Joined: Mon Oct 11, 2010 2:35 pm
Location: Northern New Mexico

Postby NmexMAX » Fri Jan 24, 2014 8:27 am

Damn, I run 30 PSI. :shock: But it's not a DD and the wheels aren't stock.

mikecfry
Posts: 7
Joined: Thu Jan 23, 2014 8:10 pm
Location: South Jersey

Postby mikecfry » Fri Jan 24, 2014 8:52 am

That makes since considering it looks like you are running much larger tires, you'd inherently run a lower PSI. I maintained the same size but moved from a passenger rated tire to an E rated LT tire, so it would need a higher pressure. I can't find the documentation anywhere, so thinking I'm going to crawl under soon and see if I can find a stamp on the rim. Should be fun under there in the snow. Yikes.

User avatar
leadpig
Posts: 100
Joined: Thu Jan 26, 2012 1:27 pm
Location: Mississippi

Postby leadpig » Fri Jan 24, 2014 2:02 pm

mikecfry wrote:That makes since considering it looks like you are running much larger tires, you'd inherently run a lower PSI.
I don't think you would, at least on road, since the air pressure is what holds the vehicle up. The load a tire can handle is a function of the pressure it can hold and an LT tire will need a higher pressure to have the same load capacity as a P. The design just allows higher max pressures so higher overall load bearing capacity with the LT, but underinflated they will overheat. I have no idea what difference the rim makes though - do rims have pressure limits? I've always assumed they were all equally air tight if the tire was within specs to fit on it. Am I wrong about that?

mikecfry
Posts: 7
Joined: Thu Jan 23, 2014 8:10 pm
Location: South Jersey

Postby mikecfry » Fri Jan 24, 2014 2:42 pm

Rims do have pressure limits, but typically it isn't a concern. I just finished airing up to 55 PSI so we'll see how it goes. Here was the quote from BFG:

"Your original equipment tires are designed to carry 2337 lbs. per wheel at 35-psi. Mike, you are absolutely correct; your new All-Terrain T/A KO tires must carry the same weight; so to carry that weight, please increase the pressure to 55-psi on all four wheel positions."

As far as larger tires go, PSI won't need to be as high since the amount of air to support the weight is constant, but you're changing the size of what contains that air. So, a larger tire contains the appropriate amount of mass to hold the vehicle's weight but at a lower pressure. Not the case with me since I kept the OE size and only changed rating.

Surprisingly the ride isn't bad at the high PSI. Our roads are still a wreck from 14 inches of snowfall this weekend, so not the best test, but not a bad start.

User avatar
NVSteve
Sponsored Member
Posts: 1985
Joined: Thu Feb 01, 2007 11:27 am
Location: Salt Lake City

Postby NVSteve » Mon Jan 27, 2014 9:19 am

mikecfry wrote: "Your original equipment tires are designed to carry 2337 lbs. per wheel at 35-psi. Mike, you are absolutely correct; your new All-Terrain T/A KO tires must carry the same weight; so to carry that weight, please increase the pressure to 55-psi on all four wheel positions."
55psi? Really? You will be hating life super fast. The most I go with mine is about 42psi, and that is a very firm ride. If you want to be completely anal about the whole thing, go to the BFG site and find their load ratings chart for your KO. You will find that 55psi will be overkill. I can't believe someone from BFG actually told you to do that. Crazy.

mikecfry
Posts: 7
Joined: Thu Jan 23, 2014 8:10 pm
Location: South Jersey

Postby mikecfry » Tue Jan 28, 2014 9:31 am

Actually I have to say at 55 PSI it hasn't been the least bit rough. I did take the time to research the load tables myself last week to be sure, and found that the OE P265/65R17 tires are rated for 2,337 pounds at 35 PSI. The new LT265/65R17 are rated for 2,270 at 50 PSI and 2,420 at 55 PSI. So in reality the inflation should be something like 53 but that's splitting hairs. By comparison, if the size increases to LT285/70R17 then you only need 40 PSI to carry 2,315 pounds.

When I had LT285/75R16 on my Jeep I only ran about 34 PSI and that was with a 150lb steel bumper and 100 lb winch, but the smaller tires just need more pressure to get the right amount of air to hold the weight. Seems like there are not a lot of folks here sticking with the OE tire size? Have you ever had any warranty issues with modifications?

User avatar
NmexMAX
Posts: 796
Joined: Mon Oct 11, 2010 2:35 pm
Location: Northern New Mexico

Postby NmexMAX » Tue Jan 28, 2014 10:16 am

mikecfry wrote:Actually I have to say at 55 PSI it hasn't been the least bit rough. I did take the time to research the load tables myself last week to be sure, and found that the OE P265/65R17 tires are rated for 2,337 pounds at 35 PSI. The new LT265/65R17 are rated for 2,270 at 50 PSI and 2,420 at 55 PSI. So in reality the inflation should be something like 53 but that's splitting hairs. By comparison, if the size increases to LT285/70R17 then you only need 40 PSI to carry 2,315 pounds.

When I had LT285/75R16 on my Jeep I only ran about 34 PSI and that was with a 150lb steel bumper and 100 lb winch, but the smaller tires just need more pressure to get the right amount of air to hold the weight. Seems like there are not a lot of folks here sticking with the OE tire size? Have you ever had any warranty issues with modifications?
It's probably safe to say that most if not all of us are out of warranty. Although, I recently had my exhaust manifold replaced under warranty (emissions, 8 year/80k) and no questions were asked, only compliments given. As always, it depends on the shop and the modification associated with the repair needed. Even though I have some aftermarket exhaust, the manifold was still warranted and replaced free of charge.

Back on subject, my 33’s were at 45, and that was horrific both on and offroad, (obviously). With the near 35”ers now, I tried 35, still a bit rough and as of recently 30 seemed to be a better bet.

mikecfry
Posts: 7
Joined: Thu Jan 23, 2014 8:10 pm
Location: South Jersey

Postby mikecfry » Wed Jan 29, 2014 12:28 am

Thanks for the thoughts NmexMAX. I know warranty us always an in the air question with these kinds of things.

I would imagine that 45 in 33s would be rough! I don't have a Goodyear table, but BFG starts it's listings for LT325/65R18 at 35 PSI for a little over 2500 lbs. Assuming GY is similar then you definitely wouldn't want to be any higher than that. Assuming they are LT correct?

User avatar
akley88
Posts: 449
Joined: Sun Mar 03, 2013 1:45 pm
Location: United States

Postby akley88 » Wed Jan 29, 2014 9:01 am

my 33" are at 45psi, but the rough ride doesnt bother me

kevinthefro
Posts: 98
Joined: Tue Aug 27, 2013 4:14 pm
Location: Torrance, CA

Postby kevinthefro » Thu Feb 27, 2014 2:13 pm

After reading this I raised the pressure in my BFG AT KOs from 35 to 55. The ride does not seem to be appreciably rougher.

It didn't make any difference in my gas mileage, but I assume my contact patch on the road is flatter and I did gain about another 1/4" in lift!

Thanks for posting, Mike.

mikecfry
Posts: 7
Joined: Thu Jan 23, 2014 8:10 pm
Location: South Jersey

Postby mikecfry » Sun Mar 02, 2014 2:24 pm

Glad it helped!


Return to “R51 Brakes, Tires, and Wheels”