I've been thinking about this for about a month now. I sliced open the sidewall of one of my BFG MTs 35x12.5x15 about a month ago. Now granted I know this tire is not known for super strong sidewalls like a Swamper or Michelin military tire, but it doesn't do bad on minis and 40s in our area. Actually, I've seen people run the same trails I'm running with these tires and have them last for 5-6 years even with monthly wheeling trips. This last weekend Uglibus sliced open two of his 37x12.50x15 Goodyear MTRs on the trail. We weren't in a section of overly sharp rock (comparitively for our area). He wasn't overly aired down either. I know a lot of hardcore guys who run the MTRs with great success on their lighter rigs in our area. In my quest to not make the same tire mistake twice I've been reading as much as I can about tires. I've noticed that almost all of the 16" rim sized tires have much higher weight ratings and ply rating than the same sized 15" rim tires. I could be mistaken, but doesn't the load bearing capacity come from the sidewall strength? If this is true, I can see where it would be very beneficial to run the larger rim sizes with higher weight ratings to prevent sidewall failures. Are 80 series too heavy for 15" rimed tires for wheeling? I also read about another 91/92 80 who also has been ripping out sidewalls on 15" rims today in California. The whole thing has me pondering the rim size debate.
Tire Theory!
- Thread starter ginericLC
- Start date
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I don't have a clue but I would guess that part of the increased load of the larger wheels is that you have less sidewall and air volumn for the same size tire. Less total sidwall area seams like it would be able to cary more weight.
R
robbie
Guest
I do think these MT/R work great on the lighter trucks. Last year I sliced two side walls on one run with in a mile or so of each other. Both tire were 315 on 16 inch rims. I really think a bias tire is the way to go with the heavier trucks. I use MT/R as a daily driver and camping tire with light wheeling. I will Travel long distances to wheel medium stuff with this set up and shy away from heaver wheeling with this set up. Before I had the two side wall slices in one run I had two other mishaps with the side wall. So in the space of 8-10 months I lost 4 tires to side wall damage. Heavier side wall protect better in some way but may not wrap around the rock in others. All seems to be a trade off. Any how what works for some may not work for others. Sorry to hear about micheal's loss, expencive tires to replace. later robbie
Rim size has little or no bearing on weight rating. Weight rating is achieved by everything from construction technique, ply materials, tread pattern, rubber durometer and thickness, etc, etc. There is no correlation to sidewall either.
In other words, you can have a 15" tire with a 4000lb rating and a 16" tire with the same tread width that is rated at 1200lbs due to these varying factors.
As was noted, sidewall strength in a 'wheeling tire is a tradeoff also. There are military grade sidewalls that will stop a large projectile (bullet), but the tire won't flex for crap at low PSI to grip rocks.
Finally, the 80 is not "too heavy" for 15" wheels for the reasons noted above. The 15" wheel was the industry standard for strength and to this day I believe there are far more choices for offroad tires in this rim size. You also get more sidewall for a given tire circumference vs a 16" tire - useful at low PSI operating pressures.
One reason a lot of serious wheelers use the bias ply is the sidewall does not have the characteristic bulge at the contact patch like radials are designed to have. Thus, there is less sidewall exposed to typical tire tearing rock.
I think you just got unlucky on that particular day. Though I will say driving style carries the day on this quite a bit. I knew people who could cut a tire on a gravel road, and have watched people on the trail behind me nail obvious rock outcroppings regularly all day long. HTH.
DougM
In other words, you can have a 15" tire with a 4000lb rating and a 16" tire with the same tread width that is rated at 1200lbs due to these varying factors.
As was noted, sidewall strength in a 'wheeling tire is a tradeoff also. There are military grade sidewalls that will stop a large projectile (bullet), but the tire won't flex for crap at low PSI to grip rocks.
Finally, the 80 is not "too heavy" for 15" wheels for the reasons noted above. The 15" wheel was the industry standard for strength and to this day I believe there are far more choices for offroad tires in this rim size. You also get more sidewall for a given tire circumference vs a 16" tire - useful at low PSI operating pressures.
One reason a lot of serious wheelers use the bias ply is the sidewall does not have the characteristic bulge at the contact patch like radials are designed to have. Thus, there is less sidewall exposed to typical tire tearing rock.
I think you just got unlucky on that particular day. Though I will say driving style carries the day on this quite a bit. I knew people who could cut a tire on a gravel road, and have watched people on the trail behind me nail obvious rock outcroppings regularly all day long. HTH.
DougM
- Thread starter
- #6
I was hoping IdahoDoug would pop up and say something. I wasn't talking about the actual rim being the problem but the rating of the tires for the 15" rim. It appears to me, and again I could be wrong, that tire makers make the tires tougher in a 16" rim. Does load carrying capacity come from only the ability to increase pressure or is the tire constructed heavier? I was thinking that to increase the tire load carrying capacity that it would be a combination of pressure increase and a stronger carcass. Is the ability to increase the pressure because of less sidewall? I really don't know. Maybe these continuing failures on 15" equipped 80s has just been a string of bad luck?
For Examples;
Interco TSL Radial:
SAM-73R
36x12.50R15LT 6ply 21/32 9.0 36.2 12.7 15x10 35 2600lbs
SAM-89R
36x12.50R16LT 10ply 21/32 9.0 35.9 12.6 16x10 65 3640lbs
So the tread has 4 more ply ratings and the weight rating jumps almost 1000 lbs from 15 to 16.
BFG AT:
35x12.5x15 2555lbs at 35psi no ply ratings on their website
315/75/16 3195 at 50 psi
Goodyear MTR:
35X12.50R15LT C 113P BSL 8.5- 11.0 10 12.5 34.7 2,535 @ 35
LT315/75R16 D 121P OWL 8.0- 10.0 8.5 12.3 34.8 3,195 @ 50
For Examples;
Interco TSL Radial:
SAM-73R
36x12.50R15LT 6ply 21/32 9.0 36.2 12.7 15x10 35 2600lbs
SAM-89R
36x12.50R16LT 10ply 21/32 9.0 35.9 12.6 16x10 65 3640lbs
So the tread has 4 more ply ratings and the weight rating jumps almost 1000 lbs from 15 to 16.
BFG AT:
35x12.5x15 2555lbs at 35psi no ply ratings on their website
315/75/16 3195 at 50 psi
Goodyear MTR:
35X12.50R15LT C 113P BSL 8.5- 11.0 10 12.5 34.7 2,535 @ 35
LT315/75R16 D 121P OWL 8.0- 10.0 8.5 12.3 34.8 3,195 @ 50
I know this doesnt help much but i had no problems with my MTR's out there in the owyhee's all though there are some trails out there that have tore up swampers too. what trails were you on? I am leaning toward TSL SX's for my next set as Fred the monsters have Riden quite nice. I know you DD your rig and that is where you are going to find your issues. Have you thought about going Military Michelin. I know Deisel Cruiser Head has a set sitting on my old rims off of my 80. Maybe i could through em on and try em out for ya. Good luck with the tire saga.
He may also be selling them if i remember right. (the tires not the rims.).0
He may also be selling them if i remember right. (the tires not the rims.).0
- Thread starter
- #8
I emailed Andre. I wonder what they ride like. I know they are bulletproof (literally). Also I think with their width I might be inclined to even push my track width even further out. Maybe 2.75" or 3.00" backspaced wheels?
alia176
SILVER Star
Take a look at the specs for BFG MT/KM on tirerack (under spec). 35x12.50 15 have a rating of C and 315 75 16 have D with a huge price increase ($158 vs $203 for metric). Someone told me that the metric sizes tend to be for commerical use, hence the higher load rating. However, my Geolander AT II 315 75 has a load rating of C. Go figure!
well sorry guys... i beat ya to Andre's michelins they will be going on 40 later tonight after the sun goes down and the temp drops....
they are gonna look sweet on "CoCoNut"
dan
they are gonna look sweet on "CoCoNut"
dan
Eric,
The failures on 80s you've mentioned don't seem to have anything to do with weight rating or rim size. They were sidewall cuts IIRC and the right rock can cut any tire.
Weight ratings. The ability of a tire to withstand heat, and its ability to not generate heat are key in building a tire that can handle weight. As a tire rotates, it flexes each time it touches the ground. This generates heat. Go faster and it generates more heat per second while the ability to shed heat only increases a little. A highly inflated tire flexes little and therefore generates less heat than it would at a lower pressure. So, inflation pressure max is highly correlated to load capacity.
What gives a tire a higher PSI max is its construction, materials and other design factors. Higher pressure load rated tires are definitely built more ruggedly, weigh more and frequently are poor choices for offroading due to the use of hard rubber and tendancy to have road-oriented tread patterns. HTH.
Having covered a bit on PSI and load carrying ability, I don't think this is what you're after for offroad durability. Many times, a tire built to flex at low pressure will go over (and drag a sidewall against) rocks unscathed that will cut a tire right behind it inflated to a higher pressure. So, an offroad specific tire might meet your damage criteria well. Unfortunately, tire design is a tradeoff like many things and it may not provide the DD stability or other factors. HTH.
DougM
The failures on 80s you've mentioned don't seem to have anything to do with weight rating or rim size. They were sidewall cuts IIRC and the right rock can cut any tire.
Weight ratings. The ability of a tire to withstand heat, and its ability to not generate heat are key in building a tire that can handle weight. As a tire rotates, it flexes each time it touches the ground. This generates heat. Go faster and it generates more heat per second while the ability to shed heat only increases a little. A highly inflated tire flexes little and therefore generates less heat than it would at a lower pressure. So, inflation pressure max is highly correlated to load capacity.
What gives a tire a higher PSI max is its construction, materials and other design factors. Higher pressure load rated tires are definitely built more ruggedly, weigh more and frequently are poor choices for offroading due to the use of hard rubber and tendancy to have road-oriented tread patterns. HTH.
Having covered a bit on PSI and load carrying ability, I don't think this is what you're after for offroad durability. Many times, a tire built to flex at low pressure will go over (and drag a sidewall against) rocks unscathed that will cut a tire right behind it inflated to a higher pressure. So, an offroad specific tire might meet your damage criteria well. Unfortunately, tire design is a tradeoff like many things and it may not provide the DD stability or other factors. HTH.
DougM
