Load Range C vs D tires (1 Viewer)

[Walking Eagle]

I've vasilated back and forth on the first set I want to get for the Lexus. Weither they should be MT's and get the street biased AT's later or do it in the reverse order. Since I sold my 40 last night, I have some cash, but I want to stay cheap. I was really set on the Yokohama Geolanter A/T+II as the street biased tires, but someone mentioned them only being load range C not D. Now I've vasilated and decided to get my MT's first. I'm going to misss the 40, and don't know when I'll get the cash for a second set, so for now, if I'll only have one - I want the rumblers

Is load range C (2535lbs at 35psi) vs. load range D (2910lbs @50 psi) a big deal? I'm comparing Yokohoma Geolander MT's in 315/75 which is C, vs. 305/70 which is D. I'm not really looking for advice on which tires, cause I'm going to end up getting what is affordable (also looking at Buckshot Mudders, but they're not available locally). What I'm concerned about is what performance am I giving up with load range C?

 

[Nay]

I think you will find load C to be a little bit soft from a sidewall perspective for a 5,000 lb+ vehicle. 2,500 lbs is fine...multiply by 4 and you have plenty of load capacity, but is that really 2,500 @ 35 PSI or it is 2,500 at max PSI of 50 or 60?

If you want some guidance from an offroad tire company, look at Interco. The trxus tires for 16" rims are D load, even though a 33 or 35x16 is clearly an offroad tire. For 15" rims they tend to be C load.

Nay

 

[IdahoDoug]

A load range C is perfectly adequate for the 80 as are the lighter duties than that. What you're getting with progressively higher ratings is a rougher ride, longer wear and slightly tougher carcass. I say slightly because generally the higher ratings are not accompanied by thicker rubber on the sidewalls or anything - they just have an additional structural wrap of steel or fiber to handle the higher inflation pressures without distorting. That higher inflation pressure is where the higher load rating comes in as a harder tire flexes less and therefore heats less.

What you're losing is grip on the road due to the harder rubber and the different shaped footprint due to higher inflation. At some point in the "higher rating" game the tire will be so lightly loaded compared to the use envisioned by the maker that it will wear funny because not all the tire is in contact with the road. Ever see someone's big manly tires at 20,000 miles with the centers worn out and the side lugs hardly touched? That's a classic screwup and may have nothing to do with overinflation - they'll wear that way even properly inflated. The tire will be tossed prematurely because the center is down to the wear strips, yet the rest of the tire face has 3/4 of its tread left.

What I'm trying to get at here is that it's not universally good to get heavier rated tires if you're not going to weigh that much (you aren't). In fact, it is more likely to be a bad thing in terms of traction and wear. If you're looking for tougher tires that can take offroad punishment, then choose tires from a company known for tires internally constructed that way, but in your proper weight classification. Don't try to get this mythical toughness by moving up grades.

DougM

 

[svensett]

Be sure to check the specs on the specific tires you are looking at. Larger "C" tires can have higher load rating than smaller "D" tires. LT generally are higher rated than an equivalent P tire.

 

[NorCalDoug]

Although it doesn't seem to be on your list of choices, I like the Goodyear MT/Rs that I have on my rig. I think it's a good compromise between decent on-road manners and (at least in my area) great off-road ability. The 315/75 R16 MT/R has a load rating of "D". I'm not sure if it's available in other places, but I saw that America's/Discount Tire (www.tires.com) has a $40 cash card available if you buy a set.


That said, the Goodyears are substantially more expensive, per tire than the Yokohamas...
Goodyear MTRs=$228 ea. (www.discounttiresdirect.com)
Yokohama A/T +II = $160 ea (www.discounttiresdirect.com)
Yokohama MT = $176 ea (ebay)
(free shipping on all the above)

I know it's not quite what you asked...but I think IdahoDoug covered the "C" vs. "D" thing.

 

[Hayes]

...and to follow NorCalDoug's example of completely disregarding your question ...

315/75 R16 Nitto Terra Grapplers can be had for about the same price as the Yokohama A/Ts, and they are D rated, if you care.

Hayes

 

[ed97fzj80]

As long as we're ignoring the original question, let's talk about running 315s on the street with stock gears. Since you're planning on a dedicated set of off-road tires, why not get something like a 265/75R16 and do a little better in the DD mileage department? I only ask 'cause I just got 285s for general purpose, and looking down the road I think it might make more sense to go closer to stock size for DD use.

Is this how "thread drift" happens?

 

[NorCalDoug]

As long as we're ignoring the original question, let's talk about running 315s on the street with stock gears. Since you're planning on a dedicated set of off-road tires, why not get something like a 265/75R16 and do a little better in the DD mileage department? I only ask 'cause I just got 285s for general purpose, and looking down the road I think it might make more sense to go closer to stock size for DD use.

Is this how "thread drift" happens?

I get better highway mileage with my 315s than I did with my 285s. City/mixed is a little less though.

 

[Mike S]

I like three ply sidewalls on off-road tires. I have changed a number of tires - kneeling next to the truck, in the mud, in the dark and rain. My flats usually seem to come from sidewall cuts. If you are going with MT type tires - get them with 3 ply sidewalls... Tires is one of the areas where it really makes sense to buy the best.

M

 

[ed97fzj80]

I get better highway mileage with my 315s than I did with my 285s. City/mixed is a little less though.

Same with my 285s vs. stock Michelins, but the amount of highway driving I do is tiny, so it doesn't really pay off.

 

[Nay]

I get better highway mileage with my 315s than I did with my 285s. City/mixed is a little less though.

That's because 33's on 4.10 gears creates worse "dead" spots in the transmission shift points than 35's on 4.10's. OD off with 35's is a better RPM match @ 70 mph than with 33's. With 33's you run about 3,000 RPM, which is a little bit higher than needed. With 35's it should be around 2,700.

Nay

 

[Walking Eagle]

As long as we're ignoring the original question, let's talk about running 315s on the street with stock gears. Since you're planning on a dedicated set of off-road tires, why not get something like a 265/75R16 and do a little better in the DD mileage department? I only ask 'cause I just got 285s for general purpose, and looking down the road I think it might make more sense to go closer to stock size for DD use.

Is this how "thread drift" happens?

I've got 265/70R16's on 16x7" 4runner rims - that's what's staying on those rims for now. They're going to look really tiny once the J's go on.

 

[ed97fzj80]

That makes sense.

That's because 33's on 4.10 gears creates worse "dead" spots in the transmission shift points than 35's on 4.10's. OD off with 35's is a better RPM match @ 70 mph than with 33's. With 33's you run about 3,000 RPM, which is a little bit higher than needed. With 35's it should be around 2,700.

Nay

But this I don't understand at all. I'm running about 2400 RPM @ 70 MPH with the OD on. It seems the mileage should be better there than at 2700 RPM with a heavier tire. I'm not saying you're wrong, just that I don't get it.

 

[DirtyHarry]

What you're losing is grip on the road due to the harder rubber and the different shaped footprint due to higher inflation.

This is the first I have ever heard about different tread compounds being used for different load range tires. I tried to find information about this on Goodyear's and BFGoodrich's website but came up empty. Can you point me to some sources Doug?

What I'm trying to get at here is that it's not universally good to get heavier rated tires if you're not going to weigh that much (you aren't). In fact, it is more likely to be a bad thing in terms of traction and wear.

I disagree. If we were talking about a minitruck or 4Runner then get the lighter load range, but 80s ARE heavy and I think that the higher load range makes sense. I am not sure why you think the wear would be worse, but I agree that traction can be an issue. This is offset though by the stiffer sidewalls not rolling over on the street and being less prone to puntures or slicing on the trail.

 

[Nay]

That makes sense.



But this I don't understand at all. I'm running about 2400 RPM @ 70 MPH with the OD on. It seems the mileage should be better there than at 2700 RPM with a heavier tire. I'm not saying you're wrong, just that I don't get it.

It depends how much the transmission is kicking down, how much you have to keep the skinny pedal to the floor because you are at the lower RPM's.

What I have found, and this is at 6,000 ft elevation plus, is that the truck is an absolute dog below about 2,600 RPM going uphill with 33's and 2.5" lift. From 2,600 to 3,200 it pulls pretty good, and 2,700-2,900 RPM seems to be the sweet spot.

That's why I don't like the gear calculators that take your gearing back to stock. This is not necessarily desirable...if you live in a hilly place, and you have worse aerodynamics due to lift, and you are pushing bigger rubber, then a stock RPM range is not always your friend (unless you have a turbo/super/V8).

But the big thing I have found with 4 speed auto trannies is the "dead spots" that become evident with larger tires, and at what speeds they are located. If you go to 33's, and it is now sitting between gear shift points at 50 mph and 65 mph, where you drive all the time, then you may find performance to be horrible. Going up a tire size may shift those dead points to spots where you don't tend to drive at a maintained speed, so the transmission isn't constantly hunting for the right gear, and you aren't constantly mashing the pedal to get it to kick down where you need it.

Going to a large enough tire allows you to lock out the OD gear reduction, without excessive RPM, to keep it in the sweet spot, while giving you a very low cruising RPM on downhills and flat surfaces. When you have a PWR mode to increase RPM's between shifts, this can actually be a very friendly combination as long as you don't mind having to manually shift out of OD. Now you aren't going to get better gas mileage than stock, and it isn't going to be faster than stock, but you may find that 35's actually feel better than 33's, because you aren't in so much of a middle ground in the transmission gearing ratios. At least where I live, 2400 @ 70 mph is not desirable...and it will dog up the long uphills, usually dropping to about 55-60 mph as a max sustained speed in OD.

But again, none of this works offroad, and that's where there is no substitute for diff gearing.

Nay

 

[ed97fzj80]

Now I see why it didn't make sense to me -- our highway cruising environments are much different. My cruising is mostly flat at 500 ft elevation, and I drive the Cruiser gently anyway. 2400 RPM @ 70 MPH is just fine here.

 

[IdahoDoug]

Harry,

Tire makers use rubber compounds tailored to all manner of applications from highway oriented (hard) to all season (softer) to offroad specific (softer yet) to winter specific (generally softest but lots of new compounds here). When a tire gets up into the D and E categories, these are seriously hard working tires and they generally have a harder compound than the same tire line in a P metric. Greater heat resistance, greater durability for a product really designed for commercial operators.

As for my wear comment, a mfr designs a tire carcass to have a certain shape at its recommended pressure and a certain static everyday load, which determine the shape of the contact patch. Running a D rated tire designed for a max load of 3000lbs with only 1500lbs on it means the tire may have a disproportionate amount of its load near the center and very little at the edges. If the tire was designed for a heavier vehicle weighing say 2000lbs on each tire, it may wear out the centers more quickly due to excess heat in the center, or to patterns of tread squirm that happen because the entire tread face is not in contact with the road as designed. Several variations of this theme are possible.

In addition, a high weight rated tire with less weight on it than the designer anticipated is somewhat like a heavy spring with less weight on it than expected in that it will bounce more. This can create improper wear as well with any slight balancing issue or roundness tolerance issue being exaggerated.

The best advice for tire selection is to choose a load rating matched to the weight range of your vehicle. In so doing, the poor hard working tire engineer who designed the tire to provide optimal wear and handling characteristics for your vehicle weight range will be satisfied with a job well done. My overall point is that choosing a super high load tire won't always get you benefits beyond bragging rights.

PS - Sounds like a great job you've carved out for yourself. Not just free lancing. Not just free lancing on a fun filled topic. But all the above plus living in (on?) Hawaii! Well done.

DougM