Light truck LRR tire question ...

[oil pan 4]

I am more worried about not running enough tire and having to pay the over heating and tread separation penalty. Been there done that, not going there again.

[ECONORAM]

That is constantly crossing my mind too, as I browse tires. I really don't want to have a tire without a sufficient load rating just because it's the "right" size I'm looking for.

[aerohead]

I'm looking at a Bridgestone, Dueller/Alenza (or something like that) LRR 235 75/R15 for the T-100.
*It has Traction AB which is better than the Grabber
*It has a treadwear rating of 800 which is almost twice that of the Grabber
*It's Revolutions per mile is less than the OEM tire and will reduce engine rpm by 4% (Rubber Gearing ).
*They were $112 each at Tire Rack's website.
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Long ago,when the metric tires were coming into the USA,at least one article came out on TPC tire technology,in CAR and DRIVER.
*Larger diameter allowed each tread element fewer road strikes per revolution,and with hysteresis factored in,the tire ran cooler,wasted less energy in deforming each tread element,for better mpg.
*Quiet bands were removed,as they absorbed power.
*Noise was an issue and the EPA was considering legislation for tire noise criteria.
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*Wider tires have greater aerodynamic drag although we can modify for that.
*Early LRR concept tires had no real world traction,so perhaps as far as safety goes,maybe we accept a compromise in efficiency until more black magic creates narrow,high grip.
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Slowing the engine down is 'typically' an efficiency move,according to Ricardo Engineering Consultants.
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And many messengers emphasize the importance for re-gearing cars which have been streamlined,to get the full benefit of a constant BSFC.

[rmay635703]

Originally Posted by oil pan 4

I am more worried about not running enough tire and having to pay the over heating and tread separation penalty. Been there done that, not going there again.

I've only had one tire "separate" and it was an old fleet farm desert dog $35 tire with 100000 miles and was over 10 years old.

All my other tires just blow the sidewall.

Wouldn't mind wearing one out due to age once again.

Ah well.

[aardvarcus]

I have experimented with various tires on my trucks and cars, as I have covered in past posts. As others have brought up, you have to consider many different points when selecting a tire, such as: Brand, Tread Pattern, Tire Weight, Diameter, Tread Width, Section Width, and Recommended Rim Width.

Then if you add the variable of potentially changing wheels to get other sizes, you have to look at Wheel Weight, Wheel Diameter, and Wheel Width.

For example, I recently bought my 2005 Toyota Tacoma 2.7L 5 Speed Manual 4x4. When I bought the truck, it had different brands of tires front to back. This is potentially very bad on a typical truck part time transfer case as there is no center differential, thus when 4x4 is engaged any difference in diameter front to back puts strain on the transfer case until a wheel skips. Turns out the brand of 245/75R16’s in the front were about ½” diameter taller than the ones in the back. So one of my first purchases for the truck was new tires.

The key elements I was looking at was maintaining fuel economy, maximizing traction, and increasing ground clearance. I chose to go from P245/75R16s on steel wheels to Michelin LTX M/S2 LT235/85R16s on factory alloys. There are obviously compromises in any tire choice you make, and your priorities may lead you to a different choice than mine.

I chose Michelin tires based on past experience with tires both on trucks and cars. I have always enjoyed great traction from them, and their M/S2 truck tire with tons of sipes is no exception. I can’t emphasize enough, get tires that match the driving you do. If you only drive off-road, don’t choose street tires. If your driving is all on road, don’t choose dedicated mud tires. If you do both on-road and off-road, choose all terrains or consider getting a spare set of wheels and having a off-road specific set of tires. At least that way when you get to use your off-road tires, they won’t be worn out from all the on-road trips.

I chose to go taller diameter (roughly 32”) for the extra ½” of ground clearance, plus the 4% increase in diameter corrected my speedometer error and slightly lowered my gearing, like going from a 4.10 to a 3.94. The downside is that extra ½” of ground clearance is an extra ½” of lift, making the truck taller and sending an extra ½” of air flow under the truck.

I chose to go with a 235/85 over a 265/75 to keep the width to the minimum necessary for my light truck. This aids in aerodynamic drag from the tires, lowers weight (all else equal), and aids traction in certain situations.

Aside: Note that I have found choice of width should be based on vehicle weight. I found heavier vehicles (like my 2001 7000 Lb Chevy 2500HD) may not enjoy the cornering abilities of a narrow but tall tire (like a Cooper Discoverer LT255/85/R16), but the exact same tire on a lighter vehicle (like my 4500Lb 1991 Chevy 2500LD) may corner just fine.

Because 235/85R16s are intended for big trucks, they are only available in a LT rated tire. This has advantages in higher max PSI and a tougher stronger tire. The downside is obviously weight. I was able to partially offset the weight gain by switching from the steel wheels the truck came with to factory alloys, losing 7-8 lbs. per wheel to offset the gain of 8-9 lbs per tire. Because the tire is further out from the center point, the rotational inertia took a bigger hit than the static weight gain increasing by 14.4% versus P245/75R16 on the factory steel wheels, where the static weight gain was about 1.5%.

So where does the rubber meet the road for fuel economy? Basically, looking at my fuel log the tire change has been lost in the weeds of typical tank variation. The positives just about perfectly balanced the negatives out. Thus my goal was achieved, getting a taller tire with significantly better traction without hurting my fuel economy.