tow vehicle tires?

I am thinking about outfitting my '05 Tundra double cab with "E" rated tires. Will this enhance tow vehicle stability or are the factory tires ok for long distance towing?

[RockyMtnRay]

Originally Posted by tracker67

I am thinking about outfitting my '05 Tundra double cab with "E" rated tires. Will this enhance tow vehicle stability or are the factory tires ok for long distance towing?

Given the relatively light Gross Axle Weight Rating (rear) of only 3670 lbs for all Tundras...including the DC, the OEM tires with their "C" load rating have more than enough weight carrying capability to handle any load that is less than the GAWR. So you definitely don't need an "E" load rated tire.

However, load rating per se has very little to do with tow vehicle stability as stability is primarily correlated with sidewall stiffness. And sidewall stiffness in turn is much higher in Light Truck (LT series) tires than in Passenger (P series) tires of even the same load rating. Toyota, like nearly all other half ton truck manufacturers, equips all Tundra models with a P series tire mainly because they ride "nicer" (softer, more road shock absorbent). They're also generally a bit quieter than LT series tires and somewhat cheaper than equivalent LT series tires. If the manufacturers didn't use a "nice" riding P series OEM tire, people doing test drives would find the ride too harsh and go to the competition.

So, first of all, your OEM tires have more than enough load capacity for long distance towing. Secondly, if you want better tow vehicle stability, trade the P series OEM tires for identically sized (or as close as possible) LT series tires with the same "C" load rating. However, don't make the mistake of going to an "all terrain" style tire; a regular "mud/snow" tread design will be much more stable and have much longer tread life.

The OEM tires on my '03 4WD Tundra were the P series quasi-all terrain BF Goodrich "Rugged Trails" model in a 265/70R16 size. Immediately (and I do mean immediately) after buying the truck, I drove directly from the dealer's lot to Discount Tire and swapped the OEM tires for a set of LT series Michelin LTX M/S in the 265/75R16 size with a "C" load rating. I chose the Michelin LTXs for two reasons: (1) stiffer sidewall for greatly improved towing stability and (2) a reputation for extremely long tread life...many reports of 70K to 90K mile tire life.

After nearly 12K miles, I am extremely happy with the Michelins as they have more than lived up to my high expectations for towing stability, have shown almost zero tread wear, and have excellent traction on dry/wet/snowy roads. This is a tire I can highly recommend.

HTH

Thanks for the advise on the tires, I am working on the conversion to the ones you recommended. I've talked with Toyota about the transmission temp gage and am looking for the brake controller (my local dealer does not carry that brand). Doug

[RockyMtnRay]

Originally Posted by tracker67

Thanks for the advise on the tires, I am working on the conversion to the ones you recommended. I've talked with Toyota about the transmission temp gage and am looking for the brake controller (my local dealer does not carry that brand). Doug

Welcome on the tire advice...I can't think of anyone who has not really liked the Michelin LTX for towing.

As for the Prodigy...lots of places to get one....but you might want to get it at RV Wholesalers for only $99.99...that's about $40 less than at Camping World and other etailers. Plus I discovered that RV Wholesalers has the Toyota specific wiring harness for only $12.95 which means you won't have use the universal harness and do your own soldering/connecting to the Toyota provided harness. Another option is this Toyota specific Prodigy kit from BrakeControlller.com for only $124.95. The good news is that installation of a brake controller on any '03 and newer Tundra with the factory towing package is very easy and definitely a do-it-yourself job.

Am most curious what Toyota tells you about installation of a trans temp gauge...AFAIK this is not a dealer or factory option. I did my own installation of the trans temp gauge itself using an Autometer gauge and A-Pillar pod and had an independent shop install the gauge sensor in the transmision pan. If interested in doing your own, let me know and I'll send you a copy of a writeup I did for some folks at TundraSolutions. Just be aware that it's neither a simple nor an easy thing to do.

After following the thread on tow vehicle tires, and specifically those for the Toyota Tundra, I started searching the web. The LT tire is only available if you go to 265 75R 16 as opposed to the OEM 265 70R 16. The 75 is about an inch taller which means speedometer and odometer readings are going to be off a bit. How much so, and does that present a problem for those of you who have made the switch?

I'll be getting the 02 Tundra ready for picking up a new 2720 SD from The Car Show in August.

Gene Storm
Anchorage, Alaska

[RockyMtnRay]

Originally Posted by gsword

After following the thread on tow vehicle tires, and specifically those for the Toyota Tundra, I started searching the web. The LT tire is only available if you go to 265 75R 16 as opposed to the OEM 265 70R 16. The 75 is about an inch taller which means speedometer and odometer readings are going to be off a bit. How much so, and does that present a problem for those of you who have made the switch?

I'll be getting the 02 Tundra ready for picking up a new 2720 SD from The Car Show in August.

Gene Storm
Anchorage, Alaska

Yes, speedo and odo readings will change by about 3% (1 inch diameter change divided by average 31 inch diameter). After checking both readings on my '03 Tundra following installation of the larger tires (using both a GPS and highway mileage markers), I determined the odo reading after the tire change was 5% less than actual and the the speedo reading was (as expected) 3% below actual speed. Which just says the factory odo reading was about 2% low with the stock tires and factory speedo was pretty close to accurate.

Until I regeared the differentials by 10% (from 3.91 to 4.30), I concluded the following:

• The 3% change in the speedometer reading was enough to be aware that when driving at 70 mph indicated, my actual speed was about 72 mph. I just made sure that I matched the indicated speed on the speedometer to the posted speed limit...in doing so I knew I was a tad above the limit but still within the margin allowed by nearly all law enforcement. No more driving at "5 over the limit" though.
• The 3% change in tire diameter effectively reduced my axle ratio from 3.91 to about 3.82. The resultant loss in torque at the rear wheels was no biggie at lower elevations on flat roads but enough to be noticeable at higher elevations (over 6000 feet) and steeper grades (over 5%). Added a bit more justification for a long and pricey series of performance mods: headers, muffler, and eventually axle regearing.
• The resultant 5% difference between indicated and actual mileage resulted in about a 1 mpg difference in non-towing highway fuel economy calculations. So each time I gassed up, I multiplied the indicated miles by 1.05 before dividing by the gallons burned.

Bottom line was the diameter change wasn't a problem per se but it did produce some considerations in torque, gas mileage calculations, and awareness of actual versus indicated speed.

[Bill]

Did you ever ...

... measure your vehicle against one of those "Measured Miles" on the Interstate or the turnpike? In every vehicle I've owned for 30 years, the speedometer has always indicated 5% more distance than I traveled (1.05 miles) and the speedometer, of course, 5% faster than I was actually going. I don't actually know that this is a conspiracy by the automakers to make my car feel SPEEDY, but it has been remarkably consistent. Putting on larger tires should bring it back toward reality, by making it actually go farther per wheel revolution, and therefore actually go faster, without changing the odo/speedo readings. If I have all that worked out right.

Bill

[RockyMtnRay]

Originally Posted by Bill

Did you ever ...

... measure your vehicle against one of those "Measured Miles" on the Interstate or the turnpike? In every vehicle I've owned for 30 years, the speedometer has always indicated 5% more distance than I traveled (1.05 miles) and the speedometer, of course, 5% faster than I was actually going. I don't actually know that this is a conspiracy by the automakers to make my car feel SPEEDY, but it has been remarkably consistent. Putting on larger tires should bring it back toward reality, by making it actually go farther per wheel revolution, and therefore actually go faster, without changing the odo/speedo readings. If I have all that worked out right.

Bill

I haven't seen any of those "measured miles" stretches in literally years, maybe a decade or more.

But after the tire changeout I did check my truck's odometer and speedometer against both regular highway mile markers and a GPS over a 10 mile stretch of level road with the speedometer set at exactly 60 mph. I chose 10 miles to even out the minor variations of distance from mile marker to mile marker, to get enough distance that the .1 mile resolution of the odometer became less of a factor, and to minimize the human factors issues of exactly when the stopwatch and odometer reset were done relative to the markers.

The results of both the mile marker and GPS measurement methods were essentially identical (the mile markers were very close to accurate IOW) and showed the speedometer was low by about 3% and the odometer was low by 5% (it's not uncommon for the errors to be different for the speedo/odo). Keeping in mind this was after a 3% increase in tire diameter, it means that at least Toyota makes a very accurate speedometer and an almost accurate odometer. I should note that speed/distance measurement system in my truck is completely done by digital electronics involving a pulse generator on the transmission output shaft and a pulse counter in the odometer/speedometer.

I again did another very long test using the GPS only after the 10% change in axle gearing and found the speedometer was now 7% high
and the odometer was 5% high after 200 miles of travel. Since both the speedo and odo had a 10% change commensurate with the 10% change in gearing, I'm quite comfortable with my numbers.

Since I had the axle regearing done, I've purchased this electronic speedometer recalibrator but haven't yet installed it. A tad pricey at about $190 shipped but worth the avoidance of mental gymnastics (and any tickets) from the 7% speedo difference. Plus it'll bring my odometer mileage back to true so I won't be needlessly using up warranty mileage.

It's always been a trick with us Four Wheelers to get the math right to keep things even when changing gears and tires. Here's the formulas to do that:

2242 = 65 x 3.08 x 336 / 30

To use an example, let's say we want to know what gears should be installed when putting 36" tires on a transmission, 3.08 gears, and 30" tires in stock form. Since the truck doesn't have a tach, we first need to find out what RPM the engine is spinning at a given speed, say 65 mph. With this information, the formula looks like this:

rpm = mph x gear ratio x 336 / tire diameter

At 65 mph, the truck's engine is spinning at 2242 rpm, which is right in the optimum powerband for most V-8 engines. Now all that's left to do is plug in the new tire size and a couple different ratios available for the truck to see which one closely matches the RPM.

2263 = 65 x 3.73 x 336 / 36

As you can see from the above formula, 3.73 gears with 36" tires is optimum for restoring stock performance with this truck. Keep in mind that not all ratios are available for every axle, so do some research to make sure there's a ratio close to what you need available for your truck's axles.

Reprinted from:
http://www.superlift.com/information/gearing_up.asp

[RockyMtnRay]

Originally Posted by RealJeep

At 65 mph, the truck's engine is spinning at 2242 rpm, which is right in the optimum powerband for most V-8 engines.

Your math is correct but the "optimum" RPM and corresponding axle ratios you used for illustration are so low they gave me a real chuckle. On the smallish 4.6 to 5.6 Liter, multivalve, DOHC V8s that are now powering the kind of trucks/SUVs that people use to tow TrailManors, the optimum powerband is about 1000 RPM higher than on the old big-block pushrod V8s.

For instance, the Tundra 4.7 liter 32 valve DOHC has to be taken to 3400 RPM to get max torque, the Dodge Dakota 4.7 (also DOHC and 32 valves) reaches max torque at 3500 RPM, and the Nissan Titan (another DOHC with 32 valves) has max torque at 3600 RPM. Because their powerbands don't even start until about 3000 RPM, these vehicles have stock axle ratios of 3.91 to 4.10 with 31 inch tires; to get them into their powerband with 36 inch tires requires ratios of around 4.88 to 5.10.

My truck came with a 3.91 ratio, I went to a 4.30 ratio to be able to have the engine right at max torque with OD off when towing at 65 to 70 mph with a 31.6 inch diameter tire. Even with headers and a tuned-for-towing exhaust to lower the max torque point/powerband RPM range, my truck's engine is just coming into its powerband at 2600 RPM. With the stock 3.91 ratio, I was seeing only about 2800 RPM at 65 mph and that just wasn't far enough into the power band for good hill pulling power at the 6,000 to 12,000 foot altitudes where I tow. When I took it up to around 3200 RPM, hill pulling went much better but that meant towing at about 75 mph...which is faster than I felt was prudent. So I regeared to 4.30. The good aspect of the multivalve DOHC designs is the powerband holds very well all the way to redline RPM. So on steeper, high altitude grades I'll often run my engine for 7 to 10 miles in 2nd gear at a continuous 4500 to 5000 RPM.