Increasing Tire Size Slightly = Poorer Towning??

[Phred]

Hi there,

I have a 2002 Tundra AC TRD, that I use to tow a 22.5' Fifth Wheel. Now the towing is great, but it's time to buy new tires.....

Standard Size on my truck is a 265/70-16, but I cannot find any tires that are more than a 4 ply in this size (to handle the extra load of the 5th Wheel) Now, before you freakout about towing a 5th, and it adding too much weight, I am right on my Gross Weight (but not over)

I was thinking about upgrading to a 265/75-16 (you can get a 8 ply easy)which is overall a 1 inch diameter increase (31.6") but I am wondering if the increase in 1 inch will be noticable while towing, or if I should just stick with the 265/70's (30.6") I'm not worried about throwing out my Speedo too much (as it will probably throw it out about 3%..

Any advise would be wonderful.

Thanks!

[RockyMtnRay]

Originally Posted by Phred

Hi there,

I have a 2002 Tundra AC TRD, that I use to tow a 22.5' Fifth Wheel. Now the towing is great, but it's time to buy new tires.....

Standard Size on my truck is a 265/70-16, but I cannot find any tires that are more than a 4 ply in this size (to handle the extra load of the 5th Wheel) Now, before you freakout about towing a 5th, and it adding too much weight, I am right on my Gross Weight (but not over)

I was thinking about upgrading to a 265/75-16 (you can get a 8 ply easy)which is overall a 1 inch diameter increase (31.6") but I am wondering if the increase in 1 inch will be noticable while towing, or if I should just stick with the 265/70's (30.6") I'm not worried about throwing out my Speedo too much (as it will probably throw it out about 3%..

Any advise would be wonderful.

Thanks!

I did the same tire replacement...mainly to be able to use LT (Light Truck) series tires on my Tundra. The 3% increase in tire diameter also causes a 3% in rear wheel torque. As a point of comparison, a really good aftermarket muffler produces about a 3% increase in torque. So, qualititatively speaking, if you can detect the very subtle real improvements (not perceived improvements because of increased noise) from a muffler swap, you may notice the 3% drop from the increased tire size. But in either case, the change is right about most human's threshold of detection.

Bottom line: the torque drop will be real but also very hard to perceive; the increase in tire strength will be more than worth the slight drop in torque.

[2000LtdKen]

Phred,

I did exactly as you are thinking. I did notice a decrease in towing power on steep grades. Bugged me a little bit so I put JBA Headers and a Gibson muffler on my truck and got my power back. Its actually a little more lively now. If you buy Michelin LTX tires, you will not be able to spin the tires. Too sticky which is actually good in other ways.

HTH,

Ken

[ThomasE]

You can go with a LT245/75/16E which are common sizes, relatively inexpensive, and same diameter as P265/70/16.

[Phred]

Originally Posted by ThomasE

You can go with a LT245/75/16E which are common sizes, relatively inexpensive, and same diameter as P265/70/16.

I was thinking about going to the 245's.. But.. with the Big TRD fender flares, I don't want it to look like little pie cutter tires stuffed under there...

Friend of mine has a 3/4 Ton Chev, and he's got 245/75/16E's on his truck.. but.. They don't look as nice as a set of 265s..

Now.. If I could find 285/65/16's.. that would rock!

[Phred]

Originally Posted by RockyMtnRay

I did the same tire replacement...mainly to be able to use LT (Light Truck) series tires on my Tundra. The 3% increase in tire diameter also causes a 3% in rear wheel torque. As a point of comparison, a really good aftermarket muffler produces about a 3% increase in torque. So, qualititatively speaking, if you can detect the very subtle real improvements (not perceived improvements because of increased noise) from a muffler swap, you may notice the 3% drop from the increased tire size. But in either case, the change is right about most human's threshold of detection.

Bottom line: the torque drop will be real but also very hard to perceive; the increase in tire strength will be more than worth the slight drop in torque.

I'm thinking this is the route I am going to go (265/75's) but.. I don't like the idea of a loud exhaust.

Anyone have any other tips for improving towing performance. I was thinking about an Electric Fan, possible a cold air intake etc... Just not fan of loud exhaust....

[rambrush]

Originally Posted by Phred

I was thinking about going to the 245's.. But.. with the Big TRD fender flares, I don't want it to look like little pie cutter tires stuffed under there...

Friend of mine has a 3/4 Ton Chev, and he's got 245/75/16E's on his truck.. but.. They don't look as nice as a set of 265s..

Now.. If I could find 285/65/16's.. that would rock!

I currently have the 245's and they don't look to bad. My problem has been with the tire being a tad narrower it has been way to ez to light them up.

If Yukon and or US gear get busy and make us some gear sets I will be switching to the 255/85/16's. Those will fill the wheel wells pretty good.

[RockyMtnRay]

Originally Posted by Phred

I'm thinking this is the route I am going to go (265/75's) but.. I don't like the idea of a loud exhaust.

Anyone have any other tips for improving towing performance. I was thinking about an Electric Fan, possible a cold air intake etc... Just not fan of loud exhaust....

First, install JBA headers...with no other changes, you'll get a very useful 7% increase in mid range torque. JBA headers have zero effect...none, nada...on exhaust loudness. Other than a fairly substantial cost, this is one mod that has no downsides whatsoever.

2nd, a Gibson muffler is NOT loud. A tad louder than stock but definitely not anything like the usual "performance" exhausts like Flowmaster, etc. And unlike most exhausts, it actually gets quieter the more you open the throttle so towing is almost as quiet as stock. I absolutely hate loud exhausts and have very sensitive hearing...yet can easily tolerate the mild growl from the Gibson.

However, installing the Gibson (or any other muffler) without also replacing the exhaust manifold with headers is basically useless for towing purposes because the manifolds are the main "plug in the pipe" and, until they are replaced, changing the muffler has very little effect. But in combination with the JBA headers, a Gibson muffler swap (muffler only...not "catback") is good for about an additional 3% mid range torque gain.

3rd (and most importantly), the stock intake airbox/stock filter IS a cold air intake. Most of the aftermarket intakes (in particular the K&N and similar) are NOT cold air intakes (they mostly suck in hot engine compartment air). Furthermore, nearly all of the aftermaket intakes (like the K&N) substantially sacrifice mid range torque to get a slight gain in top end performance. And they make a really loud, obnoxious roar at large throttle openings...the very last thing you want when towing. And finally, nearly all the aftermarket intakes use an oiled gauze filter...a device that is almost guaranteed to contaminate/destroy the sensitivity of your mass airflow sensor because of oil that gets sucked off the filter and then baked onto the heated wires in the sensor. I personally wouldn't touch any of the usual aftermarket intakes (again the K&N or similar) with a 10 foot pole...even if you paid me $100000 to put one on my truck. IMO they are really that bad a modification for towing.

Another way to substantially improve torque is to regear your axle(s) with 4.30 gears. I went that route and got a 10% across the board gain in torque at the wheels. Highly effective. Also very expensive...roughly $1500 per axle, mainly because of the very high cost of 4.30 gears.

Finally, if you feel you really must do something to improve performance and don't want to do an exhaust mod or axle regearing, then you might consider a Unichip (piggyback ECU). Pretty pricey (around $1000) and you need to make sure that you get one that's been tuned for towing. But good for about a 5% to 7% gain in useful torque.

As for electric fans in lieu of the current engine fan to reduce parasitic drag, keep in mind that the engine fan really produces a very, very small load on the engine so long as its clutch hasn't engaged. Certainly it does produce a load (though I've never been able to detect any change in performance) when it does engage. My experience is that when the engine fan does engage when towing, it usually does so for a substantial period of time. Assuming that electric fans would also stay on for a substantial period of time...and have very high current demands when they do come on...I'd be concerned about either them draining the battery or putting enough load on the alternator that there'd be very little net gain over simply running the engine fan. My gut feeling is that electric fans in the long run will load the engine about the same as the current engine driven fan when towing. But if you want to spend some fairly substantial bucks to craft a dual electric fan install (they'll need to be very large dual fans, BTW), please let us know if you really did get a measurable net gain in towing performance.

[Phred]

Originally Posted by RockyMtnRay

First, install JBA headers...with no other changes, you'll get a very useful 7% increase in mid range torque. JBA headers have zero effect...none, nada...on exhaust loudness. Other than a fairly substantial cost, this is one mod that has no downsides whatsoever.

2nd, a Gibson muffler is NOT loud. A tad louder than stock but definitely not anything like the usual "performance" exhausts like Flowmaster, etc. And unlike most exhausts, it actually gets quieter the more you open the throttle so towing is almost as quiet as stock. I absolutely hate loud exhausts and have very sensitive hearing...yet can easily tolerate the mild growl from the Gibson.

However, installing the Gibson (or any other muffler) without also replacing the exhaust manifold with headers is basically useless for towing purposes because the manifolds are the main "plug in the pipe" and, until they are replaced, changing the muffler has very little effect. But in combination with the JBA headers, a Gibson muffler swap (muffler only...not "catback") is good for about an additional 3% mid range torque gain.

3rd (and most importantly), the stock intake airbox/stock filter IS a cold air intake. Most of the aftermarket intakes (in particular the K&N and similar) are NOT cold air intakes (they mostly suck in hot engine compartment air). Furthermore, nearly all of the aftermaket intakes (like the K&N) substantially sacrifice mid range torque to get a slight gain in top end performance. And they make a really loud, obnoxious roar at large throttle openings...the very last thing you want when towing. And finally, nearly all the aftermarket intakes use an oiled gauze filter...a device that is almost guaranteed to contaminate/destroy the sensitivity of your mass airflow sensor because of oil that gets sucked off the filter and then baked onto the heated wires in the sensor. I personally wouldn't touch any of the usual aftermarket intakes (again the K&N or similar) with a 10 foot pole...even if you paid me $100000 to put one on my truck. IMO they are really that bad a modification for towing.

Another way to substantially improve torque is to regear your axle(s) with 4.30 gears. I went that route and got a 10% across the board gain in torque at the wheels. Highly effective. Also very expensive...roughly $1500 per axle, mainly because of the very high cost of 4.30 gears.

Finally, if you feel you really must do something to improve performance and don't want to do an exhaust mod or axle regearing, then you might consider a Unichip (piggyback ECU). Pretty pricey (around $1000) and you need to make sure that you get one that's been tuned for towing. But good for about a 5% to 7% gain in useful torque.

As for electric fans in lieu of the current engine fan to reduce parasitic drag, keep in mind that the engine fan really produces a very, very small load on the engine so long as its clutch hasn't engaged. Certainly it does produce a load (though I've never been able to detect any change in performance) when it does engage. My experience is that when the engine fan does engage when towing, it usually does so for a substantial period of time. Assuming that electric fans would also stay on for a substantial period of time...and have very high current demands when they do come on...I'd be concerned about either them draining the battery or putting enough load on the alternator that there'd be very little net gain over simply running the engine fan. My gut feeling is that electric fans in the long run will load the engine about the same as the current engine driven fan when towing. But if you want to spend some fairly substantial bucks to craft a dual electric fan install (they'll need to be very large dual fans, BTW), please let us know if you really did get a measurable net gain in towing performance.

WOW!

Excellent Advise. Very well explained. I will have to look into the JBA headers, they sound the way to go..

THANKS!

Phred.

[Phred]

Well... after alot of research and checking out every tire manufacturers website, I seemed to have found the only LT rated tire in a 265/70-16.

BFGoodrich All-Terrain T/A KO, in an LT265/70R16D with a 117Q load/speed rating, after checking with the local tire shop (KalTire in Edmonton) this is an 8 ply tire, and can handle 2835lbs at 65PSI

Looks like this might make a great tire for handling those heavy loads!!

Attached is a picture and the downloaded specs sheet. Let me know what you think!

Phred

Originally Posted by Phred

Hi there,

I have a 2002 Tundra AC TRD, that I use to tow a 22.5' Fifth Wheel. Now the towing is great, but it's time to buy new tires.....

Standard Size on my truck is a 265/70-16, but I cannot find any tires that are more than a 4 ply in this size (to handle the extra load of the 5th Wheel) Now, before you freakout about towing a 5th, and it adding too much weight, I am right on my Gross Weight (but not over)

I was thinking about upgrading to a 265/75-16 (you can get a 8 ply easy)which is overall a 1 inch diameter increase (31.6") but I am wondering if the increase in 1 inch will be noticable while towing, or if I should just stick with the 265/70's (30.6") I'm not worried about throwing out my Speedo too much (as it will probably throw it out about 3%..

Any advise would be wonderful.

Thanks!

[mhileman]

That is the upgrade size I used on my 02 tundra and I had no problems at all towing a 3000 trailer, the over drive was ok on the flat and 10?% to 15% grades but nothing more than that I had to down shift to 3rd, marc

[tomhole]

Excellent choice. Based on reading every tire thread and reviw I could find, the BFG AT KO's and the Revo's seem to be the top at tires folks recommend. Let us know how they perform.

Tom