Ok To Tow With 20'?

[ab]

I have recently installed Michelin LTX M/S 275/55R20 on our Sequoia. The tires and wheels are rated to carry 8800lbs total - GVWR = 6600lbs, total truck weight while towing with four passengers is 6300lbs with WDH. Travel trailer weighs about 4500lbs loaded (trailer axels) GCWR+-10800Lbs. The larger and heavier wheels seem to make the truck downshift more easily on uphill grades running empty. My question is will this be noticable during towing and will it add undue stress to the truck? It already drops to second on many long steep grades on the I-5 (with stock setup). Does anyone have any experience towing with 20" wheels / 32" tires?

[HBjeff]

i wouldnt do it. you are at the GCWR, AND you have larger tires, AND much heavier wheels. the load alone is alot of strain on the tranny, but with those taller tires, its overkill IMO.

[RockyMtnRay]

Originally Posted by ab

I have recently installed Michelin LTX M/S 275/55R20 on our Sequoia. The tires and wheels are rated to carry 8800lbs total - GVWR = 6600lbs, total truck weight while towing with four passengers is 6300lbs with WDH. Travel trailer weighs about 4500lbs loaded (trailer axels) GCWR+-10800Lbs. The larger and heavier wheels seem to make the truck downshift more easily on uphill grades running empty. My question is will this be noticable during towing and will it add undue stress to the truck? It already drops to second on many long steep grades on the I-5 (with stock setup). Does anyone have any experience towing with 20" wheels / 32" tires?

GCWR on the '03 Seq is 11800 (same as Tundra) so you have about 1000 lbs of safety margin with stock tires. I'm running the LTX 265/75R16 tires on my truck (31.6 inch diameter, 3% larger than the stock 265/70R16 which has a diameter of 30.6); your new LTX 275/55R20 tires have a diameter of 31.9 inches or about 4% larger than stock. That means you're getting 4% less torque to the road (same as using a 3.74 axle with stock tires).

Since I noticed a reduction in towing performance with my tires, you will certainly notice a towing performance loss from a 4% reduction in torque especially when towing up long grades.

Since GCWR is at least partly determined by rear wheel torque, your effective GCWR is now around 11,300 lbs. Since that's still significantly greater than your total weight, I'd say you're not putting undue stress on the vehicle.

You have several options. Since you're still below the effectively reduced GCWR, you can do nothing more and simply learn to live with reduced towing performance. Or you regain the lost torque by either regearing the axle(s) or increasing the engine's mid range torque by installing headers (or both).

Regearing is not normally a do-it-yourself project and costs around $800 per axle with OEM gears...if you regeared with 4.10 gears you'd have about a 5% torque increase (almost exactly the loss from the oversize tires); with 4.30 gears, you'd get a 10% torque gain. Regearing is effective across the entire RPM range. With 31.9 inch tires, I would not recommend going higher than 4.30...the next step up is 4.56 and that's really too high for freeway operations.

Headers are good for about a 7% mid range torque gain so you'd more than make up for the torque loss from the oversize tires. I personally think that ceramic coated JBA headers are the most cost effective option for towing but you could also get TRD headers and possibly have them ceramic coated. For a variety of reasons, I would not recommend other header brands. Cost of JBAs will be somewhere around $600 to $1100 depending on where you buy the headers, whether you get them with the ceramic coating (Titanium ceramic is recommended for towing), and who does the installation.

FWIW, I regeared with 4.30; installed JBA headers and a Gibson muffler (another 3% gain) for a total of 20% increase in usable torque compared to stock (17% over stock with the larger tires). Even at the very high altitudes that I tow at (anywhere from 6000 to 12,000 feet), I seldomly have any downshifts to 2nd with my 4000 lb trailer as long as the road grade is 6% or less.

[ab]

Thanks for the reply Ray. I thought the Sequoia and Dcabs had 4.10 gearing and the AC Tundra had 3.90? I do know that in stock form my Sequoia pulls off the line with much more ease than my AC Tundra (towing). I attributed this to the lower gearing in the Seq. If this is true the Seq. should pull, with 32" on 20's about the same as my stock Tundra? Maybe I'm all wrong on this? Thanks...

[HBjeff]

if you have 4.10 gearing, then yeah that makes a difference. i forgot about that, because the 05 Dcab has 3.90s now

[RockyMtnRay]

Originally Posted by ab

Thanks for the reply Ray. I thought the Sequoia and Dcabs had 4.10 gearing and the AC Tundra had 3.90? I do know that in stock form my Sequoia pulls off the line with much more ease than my AC Tundra (towing). I attributed this to the lower gearing in the Seq. If this is true the Seq. should pull, with 32" on 20's about the same as my stock Tundra? Maybe I'm all wrong on this? Thanks...

My bad. I forgot the '03 Sequoia came with 4.10 gearing, undoubtedly due to its weight (about the same as a DCab Tundra). So, yes, your Seq should pull...with the new tires...about the same as a stock Tundra that's equally loaded down.

That being said, if you want to get better towing performance, you'll need to go to at least 4.30 gears (which are pretty rare and expensive) if you want to regear. I think you'll be happier if you simply go the header route instead...and maybe add an aftermarket muffler after you get some experience with the headers.