Tow Ratings Conundrum

I've been trying to sort out how manufacturers arrive at their tow ratings, and quite frankly, putting a person on the moon must have been easier.  I have a 2003 Toyota 4-runner Limited, 4X4, V-8 with tow package.  I'll be buying a new TM 3023, so I'm sure I have the tow capacity -- at least several of you folks have given me assurance.

But as I look at the specs, I become more confused.  Unless you've recently been on the Toyota website, you'll find they have changed their tow ratings for the 4-Runner (at least those produced after 5/01/03 so the site says).  Used to be all 4-runners were rated at 5000# irregardless of engine.  That's not so anymore.  The V-6 is still rated at 5000#; however, the V-8 is now rated at 7300# (2WD) and 7000# (4WD) both using W/D hitch.  So what might have changed to cause the increase?

The V-8 has less horsepower (235@4800 rpm vs 245@5200 for the V-6); however, it has more torque (320ft lb @3400 rpm vs 282 ftlb @3800 for the V-6).  In terms of towing I assume more torque is better than more horsepower -- is that correct?

For giggles, I looked at the Ford website just to make some comparisons.  I looked at the F-150 and noticed that in going from the V-6 to V-8 the towing rating went from 9000# to 12000#.  Any suggestions why Ford increased by 3000# while Toyota only changed 2000#?

I've also read on "other" RV sites that wheelbase is a big item.  Usually it has to do with conversations about sway.  That makes sense to me -- shorter wheelbases might be more prone to induced oscillations (sway).  But for 2003, Toyota increased the wheelbase (don't know what the 2002 was, but it was less).  Even with the longer wheelbase and greater hp engines for 2003 (before those produced after 5/01/03), Toyota was still rating the 4-Runner as a 5000# tow capacity.  I compared the 4-runner to the F-50 wheelbase (Toy = 109.8";  F-150=119&quot.

So here's my confusion -- 4-Runner V-8 compared to an F-150 has 4 MORE horsepower and 27 MORE ftlb of torque, but 9.2 inches LESS wheelbase so how does the F-150 wind up with almost 3000# more tow capacity?

It's enough to make my hair hurt......

Ed

[kempert]

More torque is better than more horsepower.  Toyota truck engines are designed to get more torque out of less horsepower than Ford, GM, & Dodge.

[RockyMtnRay]

And towing capacity is not just a factor of engine torque and horsepower. Other factors include strength of the frame (assuming there is one), strength of the driveline behind the engine (transmission/transfer case, driveshafts, pinion gears, axle housings, axle shafts, wheel bearings & assemblies), suspension components, etc.

Even when comparing two engines of equal torque and/or horsepower, you have to consider what the shapes of the torque and horsepower curves are, especially what minimum rpm is needed to generate sufficient torque to get the combined rig (tow & trailer) moving from a dead stop. For instance, some 1.8 liter motorcycle engines are now putting out well in excess of 200 hp...but they're doing at somthing like 13,000 rpm...and I certainly wouldn't want to lash one up to 4000 lb trailer and try to start up a steep hill from a dead stop.

And finally, every engineering team (and company) has their own standards regarding margins for errors and longevity when their systems are taxed to the maximum ratings on a sustained or repititive basis.

Wheel base has something to do with it but I suggest you look at the weight of each truck. Towing makes demands that require horsepower, torque, wheel base, and weight. The weight being found mostly in the frame of the truck, a heavier frame can handle more weight in tow.

There are very few 5th wheel campers that can be pulled by half ton trucks (F150 Ford, 1500 GMC, Chevy). Most suggest at the least three quarter ton, F250 or 2500. Of course the larger the trailer to be pulled the more truck you need. The big Fivers are pulled by nothing less than the F350/3500 and most drivers prefer the F450 or F550. The funny thing is that the same engines and transmissions can be had in all weight ratings. You can get the big honking engines in the whole line.

All of this is just for your information, your SUV should pull anything TM puts out. I think you are well set. Not that the following differs from any other trailer/tow combo but you should pay notice to signs that say something like "Wind currents ahead". "Strong wind currents" anything along that line, they are placed there for a reason and the lighter your tow the more you should slow.

You guy's are forgetting an important factor in towing...
Rear axle ratio !!  The lower the ratio the more weight you can pull


Jack & Gayle

You guys are all correct.

Cooling, fuel system and brakes are also important.    

I have had the pleasure to test with Auto OEM at their proving ground and around NV, AZ, and CA.  You have probably seen these engineers around - Vegas, Kingman, Phoenix, Mesa, South Mountain, Lake Havasu, Davis Dam, Baker's Hill, Death Valley...

They use trailer dyno or actual trailers to validate the towing ratings.

Yessiree! You've covered it all. As a quick measure. Look at your vehicle GVWR on a Toyota and on a FORD, GM or DODGE truck. I'll bet you'll find that the domestic trucks are all heavier by a good bit.

As has already been discussed here, they are heavier due to componentry. Heavier duty axles, with low ratio, heavier trani's, engines, frames, cross members and larger radiators, and cooling system modules....

this all helps to bring up the towable ratings.

Gregg

As a Follow-up to RED_ APACHE's  Reply. a 'Lower Axle Rato' actually has a higher number !
For Example, an Axle Ratio such as 3.73 can tow more weight than a 3.55 !

Dr. Disk