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Perhaps someone with knowledge of towing who happens to frequent here could enlighten me on something...

Every time I look at pickups set up for towing they often use low gear ratios, as low as 5.13 in some cases. Needless to say this kills economy when you arent loaded. What I don't understand is why low ratios are so necessary...

What I mean is, is it some kind of cost cutting measure by the companies (cheaper than a new transmission design or a more powerful engine rating) or is there some other advantage i'm not aware of?

I fully understand the physics - using a 4.56 ratio instead of a 2.29 ratio means almost twice the torque to the tires. But that's what transmissions are for. After you are out of first, or perhaps second gear, does it really matter? Short of situations like ratios too widely spaced is there any reason why either a better transmission, or a more powerful engine, couldn't solve the problem equally well?

I'm confused by modern tow ratings, in part. That a given model of frame, with a certain braking and suspension setup is rated for a given weight I take to mean that it's fully competent to handle that. On certain setups or past a certain point of upgrades already otherwise made the only difference seems to be a more powerful engine and a lower axle ratio. The only two cases I see this as being critical is starting from a dead stop going uphill, and maintaining normal (excessive) speed of traffic under a high aerodynamic load with a headwind. Those of us who don't even live in the hills or are content to drive 55mph (or slower) under certain load conditions or who have streamlined flatbed loads I would think should be able to do alot more with absolutely the same level of safety of someone who didn't get the 6 liter with 300+ hp and the 5-something axle.

If i'm wrong in some other area please correct me - whereas I agree of a danger of a load you can't even start in 1st gear uphill on hills within where you actually do drive in case you had to stop suddenly, and that you should always have enough to do that without clutch slippage or transmission damage, is there some other safety hazard i'm missing?


Put another way i'm trying to design a diesel tow vehicle around numerically low ratios for mpg while unladen. Diesel = not excessive power levels of 100-200hp favoring the midrange of that, looking for a less expensive to buy diesel instead of a power monster because this will see very intermittent use at best. Tow = 5 tons plus on a superduty chassis. Axle ratio = as low as 2.29 if I can get it, probably something more commonly available though.

I see two ways of insuring I can start in 1st gear. One way is by just using an SM465 "dump truck" granny gear transmission - 1st gear is 7.05:1 meaning torque multiplication to the axle is at least twice as much, and torque to the tires is likely comparable to running that 5.13. The second way is if I have a 4x4 all of those have a Lo range anyways, intended for creeping off road usually, but here it would be an unexpected on road stop in steeper hills until say i'm at the top of one, can stop again, go back to high range, and use the downhill to get moving in normal cruise ranges. All the sudden my worst case 2.29 axle turns into somewhere from a 4.56-5.13 right there, heck maybe I could even leave it there unless there is some problem of staying in low range. (just like I don't know why staying in 2nd at 55mph with the normal ratio would be a problem since that about compares to drive with the normally low ratios expected) Now maybe I wont be running 70mph pulling a fiver in the Rockies but that's why they have passing lanes if I happened to find myself there sometime.

Another option is just plain having more off idle torque and power, such as with a low rpm turbocharger added instead of another gear. (such as for my RWD fullsize sedan discussion in another thread)