Super close gears on larger trucks?

[Chapap]

I’ve noticed that on Uhaul trucks and 3/4 and 1 ton trucks that upshifting only drops rpm by a few hundred… on some of them at least. The reasoning I came up with is that the actual “transmissioning” is done by the torque converter and the gears aren’t actually that close. Am I in the ballpark?

 

[Eddo Rogue]

I think both the transmission and axle gearing is a whole different setup. But yea larger trucks have closer ratios and lower overall gearing...that's why they are screaming at 65mph lol. An extreme case would be the big rigs that are like 15-20 gear transmissions, very low granny gears.....10mph in 5th gear, on its way to 20th gear lol. Big rigs are very amazing to me. Sometimes the same engine that is a 1/2ton will be in a 3/4-1 ton, so I'm sure there's some tweaks to make the same engine pull that much more weight.

My F150 has an engine that is also offered in the 3/4 ton F250, and it does seem my towing capacity is limited more by chassis and brakes than power. My brakes suck in general. Got a big brake kit ready to swap. Sorry if that got a little off track.

 

[Chapap]

I recently rented a fire uhaul with a 6 speed. From 10pm to 50mph the rpm would only change by 400 or so. That doesn’t seem to be nearly enough for that speed change. I figured the TC was doing most of the work.

it was similar to my old motorcycle. One gear with a TC. With a little throttle feathering, I could go from 0-75 at a steady 2500 rpm.

 

[Eddo Rogue]

TC could be locking up later, letting the engine slip instead of stall when lugged in a taller gear. Kind of like how the drag racers have high stall TC's, except the uhaul is high slip lol.

 

[scotts90ranger]

There's some of that going on but with the new 6-10 gear transmissions you aren't going to have much rpm change especially at low engine speeds... they do that on purpose to keep the engine in the peak torque range where it is efficient and clean (main reason, emissions drove transmission changes).

Most newer ratios are less annoying than the ZF5 in my '97 power stroke F350, it makes almost no boost under 2000rpm so I try to cruise at the 2000rpm point which seems to give me the best economy, the fun part is mountain passes towing a good load... up to 12000lb total it doesn't care but get up around 18k pounds and driving uphill for 30 miles without an intercooler and it loses some steam... The fun part is the 3 4 spread, when it's mad I have to go up hills at 38mph because it's 2500rpm in 3rd gear or 1600rpm in 4th gear... If I had an intercooler and new injectors I'm sure I could hold 4th at 50mph but not with these worn out injectors and no intercooler (things get warm if I push it any harder...)

 

[cschannuth]

Many trucks have eight or 10 speed transmission nowadays so twice the gears equals half the RPM change compared to a four speed.

 

[ZMan]

Keeping the rpm in the peak torque range is key when towing/hauling. Lower gear ratios also make it easier to get going.