Water-Bug wrote:
roadking59 wrote:
valhalla360 wrote:
If you are looking at new trucks, the axle ratio isn't as critical as it once was.
In the old days of 3 speed transmissions (and to a lesser but still important degree 4 speed transmissions), the ratio was important. The lower ratio rear end would give you better economy running empty but when loaded, it would drop down a gear and you would have to run at inefficient high rpm when stressed at all. Going to a higher ratio would allow you to stay in the top gear most of the time.
With the newer 6-8 speed transmissions, they can compensate by selecting a lower gear when needed but with just a modest increase in rpm and dialed in for efficiency.
Really! Who uses a dually to go off road...Funny!
FUNNY IS RIGHT!! I didn't see the term "off road" anywhere in the quoted text.
While I agree, a dually isn't a great off road truck, I never mentioned anything about duallys or off road. It applies equally well to 1/2, 3/4 and SRW 1 tons.
The point is you have to look at the gear ratio from the back of the engine to the wheel.
In the past with only 3 or 4 speeds, If you had a 3.7 (or lower) rear end, once you dropped out of top gear, the overall gear ratio changed significantly, so if you did a lot of towing, you would be running high rpm with the engine relatively lightly loaded on a regular basis when you meet even modest hills. While it shouldn't damage anything, it's noisy and inefficent.
The old solution was to put a higher ratio rear end in so that the engine wouldn't drop down unless it was a really steep hill. The down side is when empty, the rpm will run a few hundred higher than the engine really needs, so it loses efficency when running empty.
Ultimately, you looked at how much driving around empty vs loaded and pick the truck that matched your use best with the higher 4.0+ ratios favored for heavy towing.
With the newer transmissions with more gear ratios available, the truck can run at relatively low rpm when empty in the highest gear and when you load it up, it has the option to select a gear that keeps the engine rpm and loading much closer to the ideal output of the engine rather than just winder her up to the red line.
One clarification: If you are pushing to the upper limits of the towing capability, the higher ratio rear ends, I believe, still get slightly bigger tow ratings.
