Quote:
Originally Posted by Old Mechanic
1725 X 3.42/3.73=1581.6
regards
Mech
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Thanks, Old Mech. It does look pretty much like a 200-rpm drop.
As I tend to forget the details of truck spec and gear numbers I'm going to lay it out in this post I can reference in future; to show a range of what travel speeds can be made with the 3.42
across the ideal 1,300 - 1,500 rpm range per gear choice.
The calculators by
Bowling & Grippo are an old favorite of mine from when I was researching how to get max FE from a big block Chrysler set up for TT towing a dozen and more years ago.
NEW VENTURE 5600: This six-speed is used in light duty Dodge pickup trucks from 1998-2005. All forward speeds are fully synchronized. This unit has an aluminum bell housing, cast-iron case & extension housing with a top mounted shifter. Available in both 2WD and 4WD versions, this unit weighs 360 lbs. The transmission is rated medium duty capable with a GCW of 26,000-lbs.
Transmission Ratios:
FIRST 5.63
SECOND 3.38
THIRD 2.04
FOURTH
1.39
DIRECT
1.00
OVERDRIVE
0.73
Stock tire size is 265/70R-17
31.4" tall at 657-rpms per mile
(MICHELIN LTX A/S Load Index 121 (E-Range)
With these book numbers entered it looks as though I'd be able to run:
* School zone at 20-mph in Fourth at 1,081 (or in Third at 1,494-rpm)
* Town at 30-mph in Fourth at 1,527-rpm
* Town at 35-mph in Direct at 1,281-rpm
* Town at 40-mph in Direct at 1,464-rpm
* Town at 53-mph (freeway) in OD at 1,416-rpm
* Country at 55-mph in OD at 1,470-rpm
*
Target: 57/8-mph @ 1,523/1,550 rpm
(Versus current rpms of 1,725/50-rpm at this speed)
* Country at 60-mph in OD at 1,604-rpm
In other words, all 20-40 mph town driving, and all 55+ mph country driving is within or just barely atop the 1,300-1,500 desired rpm range. Can't ask for more than that! To my way of thinking, no need for a high-maintenance, questionably reliable
Gear Vendors second overdrive unit (at $4000) or in changing tire size.
Winding out each gear a bit further than at present (time/distance, not rpm) ought to also make for some smoother transitions if I am correct.
As the range for towing is generally 1,400 - 2,200-rpm I ought (with this type of lightweight aero TT) to be able to maintain headway on the flats barring bad crosswinds at these same rpms, and still be able to "pull" the mountainous terrain at only a slightly slower speed than before (and nothing was slower than a few of the big trucks I've driven).
.