2017 dsdp gear ratio

[redbaron73]

I see that the Freightliner has a 4.63 ratio, and Spartan has a 4.78. Assuming a person drives 75mph, which would yield the better economy ?

[Skip426]

Gear ratio is only part of the equation, tire size , engine RPM, torque band info.

The coach is as aerodynamic as a shoe box , fuel economy drops with speed.

Cummins produced a similar document to this ; Cat info on motor home economy; but the conclusions were the same. Worth a read.

EDIT : But if all things are equal , tire size engine etc. the ratio difference is 3% if my math is correct, assuming 2,000 RPM with the lower ratio ; would equal 2060 RPM with the higher. Slowing down, 2.25 mph would yield the same RPM and economy . Theoretically.

[Mr_D]

Our '02 Dutch Star with ISC 350 and weighing about 32,500#'s, towing our 4,500# Ody got less than 8.0 and I used 7.5 to gauge costs when planning. It was turning 1650 at 60 mph.

Our present CC with ISX 650 and weighing about 50,000#'s and towing the same Ody gets 7.6 overall. The ISX is turning 1350 at 60 mph.

[redbaron73]

The differences stated above are based on the 2017 dsdp 4369. It appears as the numbers are insignificant, which is what I was assuming. Thank you!

[fixit1957]

I would not say it is insignificance. I have been rebuilding and selling differentials fo 39 years at work. 4.63 to 4.78 is a normal 1 step difference. The Freightliner uses a Mercedes 2N Differential. Spartan is using a Dana or Meritor differential. If a customer calls in and wants to go faster at the same rpm we would sell a 4.63 if they had a 4.78. Conversely if you want more pulling power go to the 4.78 from the 4.63. If you goto our website we have a link to a ratio chart so you can see thr speed/rpm difference. PM me and i well send a link. Randy

[cwsqbm]

Originally Posted by redbaron73

I see that the Freightliner has a 4.63 ratio, and Spartan has a 4.78. Assuming a person drives 75mph, which would yield the better economy ?

I'm 90% it's a typo that's been carried over from a long time ago. In the past, when the non-tag DS had a smaller motor, the non-tag has a 4.78, and the tag had a bigger motor and the 4.63. Now, all DS have the same motor, so it'd make no sense for the light non-tag to have the 4.78, and the heavier tag models to the 4.63. I'd noticed this a couple years ago. It never mattered because there was no choice of chassis.

If you look at the info in the very end of the "2017 Dutch Star updates and standard features" pdf, the final pages are from Freightliner and shows both tag and non-tag models have the 4.78.

EDIT: I was wrong. It's actually backward, and I'm a bit confused. All data below is from brochures, so take it with a grain of salt.

2014-2016, all had 450hp ISL. Tag had 4.63, non-tag 4.78
2011-2013, all had 4.63. Non-tag had 400 ISL, tag had 450 hp ISL.

One other detail is what size tires are on the drive axle of tag and non-tag DS? That could also effect things.

Someone that cares more than me might want to ask Newmar.

[LDMcL]

cwsqbm:

I too had wondered about the axle ratios shown on the Dutch Star brochures. (Non tag axle 4:78:1---Tag Axle 4.63:1)

I took a few moments to look at the Freightliner Custom Chassis website and found the following information for 2016, (2017 information not yet posted). I did not look at any previous years.

Dutch Star non tag:

Rear axle:
Detroit DA-RS-23-4 24,000 lbs capacity axle ratio 4.78:1
Tires - Michelin XRV 305/70R 22.5 20-ply

Dutch Star tag:

Rear axle:
Detroit DA-RS-21.0 21,000 lbs. capacity axle ratio 4.78:1
Tires:
- 252" WB-Michelin XRV 305/70R 22.5 20 ply
- 288" WB-Michelin XRV 315/80R 22.5 20 ply