Anyone with an 05, riddle me this....

camshaft · February 14, 2005

Just curious if anyone with either 3.42's or 4.10's wud post what their cruising rpm's are at the following speeds:

60 mph

70 mph

80 mph

I am looking for these values using stock tire size....i think they are 265/70/17.

Any info would be great

WyRam · February 14, 2005

I have nothing to compare to but on my 03 Ram 3.5 to 3.92 there was only 75rpm difference at 60 mph...........4.10s in mine and on 2 200 mile round trips averaging 70mph I got 17.2 mpg.......

neoh77 · February 14, 2005

According to the tach I am at about 1800 rpm's at 70mph

3.42 gears/auto/4.8l

I haven't hooked up my laptop to see if that's true or not, but it would be close.

redvett · February 14, 2005

My 04 with 3:73 and 265/75R16 is running 2000 at about 71 mph wish i had 3:42 for the 1.5 mpg extra.

WyRam · February 14, 2005

My 04 with 3:73 and 265/75R16 is running 2000 at about 71 mph wish i had 3:42 for the 1.5 mpg extra.

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Noway 3.42 will gain 1.5 mpg over 3.73s.I don't think you'd see that from 3.42 to 4.10.

lrymal · February 14, 2005

...gain 1.5 mpg over 3.73s.I don't think you'd see that from 3.42 to 4.10.

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It is coincidental. I'm getting about 1.5 MPG increase in city and highway with my '05 over my '03. Could be a combination of several things with the 3.42 being one reason.

WyRam · February 14, 2005

...gain 1.5 mpg over 3.73s.I don't think you'd see that from 3.42 to 4.10.

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It is coincidental. I'm getting about 1.5 MPG increase in city and highway with my '05 over my '03. Could be a combination of several things with the 3.42 being one reason.

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I believe that but I'd say losing the clutch fan and the charging system is contributing........it could be all the gear ratio but in the above post he said 3.42 to 3.73 and I'd think 1/2 to 3/4 mpg difference would be more realistic.

AG Bill 05 Z71 · February 14, 2005

At 70 MPH my RPM is about 2100 with 4.10s. If you do the calculations, a 3.42 should be about 300 RPM less or about 1800.

My tires are 265/70/17

dewfpo · February 14, 2005

I haven't verified the 4.10 numbers with observed readings off my tach, but on paper.....

With stock tires : LT24575R16E Tires on an 2005 2500HD

MPH RPM RPM RPM

RAR 3.73 4.10 Diff.

55 1,605 1,764 159

60 1,750 1,924 174

65 1,896 2,084 188

70 2,042 2,245 203

75 2,188 2,405 217

80 2,334 2,565 231

DEWFPO

lrymal · February 14, 2005

........I believe that but I'd say losing the clutch fan and the charging system is contributing........
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Yeah, I forgot about the electric fan. I'd say with the gear ratio, fan, charging stuff, and maybe optimization of computer values, the MPG gained a bit. I also forgot the factory tires on this '05. They are rated as "mileage-efficient" according to an EPA chart. My 2003's are not listed on the chart.

SteveSierra · February 14, 2005

At 60mph, I'm right at 1500 rpms with the 3.42's.

Ape0r · February 14, 2005

0.70 = Overdrive gearing

682.2 = Approx. wheel revs/mile on 245/75/16's

60MPH:

0.70*3.42*682.2 = 1633.18 revs/mile (RPM at 60 mph)

0.70*4.10*682.2 = 1957.91 revs/mile (RPM at 60 mph)

For another speed, just use a proportion, e.g. multiply by 7/6 to get RPM for 70 mph.

70MPH:

3.42: 1906.38

4.10: 2284.23

80MPH:

3.42: 2177.57

4.10: 2610.54

camshaft · February 17, 2005

awesome, thx guys

anyone else with any observed rmp readings in their 05?

MAGNUM · February 20, 2005

awesome, thx guys

anyone else with any observed rmp readings in their 05?

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On my 05 yukon xl with 5.3 and 3.42s rpm is about 2000. on my 2000 suburban with 4.11s rpm was about 2400 and 75 mph. I get am averaging about 2.5 mpg better with the 05 but if you drive with cruise on over hilly terrain, i would not recommend the 3.42s. mine sometimes shifts into 2nd gear at 75 mph and tachs close to 5000. I personally do not like the 3.42s. That my opinion.