westport

what tire size would a guy have to go up to to get the rpms of the 06 6spd transmission the same as an 03 6spd with factory tires at highways speeds?

I sold my 03 automatic and now I'm looking at getting a 06. This time I want a 6spd. From what I've read on here the final drive ratio of the new 6spd forces the engine to runs more rpms in overdrive. I'm thinking I can just put some taller tires on the truck to get the rpms back down to what the old 6spd od would have been.

What size tires would I need?

Thanks.

STATELINE

for what it's worth I know that the new 6 speed (G56) turns around 200 rpm more at 70mph than the old one (NV5600)

6 2 Carl

NV5600 od =.73 G56 od =.79 and the factory tires are about 31.5" in diameter. So .79/.73 * 31.5" = 34.1". A 315/70/17 tire is 34.5" tall so a 315 tire will give you about the same rpm with the G56.

Your 03 auto had a overdrive ratio of .69. Using the same formula above, you'll need an 36" tire to achieve the same rpm with the G56.

The overdrive in the G56 is great for someone who tows all the time, but it is an less then ideal setup, for running around empty.

badbub

I guess we're assuming same gears in the rear ends? That's really the more critical piece to this puzzle. I'm running 4.10's with the G56. I figure that going to a 35" tire would give me the same result as putting in 3.73 gears(3.702) Would the extra unsprung weight offset my reduction in rpm's?

HOHN

Did you swap gears???

If you haven't swapped gears, you're not running 4.10s with the G56. Factory doesn't offer that combo, as far as I know. I could always be wrong.

IA_James

If you're wrong that makes 2 of us, I was under the impression that 4.10's weren't offered with the G-56 due to the deeper OD.

badbub

Was kinda concerned about not sounding stupid before everybody here so I dug pretty deep before I spoke up. My truck was a special order that was damaged coming off the carrier and returned for reapir. I, being the product of the immediate gratification generation, bought it off the lot rather than order a truck. The dealer gave me the printout of accessories. It is a Big Horn Edition with a snow plow package. It lists a G56 tranny. In 6th gear it runs right around 63 or 64 mph at 2000 rpm's. Unless my calcs are off that makes it pretty close to 4.10 gears. It's my daily driver and I would very much like to lower the range of rpm's I work in most of the time. At 80 I'm turning somewhere arounf 2700 rpm's. Fuel mileage is not the best in the world there. Is there any type of ID on the diff case that would let me know what's inside?

6 2 Carl

With the .79 ratio of the G56 2000 rpm equates to about 63-64mph with the stock tires.

rpm = (mph*gear ratio*tranny ratio*336) / tire diameter

Carl

wap

Mine does about 2500 at 79-80mph.
If you really want to make sure, pull your diff cover and divide the number of teeth on the ring gear by the number of teeth on the pinion.
I was under the impression that the g56 with 3.73s was supposed to be comparable to the nv5600 and 4.10s, I couldnt imagine havin the g56 and 4.10s, I bet its quick off the line though.

6 2 Carl

I can't tell you how much my 315's affected my mileage, as I had my tires installed by the dealership. I have never driven my truck with stock tires. From what I have heard from other members is that the bigger tires help the highway mileage, but hurt the mileage around town.

I do love my 315 /NV5600 / 3.73 combo. I can cruise at 75mph only turning 2000rpm. I have towed up to 10,000#, and it pulls fine in overdrive. If I have to pull something significantly larger I would just down shift to 5th which works out to be 2350rpm at 65mph, giving me all the power I need.

To me this is the best gearing setup. If I am pulling heavy I can run in 5th gear on the highway without the engine screaming, while still having another gear for high speed driving while empty.

Too bad Dodge had to spoil a good thing.

SkyHarborCowboy

BadBub,

You got 3.73's in there.

Joe