HotRodK

Well its in the driveway next to its big brother. Its pretty Edit having two CTDs in your driveway, which Im sure someof you know.

I still have a question about the 4.10 gears and tires. It has a brand new set of Goodyear Wranglers (265/70/17) and I have the Nitto 295/70/17s on the '06. What I really want are some 315/70 Nitto Dune Grapplers. I have been to the sites about tire height and it gives me some good into, but I need to know how much RPM drop at 78ish MPH Ill be seeing after the swap. Any help? Thanks guys!

Dodgezilla

I'm not sure about that but I would be careful with those tires. I think they are only C Rated and that's why nobody here runs them. They may have changed the rating since I looked last but you may want to check into it before you haul or tow anything heavy....

HotRodK

Thanks for the heads up. Ill check into that. Im really waiting for the Dura Grappler to be released in the 315s. Those would be nice.

D45

The 315s will fit and look great!

omaharam

without doing the math - I'm lazy - you will see 250-300rpm drop from the 265s to the 315s.

D45

Also, my truck's speedo is only off 1.5-2 MPH with the LT315s

omaharam

It's off by a percentage not a set value. At 25mph it will be off 2.17mph, at 50 it would be off 4.35, and at 100 it would be 8.7mph off.
Here's a link http://www.discounttire.com/dtcs/infoTireMath.dos

So to more accurately restate my first post, the rpm drop at 78mph would be an 8.7% drop. So with a given speed to obtain 2000rpms with the 265s, changing to 315s would net 1826rpms.

HotRodK

Thanks! Your as smart as I should be!!

Now Im still wondering, do I wear out these BRAND NEW Goodyears before buying the 315s. The $900 for tires would go a LONG way in fuel.

D45

Sorry, but at 50 MPH to 60 MPH, my truck's speedo is only off 1.5 - 2.0 MPH!

omaharam

Then it has been recalibrated - incorrectly. It has to be a percentage that is equal to the difference in tire size. If you add 10% to 100, it's always going to be 110 - always. If you add 10% to 50, it's always going to be 55 - always. If you use a tire that's 10% difference in size, it's always going to throw your odometer and speedometer off 10%. It's impossible not to. How are you determining by how much it's off?

D45

No recalibration, sorry.....bone stock.

I have my Magellan Maestro GPS with the MPH section and also I turned my squad's radar gun on and drove by as the wife watched the read out on the gun's display.

Asher

The speedo's on these trucks read fast from the factory... (gps clocked)stock at 60 mph my speedo read 62... with 285's my speedo reads 58mph at 60... Hope that makes sense.... and of course the difference will vary with speed (percentages) like said above..

J-man

When i was on a road trip with my truck, I checked the odometer against the mile markers over a 50 ml strech and my truck was off by 7%. That's with 315/70/17's.

HotRodK

Thats the size I want. Now to do the smart thing about buying or waiting. Thats the hard part...

StrokeThisCTD

Then your speedometer is incorrect from the factory. going from 265 to 285 on my 04.5 made my speedometer off by about 3mph at 65mph. I had it calibrated right after the tires were on but not before i drove it and saw how much it was off. a 315 tire will be even greater.

You are going from a tire thats about 31.5" tall to a tire thats 34" tall and you say you are only off by 1.5 to 2mph?