gearing question

We're doing you plan on running Your right at?

 

Just think if you add tall 24" drives you may reach 130 mph. You can add me to your list of people that think your crazy. J/K

Here are a list of spec's for Eaton to give you an idea of the difference between the 13, and 18spd.(Scroll to pg. 13 for out put ratio's) http://www.eaton.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/rr_rrsl-0001.pdf IMO 18 is only good for heavy haul, or for an uber low granny gear. In ordinary driving you'll skip right over them and shift it like you would any other tranny. Even using the 13spd, you'll find you normally only split the last 2 gears.

You notice, most all trannys above are O/D (over drive) meaning the top gear is less than 1:1.00 ratio. That combined with a 2.64 rear (actual output ratio =1.91), will have you down shifting and loosing speed on ordinary overpasses... thus making mountains out of mole hills.

Good luck with your project

 

I second @TheDude1969

@Cowpie1 runs the 13 and 2.64 setup in a glider I think.

3.42/3.55/3.58/3.70 paired with 13 should be versatile enough, in my opinion.

 

Going down the highway you'll be fine, be sure to use a 13 or 18 spd tranny.
The main thing it effects is startability. The ability (or ease) to get the truck to launch on a hill. If your 80,000 or less and loading pretty much on pavement or concrete you'll be fine. If your 100,000 plus loading in the mud and climbing a hill, you'll torch the clutch.
http://www.overdriveonline.com/geared-to-go/

 

I believe most folks that run 2.64s spec so that they can run in direct, and many have a direct/top gear tranny. The idea being to reduce parasitic loss of power required with o/d trannys, and improve fuel mileage.
They wouldn't work well for hauling in excess of 80k, in the hills, or off road in my opinion .

 

My peterbilt dealer says the factory won't build an 18 double over with 2.64. They will only go to 3.08. Reason being is no need for a truck with that much speed, so he tells me. It's really a balance of which gears do you want to use? Start in granny all the time and mostly use up to 16? Start in 1 or 2 and use up to 18? How often are you going to get crazy and actually cruise in the big hole with that much available speed?

Also, users here will tell you the faster the rears the shorter their life expectancy. I don't know why ... but my 3.90 gears seem to be indestructible after about 1.4 million miles so far

 

The only thing you will lose is startability. Do you drive a truck now? Just use the ratio formula to figure out what gear would be the same in your current truck as the new truck would be for the low gear, and start using that gear for ALL your starts. That will answer all your questions.

 

@gokiddogo , the reason for this is:
The faster gears sets have to have More teeth on the Pinion, which means that the teeth profile is narrower & deeper (or pointier for want of a better word) which makes them more prone to shearing off.
And the Crown wheel teeth are machined far deeper to match the profile of the Pinion gears which makes them more liable to break in between the teeth..
I hope I've explained Myself properly??
Pictures of 2 different gears sets would explain in a heart beat what I'm trying to explain..