gear ratios in direct drive vs overdrive

If anything id go to 3.73's on 22.5lp. 3.58's are great with 24.5lp.

What your thinking will not gain what you want with the equipment you have. Its already about as good as you can get. I wouldnt not spend the money on a gear change. Get a good tune and work on driving habits. This will net the best gains.

I understand mathematics your looking at. But as @wore out stated, it causes new problems and unnecessary problems. Not only would you re-gear it. You would want to add bigger driveline. SPL joints and yokes.

That 470 detroit will not like a gear numerically low.

I run a 99 BK 12.7l, 13 speed, 3.58 rears, 24.5lp pulling cover wagon and hopper in OH,MI,IN. 6.5 average for the year. Alot of 100 plus gross. About as best as its gonna get, for the money. I am still working on a 7.0 yearly, but dang winter months and warm up/idling is hard to get around.

 

Way more than most imagine.

 

Any advantage to running in direct will be off set by running a useless rear ratio, and the first time you blow a part a clutch or snap something trying to start off loaded that .00000006 of an mpg saving goes out the window anyway

 

For what it’s worth…my FLD had a 12.7 and a 10 speed, 3.70’s on low 22’s and I hauled cattle all over the country with it for 4 years. It seemed to be a fairly bombproof setup as far as getting rolling in soft terrain while heavy.

 

OP has some bad information to start with.If he has lp 22.5, and any one of the final drive ratios of a 10 speed, it doesn’t add up to 65mph.

 

I might have just figured it out. He might be running 255/70/22.5 which is spot on with his numbers. Try starting the transmission out in 2nd gear and determine if you can live with it PERMANENTLY. If you can, 2.64 gears will put you exactly the same only in 9th gear. Cheaper to try taller rubber. My first 3 screen shots are with 295/75/22.5

 

1995 379 12.6 , 24.5LP, I changed from just 3.70 to 3.55 as part of a PM rebuild on rears to lose some revenue - 13 speed, now runs 1500RPM in 12th at 60 mph, 1500 RPM in 13th at 70mph.

I like the drivability, but get 6.25 mpg all day long, 43,500 empty - 50/50 loaded to deadhead. Tuned ECM to 550hp 2050 torque, upgraded mainshaft in trans with rebuild to heavier shaft.

Added BW 171702 and ported one piece manifold.

Is this thinking coming from KR's ideas of running 2.90 ish rears and direct transmissions?

I think in your application you'd be better staying as is or swapping transmission to 13 when it's time.

Just my uninformed 2 cents.

 

Here’s an example of an old Swift Truck. Circa Summer of 2000. Back then they were governed at 54 mph. Geared with 264’s They had an epidemic of vehicles rear ending them, especially out west. They Definitely got excellent fuel economy. Probably the best of any Mega Company at the time. 7.5 and higher maybe 8. Lot of Lugging. Doesn’t sound like much fun though. KR and his ideas are all recycled crap. Nothing new.

 

By comparison this is the Truck I bought. It got over 7 mpg easy, as high as 8. Once I hit the hills heavy, it was 6.5. I probably would have made more money with the old Swift Truck. Lol. Coincidentally, the most common Truck on the highway in 1999 was a white Freighter Classic. Due mainly to Swift buying them to recruit new Drivers. They had Detroit’s with 10 spds.in them. My common looking Classic blended right in. Flyin Low. Lol.

 

In 2008 I bought an 02 9200. Ex Walmart truck. It had a 430 Detroit with a 10 direct and 2.86 or 2.89 gears. On LP 22.5. It was a solid old truck. Got good fuel mileage and pulled fair for what it was. I mainly pulled steel with it. It never averaged more than 6.5 though. I could see 10 mpg with an empty skateboard.

Bottom line is, it did well enough not to change it. However it wasn’t great enough to spec another one like it.