I just got a pair of used 245/75 R16 tires from a friend. So I mounted them up on my old aluminum mags and mount the 245's on rear axle of the truck. 

 

 

They are a bit shorter in height. The gains are great!

 

Engine load is reduced by 5% to 10% roughly. 

EGT's are about 50*F lower.

Acceleration is way better and faster. 

Cruising RPM's are right about 1,960 RPM at 65 MPH.

 

I've got to reset my cruise timing limit on the Quadzilla I need to drop from my current 25% to 20% it was holding cruise timing climbing about 2-3% grade. 

 

I'm going to document MPG usage as well in the coming days. 

Edited July 2, 20186 yr by Mopar1973Man

2 hours ago, Marcus2000monster said:

Is there anyone here that can chime in about 4:10s and tire size? Seems like everyone has 3:55s. I am getting 18.5 mpg with 4:10s and 265/70/17 right now and would like to get 20. For 4:10s do I want to go bigger to bring the gear ratio down or not?

Yes you want to go bigger, for you I would think 285/70/17 would be a good size without compromising steering parts too much.

Edited July 12, 20186 yr by Dieselfuture

I don't disagree with @Dieselfuture. I just know the bigger you go to help the rear end the more stress you put on the front end. Kind of a double edged sword.

I think 255/80R17 would be a better size, thou they may not last as long if you use you're torque often. Lighter and fit better on OEM size rims. 

 

I love skinny tires, but they don't last nearly as long with torque applied. 

3 hours ago, Marcus2000monster said:

Is there anyone here that can chime in about 4:10s and tire size? Seems like everyone has 3:55s. I am getting 18.5 mpg with 4:10s and 265/70/17 right now and would like to get 20. For 4:10s do I want to go bigger to bring the gear ratio down or not?

I just got new tires and went from 285/70/17 to 285/75/17.  My best trank with the old tires was 20.4 but usually average around 18-18.5 around town.  I will let you know if the slightly taller tires change anything.

 

L8tr

d

I'm confused. First of all I hate metric tire sizes. Mine are 265/70/17 which the calculator says is 31.5". I have 3.54 gearing in my axles but I'm not seeing 2000 rpm until somewhere around 88 mph. Maybe the.61 ratio of sixth in the Allison is taller than what you guys are running? If I'm planning on running 315/70/17's (34.4") with the 5/6 ratios of .71 and.61 respectively, what gearset should I be looking for? I do routinely drive 75/80mph unloaded. Haven't done any towing yet but I do have the ability to turn off 6th gear and stick with the higher rpm's when towing. Thoughts?

 

So I opened my mind a bit and ran a few different tire sizes through the calculator. If I go with a 305/70/17 with the 4.10 ratio that will put me at 1960 RPM's and 78 mph in 6th gear which is where I do most of my highway driving. With sixth gear cancelled I'll be hitting 1960 rpm's at 68 which seems like a pretty decent cruise speed for light/medium towing. Does that sound like a decent range? 

 

I too am contemplating new tires and don't want to end up fighting egt's or the cost at the pump.

Edited July 13, 20186 yr by Scottfunk

14 minutes ago, Scottfunk said:

I'm confused. First of all I hate metric tire sizes. Mine are 265/70/17 which the calculator says is 31.5". I have 3.54 gearing in my axles but I'm not seeing 2000 rpm until somewhere around 88 mph. Maybe the.61 ratio of sixth in the Allison is taller than what you guys are running? If I'm planning on running 315/70/17's (34.4") with the 5/6 ratios of .71 and.61 respectively, what gearset should I be looking for? I do routinely drive 75/80mph unloaded. Haven't done any towing yet but I do have the ability to turn off 6th gear and stick with the higher rpm's when towing. Thoughts?

Having a Allison tranny is going to change a lot of things. 

Not sure how this works out but on the 5 and 6speed trannys OD is .73 and .75 to 1 gear ratios. The .61 would  be quite a difference.

42 minutes ago, Scottfunk said:

Maybe the.61 ratio of sixth in the Allison is taller than what you guys are running?

 

Way taller. 

47RE is 0.68

NV4500 is 0.75

NV5600 is 0.73

 

What I'm finding for final ratio at around 3.60 to 3.70 is awesome. Mine is at 3.69:1 ratio to the ground with the 245's now.

 

I just towed the RV home tonight. I'll admit I was being abusive to the truck to see how far I could reach. Needless to say you can push pretty darn hard on it now. Few grades I left the cruise set for 60 MPH. Walked on over. The best part was a Ford flatbed tow truck was empty couldn't pass me as I left it in 5th gear hauling on over the grade doing 60 MPH. Then another grade I down shifted to 4th (direct) and beat on it some more running up the grade at 55 MPH which is up around 2,300 RPM now. But it pulled great. Still had power to spare. Transmission temperature was great floating 160 to 170*F remember that is just a factory NV4500 no coolers, no heat shields, and just the 50 SAE oil in the case. I did push hard enough to get engine coolant temperature up in the 210-220*F range. Like I said I was being a bit abusive to see how far I could reach. I'll say there is way mode towing power. Runs cooler EGT and engine wise on the flats. I'll also admit with the Quad on any wiretap mode it will pull the tires out from under itself. Level 3 is perfect you can mat the throttle to the floor and it stops just short of 1,200*F in top gear on flat ground. (Quadzilla and +75 HP injectors)

Edited July 13, 20186 yr by Mopar1973Man

@Mopar1973Man is there a way to compute an actual "final ratio" that includes the diameter of the tires? I think that might help

4 minutes ago, Scottfunk said:

@Mopar1973Man is there a way to compute an actual "final ratio" that includes the diameter of the tires? I think that might help

 

Right here...

https://tiresize.com/gear-ratio-calculator/

9 hours ago, Marcus2000monster said:

Is there anyone here that can chime in about 4:10s and tire size? Seems like everyone has 3:55s. I am getting 18.5 mpg with 4:10s and 265/70/17 right now and would like to get 20. For 4:10s do I want to go bigger to bring the gear ratio down or not?

 

I am running 4.10 sure grip rear and 3rd Gen rims with Nitto Duragrappler 285/75R17's.  Just made a round trip from Vancouver, WA to Yuba City, CA.  Averaged GPS calculated 19.8 and change and return was 20.3 and change.  Around town about 18-18.5 most times depending on where/when I go.  Probably making that trip again this next week so will see how it goes this time.  I do drive pretty conservative and keep speed about 62 on cruise.

Thanks! I see you have an auto so I bet I could get even better! 

6 hours ago, Russ Roth said:

 

I am running 4.10 sure grip rear and 3rd Gen rims with Nitto Duragrappler 285/75R17's.  Just made a round trip from Vancouver, WA to Yuba City, CA.  Averaged GPS calculated 19.8 and change and return was 20.3 and change.  Around town about 18-18.5 most times depending on where/when I go.  Probably making that trip again this next week so will see how it goes this time.  I do drive pretty conservative and keep speed about 62 on cruise.

It looks like we are pretty much the same mileage wise with the same tire size. I have Toyo AT's.

 

L8tr

D

41 minutes ago, SilverMoose said:

It looks like we are pretty much the same mileage wise with the same tire size. I have Toyo AT's.

 

L8tr

D

Are u running any tuning?

So I ran a grading calculator and I’m coming up with 3:66 for my final ratio. That’s pretty darn close to 3:55 so hopefully it will help with mpg and rpm! 

You want to come down toward the 3.73 mark more so. At 3.69 ratio 65 MPH is right at 1,960 RPM's. 3.55 is a bit better for strictly interstate travel at 80+ MPH. 3.73 seem to be way better on the standard 2 lane mountain roads and even towing. You have to consider what you do the most. Remember Quadzilla shows -1 MPH off this is actually 65 MPH.

 

15 minutes ago, Marcus2000monster said:

Are u running any tuning?

So I ran a grading calculator and I’m coming up with 3:66 for my final ratio. That’s pretty darn close to 3:55 so hopefully it will help with mpg and rpm! 

Stock except for DDRP. Tuning is my right foot. 

@Mopar1973Man what I'm looking to do is incorporate the trans final ratio into that. Do I multiply the tire/axle ratio by the trans ratio? Or maybe divide it? Just trying to calculate a level playing field so I can plan my tire/gear setup to get in a more useable range. I would be surprised if I'm getting 16mpg on the freeway although I have no real way of checking it as yet. When I do the final wiring under the hood I will be reinstalling the factory Chevy pcm so I can have my stock Speedo and odo again.

Not sure. The best way would be to see the RPM at 65 MPH then you know if you got to up or down in ratio. 

8 minutes ago, SilverMoose said:

Stock except for DDRP. Tuning is my right foot. 

 

In other words heavily retarded timing. There is a nasty hole in the middle of the map for stock. (EPA crap)

24 minutes ago, Mopar1973Man said:

You want to come down toward the 3.73 mark more so. At 3.69 ratio 65 MPH is right at 1,960 RPM's. 3.55 is a bit better for strictly interstate travel at 80+ MPH. 3.73 seem to be way better on the standard 2 lane mountain roads and even towing. You have to consider what you do the most. Remember Quadzilla shows -1 MPH off this is actually 65 MPH.

 

3:69 is what the calculator says. Maybe I should go with the 285/70/17 that would be a 3:81 ratio.

Remember higher the ratio number the higher in the RPM for said speed. This is why I'm running a pair of junk tires on the back of my truck for about a month to find out if I like the ratio or not. So far I love this 245's set up and think the 215's on the 1/2 ton will be awesome too.

Edited July 13, 20186 yr by Mopar1973Man