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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.

 

Capture+_2018-07-05-16-05-21.png

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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. :lol2:

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@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.

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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. :lol2:

 

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

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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.

 

Capture+_2018-07-05-16-05-21.png

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

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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 by Mopar1973Man

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1 minute ago, Mopar1973Man said:

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.

The main reason I want bigger tires is lower rpm which means more mpg right? I’m thinking 3:69 is going to be the cats meow. I can obtain that ratio with the 285/75/17. 

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Actually, you want to optimize your RPM so your highway travel is around 1,900 to 2,000 RPM.

 

Most of this comes from @cajflynn back in the day his old 2001 Dodge was a 3.73 ratio axle and towed like a dream. Then after see all the 3.55 geared truck and 37" tire troubles. Why I was not really messing with tire sizes. Now after a bit a experience and I'm jumping out to optimize the tires to gears to make the best setup. Remember bigger tires have more rolling resistance especially with 285mm wide face then with all the steel belt you going to have more rotational mass. Just be aware.

 

@Marcus2000monster

I would in your case follow my lead and find a pair of junk tires on the rear axle to play with first before committing on tire purchase. 

 

Like I could do a 215/85 R16 on my truck my problem is I will most likely overwhelm the tires with the amount of torque I produce. So, on the Cummins I'll stick with 245/75 R16 which is a 1 wider than the 215's. I had to change my fuel map for daily driving the fuel comes on too quick and the tires lose the battle pretty fast. 

Edited by Mopar1973Man

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6 minutes ago, Mopar1973Man said:

Actually, you want to optimize your RPM so your highway travel is around 1,900 to 2,000 RPM.

 

Most of this comes from @cajflynn back in the day his old 2001 Dodge was a 3.73 ratio axle and towed like a dream. Then after see all the 3.55 geared truck and 37" tire troubles. Why I was not really messing with tire sizes. Now after a bit a experience and I'm jumping out to optimize the tires to gears to make the best setup. Remember bigger tires have more rolling resistance especially with 285mm wide face then with all the steel belt you going to have more rotational mass. Just be aware.

 

@Marcus2000monster

I would in your case follow my lead and find a pair of junk tires on the rear axle to play with first before committing on tire purchase. 

 

Like I could do a 215/85 R16 on my truck my problem is I will most likely overwhelm the tires with the amount of torque I produce. So, on the Cummins I'll stick with 245/75 R16 which is a 1 wider than the 215's. I had to change my fuel map for daily driving the fuel comes on too quick and the tires lose the battle pretty fast. 

According to spicers calculator I would be at 2035 average rpms at 70 mph.

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2 minutes ago, Mopar1973Man said:

 

Link please I want to see this calc...

https://spicerparts.com/calculators

I may be wrong but I calculated by entering the new gear ratio hat the tires would make. I entered 3:69 for the R&P ratio and 34 inches for tire height (calculated at tire size website) and 70 mph for speed limit.

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Not to throw a stick in the spokes but I am very anal when it comes to precision.  I've been in some sort if engineering my entire career and precision is required for that.  I have the hypertech programmer to adjust my tires size.  I think that 33.25" is going to be the correct size for my new tires which are advertised as 33.9".  You will lose some diameter when tires are on a vehicle.  I do this to verify that my odometer matches GPS readings.  My last set if tires, I was right around 2100 rpm's at 71 mph. I'm estimating I will be around 2000 with my new tires.

 

L8tr

D

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20 minutes ago, SilverMoose said:

Not to throw a stick in the spokes but I am very anal when it comes to precision.  I've been in some sort if engineering my entire career and precision is required for that.  I have the hypertech programmer to adjust my tires size.  I think that 33.25" is going to be the correct size for my new tires which are advertised as 33.9".  You will lose some diameter when tires are on a vehicle.  I do this to verify that my odometer matches GPS readings.  My last set if tires, I was right around 2100 rpm's at 71 mph. I'm estimating I will be around 2000 with my new tires.

 

L8tr

D

Just what I’m lookin for. 2k @ 70

  • Thanks 1

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2 hours ago, AH64ID said:

Most tire manufactures advertise a rev/mile that is the best to use when determining rolling diameter. 

My hypertech use 1/4" diameter increments so I'm stuck with that.

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16 minutes ago, SilverMoose said:

My hypertech use 1/4" diameter increments so I'm stuck with that.

 

Just convert rev/mile to inches. 

 

5280/(rev/mile)/3.14x12= diameter in inches. 

 

The ECM uses rev/mile anyhow, the hyper tech just does the conversion. 

 

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@Scottfunk  I just went out and did some highway driving after installing a new VP44.  With my 285/75/17's I was turning 2060 rpm at 71 mph.  I was probably mistaken in my last post about turning 2100 at 71 with my 285/70/17's  It was probably 2150.

 

L8tr

d

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