New Tire Size found 235's to 245's

[Mopar1973Man]

6 minutes ago, Tractorman said:

Thanks, Mopar1973Man, for introducing the 245 tire idea.

 

Too many are after the Cool Factor. I'm after the performance factor. It might not look cool but it sure does scream down the pavement good!

[dripley]

I was thinking the same thing on the gears. I am on 265's and the only speed and rpm I remember is 70 at 2000 rpm. If you drop to the 245's you will just be making more rpm. 

 I have also always towed in 6th if I can maintain speed on a grade at 50% or so of throttle. Anytime I get near 60 and slowing I would down shift. But as far as empty I have been known to cruise at 45 in 6th. 

[Ironforger]

Thanks guys, good info. It's great to compare with other trucks running 3.55 axle ratio. 

 

I assumed mine was 3.55 based on the dealer cut sheet for my vin# 

 

Would there be any details stamped on the actual gears? Didn't think to look last time I changed the differential lube, which was less than 10,000 miles ago. Now I'm tempted to pull the differential cover just to see!  Too bad it's not quite time to change the lube. I used the good synthetic lube & I added the LSD friction modifier too. 

 

Previous owner had the truck setup as a welding rig. It's possible he changed the gears at some point.

 

If anyone had to guess based on my  engine speed / road speeds, what do you think my axle ratio may be?  

 

Maybe I should not consider the 245's after all.

[Tractorman]

1 hour ago, Ironforger said:

If anyone had to guess based on my  engine speed / road speeds, what do you think my axle ratio may be?  

 

Doing some math (3.55/410 = .865 (about 87%) and comparing your speed vs. rpm and my speed vs. rpm, I am guessing that you have a 4.10 axle ratio.

 

One way to check axle ratio is to mark a relationship spot  with chalk on the driveshaft end yoke and the rear pinion housing.  Then do the same on each rear tire to the ground.  Chock the front wheels of the truck and place the transmission in neutral.  Have a helper jack up one rear tire and rotate that tire one revolution while you observe and track the revolution of the drive shaft.  Then have the helper lower that tire to the ground and repeat the same procedure with the other rear tire.   If you have 4.10 axle ratio, then the driveshaft will have rotated 4.1 times.

 

If you have a limited slip rear axle, then both rear tires can be raised at the same.  With limited slip, both tires will rotate together.

 

Hope this helps,

- John

[Ironforger]

3 minutes ago, Tractorman said:

 

Doing some math (3.55/410 = .865 (about 87%) and comparing your speed vs. rpm and my speed vs. rpm, I am guessing that you have a 4.10 axle ratio.

 

One way to check axle ratio is to mark a relationship spot  with chalk on the driveshaft end yoke and the rear pinion housing.  Then do the same on each rear tire to the ground.  Chock the front wheels of the truck and place the transmission in neutral.  Have a helper jack up one rear tire and rotate that tire one revolution while you observe and track the revolution of the drive shaft.  Then have the helper lower that tire to the ground and repeat the same procedure with the other rear tire.   If you have 4.10 axle ratio, then the driveshaft will have rotated 4.1 times.

 

If you have a limited slip rear axle, then both rear tires can be raised at the same.  With limited slip, both tires will rotate together.

 

Hope this helps,

- John

Great info.

 

Too bad I didn't know about this 2 weeks ago, had the truck jacked up while greasing the U-joints.  I'll try it next time!

 

Yea, It's a limited slip.

[AH64ID]

On 8/6/2018 at 11:21 AM, Ironforger said:

Here are my speeds & corresponding rpm's for my 02 3500 6 speed NV5600 & 3.55 gears

 

5th gear:

35 mph  1600 rpm

45 mph  2000 rpm

55 mph  2500 rpm

65 mph  3000 rpm

 

6th gear:

60 mph  2000 rpm

66 mph  2150 rpm

80 mph  2600 rpm

 

 

No need to jack it up. You have 4.10's. 

 

 

[Mopar1973Man]

 

Now you can run larger tires to bring down your ratio...

[Tractorman]

Thought I would show a couple of photos with the new 245/75R16 tires.

 

- John

[Mopar1973Man]

@Tractorman so how are you liking the 245's now?

 

Thanks for the photos they don't look much different than the 235's I'm currently running. Here shortly you guys will see my 215's on the 1996 Dodge. 

[Tractorman]

9 minutes ago, Mopar1973Man said:

so how are you liking the 245's now?

 

I am thinking that it was a very good decision.  I was getting ready to buy the 235 tires, but you started experimenting with the 245's with even better performance for our application.  It is rather ironic though, how long it takes for us to put on the tire that is recommended on the label in the door jamb on our 2002 trucks.  How did those guys know that?

 

Another benefit for the 235 or the 245 tire that hasn't been mentioned  - a reduced chance for hydroplaning.

 

- John

[Mopar1973Man]

4 minutes ago, Tractorman said:

Another benefit for the 235 or the 245 tire that hasn't been mentioned  - a reduced chance for hydroplaning.

 

Just like I said before a smaller footprint will drive down and grab the pavement. Where a wide face tire will jump up on top of what ever material you running across. I personally love whizzing down the highway at a comfortable speed in the dead of winter as I watch all the wider tire and lift trucks struggle to hold there own on the snow. 

 

I'll admit though in mud or soft ground the wider tires do actually work out the best. Question is how many people drive on soft mud every day a majority of the time?

[AH64ID]

I've always been a fan of tall and skinny tires. For my fall/winter tire I run a 255/80R17 and it works great. It is a little wider, but with the weight of these trucks it's not an issue. I do still drag my pumpkin in snow quite a bit and a 245 would lower them by about 1.5" and that's going to cause more issues than 10mm in width. 

 

[Mopar1973Man]

Not a huge difference. 255/80 R17 is a 33.1" vs 245/75 R16 is a 30.5" so axle difference 1.3 inches taller at the axle. This is comparable to 285/75 R16 which is a 32.8" for height just 30mm narrower.

[Quadzilla Power]

On 7/13/2018 at 7:41 AM, Scottfunk said:

@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.

Unfortunately you have a custom build of the ADR base code. I think the MPG stuff went in after your custom build so I don't think you have that. Your custom trans temp from the Allison is different I think. I will have to see what Nick did to build yours.

[Quadzilla Power]

On 7/30/2018 at 8:49 PM, Scottfunk said:

Ok so I got the gears swapped out and it feels really great. The turbo lag is all but gone, acceleration is insane, and the load seems to have come down some. Only problem is I can't get the iquad speedometer calibrated. According to the calculator at grimmjeeper.com my road speed at 2000rpm with the old setup was 85 mph and the new setup should yield 77 mph. The problem is when I change the gear ratio in the iquad from 3.55 to 4.10 the speed actually reads FASTER. Has anyone ever had to do gear ratio adjustments? What's the deal?

The gear ratio will only affect how it determines which gear you are in. The tire size is really the only thing that affects the speedometer readout. You will have to figure out what you need to reprogram to get the proper gear ratio and speedometer settings. Once you have whatever it is that transmits the speed corrected for the 4.10s then you can adjust for tire size in the iQuad app. I would suggest having it set for 4.10 gears and 95.7" rolling length tires then do the tire size correction in the app. That way the gear selected and the speedo are both right.

 

Once you get the updated fuel economy stuff, you will need to correct for fuel usage. This does require a corrected speedo as described above. You don't need to know the odometer reading. You will need to fill up the truck, set the MPG offset to 100%, reset the gallons used per trip, run a tank of fuel, then fill up again. Take the actual gallons used / reported gallons used x 100 and set that as the MPG offset. This will only work if you don't use the pump tap at all, so run on level 3 or below with the V2 tuning. 

 

Once that is set properly, then you can start to trust the ECO, gallons used per trip, and the Average MPG gauge (latest version corrects what Mopar1973Man was seeing earlier). Again, you can only trust it when not running the pump tap. When you add in the pump tap all you are getting is a rough guideline at best. 

[Scottfunk]

Ahhh that makes sense. Since my quad gets gear indicator directly from the tcm then the gear ratio does nothing at all. I'll have my tcm tuner adjust for tire size and gear ratio and then I can fine tune with the tire size in the app.

[Mopar1973Man]

I've done the 215s on 1996 Dodge right now I've got to admit it shifts better, hold road speed without lugging at 55 now. MPG seems to be up another 2 or 3 MPG. Better passing power.

[Scottfunk]

Just realized I never posted a picture of the 285/70/17's I put on the Chummy. My wife picked them up at an auction for $13 so they're not exactly brand new but good enough to get an idea of how they look without paying for new ones. And good enough to help me decide to regear to 4.10.

[Tractorman]

I have now driven over 1,600 miles with the 245/78R16's and I am very happy with the results.  About 700 miles of the driving has been towing within a 60 mile radius ranging from 15,000 to 19,600 lbs gross combined weight.  With the 6 spd transmission and a 3.38:1 ratio for second gear, I can easily perform second gear starts on flat ground fully loaded now.  I like that very much.  Heavy loads are now much easier to get up to speed without working the engine.

 

Sunday, my wife and took the travel trailer from home (near Salem, OR) to Baker City and deadheaded back.  The trip out yielded 14.5 mpg (12,500 lbs GCW), the trip back yielded 22.3 mpg. I am very happy with that.  The trip each way is about 335 miles.  MPG's were hand calculated.

 

I will be taking the tractor with implements to Baker City on Thursday and will be expecting to weigh in at about 16,000 lbs.  I will post the MPG results later.

 

Everything that Mopar1973Man posted about improved performance has happened for me by going with the smaller tires.  With the new 3 1/2 turn stop to stop steering box, the new clutch, and the smaller tires, this truck drives far better now than it ever did when it was new.

 

- John

Edited August 29, 2018 by Tractorman
I made a mistake

[Mopar1973Man]

Matter of fact that is my next move. I've got to get fresh rubber on my Cummins and the RV. I've also got a quick ratio steering box also. Hopefully by next weekend ill have the tires. This also prove optimal final ratio is near 3.73. This also prove that oversize tire look cool but make for way too low of a final ratio unless you already have 4.10 or high axle gears already.

Edited August 29, 2018 by Mopar1973Man