Convoluted tire size question

[Mock Tender]

This will be a bit of a convoluted question. I have Cooper 315 75R16 on singles on my 2015 FG. After 1 year and 30,000 miles, I have yet to get stuck. The tires have about 9/32” to bald. I have been on some interesting trails (Shafer Canyon to White Rim Rd to Gooseberry Campsite, in CanyonLand NP; Toroweap, AZ- all the way to the campground, Arch Canyon Road- to the end, the nasty little straight up trail just outside St. Anthony, Newfoundland and at least a hundred more. The only thing that has turned me back, has been low hanging tree branches and quartering ditch drops. The tires have even done exceptionally well on riding the side of eroded trails that are 75 to 80 degrees.

My only problems- and I have still gotten out of them, is when I am faced with being stopped and having to go straight up or back up a rise. This has happened to me on several occasions. First time I was parked, butted up against a stump, in the mountains: 8,000 feet, below freezing and when I went to leave in the morning- it just didn’t want to back up the hill- not even a rock or rut to interfere. Another time I was going through virgin crusty snow. Around a corner, the snow was at least two feet and as far as I was concerned impassable. Into reverse and nothing. No tire spin- nothing. I had room to move forward and slightly upwards, which it would do, I stopped and with the help of gravity and pedal to the floor- back I went- again no spinning of the tires. There have been other scenarios, again that I have gotten out of, the FG would just simply not go forward and would start the alarm for over-heating. Easy to solve- but each situation I left myself an out.

Now, if I had not gone to singles and had stayed with smaller tires, would I have a more flexible truck? I have the 5.714 ratio diff. and I imagine some engineer somewhere would tell me how much low end grunt I have loss with increasing my tire size by 2.7” over stock. And as we all know, the new FGs can use all the grunt they can get.

So I will be in one place for the next 2 months- I want to get an idea from you guys- what you think? I am not trying to open the singles verses duals- only the “With the 2012+ FG’s is it better overall for a smaller set of tires or not?

Mark

 

[Aussie Iron]

Sounds like a transmission problem if it is Duonic or the clutch is slipping if manual. Sounds like low range would have been helpful in both situations.

Dan

 

[dlh62c]

Are you running the Duonic transmission in manual or automatic mode during these moments, especially when you get the temperature warning?

When you released pressure on the brake pedal, did the Duonic transmission creep function engage?

 

[Mock Tender]

Sorry about the lack of information in regards to my truck and conditions.

It is a 2015 US version with a 5.714 ratio. Most of these incidents took place prior to resetting the transmission for my finished build weight. Since resetting the transmission (twice), all of my driving has taken place above 4,000 feet msl.

In those circumstances I was in either manual or "power mode" auto.

As to the creep function, I know it works (at each and every stop sign or light), but I am not sure that I did anything other than go from brake right to the gas.

The comments that I have heard about the 2012+ not being able to get over a curb are simply not true: even from a dead stop against the curb. It takes a, my best guess, a 25% plus grade and an obstacle (except for reverse). By the way, it can easily back over curbs in reverse as well.

Mark

 

[dlh62c]

If you're having issues offroad with the Duonic transmission in automatic mode, blame it on the fuzzy control scheme.

Per Mitsubishi; The fuzzy control estimates the driver's intention from the vehicle load factor (derived from the theoretical acceleration and actual acceleration with an empty vehicle driven on a linear flat road)

In manual mode, the DUONIC electronic control unit is always monitoring the vehicle speed, engine speed, and selected gear. If there is a risk of engine over-revving as a result of manual gear shifting, no shift-down will take place even when the gearshift lever is pushed toward the “–” position. Likewise, if there is a risk of engine stall as a result of manual gear shifting, no shift-up will take place even when the gearshift lever is pushed toward the “+” position.

When I test drove a Duonic transmission, I was told there was a technique to doing it in automatic mode. Leaving from a dead stop, you don't jump from the brake pedal and immediately mash down on the accelerator. While slowing to a complete stop, the transmission will automatically downshift as speed is reduced, but you could be in 4th when you come to a complete stop. By releasing pressure on the brake pedal and allowing the creep function to engage, the transmission will downshift to 2nd or even 1st depending on the road incline and load sensed. When doing this, there's no roll back as often reported by others. Then it's just a matter of depressing the accelerator and letting the Duonic do its thing.

On the highway, with cruise control engaged and depending on road incline, the Duonic will only shift down one gear. If it senses the need to shift down further, it will disengage the cruise control, then downshift. When this happens the first time, it's a little disconcerting. Its one of those ****** moments.

 

[Czechsix]

My truck does exactly the same thing, in some places I've had to do a neutral to forward or reverse rocker to get moving. All of those places were in what I would consider to be easy obstacles if I had a true manual transmission, or an automatic.

Having experienced this, I specified the lower gear set, a ls for the front, and also a rear winch. It'll be interesting to see what happens in the months to come. I've heard it mentioned that FUSO and M-B will be looking at further improvements to the platform.

These trucks definitely have different manners, but I guess everything has pluses and minuses. So far the plus side has been outweighing the minus side, at least for us.

 

[cnick]

I've experienced similar results with our 2015, but have also noticed a few things:

The amount of times that it throws a T/Oil Temp Warning has significantly dropped once we had the software update done (I actually can't remember the last one I've gotten). Some of this might be related to the software update and some related to the transmission 'burning' in. I do know there are learning times specified for each of the clutches / pressure points in the ECU (or TCU). So maybe you'll see this get better after more use.

I also recently had the dealer set the software for the correct tire size (315/75R16) and in addition to my speedometer matching the GPS at 65, it also seems to climb over ledges and rocks better.

 

[Mock Tender]

Nick- We have 30,000 miles on the odometer and have had the weight reset twice. Unfortunately, per the mechanics, it pretty well sets itself to your weight in just a few hundred yards. So unless you are near a hill: no joy. I was also told that sometimes the reset doesn't take.

I would be very interested in what they did for your tire size. I understand that some dealers know the code for certain size tires, but otherwise they just play with it until they figure it out. We had work done at Rush Truck Center in St. George. They were very good to deal with- still more geared to their main truck line.

 

[cnick]

I understand that some dealers know the code for certain size tires, but otherwise they just play with it until they figure it out.

Rush Truck Center in Salt Lake City. They did not have a code for our tire size. He tried a few settings, but over some speed it would go wonky. So they opened a ticket with Fuso and the next day it was working great. I didn't get the setting they used, but there are only two Fuso guys at the location, so you might be able to get the St. George shop to call and get the details.

 

[Mock Tender]

Okay- I think I have a good answer for myself- but, not the final answer. I did a lot of research and found a web site that does calculations for tire size changes and how it affects your effective gear ratio compared to stock.

So since the FG I bought had 235/85R16 and the optional 5.714 gearing. That means when I went to the 34.5” LT315/75R16 tires I effectively went to having a 5.24 final gearing (or less than the std. FG with the 5.285).

Now if I drop my tire size to LT295/75R16 my ratio goes up to 5.42; and if I went to LT 285/75R16 the ratio goes up to 5.52.

Since I can't change my gearing- these sizes are all around 33” tall, E load factors not as many tires to pick from, but the weight handling is comparable and my creeping ability would improve.

Mark