35's vs. MDS

[limechallenger]

Ok ,guys with 35's under their Rams, how does the tire size change affect the factory MDS system?

 

[17CrewCab1500]

It really doesn't too much. It may take it a few extra seconds to engage as the truck needs to settle down from acceleration.

I found that the tires don't do much alone. But, the factory wheels are very light and if you go with aftermarket wheels, then... you can feel a big difference.

 

[RoadRamblerNJ]

It really doesn't too much. It may take it a few extra seconds to engage as the truck needs to settle down from acceleration.

I found that the tires don't do much alone. But, the factory wheels are very light and if you go with aftermarket wheels, then... you can feel a big difference.

17CrewCab1500, I wonder if you could explain exactly what you're trying to get across.

I've read your reply to the OP and, all kidding aside, I have no idea what you're trying to describe.

Are you saying aftermarket wheels are heavier than stock? If do, how is that affecting the MDS?

Also don't get how getting up to cruising speed would affect MDS activation.

Please explain.

I'll be going to 37's eventually.

Thanks

 

[Krein]

I've got 35's and aftermarket wheels, do I think that affects mds engaging maybe. I have a 6" lift do i think that affects MDS engaging well your guess is as good as mine but what i can say for certain is the only time it activates is going down hill while off the gas pedal. My 35 inch tires and Fuel wheels are heavy and it takes alot of power to get them moving so any grade on the road means more power which will not allow the MDS to kick on. So YES IT AFFECTS IT

 

[Krein]

17CrewCab1500, I wonder if you could explain exactly what you're trying to get across.

I've read your reply to the OP and, all kidding aside, I have no idea what you're trying to describe.

Are you saying aftermarket wheels are heavier than stock? If do, how is that affecting the MDS?

Also don't get how getting up to cruising speed would affect MDS activation.

Please explain.

I'll be going to 37's eventually.

Thanks

same here with the 37's

 

[joshuaeb09]

17CrewCab1500, I wonder if you could explain exactly what you're trying to get across.

I've read your reply to the OP and, all kidding aside, I have no idea what you're trying to describe.

Are you saying aftermarket wheels are heavier than stock? If do, how is that affecting the MDS?

Also don't get how getting up to cruising speed would affect MDS activation.

Please explain.

I'll be going to 37's eventually.

Thanks

To cover the high points as best I can with my rusty physics knowledge :

The heavier wheels and tires increase rotational inertia and as your mass increases you get less angular acceleration for a given amount of input force. This will also reduce your breaking power since inertia works both ways. MDS only operates when the truck is under light load and by removing half the cylinders from the equation you get less torque output. Since the heavier wheels and tires require more input force to get moving the truck will not see as many instances of optimal conditions in which it can enable the MDS system when acceleration changes are required. This explains part of the acceleration side of the issue and anytime minor acceleration is required where the truck could previously leave MDS engaged may now require it to disengage to get more power output.

Generally you are also going to deal with more more rolling resistance as the wheel/tire combination is heavier as well as the more aggressive tread pattern/design of an off road tire. Since they are designed, typically, for grip under adverse conditions and side wall strength they will be heavier and have a "gripper", as in more friction, optimized design. They are also going to be more likely to deform, part of the grip strategy, all of which will increase the rolling resistance. Combine this with a typically much wider tire which has a wider contact footprint with the surface and it all starts to add up. This explains part of the steady state part of the issue as it will take more constant power output in order to overcome the additional rolling resistance.

Finally you have the final drive ratio change by moving to a larger diameter tire. This will reduce the mechanical advantage available to get power to the ground via the friction (grip) between the tires and the surface. The loss of the mechanical advantage leads to less torque multiplication of the engines output which again will require more output power from the engine given the same conditions once a larger tire is in play. This is why a re-gear can help the truck significantly when larger tires are used as you regain the lost mechanical advantage restoring the lost torque multiplication. This is a factor in both the steady state part of the issue as well the acceleration part of the issue.


https://www.khanacademy.org/science...momentum/torque-tutorial/a/rotational-inertia
https://opentextbc.ca/physicstestbook2/chapter/dynamics-of-rotational-motion-rotational-inertia/

https://www.real-world-physics-problems.com/rolling-resistance.html

http://www.dynamicscience.com.au/tester/solutions1/hydraulicus/gears1mechanicalad.htm

It's been a while since I did any real Physics so I probably didn't explain something properly or otherwise screwed up, but it should be sufficient to get the idea across.

 

[muddy12]

Just throwing my $.02 out there.
Maybe the newer trucks (with the 8 speed) see a difference, but with 35’s on my 2012, the MDS kicks in very little, and I see no change in MPG.

It has become habit for me to just bump the shifter into 6 when I put it in drive, that I have the MDS turned off 99% of the time.


Sent from my iPhone using Tapatalk

 

[daveray9]

To cover the high points as best I can with my rusty physics knowledge :

The heavier wheels and tires increase rotational inertia and as your mass increases you get less angular acceleration for a given amount of input force. This will also reduce your breaking power since inertia works both ways. MDS only operates when the truck is under light load and by removing half the cylinders from the equation you get less torque output. Since the heavier wheels and tires require more input force to get moving the truck will not see as many instances of optimal conditions in which it can enable the MDS system when acceleration changes are required. This explains part of the acceleration side of the issue and anytime minor acceleration is required where the truck could previously leave MDS engaged may now require it to disengage to get more power output.

Generally you are also going to deal with more more rolling resistance as the wheel/tire combination is heavier as well as the more aggressive tread pattern/design of an off road tire. Since they are designed, typically, for grip under adverse conditions and side wall strength they will be heavier and have a "gripper", as in more friction, optimized design. They are also going to be more likely to deform, part of the grip strategy, all of which will increase the rolling resistance. Combine this with a typically much wider tire which has a wider contact footprint with the surface and it all starts to add up. This explains part of the steady state part of the issue as it will take more constant power output in order to overcome the additional rolling resistance.

Finally you have the final drive ratio change by moving to a larger diameter tire. This will reduce the mechanical advantage available to get power to the ground via the friction (grip) between the tires and the surface. The loss of the mechanical advantage leads to less torque multiplication of the engines output which again will require more output power from the engine given the same conditions once a larger tire is in play. This is why a re-gear can help the truck significantly when larger tires are used as you regain the lost mechanical advantage restoring the lost torque multiplication. This is a factor in both the steady state part of the issue as well the acceleration part of the issue.


https://www.khanacademy.org/science...momentum/torque-tutorial/a/rotational-inertia
https://opentextbc.ca/physicstestbook2/chapter/dynamics-of-rotational-motion-rotational-inertia/

https://www.real-world-physics-problems.com/rolling-resistance.html

http://www.dynamicscience.com.au/tester/solutions1/hydraulicus/gears1mechanicalad.htm

It's been a while since I did any real Physics so I probably didn't explain something properly or otherwise screwed up, but it should be sufficient to get the idea across.

Well said!
This is pretty much the best explanation I have ever read.

 

[RoadRamblerNJ]

To cover the high points as best I can with my rusty physics knowledge :

The heavier wheels and tires increase rotational inertia and as your mass increases you get less angular acceleration for a given amount of input force. This will also reduce your breaking power since inertia works both ways. MDS only operates when the truck is under light load and by removing half the cylinders from the equation you get less torque output. Since the heavier wheels and tires require more input force to get moving the truck will not see as many instances of optimal conditions in which it can enable the MDS system when acceleration changes are required. This explains part of the acceleration side of the issue and anytime minor acceleration is required where the truck could previously leave MDS engaged may now require it to disengage to get more power output.

Generally you are also going to deal with more more rolling resistance as the wheel/tire combination is heavier as well as the more aggressive tread pattern/design of an off road tire. Since they are designed, typically, for grip under adverse conditions and side wall strength they will be heavier and have a "gripper", as in more friction, optimized design. They are also going to be more likely to deform, part of the grip strategy, all of which will increase the rolling resistance. Combine this with a typically much wider tire which has a wider contact footprint with the surface and it all starts to add up. This explains part of the steady state part of the issue as it will take more constant power output in order to overcome the additional rolling resistance.

Finally you have the final drive ratio change by moving to a larger diameter tire. This will reduce the mechanical advantage available to get power to the ground via the friction (grip) between the tires and the surface. The loss of the mechanical advantage leads to less torque multiplication of the engines output which again will require more output power from the engine given the same conditions once a larger tire is in play. This is why a re-gear can help the truck significantly when larger tires are used as you regain the lost mechanical advantage restoring the lost torque multiplication. This is a factor in both the steady state part of the issue as well the acceleration part of the issue.


https://www.khanacademy.org/science...momentum/torque-tutorial/a/rotational-inertia
https://opentextbc.ca/physicstestbook2/chapter/dynamics-of-rotational-motion-rotational-inertia/

https://www.real-world-physics-problems.com/rolling-resistance.html

http://www.dynamicscience.com.au/tester/solutions1/hydraulicus/gears1mechanicalad.htm

It's been a while since I did any real Physics so I probably didn't explain something properly or otherwise screwed up, but it should be sufficient to get the idea across.

Understood it all. I was thinking OP was talking about flat ground cruising after reaching desired speed. MDS doesn't belong on these trucks. I shift to "6" so it never activates.

Thanks for a well worded answer.

 

[joshuaeb09]

Understood it all. I was thinking OP was talking about flat ground cruising after reaching desired speed. MDS doesn't belong on these trucks. I shift to "6" so it never activates.

Thanks for a well worded answer.

I agree 100%. Mine is disabled in the tune and prior to that locked out every time it went into D. I was seeing little to no difference in economy with sometimes MDS off beating MDS on, but the trucks also had 275/65R20 LT E1's on it since 300 miles or so. Once I get my old house sold and tax refund I'll be tossing some bumpers on it, likely going to 6112's or coilovers from my 5100s, and switching to 315/70R17's on it. I know my economy is gonna take a hit, but honestly I don't care much about that. Living where I live now it's more about not bending the stock 20"s anymore than they are and being more capable in adverse weather like when the "roads" wash out or the low water crossings turn into basically mud.

 

[mboymopar]

To cover the high points as best I can with my rusty physics knowledge :

The heavier wheels and tires increase rotational inertia and as your mass increases you get less angular acceleration for a given amount of input force. This will also reduce your breaking power since inertia works both ways. MDS only operates when the truck is under light load and by removing half the cylinders from the equation you get less torque output. Since the heavier wheels and tires require more input force to get moving the truck will not see as many instances of optimal conditions in which it can enable the MDS system when acceleration changes are required. This explains part of the acceleration side of the issue and anytime minor acceleration is required where the truck could previously leave MDS engaged may now require it to disengage to get more power output.

Generally you are also going to deal with more more rolling resistance as the wheel/tire combination is heavier as well as the more aggressive tread pattern/design of an off road tire. Since they are designed, typically, for grip under adverse conditions and side wall strength they will be heavier and have a "gripper", as in more friction, optimized design. They are also going to be more likely to deform, part of the grip strategy, all of which will increase the rolling resistance. Combine this with a typically much wider tire which has a wider contact footprint with the surface and it all starts to add up. This explains part of the steady state part of the issue as it will take more constant power output in order to overcome the additional rolling resistance.

Finally you have the final drive ratio change by moving to a larger diameter tire. This will reduce the mechanical advantage available to get power to the ground via the friction (grip) between the tires and the surface. The loss of the mechanical advantage leads to less torque multiplication of the engines output which again will require more output power from the engine given the same conditions once a larger tire is in play. This is why a re-gear can help the truck significantly when larger tires are used as you regain the lost mechanical advantage restoring the lost torque multiplication. This is a factor in both the steady state part of the issue as well the acceleration part of the issue.


https://www.khanacademy.org/science...momentum/torque-tutorial/a/rotational-inertia
https://opentextbc.ca/physicstestbook2/chapter/dynamics-of-rotational-motion-rotational-inertia/

https://www.real-world-physics-problems.com/rolling-resistance.html

http://www.dynamicscience.com.au/tester/solutions1/hydraulicus/gears1mechanicalad.htm

It's been a while since I did any real Physics so I probably didn't explain something properly or otherwise screwed up, but it should be sufficient to get the idea across.

Great read, thanks.

 

[16RamHemi]

i haaaattteee the mds with a passion. this "you cant even tell when it comes on" nonsense is bs. i can hear it on every gm / ram that has it activated as they drive by work. i turn it off every time i get in the truck. if i happen to forget its not long where i notice....what the hell is wrong with my truck....oh yeah mds crap, and quickly turn it off. i have a 14 sport 4x4 lifted 4" with 35X12.5 duratracs (bought 2 weeks ago) . i just went through my first full tank of gas. 14.25mpg hand calc. no highway miles. all backroads up and over a mountain everyday . im pretty happy with that. truck also saw a lot of 4 wheel drive over that time from snow/ice here in Maine.

now if i could only get this transmission tuned and away from short shifts and lugging, i would be a happy camper. tow/haul helps, but not completely.

 

[joshuaeb09]

i haaaattteee the mds with a passion. this "you cant even tell when it comes on" nonsense is bs. i can hear it on every gm / ram that has it activated as they drive by work. i turn it off every time i get in the truck. if i happen to forget its not long where i notice....what the hell is wrong with my truck....oh yeah mds crap, and quickly turn it off. i have a 14 sport 4x4 lifted 4" with 35X12.5 duratracs (bought 2 weeks ago) . i just went through my first full tank of gas. 14.25mpg hand calc. no highway miles. all backroads up and over a mountain everyday . im pretty happy with that. truck also saw a lot of 4 wheel drive over that time from snow/ice here in Maine.

now if i could only get this transmission tuned and away from short shifts and lugging, i would be a happy camper. tow/haul helps, but not completely.

There was an FCA flash that helped with the lugging and calibrating for your tires if it hasn't been done already helps a lot assuming its an 8 speed. That being said nothing quite like a custom tune to make the 8 speed that much better. Also helps that there's the extra power and MDS never comes on... ever. If it's a 6 speed the tranny tune would help, but so would gears, much more so than with the 8 speed.

 

[16RamHemi]

There was an FCA flash that helped with the lugging and calibrating for your tires if it hasn't been done already helps a lot assuming its an 8 speed. That being said nothing quite like a custom tune to make the 8 speed that much better. Also helps that there's the extra power and MDS never comes on... ever. If it's a 6 speed the tranny tune would help, but so would gears, much more so than with the 8 speed.

yes i have the 8 speed. calibration was done at dealer when p.o. had tires and lift done. as far as i know all recalls and updates are done. im not seeing any tuning available for the 8 speed. i know at one time hptuners did it. does anyone offer it any more? i dont see a hemifever or greene tune helping all that much down low. i dont need more power. just keep the truck from shifting so damn quick. its like i have to drive it like a ***** ape. cant just roll into it and tach her up. next thing i know im going 15 in 3rd.

 

[joshuaeb09]

yes i have the 8 speed. calibration was done at dealer when p.o. had tires and lift done. as far as i know all recalls and updates are done. im not seeing any tuning available for the 8 speed. i know at one time hptuners did it. does anyone offer it any more? i dont see a hemifever or greene tune helping all that much down low. i dont need more power. just keep the truck from shifting so damn quick. its like i have to drive it like a ***** ape. cant just roll into it and tach her up. next thing i know im going 15 in 3rd.

Yea my greene tow tune fixed that up and TH mode is even better about it. Not sure if it was the 14's or the 13's that have issues with Diablo tuning the 8HP70, but HP tuners can flash them for sure.

 

[16RamHemi]

Yea my greene tow tune fixed that up and TH mode is even better about it. Not sure if it was the 14's or the 13's that have issues with Diablo tuning the 8HP70, but HP tuners can flash them for sure.

good to know. its the worst when taking off from a stop slowly (without stomping on it taking off) and then anytime slowing down then needing to accelerate (like taking a turn, car in front turning etc) its always in the higher gear. would have to stand on it to get it to downshift again.

i dont necessarily need a tow tune as i never tow. when i do tune it will not be a canned tune. definitely custom...probably from Jay. i dont need more power or fast quarter times. just want a better driving experience and also make this trans last (i cannot imagine these lugging so much is too good for the trans).

 

[PolarisCobra]

Also have to consider the lift. You said you had a 6 inch lift, that is a lot more air resistance. Makes a bigger difference at highway speeds. It's takes more power to move all that air out of the way, like going up hill all the time.

 

[joshuaeb09]

good to know. its the worst when taking off from a stop slowly (without stomping on it taking off) and then anytime slowing down then needing to accelerate (like taking a turn, car in front turning etc) its always in the higher gear. would have to stand on it to get it to downshift again.

i dont necessarily need a tow tune as i never tow. when i do tune it will not be a canned tune. definitely custom...probably from Jay. i dont need more power or fast quarter times. just want a better driving experience and also make this trans last (i cannot imagine these lugging so much is too good for the trans).

I don't tow much, but the idea is the same as a the sport mode TCM mapping on the cars. Keep the damn thing in the power band and readily downshift when power is requested. When you get a tune just tell Jay what you want and he can make it happen.

 

[Iampeter]

I don't tow much, but the idea is the same as a the sport mode TCM mapping on the cars. Keep the damn thing in the power band and readily downshift when power is requested. When you get a tune just tell Jay what you want and he can make it happen.

Fairly new here. Who is Jay and what tuner are y’all referring to? I’m in a 14 2500 6.4L getting ready to put some 35s on it. TIA

 

[16RamHemi]

Fairly new here. Who is Jay and what tuner are y’all referring to? I’m in a 14 2500 6.4L getting ready to put some 35s on it. TIA

Jay Greene of Greene Racing. A great Hemi tuner. Can tune engine, trans etc. Can be found on facebook (no company website). Hemifever is another tuner recommended on here.