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Discussion Starter #21
Looks Great, Could you give a little more info on your rims? 16" you stated would you know the width and the offset.
Link were a person could purchase? Thank you
They are KMC Nomad KM716
16x7.5 5x110 bolt pattern.
 

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Thanks for the info. Your Compass looks great. Thanks for sharing with the group.
 
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It does look good Cmamisano! I have just upgraded my 2014 Gen 1 to a 2018 Gen 2 Altitude. Only 3600 on it right now, but I'd like to consider the lift kit when the factory tires need replaced.
 

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I purchased about a month ago and yesterday had the following installed:
• Teraflex Lift Kit
• 1" Spacers
• KMC 16" Wheels
• BFG KM3 235/70R16 View attachment 13453 View attachment 13454
[/QUOTE
I purchased about a month ago and yesterday had the following installed:
• Teraflex Lift Kit
• 1" Spacers
• KMC 16" Wheels
• BFG KM3 235/70R16 View attachment 13453 View attachment 13454
Wow that is a nice looking Compass. I have the same one, and this gave me some ideas for sure.
 

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Did ya hit any good trails or beaches this summer, @Cmamisano ? Its been over half a year still wondering if you got any pics parked anywhere besides your driveway or local mega-mall parking lot :p

Based on what I remember seeing on the rest of the forum over the summer not much in the way of off-road pics or videos from anyone else either... seems like my poser-point still stands (but you guys know I'm just teasing, tongue-in-cheek)

I didn't realize when I shot this off-the-cuff snapchat video that I was possibly documenting the most extreme Jeep Compass off-road action of the summer 🤣


Those of you with lifts and huge tires, feel free to post or make a thread with anything more off-roady than my video above. I will wait 😋
 

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2018 Jeep Compass Trailhawk
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Sure did not like seeing that...especially for a Trailhawk. If he had let off the gas and started trying to move again would it have engaged?
Nope. That was the video that almost discouraged me from buying a trailhawk. Now that I own one, I have experienced that 'output safety limit' many times. Keep in mind that I do frequently push the vehicle to it's limit, and am generally impressed with it's off road capabilities. Regarding the 'output safety limit', perhaps @arudlang or someone can explain how it works exactly but what it feels like to me is just the vehicle cutting power to the wheels that have no traction so the fewer wheels with no traction, the less available power, even if the accelerator pedal is pushed to the floor. The power is cut from the wheels without traction but does not seem to be transferred to the wheels with traction. When I have been in situations where only 2 wheels have traction like the situation shown in the video, It feels like there is about 50% power available, even with the accelerator to the floor. Now as long as you stay on the accelerator, the vehicle keeps the available power applied and continuously looks for a solution, and if the traction situation changes, like some loose rocks get kicked out, it very well may start moving forward again. Keep in mind that this is really only an issue on steep roads with irregular traction which is exactly what the video was trying to demonstrate. I have found that if you pick a line that keeps as many wheels as possible firmly planted on the ground, the vehicle can climb some pretty steep grades. For example, the following photo is climbing a pile of asphalt at a 28 degree angle, thats a 53% grade with no problem as there is plenty of traction all around.

14232
 

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Great informative post @Rederrabbit
Your real-world experience carries more weight than my arm-chair theories about how the 4x4 system works.

I am pretty sure my theory about how and where the PTO for rear wheel power comes out of the transmission is wrong. I suspected that the PTO unit was after the front diff and rear power taken directly off the front passenger-side axle (after the diff) but that just doesn't add up, at least not per videos such as this:


There is an open question on whether the hardware/PTO setup is mechanically any different on a Trailhawk vs non, but so far no evidence of that.

If my prior understanding was correct it should be impossible for a rear wheel to slip without the front-right wheel slipping as well, and in that video we can clearly see that is not the case (many examples of FL & RR wheels slipping together). This suggests that rear PTO happens at or before the front diff, which is good. I had thought previously that if you lost traction at the front left wheel then you had basically lost everything, but there are a good handful of videos showing that is not true, I see a fair number of examples of these cars doing inclines and diagonal inclines where the front left wheel is in the air and it can still proceed forward.

Apologies to anyone I argued with on this in the past, and my likely dis-information buried in old posts. I definitely don't know everything.

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Allow me to do some rambling, get some thoughts out of my mind and onto paper...

what it feels like to me is just the vehicle cutting power to the wheels that have no traction so the fewer wheels with no traction, the less available power, even if the accelerator pedal is pushed to the floor. The power is cut from the wheels without traction but does not seem to be transferred to the wheels with traction. When I have been in situations where only 2 wheels have traction like the situation shown in the video, It feels like there is about 50% power available, even with the accelerator to the floor.
Something I would point out here is there is only one source of power: the engine. Things are going to get really complicated when the 4xe models start coming out, but we needn't get into that here.

So you have one engine + transmission making power and 4 wheels to potentially get that power mechanically delivered to. We know we have open front and rear differentials (non-locking). We know rear power is delivered by a PTO unit (power take-off) and we know this unit "hard-locks" with a dog clutch. We also know that in the rear diff power coming from the driveshaft can be applied variably via an electronically controlled clutch (meaning whatever power is coming down the driveshaft can be variably applied 0-100%).

We have the PTO unit instead of a transfer case. This means the front axle can never be disconnected. Its a front wheel drive setup and the PTO allows power to potentially also be sent to the rear wheels, but it can never be sent only to the rear wheels, front wheels are always in play no matter what. The front wheels may be in the air or on ice or whatever with no traction, but they cannot be disconnected from the drivetrain like the rears can.

The car 'knows' which wheels have traction and which are slipping because individual wheel speed sensors know how fast each tire is turning. If the AWD is fully locked, meaning rear variable clutch is at 100%, then theoretically a front wheel cannot slip unless a rear wheel also slips and vice-versa. Open diffs front and back allow one tire to slip freely front and back until brake-lock steps in to do its thing, and this (finally) is where I think your perception of 50% power available comes in.

So the car knows when wheels are slipping, which is practically only ever going to be a front wheel or one front and one back (other than on ice). Brake lock can try to divert some power across the diff to the other side, up to a certain point. Brakes only have so much holding power, and the car knows that if it allows the engine to produce too much power in this scenario that stuff will start to break. So the engine power is cut to avoid damage, or reduced to a certain level (50% sounds reasonable). It can't really cut power to individual wheels, it can only reduce the output at the engine itself when it knows too much torque is about to be applied to only one or two wheels.

The hotter and more worn your brakes are, the less effective brake lock will be.

I have found that if you pick a line that keeps as many wheels as possible firmly planted on the ground, the vehicle can climb some pretty steep grades.
This for sure is key for a system like ours. Brake lock is limited. Better than nothing, but still limited. Best bet is to keep as many wheels down as possible so that brake lock doesn't need to be relied upon. We don't have many options there other than disconnecting front sway bars, we have a stiff unibody chassis that loves to lift wheels but lifting wheels is our traction-enemy.

Last bit of rambling. I still think with how similar the Cherokee and the Compass are (both have a 2.4L + 9 speed option with similar selec-terrain control) that someway somehow it might be possible to retrofit the locking rear diff of a Trailhawk Cherokee into a Compass.. Heck even if a person made their own separate wiring harness and switch for the lock function (rather than try to enable it in the PCM and swap interior button controls) it would still be a major upgrade. I wonder if I will have my Compass long enough for it to be old and worn enough to warrant fooling with that someday...

btw guys my lease is up next month 😉
 
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