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-   -   Why is the towing capacity so low? (http://www.jeepgarage.org/f97/why-is-the-towing-capacity-so-low-23026.html)

andyh 05-10-2011 11:30 AM

Why is the towing capacity so low?
 
What is the limiting factor in the 5,000lb max trailer weight?

soontobesrt 05-10-2011 12:29 PM

Re: Why is the towing capacity so low?
 
Quote:

Originally Posted by andyh (Post 412314)
What is the limiting factor in the 5,000lb max trailer weight?

Well the truck was made mainly to fit the performance sector of the market. That said, it has an independent rear shock/spring suspension setup. Its also a relatively small vehicle when it comes to serious towing, its not F350 haha. Most trucks use leaf spring setups and even better is a nice air setup in the back.

So like I said, I know they "tried" to make it a towing capable truck due to that being the biggest gripe from most owners and other who would have bought if it could respectably tow. BUT, I think they still tried to keep this thing performance oriented and in turn the suspension system and geometry aren't designed for a huge payload. I personally think 5k lbs is a nice load, you can certainly tow a nice size boat around :) Im just going off the top of my head, dont know the exact reasons here I mean the truck isnt even on the road yet :)

cyanideg 05-10-2011 12:36 PM

Re: Why is the towing capacity so low?
 
Your question should be, why is there a towing option at all? Im buying it for power, not to tow a boat.

ChrisL1976 05-10-2011 12:45 PM

Re: Why is the towing capacity so low?
 
I think you pretty much covered it. Its a balance between what the average Jeep owner would be towing and keeping the Jeep suspension geometry off-road capable.

Its on the flip side of owning a big 4x4 truck that will pull 10k and complaining why its not as off-road capable as Jeeps.

From a design cost point....Personal guess, 90% of jeep owners will never need to pull more that 5k, so why waste money designing it for that. I'm sure it could be done, but more than likely the number of estimate sales for the upgrade from suspension and powertrain would price it way to high. Would pay ,say, an extra $5k to be able to pull 10k pounds?

jgc4ever 05-10-2011 12:54 PM

Re: Why is the towing capacity so low?
 
The 2011 Jeep Grand Cherokee 5.7 L V8 Hemi with trailer tow IV tows more (like 7,500 lbs. I think) than the 2012 Jeep Grand Cherokee 6.4 L Hemi V8 SRT8 (5,000 lbs max). So, does anyone know why the 5.7 L V8 Hemi w/ trailer tow IV on an Overland, Limited or Laredo tows more maximum weight than the 5,000 lbs. the new SRT8 is capable of?

andyh 05-10-2011 02:48 PM

Re: Why is the towing capacity so low?
 
I understand that towing capability is not a marketing target for this car. I'm just wondering why a car with way more power/torque than the 5.7L tows 2000+ less pounds.

It is the lower towing rating due to the physical design, like the tires for example? Is it marketing? lawyers?

soontobesrt 05-10-2011 09:56 PM

Re: Why is the towing capacity so low?
 
Quote:

Originally Posted by andyh (Post 412430)
I understand that towing capability is not a marketing target for this car. I'm just wondering why a car with way more power/torque than the 5.7L tows 2000+ less pounds.

It is the lower towing rating due to the physical design, like the tires for example? Is it marketing? lawyers?

It would be the psychical design as you put would be the limiting factor. Power is only half the battle with towing so although the SRT8 has a ton of torque etc etc, the suspension isn't setup to handle a ton of weight although it has a tow mode. The suspension setup this rig has is tuned for performance over towing thus the auto/sport/track modes. They do have the tow mode though which as they have mentioned firms up the rear and basically splits torque closer to 50/50 I believe, the point of this being to try and keep the trailer or whatever your towing from swaying and dragging the jeep all over the road. In short, it basically puts a firmer grip on the whatever is behind it :)

The SRT8 does NOT have the air ride which I'm thinking is the reason why it tows 2500lbs less than the limited/overlands etc. That air ride gives those things a ton more ability to haul, hard to explain how it works but thats a pretty ideal setup, lots of big trucks and other haulers use a similar system. Not sure if the non air rides are capable of the same or not but thats my guess :)

webspoke 05-12-2011 11:30 AM

Re: Why is the towing capacity so low?
 
It's probably a transmission or differential limitation. The chassis is capable in the 5.7 versions, with and without air suspension, but the transmission is not the 545RFE used in the 5.7's and trucks. Add in the extra torque and power and it probably taxes it, and maybe the colling system too.

soontobesrt 05-12-2011 12:16 PM

Re: Why is the towing capacity so low?
 
Quote:

Originally Posted by webspoke (Post 413701)
It's probably a transmission or differential limitation. The chassis is capable in the 5.7 versions, with and without air suspension, but the transmission is not the 545RFE used in the 5.7's and trucks. Add in the extra torque and power and it probably taxes it, and maybe the colling system too.


hmmm, so even without the air ride the non-SRT is capable of towing 2200-2500lbs mores. Doubt the tranny/diff would limit it as everything the SRT used is the same part or one built for more power than in the 5.7s. The NAG1 is as capable as the 545RFE from everything Ive seen/heard and the rear diff in the SRT8 is a ZF ELSD which is very strong. The regular GC's either have the standard open rear diff I believe or with QuadraTrac II have the same ELSD as in the SRT8. So all in all, I dont see those driveline components being the limiting factors. Im going to bet its part of the suspension tuning system being as they use the same technology but different computer maps for the trucks. Just by ruling things out we can get an idea,

The 6.4 is capable of towing the load, the chassis is as strong or stronger than the regular GC's, the air ride is clearly not a determining factor as shown above. The driveline in the SRT8 is as strong as the normal as the W5A580 has been proven and the diffs that are offered are the same throughout the lineup so they can clearly handle the load. Only thing there could be like you said the added torque/hp of the SRT8 combined with he weight may be the reason but I doubt it, these drivelines are really strong, people have no idea I dont think haha. Seen stock WA580s take 750hp+ consistently with some tuning and some new shift solenoids. Lots of guys have even raced with them successfully for some time.

Don't know much about the specific ELSD used here, not sure if they are ZF's or not but Im going to assume they are pretty strong, safe to say since the SRT8 is already throwing some big power at it and they need to be built to handle all of that with some leeway for more plus last a decent amount of time. Anyone know anything about the ZF ELSD?


The SRT8 suspension is here:

"Short - and long-arm independent (SLA), coil springs, Bilstein Adaptive Damping Suspension (ADS), upper- and lower-control arms (“A” arms), stabilizer bar Rear - Multi-link rear suspension, coil spring, Bilstein Adaptive Damping Suspension (ADS), aluminum lower control arm, independent upper links (tension and camber) plus a separate toe link, stabilizer bar


Some info on the Bilstein ADS, or as they call it - (ACD):

http://www.bilsteinus.com/products/m...c-systems.html


Read from page 40 onward, good info. some info on Daimler-Chryslers Active Suspension in there
http://www.scribd.com/doc/51365510/6...ein-Damptronic


Not to sure if this is what we have or not, but if so seems its a first in the passenger car/SUV sector. This specific system from Bilstein has only been used on motor-homes it appears so should be interesting to see how it works. Unless this isn't the exact system then I dont know. This may just be another Contract between Chrysler and them to make these specifically for the SRT8s so it wouldn't be on the site. Same thing as with the Brembos on the Jeep and many other cars, they make OEM applications but you have to get the parts through Jeep or an aftermarket vendor, cant find get them from Brembo directly.

jgc4ever 05-12-2011 12:57 PM

Re: Why is the towing capacity so low?
 
I just saw a WK2 hauling a long nice camper trailer headed West on I-80 through Omaha. :cool:

Marlin 05-12-2011 05:11 PM

Re: Why is the towing capacity so low?
 
I have a theory..... maybe 5000lbs is the maximum the hitch mount and tow ball can take before an SRT launching at full throttle just plain rips it out of the back of the Jeep? :p

Hey, it's plausable, the things launch hard, and they need to engineer/warranty things for even abusive owners.

mjw930 05-13-2011 08:56 PM

Re: Why is the towing capacity so low?
 
Owning a 2011 Overland and having towed over 5000 lbs more than 2500 miles I'm pretty sure the limiting factor is the same as it was on the old F-150 Lightnings, a combination of the spring rates and the tires, it's certainly not the drive train or the chassis.

The 5000 lbs is probably there because the suspension can only take 500 lbs of tongue weight without causing too much of a rear drop, front rise. The manufacturer can't spec a tongue weight less than 10% of the trailer weight so 500 lbs of tongue weight means a 5000 lb max trailer.

I was hoping they would put the rear helper airbags on the SRT8 when the tow package was ordered like they do on the 2WD WK2's which would add the spring rate needed to support 720 lbs tongue weight my Overland can support. If they are using the self leveling secondary air bags then I have no idea what the issue is.

Honestly, I think with a proper WDH and a well balanced trailer you would have no trouble towing an enclosed car hauler with a track car, just like the Porsche's and VW's do without air suspension. (or my 16' enclosed MC trailer :) )


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