Rear Sag, Roof Cargo Box, New Tire on Vacation Trip

So my family and I traveled on vacation from Ohio to the North Carolina Coast, 2 weeks ago, the 1st big trip in our 2018 CX-9 Signature, other than a shorter one to Michigan last year.
The CX-9 did great overall. I averaged 23.5 mpg on the trip, which of course involves a lot of elevation change through the Appalachian mountains and a rood top carrier adding drag. Road noise was great as we know. The seat comfort was excellent, and I was a bit surprised at this, due to the smallish seats bottoms. But me nor my wife ever had sore bottoms after 10 hours, which cant be said for some of our past vehicles.

We were packed to the gills, 2 adults, 3 kids + 3 car seats (1, 5, 6), 1 large suit case, 2 small ones, 4 back packs, a stroller, a pack&play, 2 beach chairs, towels, toiletries, some drinks, fishing pole........tough to calculate the total weight, but I would guess around ~900 lbs. Load was distributed in the rows/seats as you would expect, about 200 lbs on the roof in a cargo carrier, luggage in the rear.

Bought a used but in great condition roof top carrier for $80, basically a Vista Sportrack XL (made by Thule) but mine was a branded version sold at Pep Boys, as there was no way to fit all our stuff in the CX-9. The three suit cases and backpacks, food/drinks where all in the 2nd and 3rd rows (we had 2 kids in the middle row outboard seats, and one in the 3rd row passenger side), and everything else in the cargo box. The carrier fit the factory roof rack very well, the the size was great at 18 cuft. Fit within the rails and roof length just right. The mounts themselves were crude, just u bolts that have twist nuts inside the carrier. I wrapped the roof rack cross bars with 2 layers of Gorilla duct tape to prevent the ubolts from damaging it, and it work good. Loading was a little tough, it opens from the rear, but Im 6'2" so could just reach up and place stuff in, then strep on the rear tire to move stuff around inside the carrier. The relatively low roof line of the CX-9 helps. Wind noise was minimal

Power was a non issue through the mountains, and the handling was just ok (not the normal great ride and handling we are used to around town, etc).........mainly due to one issue, the rear end sag. I didn't actually measure the rear sag, but with all our stuff in and all of us in it (the 900 or so lbs), the rear sag was noticeable (see pic) visually and when driving. There was what I call a porpoising, like on a boat, due to the rear biased load and sag. I didn't happen most of the time, rather only over undulating stretches of road, and over bumpy roads. I just felt like the front end was pointed up and the front sag and softness induced at the rear, cause the car to porpoise.

I would guess the rear sat a good 1/2" to 1" lower maybe (see pic close up rear). This wasn't terrible by any means, just maybe worse than I expected, based on our previous and current SUV's. And I think some of this of course is a compromise of the great handling vs load / towing capacity the designers had to make with the CX-9, and based on the chassis being more geared towards on road performance.

Vacation is once a year or once every other years, so in all but these situations, and of course towing, this would never be a problem. I had commented on some of the towing threads, that there is a lot of rear end sag with a trailer, and load distributing hitches can help that, but nothing you can do for passengers and cargo inside or on the vehicle. It would have been nice, since the CX-9 isnt a heavy duty, body on frame, type SUV made for heavy loads or towing, to have some type of load leveling rear suspension/shocks. Nivomat makes a nice product, had them from the factory on our old Volvo XC90, and previous Mitsu Montero and Toyota Landcrusier just had heavy duty suspensions (tow ratings over 5000 lbs), so sag was never an issue. On my daily driver, I have 4 corner air suspension, so that of course is another solution to eliminate sag, but admittedly one outside of what you would expect on a Mazda mid-level SUV. However, the new Telluride and Pallisade do offer load leveling rear suspension, Im guessing something like the Nivomat shocks.

I might play with air bags that you add inside the rear springs and inflate, for next year, just to maintain the stock rear ride height and see if it helps with the porpoising. Only issue will be if they make universal ones that could fit. I cant find anything in terms of even replacement shocks out there for the 2nd gen CX-9, let alone springs, helper springs, air bags, etc. There are some coil overs, but not sure the availability in the States, and if they are adjustable for height increase (most are adjust for lowering).

Had new tires for the trip also, 255/50R20 Falken Wildpeak AT trails, and they are great. Ride, handling, impacts, response, traction are all better than the pathetic OE Bridgestone's. Will have to see how snow and wear are in time. They are 3 peak mountain snowflake and have a 65k treadwear warranty, so I am sure they will hold up better than the OE tires. Noise is unbelievably good, especially when you consider the appearance and the fact they are AT tires with 3 peak mountain snow flake rating. very slight noise increase, that's hardly noticeable. I attribute a good chunk to our CX-9s excellent cabin noise attenuation. The look of these is the other reason I bought them, wanted to add a bit of ruggedness to the civilized CX-9. They have an aggressive upper shoulder, pattern, and cool sidewall lettering. Tread width is also wider so they look better especially on our wider than normal 8.5" wide OE wheels. Fuel Economy I'm sure took a hit a bit, but I don't care, maybe 1 mpg or so.

Hope this helps someone, and welcome any thoughts on how to combat the rear end sag for our next vacation trip!
 

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sm1ke

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Thanks for the detailed account!

With regard to the rear sag, I've been in talks with Ceika, who manufacture coilovers for the CX-9 (and other Mazda models). As I understand it, their coilovers are built-to-order, meaning you'd be able to talk to someone about your needs and they would tell you if they could accommodate your requests. Ceika does offer an air lift system, but it is more of a suspension assistance system for extra low cars that may need extra clearance for short periods of time, i.e. speedbumps or driveways.

They do offer the option to build a coilover kit for extra lift, to give the CX-9 suspension more shock travel for a more comfortable ride. They also offer "helper springs" that could possibly assist in reducing the porpoising effect, but you'd have to speak with them on that to be sure. Both options carry additional cost.

For the 1M kit with the extra lift and helper spring options, it would be approximately $1410 USD (including free shipping). Here is their product page.

Finally, they have also mentioned to me that they are currently developing an airbag suspension option for the CX-9 as well.

Disclaimer: I am in no way affiliated with Ceika Performance. I just like what they offer.
 

sm1ke

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On a related note, when I moved from one province to another, I loaded my CX-9 down with about 950+lbs of weight plates and other gear, plus my wife and baby. I never had any of the issues you described with porpoising, but to be fair the roads were very smooth and the drive was pretty straightforward with few hills and curves.

IMG_20180625_190106.jpg

IMG_20180625_102426.jpg
 
Thanks sm1ke, thats about what mine looked liked loaded up.
I shoulid add, this only occurred at high speeds, on the interstate, 60 mph + through the mountains of west virginia/virginia/NC, where there was smooth pavement but undulations and dips, and when there was uneven sections of road that where older.

I had seen Ceika stuff you mentioned when I did a search, so I will have to think about that option. I dont want to soften the ride more, actually I think the way it is stock and with normal loads its just about right, actually I want to stiffen it if anything, especially the rear with load.
Either way it sounds like Ceika could do exactly what I want.

Ill still look into just adding the air bags inside the rear springs, that would be the most economical solution and only be needed when using the heavier loads.

Thanks for the great feedback.
 

sm1ke

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Sounds good, please keep us posted on what you find regarding the air bags inside the rear springs. You're right about it being the most economical, especially if you're like me and don't plan to carry heavy loads often. Hope you're able to find a solution that works!