Hey all--I have a '21 TRD Pro and want to reduce the rear sag when towing a trailer. Does anyone have any experience or insight into a product like Sumosprings vs. Airbags (Firestone or Airlift)? Thanks!

Just looking at SumoSprings for a comparison to helper air bags I see a few things.
Sumo's are not ride height or load adjustable, what you have is what you get. They don't list taller options for lift, though they might be available. As a foam type support in a spring based role, will wear out and need replaced over time, possibly more often than springs. Ride is probably better than helper bags, but would not be as stable in off-road situations with side loads. If these were also inflatable to different psi I might consider them, but would wonder about the off-road situation still.

Helper air bags (like Firestone or Air Lift) can be adjusted based on load or a need to increase ride height, cost 1/2 the price, don't need replaced regularly, and ride more smoothly than stock. Because you retain the spring, are just as stable off-roading. You don't need onboard air for them (though it can be nice), even one of those battery powered drill type compressors is enough to adjust pressure because you're always below 50psi.

Having to adjust my Air Lift occasionally, I've found what happens is usually going past desired psi and let some air back out. I've never needed max psi on the bags, and usually have them barely above minimum for around town with just me. I've just made it part of checking the tires before a road trip to check the rear end and see if I need to add air. I only ever have to adjust the rear pressure if I've changed the load, driving cross county, towing trailer, etcetera. I will say routing the air lines to avoid them catching on anything while off-roading is important, but not difficult.

@Friggin Idiot Thank you--this is very helpful information. One of the things that makes the Sumosprings attractive to me is the super-easy installation w/no modification to the vehicle. I can switch back to OEM bumpstops in 20 minutes.
I am fairly confident that I can install the Airbags but cutting the OEM spring bumper makes me a bit nervous.
I will primarily be pulling a trailer or driving forest roads to get to fishing spots--not much true "4wheeling".
Your info definitely pushes me to reconsider the Airbags. Any other thoughts or experience is appreciated.

I ran Firestone Ride-Rite airbags on a second gen Tacoma (TRD Sport double cab long bed 4x4) towing a 20 ft ~3500 lb travel trailer and 2012 F150 (FX4 SuperCrew 4x4) towing a 27 ft ~6000 lb travel trailer and had excellent experiences with the setup on both. The thing I liked most about them was being able to drop them down to 5 PSI for daily driving, at which point they were totally invisible from a ride perspective, then I'd pump them up to ~30 PSI or so for towing. Made a huge difference in sag and ride/control when towing even though I was using a load distributing hitch. I didn't even mess with using a compressor or any of that...it was super easy to pump them up with a bicycle pump or a portable compressor. I usually just used the bike pump and it took less than 30 seconds per bag to pump them up. After install I never had to mess with them and had no issues with either install.

What did you go with?

I’ve been looking hard at air bags, but I think I may go with the sumosprings. They are similar to Timbrens but I think a bit softer and may result in a less harsh ride loaded than the Timbrens. They are un-engaged when not loaded so factory ride is not affected. Easy install plus no messing with air pressure is appealing to me... When camping I sag bad from payload and when I tow my boat it sags pretty bad due to the tongue weight and payload. I may get a TT so it will be even worse... Sumosprings should address that. Just need to decide between the blue or black. Blue is softer than black...

They will all be engaged during normal driving. They may not be touching the axle without load, but they're close enough that bumps will engage them. You'll find things like speed bumps more harsh with them installed. The same is generally true for air springs, but to a lesser extent because they can be deflated. Even deflated, they are not totally gone and they will still offer a significant increase in bump transmission through the chassis on larger bumps. Firestone air springs are less of an issue than Air Lift in this regard because the Firestone springs are narrow enough that they don't expand out between the coils and don't cause as much spring rate increase when deflated as the Air Lift ones do.

- Spend the extra $20 on Firestone. I have used both. The Air Lifts ones are in a box, the Firestone are in the 4Runner.

There is a third option that I haven't seen used, but could be a good middle ground alternative for folks who don't want to cut the inner bump stop. Those are air shocks. Monroe and Gabriel both make replacement rear shocks that also have air springs combined in the shock absorber so you can adjust the ride height or compensate for load. I have used them on my travel trailer for height adjustment, but never on a vehicle, so I have no idea on the ride quality. They do work pretty well for a simple air height adjustable suspension for trailers. And they're cheap.

Thanks for the info regarding Firestone vs Airlifts. I think I’ll still go with the Sumosprings and see how they do but if I don’t like them I can give Firestone a shot. Good point about speed bumps or similar will end up engaging the helper springs. I’ll have to do some before and after tests to see if I can tell the difference unloaded. I have KDSS which may make it even more noticeable for things like speed bumps since the swaybars move a lot more at low speed.

FWIW - I've looked high and low for a good solution. There's just not a perfect option. I used GX460 air suspension in the rear for a couple years (full air suspension with no coil springs) - there's a thread on here about that conversion I did. I've also used factory springs with both Air Lift and Firestone. And I've run Dobinson's 1.75" lift springs that were later revised on the lift table to be more like 2.5" lift springs.

I'm empty most of the time. Dobinson's lift springs were good springs, but they are taller than I wanted. And they're a little firmer than I need most of the time. I had the 227lb/in spring rate version. Air Lift made the ride too firm when empty - due to how they bulge out between the coils. GX460 springs ride very nice - but matching shock valving was the main issue there. And it's tricky to get them dialed in without a lot of electronics to self level like the OEM setup has. I wanted about a 1" lift for normal driving. After tinkering with a bunch of different solutions - I use a cheap 1" poly spacer, stock 180lb/in coils, and Firestone air helpers. It's not ideal, but of all of the combinations, it's worked the best overall for me from running totally empty, to towing my 5klb trailer or loaded up with a week's worth of gear.

If I keep the 4Runner - I might revisit the GX air springs, but this time I'll go deeper into the manifold system than my prior setup with some active electronics to self level and a home-brew ECU with my own programming. The problem with my last version was my manifold was designed to balance pressure left/right after height adjustment, but that's not what you want to sit level.

Out of all of the options - as you can imagine, OEM springs at stock height has the best ride.

On my Dodge Diesel I found Air bags unload the suspension. The leaf spring is working less while the airbag holds the weight. Can give a floating feeling. Generally not a fan of airbags. The longer travel rear springs of an off-road vehicle further complicates their actual use.

As long as you are at/under the vehicle capacity don't worry about it. Weight distribution accessories might be helpful.

Ping tanks for the airbags might help. However, 4runner doesn't have lots of spare undercarriage to mount spare air tanks.

Lots of great info here! Thanks. If the airbags were an easier install, (I know it’s not hard really, even for me...) I’d probably prefer it but these days I prefer to spend a little more money and a little less time under the 4Runner.

You say you pull a 5klb trailer. How does the 1” rear lift affect that? How much are you lifted up front?

It pulls like your expect with an underpowered v6. The spacer doesn't really have much effect that I've noticed. But I'm sure there's some effect. The airbags really firm up the rear end when they are inflated. I don't have any issues with sway or control. I do use a load dissing distributing hitch. But the engine isn't really good for the job though.

I'm about 2" up in the front. I have fox 2.5 coilovers and I've adjusted them to a lot of different heights from 1" to 3.5" or so. Ride quality goes down the higher you go up. Both front and rear. Best ride is stock height. There fox coilovers can't go below 1". There's not enough thread on the body to go any lower.

The weight really isn't the issue on the taller as much as wind drag. It's the giant box. The wind resistance is the killer. It's a travel trailer. 5k lbs of gravel in a dump trailer is no problem. I've towed that too.


FWIW, I wouldn't buy the big camper to tow with the 4runner. I bought an f250 at the same time. But it's turned out to be a piece of shit. So I've been towing while the truck is broke down.

Thanks. Yes, the 4Runner isn’t a great TV, but it’s my primary vehicle first and I like the ability to “off-road” with it and just think it’s a pleasure to drive normally. I pull my 18’ bayliner on a single axle that’s around 3500lbs loaded through mountains (east coast mountains...) and it’s not too bad but you know it’s back there for sure. I accept that. But the boat is low and aerodynamic.

I’m looking to get a TT that’s around 3700 dry and will be around maybe 4300 loaded. But I completely agree with you about wind. Once you hit 3500lb with the drag of pulling a brick, I’m not sure how much harder pulling 800lbs more will be. (I almost wonder if pulling a single axle at 4300 may be harder than a 4800 tandem...) I’ve pulled empty enclosed trailers and same trailer loaded and really couldn’t tell a difference. The damage has been done with drag. I know the 4Runner is not an ideal TV, but I’m willing to get a trailer that fits my TV rather than get my ideal trailer and buy a TV to suit. I just don’t want to get a 3/4 or 1 ton for my occasional towing needs...

Fortunately, someone near me has the exact trailer I’m looking at on RVShare so I’m going to rent it for a long weekend and test it out. They provide a WD hitch to renters and they are already towing it with a Highlander. I’m installing my redarc brake controller this weekend along with the Sumosprings. (My boat doesn’t have brakes....) If I’m really letdown with how it goes, then I may have to rethink everything.

I think my expectations are in line though. Most of my towing will be in the region. Maybe 400 miles round trip at the most with some longer occasional runs hitting 800 miles round trip. But that’s mostly on flat east coast. (I would like to take it to the keys which would be 2k round trip. I love kayak fishing for snapper down there!!!) I take things a lot slower than I used to. I was always in a hurry to get somewhere. Covid has honestly taught me patience. Take it slow. Enjoy the trip. See more sights along the way. Tack on a few days for travel if needed. If it takes two weeks to get in a part because they’re out of stock, deal with it... I think I’ve benefitted from it in a way...

One last question since I hijacked this thread!!! Did you install a tranny cooler for your towing? That’s the one thing I’m not sure about doing...

I think giving it a try is a great idea.

My case is a little unusual. I was planning to build a lake house this summer about 150 miles from my home. So I needed a place to stay during construction and I wanted a bigger TT with enough interior space to make it livable with our 1yr old for the summer. I also needed a truck for the project. The project is on hold because of the lumber shortage. So now I'm just going camping a lot this summer watching what lumber prices do.

But the Ford is a long bed crew cab. It's about 23 feet long. So taking it to somewhere like Yellowstone would be a nightmare. I don't think it's even legal to drive on the going to the Sun highway in glacier park. It's just a pig. I don't plan on owning it any longer than I have to.

If I were choosing the best TT for the 4R, I'd look at aerodynamics more than weight. I don't have a good reference for guessing whether single or double axle trailers would have more resistance. My guess is double axles have more drag. But I'm not sure. I don't know why, but TT manufacturers seem to put zero effort into aero. There are a few exceptions. The evergreen models. And the travel lite ones are pretty good I think. Airstreams are also pretty low drag. Frontal area is also a big factor, so the smaller profile ones like the Winnebago micro mini are pretty decent too. The next size down like the r-pods and winnidrops or things like the wolfpup - I think the 4runner would be great with those behind.

I did add a transmission cooler. I'm not sure it's necessary. Probably a waste of time and money. I think the Toyota WS is good for 250 plus temps, and I've never seen them that high without it. But it adds some level of comfort not having to even think about it. And it's pretty cheap too do. So I did add one.

The other issue I have that you may not have is posted 80mph highways. Most highways here are posted 80. Traffic is normally going 85. So driving 60 is like parking your car in the middle of 25mph traffic. It's not really safe to go that slow. I'm jamming up traffic going 70-75. And those speeds are a struggle for the 4R to keep up with a bigger trailer. If I could safely drive 60ish, it would tow a lot better. So maybe your roads are better for that issue.

Edit - one further thought down this rabbit hole; MPG. With my bigger camper last weekend over ~ 300 miles of highway, I got about 8.5mpg. It's almost like driving an EV at that level because of range anxiety. And into head wind there were segments of 5mpg. With only 20 gallons, you don't have to be that far away from the next gas station to start running through the calculation in your head and not being sure if you can make it. Half a tank might only get you 50 miles. So you may have to stop at basically every town to make sure you have enough to get to the next one. In Nevada there's a segment of interstate that's 170 miles between fuel stops. I could not make that crossing with only the gas in the gas tank. I barely made it last time I did that with my teardrop. With the bigger camper id have to bring gas cans along or drive 50mph the whole way.

Sorry to hear about your lake house plans. I just finished my basement and I’m glad it’s done with prices going up like they are... Now I can turn my attention back to the 4Runner and getting outdoors more!! (Covid gave me the time to do my basement but finishing 1100sf from start to finish (including jackhammering concrete to run drain lines) takes a lot of time and work!!)

I’m at a bit of a crossroads in doing things with my 4Runner. I lost track of miles on my tires and started looking closer at them. I have P265/70/17 Falken AT3W with 60k miles on them. Time for new tires. These have been really good though. A steal at $130/ea back in Jan of 2017. Since my wife still drives the 4Runner with some regularity for at least another 18 mos and I want to tow with it, I’m probably going to keep stock size for now. Probably go with TOYO AT3s. But I may upgrade to 5100’s all around. (Back when I originally researched lifts years ago, Bilsteins were very popular but not sure of that is still the case...) Is that still a good option to raise 0.85” to reduce rake? Or perhaps at 1.75” and put 1” spacers (keeping a bit of a rake) in the back and return the Sumosprings for Firestone air bags. I think that will still look good with a beefy AT even at stock size. Do you have any experience with ride on the Bilsteins? Seems like you have tried a bunch of different options in search of a good ride and good performance. With the 1” spacer in the back and Firestone air bags, did you not remove as many of the convoluted sections of the “overload bumper” to take up the 1”? Thanks again for your time man!

If you don't need the taller tires for offroading - I'd stick with stock size. Stock feels better gearing/power wise both empty highway cruising and also towing. The best ride and performance will be stock size for normal driving and most offroad use (until you run into clearance issues). Stock tires also will get better mpg - and that indicates to me that the engine is working less. I have bigger tires in part because of vanity, and in part for offroad performance. My next set of street tires will go back to stock size. I'll probably keep the 34" tires for offroad trips.

I haven't had bilstein 5100's on this 4Runner. I did use them on my 3rd gen 4Runner. I think they were okay. It's been almost 7 years. So I just don't remember very well the relative ride quality. I actually can't remember anything really good or bad about them. Install was pretty easy. Price was good. I think they're probably firmer than stock. And I think they're digressive valving, so they're going to transfer a little more of the small road imperfections through - cracks and potholes. I think, but I'm not totally sure, that the eibach truck shocks are the same thing with more progressive valving, so they'll be a bit softer. I'm not sure one is better than the other. Just a little different.

I think .85 up front shouldn't hurt anything. It helps with some clearance in the lowest spot. So that's a plus. But you'll need an alignment after. I would not try to "level" based on the fender heights. I think some amount of rake is important for aerodynamics. I don't know this for a fact, but I think it is true. Any lift is going to negatively effect mpg, it's just a question of how much. Most small lifts like 1" are relatively small impact on mpg.

My buddy has bilstien 6112 front shocks at 1.75" or something like that setting 5160 rears and 1.5" rear spacers with stock tire size. I think it looks pretty good and it works well for him. He likes it. Ride quality is good.

Prices have gone kinda high due to covid. The 6112/5160 was a lot cheaper a few years ago.

I did leave one extra segment in the rear bump stop for the air springs. I don't remember the part number, but there is also a taller air spring set that you could use. One thing to be aware of is that some poly spacers go on top of the spring top plate, so the distance from axle to internal rubber bumper is the same as stock and you'd just use the normal procedure for the air springs. Some spacers go between the spring and the bump stop/top plate. In that case you'd want to leave one extra segment on the bumper. The poly spacers I bought were supposed to fit between the spring and top plate - but actually didn't fit that way, they only fit on top of the top plate (I fixed it with a die grinder to fit the way I wanted). But just be aware that they can fit one of two ways.

Ultimately - if you don't need the lift, I'd stick with stock height or maybe something even smaller like a 0.75" rear lift and then you could go with a 1.25" front setting. The spacers generally come in 10, 20, and 30mm and then 1.5" for whatever reason. 1.5" is about 40mm. 20mm is about .78". 30mm is about 1.2". So if you want a .75 rear spacer, you'll search for 20mm. Not sure why it is that way, but that's how they are sold.

Also FWIW - on the rear springs, if you're comfortable around spring compressors - this is the only style I've found that works well for the rear. With these, you can swap rear springs without taking any other parts apart, just jack up the rear by the frame and support with jack stands so the axle is unloaded as far as possible (usually for me that means jack to lift under the axle, jack stands under frame rails, remove rear tires, and lower until weight is fully off of rear axle). Then you can simply compress the coils and remove them without having to disconnect any suspension components. I can swap rear springs in about 20 minutes. Other style spring compressors where the threaded rod goes through don't work for this. The threaded shaft will hit the bottom of the cab before you can free the springs. Or you can just drop the axle further as the alternative, but these make it a really easy job.