Need 2019 Rav4 Rear-only lift; modest spacers or airbags?

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Lindenwood

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Sorry if I offended anyone here.
Normally when people ask suspension questions they are either to see what others run or have no real idea how things work.
I'm not a physics instructor but I am a mechanical engineer. Most of my practical knowledge came later from off road and track racing. I'm now semi retired and teach Chassis and Brake class's. Everything from stock to heavily modified. I try to post things the same as I do my lectures which is why it's common for me to start with basic "this is how it works" .
What I wrote here was based on what I thought the OP was asking.
And again, did not mean to offend.
Not at all! I appreciated your inputs :) .
 

Wawa Skittletits

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I’m sorry that you feel there was more to this than there is @Lindenwood. At no point did I imagine that anyone else would have been offended, I know I was not. Without getting mired the main point we disagree on is that you’re apparently ok with sacrificing suspension travel and what can happen to your ground clearance as a result of being, what I consider, undersprung. I prefer to retain the suspension travel that the additional weight still compresses when weight transfers in technical terrain. To each their own and as I said I wish you luck with your rig.
 

Lindenwood

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I’m sorry that you feel there was more to this than there is @Lindenwood. At no point did I imagine that anyone else would have been offended, I know I was not. Without getting mired the main point we disagree on is that you’re apparently ok with sacrificing suspension travel and what can happen to your ground clearance as a result of being, what I consider, undersprung. I prefer to retain the suspension travel that the additional weight still compresses when weight transfers in technical terrain. To each their own and as I said I wish you luck with your rig.
Thanks :) .

I am not sure suspension travel will be reduced as you are expecting though. I'll have to really dig into it, but I think the factory coils are quite a ways away from stacking the coils. If that is the case, a .75" spacer shouldn't result in a coil so pre-loaded that the coils will stack before the control arms hit the bump stops.

You are right, though, that if I have a large load in the rear (thats what she said), the extra sag compared to properly-inflated bags aould definitely reduce available uptravel. This would indeed increase the likelihood of hitting the rear bumpstops at higher speeds on rougher roads, which is maybe what you are fairly thinking. On the other hand, I was thinking more at the types of trails where you are going 3-7mph, where the risk of unexpectedly bottoming out a whole axle is very low, but the benefits of a supple suspension are highest. In this case, I think the increased spring rate of highly-compressed airbags would largely counter the benefits of extra available uptravel for single-wheel flex.

I still really am curious about the effects of linked airbags on slow-speed articulation, thougha
 

smritte

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I still really am curious about the effects of linked airbags on slow-speed articulation, thougha
That idea has me curious. I have learned from experience (didn't listen when I was told not to) how much it increases body roll on a heavy tow rig. This idea on the other hand, could be turned on or off and it wouldn't be a difficult mod to do on my existing system. I just need two tee's and a valve. I already have extra line.
 

Lindenwood

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I was even thinking, if you teed the lines together to one inflation valve, you would only need to insert a binary valve on one side of the Tee to disconnect one bag from the inflation valve. That would effectively isolate them from each other with minimal extra hardware. Of course, if you prefered to have them completely separate for individual left/right balancing, then yeah you'd need a few extra bits to make it work.

But yeah, it is very intriguing!

As has been mentioned though, I imagine any cornering at even moderate speeds would result in increased body roll, so one would have to use caution with such a setup!
 

Lindenwood

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Some extra notes:

At the local 4WheelParts, I was able to handle and measure some spacers to determine that ones for the Wrangler TJ looked dimensionally perfect for the rear lower spring cup on my Rav.

I bought their .75" spacers which will lift the vehicle ~1.25". I took some more measurements today of various suspension components, and measured ride height before and after a scaled weight of 120lbs in the cargo area. From there, I have estimated the rear coil spring rate at ~200lb/in. (It took 120lb to drop the rear wheel wells .625", which gives a combined effective rate of 200lb/in. The coils sit 12.5" from the control arm pivot, and the center of the tire is around 25" from the pivot, giving a 1:2 mechanical disadvantage. Thus, each coil is applging twice the force as is experienced at the tire, or ~200lb/in per coil).


I am about .75" lower than stock with the weight (including the hitch, which I didn't remove) so this lift should put me about .5" above stock height (about 9.5" rear ground clearance with my larger tires). Thus, it would take another ~100lbs to sit back at stock height.

From here, basically every 200lb over the rear axle will drop it another inch. So, in all, for normal outdoor uses, with my dogs (75lb), wife (125lb, or about 65lb over the axle), kid (about 50lb) and maybe a cooler and some extra gear, I'd be looking at another ~250lb over the rear axle, which would sit me around .75" below stock, or right where I am now. I am okay with that :) .

I don't have time to do the work before I leave again next Monday, so I am paying a shop to do it tomorrow. I'll push results then.
 

Lindenwood

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It didn't work; the lower cup was slightly oversized, so once the spring was re-compressed in place, spacer kept wanting to slide to one side off the lower spring perch.

But, I am probably going to go with a full ReadyLift kit, with a small tweak to get some more out of the rear. Naturally, I built a spreadsheet to calculate exact lift / squat heights with varying degrees of gear and pax. With the lift and additional modifications, the rear will ride ~2" above stock on a daily basis (if I leave my fridge in the back, or move some gear stored in the engine bay back to the rear), and would drop to around stock height with a complete loadout (fuel, water, dogs, bikes, and family). Of course, at that point we'd have exceeded my GVWR, which then justifies convoying with my wife's 4Runner TRDP :P .
 
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Lindenwood

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I’m sorry that you feel there was more to this than there is @Lindenwood. At no point did I imagine that anyone else would have been offended, I know I was not. Without getting mired the main point we disagree on is that you’re apparently ok with sacrificing suspension travel and what can happen to your ground clearance as a result of being, what I consider, undersprung. I prefer to retain the suspension travel that the additional weight still compresses when weight transfers in technical terrain. To each their own and as I said I wish you luck with your rig.
Something occurred to me: when referring to reduced suspension travel, were you thinking I was looking into strut spacers (whether internal or top mount)? If so, indeed those would reduce available travel, but the Rav doesn't have struts in the rear :) . Instead, it uses a multi-link rear suspension with a separate shock and coil, so a spacer on the coil wouldn't inherently reduce available travel in the same way as if the spacer was put on / in a strut or captive shock.
 

smritte

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It didn't work; the lower cup was slightly oversized, so once the spring was re-compressed in place, spacer kept wanting to slide to one side off the lower spring perch.
Damn, that would have been nice. I forget, were the spacers made for your vehicle or did you use some from a different year/make?
The air springs I use work very well off road. I was a bit skeptical putting them inside my coils. I thought they would pinch or rub through. My cruiser has seen quite a bit of off road and no issues.
 
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Wawa Skittletits

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Something occurred to me: when referring to reduced suspension travel, were you thinking I was looking into strut spacers (whether internal or top mount)? If so, indeed those would reduce available travel, but the Rav doesn't have struts in the rear :) . Instead, it uses a multi-link rear suspension with a separate shock and coil, so a spacer on the coil wouldn't inherently reduce available travel in the same way as if the spacer was put on / in a strut or captive shock.
I find that the damper is usually the limiting factor and the reason they have internal bump stops. The spaced coil will recoup what was lost on flat ground but to me being undersprung will still be sacrificing clearance in weight transferring situations. Up or down steep grades for example. I have no idea the terrain you intend to tackle with this thing so this could all be wasted typing haha.
 
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Lindenwood

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Damn, that would have been nice. I forget, were the spacers made for your vehicle or did you use some from a different year/make?
The air springs I use work very well off road. I was a bit skeptical putting them inside my coils. I thought they would pinch or rub through. My cruiser has seen quite a bit of off road and no issues.
They were for a Jeep TJ. It surprised me, because they fit perfectly inside the coil, but mated very poorly onto the perch.

However, I ended up just buying the full Readylift kit, and separately ordering additional lower spring spacers for the previous gen rav4 which, based on dimensions sent by the seller, should actually fit. All said and done, with my current gear and planned mods (will eventually do a little armor up front), the front should sit around 1.5" above stock, and the rear should settle around 2" above stock.

I started to again seriously consider airbags, but decided on a full lift instead.
 
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Lindenwood

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I find that the damper is usually the limiting factor and the reason they have internal bump stops. The spaced coil will recoup what was lost on flat ground but to me being undersprung will still be sacrificing clearance in weight transferring situations. Up or down steep grades for example. I have no idea the terrain you intend to tackle with this thing so this could all be wasted typing haha.
Ah! Yes, a softly-sprung vehicle will certainly lean more in steep or off-camber situations!

*,edit*

I've been wheeling in Florida for the last while, so big cims and decents haven't bern a huge issue. Once we most West, we'll see!
 
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Lindenwood

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The spacers for the previous gen (4th gen) Rav4 worked. So, I technically lifted the rear 3.2" with both the Readylift kit + these extra spacers, but it sits about 2.1" higher right now with all my gear. Especially since I removed both anti-sway bars, the ride is as soft as ever (which I wanted). Airing down on the trails with these larger tirewalls should make offroad riding quite plush!
 
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