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Old 01-16-2019, 07:13 AM   #36
gmtech16450yz
Senior Member
 
Brand: Thor Motor Coach
Model: Vegas 27.7
State: California
Posts: 289
THOR #10907
Somebody did some homework! haha.

Valid conclusion for your situation. Don't ever feel like you have to justify what you decide to do, everyone has their own preferences and criteria for their wants/needs. You're absolutely right, Sumo springs are an "install it and forget it" mod. I totally understand that part of the decision, airbags take a little more "work" to use. For me, having total control of the ride from the drivers seat via an onboard compressor, air tank, gauges, valves and airbags is well worth the "work". I'm not you and you're not me though, and that's perfectly fine. lol.

I do have to say though in case anyone else is reading this comparing Sumo springs to airbags... You can't really compare a vehicle suspended by urethane vs. a vehicle suspended by air bags. There's a reason why airbags have been used widely on all different types of vehicles for decades and Sumo springs are kind of a niche product that isn't widely used outside of this application. Sumo springs are really only glorified bump stops. Bump stops, in the real sense of vehicle engineering, are a "last resort" device, not meant to be an active suspension device. They do not and can not work as well as leaf or coil springs or airbags. Since vehicles have had some sort of spring and some sort of bottoming device like bump stops, when the suspension gets to the point of contacting the bump stops, you lose control of the spring part of the suspension. Yes, of course I realize that Sumo springs are much more compliant than rubber bump stops, but they aren't going to have anywhere near the same spring rate and travel that the regular spring part of the suspension has.

Which actually just made me remember something about my Vegas... The axle loading on the front was different from side to side. I don't remember how much or which side was heavier, but I realized it BECAUSE OF the Sumo springs I had installed. When going over speed bumps, the front end travel wasn't even side to side. As the suspension compressed, I could feel one side "bottoming" before the other. I looked at the Sumo springs and sure enough, one was almost against the I beam and the other was about an inch above it. So of course if the weight on both axles isn't even, the Sumo springs will hit at different times. Since the Sumo springs are a pretty "hard" feel compared to the coil springs, you (or at least I) can feel it.

What I did... even though I'm not a total fan of the "airbag inside the coil spring" design, I added Firestone airbags to the front. (Talking about tools in the other thread, I actually installed them in the middle of our 6500 mile trip from California to New York and back! I ordered them while we were in Iowa and had them shipped to our daughters house in New York. I installed them in her driveway with the tools I had onboard in the Vegas. lol.)

I did the airbags for two reasons, the biggest reason was camber. With the added track width the front wheel swap created, it put more leverage on the front suspension, which resulted in the front end being a little lower than ideal. When the Ford twin I beam suspension is too low, negative camber goes too far. The twin I beam suspension has the drawback of camber traveling in an arc through the suspension travel, which makes proper ride height critical. Adding the airbags meant I could raise the front end to get the camber back in line. (Yes, I aligned it in my daughters driveway too. lol.)

The other reason I did the airbags, to get the suspension up off the Sumo springs so it could actually use the coil springs and airbags instead. The result? Greatly improved front suspension action, ride, and wheel alignment/tire wear.

So Ken, I TOTALLY understand your desire for an easier "install it and forget it" solution. The Sumo springs will give you that. My solution was/is a lot more work. Just realize that there are other pros and cons that a Sumo spring salesman may not mention or even realize. My advice for you personally and your specific application... Have your Vegas corner weighed before you decide. If your front end loading is different side to side and you can't "fix" it by moving your loads around, you may find that you'll be able to feel those Sumo springs unevenly. The rate vs. travel of that urethane is very short/steep and they can end up causing an uneven suspension feel. (You can put washers under the Sumo springs to even out the gap between the I beams, but you can only add about 1/2" before you run out of bolt threads.) And if your ride height isn't correct, the only way you're really going to fix it is with airbags. When you align these front suspensions, you want a lot of caster and since they effect each other, camber is hard to get right if the ride height isn't right.

You clearly want to make informed decisions, that's why I typed out this novel, to give you and others information that might help in decision making. Hope it helps!
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Check out my V8 swap roadster video, don't forget to turn up the sound!...

httphttps://youtu.be/2q9BuzNRc3Q
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