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Old 05-14-2009, 06:04 PM   #1
Jeremiah
 
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FAQ(2): SPUA vs SPOA (+ hidden costs)

SPUA (SPring Under Axle)
Pro's:
* Cheaper
* Easier to install
* More stable in turns / jumps - Sean Devinney's (of Aftermarket 4x4) race rigs are mostly (all?) SPUA for this reason
Con's
* Less leverage on the suspension (doesn't articulate as easily)
* More things below the axle = more things to snag on rocks / drag in mud
* Only good to about a 31" tire (maybe 33" if you don't fear fender cutting, & BFH)

SPOA (SPring Over Axle)
This re-locates the leaf springs above the axle. This action automagically lifts the rig 3 to 4.5" - neat eh?
Pro's:
* "Cheap" way to gain big lift numbers
* Suspension articulates easier (it's a physics / leverage thing)
* Moves more of the bits out of the way of rocks & mud
* Virtually unlimited on the upper limit of tire size
Con's:
* Cost (see hidden costs below)
* Generally requires more tools & higher mechanical skill set
* More body-roll in turns

Below I'll break down the SPOA into "minimal" and "proper / complete" conversions. Going from SPUA on 29" tires to SPOA with 31" can EASILY be $1000 more in TIRES & WHEELS ALONE. Minimal setup is my (non-engineer) opinion on the minimum needed to safely get down the road. I am NOT an advocate of doing the minimum needed for SPOA. If you're just looking for height to mall-crawl, go with taller springs and / or body lift. If you're wanting it to go off-road, just doing the minimum is cutting corners on usability & reliability. I also tend to round up / include estimated shipping for heavy items (Remember: this article is about hidden costs). Can it be done cheaper if you have the right tools to fab stuff on your own? Sure. Might you have a friend's cousin's borhter's uncle that can give you free parts? Sure. But again - that's not what this article's about.

NOTE: I'm a HUGE advocate of doing lockers before lifts & tires. See FAQ 1.
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96 Tracker, 2" OME Struts & Springs, Pep Boys 235/75/15 (29") M/T
83 SJ410 SPOA, RUF, 1.3L, Toyo 31" M/T
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Old 05-14-2009, 06:05 PM   #2
Jeremiah
 
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The minimum needed to technically / safely run a SPOA:
* Spring perches
This is what your leaf springs are going to sit on. They're also used to center / locate the springs properly.

* Drive shaft spacers
If you don't use these, drive lines fall apart.

* Extended break lines
So you don't rip out your break lines when the axle drops in a hole.

* Steering correction
Re-locating the axles in the suspension changes the geometry of the steering system - making it difficult to control the vehicle. At minimum, a Z-link bar should be used. Over The Top (OTT) steering re-locates steering components up and out of the way of things like rocks (which tend to bend / break steering components).

* Re-locate shock mounts

There are many many kits out there (most of them are far from complete), but there's kits that have the above bits in the neighborhood of $600 shipped (minimum).

* Tires: $750
All five of them. By far, tire failure is the #1 failure off road. Along with your tire repair kit (you do have a tire repair kit, and ability to inflate tires right?), a full sized spare to get you home is a must. A full sized spare is especially critical when running a non-selectable locker. Let's not forget tire installers like to gouge you for mounting and balancing M/T tires.

* Offset wheels: $550
Wider tires need to be moved away from the frame (to keep from rubbing).

Anything less than 31" on a SPOA looks dumb, so let's do our baseline price @ $1300 for five 31" Super Swamper tires mounted & balanced on cheap steel wheels. Add that to our minimal SPOA kit, and we're up to about $2,000.


The bits that make it a proper SPOA:
* Shocks: $80+
Stock shocks will limit suspension travel. Think cheap here ($15 - $50 per shock). More expensive shocks provide more resistance to suspension travel - good for heavy rigs, BAD for light vehicles like ours. People report good success with Monroe, Napa and Doetsch DT3000 shocks.

* Bump stops: $100
Needed to keep your springs from moving the wrong way & destroying them.

* Gearing correction (T-case, diff, both): $400-$1,000
Suzuki engines love to rev, so it's especially important to be geared properly (improper gearing KILLS power & MPG). Samurai has is the only transfer case that reduces both hi and low range. This is fantastic news, since you can re-gear for street use, and automagically be reduced (even lower than stock) in low range! It's up to you what's more important: value, or reliability. I prefer t-case gears (better value), as I hardly hear about people blowing up properly setup diff gears. Brent @ Trail Tough strongly disagrees: http://www.trailtough.com/index.php?...tent&Itemid=60
Another hidden cost: Breaking open the diff or the t-case = new fluid & rebuild kits ($100)

Don't forget about...
* Power Steering: $250
If you ever plan on running any real trails which require aired down tires - power steering is the only way to fly. I've boiled over my power steering with 29" tires, so now every rig I run how P/S coolers ($50). And, let's not forget the price of P/S fluid ($10).

* Swing away tire carrier: $500
Four options: a) Keep the larger / heavier tire on the tailgate, and risk ripping it off. b) Moving the tire into the vehicle and killing a lot of valuable storage space. c) Move the tire to the roof and raise the center of gravity. d) Install a swing-away tire carrier that transfers the weight to a heavy-duty bumper (which is tied to the frame). Proper SPOA = option d.

* Stronger axles: $250+
Stock axles are generally accepted as safe up to 31" (all of this depends on your driving style, terrain & a little luck). A few can make 33" survive reliably. The most common upgrades are Trail Tough's Double Toughs (http://www.trailtough.com/index.php?...mart&Itemid=53), Toyota axles, or Dana 44. Double Toughs are stong, relatively cheap, and the easiest to install. Full axle swaps are more difficult, but open up more locker / gearing / axle possibilities. Toyota (easier to adapt) and Dana 44 (a bit harder) are the most common axle swaps.

* Armor: $300-$2,000
A must-have for rock crawlers, and probably useful for anyone else planning on off-pavement fun. Rock sliders, axle trusses, t-case and diff protection add up $$$ quickly. A roll cage will double armor costs (but my head's important to me).

* Bigger breaks: $300+
I can definitely feel a difference between my stocker & my SPOA'd rig on 31" tires. Breaking distance is increased, and it's more difficult to keep the tires from locking up (and therefore loosing control) in inclement weather. IHMO upgrading the breaks is a "should do" with 31"+ tires, and a "must do" for people with 33"+. yeah yeah - safety's boring, but it's also important. Hidden cost: e-brake kit, new pads & fluid. May require upgrading the break master cylindar as well ($100+).

Can you see how quickly a complete & properly setup SPOA will easily get into the $3,000 "true cost" range? We haven't even got into other spring options (RUF, CJ, YJ, Toyota, coil & links, shackle reversal...). And, you've already installed that locker right?
__________________
96 Tracker, 2" OME Struts & Springs, Pep Boys 235/75/15 (29") M/T
83 SJ410 SPOA, RUF, 1.3L, Toyo 31" M/T
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