Toyota Tacoma Forum banner

Sway Bar Calcs for the Geeks, S-Rnr vs. 4cyl/2wd

17K views 58 replies 26 participants last post by  Enola Gaia 
#1 ·
I just bought some used S-Runner anti-sway bars to put on my truck, thanks AFP520!!


I was wondering how much stiffer the new bars will be so I did some calculations. For those that don't care about the calculations, jump to the bottom of this post for the result.

S-Runner bar diameter:
27.7mm front
22.2mm rear

My truck's bar diameter:
27.0mm front
No stock rear bar, but the Hellwig bar is 19.2mm

I was thinking the front bar wouldn't be too much stiffer, however I recalled from long ago engineering shool that in the equation that was needed, the bar diameter is raised to the 4th power. Therefore a small change in diameter makes a big change in torsional stiffness.

Here is the equation:
k=GJ/L
k=spring rate of the bar
L=length of the bar
G=Modulus of Rigidity of the material
J=polar 2nd moment of inertia (depends on the material shape)
in the case of a solid round bar, J=(pi*d^4)/32

Therefore k=(G*pi*d^4)/(32*L)

Assumptions
1) The material in all the bars is the same. This is a safe bet for the OEM bars, and I believe the Hellwig bar is also spring steel (Addco bars are supposedly not spring steel, so G will be lower for those bars, so they aren't as stiff as you think).
2) The lengths are nearly identical, s-run front bar vs. 2wd front bar, and s-run rear bar vs. hellwig rear bar; good assumption for the two OEM front bars, but not so good for the S-runner rear bar compared to the Hellwig bar, but close enough for me.

3) My measurements are accurate. The paint on the bars is pretty thick, so my numbers could be off if the paint thickness varies from one bar to the other, and small numbers make a big difference in this calculation.

So I end up with an equation where the only difference from old bar vs. the new is the bar diameter, which is raised to the 4th power.

Result (trust me):
S-Runner front bar is 11% stiffer than my OEM bar (may not be noticeable)
S-Runner rear bar is 79% stiffer than the Hellwig bar and infinitely stiffer than stock!!

It's gonna be a while before I get the rear bar mounted, since I need to figure out how to mount it to the rear axle housing.
 
See less See more
2
#2 ·
Interesting...
I wonder if daveds50 will show up in this thread. He's a serious suspension engineering analyst...

I wouldn't doubt your results, tho' I can't confirm them... I've ridden in other Tacos with Hellwigs in the rear, and they seemed nowhere near as stiff and flat as my SR...
 
#3 ·
It's gonna be a while before I get the rear bar mounted, since I need to figure out how to mount it to the rear axle housing.
How does it mount to the Srunner? I would think that would be the easiest route.
 
#8 ·
I may use parts from the Hellwig. It has axle u-bolt clamps. I'm a bit worried about it rotating on the axle housing since the bar is so much stiffer, so it may need to be welded in place.

I've got the parts, now I've got to find the time to look underneath the truck and figure it out!
 
#11 ·
I had the Hellwig rear bar on mine and the axle clamps never moved. The worry area is where the bar ends clamped to the frame.
yah those silly pinch brackets are weak. Better to drill holes in the frame & brackets for bolts or weld on.
After I bought the Hellwig bar, mounted it and had the idiotic pinch plates come off the frame several times, I got pissed off. So I spent quite a bit of time communicating with Hellwig, sending them pictures about how the clamps don't mate up on the '01+ frames (there've been several posts about it here). Helwig said I was the first person to complain! Blah, Blah, Blah. They sent me some other brackets, but it still was not a good fit, so that set me on the path to mounting up the S-Runner bar. I figured if I had to do any welding or fabricating, I'd make it worth my while the the BIG S-Runner anti sway bar.

So anyway, the end links of the S-Runner bar have brackets that bolt to the frame on the S, and I'm hoping will bolt onto my frame the same way ( I think the hole is already there). So that leaves the axle mounting, for which I'll try to use the Hellwig u-bolt clamps to start out, and then I'll see if welding is necessary. I'm super busy right now, so I don't think I'll get to it this weekend. Too many projects and so little time!
 
#12 ·
If you look at the parts list for the 01 and up tacos in the tech section you can see the mounting "tab" that the end links bolt into. I'm pretty sure these sit inboard of the frame and are a separate piece. Could be wrong though.
 
#14 ·
Interesting...
I wonder if daveds50 will show up in this thread. He's a serious suspension engineering analyst...
here i am ! been busy with a truck load of stereo equpment... ( semi truck, not Taco )

i have not done the math on the 4 cyl stuff, as my 83 year old dad has no desire to upgrade...
he likes the mushy feeling.

however, i have seen Kaffee's truck, and was real suprised how small the Helwig bar is.

all i can say, is the anti sway bars on the SR seem about perfect. Toyota did the engineering for me. when i get the other 1000 motorized projects done around here, i will do the springs and shocks, but not the swaybars.

if you need any mounting pics, i can crawl under the truck tomorrow night... as for now, im going back to the shop... yes, at 1:41 AM PST... i got a lot of work to do.
dave
 
#15 ·
I mounted up the front bar yesterday, only took a few minutes. Now that I had it off the truck, I could measure it better, the stock front bar on my truck is 26.9mm (not 27.0 as I said before). So this makes the S-Rnr bar 12% stiffer. Okay, not a big deal.

Driving the truck with just the S-Rnr front bar, it might have made a noticeable difference, or it might not.

For the front bar, all you need to buy from Toyota (or used) is listed below. Since I bought the parts used, I can't say for sure that the following part numbers are correct. But using this list as a guideline and ordering from your dealer, you should get it to work out.
FRONT BAR PARTS-see the parts list, Page 1429:
48811-AD040 Bar, Stabilizer w/S-Runner model
90948-01080 Bushing, Link w/S-Runner model, 4 total
48815-AD020 Bushing, Stabilizer bar w/S-Runner model, 2 total

To tell the truth, I forgot that the link bushings (4 total above) had a different part number, and even though AFP520 supplied me with the S-Runner bushings, I re-used the stockers. Looks like I'll be swapping the bushings out!

I should have all the parts needed to mount up the rear S-Rnr bar by next weekend. I will be using the axle clamps that were provided with the Hellwig kit. What I had to order was a set of Energy Suspension greaseable sway bar bushings to mount to the Hellwig axle clamps, since the S-Rnr bar is thicker. I probably could've drilled out the hellwig bushings, but I figured I'd go ahead an do it right the first time.

I'll provide pictures and a complete parts list (Toyota parts, Hellwig parts, and Energy Suspension parts) once I get it all sorted for the rear bar, so that it will be easy for others to do the same thing. The front bar is so easy and looks the same as the stocker that I didn't bother with pictures.
 
#20 ·
The front was a simple bolt-on, but as I noted above, it is only about 12% stiffer than my stock bar ('02 2rz extra cab).

I finally put the rear bar on last night. It was a bolt on to the frame: mounts exactly the same as the S, and the holes are in the frame (the axle mount is NOT a bolt on, see next paragraph). I really like how clean the frame mount is on the S-R rear bar, and the endlinks are a really good design. In contrast, the Hellwig rear bar doesn't fit the '01 and up Tacos without welding (contrary to their application chart), and I ended up taking it off right away. Even if I did the welding, the endlinks are too short for a standard height '01 or later. It was this horrible fit that got me to look at the S-Runner bar.

However, the S-Runner has mounts welded on to the rear axle housing, and the 2rz axle doesn't. I chose to use the axle clamps that were supplied with the Hellwig rear anti sway bar, combined with Energy Suspension bushings #95158. An alternative would be to have mounts fabricated and welded onto the axle housing.

I'll post pics and a driving report by this weekend. Gotta wait for the rain to stop so that I can really test out the bar!
 
#22 ·
Got in a few miles of twisty road today, all I can say is AWESOME! It feels really well balanced, and I lost a whole bunch of understeer, as expected. This is how the truck always should've handled off the showroom floor.


Two minor downsides, both expected:
- The inside rear tire gets light while cornering, so its easier to light it up powering out of a corner, so the LSD has moved up to a higher priority
- The ride is only slightly diminished, mostly just noticed when pulling out of a parking lot, crossing the junction from the ramped exit onto the road, stiff rear bar makes the truck rock back and forth roughly.

And to all you 2rz guys with no rear anti sway bar:
 
#26 ·
I'm ordering an Addco rear sway, it's the same size (thanks Ochizon)
However, know this.
swaybar thickness has less to do with stiffness, than the length of the "arms"...
a slightly smaller bar with shorter arms can have more roll resistance than a thicker bar with longer arms.
know also that the Addco rear bar mounts different. it is a different design.
my past experience with Addco, is not good... in all vehicles that i've used them on, the vehicle tends to understeer at the limit. ( they did this on purpose... probably for liability so the average driver will not spin )
seems that Suspension Techniques bars are a much higher quality than Addco, but they dont make Taco bars.
however, take this for what you paid for... i have no experience with Addco on a Taco.
however, the SR bars make for perfect 4 wheel drifts when taken past the limit. as balanced as you can get.
dave
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top