Is this new?

just noticed mention on suspension forum. From the Hotchkis website:

Features:
Front Sway Bar:
Lightweight, durable and adjustable 1-5/16” (33mm) hollow

110% stiffer than the stock sway bar with a rate of 970 lbs/in
150% stiffer than the stock sway bar with a rate of 1150 lbs/in
195% stiffer than the stock sway bar with a rate of 1370 lbs/in

Seems like just the ticket for BS.

 

deleted my previous comment

someone told me they rigged a custom test rig using this bar and the numbers were close

strictly from a theoretical calculation they don't seem to make sense, but that's all I've ever had to base any numbers on. I've never seen any hard data collection done except on the splined-type speedway sway bars

 

I went back and ran the numbers myself, and can match the rates quoted using some reasonable assumptions on tube thickness. However, I only just this moment finally figured out the % increase relative to stock. I was thinking the low setting was 110% of the stock stiffness, but it is actually 210% of the stock stiffness ("110% stiffer"). Now the math finally makes sense. Now I believe this bar is probably too stiff for BS.

 

an 85% range theoretically equates to endlink hole spacing beyond what the OE endlinks can handle, but the source indicated that they visually didn't seem to be that far apart

 

Not true... The center hole is in the same area as the OE hole. So it is a matter of moving the link about a 5/8" forward or back to adjust. You can read all about it in the Apr 2008 SportsCar.

 

I'll look forward to the article.

I don't have my measurements in front of me, but when I drill the extra hole in the OE FSB, it should move the endlink points forward by roughly a 1/2"-3/4". Any idea how much % stiffer the bar becomes (over the stock setting)? Is this question perhaps answered as well in the SportsCar article?

 

Only way to know is to test an OE bar with the extra hole. What we found on the stuff we tested will not equal the same change on an OE bar, because of the tube size and wall thickness is not the same.

 

I think you misunderstood what I was trying to say

I've used the same spacing on my bars from several years back, and again it doesn't theoretically calculate out to an 85% adjustment range

OE hole is 7.375" from the main bar centerline, that means the forward most hole would be at 6.875" and the rearmost hole at 8.0"

Just look at the ratio of a 1.125" adjustment range relative to the length of the arm, it's nowhere near 85%

Based on theoretical calculations, an 85% adjustment range relative to a nominal endlink hole position 7.375" would be outside the angular reach of the OE endlink. I have plenty of tested rate data on splined speedway bars and it matches the calculations well.

http://www.intercomp-racing.com/Prod...TESTER_778.cfm

if you read my earlier post, I'm trying to understand why the two aren't lining up (no pun intended)

 

I cant get into to much detail at this time, we did not test that application. However, the bar they sent us that we did test was very near the range of % of change they advertise.

 

Gotcha. Thanks Jason.

 

That was my confusion at first also, but the actual rates don't vary by 85%. The rate INCREASE varies by 85%.

The soft setting is 110% stiifer than (or 2.1 times) the stock rate, and the stiffest is 195% stiffer than (or 2.95 times) the stock rate. Nominal is 150% stiffer than (or 2.5 times) the stock rate.

Therefore the adjustments amount to +18%/-16% or about what you would expect.

 

my mind is too jumbled to think it through at the moment, but if you're right then that'd definitely be too stiff for BS

sorry that I missed your earlier mention of it

 

The relative increase is proportional to one over the arm length squared.
For 1/2", this would be (7.375/(7.375-.5))^2=115%
For 3/4" it would be (7.375/(7.375-.75))^2=124%

The stiffness of the arm itself has a VERY slight effect on this, not worth worrying about.

 

FWIW, I estimated the following in terms of relative stiiffness based on available diameters and wall thicknesses:

Stock = 1 (baseline)
Stock redrilled = 1.2
Mazdaspeed =1.2
Whiteline =1.5 (center hole) ~1.2-1.7 estimated range
Racing Beat = 2.1
Progress = 2.6 (center hole) ~2.1-3.1 estimated range
Hotckis =2.5 (center hole), 2.1-2.95 range

 

^Thanks for those figures. Those were the kind of estimates I was looking for...

 

If accurate, that is an awesome post

 

I believe the Whiteline front bar only has two holes, are sure what's posted is correct?

I also don't think people are getting that much distance for the second hole on the OE bar either.

 

True...and true.

The Whiteline 27mm solid bar has three adjustments, i.e. two holes per side.

Center to center, we got 1/2" forward on the stock bar, IIRC.

 

I don't know the exact hole locations for any of the above, but I assumed center was same as stock, and +/- 10% (~3/4") for the adjustments.

What is the spacing on the Whiteline holes? If they straddle the stock hole location then that rate would be about right for the "middle" adjustment (one forward, one back), but the range may be smaller.

 

Most companies use 5/8" spacing, not sure why unless they all use the same company to manufacture them or they just copy cat each other

 

Anyone have any info on the Tanabe swaybars? I found some references in a search, but no details or discusion of BS use.

30.5mm, hollow and chrome-moly is all I can find. I can't find any data to support their claim that CrMo is substantially stiffer in torsion (as opposed to stronger/tougher) than other steels, but the diameter seems like it would be in the right range for BS (though not adjustable).

 

So what is your criteria for the "right swaybar" for a BS RX-8? What are you looking to get out of your choice? Have you run your car yet? What are you trying to change/get the car to do?

 

No I haven't, but I need to do something to keep myself distracted until the season starts

Seriously, I don't plan to make any changes until I get a bit of a feel for the car, but I would like to know what the options are. My thought is that the car will probably be faster with a little more roll stiffness, but I know that discussion has been beat to death.

Looking forward to the first local event in <2 weeks, then into the fray at the Dixie Tour.

 

Does anyone have and test and tune data on slalom times with stiffer FSB settings?

I need to get my Maxqdata thing working so I can look at some of these variables better (actually never really have, so anything will be better) this year.

 

Found my own answer. Cr-Mo is about 10% stiffer than carbon steel, so I'm guessing the Tanabe bar is about 1.7X the stock bar., similar to the Whiteline on stiffest setting, a little lighter, but no adjustability.