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914World.com _ 914World Garage _ Tarett Prototype Rear Swaybar

Posted by: Cloudbuster Mar 29 2005, 04:23 PM

I'm the lucky sap who got to work with Ira at Tarett Engineering and have my car be the test mule for rear swaybar development.

We got a chance to test the prototype rear swaybar at the PCA SDR autocross last weekend.

Here's all the gory details. I felt the need to be wordy so as to help provide and accurate picture.

(The content are my own words. Although I have been given permission to discuss this, I want to make it clear that I am not speaking for Ira.)

Attached image(s)

Posted by: Cloudbuster Mar 29 2005, 04:25 PM

There were concerns that a rear swaybar causes inside wheel spin. This didn't seem to be the case, but I'll describe the course to qualify that.

The course went uphill from turn 4, crossed the slope and came back down around turn 8.

Turn 1 was the tightest section of the course, requiring a redlined 2nd or bogged 3rd gear entry. There was no inside wheel spin here.

Most wheelspin seemed to happen around Turn 4, an on-camber (?) corner.

The right-left dogleg at 5 was more of a chicane/kink.

Turn 7 & 8 where off-camber and the car tracked nicely through them as well.

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Posted by: Cloudbuster Mar 29 2005, 04:26 PM

The Car:

'Tinkerbell' 1975 914 with 2.0 D-jet Type 4. Open differential.

Front: 21mm torsion bars. Tarett swaybar- 22mm effective, set 55% stiff for entire day.
Rear: 200 lbs springs. Tarett swaybar - 16mm effective. 50% stiff first half. Full soft second half.
Shocks:Koni Yellows at all 4 corners. All set at half.
Tires: Although the CS class permits use of stickier tires, Falken Azenis were fitted due to the car owner being a CSOB and having only one set of suitable rims. Tire pressures were finalized at 26 psi hot for timed runs.

Posted by: Aaron Cox Mar 29 2005, 04:26 PM

way cool! it looks like it doesnt mount in the OE location.
if it is anything like the front bars they make...im sure they will be bitchin!

Posted by: Cloudbuster Mar 29 2005, 04:29 PM

The Drivers:

Might as well explain who was driving the thing.

Sometime club member DB-- 2003 PCA-SDR CS class champ. Ex-motorcycle racer, starting 4th season of autocross.

Me: 6th autocross. Usually 4 seconds behind DB at previous events.

TTOD was 1:10.

The majority of 914-4s were in the 1:23 to 1:25 range (some on Kumho Ecstas). The outlier of the event was the CS class winner on brand new Kumhos at 1:19.xx (jerk!). DB posted a best time of 1:23.11, I posted a best of 1:24.72.

Posted by: Cloudbuster Mar 29 2005, 04:38 PM

Initial set-up, rear swaybar at 50% stiff
On slow transitions into sweeping turns, oversteer existed but was not a terrible problem. However, negotiating the slalom was very difficult. The car would make the first turn, but the rapid transition to the next would just swing the back end right out. The abruptness instilled a bit of hesitation in me on the slalom for the remainder of the day. There were occasional incidents of inside rear-wheel spin, but also some incidents of (slight) throttle-on oversteer.

Second set-up, rear swaybar at full soft
Great improvement. The oversteer had gone from abrupt to very mild/just right. The car became very predictable. Happiness was restored. DB went from dissatisfaction with the car to pleased. The car could be tossed from side to side without worry of the back end coming around. There seemed to be more incidents where the car could coaxed into throttle-on oversteer and very little (zero?) incidents of inside rear-wheel spin.

Posted by: Jeroen Mar 29 2005, 04:42 PM

post more pics!!!
lets see the mount

Posted by: brant Mar 29 2005, 04:49 PM

I'd be curious if there was a control, where the drop link was disconnected and the car was run with no bar?

Posted by: Aaron Cox Mar 29 2005, 04:51 PM

QUOTE (brant @ Mar 29 2005, 03:49 PM)
I'd be curious if there was a control, where the drop link was disconnected and the car was run with no bar?

aahhhh...

fulfilling the scientific method

Posted by: Cloudbuster Mar 29 2005, 04:52 PM

Location of the swaybar was an exercise in compromise – Will only racers use these? How stock will people want their cars?

The stock swaybar attaches to pads welded onto the cross member and bends around the transmission mounts. Hollow swaybars are straight, so the normal ‘stock’ position wasn’t too likely. The bar had to either be entirely in behind or forward of the transmission mounts.

With the bar located behind the transmission mount, there were clearance issues because of the muffler heat shield (red arrows). To avoid the head shield, the bar would have to be set up fairly high, necessitating the arms to have a dogleg shape to get back underneath the crossmember. During initial brainstorming there are also issues with ’75 and ’76 cars which have additional gussets for mounting the ugly bumpers (blue arrow).

Locating the bar forward of the crossmember permitted the use less complicated arms. It fits neatly above the transmission.

Attached image(s)

Posted by: Aaron Cox Mar 29 2005, 04:54 PM

lets see the mounts and a top view from inside the rear trunl

Posted by: grantsfo Mar 29 2005, 04:56 PM

I wonder if running higher pressures in the Falkens would have helped with the slalom. I have always felt Falkens get real sloppy in transitions at anything under 34 psi and I often run them even higher. I can get my car to become much more "whippy" in transitions when I bring Falkens below 30 psi.

Posted by: Aaron Cox Mar 29 2005, 04:58 PM

QUOTE (grantsfo @ Mar 29 2005, 03:56 PM)
I wonder if running higher pressures in the Falkens would have helped with the slalom. I have always felt Falkens get real sloppy in transitions at anything under 34 psi and I often run them even higher. I can get my car to become much more "whippy" in transitions when I bring Falkens below 30 psi.

i agree... i run 38 PSI rear and 36 front

Posted by: Cloudbuster Mar 29 2005, 05:00 PM

QUOTE (brant @ Mar 29 2005, 02:49 PM)
I'd be curious if there was a control, where the drop link was disconnected and the car was run with no bar?

Alas no. The scientific method was not completely employed, although I tried.

Time constraints between run groups limited the amount of twiddling. We also didn't have any baseline settings for a front-only setup, so that would have consumed practice laps as well.

The desire to not get completely whomped during timed runs factored in as well -- coming in dead last wouldn't be a good testimony for the product, even if the product had nothing to do with it.

The final mount design is still under consideration. Right now the mount is assembled together from the parts bin and bolted to the trunk floor with additional metal stiffeners. Pictures of it would elicit a GADZOOKS! or worse. Probably worse.

Posted by: Cloudbuster Mar 29 2005, 05:11 PM

Thanks for the tire pressure info!

Tire pressures were a gray area... I think the low pressures were carried over from Kumho Victoracer experience. There were reports of some guys running 42 psi with Azenis, but that seemed a little extreme.

Posted by: Aaron Cox Mar 29 2005, 05:13 PM

QUOTE (Cloudbuster @ Mar 29 2005, 04:11 PM)
Thanks for the tire pressure info!

Tire pressures were a gray area... I think the low pressures were carried over from Kumho Victoracer experience. There were reports of some guys running 42 psi with Azenis, but that seemed a little extreme.

35 psi is theminimum i run mine, they just dont stick under that threshold...... feels sloshy

Posted by: trekkor Mar 29 2005, 06:04 PM

Nice progress report!

I agree as to the higher tire pressures. I used to run 41psi rear and 39psi front with great schticktion.

Give us more pics and tuning experiences.
Do you need to jack up the car to adjust or is there room to work? Does the bar preload as you adjust from side to side?

KT

Posted by: Dave_Darling Mar 29 2005, 06:13 PM

How are the arms of the bar oriented when the car is at rest with weight on the rear wheels? I would be worried that the arms might under some circumstances contact the trunk floor, which really sucks for handling let me tell you. The stocker does this some times on lowered cars with soft-ish springs. Especially when the car encounters a bump in the turn.

--DD

Posted by: Cloudbuster Mar 29 2005, 06:19 PM

Even though I'm a very thickly torsoed, I was able to squeeze under the rear valence and make adjustments. But, my car was running about 1 inch higher compared to other cars.

This brings up a good point. It would be good to know what the average ride height of A-X and race 914s are to get an idea of the final droplink length. Measured from ground to fender top, at wheel center.

The bar does preload from side to side, but it is slight. I could hand crank the droplinks a few turns with the car on the ground.

Posted by: Cloudbuster Mar 29 2005, 06:22 PM

Here's a close-up of the shock bolt.

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Posted by: Cloudbuster Mar 29 2005, 06:37 PM

End-on shot for side-side alignment / clearance.

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Posted by: Travis Neff Mar 29 2005, 06:54 PM

I think that trying your setup with softer rears springs (same front) would be another nice test. your setup without the rear bar is a fairly "complete" setup with the high rate rears already.

Posted by: Ira Ramin Mar 29 2005, 09:25 PM

Like Mark stated, there wasn’t a lot of time to do a controlled comparison with and without the rear bar but I do have other customers running with similar setups, except without the rear bar. They usually need to run the front bar close to full soft to get the car to turn in. A rear bar will allow you to take advantage of a stiffer front bar and springs without requiring much stiffer rear springs.

Overall the 16mm bar was a little on the stiff side. We never even considered trying the 18mm one. Trekkor, maybe you could use it to balance out your front bar. It looks like there is some room to make the arms longer to facilitate softening it up a little. I’d be worried about making the bars wall thickness any thinner. Softer rear springs or stiffening up the front would have also helped.

The car had very little body roll on the corners yet still looked smooth. Even in the transitions, you couldn’t see it move much. Below is a picture of Mark coming out of turn seven.

With a rear ride height of 22” at the fender lip, there was a little more than 2” of drop link to trunk clearance. The drop link can go another .75” shorter, and I have another one that’s 1” shorter than that. We need to figure out what length will cover most cars. Feel free to post your ride heights

Adjusting the stiffness or preload was pretty easy with out raising the car. You do have to lie on your back though.

There’s still some work to do on the mounting. Even with the bar mounted next to the cross member, there was more flexing than I’d like to see. Once that’s all worked out and we do a little more testing, I can do a small production run.

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Posted by: drew365 Mar 29 2005, 09:45 PM

Sounds like you need to come to WCC and let us all test drive for you. We plan on doing some skid pad runs in the morning. Good place to test bars.

Posted by: airsix Mar 30 2005, 12:06 AM

QUOTE (Ira Ramin @ Mar 29 2005, 07:25 PM)
With a rear ride height of 22” at the fender lip, there was a little more than 2” of drop link to trunk clearance. The drop link can go another .75” shorter, and I have another one that’s 1” shorter than that. We need to figure out what length will cover most cars. Feel free to post your ride heights

Ira,
This looks great. Regarding the drop links - I know there is a target geometry, but my concern is, what happens if the rear suspension goes to full bump (shock on the stops)? Will there be enough clearance? I'd want the shock to hit the bump stops before the bar arm bottoms out on the trunk floor (and something gets bent).

The "how stock will people want" comment made me laugh (at myself). I am thinking about mounting my rear bar INSIDE the trunk.

-Ben M.

Posted by: nine14cats Mar 30 2005, 08:21 AM

Great Thread!

Thanks for sharing!

Hi Ira,

I´ve got your prototype rear bar for my 3.6 liter ....aka...¨The Beast"....that Brad and Scott Yeaman will be mounting on my car in a few weeks as we get closer to painting the body.

Do any changes need to be done to the bar you sent Brad and Scott? My car is tube in back, no trunk sheet metal....

We will try to make it to a big track as soon as we can.

Thanks,

Bill P.

Posted by: Ira Ramin Mar 30 2005, 09:02 AM

Ben,
The drop links currently on Mark’s car are actually longer than stock. We put them on to improve the geometry. There’s about 2.25” of clearance, but they don’t hit because his suspension is relatively stiff. As you point out, that’s not always going to be the case.

We previously had some other links installed that could adjust to be slightly shorter than stock. To cover the full range of applications I may need to provide both sizes in the kit. I could also provide an optional longer link for bars that mount in the trunk.