944Fest (aka Dan P)

I ordered the redline rollbar, and I've been told production has begun. This isn't an off the shelf item, he builds them a batch at a time when he gets the orders, so don't expect to throw $500 at him and have the bar delivered in a few days. I guess quality is worth waiting for. FWIW, I've heard nothing but raves about that setup.

Anxious for arrival, first DE is in May at Mid-Ohio.

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Tom Pultz

[quote]Originally posted by smokey:
One thing that doesn't make sense to me is to run belts over a harness bar and to then attach the harness to the seat belt mounts. If you add the force vectors, this puts much more force on the harness bar than simply attaching the belts directly to the bar.<hr></blockquote>It's not the magnitude of the force, but the vector direction that's important. I'm not aware of any 944 harness bar that attaches to just the B-pillar that is designed to have the belts connect directly to it. My B-K bar attaches to both the B and C-pillars, and since the vector force points forward and down, the force is in the direction of the C-pillar rods.

[quote]What is the rationale for not using the harness bar as the attachment point?<hr></blockquote>Because they are not designed to support the forces. [quote]If the harness bar is too weak to take the forces, increasing the forces by 40% doesn't solve the problem.<hr></blockquote>Yes it does, at least with the B-K bar. If you attach belts directly to a bar that is lower than your shoulders, the force on the bar will be forward and up. Attaching to the rear seat belt mounts shifts this to forward and down.

*eurospeed951*

Would the redline roll bar or the autopower roll cage be better? they are the same price

Tom

For my first 944, I got an Autopower rollbar (bolt-in). Had to remove the rear quarter windows to put it in. It did allow the rear seat to be down so I could carry stuff in back especially with the bracing removed.

For my current car I have the Redline bar. Putting it in the second time took less than 1/2 hour and involved 4 bolts (there are some tricks I learned fron the first install). The Redline bar is supposed to be PCA Club Race legal although I might want more protection if I were doing that. The only drawback is that the back seat has to be up. It is much less noticeable in the car.

The Autopower (or other) cage would be more extensive as it would have door bars and extensions around the door to install. Much more intrusive.

A harness makes a big difference even in autocross and the harness would be much easier to get out of if you wanted to leave in a hurry. I've also seen cars rolled at autocrosses.

I've also seen 944's rolled. I think the roof structure would strong enough to hold up but as the pictures indicate, the extra safety may be a lifesaver.

Most of the crashes I've seen at DE's have been in the "just up from novice" group. The speeds may be slower but there is also less experience to recognize when the limits are approached and react when they are exceeded. I think the safety equipment is justified once you recognize you're hooked and this is more than a once or twice a year hobby. The more events you attend, the greater the exposure.

Bri Bro

Dan P, I see you are one of the people on Redlines last Email status report. I hope he gets them done by the beginning of next month.

As for construction, both look like quality products. The redline looks like a stronger design to me, look at the pictures and judge for yourself.

Autopower Dist
<a href="http://www.ioportracing.com/rollbar.htm" target="_blank">I/O Port Racing</a>

Redline
<a href="http://www.homestead.com/redlinerennsport/SafeguardPage.html" target="_blank">Redline</a>

Ahmet

I've got a harness bar in my car that I think would be adequate to attach harnesses to, directly. It sits above/behind the rear seats, and mounts to the C pillar (only), at the point above the rear seat 'anchor', to a bolt hole that's currently occupied with a plastic screw. I believe this is one of the points where the rear seat belt attaches to on the newer cars. I'm not sure if this bar is adequate, so I'm considering a rear roll bar, however I need something that can be left in the car and doesn't make my rear seats completely useless, or hinders the operation of the rear seat back. Limiting the movement of the front seats is not a big problem, anybody have suggestions?
Ahmet

Riff

Smokey-

The way you explained the forces/vectors is good, but the initial assumption and the later example are incorrect. In the first example of tug of war, the tension the rope is seeing is actually 2000lbs. Don't think so, imagine you cut the rope in the middle, tie each section to a hanging scale, then have the teams pull again. The scale will read 2K lbs.

Now with both teams pulling on the same rope draped around the pole (same direction) the pole sees 2K lbs. Exactly as a harness bar with the belts directly attached to it.

By mounting the belt to the floor and running the roughly 90 deg. angle, you actually decrease the force experienced by the bar as you have shown in your calculation. The bar only sees 1414 lbs. in a down and forward direction instead of 2000lbs. directly forward. A reduction of 30%

Hope this clears up any confusion.

Cheers

smokey

Zoltan, thanks for the advice on smilies. Assembler, huh? I'm impressed. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Tom, you're absolutlely right re direction. You never want significant downforce on the belts, or you get compression of the spine, so the shoulder harness should never ever be attached directly to mounting points significantly below shoulder level. However, as far as the actual amount of force involved is concerned, I stand by Newton. If you route the belts around the harness bar to a mounting point below the bar, the bar acts as a pulley, and you increase the force on the bar. The total force on the bar is minimized with a direct connection around the bar.

Over1g, you have exactly the set-up I had before I got the Redline roll bar.

Riff, I'm not confused at all. Prior to Isaac Newton's birth, many people would have agreed with you. However, by your calculation, with a force of 2000 lbs on the rope and only 1000 lbs from the tug-of-war team, the team would be on the receiving end of a 1000 lb force (2000 lbs minus 1000 lbs). That team would be in big trouble, because, by Newton's Second Law, they would be accelerating at 32 feet per second per second, or 1 G, toward the other team. Big, big trouble.

Riff

Smokey-

I am sorry if I offended, the confusion comment was not directed at you. As for the why the tug of war teams do not move it is because the forces act in equal and opposite directions. I was stating that the tension IN the rope is 2000lbs. This tension has not bearing on the teams at the ends as it is the result of their efforts on the rope.

As Tom noted, force has a magnitude and direction. Please check out the attached image for graphical representation of what I was trying to write.



Best,

smokey

Riff, all you drawings are correct, and I wish that I could have drawn those vectors. It would have saved a lot of verbiage. Your only error is in the first drawing: the tension on the rope is 1000 lbs, not 2000 lbs, but I'm at a bit of a loss to explain why. It's basic physics. I wish I could draw it, but here goes a verbal explanation.

You've caught a ten pound fish. You attach a scale to the fish, and lift the fish by the scale. Ignoring the weight of the scale, you will need to exert ten pounds of upward force to weigh the fish. The scale will show a weight(force) of ten pounds, not twenty pounds, even though there is an upward force of ten pounds from your hand and a downward force of ten pounds from the fish on the scale. The definition of a tensile force of x lbs is that the object is being pulled apart by two forces of x lbs acting in opposing directions.

I don't know what else to say.
Can anyone else help?

JGriff

[quote]Originally posted by Tom:
<strong>For my first 944, I got an Autopower rollbar (bolt-in). Had to remove the rear quarter windows to put it in. It did allow the rear seat to be down so I could carry stuff in back especially with the bracing removed.

</strong><hr></blockquote>

For those interested in a pic or two, here is the Autopower roll bar and Crow harnesses installed in my S2.





The previous owner installed them, so I can't really comment on the price or ease of installation.

Nonetheless, I hope the pics help.

Jim

Crackhead944S

Jim,
I saw the pics on your site the other day. One question, are those stock seats and do the harness straps need to go through the seat (Obliviously not through the stock seats)?


Mark

Robert Lavigne

All I know is that based on Smokey's description of his car and harness I would say that he has stolen my car's track name for his ID ;-)

Smokey Joe (UCR all the way)

Z-man

[quote]Originally posted by Crackhead944S:
<strong>Jim,
I saw the pics on your site the other day. One question, are those stock seats and do the harness straps need to go through the seat (Obliviously not through the stock seats)?
Mark</strong><hr></blockquote>

I don't think Jim's seats are stock, but you can get a harness setup with stock seats, but the shoulder straps will (obviously) not go through the seats. Although not as safe as going through the seats, you can order shoulder straps call "H-style" straps: there's a piece of harness material that links the two shoulder harnesses together that sits right behind the seats. This is supposed to help prevent the shoulder straps from slipping off in high-g cornering or accidents. I don't think Jim's shoulder straps go through the seat: it doesn't appear to have the necessary eye holes to do that.

IMO, the H-type straps are a must for use with stock seats, but they can still slip off.

BTW: Nice setup Jim!
-Z.

Al P.

All well stated but,

1. neither of the rather flat cars were Porche. They make a good case for why there is no substitute.

2. You really have to experience a severe impact with a stock belt to appreciate how spreading the load over a wider belt will cause far less soft tissue damage.

3. speak for yourself Z I'm peddling as fast as I can.

Al P.
1987 924S