Tow Bars -- The Rest of The Story

Kelley - Man that is a lot of work.  Well done.  My sway bar goes up in front and I had to cut hunk out of the front bumper brackets to clear the sway bar.  That gave me room for the tow bar - I guess my sway bar was inverted. I do have to get quite far under car or jack it up a bit.

The weak link in your solution are the large U bolts that go around the front beam as they appear to be simple muffler U bolts on my CMC.  Make sure you keep eye on them for cracks.  The rear safety chain should go around that front beam.

Well done!

Gregg, does that sway bar rub on the tow bar? I thought the sway bar goes up and down as the suspension move up and down?

@ Kelly

It's difficult to tell in the photos but if I understand you correctly you have welded a new tube and side plates to the bracket system that is the support for the front bumper? And then you attach the tow bar to the new tube?

Excellent fabrication for towing your car, Kelly! Towing adds another dimension of enjoying your Speedster in distant destinations. 

Bill - Yes it did hit.  First photo is when it was ump on jack stands.  It hit when it was lowered to ground. That was why I had to notch the bumper bracket and re-weld it.

Bob not poopie: Yes precisely.  Bringing the "tow tube" forward a bit and being able to put it at just the right height makes attachment fairly straight forward.  You still have to lie on the ground, but you can reach and see what you need to.

Greg: the clamps that hold all to the two torsion tubes look pretty stout to me.  Attached in four places, eight bolts.  I sure can go in there now and then and look them over.  What I keep telling my self is that the car is is pretty light, so the loads here are not excessive.  time will tell.  My safety chains (actually cable) will go around the torsion tubes.

I remember Jim your tow set up was very nice as well.

The only thing I might worry about with this approach, is that there is minimal side support for the bumper mounts.  Were it not for the body (and the size of the holes for the bumper arms), there isn't much keeping the bumper end of the mounts in place.  I understand how the tow bar arms are held separated and, therefore, hold the bumper mounts more-or-less in place, too, when it's all assembled, but the whole structure becomes a parallelogram when it's all put together.  When you're making sharper turns (into and out of parking lots, for instance) there might be a lot of lateral pressure where the bumper arms go through the body as you pull the nose of the roadster sideways.  This doesn't happen when the car mounts are bolted directly to the torsion tubes.  You could install a couple of diagonal arms from the front of the bumper mounts to the center of the torsion tubes to provide a triangle and give it strength if this proves to be a design issue.

So, my only advice on an otherwise thoughtful project is to take it out and drive around with it, then closely inspect the body where the bumper arms go through to see if there is any wear.

Better yet, strap Babs on the hood of the roadster, head down towards the tow bar (she can hook her toes over the top of the windshield, if she's modest), and have her watch for any flexing of the bumper arms/body while you're driving around in a spirited manner.  That should tell you a lot about the relationship.  (of the tow bar to the roadster, of course!)

Hey.....It worked for the "Car Talk" guys!

Stick a GoPro under the front and film the relationship in motion.

Not to be a nay sayer, but that has cracked fiberglass written all over it.... good luck, I'm eager to see how it does.

Kelley said:  the clamps that hold all to the two torsion tubes look pretty stout to me.  Attached in four places, eight bolts

If JPS uses same solution as CMC - instead of 8 bolts, it is actual a U shaped muffler clamp.  So if one "bolt" goes the other is compromised since clamp is now a J and not a U. I like the go-pro idea.  

I towed mine 1000 miles to FL and around in Fl.  I noticed all the bumper bolts, luggage rack and engine  lid bolts has vibrated loose and that was on interstate (95, 85,65).

In Volume 1 of this adventure, several concepts were presented with pictures and etc.  On showed the towing hardware just bolted to the bumper suppoprts exterior to the body, i.e., where the bumper itself is attached. Looked pretty clean, and easy to work with, for sure, but one does wonder about the side loads of such an arrangement stuck way out there -- lots of moment arm to the basic attachment back at the torsion tubes, and little by way of triangulation to resist racking of the box frame.  I considered all of this, and decided that the extra material being welded would in fact stiffen the box frame a bit more than it is already, and that the car is so light and the turning pretty much unrestricted with a free steering wheel, that it should be good.  And the clamps that hold the box frame to torsion bars are full thickness U clamps.  I am sure the stresses here are well within material limits, and the tightness and susceptibility of the lash-up to vibration will be checked.  Not via personal and real time inspection by right-seater, as Gordon suggests, however.

Just trying to help save you some costly body repairs.

Engineering 101

Here is an idea. Go and buy a new muffler clamp the same size as the ones on the front beam. install one on the front beam then start to tighten it. use a torque wrench to see how much torque your putting on it. A standard muffler clamp is only recommended to be tightend to 30 fpt. I'm guessing a new will break / fail by 50 fpt.

Now how much does that speedster weigh? more then 400lbs, meaning these clamps will fail not long after being towed even in a straight line, let alone going around corners and seeing side loads.

Just my .02 cents. I hope I helped......

by the way, if you guys want tow bars that will attach properly to your speedsters and be safe. let me know and I'll be happy to engineer one.

www.CoolRydesCustoms.com  

Leon C.  did have a unique design on his Inca gold Speedster that utilized the bumper brackets - he removed his nerf bars and attached them there.  He towed from GA to Carlisle a couple times so at least for occasion use it does hold up.

I am considering cross bracing to mitigate the tendency of the  box frame to rack a bit with side loads.  Would be easy to do.

The computations above about foot-lbs and so forth as related to towing loads is not quite the way it works.  Mostly, the loads here are carried by the bolts, of which there are eight, made of steel.  The combined carrying load in tension for these eight bolts is significantly more than the car weighs, I'd be willing to bet.  I'll look it up.  Common steel is capable of carrying about 30,000 pounds per square inch.  These eight bolts might have at least a square inch of area in tension.  Meanwhile, all comments are welcomed and appreciated.

Do what you want, but your off by a lot. All of those bolts have been cold worked into a U shape. Do you have any idea what that does to the steel? Also it is not just the weight of the car your dealing with. You will have impact loads, shear loads, and torsional loads. But hey if your willing to bet 3,000 to 20,000 in body and paint work over spending the money up front to build it correctly,  please promise to post pictures when it fails..... notice I did not say "if"......

Do what you want, but your off by a lot. All of those bolts have been cold worked into a U shape. Do you have any idea what that does to the steel? Also it is not just the weight of the car your dealing with. You will have impact loads, shear loads, and torsional loads. But hey if your willing to bet 3,000 to 20,000 in body and paint work over spending the money up front to build it correctly,  please promise to post pictures when it fails..... notice I did not say "if"......

Just a thought......

I wonder why the original engineers of the VW tow bar just didn't attach to the front bumper of the beetles. You would not even have to get on the ground to install it. Think of how many more they could have sold and how much they could have saved on all that extra steel they would not have had to use... hmmmmmmmm

I'm going with Kevin on this one. Your car will take some hard knocks while towing. That square tubing isn't strong enough and those welds will break endangering your car and other peoples lives!!

Does that sound too liberal? I can rephrase.

Here you go... That design is too weak and not structurally supportive enough. One good bounce will bend or break that assembly and you'll have a very misaligned bumper or worse! Don't do it!

I have flat towed at least 30 different Vintage and JPS Speedsters with my modified towbar and never had an issue connecting it to the beam.   A lot of them had anti sway bars that were lower than the beam and in those cases all I had to do was lift the front end slightly by hand to get the tow bar past the sway bar.

I might have missed something in this thread, but I don't see the need for any modifications like are being discussed here. 

Agree with Kevin.... cold rolled steel has little strength...think about how easy it was the time you twisted off a nut from a muffler clamp using just a short 9/16" wrench .... and nearly bleed to death from the knuckle that got gashed :~)

Agree with Troy too, I have towed 75 MPH for hundreds of miles with a modified VW tow bar that retained the tow bar H/D U' saddles ..stable and without a single issue.

Just to be clear, I'm not saying you can't tow from the beam. The mods that are being discussed are dangerous. I'm simply trying to help the author and anyone thinking of following the idea, to not do so, as it is not going to end good.

We will see . . .

You need to post it for sale, El Frazoo: then we can all criticize the design AND call you a crook.

Everybody else: the way you are going on, you'd think the bar itself was made of high-tension steel, and welded by pipefitters in a nuclear plant, rather than conduit welded by a 10 year old kid in some mud hut in Asia. I'm not wild about the design, and will agree that the whole thing probably isn't needed-- but for pity sakes: it's at least as strong as the towbar itself.

As far as cold-rolled muffler clamps-- I'd bet you a donut Kelly could hang the car from 4 of those clamps. Ideal? No-- but I'm betting they wouldn't break in 10 years of towing the car. Yes, it weighs between 1500- 2000 lbs, but it's not like the car is hanging from the hitch-- there's probably not 150 lbs of force required to get/keep it rolling. He's chaining the thing as well.

I'd give it a rest.

Not saying anybody is right or wrong here, but consider this:  The lash up I imagine here is riding along and the tow car hits a big bump.  What happens?  First thing that happens is the shocks on the tow car absorb most of the energy of that bump.  The pitching motion of the tow car may lift the tow bar a bit but the ball will not transmit any bending moment -- it will just swivel.  And the stirrups on the attach point will also swivel (rotate in the pitch plane with no resistance).  Then the towed car hits the same bump, and the same thing happens: the shocks on the towed vehicle absorb most of the impact and the towed car may ride up and down some. there is no mechanism where that up and down motion transmit in a meaningful way into the structure as the saddle of the tow bar to tow tube interface simply rotates, and so does the ball on the tow bar-- within limits, of course.  As to pitching up and down, the lash up is very loosey goosey, in my view.  Low speed sharp turns seem to me to be the toughest problem, possibly twisting the box frame.  May want to stiffen that up some.  And I am telling you there is NO WAY the tow bar I have will attach to the lower torsion tube without changing the sway bar, and I was not wanting to go there.

Keep 'em coming guys, all good stuff.

And thank you Stan. Seems there is more than one engineer in the house.

I have actually thought I would take a similar size muffler clamp and take it to the lab (which I could do) and pull it in a tensile machine until it breaks.  That would be interesting.

Kelly,  When you come to my shop bring the tow bar along ,  if it will fit in the back seat area, roll a old throw rug around it.........we'll see what can be done with it.    Alan

Ok, Stan and El.... good luck. You both know more then I do. I've only been playing, building and having fun with these cars for over 20 years. I have seen multiple bent tow bars. I also manufacture performance parts, engineer, weld, fabricate, and build vehicles. But hey what do I know. Go ahead and screw up your car. Just.please do 2 things. 1) add safety chains to your tow bar, both from the tow bar to the beam, and one from the tow bar to the tow car. So that the car does not come loose and takes out an innocent person.  2) please promise to post pictures when this contraption fails. 

Good luck I'll wait for the pictures with my popcorn

coolryde posted:

Ok, Stan and El.... good luck. You both know more then I do. I've only been playing, building and having fun with these cars for over 20 years. I have seen multiple bent tow bars. I also manufacture performance parts, engineer, weld, fabricate, and build vehicles. But hey what do I know. Go ahead and screw up your car. Just.please do 2 things. 1) add safety chains to your tow bar, both from the tow bar to the beam, and one from the tow bar to the tow car. So that the car does not come loose and takes out an innocent person.  2) please promise to post pictures when this contraption fails. 

 

Good luck I'll wait for the pictures with my popcorn

You know what, Kevin? I recommended you to a guy just yesterday

... then today came,

People who presuppose everybody else is an idiot generally can't/won't see possible flaws in their own thinking.

So... gotta ask-- how's the bump-steer on that A-arm?

Your popcorn will get pretty stale.  Of course safety cables will be part of the rig. And I'll be happy to post pictures of whatever happens.

Alan: can do.  Was actually thinking about towing the car up, as a practice run.  then I thought: would be more fun to drive it.  In any event, will look fwd to seeing you soon: Any idea when it can be?

Stan and El. 

First my intention was not to say that anyone is an idiot. I simply saw a thread that I thought I could help someone or a few people from having problems with a design that looked to have major flaws to me. I have been under a fair amount of speedsters and seen the U bolts broken off. Plus I have seen how easy it is to bend and twist the frame work that is being built off of. Sorry if you took is personal, but I stand next to my feelings about this design. 

As far as my front ends, there is no bump steer. Our tie rods run parallel to our upper a arms, and the space between our pivot point both on the upper a arm and the tie Rod is the same. 

Did you have any other questions about our front ends?

coolryde posted:

Ok, Stan and El.... good luck. You both know more then I do. I've only been playing, building and having fun with these cars for over 20 years. I have seen multiple bent tow bars. I also manufacture performance parts, engineer, weld, fabricate, and build vehicles. But hey what do I know. Go ahead and screw up your car. Just.please do 2 things. 1) add safety chains to your tow bar, both from the tow bar to the beam, and one from the tow bar to the tow car. So that the car does not come loose and takes out an innocent person.  2) please promise to post pictures when this contraption fails. 

 

Good luck I'll wait for the pictures with my popcorn

Wow, I just re-read what I wrote. I am sorry to Stan and El. I did not mean to come off like that. I just.got frustrated, because I dont want to see anyone screw up there car and thought I could make you guys rethink the design.

For that I am publicly sorry to both of you and anyone else I offended. 

I'm not really diplomatic... 

I remember why I don't go on forums anymore.... 

Coolride, FWIW: no (or at least very little) offense taken. I've been called an idiot before, and while I never liked it, i have tried to take it constructively.  Believe me,. I am the last person who would want my car to get f---ed up.  I will go cautiously and take your recommendations as intended.  I believe the framework I am dealing with here is stout enough to cope with the loads intended.

A quick review of no less an authority than Wikipedia claims that for cold rolled bar stock:

"A value of 29,500 ksi (203 GPa) is recommended by AISI in its specification for design purposes."

They go on to say that the upper value for this material could reach 80,000 psi.

 Which is not to say that one can't twist off a nut on a muffler clamp with too much torque on the old wrench.  Also, be advised that actual muffler clamps can get very hot, and go through innumerable heat/cool cycles, and so can fatigue, which would lower their yield stress considerably.  Just sayin'.  Off the shelf, these four clamps, as attached currently, could lift the entire car and hang it vertically off the ground forever. Not that I have any idea to do so, just sayin' . . .

K now I'm dizzy and starting to see double posts...