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Keith
Keith SuperDork
7/23/08 10:42 a.m.

Is there a rule of thumb for how strong a tie-down strap has to be based on vehicle weight? For example, I'm tying down a 2000 lb car with four straps. Do I need a working load limit of 1000 lbs per strap, 3000 lbs per strap, 5000 lbs per strap, ??? Obviously, too much will work just fine. But somewhere between a 1" Harbor Freight cheapie and a 6" commercial strap designed to hold bridge parts on to semis is the right answer, and I want to make sure I have what I need.

Given the size of the trailer, nothing heavier than 2500 lbs is going to fit inside to be tied down inside :)

Per Schroeder
Per Schroeder Technical Editor/Advertising Director
7/23/08 10:46 a.m.

We're using the basic tie downs from tracksidetim.com but have a pack from Mac's Tie Downs that we're going to be evaluating shortly....both are 3" webbing and what we consider appropriate for any 'real' car.

http://www.macscustomtiedowns.com/product/79/UltraPacks

We use either 2 straps in the front and two chains in the rear, or four straps...depending on how the car sits on the trailer.

In short, not an area you should cheap out on. Safety, liability, etc.

44Dwarf
44Dwarf New Reader
7/23/08 11:04 a.m.

Most guys laugh at how many i use on my trailer plus i chain and pad lock it just incase. I know i'd feel bad if i lost a load and hurt someone with sraps in the back of the truck. IMO there is no such thing as overkill on tie downs.

44

wreckerboy
wreckerboy SuperDork
7/23/08 12:06 p.m.

For the difference in price and the increase in the security of the load, it's really a no brainer. For my Miata (open trailer) I use four 5K rated straps. And when they get frayed and tatty I replace them. With my usage (about ten weekends a year), that seems to be about every three years, on average.

Overkill? Perhaps. But then I look at all of the work I have put into the car and the potential for harm and damage and it starts looking cheap. Besides, it allows you flexibility should you find yourself looking to drag something larger around in the future.

John Brown
John Brown SuperDork
7/23/08 12:14 p.m.

Get the biggest straps possible. Period. Add a redundant chain that stops the car or add peg holes and chocks to stop any accidental movement.

Towing is serious business and your E36 M3 is too cool for us to lose ;)

DILYSI Dave
DILYSI Dave SuperDork
7/23/08 1:27 p.m.

I go with a 10,000# logging chain in the rear, and 3" (10,000# each) straps in the front.

foxtrapper
foxtrapper SuperDork
7/23/08 1:33 p.m.

No simple easy answer. I've had big 4" straps fail holding down a little Triumph Spitfire before.

The best judge of straps I've found is my eyes and hands. Cheap straps invariably feel and look cheap and cheesy. I don't care who's name is on them, or how much they cost.

Straps truly hate abrasion. That what did in my nice brand new and expensive wonder strap on the Spitfire. It was going through the tiedown eye, and the little bit of fretting it got from the car wiggling on the trailer was enough to cut through it. Lesson learned. Relearned actually, I knew better, but thought I could get away with it.

Those massively heavy straps, those sure have been handy more times than I expected. I'm pretty glad I got them.

Four moderate straps, properly applied, will do a far better job then for heavy duty straps improperly applied.

oldopelguy
oldopelguy HalfDork
7/23/08 1:58 p.m.

For my $ and my equipment I use a 5/16" or 3/8" chain at each end to ensure the car can't some off, then strap it down tight with 2" ratchet straps or 2" strap winders on each end. The straps are really holding the car, and can be tigthened enough to make me happy and keep the car from bouncing, but if everything goes wrong there's a chain on each end to keep the mess all together.

I don't trust 1" wide straps with cars, and my big 3" ones are almost too wide to use on most of my small stuff. For me the 2" straps are the best compromise for a small car. Now that I found a cheap supplier for e-track, it's even easier to make the decision since there are some nice 2" straps with e-track ends already on them.

FWIW, you might want to check what the laws in your neck of the woods say. There are rules tow truck operators are required to follow with regards to properly strapping down a car, and while most times a private owner isn't going to get in trouble for not meeting them there may be just that one Highway Patrolman who insists. To the best of my knowledge a chain at each end is enough in every state and is a good default, but some states do or do not allow straps only to secure a car as a load. If they do allow straps only there would be a minimum spec, and it would be a good place to start.

John Brown
John Brown SuperDork
7/23/08 2:18 p.m.

Also build some "suspension stops" to place under the car. when you load the straps there will be no "bounce causing the straps to break.

A simple 4x4 (or rather FOUR simple 4x4) cut to length will do.

wlkelley3
wlkelley3 Reader
7/23/08 5:55 p.m.

I spent some time as a crewmember on cargo aircraft and our rule of thumb was basically 1 aft and 2 forward restraints. Meaning double the tiedown wieght preventing load from going forward. 2000-lb load would have 4000-lbs of restraint pulling back and 2000-lb restraint pulling forward. This is minimum requirement, as mentioned it doesn't hurt to over do it. I would at least use two 1500-lb straps on the front for aft restraints and two 2500-lbs on the rear as forward restraints. I find it easier though to keep straps of equal rating so four 2500-lb straps is what I would keep. On cargo aircraft we also generally had 2 seperate forward restraints meaning 4 straps pulling aft (2 at the rear of the load and 2 from the front of the load pulling back) as a reduntant system. I generally try to do this for cars on trailer also. That would mean a total of six 2500-lb straps Hope this makes sense.

Keith
Keith SuperDork
7/23/08 6:34 p.m.

I know the obvious answer is "tie it down with battleship chains" :) But I was looking for rule of thumb info such as that offered by wlkelley3. Thanks, that gives me a way to judge if it's time to go for the next size up. I'd noticed that most of the e-track straps were 2", which seemed a bit on the small side to me. But I can easily get 2" straps rated for 3,333 lbs working load, and it sounds as if that would be more than sufficient. I can also find 3" straps with lower ratings.

The size of the trailer really prevents me from carrying anything much heavier than a Miata (or at least physically larger).

On my Miata, I tie the car down with the control arms. Not that there's much bounce in it anyhow, but it does prevent the shock loads on the straps. I also cross the straps (RR goes to LR, LF goes to RF, etc) - any words for or against that? Hasn't been a problem in the last 10,000 miles of towing or so, and I know it makes a big difference on a roller dyno with a FWD car if you do cross them.

wlkelley3
wlkelley3 Reader
7/23/08 7:38 p.m.
Keith wrote: I also cross the straps (RR goes to LR, LF goes to RF, etc) - any words for or against that? Hasn't been a problem in the last 10,000 miles of towing or so, and I know it makes a big difference on a roller dyno with a FWD car if you do cross them.

I kind of left that part out but that's also how we do it on cargo aircraft. Straps work best with an angle between load and tiedown point and the easiest way to get that angle using the least amount of room is to cross them. Also by crossing them you add lateral stability (restraint). So by crossing the straps you will have fore-aft restraint and lateral restraint. Don't use straps verticle or near verticle. There will only be up-down restraint and no fore-aft or lateral restraint with the straps verticle. I knew all those years as a Flight Engineer on Chinook Helicopters would come in handy one day. I also learned how to rig loads as external cargo (ie: lifting by crane but mainly under the helicopter)

wreckerboy
wreckerboy SuperDork
7/24/08 7:09 a.m.
Keith wrote: On my Miata, I tie the car down with the control arms. Not that there's much bounce in it anyhow, but it does prevent the shock loads on the straps. I also cross the straps (RR goes to LR, LF goes to RF, etc) - any words for or against that? Hasn't been a problem in the last 10,000 miles of towing or so, and I know it makes a big difference on a roller dyno with a FWD car if you do cross them.

No, no, no. Use the factory tie down points or the tow hook points most sanctioning bodies now require. The last thing you want is the car, tied down by the control arms, free to bounce along and oscillate to it's heart content, independent of whatever rate the trailer is bouncing at. You can end up with what could be considered a variation of a motorcycle head shake that may well be uncontrolable. Snug the car down so that it doesn't move, but not so far down that the shocks are bottomed out.

Crossing the straps is a nice idea, but not really necessary. Apparently the crossing comes from the drag race world where the soft sidewalls of the slicks allowed the cars to walk back and forth on the trailer. I used to cross my straps front and rear until I discovered that in my application the M-speed tow hook was not really designed for side loading like that in the back. I still cross the fronts and use a sleeve between them to control/limit abrasion. I've been towing for four years on that set up (probably in excess of 10K miles) with no load shifting problems.

SoloSonett
SoloSonett New Reader
7/24/08 7:50 a.m.
wreckerboy wrote:
Keith wrote: On my Miata, I tie the car down with the control arms. Not that there's much bounce in it anyhow, but it does prevent the shock loads on the straps. I also cross the straps (RR goes to LR, LF goes to RF, etc) - any words for or against that? Hasn't been a problem in the last 10,000 miles of towing or so, and I know it makes a big difference on a roller dyno with a FWD car if you do cross them.
No, no, no. Use the factory tie down points or the tow hook points most sanctioning bodies now require. The last thing you want is the car, tied down by the control arms, free to bounce along and oscillate to it's heart content, independent of whatever rate the trailer is bouncing at. You can end up with what could be considered a variation of a motorcycle head shake that may well be uncontrolable. Snug the car down so that it doesn't move, but not so far down that the shocks are bottomed out. Crossing the straps is a nice idea, but not really necessary. Apparently the crossing comes from the drag race world where the soft sidewalls of the slicks allowed the cars to walk back and forth on the trailer. I used to cross my straps front and rear until I discovered that in my application the M-speed tow hook was not really designed for side loading like that in the back. I still cross the fronts and use a sleeve between them to control/limit abrasion. I've been towing for four years on that set up (probably in excess of 10K miles) with no load shifting problems.

I agree, after 40 some years of car haulin' I would NEVER use an A arm And NEVER block a suspension solid. That is just begging for damage. The car needs to move.. some. and cinching the suspension down some keeps the straps or chains tight.

The only time I've had a car come loose? When AAA flatbeded my Sonett home from an OVR autocross ( after blasting a throwout bearing...) he hooked the rear tie down to the original factory tie down hole in the sheet metal tub. He had to E stop and the thrity year old sheet metal hold down gave way to rust. And crushed the nose of the car into the front of the flatbed!

IMHO, I double the load rating for straps. Cross strap for any trip longer than a block or two.

The only time I used a chain and solid cinch was on my gas dragster with no rear suspension, except the slicks

Keith
Keith SuperDork
7/24/08 9:01 a.m.

A Miata on race suspension doesn't move much, I've never had any misbehaving from having it attached via the control arms - even when the car is twice as heavy as the trailer. And the factory tie-down points are long gone on most of my cars. Recovery points are not the same as tie-down points.

With a car on a small trailer, crossing the straps works better from a packaging standpoint. Uncrossed straps make it difficult to find room for the ratcheting mechanism.

Wall-e
Wall-e SuperDork
7/24/08 9:02 a.m.

I would second using the factory tie down points, that's what they were made for. You can also find some neat hooks for such a purpose that makes life even easier. I never noticed a difference between crossing the straps or not. that was usually determined by the size of the car vs. trailer. Sometimes I had to cross them because the tiedown was too close to the anchor on the trailer and crossing will give you some extra length.

Keith
Keith SuperDork
7/24/08 2:31 p.m.

Update: I stopped by the local wire & rope place and asked about strap ratings for a 2500 lb car. The guy laughed and said I could use anything there. His smallest strap was a 3000 lb 2", and he figured it was far more than I needed.

I also took a look at the tie-down points. The typical recessed ring mount used on trailers? Rated for under 1700 lbs. The D-rings that I'm using? 3600. So I'm thinking my 3300 WLL straps are probably going to do just fine, given that they're stronger than the tie-downs in most trailers.

wreckerboy
wreckerboy SuperDork
7/24/08 8:03 p.m.
Keith wrote: A Miata on race suspension doesn't move much, I've never had any misbehaving from having it attached via the control arms - even when the car is twice as heavy as the trailer. And the factory tie-down points are long gone on most of my cars. Recovery points are not the same as tie-down points.

It does. Mine is a 1.6 Spec Miata (2270 lbs., 1700 lb. trailer) and it moves along quite nicely. Thats with the hellish 750/350 spring rates these things run. My tie down points were long gone when I got the car and I actually had to add them back in.

Although I do not currently tie to the control arms, back before I knew any better I did, and even with the control arms torqued to two clicks past "urrrrhGHHHGG" I managed to adjust the alignment on the right rear. If this is your Targa car, tow points are required anyway, right?

Keith
Keith SuperDork
7/25/08 10:02 a.m.

I paid more attention when I tied the car on to the trailer last night. Turns out I use the rear subframe in the back and a big hole near the inner edge of the control arm on the front - so it's more tied down than simply looping a strap over the wheel would be. And the car she don't move. I haven't kept track of mileage, but I've probably got around 5,000 miles of Miata dragging with this setup and no trouble.

Tow points aren't tie down points. Some can be used both ways, but not all. If they were the same, you'd just use the factory tie-downs as recovery points on Spec Miatas.

wreckerboy
wreckerboy SuperDork
7/25/08 11:02 a.m.
Keith wrote: Tow points aren't tie down points. Some can be used both ways, but not all. If they were the same, you'd just use the factory tie-downs as recovery points on Spec Miatas.

Clarification please, because I am not sure I understand what you are saying.

The reason that the factory tie downs cannot be used as recovery points on SMs is because the rules require a two inch opening, which the OE assembly does not have. However, the majority of cars I see have had modified or aftermarket recovery points attached in the OE position.

The reason is to simplify EV's job when trying to extricate a car, often on a hot track. Typical extraction methods are quick and dirty, and the extra space to work within is a blessing.

Or is this a rehashing of the endless Miata.net debate about towing with the factory point?

Keith
Keith SuperDork
7/25/08 11:24 a.m.

The factory points are strong enough to tow with, but there's a good chance of body damage due to the angle of the strap. Basically, you'd probably end up removing the front bumper cover.

Extrication involves a slight upwards angle on the strap but is mostly forward. Tying a car down has the strap mostly going down so there's as much down (or more) downward force on the hook as there is forward. I wouldn't be comfortable pulling down that hard on my Spec Miata front toe hook, and the rear recovery point (modeled after a MX5 Cup strap) is not designed for a downward pull at all.

Jack
Jack SuperDork
7/28/08 10:59 a.m.

But whatever you do, do not use tie down straps for supporting an engine.

Yeah, I did, but only one broke and didn't damage anything. Stupid shortcut nearly cost me body parts, a newly built engine and lots of sheet metal.

Jack - older and somwhat smarter now

RussellH
RussellH New Reader
7/28/08 4:09 p.m.

Keith, you probably remember what happened to the OTC NSX on the way back from Buttonwillow? It's been a long time but I remember the trailer flipped and the NSX was saved because it was hanging upside down by the tie-down straps.

Keith
Keith SuperDork
7/28/08 5:51 p.m.

I do remember that, I passed the upside-down trailer on the side of the road. I think it was just on its side, actually :)

But that doesn't tell me what the rating was on the straps or the tie-down points. If it was a commercially-built trailer like a Pace, they were probably 1600 lb tie-down hooks and a ~2800 lb car. I have 3600 lb hooks, 3300 straps and a 2100 lb car. So should I choose to roll my trailer, I would expect my Miata to stay attached to the surface previously known as the floor.

With regards to my control arm tie-down points, the car does squat down when I tighten the straps. The hooks are placed very close to the control arm pivot points. So it's not much different, functionally speaking, from tying directly to the chassis.

44Dwarf
44Dwarf New Reader
7/28/08 8:43 p.m.

One thing to remember is if the trailer is enclosed you need to limit the suspension travel by use of blocks or air bags and straps. There no air movement inside a trailer and the shock / struts will over heat in no time.

Fed's mandate 4 point minimum tie down me personally on my 1100 lbs dwarf i use a crap load. 4 inch wide DOT cert winch strap to front bumper. wheel chocks nailed in to the floor. 1 ratchet strap next to the winch strap. the rest are 1 inch straps rated at 2000lbs with 4000 breaking strength. up front one on each side of the front Nerf bars. In the back (qty 2)4000 lbs eye bolts in the frame i run a strap from eye bolt to just a head of the lower control arm pivot point on the Nerf bar. Pull theses tight before using winch strap this way the winch loads the heck out of them. then i use 2 more straps that cross the back bumper to keep the rear end from hooping a round. so that 6 straps, 1 ratchet strap, 1 hd winch strap, and last but not least a chain i can but a 3/8 shackle pad lock in to go trailer frame to car frame. This is on my no suspension open trailer.

In the enclosed box truck trailer i have E-Track Use bonnets on the rears and over straps on fronts. "lab jacks" at four corners and more e-track straps to hold car down to the jacks. oh and a 1/2 inch 8400lbs pull electric winch cable.

44

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