I'd need to make a run of at least 10 to get the price into the $50 - $75 range. It would be a length of M16x1.5 threaded rod with a custom 1.5" long coupling nut Loctited onto the end. Most likely the threaded rod would be a high strength bolt with the head cut off as that isn't an off-the shelf size. The coupling would also be custom made. Would be awhile before I could get to it as I'm booked solid for the next month or so.
well what you don't want happening is what happened to mine. My eyebolt looks to be an M12 though I'd have to measure it to be sure. The one time I needed to actually use the dang thing to tow the vehicle it freaking bends! Now it's stuck in there till I cut it out. Shock loads from actually towing can be fairly high. Image Unavailable, Please Login
I can't believe that no one at the Ferrari factory never actually tried to screw one of these in the receiver behind the bumper, no way the 7 1/4' factory tow eye will fit. That is the problem too and I have been told by more than one F car mechanic that they see the longer tow eyes bent all the time. What really works best is a tow hook no longer than about 3 1/4" that is so short it is difficult to bend, but then you have to be careful how you pull so you don't damage the grill or bumper. I am making a short one for my car too. I can do that myself by cutting off a threaded bold and cutting threads to fit a 3/8" tow eye. I am pretty sure from the discussion on the Mondial board that 10+ owners would buy an adapter, 2" threaded coupling with a threaded rod or cut off bolt sticking out about 1" to make a 2" extension. My town/area is too small and sparsely populated to have a machine shop interested in this kind of work. Whoever makes them owes me a freebie though, lol! Alden
what's best is to weld a loop to the frame and not ever worry about it again. That's what I'm going to to, two loops one on the drivers and one on the passenger side, that way a tow strap can be used to center pull if the need arises.
I do not want to assume any liability for this so, I cannot offer a design analysis for you. But, if you use this back-of-the-envelope calculation, you should be fine --- this is very conservative using mild strength steel and safety factor of about 3 (assuming you do not exceed a 45 degree ramp/slope angle when pulling). That said, you should probably also run a simple calculation for the loading on the threads --- there are very easy to use thread loading calculators available online, just google it. My quick SWAG is that so long as you have 1-inch of thread engagement on both ends...... you should be okay..... you may even be able to get away with less ( but use the calculator to verify that ! ) Image Unavailable, Please Login
Dave my concern would be the shock loading from slack/no-slack. In most cases the tow hook would be used for dragging onto the flat bed, no real issue. But in my own case I needed to get my mondial home from a couple streets away. Used the truck and a tow strap, went as careful as possible, still the change in slack was enough to cause problems and the off-center location of the eyelet does not help at all.
Agreed. My advice would be DON'T DO THAT I am assuming a predominantly slow, static pull. I doubt too many F-car owners would want to try and pull their cars down the road with another vehicle and a tow strap ---- unless you are in the middle of nowhere, a flat bed pick-up/tow is always just a cell phone call away .
Yeah, but at the track you're going to get shoved off or pulled away with a strap. On the road a flatbed will usually be the option. In my case I had taken the boys to school, literally a couple streets away and it decided it didn't want to start again. Too close to fuss with a tow truck so I grabbed my neighbor and we towed it back. However that all said, the eyelet bolt will bend just pulling it onto the flat bed as it's off center and the force is a bit higher going up a 15* slope, that's why the tow guys prefer to strap to the lower front suspension on both sides to get a center pull. With a low ground clearance Ferrari that can be a real PITA or impossible like mine where ground clearance is just about 3.5" So for me, I'm going to have two loops welded in, then anytime I need to have it towed or shipped its' fast and simple with no risk to the lower chin fiberglass or suspension.
Who in the hell is going to be tracking a Mondial ?! LOL But, indeed, it is always best practice (when pulling any vehicle by its tow eye) to align the strap/chain line of action as close as possible to the axis of the tow hook shaft. If kept closely aligned, pulling at a single, off-center point makes no difference (assuming the frame/chassis of the car has been built to handle it ). I once saw a knuckle head (accidentally) pick up a crashed Lotus Elise almost completely off the ground by its corner-mounted tow eye ! .
OK, I came up with 3/4" at each end, with about a 2x safety factor, your 3x safety factor estimate is more conservative &n makessense. I agree that you really don't want to do a tow like SMG2 describes except in an extreme emergency that justifies risking bending other things as well. One advantage with the coupling is that the bend would most likely be where it the extender attachés to the frame, so you could remove the eye & work the extender out. Less risk of bending your OEM tow eye that way.
My WAG for the design was a 2" coupling with 1" of thread engagement from the tow eye and the extension, so I guess that will be OK. Bending the tow eye is always a possibility but you can't bend it or use it if it won't fit the car so I think the adapter is a great way to have a usable "emergency" tool available while keeping the factory supplied part in original condition. Flat bed, yes. Bubba pulling me out of the ditch in an emergency, maybe. I have heard about some M12 threads out there too. I guess they just grabbed whatever was in the bin for the tow hook mounting part too, lol! Alden
I have found a shop that will do this for us, but I have to supply the materials. Is this tubing suitable or do I need something stronger: Low-Carbon Steel Tubing, 1" OD, .5" ID, .250" Wall Thickness. Also, I need a head count for folks who are interested in this adapter. Please post to the thread below if you want one: http://www.ferrarichat.com/forum/mondial/499703-who-wants-tow-eye-adapter-extension.html#post144189717 Alden
Had some time on my hands and this little project got me thinking.. went and dug up the engineering data. bolts & wire rope should have a FoS of ~8.5. Then did a quick search thru engineersedge and pulled up the calcs for tensile strength and thread yields. Dropping in the relevant data per the OP and long calcs short: for 1" or 25.4mm of thread engagement the material needs to have a min of 150,000 psi of yield strength. the list: Yield strength of material, Calculated axial load yield for bolt/nut, Factor of safety. 32kpsi = 6665 = FoS 1.9 38kpsi = 7915 = FoS 2.26 45kpsi = 9372 = FoS 2.67 70kpsi = 14580 = FoS 4.16 110kspi = 22911 = FoS 6.54 150kpsi= 31242 = FoS 8.92 I used 3500lbs for the weight as the Mondial is over 3k lbs, doesn't hurt to round up for safety. Bear in mind these are est and many factors can alter them, esp coefficient of friction between threads and any preload tq once installed. I highly suggest testing the assy or having it yield tested before selling any to anyone. The risk of property damage and personal injury from a sheared bolt under tension is fairly high when/if it fails. It sucks but it's prudent to test and insure it's not going to fail.
I did a bit more digging and found that an acceptable FoS of 5 for shackles and clevis joints for towing and pulling vehicles onto flatbeds. A FoS of 3 is on the low end of safe and not advisable for towing purposes, I guess you could get away with it provided it's used only when the vehicle can freely roll and in a controlled jerk free manner. Makes sense as the ramp angle and friction of pulling a vehicle that can not move under it's own power for a variety of reasons will increase the load that connection is under. God forbid a damaged Ferrari needs to be hauled up and the hook fails.
This $14 racing style tow hook on Amazon is advertised to fit a number of BMW models and the screw thread specification matches the one for your car. I suspect the screw thread may be standard for some European cars. Many aftermaket hooks appear to be modular, allowing different size bars to be interchanged with the hook since the hook does not need to be different for each car. I've also seen 9" long tow hooks for a Lancer EvoEX. So I suspect you might be able to find a ready-made properly-spec'd model from a racing accessory supply house or a local racing/tuner garage. Image Unavailable, Please Login
BMW is M16x2 I think that mistubishi lancer is M16x1.5 Tow Hooks (New Swivel Design) Parts & Products English page CUSCO one option
Not cheap but its' all in one. M16x1.5 mounting thread length is 30mm, shaft length is 140mm, overall length is 195.5 mm without hook. Cusco Rear Tow Hook Red | Tow Hooks
OK last time, I think... Subaru Impreza & WRX STI, are M16x1.5 lengths are dependent upon, yr and front rear mount. Looks like a number of choices there. Cusco and Beatrush are the two mfg it seems for these on the Japanese models.
Well, the stock tow eye bolt (@ 16mm ) only has a x-sectional area of approximately 0.31 [in^2]........ so, there is no advantage in exceeding that with your coupling. At your dimensions above, you have a x-sectional area of approximately 0.59 [in^2] --- more than enough.
True, the factors to consider are thread engagement and tensile yield of the material. The shear area of the thread pitch determines the thread depth so as to not shear threads before the yield limit. As you probably are very aware the bolt should shear before the threads strip. It's not a difficult engineering problem but it should be engineered to insure safety. I had suggested the 1" od tube option before the full scope of the project was known. Given the application I'd shy away from the original thought and have a male/female stud machined from 150kpsi steel rod, prefere rolled threads too vs cut. The unknown though is the tensile yield of the factory bolt.
That's a great suggestion, expensive, but would produce a very high quality part. However, if you don't go that way, I recommend using steel hex bar instead of tubing. That way you can use a wrench on it. Ideally would be metric hex.
To eliminate the slack, one has to drag their brake. It is standard practice when getting towed on track to drag your brake so the tow rope is always on tension.
