If the passenger is in good enough shape to board as described I don't think there's a worry......if you get what I mean. Now personally, I have heard of the bolts letting go on bagger floorboards but I have never seen it in person.

 

Because of the hardening of a grade 5 bolt it will bend were a grade 8 bolt being harder will break. Race cars use grade 5 bolts in areas were shear forces come into play. Sometime it is better to bend than break. For pulling strength a grade 8 bolt and nut is stronger, but for shear a grade 5 that bends is sometimes the way to go.

 

This whole read is based on the idea that there is some shortcoming in the design of the bracket and its connection. The proof strength of a 3/8 16 grade 8 bolt is around 9900lbs. There is some reduction if you calculate in shear I think 50% and some additional strength due to the pin formed on the forging. If the bolt broke and the pin is undamaged then the effect of shear can probably be ignored. That leaves only the leverage calculations which would be the distance from pin to bolt divided by arm length X 9900 lbs. tensile. If we guess this to be 1/3 then the force to deformation would be about 3300lbs. Thats about the weight of a Goldwing with a couple of chubby chicks on it.

 

I fully agree with this, these bikes are everywhere and have been the same for years at the passenger footpeg and it hasn't been a big issue. HD could have easily made the footboard mount have more than 1 bolt through it, the frames have additional holes for different locations and all they would have had to do is make the footboard bracket have additional holes for more bolts, they obviously didn't see a need for it from testing.

 

One thing to keep in mind is that bolts are not all equal just because they are the same grade. There are some variables concerning the ones who have had this footboard bolt break, was the bolt really a good grade 8 bolt, or was it torqued properly. I also want to say that I in no way feel a grade 5 is stronger than a grade 8 but I have had and seen situations where the grade 5 is better for what it is being used in because it will bend. In most applications that require a grade 8 that is what's needed, but there's exceptions to everything.

 

Funny this should come up. Last weekend the wife and I went for a ride. Returned to the house, she went to get off and I thought her slightly inebriated 98 lb. butt had slipped off the board because as she was going down she grabbed my jacket and almost pulled me and the bike over with her. Turns out, the bolt holding the board on had broke. First thing I though was I must have over-torqued it last time I changed the oil in the primary. Hope I can get the broke piece out, she needs the boards as high as they will go.

 

As an engineer by education, it really scares me when I hear stories like replacing grade 8 with grade 5 on machinery so the mechanic can see the bolt starting to fail. In cases like this, the "engineer" who designed the machine and spec'd a grade 8 was not designing the machine properly. He probably should have spec'd a larger bolt, higher grade bolt, multiple bolts, or in some way redesigned the parts to reduce the fatigue.

A grade 5 will bend and shear before the grade 8 of the same size, condition, and properly installed/torqued will fail.

Harry

 

Wow! I didn't know I would create such a debate. The grade 8 bolt sheared off with no weight on it at the time and less than 2 weeks in service. You can debate the tensile strength shear etc but the fact is the same, THE BOLT BROKE. I am no engineer or scientist but I do know that grade 8 bolts are harder, less flexible, and tend to break rather than bend (tree analogy). The size of the bolt that holds the foot board on is rather large and I think a grade 8 bolt is a little overkill. A grade 5 bolt that size place in double shear could prabably lift a good sized car without failing. A 200 lb load should be well within tolerance and not be any problem. The dealer replaced my bolt with the same grade 8 bolt but if I experience another failure I will replace with grade 5 bolts. Judging by what others had said, my was not a isolated failure.

Mark

 

Bolts, schmoltz - I've hear this story way too many times now... Mostly with late model (06-08) bikes if I recall. Makes me a little nervous myself...

 

MKBrower,

Most likely the bolt was overtorqued or defective. And while you may not be an engineer, an engineer spec'd that bolt. That spec calculation included SAE standard factors of safety, design factor of safety, intended maximum loading, etc. If it's grade 8 from the factory, then grade 8 is the correct bolt. You're admission of not being an engineer makes you completely unqualified to select a different fastener.

Harry