Respectfully, that's just it: Looking at it, I think it's more of an oversight than engineered.

Drag Specialties puts out a lot of products. Some are generic crap that barely fit their intended application, some are pretty d@mn good. I don't trust my life against their decisions to save a few bucks on the design. Because I know the Chinese manufacturer doesn't give a flyin' frig about my life, I question these things.

I bought the risers knowing the problem. I intended to drill and tap as others have done to the same risers, based on the reviews on fortnine. But I will take Scuba's advice and chop the bolts a bit. He knows his stuff. I can always buy the oem bolts again at the dealer and tap it later if not comfortable with the results.

Thanks for reading and replying. I appreciate all opinions.

 

The first 3 threads of a bolted joint are responsible for 84% of the clamp load. In aluminum, we design to bolt diameter x 1.5 as the minimum depth for a coarse thread. At 5/16" coarse thread, your minimum thread depth should be ~1/2" which is 9 threads. You're more than fine for the moderate load a riser bolt holds.

 

 

Yeah, most bolt designs have a high safety factor. Standard automotive design prioritizes safety issues (handlebars falling down while riding would be a safety design) and the safety factor would be minimum 2. That's pretty conservative overall. Airlines might see a SF of 1.1, while civil engineering like roadways and bridges can see 5-10. non-safety issues you might typically see a safety factor of about 1.25-1.5 due to material variances and assembly condition variances. That's perfectly acceptable and yields little to no warranty issues.

But like I said before, bolted joints carry all their load in the first 5 threads, When I design a new joint, there is a formula for thread pullout that uses the strength of the fastener, nut material, thread engagement, thread class, bolt grade, etc. to get the total engagement area and other factors, and you use that to determine the force in the joint at which the threads will strip. It should be in the nut material (female threads) if designed properly. When looking at the overall joint you have to account for the stress in the weakest material and determine if the bolt preload allowed is at a satisfactory level for that joint.

You could do the math and see that the handlebar clamps are designed extremely conservatively (in my opinion). And considering we're working outside of the first 5 threads here the entire effect of trimming the bolts is pretty much insignificant.

If anyone is more curious on fasteners and bolted joints I would be happy to make a thread devoted to the design behind them and how they work. I find it fascinating. Then again, I do it for a living so I might be biased.

 

Thanks Scuba. I'm really glad for your knowledge on this topic.

I'll be installing tomorrow afternoon.

 

Quote:

there is a formula for thread pullout that uses the strength of the fastener, nut material, thread engagement, thread class, bolt grade, etc. to get the total engagement area and other factors, and you use that to determine the force in the joint at which the threads will strip.

I read some about all of this which is why I couldn't be sure about just blindly cutting the bolts down.
It does beg the question though why the manufacturer of this particular riser did not make it user friendly to use the existing bolts that are on the bike presently as is?
The only thing left is to ensure the clamps don't touch the riser on both sides.

 

First thing I will check. Thanks.

The finish on them is nice. Threads are clean. We will see later today how they fit.

 

Because not all top clamps are built equally.

 

I don't know how anyone else does it but this is what I did to change the risers:

because I wasn't born with 4 hands, I used this strap to hold the bars up off the bike, slung over the garage door opener...lol.


old risers off, comparing to new-


chopped 3 threads off the original clamp bolts, that's all it needed-


3.5" risers on-




still waiting for the shorter brake line. not a fan of kinking it like that but whatever.
the wires going to the speedo are at the absolute max. (marked with blue smudge) Wondering if there might be another 1/8 of an inch slack in the headlight bucket....