Bustin

Glad you got out of this one alive, although busted ribs are no joke.

The guy who coined the phrase "laughter is the best medicine".....never had effed up ribs !

I had a rear caliper lock up tight at around 40mph on my first street bike, a Honda FT500 Ascot, back when I was as noobish as a noobie can be... sixteen-something. My dirt riding skills kicked in, and I somehow worked it over to the curb without crashing.

This was back in the 80s ... so naturally I just wrenched the caliper off and rode home without a rear brake. No worries.

smokinjoe73

Aw, tis a mere flesh-wound!.....

But really, sad to hear about the get-off. I always hate to hear about those but for real you gotta count your blessings. (and ribs).

Feel very blessed it was not worse. Any crash you can walk away from......etc.

Amazed you are ready to jump back on so quick. When I did my ribs it was a good while before I was ready to risk landing on them again. Of course I also had a broken collar bone each time (4 ribs, both collar bones).

Eat healthy, get lots of sleep and you'll be good as new in no time.

Keep us posted on the new build. Maybe stick with stock brakes.

AndyMX47

Best wishes for a quick recovery. Glad you're at least mostly ok!


Enjoy the new SuperHawk!

E.Marquez

You sound like my wife
And i am absolutely sticking with stock brakes. Not a thing will be touched.....they will remain stock......until it comes off the trailer next week,,, then not so much.

Just placed my order for some chromoly steel rod. New brake stay will weigh a bit more than the old one. but will be significantly stronger.

Pidge

Make the Brake stay longer. Picture the pivot point at the caliper, the rotational force from the brakes must push on the stay in a straight line to the other pivot point on the swingarm.

E.Marquez

Good observation, but not applicable to my set up.
I actually had that problem in an earlier version, broke the caliper mount itself ..
This stay setup is generally correct, it was just a poor materials choice or bad design of the arm itself with the materials chosen..whichever way you want to think about the issue.

I made the arm too small dimensionally for the material I used.
I can use the material differently (roll threads vice cut, larger cross section at the rod in threaded point, or I can use a stronger material and keep the dimensions (various diameters I use)
Using a 4130 chromoly steel this time which means I don't have to install a SS thread insert so that a plus.
At this I'll suffer some additional weight for an overage of strength.
chromoly steel can be used to find a happy medium... just won't be shiny like polished like the one I made from 7075

E.Marquez

Some asked to see the failed part, now that Im past all the admin stuff, I own the bike again...blah, blah, blah

The strut rod I DESIGNED AND MADE.. failed.... simple as that.

I patterned it off of others that had worked oem and home made..and I underdesigned it.
In effect i did what an engineer might do as part of the R&D, destructive failure testing ...very destructive

The strut was made from 7075 3/4" solid bar. Turned down to 1/2" on one end tapered to 5/8 on the other.
Threaded on both ends and a stainless steel thread coil installed.
7075 has a Ultimate Tensile Strength, psi 83,000 and Yield Strength, psi 73,000
I accounted for the micro fractures that happen when you cut the material, generially considered to go 1/2 the depth of the cut. the OD of the strut was ground and then sanded down to final dimensions.. The ID was drilled, then threads cut using a tap.

I failed to leave sufficient material thickness at the larger end, for the rod end going to the caliber. The material fractured at that point.



Going forward..
New strut will be made from .500" 4130 Chromoly steel having Tensile Strength, psi 97,200, Yield Strength, psi 63,100

It will be turned down at the minimally to clear the swingarm mount, but otherwise will remain .500" OD. threads will be cut on both ends, but directly into the material, vice having to bore a larger hole as I did with the Aluminum one for the thread inserts.

Jack Flash

In my line of business, this is an image I see quite regularly. Al rod snaps at the tie rod end joint.

I remember the first time I saw the pics of your setup, and that image came to mind. I'm kind of sad I never said anything back then. We all have 20/20 vision when looking back.

Have you given any thoughts other than bigger OD to your rod ? Maybe something like this;
Brutus Electric Motorcycle

Scroll down to the dual caliper pic. Obviously, you don't want 2 calipers, but the rod design is worth looking at. By no means am I trying to tell you what to do, but just throwing thoughts at you.

smokinjoe73

For sure I think going to chromoly is a good one over the 7075. I am sure you have but flash has a good point of modeling off successful design on proven bikes.

There are a lot of really smart guys doing redundant checks on other really smart guys in the big OEMs. Why not stand on their shoulders (Thomas Edison).

E.Marquez

Thanks guys, your ideas and suggestions are not falling on deaf ears. I do what we all do with suggestions, Use um, Lose um, or modify as needed for me... But I am listening

In this case, I know where the weak link is, and I know what parts stood up. I'll address the weak link, but not redesign an otherwise function part.

The front rod end was a 3 piece design with a dynamic load limit of 2,234 foot pounds. It did not fail in any way. Inspection by the manufacturer shows NO deformation at all, which would have indicated impending failure.

I had a mechanical engineer friend of mine run the part in his non destructive failure analysis software using 4130 as strut material, in the new dimensions I plan on, and the size and type of threaded hole I'll be using. He found we are well over the dynamic load rating of the smaller M6 rod end that did not fail...

Add in, I am upgrading both rods ends to a chromoly 3 piece, the smaller one has a dynamic load limit of 7,487 ft lb., the larger rear one 33,647 ftlb
That means the old strut failed somewhere well below 2234 ftlb, the new strut material held up well past 7,487ftlb.
If the new strut system fails, it will be the welded bracket on the swing arm..or the caliber mount itself.

As for following in the foot steps of others.. GREAT IDEA...and I am,, this exact design other than materials has been in use on many bikes before mine,, both track and street.
I simply choose the wrong material, and a less good way of putting threads in the large end... With those two points addressed and stronger rod ends.

Thanks for the thoughts all...