Axle broke traveling 30mph.

[bike4life]

My trailer has been working fine for about a month. Today the 5/8 axle sheared when I was biking at 30mph. The trailer become wobbly and the bike rocked back and forth but I kept it upright and decelerated to a stop and then got up unharmed. Lucky I guess. I am still an atheist but that has questioned stuff a little lol.....I plan on upgrading to 1” axle which fits a trailer hub. Should work good. I dont think it should shear as it will have 2.56 times the cross sectional area as its proportional to radius squared...

It would be epic though to get a 4” train car axle would look sick but that’s out of budget/build spec.
The day before my gear got loose and I got stranded and had to walk it home till a nice guy let me borrow some tools. so today I brought some tools which turned out handy to disassemble the trailer from the bike. Then my dad drove me home and we fit the trailer and bike in the trunk in 2 trips.

Also don’t use Hf hand truck tires/wheel hub. Last month my tire and rim exploded with that combo, but only traveling at 20ish. I was unharmed. This month I upgraded to a 4 lug trailer tire....

 

[Karl Snarl]

sounds like you had a defect in the shaft or a bad bearing ground it down. i've used 5/8 shafts for up to 8 hp for years an haven't ever had a broken axle or jack shaft. either that or you were using a like a grade 2 rod. gotta be at least grade 5 / 8.8 metric. i prefer grade 5 because it bends before breaking, where a b-7 hardened rod with shear off with very little flex before it happens.

 

[bike4life]

sounds like you had a defect in the shaft or a bad bearing ground it down. i've used 5/8 shafts for up to 8 hp for years an haven't ever had a broken axle or jack shaft. either that or you were using a like a grade 2 rod. gotta be at least grade 5 / 8.8 metric. i prefer grade 5 because it bends before breaking, where a b-7 hardened rod with shear off with very little flex before it happens.

If you look at the pictures you can see that it failed really close to the wheel. It also spans about a 12" distance and i know that the deflection of static beams drop off when they span long, by a factor of x^3 but not sure how that relates to dynamic/spinning axles. Maybe the weld weakened the metal or perhaps just simple beams laws say the highest stress on a beam is dead center, and that was the closest point to the center it could fail. In fact, about 1/2" above the weld.... It was cold rolled steel. A day before the axle broke i did notice it was slightly bent inwards, due to the large forces on the wheel.

I think an upgrade to 1" mild steel is a good idea. I was gonna use cold rolled but its not in stock, and i think 1" should be pretty dam strong. I cant see that failing. Plus i am gonna weld gusset plates around the axle to the wheel hub to increase its diameter and toughness. I dont understand how you can buy grade 5 or 8 rod stock, i thought only bolts. This axle below is huge, crazy for that thing to break...

 

[CrazyDan]

You might want to bring the frame inwards as far as you can to put the pillow block bearings closer to the wheels. You had way to much of a gap from the hub to the axle mount. Look at go karts, their axle bearings are as close as they can get to to the hub as can be.
If you want v2 to be indestructible, make an inboard and outboard bearing mount on a peerless 100-007b with a 3/4" axle or a peerless 141-d with a 1" axle. Gives you limited slip differential so the outside tire doesn't chirp on turns, but both tires are under power on the straights.

 

[FNTPuck]

Never would have guessed you'd have issues with those HF wheels and tires! ...oh yea, I actually told ya multiple times not to run them lol. Glad you weren't hurt, but try to listen to majority advice next time. Was legitimately concerned for your safety imagining a 30+mph pusher trailer with terrible brakes and harbor freight wheel barrow tires and was trying to help.

Trailer tire is a great upgrade though, great job. I'm not too surprised that axle snapped though, pillow block bearings are not meant to be used as far apart axle hangers and allow a lot of deflection which will over time fatigue the axle at the worse point of deflection - which would be just off to one side of the tire. Get a proper gokart axle+sealed bearing axle hangers and you will be good to go

 

[bike4life]

My plan is to move the pillow blocks inwards by running cross peices of angle iron across the frame. This will drop that 12” gap to maybe like 6”. Then the axle will be upgraded to 1” steel rod, which will sit in 1” pillow blocks. I was going to use 1.5” axle but I can’t find any 1.5” bore gears with the specs I need. I think 1” rod will work well if I drop the distances.
Yes mtpuck thx for your approval on their trailer tires lol, their carisle btw...

 

[mark20]

My plan is to move the pillow blocks inwards by running cross peices of angle iron across the frame. This will drop that 12” gap to maybe like 6”. Then the axle will be upgraded to 1” steel rod, which will sit in 1” pillow blocks. I was going to use 1.5” axle but I can’t find any 1.5” bore gears with the specs I need. I think 1” rod will work well if I drop the distances.
Yes mtpuck thx for your approval on their trailer tires lol, their carisle btw...

you need to use gussets, the axle needs to be supported, (i would use 4)
and get some hardened axles. the higher grade the better.

 

[bike4life]

you need to use gussets, the axle needs to be supported, (i would use 4)
and get some hardened axles. the higher grade the better.

Unfortunately, idk where to get grade 5 rod and the cost would be much higher than mild steel. It’s always cheaper to upgrade the diameter than increase the grade. With a tiny span by moving in the pillow blocks and 1” diameter mild steel with gausset should work.

 

[mark20]

You would need the change the pillow blocks as well, unless you have then laying around, you could try a old motorcycle axle

 

[bike4life]

You would need the change the pillow blocks as well, unless you have then laying around, you could try a old motorcycle axle

I am lazy and the moving the frame inward wont really work that well. Do you think 1" mild steel rod will do the trick at a distance of 12" span or should i go thicker.... THX