Cracked rim halves

[Jeff 8]

I cracked a rim half the other day, at about 200 kmh, resulting in a rapid tyre deflation and some increased heart rate, but luckily not much damage.

The rim is held together with 8mm bolts, where all my other ones are 6mm. Would this leave too little material in the rim half, causing the crack?

Do they just work harden and need to be replaced after a certain amount of use?

Does rough tyre changing lessen the life?

Jeff

[Dave Brand]

Looking at your photo it seems as though the cracking has occurred only around the holes which have studs through them - the holes with caphead screws appear to be intact. I'm guessing that the capheads are the original M6 screws while the studs are M8?

If so, I can see two possible contributory factors for the cracking:

1. Drilling the holes out to accommodate the M8 fasteners has weakened the rim.

2. Drilling the holes out has left a rough finish in the bores, producing stress raisers which have facilitated crack propagation.

[Jeff 8]

Originally Posted by Dave Brand

Looking at your photo it seems as though the cracking has occurred only around the holes which have studs through them - the holes with caphead screws appear to be intact. I'm guessing that the capheads are the original M6 screws while the studs are M8?

The bolts and nuts are the same, they just alternate around the wheel for some reason.

Jeff

[terence]

Those wheels look to be quite old? Very much doubt that 8mm drillings would be a good idea anyway,it was six for a reason. I would have thought the combination of over drilling and possibly over tightening would have caused your problem.

[Dave Brand]

Originally Posted by terence bower

Very much doubt that 8mm drillings would be a good idea anyway,it was six for a reason.

Not something I'd ever do unless there was a LOT of metal around the holes.

possibly over tightening would have caused your problem.

Reminds me of one of our fitters whose technique for tightening capheads was to slide a pipe over the Allen key, tripling its effective length, then hammer on the pipe! I never could explain to him the dangers of overtightening.

[Notso Swift]

He is not a fitter, he is a fuc ker!


As for age, crack testig would n't be a bad idea every year or so depending on use

[Jeff 8]

Cracked another one on the weekend at Phillip Island. Thankfully, it didn't go flat suddenly at speed this time, but felt slippery, making me slow down until I realised what was happening. I think I will replace them all with new ones.



Jeff