M5 or M6 rack bolts?

[UpWrong]

My first eBike conversion, using a rack kit from Woosh. My donor bike has dedicated M5 (i.e. 4 mm) rack bolts. I'm wondering if these are adeqaute for the battery/controller plus whatever shopping or kit is added. So wondering whether retapping the aluminiun frame for M6 bolts would be a good idea. Anyone had problems with M5 bolts not being up to the job?

[Jdsk]

Please could you add a picture of how it's mounted so that we can think about the loads.

Thanks

Jonathan

[Pinkie]

My first eBike conversion, using a rack kit from Woosh. My donor bike has dedicated M5 (i.e. 4 mm) rack bolts. I'm wondering if these are adeqaute for the battery/controller plus whatever shopping or kit is added. So wondering whether retapping the aluminiun frame for M6 bolts would be a good idea. Anyone had problems with M5 bolts not being up to the job?

Think I'd just make sure I had decent quality m5 bolts to be honest, you can hang weight into the 100s of lbs off them, think they can hold a small % of an ebike battery weight.

You are more likely to break the rack, if you load it up with shopping, which are generaly rated at about 50lbs but do seem to hold quite rotund youths with out a problem

[jb]

5
M5 will be fine. M6 is more likely to weaken the fixing points & reduce the number of threads in the hole.

[UpWrong]

I think you're right about possibly weakening the fixing points. The rack has gone back to Woosh. One of the legs was twisted and I couldn't get the bolt to go straight into the frame - it kept cross-threading. I'm not sure if the rack leg eyes would take M6 bolts anyway. I sent the rack back before checking.

[pete75]

If you're worried about breaking the bolts don't use stainless, use 10.9 alloy steel.

[Jdsk]

The rack has gone back to Woosh. One of the legs was twisted and I couldn't get the bolt to go straight into the frame - it kept cross-threading.

Very wise. For optimal strength the bolt should run in freely without having to force any alignment of the parts, as once pointed out by Brucey.

Jonathan

[Jdsk]

And he also commented that using a longer bolt and a nut changed the forces and could be employed to advantage.

Jonathan

[jb]

The thing to remember is fatigue will break things long before the load will. If nothing moves no fatigue can take place.
There will always be movement, the trick is to confine it to the parts that can cope with it i.e. not the bolts.
Bolts are good at holding things tightly together; but not flexing.
The bolt fixing points don't want to flex either. But the rack struts can flex a little. So movement should be confined to the rack members but not the fixing points or the bolts.

[Slowtwitch]

M5 is my weapon of choice

[stodd]

Just make sure it remains well tightened (I must admit I don't check mine often enough).

Once it gets a little loose it will have many more disturbing forces on it and could break quite quickly.

[UpWrong]

And he also commented that using a longer bolt and a nut changed the forces and could be employed to advantage.

Jonathan

Makes sense, thanks.

[squeaker]

If nothing moves no fatigue can take place.

Not strictly true: fatigue failures are the result of an oscillating load below the static failure load level. Loose fittings will be likely to increase the peak loads, though.