Forged Cranks, Anygood?

[Paperclip]

OK this is unusual for me, as im in the know about everything on my bike haha, but i feel i may aswell ask

this is my question so you dont get mixed up and just say there good because you have a pair..........

I have since i started trials, a pair of echo 7075 cranks, had them for around 3-31/2 years now and untill the otherday they have been soild, taken some right stick had loads of difrent pedals in them, and many bb's.

so my question's are to everyone,

would a pair ot trialtechs last the same, with loads of battering? would the splines wear out faster on forged? would the pedal threads die on me? is it worth just saving up longer for some 7075 echos again?

I feel all dumb, but the end of the day ive never had a real experiance with forged cranks, it all comes down to money. 50 pounds or 100 pounds pretty much.

[forteh]

The forged cranks (echo/trialtech) use 6061 whereas the cnc cranks use 7075, typically 7075 is a higher strength alloy.

6061 T6 has an ultimate tensile strength of around 290MPa whereas 7075 T6 has an ultimate tensile strength of around 520MPa, this gives a direct comparison of the different materials. T6 refers to the heat treatment used, not sure how cranks are typically heat treated though, tarty only state the material.

Forging vs CNC from billet actually produces a stronger crank as the forging process directs the material grain flow and helps prevent stress risers. Ideally you want to forge and then CNC machine to shape from 7075, this is how middleburns are made.

Im pretty sure that the echo 7075 cranks are machined from plain billet, as such they cant be as strong (for a given weight) as a forged crank; this would explain why middleburns are 25% lighter yet retain the strength

Any clearer?

edit: basically: -

The forged cranks get their strength from the manufacturing process and by using more material which in turn increases weight, however because the material is a lower strength the pedal threads and splines are possibly more likely to fail if not looked after.

The CNC cranks get their strength from the material alone (no benefits from the forging process), however because theyre not forged you need to use relatively more material (only slightly lighter than the 6061 forged cranks). Because the material is harder the pedal threads and splines will last longer before wearing out.

The forged 7075 cranks (middleburn and I guess tryall and rockman are also 7075 or similar) can be made lighter because they use the strongest manufacturing process and the strongest material.

Edited October 9, 2009 by forteh

[Paperclip]

yeah I understand your point fully, and strenth of cranks these days dont really matter as its very rare they snap,

my only worry is the threads and splines, im more curios to how long they tend to last

as id be getting a new bb cranks and pedals, so really im just after some long lasting cranks over anything.

if i can get a few more lads let me know how long they have had there cranks , or had any problems with forged let me know,

ill leave this topic threw the weekend and make up my mind for monday

[Danny Metcalfe]

You not wanting My echo cranks now then?

[Ashley-Wood]

ive had my trialtech cranks since they came out,, and have gone through alot of bashring,,, aslong as you keep everythign done up tight, theyll last ages... they have been street abused haha

[forteh]

To be honest I cant see there being a problem with the forged 6061 pedal threads and splines, just make sure theyre greased before fitting and keep them tight