How Tight

[old bell]

I have changed the saddle on my bike for a new one and the instructions say to tighten the bolt to 12NM. Not having a torque wrench and being cautious I have not tightened it enough, in that the saddle has moved when riding.

Can anyone let me know whether 12NM is fairly tight, very tight or as tight as I can get it, using just a regular allen key. I know the real answer is to buy a torque wrench, but it would be a case of spending maybe £50 for a tool I will probably only use once.

 

[Archie_tect]

Could you call into your LBS when you're next riding past and ask them to check it for you to 12Nm with their torque wrench- that would give you a feel for how much to tighten the allen screw by next time?

 

[slowmotion]

Is this the bolt that fixes the rails to the seat post? If it is, you will probably need a 5mm hex key. A 5mm hex key (the L shaped ones) have a long arm that is 80 mm long. A torque of 12 Nm equates to hanging a 1.2 kg weight on the end of a metre long stick. This is equivalent to hanging a 33 pound weight on the end of the 80mm arm of the hex key.

That's tight!

 

[old bell]

Wow, that is tight. What you are saying is that using a 80mm long alen key I need about 15kg weight behind it, ie 33lbs.

Thanks for that.

 

[Alembicbassman]

If it moves when you sit on it it's too loose

 

[slowmotion]

Wow, that is tight. What you are saying is that using a 80mm long alen key I need about 15kg weight behind it, ie 33lbs.

Thanks for that.

Yep. If the short arm of the key goes in the bolt, and the long arm is the bit that you grab, and it is 80mm long, applying a weight of about 15kg to the very end of the 80mm arm gives you a torque of 12Nm.

If you have a spring balance, you can improvise your own torque wrench!

Good luck.

 

[numbnuts]

If it moves when you sit on it it's too loose

 

[Herzog]

As the others have said, 12Nm is very tight. Using a regular allen key (i.e., the length of finger), you'd need to put some serious effort into getting it to 12Nm.

 

[zacklaws]

Alembicbassman, on 16 June 2011 - 16:45:08, said:

If it moves when you sit on it it's too loose


I once thought I had my saddle tight after doing an adjustment on the road, till a bit further on going fast downhill, I hit a bump and the next thing I knew my saddle was nose up pointing verticle. All I could do was hang on like Ben Hur in his chariot till I got to the bottom

It was one of my best buys a torque wrench and it does get well used, for the bars, headset, seat post, front and rear mech, saddle etc

 

[Alembicbassman]

If you think 15Nm is tight, I recently installed a bottom bracket that was rated at 70Nm !

 

[lulubel]

Is this the bolt that fixes the rails to the seat post? If it is, you will probably need a 5mm hex key. A 5mm hex key (the L shaped ones) have a long arm that is 80 mm long. A torque of 12 Nm equates to hanging a 1.2 kg weight on the end of a metre long stick. This is equivalent to hanging a 33 pound weight on the end of the 80mm arm of the hex key.

That's tight!

Very tight. I tried to undo that bolt today to move my saddle back slightly, and I couldn't shift it. The annoying thing is, I'm sure it was me who did it up!

 

[slowmotion]

If you think 15Nm is tight, I recently installed a bottom bracket that was rated at 70Nm !

With a 5mm A/F hex key ......?

EPIC!

 

[asterix]

Yes that's a strong allen key! I'd have bent it.

 

[Moderators]

Unless it's a carbon component, there's a fair amount of room between "feckin' tight" and "FECK!!!"

Oops, still got me Mod hat on

 

[e-rider]

BBs are usually about 40+Nm which is about as tight as you can get it. Brake levers on the other hand are more like 4Nm which isn't that tight at all.



12Nm is pretty tight - just use you finger tips on the allen key but give it some!