Truvativ crankset. Made of cheese?

[si_c]

Aah rrh, ehh ..........My Truvativ cranks certainly weren't cheap and at least all the rings are aluminium and removable/replaceable unlike cheap Shimano (S)crap.

Never said they were cheap. But the bulk of the crank sets they produce are aimed at the more price conscious end of the market. That being said they do do some nice 1x direct mount crank sets that are fsking expensive.

 

[Yellow Saddle]

I thought it was the Coriolis effect

That has an effect but only if you travel north-south over a long distance.

 

[winjim]

All fixed now.

 

[Smokin Joe]

Isn't the movement of the RH pedal anticlockwise relative to the crank? So if the pedal axle is at all stiff, wouldn't that apply an anticlockwise force to it, thus unscrewing the conventional right handed thread?

The movement of the pedal is, but the ball bearings are being turned in the opposite direction.

 

[Gravity Aided]

Precession is the reason they're not both standard right hand threaded. They can't unscrew themselves.

Another Wright Brothers invention, along with the airplane.

 

[winjim]

The movement of the pedal is, but the ball bearings are being turned in the opposite direction.

I need to sit down and draw a picture.

 

[Yellow Saddle]

Isn't the movement of the RH pedal anticlockwise relative to the crank? So if the pedal axle is at all stiff, wouldn't that apply an anticlockwise force to it, thus unscrewing the conventional right handed thread?

The movement of the pedal is, but the ball bearings are being turned in the opposite direction.

Joe, it doesn't quite work like that. It hasn't anything to do with the direction of the ball bearing.

Precession in threads is quite difficult to describe, but let me try. Let's start with classic precession where the earth and the moon turn around each other, but not around a single axis. If you were to draw the path of the centrepoint of the axis of those two bodies it would be a circle. Compare that to the path of the centrepoint of a wheel turning on an axis, which is just a point.

Now let's move on to the crank and pedal axle. Don't try and visualise the pedal axle as something turning around a point. Instead visualise it as turning around a small circle, as our earth and moon example above. Reason being that your pedaling force has direction which always tries to move the centrepoint of the pedal axle away from the middle of the hole in the crank. Visualise the crank hole being elastic and see what happens - precession.

Make an O with your left hand fingers and stick your right hand forefinger inside the O. Now "rotate" your forefinger and allow the O to stretch so that you can move your forefinger around inside the O. (forget about rotation for now, just enlarge the O and make your forefinger stir the sides of the O as if you are stirring a cup of coffee with a spoon all around the inside of the cup.

Now for the final trick. Imagine your finger is threaded with a nice 1mm metric thread and your left hand's O is also threaded with a 1mm thread, even though the diameter is much larger. Now visualise how the threaded components stirring around each other will react to the thread. Depending on the thread direction and component rotation, it will either want to turn in or out.

Pedals and cranks are designed to always tighten themselves.

Precession is also found in the BB, where the same occurs.

Note that precession will not happen if your crank was powered by multiple pistons, such as found in an aeroplane with a rotary engine. Therefore it has nothing to do with the bearing turning direction.

 

[Smokin Joe]

Joe, it doesn't quite work like that. It hasn't anything to do with the direction of the ball bearing.

Precession in threads is quite difficult to describe, but let me try. Let's start with classic precession where the earth and the moon turn around each other, but not around a single axis. If you were to draw the path of the centrepoint of the axis of those two bodies it would be a circle. Compare that to the path of the centrepoint of a wheel turning on an axis, which is just a point.

Now let's move on to the crank and pedal axle. Don't try and visualise the pedal axle as something turning around a point. Instead visualise it as turning around a small circle, as our earth and moon example above. Reason being that your pedaling force has direction which always tries to move the centrepoint of the pedal axle away from the middle of the hole in the crank. Visualise the crank hole being elastic and see what happens - precession.

Make an O with your left hand fingers and stick your right hand forefinger inside the O. Now "rotate" your forefinger and allow the O to stretch so that you can move your forefinger around inside the O. (forget about rotation for now, just enlarge the O and make your forefinger stir the sides of the O as if you are stirring a cup of coffee with a spoon all around the inside of the cup.

Now for the final trick. Imagine your finger is threaded with a nice 1mm metric thread and your left hand's O is also threaded with a 1mm thread, even though the diameter is much larger. Now visualise how the threaded components stirring around each other will react to the thread. Depending on the thread direction and component rotation, it will either want to turn in or out.

Pedals and cranks are designed to always tighten themselves.

Precession is also found in the BB, where the same occurs.

Note that precession will not happen if your crank was powered by multiple pistons, such as found in an aeroplane with a rotary engine. Therefore it has nothing to do with the bearing turning direction.

I'll bow to your knowledge but I won't try to understand it. Paragraph 1 was enough to bring on a headache.

 

[MontyVeda]

I've had two Truvativ crank sets to date and will probably buy another when the need arises. Never had any issues with them.

 

[C R]

The Wiki entry on mechanical precession is a good read:

https://en.wikipedia.org/wiki/Precession_(mechanical)

 

[Levo-Lon]

Yeah, it was all put together in the shop. Don't worry, they're going to sort it, no problems there.

That's the one, pedal not done up.
As much as i like Rutland Cycles they can be a bit hit a d miss on PDIs.

Ive had similar problems before.
I fit spds to all new bikes now so it's my fault if a thread sheers

 

[fossyant]

Make an O with your left hand fingers and stick your right hand forefinger inside the O. Now "rotate" your forefinger and allow the O to stretch so that you can move your forefinger around inside the O. .

WARNING - Just don't do the above in public, you might get arrested, or at least some very strange looks.

 

[silva]

Tried but my fingers are too thick

 

[midlife]

Crikey!

https://en.m.wikipedia.org/wiki/Precession_(mechanical)

 

[sleuthey]

In my experience of working on cars and bikes in general, 2 or 3 times I have stripped threads due to the bolt or female thread having a manufacturing defect. Ie the material can be too soft or the thread spiral can be angled differently on the nut than it is on the bolt. Whilst I agree truvative is a reasonable brand, it is probably not cost effective for them to undertake quality control checks on 100% of the components they import that make the final product.