THM cranks and PF30 BB - need your advice!

[Rippin]

Hi all,

To those that have THM cranks installed in their PF30 frame sets, which bottom bracket did you go with? Did you stay with THM and use their bottom bracket, or did you find a better alternative with another brand? I do like the fact that the THM PF30 BB threads in to each other ensuring that both cups are parallel to each other, but I do find their bearings tight. Let me know what you are using. Thanks.

[spdntrxi]

I used the THM Bb ... Never had a problem with it. I never really looked into it... But assumed you had to use their BB

[highdraw]

Rippin,
Maybe you could explain what you mean by the THM PF30 bearings are tight.
This is largely misunderstood.

[LeDuke]

Enduro TorqTite PF30 with angular contact ceramic bearings.

[kode54]

i use THM BB in all my bikes. no issues with the BB. never looked into any other option...as THM had many since i moved from threaded to press fit.

[Rippin]

@highdraw. What I meant is that I've found that the cranks doesn't spin as freely with the THM crank and BB combination, as compared to a full Shimano set up. My experience with both is on BSA threaded bottom brackets.

[highdraw]

What is misunderstood Rippin is...bearing seals contribute greatly to the free spin capability of a given crank not under load. Bearing seal resistance is generally nebula compare the cruising down the street with 150watts power to the pedals. Seals exist to keep contamination out. So in theory cranks that spin freely don't have a good weather seal and let a lot more dirt and water in when caught in the rain which happens a lot. Don't based your BB buying decision by how freely cranks spin when unloaded would be my suggestion.

[Rippin]

I totally understand that explanation and it's duly noted. Mind you, I've never had any contaminant problems with a Shimano bottom bracket, and they definitely spin more freely than THM's, but I will also admit that the extra resistance in a properly installed BB makes little to no difference during a ride. Thanks.

[highdraw]

Agree and too find Shimano BB's tend to spin very freely...more freely than say Campy UT Record with seals. I too don't suffer contamination from either but generally don't ride in rain and moved from the north with worse weather conditions.
A last bit...Shimano cranks spin in the free state well yes due to low seal drag by design but I believe the principle reason is they rely on mechanical preload versus a wave washer...the latter contributes to fractionally more drag. In theory, mechanical preload of Shimano cranks can be adjusted to put less lateral load on the bearing inner race and therefore not include this small amount of drag which fractionally loads the inner race against the ball bearings captured by outer race...all of which a very small contribution in overall drag relative the rider wattage and not felt on the road.

[sedluk]

The great thing about THM bottom bracket is that you can replace the bearings. You install the BB cups once and then just change the bearings as often as you like.

[androidavies]

I used THM BBRight bottom bracket with M3 crankset in Cervelo S5. Spins very freely after taking plenty time to play around with bearing/axle shims, rather than rely on the THM preload cap alone.
As mentioned in an earlier post, you can also change the THM bearings fairly easily as well.
I've also used the THM BSA threaded cups with a Clavicula crankset, and found the bearings very smooth, free spinning and reliable as well.

[Calnago]

Agree and too find Shimano BB's tend to spin very freely...more freely than say Campy UT Record with seals. I too don't suffer contamination from either but generally don't ride in rain and moved from the north with worse weather conditions.
A last bit...Shimano cranks spin in the free state well yes due to low seal drag by design but I believe the principle reason is they rely on mechanical preload versus a wave washer...the latter contributes to fractionally more drag. In theory, mechanical preload of Shimano cranks can be adjusted to put less lateral load on the bearing inner race and therefore not include this small amount of drag which fractionally loads the inner race against the ball bearings captured by outer race...all of which a very small contribution in overall drag relative the rider wattage and not felt on the road.

Are you theorizing that the wavy washer in a Campy Ultratorque crank provides enough preload to actually "squish" the outer race of the bearing, causing some friction that would otherwise not be there? Because at no point in the system does the wavy washer actually touch the inner race of the bearings.

[Calnago]

^ Agreed, but @Highdraw is theorizing that there is some added friction on the inner race of the bearing caused by the wavy washer, which is a different thing than what you're talking about relating to the overall design issues.

[Calnago]

Ah, well it's a good observation.

[highdraw]

^ Agreed, but @Highdraw is theorizing that there is some added friction on the inner race of the bearing caused by the wavy washer, which is a different thing than what you're talking about relating to the overall design issues.

Calnago,
You seem to take an interest in crank and BB threads so a bit more clarity. Not sure if you believe what I write but to me the physics behind my assertion are pretty irrevocable comparing a mechanical preload crank to one with a wave washer say like Campy Ultratorque. This plays into the misconception about bearing integrity. I talked about seal contribution when it comes to drag. Yes it is nebula compared to say an average rider power output of 150 watts but discernible when spinning a crank by hand without a chain installed. Same for the very modest contribution of lateral preload. So yes its true whether you believe it or not because the physics are undeniable. Is it significant? No. That is why wave washers exist which are very functional and in fact offer a benefit over mechanical preload relative to bearing bedding over time when mechanical preload can fall out of adjustment and of course wave washers are sensitive to BB tolerance stack up..where many fall off the apple cart during installation. Further a mechanical preload crank say like Ultegra and DA can easily be adjusted to apply more mechanical preload than a wave washer which will further add to internal bearing stresses and increased drag and actually reduce bearing life...and conversely can be set up virtually line to line with no preload and negligible lash. But with less lateral preload there is less internal bearing friction if you can visualize the relationship between inner and outer race and balls captured between.

Below are a couple of pictures for Campy UT of a crank I own. As to the application of lateral force...the wavewasher with Campy presses on the outer race of the bearing. The inner race of a Campy UT is a press fit to the Campy UT crank spindle. Lateral pressure on the outer race of the bearing when the inner race is captured and restrained by spindle length, applies a tangential pressure on each of the ball bearings. So it is real. How much force? Very small and why wave washers exist as lateral force can be very similar to lateral preload of mechanical preload cranks. But every single Shimano crank and Campy crank I have seen and set up...when Campy cups are Record with seals and not Super Record don't spin as freely a Shimano DA crank set up with very light preload. Its basic physics. On the bike does this matter? No. Its noise or nebula in the grand scheme of driveline friction subtracting from rider power over time....but...discernible with a free spin test....if its a .05 watt difference, I would be surprised.

Below pics: