Ceramic?

[fdegrove]

Hi,

In summary though don't waste your money. Unless you are really that good a rider that you need to go searching for that last 0.010 (give or take 0.005) percent gain.

I think you're quite missing the point.

Ciao,

[prendrefeu]

"Wow these new bearings feel super smooth"
"Yeah, no shit, they're new."

Period.

[jbf]

No

[Zoncolan]

http://search.bikelist.org/beta/TreeView.aspx?id=148935

http://groups.google.com/group/rec.bicy ... 5dadee264e

And the most relevant post,

Mike Kruger <Mik...@mouse-potato.com> wrote:
> [Zinn punted on the question and quoted Zipp: ]
> "For an average trained cyclist developing 250 watts, that's a savings of
> approximately 10 watts. At any level of competition, that is significant.
> The key is every part of the bearing system has seen marked improvements in
> precision resulting an a total benefit greater than the sum of its parts. ...
> But, as I said, I'm no engineer. So, for all you engineers out there, can
> there possibly be that big a difference in total system efficiency in
> changing from high-quality steel bearing systems to anything else?

No.

This question would be more appropriate for rec.bicycles.tech than
r.b.misc, so I'm crossposting it and setting followups there.

I calculated that the power dissipated in two standard steel
ball bearing hubs is about 0.33 watts for a 75 kg rider+bike
traveling at 10 m/s. It's hard to see how an improved bearing could
shave more than some percentage of that (10-20% ?), which verges on
negligible, I'm sure the aerodynamics of your shoe straps are more
important.

Since I already wrote up the calculation, here it is:

Typical coefficient of friction for a ball bearing is about mu=1.5e-3
(for example, http://www.ntnamerica.com/Engineering/P ... ictemp.pdf)
Power dissipated in one bearing is

P1 = mu * (m/2) * g * V_bearing where m is mass of rider+bike
V_bearing is linear speed the
bearing rotates at.
P_bearingloss = 2*P1 total power lost in two wheels
V_bearing = V_bike * d/D d = bearing race diameter
D = wheel diameter
P_bearingloss = mu * mg * d/D * V_bike

P_bearingloss = C_bearingloss * mg * V_bike
where C_bearingloss = mu * d/D, can be compared to C_rolling resistance of tires

For a bearing race diameter of 20 mm and wheel diameter of 668 mm (700x23)
C_bearingloss = 4.5e-5
for comparison, C_rolling resistance is supposed to be 4e-3 for
smooth pavement (e.g. from www.analyticcycling.com), or 100x higher.

For a rider+bike of 75 kg traveling at 10 m/s, the power dissipated in
wheel bearings is 0.33 watts. A major technological breakthrough that
cut bearing friction in half would only gain 0.16 watts. It might be
significant in hour records or even the pursuit world record. At
normal levels of competition, I think the sleep gained in not worrying
about it has a greater performance benefit.

[thisisatest]

For a rider+bike of 75 kg traveling at 10 m/s, the power dissipated in
wheel bearings is 0.33 watts.

the info i have gotten from zipp is just a little more optimistic:
their ceramics vs their steel bearings= 1-3 seconds over a 40k.
their estimates equate 3 watts to 1 second over a 40k.
therefore, they see the potential savings from 0.33-1watt.

so a little more than your calculations, but quite miniscule still.

as a comparison, the dimples on the hubs of zedtech wheels is said to save 3-5 seconds, or approximately double or triple the benefits of their best bearings.

[HammerTime2]

their ceramics vs their steel bearings= 1-3 seconds over a 40k.
their estimates equate 3 watts to 1 second over a 40k.
therefore, they see the potential savings from 0.33-1watt.

Did you mean to say "equate 3 seconds to 1 watt over a 40k"? As written, it is inconsistent.

[leej88]

I've got ceramic BB and rear wheel bearings but I'm finding it hard to maintain an average of 30km/h. So what else can I "ceramic-it" to save more watts?

[HammerTime2]

Get a Gruber Assist with ceramic bearings.

[fdegrove]

Hi,

ROTFLMAO.

Ciao,

[Mikmik]

I've got ceramic BB and rear wheel bearings but I'm finding it hard to maintain an average of 30km/h. So what else can I "ceramic-it" to save more watts?

Although a bit hard hitting it - book yourself in for a double hip/knee/ankle surgery for replacement of cartlidge to ceramic coating. Get back to us when you are healed

[fdegrove]

Hi,

Bottomline is, and it's been said before, if it's about sheer speed, forget about ceramic bearings unless you're a top athlete.
OTOH, ceramic bearings (good quality ones and the best example being Campa's Cronitect venture) can save you weight and bucks by their lack of need for maintenance and replacement.

Given that the price difference is hardly astronomous, what would you choose?

Done the math years ago and won't be looking back: good hybrid bearings + fine mineral oil for me.

And yes, they do make you faster but not by much. You'll stil have to pedal the thing....

Ciao,

[Ghost234]

My ceramic BB didnt make that much difference. It was more to do with showing everyone how smooth the cranks spun backwards!

This thing is what I love most about my ceramic BB. My crank spins so nicely backwards! But that said, I wouldn't really spend the money on it, with a few exceptions:

- Same/lower price as regular bearing equipped item
- It is for a TT/long distance tri where every possible watt can make a difference
- You have the money to spend on bling


For example, I have been shopping for a new wheelset and picked one up today. One LBS had Ksyrsium sl's for $900, and I almost bit the bullet and picked them up. However, another LBS was having a blow out sale on a set of Fulcrum Zero's (ceramic bearings and slightly lighter). They were selling them for the same exact price. Needless to say I grabbed the Zero's and am quite happy.

[fdegrove]

Hi,

But that said, I wouldn't really spend the money on it,

In the long run you do save money. At least you could if you shop wisely.
That is the point I've been hammering for quite awhile now.

Ciao,

[Mikmik]

My ceramic BB didnt make that much difference. It was more to do with showing everyone how smooth the cranks spun backwards!

This thing is what I love most about my ceramic BB. My crank spins so nicely backwards! But that said, I wouldn't really spend the money on it, with a few exceptions:

- Same/lower price as regular bearing equipped item
- It is for a TT/long distance tri where every possible watt can make a difference
- You have the money to spend on bling


For example, I have been shopping for a new wheelset and picked one up today. One LBS had Ksyrsium sl's for $900, and I almost bit the bullet and picked them up. However, another LBS was having a blow out sale on a set of Fulcrum Zero's (ceramic bearings and slightly lighter). They were selling them for the same exact price. Needless to say I grabbed the Zero's and am quite happy.

The highlighted bit above; Very well said!! That is where AND only time I'd ever consider buying ceramic bearings.

Being an amateur cyclist I can say with nearly 100% certanty that if you did buy ceramic bearings AND of course showed off to your racing advesaries how easily the cranks spin backwards it might be enough to phsyche them out .....that would be worth it, no ?

Bearings being at nearly the very centre of the wheel or crank or kockey wheels mean that they have far less negative influence on rotation than say.....your tires's rolling resistance.

I did an experiment on my steel bearings in my Corima disc wheel upon learning that the ceramic bearing run dry.....

Step 1;Removed the rubber dust covers on all 4 bearings = major inprovement in reducing rolling drag
Step 2;Washed out all grease with petrol = again a good improvement on rolling resistance
Step 3;Lightly oiled bearings = slightly increased the rolling resistance
Step 4;I have put back the 2 outer bearing's outside dust covers to allow no grit to get in and put the hub back together = very very slight improvement in rolling of the disc wheel IF any.

What all that work translates in real life in a 40km TT?.... , not much I think.

[HammerTime2]

Being an amateur cyclist I can say with nearly 100% certanty that if you did buy ceramic bearings AND of course showed off to your racing advesaries how easily the cranks spin backwards it might be enough to phsyche them out

I don't know about psyching out, but far more races are won based on spinning cranks forward than by spinning them backwards.