Why Are C3 Bearings Used in Hubs?

[Simon_A]

It seems to be relatively common to specify C3 bearings in hubs.  Can anyone explain why?

The following bearing supplier FAQ nicely summarises the general purpose of C3 bearings (http://simplybearings.co.uk/shop/faq.php?cID=1#1) and the info is consistent with other sources, so I see no reason to disbelieve it:

    C3 bearings are bearings that have an additional internal radial clearance to cope with high speed environments where excess
    heat is generated
    ...
    Applications like motorcycle wheels or bicycle wheels do not require C3 rated bearings.
   
A quick calculation shows my 700c wheels will only be rotating at 600rpm for ~77kmph, so hardly high speed.  Excessive heat seems unlikely due to air cooling + rim brake heat would have to conduct a long way down through the spokes which again are air cooled.

Could it be that the additional 'looseness' of C3 bearings will not be noticed on a bike wheel and helps reduce 'drag' that would occur with non-C3 bearings?

Comments welcome!!!

[mzjo]

I thought that C3 was the class of bearing normally supplied so I have just consulted my SNR catalogue which is a PDF (and I only have the single row radial ball bearings but I do have the theory pages) and there is a class N which is not really defined but which lies between C2 and C3 and which does for common everyday applications like bicycle wheels. What you definitely don't want is C2 which loses virtually all the play at temperature and requires a very high level of precision in manufacture, fitting and use.
I think C3 wouldn't do any harm, the extra play might be handy in a tougher environment.

[contango]

C3 is used because C4 was shown to be too unstable in collisions?

[Simon_A]

Thanks for the replies and apologies for my slow response.

mzjo, I've also now looked at the SNR SNR General Catalogue Ch.1 General Data Pg.34 which is interesting (?!?!):

   Clearance frequently used in the following cases:
   - tight interference fit of one ring or slight on both rings  => Bearings seem to be generally a tight fit in hubs
   - possible misalignment, bending of shaft                         => In the interests of cost perhaps the manufacturing tolerances of the
                                                                                                  overall hub / axle system then needs the additional movement allowed
                                                                                                  by C3?
   - to increase the contact angle of highly-loaded radial      => Are Radial Bearings used?
     contact ball bearings
   - high temperatures                                                           => Can't see this one personally as already noted

Agreed C2 would appear not be a good idea!!!  Looks like Class N is normal clearance as specified by ISO 573.

Being a Telecoms and not Mechanical Engineer ultimately I'm not going to question a manufacturers choice, but my training to always consider 'why' tends to lead to such questions...  I also spend a lot of time reading specifications, hence latching onto things like C3.

Anyway, replacing as per manufacturers instructions or like-for-like is clearly best, so that's what I'll do when necessary.

Thanks, Simon

[PhilO]

  => Bearings seem to be generally a tight fit in hubs

Not really. They're a press fit, but not really tight by engineering standards.

Are Radial Bearings used?

Absolutely. Anything with a '6' at the beginning is a deep-groove radial ball bearing. Artificially creating a contact angle by excess internal clearance crossed my mind as a possibily, but (without doing the calculation) I can't see the angles generated being large enough to make a difference, and the face-control of the hub and axle abutments would have to be very good. Plus bicycle wheel bearings are extremely lightly loaded.

high temperatures      => Can't see this one personally as already noted

Agreed. Very cool, if anything.

=> In the interests of cost perhaps the manufacturing tolerances of the overall hub / axle system then needs the additional movement allowed by C3?

...would be my best guess.

Actually, my best guess would be that somebody somewhere has just assumed that 'C3' is better quality than 'CN' (or that buyers will assume so) and specced on that basis. And the decision has stuck.

<--- Ex production engineer at a bearings factory.

[Simon_A]

Thx PhilO

  => Bearings seem to be generally a tight fit in hubs

Not really. They're a press fit, but not really tight by engineering standards.

OK, interesting to know and I was wondering exactly how tight is 'tight'

Are Radial Bearings used?

Absolutely. Anything with a '6' at the beginning is a deep-groove radial ball bearing. Artificially creating a contact angle by excess internal clearance crossed my mind as a possibily, but (without doing the calculation) I can't see the angles generated being large enough to make a difference, and the face-control of the hub and axle abutments would have to be very good. Plus bicycle wheel bearings are extremely lightly loaded.

Agreed Radial, sorry, was being a bit thick...

Actually, my best guess would be that somebody somewhere has just assumed that 'C3' is better quality than 'CN' (or that buyers will assume so) and specced on that basis. And the decision has stuck.

Yes I can imagine that as well, though I'd like to think it's primarily due to sound engineering reasons.

<--- Ex production engineer at a bearings factory.

Ha!!!  Marked man for any future dumbass questions

[PhilO]

<--- Ex production engineer at a bearings factory.

Ha!!!  Marked man for any future dumbass questions

Is it too late to mention I left RHP 14 years ago? 

[Simon_A]

Way too late!!!!!!!!!!!! 

[Gattopardo]

What is the cost difference between cn and c3?

On motorbikes I changed to what ever was cheaper and found that c3 were cheaper.

[Mr Larrington]

  => Bearings seem to be generally a tight fit in hubs

Not really. They're a press fit, but not really tight by engineering standards.

OK, interesting to know and I was wondering exactly how tight is 'tight'

A pity that I didn't keep a copy of "How To Fit New Bearings To A Hope XC Hub" from 2007.

Tools required included a large hammer and a gas stove

[Gattopardo]

Essentials being a warm beverage.

[Simon_A]

What is the cost difference between cn and c3?
On motorbikes I changed to what ever was cheaper and found that c3 were cheaper.

From what I've seen it's pennies either way, if anything at all, but that's only on 6001 bearings.  I guess this makes sense as assuming the basic materials cost is the same, then the machining cost should also be similar if it's the same tolerance just on a different nominal radial clearance.  Perhaps the numbers produced may make a difference, but as I'd guess both would be in the thousands (if not tens or hundreds of thousands) then this would also be minimal.  All of that said, I'd defer to PhilO's opinion

A pity that I didn't keep a copy of "How To Fit New Bearings To A Hope XC Hub" from 2007.
Tools required included a large hammer and a gas stove

Thinking back to the 'good old days' of fixing my Triumph Spitfire in the late 80's, whilst I never did it I seem to recall it wasn't unusual to use a blowtorch in various ways to loosen & fit things.  I also seem to recall that being careless with a blowtorch was the cause of many a garage fire / end of a restoration project!!!

[Mr Larrington]

I'd have used a blowtorch if I'd had one, but necessity is the wossname of improvisation, unless you're a jazz musician.

[mzjo]

I'd have used a blowtorch if I'd had one, but necessity is the wossname of improvisation, unless you're a jazz musician.

For motorbike enthusiasts the required tools were a domestic oven and a deep-freeze. I generally use a hot-air paint stripper on the casings of my bikes. The best I have seen was a pair of belgian technicians doing cardboard machinery who had a deep-fat frier (at first I thought it was for them, being belgians, but afterwards the penny dropped). Saucepans of oil over camping stoves can work for heating bearings but the chip frier is much better because you can set the thermostat low. Domestic ovens have advantages over paint strippers for the same reason. There is however a slight disadvantage in using the domestic stuff; sensible people find secondhand ones to put in the garage, along with the fridge for the beer. Insensible ones sometimes end up divorced.

[PhilO]

What is the cost difference between cn and c3?
On motorbikes I changed to what ever was cheaper and found that c3 were cheaper.

From what I've seen it's pennies either way, if anything at all, but that's only on 6001 bearings.  I guess this makes sense as assuming the basic materials cost is the same, then the machining cost should also be similar if it's the same tolerance just on a different nominal radial clearance.  Perhaps the numbers produced may make a difference, but as I'd guess both would be in the thousands (if not tens or hundreds of thousands) then this would also be minimal.  All of that said, I'd defer to PhilO's opinion

Unless you're willing to pay an absolute fortune in machining costs, the components can't be manufactured to the necessary accuracy anyway. So the way it works is this:

The rings are ground to a tolerance of +/- 13 microns. The radial internal clearance (RIC) has a tolerance of +/- 3 microns. So in Assembly, the components are "graded out" (individually measured) and match assembled. Ie, a +10 outer ring and a +10 inner ring are assembled with a nominal ball to give a CN bearing. A +2 outer and -3 inner are paired with a +2 ball. To get larger or smaller RICs, the ball size is adjusted a micron or two either way.  So the manufacturing costs should be the same for all variants.

[nb. Above figures are from memory, so may not be 100% accurate, but you get the idea....]