Resistance in hubs?

[colly]

Does it make much difference?

Prompted by a thread on here the other day about how much faster some tyres might be than others.

It got me wondering just how much difference a good set of hub bearings would make to rolling resistance. I would have assumed it would make some difference not much perhaps in percentage terms but taken say over 50 or 100 miles.......maybe a few hundred yards for the same energy expended.

However, last Sunday I was out riding with another forum member and I noticed that coasting downhill he would always edge in front of me, not by a few inches but by quite a margin. If I hadn't pedalled to keep up I would have been well behind at the bottom of every hill. We are a similar build and weight, roughly, my bike I think would weigh slightly more and we would begin coasting at pretty much the same speed.
Now his bike, and by extension the wheels too are a much better bit of kit than mine. My wheels are older too but the hubs are still smooth and silent. The only difference I can see would be the amount of resistance caused by the rotation of the hubs.

So over a long ride with a really cracking pair wheels/hubs would I end up either getting back much sooner, and, or, feeling less tired? Would I really notice that much difference?

 

[peelywally]

interesting ,

i was thinking about this over the last few weeks ,

my friend has similar groupset wheels to me yet his have a slight resistance when back peddling and coasting ,

we both noticed noticed it same way you did ,coasting ,

i suggested a strip down of hub and bb to lube , that dismissed we took chain off and checked resistance again , none found , so bb ok ,




chain back on rear wheel swap checked again , elimination the easy way lol , no resistance




it had to be the chain causing drag ?

new chain attached and way hey no change ?

deraileurs are fine , so it must be a culmination of tiny differences in each component creating a noticeable overall effect ?

 

[Cubist]

Bearing age, bearing quality, bearing play, lube quality, it could be any number of factors. The fastest bearing races would be completely dry, but wouldn't last long. The age of new bearings also plays a part, there's always a bit of resistance in new hubs, but when they bed in and the grease starts to thin out they speed up.

Don't forget other possible factors, such as tyre rolling resistance, (pressure, wear, contact area, tread pattern,) aero wheels/ fork , drag of looser clothing, unshaved arms, etc etc etc.

My XC wheelset is noticeably smoother and faster than Cubester's bombproof Hope Pro 2 AM wheels

 

[HLaB]

I've just seriously started taking apart my hubs this year and it good to note despite being a lightweight I'm freewheeling downhill better than some folks, the jobs a good un :-) The hubs are slightly pitted however and need replacing.

 

[Paulus]

I have a pair of Campag Scirocco wheels on my bike, 6 years old and never need any attention and they roll very very well. My mate bought a new Specialized Secteur, his wheels are brand new, well adjusted and have no resistance, and he comented that I can still roll down hills faster than him! We have the same size tyres, 25mm's but different makes. I am a bit heavier than he is, maybe that is it?

 

[upsidedown]

My Hope Pro Evo IIs are much slower than my Deathlon own brand hubs. I put it down to energy being converted into sound !

 

[gbb]

One of the biggest factors is the thickness..there's a word for it ...viscosity of the grease being used.
As Cubist says, as the bearings run in and the grease thins out, they'll speed up.

To give you an idea, i replaced the bearings in my FSA BB with low friction cartidges. Spun the cranks without the chain on...they flowed effortlessly. As i wanted to seal the whole thing a bit better against water ingress, i put a good smear of heavyish grease between the bearing face (NOT in the bearing itself) and the outer cover. Spun the cranks...instant resistance, really really noticeably so.

I always had it in mind to find a low viscosity grease for my hubs, and it will exist, but i got some new wheels and put low friction cartidges in them. Now on a hill i used to go down at 26/27 mph, i'm now freewheeling down at 28/29mph.

There's always a fly in the ointment though, the thinner the grease, the faster the hubs, but it'll have less resistance to water ingress, heat (if ever that was a factor) and loss of lubricant. You'd have to (IMO) maintain the hubs more often.

 

[fossyant]

Coasting is for loosers !

 

[gbb]

Coasting is for loosers !

 

[brockers]

I ain't no tribologist but I'd say hub spinniness has lot to do with bearing quality. Cheap bearings are more likely to be different sizes (by a miniscule amount), and all the load (rider weight plus most of the bike) would fall on the larger bearing or bearings, which would cause the races to wear; the smaller bearings would be doing pretty much nothing, just being there to fill space and go along for the ride. I'd guess this is why people like Chris King manufacture their own bearings and can stipulate tolerances, so that the load is shared equally among all the bearings, ergo the hub is smoother. I don't really think the grease thickness has a lot to do with it, because as soon as there is a shear force on the grease it basically becomes the viscosity of the constituent oil.

So maybe when you buy a new wheel, it might be an idea to whip out the bearings if they're the loose type, and replace them with higher quality ones which would all be, hopefully, exactly the same size.