So we have three basic styles (I think), old square taper, ISIS/Octolink, and external bearing BBs. The old square taper has large diameter ball bearings, the ISIS had smaller bearings and more of them to fit inside the shell (I’ve heard this is the weak link in this design), and the External BB have even more bearings and are not limited to the ID of the BB shell.
Typically more bearings and surface area means more friction (i.e. power loss). The reason BB have migrated to the external was for less flex between crank arms. But most tri’s are done at relatively low watts, no one is standing up sprinting (for the most part).
So is there anything wrong with staying with the old square taper BB that the track guys use with light weight oil for less friction and increased efficiency?
Anyone looked at this before here?
I have seen some engineers explain that once the BB is loaded, the power loss difference is like .1 watt or less between bottom brackets.
But I haven’t seen testing data myself. A lot of the ‘tests’ are just spinning unloaded cranks which doesn’t mean anything.
The best is likely square taper, loose ball. Square taper due to the size of the bearings and loose ball due to the inherent lack of friction compared to cartridge bearings.
Also keep in mind that many smaller bearing designs (isis, octolink, etc) had more than 2 bearings, which increased life and friction.
OK, this is what I was thinking, I’ve even heard that the track guys would take the old square taper bearings and lube them with sewing machine oil right before a race. Ultra low viscosity, but also short life span. However, our sport is seeming to got this route.
I was interested trying to reduce the drive train friction as much as possible, BB and rear der’s pulleys
Think I have an old BB square taper with loose bearings, maybe everything old is new again.
Does it really matter? It’s in the noise…
Depends on what level one chooses to look at. Yes, it would be difficult to measure (i.e. in the noise). However, the friction is there, we know this to be true wether we can measure it or not.
Just like another thread I saw today on using Conti Gatorskins for racing. They have a thicker casing, and create more rolling resistance. This is another case where the difference would be almost lost in the noise of quantifying the difference between a Gatorskin and say Vittoria CX. Those that have used both of these tires will tell you they would use the CX for trying to set a PB for the bike leg.
My point is that many small losses are cumulative. Think of a rivet on an airplane wing, one sticking up will not make a difference, 10,000 will kill it. Now air resistance increases exponentially to vs. speed. So we have all focused on the aero aspects due to the drag curve with respect to velocity. I was just looking at friction due to rotating bearings as another area to reduce loss.
The watts lost to gatorskins vs a regular tire is something like 15 to 20 watts
the watt difference between bottom brackets is (according to some engineers I’ve seen discussing it) more like 0.1 watts.
that is two orders of magnitude less of a big deal. given the downsides of unsealed bearings and lower viscosity oils this probably isn’t worth spending time/money on, or at least you should be addressing things like how aero are your bottle cage bolts first
UNLESS, I am very wrong about the friction differences, and I may be, like I said, I haven’t seen any sort of comparison table where this was carefully measured by anybody. there might be some BAD bottom bracket setups to avoid. but you can’t tell just by spinning them unloaded with your hands.
Depends on what level one chooses to look at. Yes, it would be difficult to measure (i.e. in the noise). However, the friction is there, we know this to be true wether we can measure it or not.
Just like another thread I saw today on using Conti Gatorskins for racing. They have a thicker casing, and create more rolling resistance. This is another case where the difference would be almost lost in the noise of quantifying the difference between a Gatorskin and say Vittoria CX. Those that have used both of these tires will tell you they would use the CX for trying to set a PB for the bike leg.
My point is that many small losses are cumulative. Think of a rivet on an airplane wing, one sticking up will not make a difference, 10,000 will kill it. Now air resistance increases exponentially to vs. speed. So we have all focused on the aero aspects due to the drag curve with respect to velocity. I was just looking at friction due to rotating bearings as another area to reduce loss.
I was interested trying to reduce the drive train friction as much as possible, BB and rear der’s pulleys
Enduro XD-15 FTW!
http://www.competitivecyclist.com/product-components/2011-Enduro-XD-15-Ceramic-Bottom-Bracket-9183.19.1.html
OK, this points out that people do recognize the importance of reducing friction in bearings. Zipp will sell you crazy expensive ceramic bearings as well for their wheels, as will others. Do people find value in these but not in BB and other bearings? For instance the front and rear wheels have 2 sets of bearings each. So there are 4 bearings taking the weight. Weight distribution front to back does not change all that much. In tri’s it is probably close to 50/50. The BB have 2 bearings, and during the pedal stroke one side could take almost all of the load. It would seem to me that this would make a difference, although small.
Airbus chose XD-15 as it could handle extremely high loads with minimal friction and also be able to withstand the corrosive de-icing fluid used…
Traditional bottom brackets use radial bearings. Unfortunately, radial bearings have a hard time dealing with lateral loads that come with using external BB cranks. The newer crank designs can put unwanted side load on the bearings causing increase friction and wear.
The above statement from XD-15 raises a question…If I use an old square taper BB with radial bearings is it just as good as a $190 BB that uses external cranks/BB with angular contact? I know these differences are small, however and angular contact will increase bearing pressure when radially loaded. (e.g. contact angle of 45 will produce a load on the race about 42% greater than if just radially loaded).
Not to turn this back into a Gatorskins thread, but if Gatorskins are 15-20 watts more on the road, do you estimate they should show up at 50 W more on rollers? I think rollers are the only way to accurately measure the wattage difference (basically just change your tire, ride at the same speed on the rollers and measure delta in wattage). Also the psi diff on rollers vs road amplifies the difference. Likewise gatorskins should show up as a major diff on rollers (not just 10-20W as purported on road) ?
Wow, are people really seeing a delta of 20 or so watts from tire selection? This is more than I would have thought.
This would really show up in times during racing.
Best of all worlds: Superstar Isis BB. Long lasting and you get the crankset you want for peanuts.
Trust me on this one, people.
Cool, thanks! I just checked this BB out and think I found my new BB. I already have an ISIS BB and also wanted to try a 170mm crank (have a 172.5 now). So this gives me a smooth BB with the inexpensive crank arm options. Great tip thanks.
I just had an offline discussion with Jackmott on this topic.
I have seen a 20-30W difference between two sets of tires on the rollers. However, rollers are an amplifier of the real effect on the road.
The question is how much the rollers amplify the delta given that you have a round contact point touching another round contact point which amplifies the force at the point of deformity. On the road, you have a flat contact point touching a round contact point, reducing the force at the point of tire deformity.
If the rollers act as an amplier of say 10x compared to the scenario on the road then the 30W delta on the roller becomes 3W on the road. If is is 15x, then it is 2W. If it is 2x amplifier then it is 15W on the road.
If you have ridden on 3 inch rollers vs 4 inch rollers, you know the dramatic difference in Crr related wattage by simply changing the radius of the roller from 1.5 inches to 2 inches.
Now the road , is in effect a roller with a radius that is infinite (it is flat and has no curvature). How much delta is there in the force at the point of deformity on road vs roller 4 inch roller. I appreciate there is some…I just want to know if the amplification factor is 2x or 10x. If it is 2x, i really care. If it is 10x, i barely care. if someone can point me to the amplification factor then I’m all in.
As I mentioned on the other tread, Fredrick Van Lierde won Abu Dhabi tri on Gatorskins. I seriously doubt that at that level that an athlete can really give away 20W and finish the bike in first place and hold on during the run. Yeah, Fredrick can do stupid things and get away with it because he has a big engine, but all the boys he is racing have massive engines.
I can believe that he gives away 2-5W and still wins, especially when riding in a group, but not 20W!!! Which is why i’d like to see some roller amplification factors when measuring Crr vs road.
Dev
I’m not sure if AFM adjusts for the ‘roller amplification’ issue in his table but I note first that Tom’s field test showeda higher crr on road than on the smooth rollers:
http://www.slip-angle.com/aeroweenie/vittcrrvspressyo5.jpg
and in AFM’s spreadsheet he notes:
“Crr values are typical for very smooth surfaces - Crr on typical road surfaces may be 50 to 100 % higher”
he would only be giving away 20 watts if everyone else was on top notch tires. some of them are surely not, so maybe just 5, 10, 15 watts vs many of the others.
plus the 100 other watt killing or saving decisions you can make. one mistake here or there won’t end you.
cool so you figured out how many watts you actually save? how?
=)
Cool, thanks! I just checked this BB out and think I found my new BB. I already have an ISIS BB and also wanted to try a 170mm crank (have a 172.5 now). So this gives me a smooth BB with the inexpensive crank arm options. Great tip thanks.
PM me your email and I will send you some scans of equations for cylindrical contact contact pressures. These can be used for both cylinder to cylinder (like rollers) or Cylinder to plane (like the road / tire interface).
No, sorry, I kind of got off topic.
To put it back on topic, I have a taper square BB. The reason for this is that I got my SRM from Jens who went taper squared because he felt the Campy BB was the best spinning BB option with the lowest drag. Since the Campy BB died, I just stuck an old Shimano UN72 BB in there. Probably the drag is now the same as the outboard options with the UN72. The UN72 is also heavy compared to the Campy that I had.