Lowest friction freewheel?

Discuss light weight issues concerning road bikes & parts.
Zoro
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by Zoro

Anyone know of any tests on lowest friction freewheel?

This is for TTs on junior gears (52X14) and coasting is the method of choice for long descents.

Mr.Gib
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by Mr.Gib

Give it up - difference between freewheels will be of no consequence. Maximize aerodynamics or failing that just get behind the biggest guy.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

TheKaiser
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by TheKaiser

@Mr.Gib, Aerodynamics are for sure paramount, but I think the OP said this is for TTs so there would presumably not be any opportunity to draft the "biggest guy", no?

@Zoro, I thought that I had heard that this guys (http://www.friction-facts.com/test-resu ... al-reports) was going to be testing hubs, but I just checked that link and only see BBs, Chains, Derailleur Pulleys, etc...maybe it is still on the drawing board.

Regardless, I have heard of people removing pawls from freewheels to reduce friction, although this only works in instances where there are 2 or more sets, that are offset so that they engage at different times, and where each pawl has an independent spring. In other words, you trade a 50% cut in pawl based friction, for a doubling of the degrees of rotation before the remaining set of pawls engages, which probably wouldn't be a problem for this application, but you would want to test it to be sure. Again, this only works on hubs with an offset configuration like that. Also, if you are using a cartridge bearing hub, you could remove the inner bearing seals on the cassette body. Many hubs use 2 bearings for the cassette body alone and several of those seals are not really doing anything other than adding drag.

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Zen Cyclery
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by Zen Cyclery

Mr. Gib is right on this one. Entirely inconsequential. Freewheel resistance is only noticeable by hand. Once your riding it will make no difference.

eric
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by eric

Freewheel resistance is not zero. Some people with very low friction drivetrains (pulleys and BB) see the cranks turn when the wheel is turned in the workstand.

Removing half the pawls is fraught- I seem to remember Tyler Hamilton having an ugly crash from a freewheel that broke due to missing pawls. I'd leave them all in.

With a typical freehub the freewheel and hub are side by side on a common axle. The freewheel is turning on the axle when the pedals are turning but is stationary when the pedals are not moving. When you're coasting you will have drag from the frewheel but not from the bearings. Some freehubs have the freewheel on the hub (some Shimano, the new Alchemy).

I'd use a good light grease like Krytox. If you're really a weenie you could polish the pawls where they drag across the ratchet but that'll happen over time anyhow.

It would be interesting to see if there is a difference between designs, like the traditional spring loaded radial pawls vs the two splined ratchet rings on DT hubs or the magnet "sprung" versions in a few hubs.

Zoro
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by Zoro

@TheKaiser - thanks for reading my post.
@others - At my son's downhill speed on a 1-2% grade of 40-50mph on a 53X14 that is 135rpm to 168rpm. His technique is burst spin and coast. It is more aero (faster) and easier than spinning 150rpm+. His will spend 10 min above 40mph - it matters a whole bunch. It is completely consequential. It can make a 2-3 place difference in a junior - gear limited TT with a long down hill. We know this. TT places are often a fractions of a second apart.

I heard from Jason at Friction-Facts - and no test he knows of. He may be doing one soon.

Causidicus
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by Causidicus

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Last edited by Causidicus on Wed Jun 18, 2014 12:05 am, edited 1 time in total.

davidalone
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by davidalone

agree with the comments on substituting a lighter oil rather than your normal grease in he freewheel.

fdegrove
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by fdegrove

Hi,

Remove grease from pawl area, freehub/hub seal area and freehub bearings. Replace with a pure PFPE lube like GPL105.


Bingo.
The Krytox additive will modify the metal's surface area so it will be smoother even when Krytox is no longer (visibly) present or applied regularly.
If running semi-bushing semi-cartridge bearing type freehubs you should definitely apply GPL105 to the area(s) of the axle where the cartridge bearings evolve around it. (Campa for instance).

You could apply the same trick to the pulley wheels and bolts as well etc....
Short of GPL105 you could lap (polish) the metal contact surfaces as well.

Ciao, ;)
Being a snob is an expensive hobby.

Mr.Gib
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by Mr.Gib

Sorry - overlooked the TT bit.

Still, unless the lower friction freewheel was part of the overall best rear hub/wheel that I was willing to buy, I wouldn't go chasing such minimal gains. Sure optimize lubrication but brand switching won't be worth it.

But if you insist... do a spin down test on a stand. Get a whole bunch of rear wheels featuring the exact rim/tire/spokes/build that your son will use. Have each one built with a different hub - I recommend all the best brands should be tested. Then crank the pedals at the desired RPM and time each different wheel build till it stops. That will give you a good idea of which will be best. When your done you can send all the slower wheels to me. :D

Seriously there is a lot more to be gained by working on those things that can save time when he is putting the power down than the differences between freewheels while coasting. Even while descending an improved line in a curve will save many multiples of whatever the difference between the best and worst freewheel might be.

And finally how do you get to 50 mph on a 2% gradient? While only peddling occasionally? That's 73 km/h. I don't think so. You need over 10% for that.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

fdegrove
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by fdegrove

Hi,

The way I look at it is that the freewheel area should be optimized for both types of use: riding normally and coasting.
It always bothers me no end that you have these finely tuned bearing running super smooth on both wheels but stick a freehub on the rear wheel and all the effort is down the drain.

It really is an area where there's still room for improvement IMHO as far as the major gruppo/wheel manufacturers are concerned.

Ciao, ;)
Being a snob is an expensive hobby.

Zoro
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Joined: Wed Oct 30, 2013 12:52 am

by Zoro

Thanks for the input. Going to look at the GPL105.

Just ran over my Zipp 900 yesterday with my car - really bummed. Its cracked but straight, still, not something I want my kid on. Might go for a heavier laminar flow type wheel after taxes are paid. But certainly going to work on the coasting. Really that Zipp 900 after 5 years may have 1000K on it.

Zoro
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Joined: Wed Oct 30, 2013 12:52 am

by Zoro

Mr.Gib wrote:...But if you insist... do a spin down test on a stand. Get a whole bunch of rear wheels featuring the exact rim/tire/spokes/build that your son will use. Have each one built with a different hub - I recommend all the best brands should be tested. Then crank the pedals at the desired RPM and time each different wheel build till it stops. That will give you a good idea of which will be best. When your done you can send all the slower wheels to me. :D...
Its not a valid test unless all wheels have the same moment of inertia. That is too hard to get.

maxxevv
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by maxxevv

If they have the exact rim/tire/spoke/lacing (as Mr Gib listed ) .. how measurable a difference in moment of inertia would there be ?

Zoro
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by Zoro

maxxevv wrote:If they have the exact rim/tire/spoke/lacing (as Mr Gib listed ) .. how measurable a difference in moment of inertia would there be ?
"Measurable a difference" - its very hard to measure. And unless you know it/have the same MofI wheels the friction test will not give good results. It is generally calculated, or felt by the rider.
http://velonews.competitor.com/2008/07/ ... tia_157317

Moment's of Inertia describes the distribution of weight as well as weight. It is the rotational willingness of a wheel, often called the "freewheel" effect. I think less is always better. For example I have a set of wheels with Extralite hubs that are 150g lighter than another pair of wheels with a Richey (heavy) hub and light rims and the heavier wheels have a lower MofI. The MofI affects the force it takes to spin up/spin down and stability / inertia of the wheel.

So if spinning - equal in all but weight - a heavier wheel with lighter rim at the same RPM as a wheels with more rim weight, the heavier rim wheel will spin longer, at the cost of taking more energy to get to the RPM in the first place. It does not measure the friction of the system.

I'd choose the lighter wheel - or lowest Moment of Inertia - for racing - always.

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