viernes, 16 de abril de 2010

Evaluating High Performance Bicycle Wheels

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The well-oiled marketing machines in the bicycle industry are constantly touting the latest and greatest technology.  With so many different brands available and broad-sweeping claims made, we consumers can often times become confused.  In the next few minutes, I will help you wade through the facts and provide some unbiased data on the high-end wheel offerings.   In the end, it should be possible to determine exactly what you get when you spend $800 on a set of the hyped-up high performance wheels.  However, we first need to investigate how I approach the wheel selection/evaluation process.

The first step in choosing the optimum wheel is in defining an optimization/evaluation function.  This function is based on the primary design variables of price, performance, and durability.

I believe that there are three different types of bicycle wheel consumers that have the following weighting values for the above evaluation function:

Performance based (x = 0.05, y = 0.05, z = 0.9)

Price/Durability based (x = 0.45, y = 0.45, z = 0.1)

All design variables are equal (x = 0.33, y = 0.33, z = 0.33)

Essentially, performance based consumers don’t care how much the wheel costs or whether it is durable, whereas the price/durability consumer doesn’t really care too much about performance.  I will give a final wheel rating on a scale of 1 to 4 “D’s” based on the even weighted rating function; keep an eye out for the “Performer” and “Durable” identifiers if you fall into this category of wheel consumer.

The Wheels

Mavic Ksyrium

 Price: $799
F/R Mass (w/o skewer - clincher): 770g/920g
F/R Mass (ready for tire - clincher): 824g/978g
F/R Spoke Count: 18/20 – radial front and cassette side, 2 cross non cassette
Rim Depth/Width (mm): 24.5/19.5
Marketing Features:  Aluminum spokes, spoke attachment method, radial drive side lacing, sealed bearings, machined brake track, welded rim, low spoke count
Claimed Benefits: Lightweight and aerodynamic for all around performance

Shimano Dura Ace

Price: $750
F/R Mass (w/o skewer - clincher): 743g/974g
F/R Mass (ready for tire - clincher): 821g/1056g
F/R Spoke Count: 16/16 – 1 cross
Rim Depth/Width (mm): 29.7/18.5
Marketing Features: “lateral crossover” spoke attachment method, low spoke count, nipples at hub, lighter rim, titanium freehub body, bead blasted braking surface
Claimed Benefits: low inertia, aerodynamic, lightweight

Campagnolo Nucleon

Price: $660
F/R Mass (w/o skewer - clincher): 693g/920g
F/R Mass (ready for tire - clincher): 776g/1006g
F/R Spoke Count: 22/24 - radial front/non drive, 2 cross drive
Rim Depth/Width (mm): 18.9/20.9
Marketing Features:  Asymmetric rear rim, titanium pawl carrier, straight pull spokes (“Ultra-linear geometry”), thicker drive side spokes, cartridge bearings, machined braking surface
Claimed Benefits: lightweight, stiff, ideal for climbing and sprinting

28 hole Chris King/Mavic CXP-33 DT Revolution Spokes/Aluminum Alloy Nipples

 Price: $490
F/R Mass (w/o skewer - clincher): 690g/844g
F/R Mass (ready for tire - clincher): 768g/926g
F/R Spoke Count: 28/28 - 3 cross
Rim Depth/Width (mm): 23.5/19.7
Marketing Features:  RingDrive freehub ratchet, machined braking surface, welded rim seam, custom designed and manufactured cartridge bearings, oversized aluminum axle, 5 year hub warranty
Claimed Benefits: lightweight, stiff axle, nearly instant freehub engagement and high torque resistance, long bearing life, consistent braking

Lew Palermo (tubular only)

Price: $1800
F/R Mass (w/o skewer - tubular): 502g/715g
F/R Mass (ready for tire - tubular): 552g/770g
F/R Spoke Count: 16/20 – radial front and non drive, 2 cross drive
Rim Depth/Width (mm): 42.7/17.2
Marketing Features:  all carbon rim, ceramic impregnated braking surface, deep and narrow rim, aluminum freehub body
Claimed Benefits: lightweight, aerodynamic

 Performance Evaluation


The variables that significantly impact wheel performance are aerodynamics, mass, and potential for brake rub.  Based on previous mathematical modeling efforts, it has been shown that aerodynamics dominates overall wheel performance by nearly 10 to 1 when compared to wheel mass.  The wind tunnel entries I have participated in and the literature I have read have led me to believe that the factors (in order of importance) that affect wheel aerodynamics are:

Rim depth/shape (~80%)

Spoke count (~10%)

Hub shape (~8%)

Spoke shape/diameter (~2%)

It is important to note that tire selection is a wildcard in determining aerodynamic wheel performance.  With a wide tire, you may benefit by decreasing rolling resistance, but you will reduce the aerodynamic gains of a deep section rim.  As your speed increases, the trade-off between rolling resistance and aerodynamic drag begins to favor the improved aerodynamics of a narrower tire.  Quite simply, if you want to go really fast, choose a deep section rim (>30 mm), slap on a tire that is as narrow as your rim and jack up the tire pressure.

It should also be mentioned that as rim depth increases, the more difficult the wheel becomes to handle in a crosswind.  However, the wheels tabulated above should not pose a problem for a competent cyclist.


Overall mass is most significant when climbing steep hills at low speeds.  However, the weight of your wheels is still only responsible for around 1% of total power requirements and rotational inertia effects are so small, that I will ignore them as a performance indicator.  The following table lists wheel mass just before a tire is installed, and the overall mass evaluation rating.

Wheels                                         Mass (g)                           Rating
Mavic Ksyrium                                 1802.4                           3.3
Shimano Dura-Ace                         1876.6                           2.5
Campagnologo  Nucleon                 1782.3                           3.6
Chris King Mavic                         1694.7                           4.6
Lew Palermo                                 1322                           9
Standard wire wheel                         2000                           1
Stiffness/Brake Pad Rub

Stiffness or deflection under load is the last performance variable I investigated, and it does not significantly affect performance unless brake pads rub the rim.  However, some people simply prefer a stiffer wheel because the perception is that stiffer is better.  All of the wheels tabulated below are at the soft end of the wheel stiffness spectrum. Unfortunately, all of the rear wheels tested, except the Ksyrium, rubbed my rear brake pads (2 to 2.25 mm of clearance on each side) when fixtured in my old-school Titanium frame from the early 90’s.  This rubbing occurred during low speed sprints and strong efforts on steep climbs.  I weigh around 165 pounds and have never been considered a powerful rider, so these results were disappointing.

All of the front wheels performed satisfactorily when my dual pivot brakes were opened all the way up (the Lew’s rubbed initially so I had to open the pads up a bit more).  The static deflections below are under a constant load while fixtured in the front fork and rear dropouts of my bike.  The boundary condition (how solidly the axle is gripped) at the dropout in this configuration is not fully rigid, but it is interesting to note that the trends are consistent with previously published data.  To my knowledge, dynamic rim deflection between the brake pads has not been previously published.  Note:  less deflection means the wheel is stiffer.

The poor performance of the rear wheels is largely due to low spoke counts, flexible axles and possibly, a flexible frame.  Further analysis of the data collected has led me to believe that ~50% of the motion between the brake pads is due to chain loads and the other ~50% is due to lateral loading of the rear wheel.  It also appears that the frame/fork’s ability to resist bending moments plays a significant role in the magnitude of the rim deflections.

Overall Performance Rating

The results summarized below might surprise some people.  When cost is no object, the Lew Palermo is clearly the way to go.  With its lightweight and good aerodynamics it wins the “Best Performance” label easily – but at $1800 I don't think many people will be able to afford them.  For nearly equal performance try looking at a set of the Zipp wheels for around $800 less.  It is also interesting to note that the other expensive wheels perform very similarly to the slightly cheaper, custom-built Chris King/Mavic wheels.  The question then becomes, how much are you willing to spend for fractionally better racing performance?  And, how much are you willing to sacrifice in durability?

Clearly, the best way to evaluate a wheel’s durability would be to put it on a test fixture and let it run until failure.  Unfortunately, and I do not have this type of budget (as evidenced by my hi-tech wheel stiffness fixture – my bike, a vice, living room floor, and a gallon of water).  However, there are general rules of thumb that will give us a pretty good idea on what wheels will be more durable.

It is very difficult to improve on the durability of a well-built 36-hole steel-spoked bicycle wheel.  This type of wheel, and any wheel for that matter, should last until the brake track is worn through – in my experience this is equivalent to 15,000 to 30,000 kilometers depending on how much you ride in the rain.

The most important thing in wheel durability is the quality of the build.  Spokes should have consistent and high spoke tension and they need to be stress-relieved (done by grabbing opposing pairs of spokes and squeezing them together as tightly as possible to eliminate residual stresses) during the final stage of wheel building.  Failure to stress-relieve wheels is the primary reason behind steel spoke breakage.  Properly manufactured and stress-relieved steel spokes simply don’t break during normal use.

I won’t bother you with any more details, but I would suggest that you read “The Bicycle Wheel” by Jobst Brandt if you are interested in more information about how bicycle wheels work.  In general, wheel durability is diminished when spoke count is decreased, radial spoking patterns are used, non-steel spokes are used, and poor seals/undersized bearings are used.

With nearly perfectly even tension on the front and fairly even tension on the rear, the Chris Kings appear to be the best built out of all the wheels evaluated.  The overall tension on these wheels seems like it could be a bit higher, though.  If you are looking for even more durability, you could increase the spoke count, use 2.0/1.8 spokes, and brass nipples.  Furthermore, the hubs have well-sealed cartridge bearings, and a correspondingly high amount of seal drag.  If you turn these axles in the shop they are not as easy to spin as the rest.  This extra seal-drag will not affect your cycling performance significantly, however.

Both the Dura-Ace and Ksyrium rear wheels went significantly out of true during my brief period with them.  This is indicative of a poor wheel building process and in the case of the Ksyrium, there is simply not enough spoke tension to support my hefty 165 pound butt.  The Dura-Ace wheels exhibited significant rim deformation where the spokes enter the rim.  The large spoke bending moment here will eventually cause a crack to form at this location.  Rims should not deform like this during the wheel building process.

All bicycle wheels will break eventually, and when they do, either you buy new ones or you repair them. The non-traditional component wheels (Ksyrium, Shimano, Lew) sacrifice some of your ability to quickly and inexpensively make repairs.  Often times, the manufacturer will require you to send in the wheel to be serviced (meanwhile you are without your wheels) or you simply cannot even true the wheels due to extremely high spoke tensions and low spoke counts.  These wheels may also require expensive replacement parts ($10 spokes anyone?). On the other hand, with a conventional wheel that uses standard hubs (Campy/Shimano), replacement parts are readily available and you can even make the repairs yourself if so inclined.

Price Evaluation

This one is easy.

Overall Ratings/Final Comments

The furthest column to the right shows that on a scale of 1 to 4 deltas the Chris King/CXP-33 wheels had the best overall rating.  These wheels also ranked the highest in the Price/Durability category.  The other high priced wheels failed to excel in any of my evaluation categories and leave me wondering about how good a value they really are.


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