Wheel Stiffness Test

Damon Rinard's

Data table: data.htm

This test continues as wheels are loaned. I would like to measure Rolfs, SpinergySpox, LEWs and any Mavic pre-built wheel like Heliums, Classics, Elites orCosmics. Please let me know if you would consider shipping your wheels to me fortesting: [email protected]

Lateral stiffness is how well a wheel resists flexing laterally (sideways) when a given load isapplied in that direction. Stiffness is the ability to resist flex. A stiff wheel flexes very little.

Mathematically stiffness is the inverse of flexibility. It must be emphasized that wheelstiffness is not wheel strength, and in fact may be unrelated to it. I am measuring stiffness,

not strength.

Wheel CoordinateSystem

X is the forward direction oftravel when the rider rides thebike. Y is to the side; this is thedirection of the load I appliedand the deflections I measured.Z is elevation.

You can see in this photo that the rider's weight on the left pedal causes a reaction force atthe ground contact point with a component in the lateral or Y axis direction. This is the

deflection I am measuring.

How important is wheel stiffness? There are plenty of parameters besides wheel stiffness thathave a much larger bearing on bicycle performance, such as aerodynamics and training.

However, recently there has been debate about the lateral stiffness of bicycle wheels. The

Wheel Stiffness Test http://www.sheldonbrown.com/rinard/wheel/index.htm

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increasing popularity of Rolf wheels and the recent introduction of Shimano wheels has madepeople wonder whether low spoke count wheels can be stiff enough laterally.

Howard Sutherland is quoted as saying "One measurement is worth 50 expert opinions", andso I decided to measure the lateral stiffness of as many wheels as I could get my hands on.While I was at it, I decided it might also be easy to answer some more academic questionsabout wheel stiffness in general. Measuring the lateral stiffness of all these wheels has two

purposes, as I see it:

To rank the wheels according to their lateral stiffness.1.To answer some general theoretical questions about how wheels flex.2.

In order to measure the lateral stiffness of a bicycle wheel, I had to

Hold the wheel rigidly,1.Apply a known load,2.

Measure the deflection.3.

A milling machine's table makes a very rigid base, so I machined aluminum blocks to hold thehub axle in the vice and quill of the mill (see Figure 1). I turned the blocks from an aluminumbar and bent a hook from a three-foot length of 5/16 inch diameter steel rod. I used the lathe

and mill at San Diego State University's student projects lab.

Machined aluminum blocks with through hole to receiveaxle. Using these blocks I mounted the wheel between the

bed and quill of a milling machine.

Method of holding wheel and measuringdeflection at the rim. Hooked end ofweight will be hung next to the dial

indicator.

Assign a wheel number, weigh, photograph and record description of wheel.1.Measure deflection several times in several places and record data. If bearing play is

present, gently push rim to take up the slack before measuring deflection.2.

Ship wheel back to the owner.3.


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Add data to this page.4.

The load is 25.78 pounds (11.7 kilograms or 115 Newtons). There is no magic significance tothe 25.78 pound load, but it has some advantages over larger or smaller loads:

It is large enough to avoid some of the difficulty of measuring smaller deflections atlower loads.

It is small enough not to damage any wheels.I have a convenient 25 pound weight that hangs nicely from a 0.78 pound rod ;-).

The load is applied at the center of the rim's brake track, normal to the plane of the wheel.Deflection is measured at a spot within 3/8 of an inch (10 mm) of the point of load

application, which I consider to be essentially at the point of load application. This 25.78pound load did no damage to any wheel. Every wheel was perfectly rideable after testing.

A 25.78 pound lateral load is almost certainly more than road bike wheels see in normal use. Ichose 25.78 pounds because the deflection at a lower, more realistic load may be small

enough that my measurement error of +/-0.002" (0.05mm) might become an inconvenientlylarge fraction of the measured deflection.

I hope to measure enough wheels of different configurations to answer the following theoretical questions:

1. Does stiffness vary with spoke tension?

Some believe that a wheel built with tighter spokes is stiffer. It is not. Wheel stiffness doesnot vary significantly with spoke tension unless a spoke becomes totally slack.

I measured the deflection of Wheel #2 while gradually loosening the spokes in quarter turnincrements. The wheel did not display any significant change in stiffness until the spokes were

so loose some became totally slack.

If the spokes are so loose that some become slack, the wheel becomes much more flexible.The last two data points below, 9 and 10, taken when the spokes were so loose the wheel wasalmost sloppy, show that the wheel becomes significantly more flexible when spokes on thedetensioning side of the wheel actually become slack. That is expected: a slack spoke cannot

add stiffness to the wheel; it buckles easily in compression.

A wheel whose spokes become slack while riding is a weak wheel, because slack spokescannot support the rim. This can be avoided to a large extent by building wheels with tighter

spokes. If spokes are tighter initially, then the sudden increase in flexibility shown in datapoints 9 and 10 is less likely to occur in use because a tighter wheel can bear a higher load

before spokes become slack.


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Deflection, inches, for 25.78lb.

Wheel #2, MA2 32 spoke front.

No. quarter Deflectionturns looser 10/19 11/12============ ===== ===== 1 0.075 0.070 2 0.071 0.069 3 0.070 0.068 4 0.070 0.067 5 0.069 0.067 6 0.068 0.067 7 0.068 0.067 8 0.069 0.068 9 0.079 0.085 10 0.130 0.157

2. Are front wheels stiffer than similar rear wheels, and if so by how much?

Most front wheels are stiffer than similar rear wheels. Structurally this is because front hubflanges are typically wider than rear hub flanges. Rear hub flange spacing is constrained by

industry standard dimensions, such as cassette width, drop out spacing and symmetricalframes.

Most rear wheels I tested are between 40 and 60% more flexible than similar front wheels.Although it may be the case that stiffer front wheels have been developed intentionally for

more stable handling, it is possible that many front wheels are simply overbuilt or many rearwheels are underbuilt.

Track wheels are an exception: rear hub flanges are often much wider than fronts, andtherefore such wheels are slightly stiffer laterally than similar front wheels. Compare track

wheels number 83 and 84 (below) for an example.

Besides flange spacing, the other parameters that could affect stiffness are often held constantbetween front and rear wheel pairs: number and gauge of spokes, and rim cross section.

However, it is becoming more common to see wheel pairs sold with a different number ofspokes in the front and rear wheels. On the other hand it is still the rare wheel pair that is sold

with different rims front and rear.

Some pairs whose front and rear wheels are closer to the same stiffness are:

Specialized Composite wheels. Since these wheels are the same except for hub guts,they do not differ significantly between front and rear wheels. In fact the front can be

used as a rear by changing the axle.Velomax Javelin. The rear wheel is slightly stiffer than the front wheel (8%).

Structurally this may be because of two design features: the narrow front hub flangespacing decreases the bracing angle on this wheel compared to more typical front hubswith wider spacing, and the higher spoke count in the rear wheel compared to the front

(24 spokes in the rear versus 18 in the front) adds stiffness to the rear wheel to morenearly match the front.

Spinergy Rev-X. The RevXs I measured showed a large range of deflections from thefour spots around the wheel: +/- 0.010" to 0.016" out of about 0.150", (0.25mm to

0.41mm out of about 3.81mm) or 11%. For this pair of Spinergies (wheels 56 and 57),the front is about 12% to 16% more flexible than the rear. There is no dimensional

explanation for this (flange spacing and other dimensions are the same), so I attribute


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the difference to variation in manufacturing from wheel to wheel. The next pair mighthave the front/rear relationship reversed.

Aerospoke. Like the Specialized, these wheels are the same except for hub guts.Consequently, they do not differ significantly between front and rear wheels.

3. Do dished wheels flex differently from one side to the other?

Dished wheels do not flex significantly differently to the left or right.

A dished wheel might deflect slightly more due to loadsapplied from the flatter side than it does due to equivalentloads applied from the other, but it is unclear from this datawhether this is really the case. It may be true in theory,because of the difference in bracing angle between the rightside spokes and the left side spokes: the more favorablebracing angle of the left side spokes may be better able torestrain the rim against deflection to the right than the rightside spokes might brace the rim against deflection to the left.

If it exists, the difference is very small: on the order of just a fewthousandths of an inch, i.e. within the error of my measurement,even under the larger-than-life load of 25.78 pounds that I used forthis test. Even if a small difference exists in this artificially high loadcase, no one will notice the even smaller difference the wheel mightdisplay while riding.

In the chart above, the length of the vertical lines represent the range of deflections obtainedfrom loading the wheel and measuring deflection at four or more random locations around the

wheel. There are two vertical lines for each wheel:

Range of deflections due to loads applied from the left hand side (indicated by the LHafter the wheel name) and

1.

Range of deflections due to loads applied from the right hand side (indicated by the RH2.


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after the wheel name).

The average of all four (or more) measurements is near the middle of each vertical range line.The slanted line between each range connects the average deflection of the left and right

sides. The fact that this line is slanted upward toward the right in every case shows that, onaverage, rear wheels may flex more in response to loads from the right side than to loads from

the left. However, the range of measurements (length of vertical lines) shows that thedifference between left and right is often smaller than the measurement error or the range of

response of one side of the wheel.

4. How does the shape of the wheel change in response to a lateral load?

This question comes up because some people worry about the rim rubbing the brakes whileclimbing. There is no doubt rims rub sometimes on MTBs, because occasionally you can hear

the brake shoes rub. But the wheel is not the only thing flexing: frames and forks flex, too.

In describing how the rim flexes at points far away from the point of load application, JobstBrandt describes a saddle or taco shape [1]. I measured and found this to be accurate. Let the

the point of load application be called 0 degrees. Then the two other locations I measuredwould be called 90 degrees away and 180 degrees away, i.e., one quarter and one half wayaround the wheel away from the point of load application. To form a saddle shape, when a

load is applied at 0 degrees in the positive direction, the deflection at +/-90 degrees should bein the negative direction, and the deflection at 180 degrees should begin to return in a

relatively more positive direction again. This is exactly what happened.

The chart below shows the (exaggerated) shape of several rims when loaded as describedabove. The zero-deflection base line is horizontal, and the various colored plots of the

different wheels show the lateral deflections measured at 0, 90 and 180 degrees.

The load is applied at 0 degrees, at the left end of the horizontal axis. The deflectionsmeasured at 0, 90 and 180 degrees show the wheels assume the expected arching or saddleshape. At 180 degrees, even though the rim is headed in the positive direction, it does not

often cross back over to the positive side of the zero-deflection base line.

Between 90 and 180 degrees is where most bikes have their rim brakes. The deflection here is


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fairly consistent among all the wheels, and did not vary significantly between the stiffer andmore flexible wheels.

For this 25 pound load all wheels flexed about 0.020 inches or half a millimeter in this region.This flex is in the direction opposite the load. This is the same direction the frame is likely to

flex under a lateral load at the tire contact patch, such as occurs when climbing out of thesaddle or sprinting. That means the brake and wheel will move in the same direction, thusreducing the relative motion between the rim and brake that may cause the brake to rub.

5. Do paired spokes change lateral stiffness? (Rolf, Shimano)

Some wheels pair the spokes together at the rim, so there arelarge spans of unsupported rim between spoke pairs. Does thismake the wheel flex differently? The usual worry is that the rimwill be more flexible in the long unsupported span.

I compared deflection measured when the wheel was loaded atpairs of spokes to deflection measured when the wheel wasloaded between pairs of spokes. So far I have measured fivewheels built with some kind of paired spoking. There is nosignificant difference in the flexibility of these wheels anywherearound the rim, either at spoke pairs or between them.

Wheel Increase in flexibility between spokes

Rolf Vector 20 spoke front 1.5%

Rolf Vector 24 spoke rear 1.2%

Rigida 12 spoke front 4.2%

Shimano WH7700 front -1.2%

Shimano WH7700 rear -0.7%

The results are mixed, but generally paired spoking for any given wire spoked wheel does notlead to a significant increase in flexibility between the spoke pairs compared to flexibility atthe spoke pairs. Such wheels are about the same stiffness at spoke pairs as they are betweenspoke pairs. In fact the Shimano wheels are actually slightly stiffer between spokes than they

are at spokes, but again this difference is insignificant.

In contrast, the muti-spoke composite wheels showed a marked difference in stiffnessbetween spokes compared to the stiffness when loaded at the spokes, with a few exceptions.

Wheel

Increase inflexibilitybetweenspokes

Comments

Zipp 3000 135% Largest difference in this test.


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Specializedfront 700cclincher

57% Taller rim and wider spokes make animprovement in this design.

Specializedrear 700cclincher

59%


56%


57%

SpinergyRevX, newstyle

49% Four spoke pairs shorten the length ofunsupported rim.

Corima 4spoke 23%

Four wide spokes shorten the length ofunsupported rim even more.

Aerospoke 5spoke 0%

These wheels are the most flexible wheelsI've ever tested. There is no difference ator between spokes primarily because theyare so flexible everywhere.

SpinergyRevX, oldstyle

-17%

Yes, these wheels are actually stifferbetween spokes. But this is only becausethe spokes are so loose that the bottomside spoke becomes slack at a very lowload. When loaded between spokes, therim is stiff enough to recruit two pairs ofspokes and make the underside spokes goslack on both pairs. The wheel is stiffer inthis case because slackening comes at ahigher load.

For example, the Specialized wheel is over 50% more flexible when the load is betweenspokes than when the load is at a spoke. In spite of this large difference, many people ride

Specialized Composite wheels with great success, although there have been reports ofdisconcerting handling when they are used in track sprinting or all-round riding on steeper

tracks.

6. Do Shimano's laterally crossed spokes make the wheel laterally stiff?

In a word, no.

The Shimano WH7700 (Dura-Ace) wheels have anumber of fairly unusual features, one of which is aspoking arrangement in which the spokes originating at


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one side of the hub attach to the rim on the other side.

Shimano claims "...the wheel's lateral rigidity is significantly increased...", and maybe it iscompared to a similarly light 16 spoke wheel without the lateral crossover. But it's still apretty flexible wheel. The most similar wheels in this test are the Mavic Cosmics. Eventhough the Cosmics are heavier, they serve as a fairly good comparison since, like the

Shimanos, the Cosmics have a fairly deep rim and 16 spokes. The significant differencesbetween the Cosmics and the Shimanos are wider hub flanges and a slightly larger rim cross

section on the Cosmic, both of which add stiffness as well as weight.

moredetails

Shimano WH-7700 16spoke front. 2.6 x 1.4 mmelliptical spokes. Thanks toHi-Tech Bikes.

739g

18.8 x29.6mm

2.11mm

moredetails

Shimano WH-7700 16spoke rear. 2.6 x 1.4 mmelliptical spokes. Thanks toHi-Tech Bikes.

963g

18.8 x29.6mm

3.81mmfrom RH

3.78mmfrom LH

big picture

Mavic Cosmic 16 spoketubular front. 2.8 x 1.4 mmelliptical spokes. Thanks to DarrylMataya.

917g

18.3 x37.7mm

1.70mm

big picture

Mavic Cosmic 16 spoketubular rear. 2.8 x 1.4 mmelliptical spokes. Thanks to DarrylMataya.

1097g

18.3 x37.7mm

2.46mmfrom RH

2.36 fromLH

7. How does spoke gauge affect stiffness?

Thicker spokes make a wheel stiffer, if all else is equal. A typical 32 spoke wheel builtwith 2.0mm spokes is about 11% stiffer than a similar wheel built with 2.0-1.45mm swaged

spokes.

Compare the deflection of two wheels: numbers 39 and 47. Wheel 39 is built with2.0-1.45mm swaged spokes, but wheel 47 is built with 2.0mm straight gauge

spokes. Hub dimensions are effectively identical, spoke count is the same and therims are the same make and model, so the only structural difference is the spoke

gauge.

Result? The wheel with thinner spokes deflected 0.051" (1.30mm) in font and0.067"1.70mm) in the rear, but the wheel with thicker spokes deflected less: only 0.046"

(1.17mm) and 0.055" (1.40mm) for front and rear, respectively. That's an 11% increase instiffness for the thicker spoked wheels.

Interestingly, wheel stiffness depends on more than just spoke thickness; the rim and other


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factors also contribute, so only part of the increase in raw spoke stiffness shows up inmeasured wheel stiffness. The thicker spoke by itself is nearly twice as stiff axially as the

thinner spoke!

8. Does having a tire inflated matter?

This is really a theoretical question, because no one rides without inflated tires. But Imeasured a few wheels with tires inflated and compared them to the deflection when

completely deflated. An inflated tire increases stiffness by about 5 to 8% compared to awheel with the tire deflated. But this effect is negligible compared to the effects of tireinflation pressure on other variables. Don't choose higer pressures to get stiffer wheels!Choose tire pressure for other reasons (comfort, traction, avoiding pinch flats and rim

damage, rolling resistance, etc.)

9. Does stiffness vary with spoke cross?

I need more wheels to measure the effect of spoke pattern. If you have a wheel similar to onethat's already listed, but with different pattern, please send it to me. E-mail Damon Rinard.

10. Are radial wheels stiffer elbows in or out? How much?

Because the bracing angle is increased, radial wheels are about 13% stiffer elbows out, allelse equal.

Todd Kuzma sent me a wheel built elbows in, and after measuring lateral stiffness I rebuilt itelbows out. The wheel's deflection was 0.050" (1.27mm) with elbows in and 0.044" (1.12mm)

with elbows out, for a difference of 0.006" (0.15mm) more flexible in the elbows inconfiguration, all else equal.

Wheel #95 is an example of a wheel built with spokeelbows out.

Wheel #5 is an example of a wheel built with spokeelbows in.

In the table of results, the two wheels I compared are #94 with elbows in, and #95 with


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elbows out.

11. Is there an optimum left flange location?

For highest lateral stiffenss, wider flanges are always better. Front hubs already have nearlythe widest flange spacing that will fit in the fork, but rear hubs have room to widen flange

spacing by moving the left flange outboard. But as always there is a tradeoff. The farther theflange moves, the looser the spokes. Loose spokes make for a weaker wheel.

12. How do 650c wheels compare to 700c?

Smaller wheels are stiffer than larger wheels. If they are built on the same hubs, then thebracing angle is larger for smaller rims. If everything else is the same, 650c wheels are about

25% stiffer than 700c wheels.

Note: smaller wheels often have fewer spokes than larger wheels, and this is as it should be.For similar strength, spoke spacing at the rim is what should be held constant, not spoke

count. Consequently, a 650c wheel with 28 spokes is about the same strength as a 700c wheelwith 32. This is the case with the wheels I measured to get this 25% difference in stiffness:

wheels 69 and 71.

13. Are newer Spinergy RevXs stiffer than the old ones?

Yes, the newer Spinergy I measured (Serial 315036) was stiffer: it showed only a third asmuch deflection under the test load as the older model (Serials 107760 and 107875). The two

older RevXs I measured were among the most flexible wheels (0.119" to 0.160"deflection(3.02mm to 4.06mm)), but the newer RevX of the same size is the stiffest wheelI've ever measured (only about 0.050" (1.27mm) of deflection). Why? Because the olderSpinergies' bottom side spokes became slack under the test load. In contrast, the newer

Spinergy's spokes did not go slack. Slack spokes cannot contribute to wheel stiffness; thus theolder model deflected more.

While spoke tension normally does not have a significant effect on wheel stiffness (Seequestion number 1 above), this is only the case as long as no spokes become slack. That is

one reason high initial spoke tension is important. In comparing old versus new Spinergies, theinitial tension was low enough in the older Spinergies that spokes did become slack, making

the older wheels more flexible as a result.

14. Is the Spinergy RevX SuperStiff stiffer than a regular Spinergy RevX ?

Yes, the SuperStiff I measured deflected only 3/4 as much as the regular model (0.046"(1.17mm) for the Super Stiff compared to 0.059" (1.50mm) for the regular model). The SuperStiff is about 25% stiffer than a regular RevX. Both of these are quite new (Serial 301526 for

the regular RevX and 357185 for the SuperStiff).

15. Do Spinergy X-Beams make a measurable difference?

Nope. The difference is smaller than the precision of the measurement. Strangely enough, theRevX I measured was actually more flexible after I installed the X-Beams, though the


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difference is insignificant (0.059" or 1.50mm of deflection with the X-Beams compared to0.057" or 1.45mm without).

16. How does rim weight affect stiffness?

For rims of similar design, the heavier rim makes a wheel stiffer.

Is deflection linear with load?

How does lateral tire flex compare?

Does tying and soldering affect stiffness?

Relative contribution of the following to stiffness:

number of spokesspoke gaugerim weight

hub flange spacingrim height

Data table: data.htm. Compare these results with Franois Grignon's research. Does wheelstiffness even matter?

This test measures lateral stiffness alone. It does not include the radial load allwheels see in use. It does not measure radial stiffness, nor strength of any kind.

Never! How could infinite lateral stiffness be bad?

Maybe. Control issues? Contribute to speed wobble?

1. Brandt, Jobst, The Bicycle Wheel, Avocet Press, Palo Alto, California, 1995.


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2. Brandt, Jobst, "Tied and Soldered Wheels", rec.bicycles.* newsgroup FAQ.

4. Grignon, Franois, Aero Wheels Under Scrutiny, Club Cycliste Beaconsfield CyclingClub, 1998.

3. Smith, Jeff, Re: Spoke tension and stiffness?, rec.bicycles.tech newsgroup message,November 07, 1999.

Rob Bernhard, Jobst Brandt, Vic Copeland, Franois Grignon, Todd Holland, EricHollenbeck, Brad Hunter, Jon Isaacs, Todd Kuzma, Darryl Mataya, Barney Milner, Hank

Montrose, Chuck Davis, Dan Rock, Charles O'Toole, Jane Rinard, Ken Robb, Russell Seatonand Shaun Wallace.

Home back to Damon Rinard's Bicycle Tech Page

Copyright 1999-2001 Damon Rinard

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