# Short Track Inline Speed Skating - 110 mm Wheels vs. 125 mm

Ron M
Hi All, New to the forum. I am a lineman by trade so I have an understanding of physics as it applies to not getting yourself killed when setting telephone poles and line tension. I am also a short track inline roller speed skater and they just announced that they will be allowing 125 mm wheels in certain events. Since these wheels are new, they carry a much larger price tag than the 110 mm wheels used now. Currently my set up is 4, 110 mm wheels per skate with a hardness of 89A. (standard urethane hardness guage). A 125 mm set up would be just 3, 125 mm wheels with a hardness of also 89A. My question is, what is the difference physics wise in roll, etc between the two in a percentage form? You can also get 100 mm setups (also 4 wheel). Is it as simple as you get around 10% more roll per push as the wheels are approx. 10% larger than each other? Do you gain even more counting friction when you go to a 3 wheel set up instead of 4? Thank you for your input.

Gold Member
In bicycle wheel rolling resistance, the effect of diameter disappears in the other parameters' effects and the hyperbole of marketing.

I have ridden 700c, 26", 20" and 16" and attribute no detectable difference to diameter. ATM I'm riding with a 26" rear wheel and two 20" front wheels.

Gold Member
Hi . Is it as simple as you get around 10% more roll per push as the wheels are approx. 10% larger .

The diameter is 10% larger, and so is the circumference. So, yes, the 125 mm wheels will have a smaller angular velocity than the 110 mm , when compared against a constant translational velocity. And that is about anything concrete one can actually say about the setup.

Rolling resistance would be an addition of that from the contact of the wheel and the surface, and that of the bearing:
The urethane flexure on contact with the surface would be different due to the number or wheels and the size of wheels.
The bearing resistance would be different due to the number, the stress on each bearing, and angular velocity.
Has the size of bearing changed?

Larger wheel might means more/less weight for your foot to swing around. That could be a factor fatigue and endurance.

You will have to sift through the literature, and as Doug has said, expect hyperbole.

Homework Helper
Gold Member
Larger radius is a longer lever putting more side load on bearings (and ankles). Larger radius is also a "longer" leg length for the "push." Three wheels is one less alignment problem per skate. Give a little here, get a little there, bet your money and take your chances.

Gold Member
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For general inline hobby skating, a larger wheel allows less "tread" compression forming on rough surfaces (asphalt) by spreading the load per unit area. This could translate to less loss of energy (in the form of heat) lost in material compression of both wheelsets and vibrated/accelerated bone/tissue.

Losing one wheel (4 to 3) may actually increase loading per unit area. If your track is smooth (concrete) then it may not matter much. Offhand, there may be some slight gain by having a dual hardness wheel - hard center for low vertical roll resistance and softer shoulder for increased camber traction (propulsion/turning).

A harder wheel (tread) material could partially aleviate wheel (tread) compression loss, but with a corresponding loss of traction on smooth surfaces, since the lesser compressed contact footprint would be slightly diminished. When it comes to tires and friction in the real world, more contact (even with identical weight) provides increased traction (friction) compared to the higher loaded psi friction of less contact surface. This seems to defy physics, but other facters intervene.

You can experiment with rolling resistance by having someone tow you while connected with a rope. Incorporate a portable fish scale to measure towing resistance. Low cost scales (with hooks) are available in any sports store and extreme accuracy is not necessary, just that a difference in tension may be noted.

Wes
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Heros
Intuitive thinking says bigger wheels are better, but lets examine...
Rolling resistance in reality do not decrease linearly with radius, in fact in many experments i have made it has almost no effect.
The mass of the actual wheel may increase with square of radius, so a wheel that is twice the diameter weights about 8 times, BUT, you have consider the buckling resistance so the increase in weight is even bigger, and even more if you loose a wheel.
The bearings friction increase as internal radius increase, and if you have to loose a wheel you have to increase bearings diameter cos each wheel will support more force.

That without considering that if you are closer to the floor you will get less torque on ankles and lighter boots and chassis are usable.

In fact i'd add a wheel and make them even smaller...