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I've seen inline skates (for speed skating mostly) in a wide variety of set-ups w/r/t wheel diameter:

  1. OOOO: 4x100; 4x110 (typical)
  2. OOO: 3x110 (a Powerslide model)
  3. OOoO: 3x100+1x90; 3x110+1x100 (again some Powerslides)
  4. ooooo: 5x80 (I used to see some setups like this)

I assume the bigger the wheels, the better - in general.

The justification for setup 3 seems to be to lower the skater's center of gravity while keeping most wheels big. Does this really make a difference?

How does wheel count affect performance? My intuition fails me here- less bearings seem to imply less friction, but OTOH more stress on each bearing could result in more friction overall. What's the rule here? What's the profit from using a 3-wheel setup instead of a 4-wheel setup?

6

As your question already suggests, there are many contributing elements:

Wheels:

  • diameter – although there is some controversy over the exact amount by which the diameter contributes, generally the rolling resistance depends on diameter in inverse proportion. In short, bigger wheels equals smaller resistance. Also, on a rough surface, bigger wheels will bridge the holes more easily, resulting in a smoother and more comfortable ride.

  • hardness – indicated by durometer (common range 73A - 92A) is again inversely proportional to the amount of deformation of the wheel under the load. The more is a wheel deformed, the bigger is its contact area with the ground. In bigger wheels, the ratio of deformation length to the wheel size is smaller, hence the wheel is closer to the ideal circular shape.

  • heat disipation – with deformation, there comes a heat production. Over the same distance, a smaller wheel receives more deformations (as it makes more revolutions) than a bigger wheel, thus the smaller wheel heats up more. The same applies for a heat received from the contact with a hot surface (sunlit asphalt road). Heat makes the wheel softer.

  • mass distribution – affects rotational inertia. Bigger wheels, although not necessarily heavier than smaller ones, have the mass farther from the axle, thus better conserve the rotational momentum. So the bigger wheels are harder to get rolling, but once they roll, it's easier to keep them rolling. You want this for a marathon, not for a sprint.

  • cross-section profile – from flat, through circular, to elliptic. A more tapered wheel has a smaller contact area with the ground, which comes with less rolling resistance. A bigger wheel can be more tapered than a small one, due to a better width / height ration of the cross-section.

  • spokes design – in higher speeds, let's say 25 km / h and over, air resistance becomes quite important (it's quadratic with the speed), so with the same design, a bigger wheel's spokes receive more drag. Spokes design also contributes to the wheel's hardness, weight and mass distribution.

Bearings:

  • number of balls – a bearing is typically composed of 5 to 7 balls, with fewer balls inducing less friction, but putting a higher demand on the quality of the ball surface. In speed-skating, also the weight difference can be important.

  • size – bearings come in two possible sizes: standard 608 and mini (or micro) 688. Again, the weight difference may be important. Mini bearings have less friction, but they wear off more quickly due to a lower dirt tolerance and a smaller contat area size to bear the load.

  • lubricant – since smaller wheels have to rotate faster than bigger wheels to achieve the same forward speed, the resistance of a lubricant will be higher. While you can be fine with grease while using bigger wheels, to get the same speed with smaller wheels you'll have to switch to oil.

Setup:

  • number of wheels – more wheels decrease the load per wheel, thus reducing the wheel's deformation and consequently rolling resistance. The resulting length (front wheel to back wheel) adds to the stability when leaning forwards or backwards, and also makes it easier to bridge holes in a rough surface. On the other hand, it makes it harder to cross legs over in turns.

  • wheel diameter – when using bigger wheels, besides the effect on the height of skater's centre of gravity (less than 2 %, which is not a big deal for a non-beginner), there's a bigger one: an increase in the flexing force affecting the ankle (more than 15 %). You can feel it especially in the inner push part of a double push.

  • frame – more wheels or bigger wheels, both mean a longer, heavier and more flexible frame. Longer frame, albeit more stable, is harder to turn with. Flexibility means loss of energy. With more wheels you need more screws (more weight). When the 2nd wheel is 1 cm smaller, the axle has to be 5 mm lower and some frame models are quite thin at that 2nd axle point, thus prone to cracking.

  • 2nd wheel smaller – it's more difficult to buy new wheels for this setup, since they are usually sold in packs of 8 pcs of the same size. The two smaller wheels have a different rotational inertia and a different wear period. Also the wear-leveling wheel rotation pattern has to be modified accordingly.

  • shoe – with an increase in the flexing force affecting the ankle when using bigger wheels, you may find it hard to use speed-skating shoes. They tend to end no higher than the ankle joint, thus giving no support to it. Until you get the ankles stronger, you may have to resort to mid-high shoes.

  • weight – wheels can account for more than 60 % of the total skate weight, depending on the size and the number of the wheels (plus 2 bearings and 1 screw per wheel). Wheels of the same size can still have a different amount of the wheel mass, with more mass giving a longer life span, but also a worse conservation of the rotational momentum due to a different mass distribution.

Summary:

  1. OOOO (4×100; 4×110) – this is the standard used by speed racers today

  2. OOO (3×110) – advanced fitness skater, big wheels for inertia, short frame for agility (can be good for a down-hill slalom race)

  3. OOoO (3×100+1×90; 3×110+1×100) – some models prone to frame cracking at the 2nd axle, minor benefits due to a lower shoe stance (more to the ankle flex, than to the skater's gravity centre)

  4. ooooo (5×80) – falling out of favour nowadays, some benefits due to a much lower shoe stance, other than that it's similar to 4×100, but with all negatives of small wheels


Just to complement, the setups I have excessively skated for several years:

  • 2 × 80 mm / 80a, ABEC 5, plastic frame – didn't have spare bearings for the broken ones :o)
  • 4 × 80 mm / 80a, ABEC 7, aluminium frame
  • 4 × 90 mm / 82-85a, ABEC 7, bamboo frame
  • 3 × 90 mm + 1 × 80 mm / 82a, ILQ 9, aluminium frame
  • 3 × 100 mm + 1 × 90 mm / 86a, ILQ 9, aluminium frame
  • 4 × 100 mm / 86a, ILQ 9 Pro, magnesium frame
  • 4 × 110 mm / 85a, ILQ 9 Pro, magnesium frame
  • 3 × 150 mm pneumatic tyres, ABEC 5
4

The real reason for using O°°O or OO°O is to allow you to perform rail tricks more easily, and without grinding away the wheels so much as it allows the rail to touch the skate, rather than the rubber wheels.

OOO tends to give you a shorter wheelbase, which can allow you to spin and change direction more rapidly.

ooooo is quite stable at speed, and may allow you to accelerate faster, but is harder to turn.

  • Neither OooO, OOoO, nor 000 are for rail tricks, especially with wheel sizes 100mm+. Did you mistake it for O°°O? – charlie Sep 17 '12 at 12:17
  • Yes. Couldn't get those degree signs from my computer - thanks - have copied them into the correct place. – Rory Alsop Sep 17 '12 at 12:19
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The different wheel combinations are based designs to overcome the limitations of 165 mm bolt spacing used on ice speed skating boots. When the manufactures decided to redesign the boot to take advantage of larger wheels they made frames with a 195 mm bolt spacing or added another mounting point like the Bont 3 point frames.

I still use the 5x80 mm wheel setup (ooooo) with my short track boots for summer training as I'm not interested in maximum speed and I'm too cheap to buy dedicated in-line skates.

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Frames with 3 wheels are for people, mostly kids, who want big wheels but cannot manage a full length frame. Frames with 5 wheels were the standard when all there was were 84mm wheels. They are now mainly used for downhill skating or vintage speed skating. Nowadays people use a frame with 4 wheels, in speed skating they range from 100 to 110mm. You should probably start with 4x100mm and work your way up if you decide to stay in the sport.

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I find I love the 3x125mm setup for generally everything, however the 4x90mm is just wicked and has a positive feel when skating. I feel more planted with this setup. I feel more confident and get a full workout. Its faster off the mark and generally a beast. I still cannot decide if I have a preference. I wanna try a 4x110mm then I will see.

  • This is all opinion, I'm afraid. – TrueDub Nov 5 '15 at 12:20

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