the oysi frame (and aggressive skate wheel rockering)

This post is here to document my oysi frame wheel mix and to explain the logic behind it. Skip to the “oysi frame section” if you don’t want all the background.

Rockering Aggressive Skates
My first aggressive inline skate was the Rollerblade TRS, as it was for most people who started rollerblading in the early 90’s. My second skate was the K2 Fatty. I had a love/hate relationship with my K2s. I loved their look and frame innovations, but I hated how flat they felt and how stiff the cuff was. I was eager to loan them out to friends who wanted to try them so that I could spend a week or two with their Majestic 12s. I eventually destroyed my K2s and needed a new pair of skates. Did I get Majestic 12s? No. Instead, I chose to get a pair of K2 backyard bob’s (essentially the fatty with different colors). Why would I do this? I realized I loved the hexagonal frame spacers that let you rocker the wheels in a variety of ways. Eventually I would get a pair of Majestic 12s in a final swap, but I always missed those frame spacers.

Once I had K2s I started riding small flat wheels (55 mm or so) exclusively. The innovations K2 made to the skate frame made riding flat with little to no compromise in grinding ability possible

 

image;s=1000x700.jpeg

The K2 incorporated an “h-block” in the middle of the frame for grinding, and therefore you could ride a flat setup, or experiment, even if you couldn’t in your TRS skates. The groove was TINY by today’s standards at ~1″ or so in width, but massive when compared with the TRS.

Another great feature K2 brought was a set of hexagonal frame spacers that allowed users to change the height of each wheel relative to the others. They just assumed that since they gave aggressive skaters a viable flat riding option that they would want to push the new found agility further by rockering the front wheel a bit higher, etc. interestingly, K2 still have this “hexagonal washer system” in their UFS frames:

olA8mNl.jpg
(Photo via be-mag forum user andreas542: https://www.be-mag.com/msgboard/hardware/68939-a-closer-look-at-those-new-k2-frames)

Note, in the image above, the back wheel is lower than the adjacent wheel by a small amount because the bolt hole is on different sides of the hexagon. This allows a wheel to be moved away from the h-block, or further into the frame etc.

I used the hexagon system to give the skate a slight forward tilt of about 3 mm or so by progressively going from lowest in the back to higher in the front. After wearing a new set of wheels a bit, I would end up with what felt like a very stable, yet dynamic skate. I could just apply my weight naturally to the skate and the wheel base felt normal, but if I positioned my weight more in the back or front I could get a slight rocker and turn very quickly etc. Also, this tilt helped make the K2 skate (which was flat) feel a bit more like the TRS and the Majestic 12 without a squishy heel orthotic in. With that said, getting a tilt was not the main attraction to the K2 rocker system, it was being able to rocker the wheels in general.

The Wizard frame implements a tilt and natural wheel rocker in an ideal way, and in a free-skate format where its utility is maximized:Screen Shot 2019-01-03 at 10.29.05 PM.png
(image via Thuro: https://thuroshop.com/products/wizard-frames-v3-90mm-100mm-or-110mm)

Conceptually, rockering anyway that feels good for you can be achieved with different wheels, but the available mix of commercially available wheel profile and diameters limit the options.

The Oysi Frame
If you aren’t familiar with the Oysi frame, it has been described better elsewhere, in particular by the creator of the frame:

The key features of the Oysi frame are:
a) Longer wheel base.
b) Massive grind block area.
c) Lower and recessed middle wheels.
d) Higher outer wheels.
e) Incredible injection molding (the plastic is fast).

There is ~13 mm height difference between the outer and inner wheels. The most common wheel setups I’ve seen used are:

a) 72 mm Go Project wheels on the outer spots + 60 mm Go Project (or UC) wheels in the center. This gives a very slight banana rocker (very slight).
b) 68 mm UC Richie Eisler wheels on the outer spots and 54 or 55 mm Eulogy wheels in the center spots (to get a true flat or slight rocker).

I wanted to see if I could use the hi/lo arrangement of the Oysi frame and available wheel options to get a 3.5 mm tilt and a bit of a natural rocker like the Wizard frame has, and I used to do with my K2s. Because the wheel base in much longer on the Oysi than old K2s I was expecting that the benefits of this kind of rockering would be more pronounced.

First, just to be clear about the Oysi frame’s characteristics this is a true-to-scale figure of what installing four 68 mm would give us:Screen Shot 2019-01-03 at 11.05.35 PM.png
Notice how the wheels bump into each other and there is a massive difference in height. There is a 13 mm difference between the height of the middle and outer wheels, so the gap between the bottom of the outer wheels and the ground is half of the axle differences, so there is a 6.5 mm rocker.

Thus, to get a flat setup from the Oysi we do the following:

Screen Shot 2019-01-03 at 11.11.22 PM.png
Because we need to close a 13 mm diameter gap, we put 55 mm wheels in the middle. The 55 mm wheel is a popular aggressive skate wheel diameter and Undercover, Ground Control and Eulogy make 55 mm wheels in 89 to 92A durometers.

The same thing can be achieved with the 72/60 combo and it results in a very useable ~0.5 mm rocker. This is because there is an axle height difference of 13 mm, but this combo accounts for 12 mm of that with the diameter differences. The amount of rocker is half of the 1 mm difference, because half goes to the top of the wheels and half to the bottom.

Screen Shot 2019-01-03 at 11.20.36 PM.png

Now, if we want a 3.5 mm tilt we can calculate a slope factor, and then use that to determine how to scale wheel diameters from the 4th wheel (the wheel under our heel) to the 1st, despite the fact that there are two different distance gaps we are working with (i.e. the distance between wheels 3 and 2 is larger than 4-3 and 2-1). The Oysi frame has a length of 281 mm from the middle of the 4th and 1st wheel (see first figure) so to get the slope we take dy/dx where dy (height difference) is 3.5 mm and dx (the length) is 281 mm. This is a slope (k) of 0.0125 mm/mm (clearly the units cancel, but the concept is important so I keep them).

Now, the outer wheel choices are easy because that distance is fixed and we know how much difference we want. If we used the 72 mm and 68 mm wheels, we would have a 4 mm diameter difference, but half of that is the tilt which would be 2 mm. A better choice would be the 72 mm and a 65 mm wheel. That combination would be a 7 mm diameter difference, which if we cut that in half, we get our 3.5 mm tilt. Go Project makes a nice 65 mm wheel.

The harder choices are the center wheels, and we have to use our slope factor for those. The distance between the 4th (back; 72 mm) wheel and the 3rd wheel is 66.44 mm, which means 5.56 mm of length. We can get the diameter of the 3rd wheel that we should get to maintain the tilt by scaling the 66.44 mm by the slope and also subtracting the 13 mm axle difference.

Next Wheel Diameter = (Last Diameter * (Last Diameter * Slope)) – Axel Difference

If we do this sequentially for all wheels we get the following:

Screen Shot 2019-01-03 at 11.47.42 PM.png

There are no 57.3 mm or 53.7 mm wheels commercially available, but there are 57 and 54 mm Eulogy wheels. Interestingly enough, the difference between the actual diameters we can get and the ideal wheels to keep the 3.5 mm plane are the same (300 um), but in different directions. This will result in an interesting 0.3 mm rocker. When I sketched this out I wasn’t certain I would notice the rocker, or if it would be pleasant, as I don’t know what tolerances to expect. Nevertheless, if you compare the predicted rocker from the asymmetric setup (example 2; blue line) to the rocker from the 72/60 setup (example 1; black line) you can see the rocker range is close in magnitude:

Screen Shot 2019-01-03 at 11.54.38 PM.png
Again, I didn’t expect much from this because once weight is applied the differences normalize, but I have been happy to discover that I can get differences by centering my weight differently along the boot, like a relatively natural rockered skate.

Here is what the mix looks like:
IMG_0156.JPG

IMG_4644.JPG

The wheels from left to right (back to front) are:

* 72 mm Go Project (https://goblading.com/collections/wheels/products/go-project-72mm-wheels-white) – Bullet Profile

* 57 mm Jeff Dalnas Eulogy Wheels (https://www.locoskates.com/eulogy-dalnas-pro-anchor-wheels-57mm/p4516 or https://thuroshop.com/products/eulogy-jeff-dalnas-2018-pro-wheel) – Flat Profile

* 54 mm Metatron Eulogy Wheel (https://thuroshop.com/products/eulogy-metatron-54mm-wheel or https://www.intuitionskate.com/products/eulogy-54mm-wheels) – Flat Profile

* 65 mm Go Project Joe Atkinson Wheel (https://goblading.com/collections/wheels/products/go-project-joe-atkinson-65mm-wheels-grey) – Flat Profile

I’m having a lot of fun skating on it. It has a slight tilt, but it feels good and stable. Also, with natural weight on the skate the rocker feels flat, but if you shift your weight more forward the back wheel touches less, and vice-versa. Thus, I feel like I’ve replicated the thing I used to love about the K2 frame, but I enjoy it more because the Oysi frame is more of a free-skate/aggressive frame given its long wheel base etc. I was skeptical of having only the back wheel as a bullet profile (conceptually if I had to use one bullet profile wheel, I’d put it in front), but I’ve been happy with it and I like dynamic it adds.

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