Bigger Wheel Skates: Testing 125mm Wheels
By Peter Baum

Background and a Brief History
Recently skaters have been moving to larger diameter wheels. Beginning with the tiny quad wheels they moved to 76mm and then 80mm for inline wheels. The diameter stayed at 80mm for a long time until 84mm wheels were introduced in the last year- 2002. Concurrently a few pioneers like Andy Lundstrom of Xenan, Jonathon Seutter and Brett Mack had been skating on 100mm diameter scooter wheels for a couple years. Then manufacturers caught on to the big wheel's allure and in 2003 the Belotti Group introduced its Sento 100-80-100-100mm frame as well as a new and much improved 100mm wheel. Shortly thereafter Millennium Skates came out with the Millennium Marathon 100-84-100-100mm frame which had one larger wheel than the Belotti Sento. (I have been skating on this frame so a picture of this setup appears later on in this report.) Now I understand that Mogema, Bont, and others will come out soon with a frame similar to the Millennium 100mm frame. And now FILA will introduce a 100-100-100-100mm frame. FILA's 4x100mm skate is linked here. The significance of the second 100mm wheel is that it gets around the problem that the inline boot with its traditional 6.5 inch hole spacing has a mounting block just above the second wheel and that means that the front of the boot has to rise, or the boot mounting has to change or the second wheel has to get smaller (hence the 80mm and 84mm in the first 100mm skate setups. FILA has modified the boot's front mounting to use the 100mm wheel.

Here is a picture of my 100-84-100-100m Millennium 12.1 inch setup with an early Miller boot and two Belotti wheels at the rear.

Investigation, Testing and Experimentation
Now I was quite impressed with the Millennium frame and in fact several several top spots were won on it in the recent Australia-New Zealand competition. So I asked what would happen if even larger wheels were tried, say 125mm wheels, but I got no answer. I was referred to a few "skates" using even larger wheels but they were a skating version of a rollerski and were clearly intended for downhill or powering with poles and not through ordinary skate powering. They did not satisfy the requirement that the overall skate length be less than 500mm so I do not consider them skates at all.

It became clear that I might have to wait quite a while to find my answer unless I took the bull by the horns and did it myself. It was with considerable reluctance that I undertook this task as my work bench is equipment-challenged having neither an extrusion facility nor a CNC mill. Nevertheless, I came up with a method to test the 125mm wheels using a hacksaw, drill and assorted hand tools. I built up a homemade aluminum frame, essentially a U-channel (cut from a 1/8 inch wall aluminum rectangular tube) able to hold 125mm wheels at the front and back and 100mm wheels in all positions.

My test frame has 4 axle holes for 100mm wheels equally spaced along a length of 12 inches which allows a gap of only 1-2mm between wheels. Now by adding another hole at the front and rear about a half inch from the 100mm axle holes I can test a 100-100-100-125 at 12.5 inches long setup and 125-100-100-125 at 13.0 inches long. Note that the 100mm wheel is very close to 4 inches diameter and the 125mm wheel is nearly 5 inches diameter. I was skating with a Millenium 100-84-100-100mm frame on the left and the custom test frame on the right. I tried the custom 100-100-100-100mm setup only long enough to verify that it matched up pretty well against the Millennium 100mm frame and moved right on to 125mm.

The U-channel can contain all the 100mm wheels but the top of the frame had to be cut out for the 125mm wheels to protrude through. The U-channel is level with a height of 105mm above ground. If you want some pitch a heel riser can be added on top of the U-channel at the heel. To keep the heel as low as possible I inserted only a washer at the heel giving 1mm of pitch. The result was reasonable stability and no problem with performance. So for these tests the boot's mounting block sat 105mm above ground in front and 106mm above ground at the rear. For comparison the Millennium had a front elevation of 90mm and 100mm at the rear. So effectively my setup sat about 6mm higher than the Millennium (or a conventional 80mm skate). The stability seems to come from the heel which is only 6mm higher and not the ball or plantar area which was 15mm higher. There was really no stability problem with these dimensions during my tests but improvments are likely needed for longer distance skating. I got 125mm scooter wheels from Skates Away having a choice of 78a Yak wheels or a blue unbranded 85a hardness wheel.. For the first tests I chose the 85a blue wheels. For this first prototype frame I used steel bolts for axles and have made no attempt to cut the weight by carving the aluminum artistically.

My first tests of the 125mm wheel had the boot mounted forward of the position shown in the following pictures but I soon moved it back to the location shown as it improved steering and acceleration. My later tests of the 100-100-100-125mm skate were a huge success in my estimation. I found no noticeable difference in performance between the Millennium 12.1 inch setup and the 100-100-100-125 12.5 inch setup. Both had great manueverability and acceleration and responsive turning. But the 125mm version had the roll advantage and was more comfortable on rough terrain. The quick turning of both skates made it quite easy to double-push and to move into a sprint.

Then I turned to the 125-100-100-125 frame and found that it behaved like a normal 13 inch frame but with incredible roll. I couldn't push it to the limit as the front 125 wheel started to slip toward the end of the stroke (because of too hard wheel compound and left-right frame placement off a little.) It was possible to double-push with the 125-100-100-125mm frame but it turned a little slower than the others so the stroke rate was a little lower and more strength was needed to push it. Because of this it was not as much fun to skate on but in a marathon or on a very rough road it would be very welcome.

Conclusions
I was surprisingly pleased by the performance of both the 100-100-100-125 and the 125-100-100-125 frames. And the additional 6mm height presented no problem with my boot. I am now much more interested in designing an improved 125mm prototype and getting a more practical version constructed for my regular skating than in getting a 100-100-100-100 skate. The 100-100-100-125mm frame makes an awesome all-round skate and the 125-100-100-125mm will be welcome under tougher conditions and may be the frame of first choice for the stronger skaters.

Some comparison between 5x84mm and 4x100mm skates:
The total wheel circumference of a 5x80 frame exactly equals that of a 4x100mm frame. But the total circumference of a 5x84mm skate has 5% more circumferential area than a 4x100. This seems to say the wheels on a 5x84mm frame wears ~ 5% slower to start. But I think the 4x100mm skate catches up in wear rate later on. So these are nearly comparable over a long race I think.

Then I plugged into my power loss model for a 5x84 vs a 4x100 and the 4x100mm skate came out 1% lower in rolling loss. But now if you take into account the different hub/tire radius of the Belotti wheel the 4x100 comes out a few % lower in rolling loss. The result seems to say that there will not be a really dramatic difference between the best 5 wheel and 4 wheel skates until wheels get larger than 100mm diameter. But the 4 wheel frame has the powering advantage as it is shorter and turns faster the stroke rate can be higher than a 5x84mm skate.

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