Wheel durameter vs coefficient of friction
I have a vulgar amount of quad wheels. I also own a Bestone shore hardness tester. A few years ago I used a pendulum skid resistance tester to measure the coefficient of friction on most of the wheels I had at the time (about half of what I have now). It was a big $6k unit we used at my job. I quit doing it because I used a fairly painful method to insure the contact patch was the same size on all wheels I tested.
What I found was interesting. Softer wheels on the Shore A scale didn't always result in a greater coefficient of friction. Frequently the two correlated, but not always. Generally, we tell new skaters to go hard in the rink and soft outside. However, the CoF is, in my opinion just as important as the durameter yet it's always just assumed it'll track in a direct relationship with durameter.
A great example of the counterintuitive nature of these experiments is comparing a Team Rollerbones 98A wheel with a Sure Grip Fame wheel. The Rollerbones has a much higher CoF even though it's 98A vs 95A. I'd worn the reeding off the Rollerbones wheel I tested. So, maybe that raised it's CoF a bit, but still. The Fame is a very "slick" wheel and slides a lot more than the Team Logo Rollerbones.
This is why I really like to fingernail the wheels before I buy them or decide what they are for. It's a rough approximation of the CoF. Also, my value system fits my style, some people are "sliders" and love the slidey wheels I dislike such as the 103A Rollerbones Elite stuff or clay/fiber wheels.
What do you guys think about CoF vs durameter? Notice what I'm talking about?
Comments
Duro is for roll or comfort. Comfort if skating outside vs roll and a skaters weight. Skating too soft of a durometer kills speed and increases work of the skater just to stay up to speed. Heavier skaters require harder duros than lightweight skaters over the same surface(course).
Friction is from chemical makeup of the urethane. Better thane, better grip or slide(derby).
Yep, I agree. I do think durameter has some predictive power over friction, but it's often surprising how decoupled they can be in some examples. The Sure Grip Fame wheel is my favorite example. Durameter of 95A but a CoF lower than many 99A or 100A wheels I own.
some of the slickest wheels I tested were low duro. Some of the stickiest wheels I tested were 97/98 duro.
Some compounds just roll better, regardless of either durometer or CoF.
Indoor Inline: Pinnacle Full Customs | Junk Fury 4x110 | TLTF/Simmons Wheels | NMB
Outdoor Inline: Simmons Full Customs | Junk Fury 4x110 | Junk Wheels | NMB
Quads: Reidell 911 | Roll-Line Giotto | Corey Super-Ds/JG Hubs/B-Skater 71mm Outdoor | Bones Swiss/NMB
Metal hubbed wheels do that..
I also think durameter and CoF are not the full picture. As you guys point out, hub stiffness is another big factor. Hmm, let's see, what else. I'd say also these things matter for roll and "feel" too:
Hmmmm, anything I'm forgetting? Probably a lot!
wobble of bearings, not much of an issue, depends on how course the surface is.
Weight makes a difference as tested by Armadillo for years building ultralight weight skates.
Edges could make a difference. It depends
Contact patch/duro, big variables here
Wrong sleeves... I got tons of 7mm sleeves... somewhere, I don't have any use in them at all.
Treads and depth. Same variables as duro. Speed skaters wear a set in to a depth they like. Or choost to skate off the tread on a measure duro wheel. Personnal preferences by knowledgable skaters.
Temerature. Never had an issue with temps. Every skater is the race will be subjected to the same temps, no noticable difference from skaters.
Best performance Ive gotten from axle nut adjustment, no spacers(lose the weight), thighten till snug, back off exactly 1/2 turn. BTW, if spacers were all that important, flips would never have been invented. Flips prove spacers are not needed.
Wheels, wheels wheels are the number one variable. There are so many variables. Not one thing makes the perfect skate for each person. You should talk to Doc about bearings and his tests.
Pretty much what I have seen from wheel testing for years.
This is pretty interesting considering I do artistic skating and we have to slide our turns in order to get credit and for it to be considered good technique. From feel alone, at an equivalent hardness the thermoplastic wheels vs urethane are always easier to slide turns on.
Do you think a CoF rating should be provided on skates wheels as well?
@sevenspirals
The shop I go to doesn't let you "test" the wheels in any capacity before buying. I think that is a huge let down and makes me more wary about getting something when I don't know how it's going to perform. Can't do a finger test either; wheels are wrapped up.
A complimentary brief article on this topic here: https://roller.sk8.berlin/bounce-rock-skate-roll/
It certainly would be nice to know a wheel’s coefficient of friction before buying for outdoor use.
John, that is a great article. Thanks for linking to it. I agree with the author's points quite strongly. I too wish there were more technically correct and standardized wheel metrics. I'd even like them separated into elastometric response (ER = bounciness) and coeffecient of friction (CoF) though the two are often related. As someone else pointed out, even scratching with a fingernail is better than buying blind.
The majority of wheels today are of polyurethane materials. However, rollers vary in the formula used to produce urethane, which causes texture differences. It’s best to have wheels with a smooth finish. Otherwise, the rollers will feel sticky, leading to slower acceleration.