Editing Inline skates (section)

=== Dual density wheels ===

For nearly two decades after polyurethane wheels became standard on modern inline skates, skaters faced a difficult compromise: selecting a single wheel hardness to balance two conflicting sets of needs. On one hand, softer wheels were desirable for shock absorption over rough terrain and for maintaining grip at deep edging angles. On the other hand, harder wheels offered better wear resistance on abrasive surfaces and allowed for higher top speeds while gliding upright. Skaters had to weigh these trade-offs carefully, as no single hardness could perfectly satisfy both demands.<ref name="us-patent-6227622-k2-dual-density-pu-1997">{{Cite patent
|country=US
|number=6227622
|fdate=1997-06-20
|pubdate=2001-05-08
|gdate=2001-05-08
|title=Multilayer skate wheel
|inventor1-first=John A.
|inventor1-last=Roderick
|inventor2-first=Albert C.
|inventor2-last=Chiang
|inventor3-first=James A.
|inventor3-last=Vandergrift
|assign1=K2 Corp
|assign2=Fleet National Bank
}}</ref><ref name="le-roller-en-ligne-on-dual-density-wheels-2015">{{cite web
|url=https://www.rollerenligne.com/dossier/dual-density-skate-wheels-where-does-the-technology-comes-from-and-what-is-the-use-of-it/?lang=en
|title=Dual density skate wheels: Where does the technology comes from and what is the use of it?
|first1=Alexandre 'alfathor'
|last1=Chartier
|date=2015-01-18
|website=Le Roller en Ligne
|url-status=live
|archive-url=https://web.archive.org/web/20250419024148/https://www.rollerenligne.com/dossier/dual-density-skate-wheels-where-does-the-technology-comes-from-and-what-is-the-use-of-it/?lang=en
|archive-date=2025-04-19
|access-date=2025-04-19
}}</ref><ref name="le-roller-en-ligne-on-physics-of-inline-skate-wheel"/>

[[File:K2 Corp-US6227622B1-1997-Multilayer inline skate wheel-Patent Drawing-FIG 1A 1B 1C.png|thumb|right|180px|Dual durometer wheel]]

In 1997, K2 filed a patent for what it called a '''dual durometer''' wheel - later known in the industry as a '''dual density''' wheel - designed to offer the comfort of a '''smooth ride''' over rough terrain without sacrificing the key advantages of hard wheels: '''wear resistance''' and '''high top speed'''. Unlike conventional wheels made from a single polyurethane compound, this design featured two layers: a hard outer tire, typically rated between 70A and 100A, and a soft inner ring, rated between 20A and 75A. The compressible inner ring absorbed shocks and vibrations, while the hard outer layer maintained durability and top speed.<ref name="us-patent-6227622-k2-dual-density-pu-1997"/>

[[File:Hyper Wheels-US5922151A-1997-Shaped foam core inline skate wheel-Patent Drawing-FIG 10 FIG 11.png|thumb|right|x100px|Foam mandrel]]

That same year, Neal Piper and Tom Peterson of Hyper Wheels filed a patent for a similar concept, but with a key difference: instead of using a soft polyurethane ring, their design featured an inner foam mandrel with a triangular cross-section. This approach aimed not only to deliver the same advantages offered by K2’s dual-durometer wheels, but also to enhance '''grip during deep edging'''. The foam mandrel was encased in an airtight skin, which shaped load-bearing side walls in the hard outer tire. The triangular foam shape preserved the tip of the wheel profile from deforming when skating upright, while allowing the sides of the profile to deform under the angled loads of striding and turning at around a 30° tilt, improving grip during these maneuvers.<ref name="us-patent-5922151-hyper-wheels-dual-density-pu-1997"/>

{{multiple image
 | direction = horizontal
 | total_width = 400
 | image1 = Neal Piper-US7090306B1-2004-Inline skate wheel w soft tire n internal support-Patent Drawing-FIG 4A 4B 4C-rearranged.png
 | image2 = Revision Flex Hockey Wheels-80mm-Firm-back-76A-IMG 7141-bg-FRD.png
 | image3 = Revision Flex Hockey Wheels-80mm-Firm-back-76A-IMG 7101-bg-FRD.png
 | footer = Soft tire molded over harder support: Revision Flex
}}

In 2004, Neal Piper, widely regarded as one of the most influential skate wheel chemists,<ref name="le-roller-en-ligne-on-physics-of-inline-skate-wheel"/> filed a patent for a multi-density wheel that approached the same problem from the opposite direction of his earlier 1997 Hyper Wheels design. Instead of using a hard outer layer with a soft inner ring, this new design featured a soft polyurethane outer layer, typically rated between 60A and 75A, molded over an internal support structure made from much harder materials, usually rated between 80A and 95A or even higher. The concept first materialized as the Revision Variant hockey wheels, and later evolved into the Recoil and Flex product lines. These wheels allowed hockey players to achieve '''top speed''' without sacrificing ''' high grip'''.<ref name="us-patent-7090306-neal-piper-multi-density-pu-2004">{{Cite patent
|country=US
|number=7090306
|fdate=2004-06-04
|pubdate=2006-08-15
|gdate=2006-08-15
|title=Inline wheel with softer tire and internal support structure
|inventor1-first=Neal
|inventor1-last=Piper
}}</ref><ref name="revision-hockey-wheels-multi-density-flex-recoil-variant">{{cite web
|url=https://www.revisionhockey.com/wheels
|title=Reivision wheels: Flex, Recoil and Variant
|website=Revision Hockey
|url-status=live
|archive-url=https://web.archive.org/web/20250420035314/https://www.revisionhockey.com/wheels
|archive-date=2025-04-20
|access-date=2025-04-20
}}</ref>