# What is the purpose (and name) of this little outsole extension on the heel of trail running shoes?

**URL:** <https://boards.straightdope.com/t/what-is-the-purpose-and-name-of-this-little-outsole-extension-on-the-heel-of-trail-running-shoes/943883>\
**Category:** Factual Questions\
**Created:** [June 9, 2021, 2:11am UTC](https://boards.straightdope.com/t/what-is-the-purpose-and-name-of-this-little-outsole-extension-on-the-heel-of-trail-running-shoes/943883 "2021-06-09T02:11:32Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![Dr.Colossus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.colossus/32/9423_2.png) [@Dr.Colossus](https://boards.straightdope.com/u/Dr.Colossus)\
**Post date:** [June 16, 2021, 2:39am UTC](https://boards.straightdope.com/t/what-is-the-purpose-and-name-of-this-little-outsole-extension-on-the-heel-of-trail-running-shoes/943883/22 "2021-06-16T02:39:12Z")

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HAPPY TO REPORT BACK.

_ **I have an answer.** _

Turns out the flappy thing is called a “trail rudder” and is very much a useful addition: It (as someone here already guessed) helps with control running downhill. It’s akin to a “snowshoe” effect, but just on a much smaller scale. It seems to primarily help with downhill angles and prevents ankle rolling or heel slippage. Which, is easy to imagine in your head.

It also offers (again, as someone upthread guessed) more surface area for more traction in general, kind of like fatter swamp tires on a truck.

Shoe companies say that this helps with the heel-strike and use it in conjunction with other trail-running features such as a wider toe box so your toes can splay more naturally with each running strike. Hoka has a proprietary term for theirs, and “trail rudder” seems attributed to Altra, but also in general.

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**Author:** ![TroutMan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troutman/32/6721_2.png) [@TroutMan](https://boards.straightdope.com/u/TroutMan)\
**Post date:** [June 16, 2021, 3:19am UTC](https://boards.straightdope.com/t/what-is-the-purpose-and-name-of-this-little-outsole-extension-on-the-heel-of-trail-running-shoes/943883/23 "2021-06-16T03:19:31Z")

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Cool! I remain a skeptic that it’s big enough to make a difference, but that’s because I’m crotchety, not because I know anything.

Enjoy the trails!

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**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\
**Post date:** [June 16, 2021, 3:28am UTC](https://boards.straightdope.com/t/what-is-the-purpose-and-name-of-this-little-outsole-extension-on-the-heel-of-trail-running-shoes/943883/24 "2021-06-16T03:28:20Z")

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> [@Dr.Colossus](#):
>
> It seems to primarily help with downhill angles and prevents ankle rolling or heel slippage.

On a related note: when I walked barefoot, I learned to place my foot flat and land on the ball of my foot. When I did that in leather soles, _the leather soles slipped on wet surfaces_. Since my weight was behind the shoe, I would fall back and the shoe would slip forward.

I learned that I had to heel plant and draw the shoe towards and under me to get good traction and balance on slippery surfaces.

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