# Speed inconsistency

**URL:** <https://forums.zwift.com/t/speed-inconsistency/3059>\
**Category:** Archived: Tips and Troubleshooting\
**Created:** [May 2, 2017, 1:29pm UTC](https://forums.zwift.com/t/speed-inconsistency/3059 "2017-05-02T13:29:04Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![BigG](https://sea2.discourse-cdn.com/gozwift/user_avatar/forums.zwift.com/bigg/32/326374_2.png) [@BigG](https://forums.zwift.com/u/BigG)\
**Post date:** [May 2, 2017, 1:29pm UTC](https://forums.zwift.com/t/speed-inconsistency/3059/1 "2017-05-02T13:29:04Z")

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Just started my seven day trial.&nbsp;I have hooked up my Garmin GSC10 to Zwift, I am using it with a Roto magneto trainer.

The speed on my Garmin computer and the speed on Zwift differ significantly.

According to Garmin I was at a steady 20mph. Zwift said I was doing 10mph then speed up and at one point Zwift said I was doing 30mph, my Gamin has remained steady at 20mph.

I have looked in the setting and tried to search to see what the issue may be but cannot find anything.

Anyone got any ideas?

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**Author:** ![Paul\_Allen](https://sea2.discourse-cdn.com/gozwift/user_avatar/forums.zwift.com/paul_allen/32/414916_2.png) [@Paul\_Allen](https://forums.zwift.com/u/Paul_Allen)\
**Post date:** [May 2, 2017, 1:34pm UTC](https://forums.zwift.com/t/speed-inconsistency/3059/2 "2017-05-02T13:34:12Z")

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The speed within Zwift and the speed on your Garmin will hardly ever match, so ignore what your Garmin is displaying

Zwift calculates in-game speed based on a number of factors including your rear wheel speed (this produces virtual watts), your weight, the power curve of your trainer, the virtual elevation changes (which your Garmin knows nothing about), the type of bike used in-game, and drafting effect.

This might be a good read for you:&nbsp;[http://www.titaniumgeek.com/cycling/zwift-user-manual-unofficial-running-updates/](http://www.titaniumgeek.com/cycling/zwift-user-manual-unofficial-running-updates/)

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**Author:** ![Gerrie\_Delport\_ODZ](https://sea2.discourse-cdn.com/gozwift/user_avatar/forums.zwift.com/gerrie_delport_odz/32/437556_2.png) [@Gerrie\_Delport\_ODZ](https://forums.zwift.com/u/Gerrie_Delport_ODZ)\
**Post date:** [May 2, 2017, 1:57pm UTC](https://forums.zwift.com/t/speed-inconsistency/3059/3 "2017-05-02T13:57:40Z")

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Welcome to Zwift.&nbsp;

This has be discussed before, see the search results:

[https://support.zwift.com/hc/en-us/search?utf8=%E2%9C%93&query=speed+difference&commit=Search](https://forums.zwift.com/hc/en-us/search?utf8=%E2%9C%93&query=speed+difference&commit=Search)

Hope to see you on the road soon.

Ride On!

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<div class="post-metadata">

**Author:** ![BigG](https://sea2.discourse-cdn.com/gozwift/user_avatar/forums.zwift.com/bigg/32/326374_2.png) [@BigG](https://forums.zwift.com/u/BigG)\
**Post date:** [May 2, 2017, 2:08pm UTC](https://forums.zwift.com/t/speed-inconsistency/3059/4 "2017-05-02T14:08:17Z")

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Thanks for the prompt responses guys. That helps.

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**Author:** ![Jason\_K](https://sea2.discourse-cdn.com/gozwift/user_avatar/forums.zwift.com/jason_k/32/266_2.png) [@Jason\_K](https://forums.zwift.com/u/Jason_K)\
**Post date:** [May 3, 2017, 6:53pm UTC](https://forums.zwift.com/t/speed-inconsistency/3059/5 "2017-05-03T18:53:23Z")

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Also just want to add that it sounds like your trainer isn’t supported, so you’re not going to get accurate readings in Zwift. You can see [our list of supported trainers here](https://forums.zwift.com/hc/en-us/articles/203152565-Which-trainers-does-Zwift-support-?section=201088439).