# calculating speed offset with bigger wheels

**URL:** <https://forums.speedlife.net/t/calculating-speed-offset-with-bigger-wheels/99956>\
**Category:** SON240sx Automotive\
**Created:** [September 16, 2006, 10:12am UTC](https://forums.speedlife.net/t/calculating-speed-offset-with-bigger-wheels/99956 "2006-09-16T10:12:05Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![jdulberg](https://avatars.discourse-cdn.com/v4/letter/j/71e660/32.png) [@jdulberg](https://forums.speedlife.net/u/jdulberg)\
**Post date:** [September 16, 2006, 10:12am UTC](https://forums.speedlife.net/t/calculating-speed-offset-with-bigger-wheels/99956/1 "2006-09-16T10:12:05Z")

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I got pinched by the cops last night on HWY6 going 30 over but it sure didn’t appear that way on my speedo. Any suggestions on how to figure out the speed offset by increasing the size of the wheels from 50/16’s to 50/17’s?

The cop was pretty nice though, reduced it to 15 over - no points.

Thanks,  
Jason

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**Author:** ![cgguy](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/cgguy/32/5508_2.png) [@cgguy](https://forums.speedlife.net/u/cgguy)\
**Post date:** [September 16, 2006, 10:15am UTC](https://forums.speedlife.net/t/calculating-speed-offset-with-bigger-wheels/99956/2 "2006-09-16T10:15:49Z")

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Use this

[http://www.eunos.com/tirecalc/](http://www.eunos.com/tirecalc/)

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**Author:** ![jdulberg](https://avatars.discourse-cdn.com/v4/letter/j/71e660/32.png) [@jdulberg](https://forums.speedlife.net/u/jdulberg)\
**Post date:** [September 16, 2006, 11:01am UTC](https://forums.speedlife.net/t/calculating-speed-offset-with-bigger-wheels/99956/3 "2006-09-16T11:01:15Z")

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Thanks for the link… it calculated a 7.4% error at the spedometer.

Jason

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**Author:** ![Lith](https://avatars.discourse-cdn.com/v4/letter/l/fbc32d/32.png) [@Lith](https://forums.speedlife.net/u/Lith)\
**Post date:** [September 16, 2006, 11:12am UTC](https://forums.speedlife.net/t/calculating-speed-offset-with-bigger-wheels/99956/4 "2006-09-16T11:12:34Z")

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7.4% is huge… you should definitely get a smaller profile on those tires…

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**Author:** ![jdulberg](https://avatars.discourse-cdn.com/v4/letter/j/71e660/32.png) [@jdulberg](https://forums.speedlife.net/u/jdulberg)\
**Post date:** [September 16, 2006, 1:06pm UTC](https://forums.speedlife.net/t/calculating-speed-offset-with-bigger-wheels/99956/5 "2006-09-16T13:06:29Z")

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Yes it is quite a big margin of error. They are stock '05 350z rims & Bridgestone RE40 tires… I’m just waiting for the tires to go before I buy some new lower profile ones. I got new toyo proxes for my old 16" rims just before I got a deal on the 350z rims so that blew my budget for a little while.

Jason