# Do bigger wheels put less miles on your odometer?

**URL:** <https://boards.straightdope.com/t/do-bigger-wheels-put-less-miles-on-your-odometer/219985>\
**Category:** Factual Questions\
**Created:** [December 19, 2003, 4:16pm UTC](https://boards.straightdope.com/t/do-bigger-wheels-put-less-miles-on-your-odometer/219985 "2003-12-19T16:16:34Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![Rocketeer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rocketeer/32/4437_2.png) [@Rocketeer](https://boards.straightdope.com/u/Rocketeer)\
**Post date:** [December 19, 2003, 9:27pm UTC](https://boards.straightdope.com/t/do-bigger-wheels-put-less-miles-on-your-odometer/219985/21 "2003-12-19T21:27:32Z")

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There’s two ways to adjust the speedometer to compensate for oversize wheels and tires.

The speedometer cable has a “drive” gear on the end that inserts into the transmission; it engages a gear on the output shaft of the transmission. You can change the size (number of teeth) of the speedometer cable gear; typically it’s held on the cable by a little clip. The rule of thumb is that a change of one gear tooth on the drive gear(say, from 17 to 18) changes the speedometer by 4 miles/hour.

The second way, if changing the drive gear won’t get you there (no replacement gears available in the size you need)is to have a speedometer shop make up a little gearbox to go between the cable and the speedo. I had this done on my Hudson many years ago, and it worked great.

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**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\
**Post date:** [December 20, 2003, 12:48am UTC](https://boards.straightdope.com/t/do-bigger-wheels-put-less-miles-on-your-odometer/219985/22 "2003-12-20T00:48:48Z")

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Oh yeah. This reminds me of a guy who I used to know. Had a daughter commuting to college 60 miles away. He just flat-out DISCONNECTED the vehicle speed sensor in the car she drove for a few months at a time, and taught her to judge speed by RPMs in this (manual) vehicle.

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**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\
**Post date:** [December 20, 2003, 3:04am UTC](https://boards.straightdope.com/t/do-bigger-wheels-put-less-miles-on-your-odometer/219985/23 "2003-12-20T03:04:38Z")

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> [@](#):
>
> \*Originally posted by smam \*  
> \*\*Can I ask a related question? Is a point close to the centre of the wheel moving at the same speed as a point close to the outside of the wheel? \*\*

The center of the wheel is moving at the same speed as the car all of the time.

A point on the periphery (on the tread) moves at zero speed when in contact with the pavement and increases to a bit more that the speed of the car when at its highest point away from the pavement.

All points on the wheel trace a path known as a trochoid.  
“A curve traced by a point on or connected with a circle as the circle rolls along a fixed straight line.”

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“Beware of the Cog”

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