Speedometer gear changes (on tire size change)

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Due to relative lack of availability of 14” tires, I’m thinking about buying new rims/tires.  I haven’t landed on the size as of yet, but I am curious as to the impact of a larger diameter tire on the accuracy of the speedometer.

I am curious as to if it might be a good idea to think about changing out the speedometer gear at the same time as the tire size change (to limit unwanted speeding tickets).  Given the use of KPH (kilometres per hour) here in Canada, in combination with a stock mph speedo, it can be easy to get cross-threaded as to how fast your going.

 I see there are formulas all over the internet for proper gear teeth calculations to work with a C4 automatic transmission.

Any rule of thumb, you guys use on the topic, or is this something to just ignore (if it doesn’t make a material difference to the Speedo?)  Presumably if I make a radical change (say from 14” -> 17” or 18”) it makes a larger difference on the speedo...and should be a larger concern for a speedo gear change.

As always, I appreciate any advice from the experts on the forum

thx

rd-72

 

MikeGriese

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Don C

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The spreadsheet in this thread may help you.



And the spreadsheet in this thread will help you with tire sizes




 
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