Speedometer drive

[jpettigrew]

It appears that my 1970 CL175 originally had a 2.75-18 front tire. I didn't like any of the treads on the tires on that size so I bumped up to a 3.00-18. I now wonder about the accuracy of the speedometer. It doesn't appear that there are different speedo drives to compensate for this. Any thought?

 

[ancientdad]

My thought is that it won't change your speedo reading too much as it's only one size up, and the truth is it will probably make the already-optimistic speedo readings more close to reality as it will read slightly slower. It won't be much, maybe a couple mph, but our speedos are usually around 4 to 5 mph higher than reality anyway. No worries

 

[J-T]

You can determine what difference this will make by comparing the circumference of the two tires. If your new tire has a circumference 5% bigger than your old tire your actual speed will be 5% faster than it was at the same indicated speed with your old tire, Speedometers are often optimistic so you may have just cancelled out the built in error.

 

[tomeben]

Try this:

https://tiresize.com/comparison/

There are a few different calculators if you look through the entire site.


Tom - 1982 CM450E