Can somone calculate tire size change?

[mcdonaldroadcapt]

I have an 08 Trog running the standard 225/60/15 rear tires. These tires have a diameter of 25.6 and at 70MPH I am turning 2750 RPM. If I drop down to a smaller diameter tire size of 225/50/15 which has a 23.9 diameter, what will be the difference in RPM at 70MPH?
225 60 15 25.6 Diamenter= 2750RPM @ 70 MPH
225 50 15 23.9 Diameter = ? @ 70MPH.

I know speedo will need to reclaibrated but no problem with that.

Would like to make this change if possible in lieu of having to change out the front sprocket from 32 to 30. Need lower gearing for pulling my trailer.

Any good math guys out there? Thanks.

[iaff84]

I have an 08 Trog running the standard 225/60/15 rear tires. These tires have a diameter of 25.6 and at 70MPH I am turning 2750 RPM. If I drop down to a smaller diameter tire size of 225/50/15 which has a 23.9 diameter, what will be the difference in RPM at 70MPH?
225 60 15 25.6 Diamenter= 2750RPM @ 70 MPH
225 50 15 23.9 Diameter = ? @ 70MPH.

I know speedo will need to reclaibrated but no problem with that.

Would like to make this change if possible in lieu of having to change out the front sprocket from 32 to 30. Need lower gearing for pulling my trailer.

Any good math guys out there? Thanks.

Just a guess: .072 increase or 2948 RPM. Like I said, a guess. Been awhile since high school math!!!!!

[mcdonaldroadcapt]

You're doing better than me. I can't even remember high school math at 75 years old.

[FLTR2008TRIKE]

60 on your Speedo you will be doing 56
70 on the Speedo you will be doing 65

Your rpms will increase around 150 to 200 rpms with the smaller diameter tires.

Evo Industries also offers a 49 tooth clutch assembly or rear primary sprocket that will give you a little more torque and higher rpms

[87Trike1200]

Here is a handy tire size calculator. Enter what you have now, then enter various size options in the proper boxes. Whala! All the info you are probably looking for (and then some) is calculated for you.

Hope this helps... click HERE

[screwball]

Changing from a 25.6" diameter to a 23.9" diameter will give you a 7% reduction in gearing.

Changing from a 32 tooth to a 30 will give you exactly the same 7% reduction.

Sounds like a push.

IF IT WERE ME I'd leave well enough alone, downshift if necessary. You are talking a lot of money for a 7% reduction in RPM.

Good Luck and happy decision making

[mcdonaldroadcapt]

Changing from a 25.6" diameter to a 23.9" diameter will give you a 7% reduction in gearing.

Changing from a 32 tooth to a 30 will give you exactly the same 7% reduction.

Sounds like a push.

IF IT WERE ME I'd leave well enough alone, downshift if necessary. You are talking a lot of money for a 7% reduction in RPM.

Good Luck and happy decision making

My problem is taking off from idle pulling my trailer. Gearing just too tall. Got my 225x50's coming. Thanks for reply.

[icebite1]

Here is another handy calculator http://www.tacomaworld.com/forum/tir...0r18-100-80r19