[MOMZ]

It was asked if installing a larger tire would effect the speedometer error and if the speedo drive is on the front or rear.

The speedometer gets a digital speed signal from a electronic component in drive line output.
So the answer is NO!,....no real connection to the wheels, but it may effect the speedo error to a relatively minor amount. Odometer and Speedometer accuracy varies with tire sizes, but also with tire wear.

I have experimented with this for over 40 years and have come to the conclusion that most speedometers will read faster than the indicated speed traveled. So unless your are replacing your rear wheel/tire with something utterly radical,.....don't worry.

 

[Max Kool]

The speedometer gets a digital speed signal from a electronic component in drive line output.

...which has a direct relationship with one of the wheels... either the front or the rear. Don't they use one of the ABS rotors for speed pickup (I would guess the rear one)?

Going up a tire size in the rear will most likely make the speedo more accurate, that I agree on. But definitely there is a "direct" connection between the wheel and the speedo. A friend of mine used to water cut custom ABS rotors for BMW's to adjust for a 21" front wheel on GS's...

 

[floyd]

Thanks, MOMZ!

I guess my biggest concern is more with the odometer reading. An inaccurate speedo plus or minus 1-2 mph isn't a big deal to me. I just don't want the odometer to be adding mileage that isn't being driven.

 

[reinie]

A tire with a larger outside diameter will turn fewer revolutions per mile and give a lower odometer reading and a tire with a smaller O.D. will turn more revolutions per mile and show a higher odometer reading.

 

[floyd]

A tire with a larger outside diameter will turn fewer revolutions per mile and give a lower odometer reading and a tire with a smaller O.D. will turn more revolutions per mile and show a higher odometer reading.

Makes sense...
The overall diameter of the 180/65 tire is .2 inches (25.2" or 79.2" circumference) smaller than the stock 150/80 tire (25.4" or 79.9" circumference).

If there are any mathematicians out there (I was awful at math in high school): If I were to travel 500 miles on the stock tire, then trace that same route on the 180/65 tire, how many miles will the odometer say I've traveled?

 

[Max Kool]

A 180/65 tire would give you (79.9"-79.2")/79.9"x100%x500miles =3.5miles more on the odometer over a 500 mile distance...

 

[floyd]

A 180/65 tire would give you (79.9"-79.2")/79.9"x100%x500miles =3.5miles more on the odometer over a 500 mile distance...

So if I install the smaller tire and ride it for 8,000 miles, the speedometer will show an extra 56 miles. I can live with that.

 

[Max Kool]

Yep, negligible...

 

[riteonjohn]

In the grand scheme of things—Who cares if she’s kind of “off” by a little when she looks like this:

If your wife was hot AF, she’s not gonna be perfect.

Instagram: @rite_on_john
(Not an engineer)


Sent from my iPhone using Tapatalk

 

[floyd]

Right on, riteonjohn!

 

[floyd]

A 180/65 tire would give you (79.9"-79.2")/79.9"x100%x500miles =3.5miles more on the odometer over a 500 mile distance...

You were obviously paying attention in math class while I was sleeping!

 

[mbrownp1]

If your wife was hot AF, she’s not gonna be perfect.

She is. And she is.

 

[floyd]

A good number of owners have installed a 180/65 tire on their Bobbers. But so far no standard Scout owner has commented on installing the 180/65 tire. I'm thinking the Bobber's anatomy is similar/same to the regular Scout, so fitting "shouldn't" be a problem. But I would like the peace of mind I get with a Scout owner explaining he/she has installed the 180/65 without any issues.

 

[George4]

Wouldn't a 180 70 r16 be a closer overall diameter to the factory size as opposed to a 180 65 r16?

 

[floyd]

Wouldn't a 180 70 r16 be a closer overall diameter to the factory size as opposed to a 180 65 r16?

Hmm...
I wish I could find a tire-size comparison website for motorcycle tires. Found a couple for auto tires but nothing for bikes.

 

[George4]

It would still be the same concept
150 80/16 ------- 793 Revs/Mile *stock tire
180 65/16 ------- 800 Revs/Mile
180 70/16 ------- 778 Revs/Mile

Its pretty close. Just wondering why anyone would go with a 65 aspect ratio if a 70 ratio would be closer. But a 180 65/16 would definitely give more room with it being a little shorter as opposed to taller.