I was wrong! 205/65/16 CT is taller than stock 180/70 MC tire.

[Tropic traveler]

Butt dyno said the 205/65/16 Michelin HydroEdge I had on my '99 was upping the RPM more than the 180 Avon MC tire that was on my '97. As the pic shows I were wrong.


Anyhow, the CT is going to be a yard sale item unless any of my Florida Valk friends want it {has a hole near dead center} & the Avon is on.
Mounted & dismounted the tires on the garage floor! {Enter Tim Allen grunts here!!}
Tire machine??? I don't need no stinking tire machine!!!!


New metal stem & Dyna-beads installed.

[tank_post142]

larger tire = lower rpm. Am i wrong? 

[R J]

Splain to this ole timer how a taller REAR tire is going to up or decrease your RPM's.

[Stude]

RJ

 I think he is talking about in relationship to a set mph... 70mph with a taller tire compared
to a shorter tire at 70mph the RPM of the motor would be different

[MacDragon]

RJ

 I think he is talking about in relationship to a set mph... 70mph with a taller tire compared
to a shorter tire at 70mph the RPM of the motor would be different

That is correct.  Example: If the speedo was spot on for the smaller tire at 70mph... you would go exactly 70 miles in one hour. 
With a larger tire, with the same speedo setting at 70mph, the distance would be a bit further for the same revolution... in that same hour, you would actually travel,...say... 72 miles instead of 70 miles. (rough estimate) Speedo would have still said 70mph... but you were really travelling 72 mph with it indicating 70mph.

So with a larger tire, with a goal of going exactly 70 miles in distance, and the same speedo... you could run, say, 68mph (indicated) to stop at 70 miles.  Your RPMs would be, of course, lower with the larger tire to go the exact same distance. 

[Ferris Leets]

"So with a larger tire, with a goal of going exactly 70 miles in distance, and the same speedo... you could run, say, 68mph (indicated) to stop at 70 miles.

  Not on a bike where the odometer is on the FRONT tire.   

[Skinhead]

The speedo runs off the front tire, with a larger rear (tire), @ 70 mph indicated, your RPM would be slightly lower.

[BIG--T]

That taller tire would give you a higher gear thus turning lower rpm. Think it would be enough to improve mpg?

[R J]

"So with a larger tire, with a goal of going exactly 70 miles in distance, and the same speedo... you could run, say, 68mph (indicated) to stop at 70 miles.

  Not on a bike where the odometer is on the FRONT tire.   

You hit my question right on the button.

There ain't no firkin difference in RPM with either rear tire at 70 MPH.

[Willow]

There ain't no firkin difference in RPM with either rear tire at 70 MPH.

Well, yes, there is. 

Rear tire size impacts the RPM at any given speed.  Front tire size impacts speedometer reading at any given speed.    

[The Anvil]

"So with a larger tire, with a goal of going exactly 70 miles in distance, and the same speedo... you could run, say, 68mph (indicated) to stop at 70 miles.

  Not on a bike where the odometer is on the FRONT tire.   

You hit my question right on the button.

There ain't no firkin difference in RPM with either rear tire at 70 MPH.

Oh yes there is. It might be minimal when the overall diameter/curcumference is minimal but rpm at a given speed absolutely does change with tire diameter/circumference changes. Which is why people change gearing on 4X4's that get upsized tires.

[designer]

That taller tire would give you a higher gear thus turning lower rpm. Think it would be enough to improve mpg?

In theory, you would get better MPG since the RPM to do 70MPH is lower with a taller (larger circumference) back tire.  Each rotation would take you a little farther down the road without chaning the RPM's.  so, if you slowed down to maintain the 70MPH you would be going slower... lower RPM's.... less gas.  Since the drive tire is the back its the only one that counts when calculating RPM / MPH / MPG, the front is only the witness.


Myth busters did the same thing with an airplane trying to disprove the airplane wouldn't take off if it was on a converey belt, but the drive was the engine prop not the wheels.

[Stude]

 Sell your house move to Missouri... the show me state. Take your bike for a ride and when you reach 70mph mark where the pointer is on the tach. Then mount a taller tire on your bike and when you reach 70mph again mark where the pointer is at on the tack.
 

[designer]

Sell your house move to Missouri... the show me state. Take your bike for a ride and when you reach 70mph mark where the pointer is on the tach. Then mount a taller tire on your bike and when you reach 70mph again mark where the pointer is at on the tack.
 

Won't work, if the tire is taller the speedo will be off which will give a false reading on the tach.  You'll need a gps for you speed.  But if your willing to move to Missouri then that little bit will be the lest of your expenses......

[Willow]

Won't work, if the tire is taller the speedo will be off which will give a false reading on the tach.  

The speedometer is run off the front wheel.  No rear tire changes that reading.

The tach measures engine speed.  No tire distorts that reading. 

[designer]

Won't work, if the tire is taller the speedo will be off which will give a false reading on the tach. 

The speedometer is run off the front wheel.  No rear tire changes that reading.

The tach measures engine speed.  No tire distorts that reading. 

You are correct, I hate it when I confuse myself. 

[Willow]

You are correct, I hate it when I confuse myself. 

You're in good company.  We all hate it.  Most of us do it from time to time to remind ourselves how much we hate it.