Interesting read on Final Drive Gear ratio's

[CIP57_imp]

Good article:
http://www.superstreetbike.com/how-to/bigger-rear-sprocket-makes-more-horsepower-mythbusters

 

[the Ferret]

Surely nobody really thinks altering gearing makes more horsepower!

 

[Inhouse Bob]

Surely nobody really thinks altering gearing makes more horsepower!

Only adding stickers adds horsepower.

 

[the Ferret]

now that's true :rofl:

 

[CIP57_imp]

Surely nobody really thinks altering gearing makes more horsepower!

Correct Mickey, you would think it would remain unchanged, but to lose over 2 LB FT of torque on top is surprising with -1 +2 which is a common change.

 

[CA200_imp]

The red ones have more HP.

 

[Inhouse Bob]

The red ones have more HP.

No need to be stating the obvious :banana::banana:

 

[Rocky_imp]

The red ones have more HP.

Sorry, you got it wrong, only the Spencer blue ones have more HP

 

[CIP57_imp]

OK OK have a laugh at my expense, I can take it!! Wait till your sleeping at the rally and I change your gears

 

[Inhouse Bob]

OK OK have a laugh at my expense, I can take it!! Wait till your sleeping at the rally and I change your gears

No worries. My bike sleeps next to me in bed. Please don't judge me.

As to the original article... there isn't a horsepower change when changing sprockets, but you are changing the way that horsepower is applied. With a lower gear ratio you get to use more of that horsepower off the line, and a higher ratio gives you a higher top end speed. that is assuming that you have enough horsepower to handle the higher gear ratio.

I dreamed last night that someone stole my bike and the insurance company bought me a 2014 DLX. I liked the six speed! Woke up grinning and my wife hit me. Not sure what she thought I was dreaming of...

 

[the Ferret]

Without dyno charts it's difficult to see what is happening with horsepower and torque and I notice they quoted horsepower at torque and not peak horsepower at a given rpm and peak torque at a given rpm. Changing sprockets just rearranges where the peak hp and torque numbers come in the rev zone.

When I raced motocross we had a stack of front and rear sprockets on a dowel for use at different tracks. If it was a tight track you geared it down, if it was an open track with long straightaways you geared it up. Find the right gearing for a particular track and you'd write it down so the next time you came to race you could concetrate on lines and not working to get the gearing right on the bike.

It's why MotoGP bikes have cassette type gear boxes. They have gear clusters already set up for each track which they have recorded from past races.