I don't think the gear ratio has been changed. The rear sprocket has a couple more teeth which raises the final drive ratio to the rear wheel.

 

i understand Dancemax question as, being italian, I wondered somewhat at the term. I surmised it was about running the engine at low rpm on too high a gear, but wasn't sure till some time ago I could understand due to context it meant actually that.
It's called "guidare sottocoppia" in italian, that means literally - to ride (or drive, the term is the same both for cars and bikes in italian) "undertorqued"-
This doesn't mean I ride or drive lugging my engine.
Why lugging is bad?
Because the power of the engine is discharged on the engine's mechanical parts themselves rather than in speed and acceleration.
When it's so bad that you get pinging, it's actually like firing a gun with another bullet stuck in the barrel. NOT good.
You may ovalize your cylinder, punch a hole in a piston, get a flywheel out of timing, crack a connecting rod and other such amenities...


Lurching is riding in lurches, with the bike cracking on abruptly then coming to a sudden slow down. It's dangerous to stability.
It happens when you try to maintain a slow speed at slow gear (usually first gear) using the throttle rather than the clutch.
HD have oil bath cluthces that could take a Peterbilt eighteen wheeler... use it to ride slow and smooth.

 

OK: now let me get a handle on ratio business. I understand a ratio of 3 means 3:1, that the engine shaft turns 3 times to transmit 1 turn at the end of transmission?...this will be low gear. IN a ratio of 1, being writte as 1:1, the engine shaft and transmission turning is equal and this is high gear. Is that right. In an ordinary bicycle we accomplish this by the rear sprockets, changing from bigger sprocket (low) to smaller (high) but dont know how it is accomplished in a motor cycle or car. Enlighten

 

Exactly the same way, plus the transmission.
There is a "fixed" ratio, and a variable one.

The sprocket to crown ratio, or differential ratio, also know as "final" is the equivalent of that of the bicycle, and is fixed.

Moreover you have a primary in the motorcycle, bringing power from engine to transmission, which contributes to the fixed part.

Unlike bycicles, where you change gear by changing the sprocket and or crown the chain rides on, in motorcycles this happens much as in cars, as it would be impractical (impossible) to make a gear drive like that of a bycicle.
There are two shaft, a direct one, connected to the engine via clutch and primary (or clutch on a car) and a driven one. They both have gears.
The gears are fixed on one shaft, free on the others, and are connected to the shaft by selectors driven by the gear pedal or lever.
Selectors connect a given gear to the shaft, changing the transmission ratio.
On www.howstuffworks.com you may find nice animations on how a sequential selector (like that of a bike) or an "H" selector actually work.
Since a shaft wil turn at different speeds, depending on which gears are engaged, you need both shafts to turn at the same speed to shift into the new gear. Going up it's easy: you just need to let the shaft drop to the new rev speed.
Going down is another thing entirely. You need to rev up the driven shaft to the primary shaft speed to engage the new gear.
This was done on cars by putting the selector in idle, releasing the clutch and revving up briefly the engine, then pushing the clutch again and shifting into the new gear.
Modern drives have synchros, which are sort of "clutches" which bring the shaft up to speed.
Sequential drives, with dog selectors don't need synchros. They aren't used in cars due to their noise.

 

+1

 

Buon giorno Max,
Very nice explaination about lugging and you are exactly correct about the ratios too. The way you would determine the gear reduction ratio on your motorcycle is exactly as you described, except it is accomplished in the transmission vs. the rear sprocket. This is why a 1:1 RR on the HD six speed and a 1:1 RR on a five speed are different. As someone else said, they added teeth to the rear sprocket witch lowered the final drive ratio. If they had added the teeth without adding the middle gear, the bike would not have had the tourque required to use each gear smoothly throughout the range. If they had added a gear without adding a tooth, what would have been the point?

The RR of a Baker 6 speed, made to replace earlier 5 speeds, is 0.86:1. They basically left the middle gearing the same, and added a high speed gear. I could accomplish the same thing by adding a tooth to my rear sprocket on my Shovel. I would gain highway "rideability" but I would lose performance in town.

As to exactly how it is accomplished in the transmission, you can look at the pic that Gumpy posted (post 16 this thread). The gear box used two shafts that mesh via gears. The ratio is determined by the size difference of those two gears. It is the same as your bicycle, except the gears are touching, and not being connected by a chain.

va bene?

 

Damn Octane..... you must type faster than I do....

I hacked out that reply and you explained it better than I did, with a link too.... before I could get done.........