Best way to lower the gearing?

[Grindle]

I have a modern model Fireblade which i have no interest in using above 100 mph at any stage and would like to lower the gearing to make the bike livelier generally but mainly to lower the tall first gear.
So smaller front or bigger rear sprocket. Which way is best, 1 tooth less on front or 3 more on rear? I am not sure the chain will have enough length to deal with 3 more but i am sure 1 less at the front can be adjusted up.
Would a smaller front sprocket give any problems does anyone know?

[PIGINAWIG]

Drop the front sprocket down 1 tooth. Will actually make the speedo more accurate as they usually read 5-10% more than actual speed. Best way to check speed is gps on phone or nav.

And it pull wheelies easier, which is why you’re doing it right?

[Olivergt]

I'm not an expert, but I would have thought that a larger rear sprocket would be safer from an engineering perspective. The Front sprocket will only have a few teeth engaged with the chain at any given moment and changing to a smaller sprocket would reduce it even more.

Speedo would change with either a front or rear sprocket change.

I'm happy to be corrected though.

[SAS Tom]

Bigger rear sprocket is better as far as I’m aware. Better chain wear and changing he front changes anti lift or something to do with rear suspension.

[Steve Bass]

Changing the rear is better but in reality it will make very little difference.
Calculate the change or use Gearing Commander and you'll see what difference the various final drive combinations yield.
However going too small on the front and/or too big on the rear can negatively affect the suspension and bikes dynamics as it messes up the squat or anti squat properties depending on the Honda set up.

[SAS Tom]

That’s the one, anti squat not anti lift.

[gareth_r]

PIGINAWIG said:

Drop the front sprocket down 1 tooth. Will actually make the speedo more accurate as they usually read 5-10% more than actual speed...

Lowering the final drive gearing will actually make a gearbox-driven over-reading speedometer less accurate.

The gearbox output shaft will be turning faster at any given road speed, so the speedo drive will turn faster, and the speedometer will show a higher speed.

For example, if the sprockets are 16/48 (48 ÷ 16 = 3:1), and the speedo reads 60mph at a true 56mph, then changing the gearbox sprocket to 15 teeth (48 ÷ 15 = 3.2:1) will mean that the speedo will read 64mph (60 ÷ 3 × 3.2 = 64) at a true 56mph.

Conversely, a 17-tooth gearbox sprocket (48 ÷ 17 = 2.82:1) would make the speedo read 56 (60 ÷ 3 × 2.82 = 56.4) at a true 56.

[catso]

As said above, a bigger rear is a better solution as a smaller rear puts more load through the chain etc.

Depending on the current setup an increase of 3 on the rear would probably be about the same as one less on the front, however fitting a +3 on the rear will almost certainly require a new chain which, if you're doing it right also a new front sprocket etc. and so will cost considerably more to do it.

If you're changing the chain/sprockets anyway then this is the best route but if the chain and rear sprocket are good and you want the cheaper/easier option then a smaller front makes more sense, probably £20 or less as opposed to £150-ish.

[gareth_r]

Also, will a smaller gearbox sprocket cause the chain to rub (more) on the swinging arm?

Unlikely with a 1 tooth change, I guess.

[Benni]

Did all blades have the same primary drive ratio from crank to clutch ?

Leftfield opinion, and costly, but maybe there was a shorter ratio available ?

[SAS Tom]

Benni said:

Did all blades have the same primary drive ratio from crank to clutch ?

Leftfield opinion, and costly, but maybe there was a shorter ratio available ?

Why bother when a £15 sprocket will do the same thing?

[Ho Lee Kau]

1 tooth less in the front = 3 teeth more in the rear

potentially get Healtech Speedohealer
https://www.healtech-electronics.com/products/sh/

check this page for speeds/RPMs and the chain/sprocket wear:
https://www.gearingcommander.com/

(For my CBR600F4i I went -1 front (15), +2 rear (47) and installed speedohealer)

Edited by Ho Lee Kau on Friday 1st February 08:36

[Krikkit]

gareth_r said:

PIGINAWIG said:

Drop the front sprocket down 1 tooth. Will actually make the speedo more accurate as they usually read 5-10% more than actual speed...

Lowering the final drive gearing will actually make a gearbox-driven over-reading speedometer less accurate.

The gearbox output shaft will be turning faster at any given road speed, so the speedo drive will turn faster, and the speedometer will show a higher speed.

For example, if the sprockets are 16/48 (48 ÷ 16 = 3:1), and the speedo reads 60mph at a true 56mph, then changing the gearbox sprocket to 15 teeth (48 ÷ 15 = 3.2:1) will mean that the speedo will read 64mph (60 ÷ 3 × 3.2 = 64) at a true 56mph.

Conversely, a 17-tooth gearbox sprocket (48 ÷ 17 = 2.82:1) would make the speedo read 56 (60 ÷ 3 × 2.82 = 56.4) at a true 56.

Are they all using a gearbox sensor these days, or do they use the ABS wheel sensors to measure ground speed?

[Freakuk]

Krikkit said:

Are they all using a gearbox sensor these days, or do they use the ABS wheel sensors to measure ground speed?

That's what I was thinking???

[Grindle]

Thanks for the views guys, i did one less on the front and the bike feels much livelier. It's easier to pull away with less clutch work and top gear performance on the open road is better, i never need to change down hardly.
The bike has around 200 bhp, due to the increase in power the full Akrapovic system and Power Commander added and it has a free-flow air filter also. 200 bhp is fairly decent in a 1500 kgs car, so no surprise that it goes like absolute stink weighting 195 kgs.