Sprocket question

[TheWrightKat]

Ok I was reading on a parts website about sprocket upgrades. They talked about take off power vs top end speed.

Her is what I gathered from the site:

Larger rear and/or smaller front = more take off power

Larger front and/or smaller rear = higher top end speed

They claim for every tooth you drop you rear sprocket you gain about 2% higher top end. ie. 47 to a 46 would gain 2% top end speed.

Is this accurate?

[Black_peter]

No..
You need to calculate that on your own.
To be clear, thick back to you ten speed days

As the gearing approaches 1:1 the top speed increases.
(then the rear wheel would be spinning the same speed as the engine). You can do this two ways:
Increase the size of the front sprocket.
Decrease the size of the rear sprocket.

But as you might remember it was hard to pedal the ten speed in high gear. So as you match the ratios the engine looses mechanical advantage and wont get up and go as easy

If you do the math you'll see that in the 40 tooth range 41 to 49) every tooth removed is pretty darn close to 2%..

[philwecksr]

http://www.motorcycleanchor.com/motorcycle/how_to/mc_sprocketmath.html

[steves]

Calculating the sprocket drive ratio:

(Rear tooth count) / (front tooth count) = drive ratio

Example 1:
Bike ships stock with 47 tooth rear sprocket, 15 tooth front sprocket.
47 / 15 = 3.13333
So 3.13333 is the stock sprocket ratio.

Example 2:
You buy a 50 tooth rear sprocket and a 15 tooth front sprocket for the above bike.
50 / 15 = 3.33333
So 3.33333 is the new sprocket ratio.

http://www.motorcycleanchor.com/motorcycle/how_to/mc_sprocketmath.html

and

http://www.motorcycleanchor.com/katana/Katana_sprockets.html

[philwecksr]

HA I win!!

[steves]

HA I win!!

Ah, but you neglected to post the link to the page with all the math for a kat done...

[philwecksr]

BLAST!

[The CyberPoet]

Actually I WIN since I bothered to actually write that stuff up in the first place (but it really is nice seeing other people quote me verbatim -- it means someone is listening at least part of the time ).

WrightKat, although you could reduce your RPMs at any given cruising speed by going up in the front and down in the back (and reduce your fuel consumption during long hauls as well), the reality is that it almost assuredly won't give you a higher top-end speed. In 6th, the Kats normally can't reach the rev-limiter simply because of aeronautic drag, so anything that drops the ratio will go unused.

PS - You can't fit a 17 tooth front sprocket on a 98+ Kat. I know this because someone tried

Cheers,
=-= The CyberPoet

[MarkGodfrey]

I dropped one on the front for a little more "pulling power" lets face it .. if you use the bike regularly, you probably wont miss that couple of kms an hour at the top .. but getting off the lights quicker has more practical advantages .. just a non math opinion 8)

[TheWrightKat]

Actually I WIN since I bothered to actually write that stuff up in the first place (but it really is nice seeing other people quote me verbatim -- it means someone is listening at least part of the time ).

WrightKat, although you could reduce your RPMs at any given cruising speed by going up in the front and down in the back (and reduce your fuel consumption during long hauls as well), the reality is that it almost assuredly won't give you a higher top-end speed. In 6th, the Kats normally can't reach the rev-limiter simply because of aeronautic drag, so anything that drops the ratio will go unused.

PS - You can't fit a 17 tooth front sprocket on a 98+ Kat. I know this because someone tried

Cheers,
=-= The CyberPoet

Yeah that's pretty much what I had thought. It just didn't sound right reading it on that page that you could gain a significant amount of top end speed. I was thinking about going up to a 50 on the rear and leaving the front alone. That is until I read your right up. The extra torque on the take off sounded good until I started looking at the mpg loss. Loss of top end speed didn't bother me so much due to the fact that if I have it figured out right top end would still be in the 123 - 128 range which is 8 - 13 mph faster than I have gotten my Kat up to. Cyber you're the wizard I currently get around 40mpg if I went 15/50 what kind of estimate would you give on mpg?

[md86]

PLUS , if you gear it for the moon , will your bike have enough power to actually GET to it's new potential top speed anyway ? I doubt it .

[TheKlic]

My kat is geared 14/50
katanasport600's is 15/50

Mine is marginally quicker down low and we erm.. Opened them up on an empty freeway and we ran about the same speed, 142 ind for me, 150 ind for him (different speedo pickups)
my highway gas mileage went from 48-50 my in town mileage went from 45-42
BTW that puts me at 3.57:1
I love it, I'd highly recommend it.

[The CyberPoet]

I was thinking about going up to a 50 on the rear and leaving the front alone. That is until I read your right up. The extra torque on the take off sounded good until I started looking at the mpg loss. Loss of top end speed didn't bother me so much due to the fact that if I have it figured out right top end would still be in the 123 - 128 range which is 8 - 13 mph faster than I have gotten my Kat up to. Cyber you're the wizard I currently get around 40mpg if I went 15/50 what kind of estimate would you give on mpg?

If you're getting 40 mpg now at steady cruising, I would guess that you'd get something around 36 - 37 mpg afterwards doing exactly the same speeds. On the other hand, if you are spending an aweful lot of your time accelerating up to speed (because of the spacing & timing of traffic lights, stop signs, etc.), then you might actually see a small net gain, because the added ratio will help you accelerate up to your cruising speed quicker (based on the concept that you use much more fuel accelerating to a speed than you do once you get a neutral-throttle for flat-speed cruising).

Cheers,
=-= The CyberPoet

[Wade-Kat600]

I just put on a 15/45 configuration on mine - rpms are down to 5500=75mph - its nowhere near as poppy but it still has good guts - I used to run at much higher rpms with my 14/47 setup - so I'm guessing I am gonna get better mileage now - i'll let ya'll know.