Lets talk sprockets!

[Cochese]

Okay folks...

I will soon have a full exhaust, jet kit, filter, airbox and kleen sys delete all installed and dynoed. I need to bring the RPM's down. I took it on the interstate yesterday at 80 mph and it was too high for me.

I want to bring down the revs and not kill my power. With the listed mods, what tooth count do I need for front and rear? Do I need to do BOTH front and rear or just front? Or just rear??

Which brand is the best for weight and strength vs price?

I want black ones since black is fastest and undetected by radar.

Thanks!

[g21-30]

Originally Posted by Cochese

Okay folks...
I took it on the interstate yesterday at 80 mph and it was too high for me.

Of course, you were on "Police" business, i.e. road testing your new "pursuit" vehicle! Are you going to put white "swooshes" on it, in order to make it an official "black and white"?

[g21-30]

Also, check this DIY. It may answer some of your questions!

http://www.ninjette.org/forums/showthread.php?t=10273

[VeX]

I did this speal one time on another forum:

OK this got a little long...

First you have to figure your 'total gearing'. Just divide the front sprocket by the rear sprocket.

ie. .................................................. . And just for fun
14/45 --- 15/41 --- 15/42 --- 15/43 --- 14/49
.311 ---- .3659 --- .357 ----- .3488 --- .2857


Then start with something 'known' like the STOCK 14/45 gearing (which overall gearing is .311)

1st - 36.1
2nd - 52.57
3rd - 66.75
4th - 81.1
5th - 94.1
6th - 105.4

Then just find the difference between two sets of gearing and multiply each gear: and then multiply the known gearing (ie. the 14/45 max RPM speeds) by that number

------- 14/45 ---- 15/41 ---- 15/42 ---- 15/43 ---- 14/49
--------1.0 ------ 1.176 ---- 1.147 ----- 1.121 ---- .9186
1st ---- 36.1 ----- 42.45 ---- 41.4 ----- 40.5 ------ 33.2
2nd --- 52.57 ----- 61.8 ----- 60.3 ----- 58.9 ----- 48.3
3rd ---- 66.75 ---- 78.5 ----- 76.5 ------ 74.8 ----- 61.3
4th ---- 81.1 ----- 95.4 ------ 93 ------ 90.9 ----- 74.5
5th ---- 94.1 ----- 110.6 ---- 107.9 ---- 105.5 ----- 86.4
6th ---- 105.4 ---- 123.9 ---- 120.9 ---- 118.1 ----- 96.8

Then to figure what RPM you'd be spinning in say 6th gear, just figure out what that speed is compared to the top speed, so...

---------14/45 ---- 15/41 ---- 15/42 ---- 15/43 ---- 14/49
6th ----- 105.4 ---- 123.9 ---- 120.9 ---- 118.1 ---- 96.8
65 mph - 61.6% --- 52.4% ---- 53.7% --- 55% ------ 67%

Then multiply THAT percentage by the max RPM (13,000) to figure out the RPM you'd be spinning at that speed

--------- 14/45 ------ 15/41 ----- 15/42 ------ 15/43 ------ 14/49
65 mph -- 61.6% ----- 52.4% ----- 53.7% ----- 55% ------- 67%
--------- 8000 RPM -- 6810 RPM -- 6981 RPM -- 7150 RPM -- 8710 RPM

[kkim]

Cliff notes, Vex!!! what does he need??

[Cochese]

Originally Posted by g21-30

Also, check this DIY. It may answer some of your questions!

http://www.ninjette.org/forums/showthread.php?t=10273

Cool! Thanks!

Originally Posted by g21-30

Of course, you were on "Police" business, i.e. road testing your new "pursuit" vehicle! Are you going to put white "swooshes" on it, in order to make it an official "black and white"?

Here in God's country, the speed limit is 75 on I-25. Uncorrected 80 mph = about 72 mph in the real world...

Pig!

[Cochese]

Originally Posted by kkim

Cliff notes, Vex!!! what does he need??

No ****!

[Cochese]

Originally Posted by VeX

I did this speal one time on another forum:

OK this got a little long...

First you have to figure your 'total gearing'. Just divide the front sprocket by the rear sprocket.

ie. .................................................. . And just for fun
14/45 --- 15/41 --- 15/42 --- 15/43 --- 14/49
.311 ---- .3659 --- .357 ----- .3488 --- .2857


Then start with something 'known' like the STOCK 14/45 gearing (which overall gearing is .311)

1st - 36.1
2nd - 52.57
3rd - 66.75
4th - 81.1
5th - 94.1
6th - 105.4

Then just find the difference between two sets of gearing and multiply each gear: and then multiply the known gearing (ie. the 14/45 max RPM speeds) by that number

------- 14/45 ---- 15/41 ---- 15/42 ---- 15/43 ---- 14/49
--------1.0 ------ 1.176 ---- 1.147 ----- 1.121 ---- .9186
1st ---- 36.1 ----- 42.45 ---- 41.4 ----- 40.5 ------ 33.2
2nd --- 52.57 ----- 61.8 ----- 60.3 ----- 58.9 ----- 48.3
3rd ---- 66.75 ---- 78.5 ----- 76.5 ------ 74.8 ----- 61.3
4th ---- 81.1 ----- 95.4 ------ 93 ------ 90.9 ----- 74.5
5th ---- 94.1 ----- 110.6 ---- 107.9 ---- 105.5 ----- 86.4
6th ---- 105.4 ---- 123.9 ---- 120.9 ---- 118.1 ----- 96.8

Then to figure what RPM you'd be spinning in say 6th gear, just figure out what that speed is compared to the top speed, so...

---------14/45 ---- 15/41 ---- 15/42 ---- 15/43 ---- 14/49
6th ----- 105.4 ---- 123.9 ---- 120.9 ---- 118.1 ---- 96.8
65 mph - 61.6% --- 52.4% ---- 53.7% --- 55% ------ 67%

Then multiply THAT percentage by the max RPM (13,000) to figure out the RPM you'd be spinning at that speed

--------- 14/45 ------ 15/41 ----- 15/42 ------ 15/43 ------ 14/49
65 mph -- 61.6% ----- 52.4% ----- 53.7% ----- 55% ------- 67%
--------- 8000 RPM -- 6810 RPM -- 6981 RPM -- 7150 RPM -- 8710 RPM

Tag.

Now I can go find an engineer to figger out this here mathematics for me!

[Cochese]

So the lowest RPM in 6th gear without sacrificing power or acceleration below an acceptable level would be a 15/41 at 52.4% / 6810 RPM / 65 mph?

[kkim]

I believe most that re gear for the highway recommend the 15/41 combo.

[Cochese]

Thanks Kelly!

[noche_caliente]

This might also be helpful:
http://www.gearingcommander.com/

[g21-30]

Originally Posted by noche_caliente

This might also be helpful:
http://www.gearingcommander.com/

Very Good!!!

[Viper-Byte]

Originally Posted by noche_caliente

This might also be helpful:
http://www.gearingcommander.com/

That is very helpful!

I too am considering changing my sprockets as ~80% of my riding is at 100kph (62mph) and would like to have the bike rev lower at this speed.

Would running a 15/41 reduce accelleration by much? (changing the sprockets will be done after I have finished with my engine mods.)

[Alex]

Originally Posted by Viper-Byte

Would running a 15/41 reduce accelleration by much?

Yes. Once you're up and moving > 20 mph, the difference won't be as noticeable. But starting from a dead stop with 15/41 instead of 14/45 will be very noticeable.

[kkim]

Which is why this gearing mod should be done in conjunction with the jetting/power mods. It will sure help the anemic low end of a stock bike.

[Viper-Byte]

Originally Posted by Alex

Yes. Once you're up and moving > 20 mph, the difference won't be as noticeable. But starting from a dead stop with 15/41 instead of 14/45 will be very noticeable.

OK, I thought as much, question that will be hard to answer coming. What about the accelleration of the 15/41 combination with AP full exhaust, stock jets shimmed (possiblly dynojet stage 2 ket) and snorkel removed, Kleen air system removed, compared to a fully stock bike?

[Alex]

Simple question, yet impossible to answer simply. Much of what you'll get online (even from the very best forums like this one ) depends on "it feels fast", "it feels smoother", "it sounds better", "the powerband is more noticeable". All of these things may or may not be true, but it's really impossible to know. If it is of concern to you, take some objective performance measurements now, as accurately as you can, and then take the same measurements after the mods to see if there is a noticeable difference to you. One way is going to a drag night at a local drag strip, another way (perhaps not as accurate, but certainly easier to arrange) is simply timing acceleration runs yourself, or with a friend to man the timer.

[noche_caliente]

Originally Posted by Alex

One way is going to a drag night at a local drag strip, another way (perhaps not as accurate, but certainly easier to arrange) is simply timing acceleration runs yourself, or with a friend to man the timer.

If you or a friend have an i-phone you might be able to use the accelerometer on it....

[Alex]

As I read back my post (#18) I wasn't happy with it. You're looking for a simple answer, and you're entitled to one, so I'm going to give it another shot.

Increasing the gearing from 14/45 to 15/41 is a 17% increase. That is significantly taller.

A stock new-gen ninjette motor dynos somewhere around 26 hp at peak. Give or take 1 hp.

The strongest claim I've ever seen for a new-gen motor with every mod you've described will dyno somewhere around 31 hp at peak. A 19% increase in power.

Put those two pieces together, and a back-of-the-envelope guesstimate says you'll end up with roughly the same acceleration as a stock bike. But with about 17% less revs at highway speed. Perhaps in the 8000 range instead of the 9800 range at a good highway pace.

If it were me, I'd spend the money & time on trackdays and rider skill improvement rather than bike improvement, but last I checked I'm the only me.

[kkim]

Except the people doing this gearing mod are looking for a smoother running bike at prolonged highway speeds thru lowering the rpm at set speeds. No amount of track time will affect the bike's inherent mechanical abilities.

[Alex]

True. I just don't hear, feel, or sense much difference in a ninjette engine doing 8000 rpm vs. one doing 10000 rpm. Both of them feel like an engine that is spinning surprisingly quickly, yet given normal maintenance can be counted on to do so reliably for years.

People like to tweak, and there's no reason to discourage that. I just wish that along with the tweaking there were more objective measurements available (dyno tuning, acceleration testing, calibrated top-speed measurements) after the tweaking. It would give people a better idea of what to expect with the changes they were contemplating, like these sprocket mods or anything else.

[Viper-Byte]

Originally Posted by kkim

Which is why this gearing mod should be done in conjunction with the jetting/power mods. It will sure help the anemic low end of a stock bike.

Yeah, that is what I was planning.

Originally Posted by Alex

Simple question, yet impossible to answer simply. Much of what you'll get online (even from the very best forums like this one ) depends on "it feels fast", "it feels smoother", "it sounds better", "the powerband is more noticeable". All of these things may or may not be true, but it's really impossible to know. If it is of concern to you, take some objective performance measurements now, as accurately as you can, and then take the same measurements after the mods to see if there is a noticeable difference to you. One way is going to a drag night at a local drag strip, another way (perhaps not as accurate, but certainly easier to arrange) is simply timing acceleration runs yourself, or with a friend to man the timer.

Yeah, the main reason I ask is the passing power of the 250 is not a lot as it is (understandable as it IS only a 250 ) and to reduce that would not be good for me as I rely on accelleration often to pass slower vehicles quickly. I though as much, I guess it would have to be measured to give actual increases/decreases as a persons feeling of accelleration can be influenced by many things, but worst case I can always change the rear and allow it to rev higher than 15/41, but still lower than stock. I guess it is all down to my preference and I can only say what I want to run with when I actually try it.

Originally Posted by noche_caliente

If you or a friend have an i-phone you might be able to use the accelerometer on it....

That is not a bad idea.

Originally Posted by Alex

As I read back my post (#18) I wasn't happy with it. You're looking for a simple answer, and you're entitled to one, so I'm going to give it another shot.

Increasing the gearing from 14/45 to 15/41 is a 17% increase. That is significantly taller.

A stock new-gen ninjette motor dynos somewhere around 26 hp at peak. Give or take 1 hp.

The strongest claim I've ever seen for a new-gen motor with every mod you've described will dyno somewhere around 31 hp at peak. A 19% increase in power.

Put those two pieces together, and a back-of-the-envelope guesstimate says you'll end up with roughly the same acceleration as a stock bike. But with about 17% less revs at highway speed. Perhaps in the 8000 range instead of the 9800 range at a good highway pace.

If it were me, I'd spend the money & time on trackdays and rider skill improvement rather than bike improvement, but last I checked I'm the only me.

That is some very good and factual info Alex, just what I like to hear, I have noted it down. Thanks .

Kelly has it exactly right regarding the tracktime statement, I would like my bike to run as nice as I can get it before I start on track days.

Originally Posted by kkim

Except the people doing this gearing mod are looking for a smoother running bike at prolonged highway speeds thru lowering the rpm at set speeds. No amount of track time will affect the bike's inherent mechanical abilities.

[Sailariel]

It sounds like this whole gearing discussion is predicated on how your bike will be used. In my humble opinion, if the bike is used primarily on secondary roads and only periodically on turnpikes, the stock gearing is OK but not ideal. Riding on the New York State Thruway from Troy to Syracuse, I was keenly aware of how underpowered my bike was. Realistically you can only do so much to a 250. Were I making regular trips of this kind, I seriously doubt that the Ninjette would have been the bike I chose. The 650R would have been a much better choice. Since Route 5 paralells the Thruway, I can always use route 5 with the Ninjette and be in my element. 90% of ny riding is on secondary roads with a speed limit of 55 to 65mph. That`s perfectly fine for the 250. The scenery is also better and there is less traffic to contend with. A great part of the enjoyment one gets from riding a bike is being able to appreciate the sights and sounds of one`s surroundings.

[Broom]

maybe this was mentioned already, not sure....

don't forget that you need to buy a new chain too if you have very many miles on your current one. sprockets and chains need to be changed as a set or they'll wear each other out faster.

[Cochese]

Originally Posted by Broom

maybe this was mentioned already, not sure....

don't forget that you need to buy a new chain too if you have very many miles on your current one. sprockets and chains need to be changed as a set or they'll wear each other out faster.

I don't think my 60 miles have been too hard.

When the sprockets go one, it'll be in conjunction with a FP 3.0 kit, K&N, airbox and Kleen delete and Area P/HR1 bastard full exhaust.

Just need to pick the best sprockets from the available selection. My only requirements are the highway setup 15/41 with light/strong and hopefully black sprockets.

Suggestions on brand?