In case you were thinking about changing your front sprocket...

M-Oorb · January 12th, 2009, 02:56 PM

Just finished changing my front sprocket. First I'd just like to say...if you are going to do this read and follow the DIY..I did step by step and the process was fairly simple and straight forward and worked well. On that note...I must stress that the nut the holds in the sprocket is verryyyyyy tight. I used a 15in breaker bar with a 2 foot piece of PVC pipe added for leverage with the bike in gear with the rear break on and PVC wedged in the back rim and it still took a lot of strength but it came.

I swapped the stock 14 tooth for a 15 and left the rear stock.So my overall impression...Well my engine is pretty much stock save for the removed snorkel and 1 washer under each jet in the carb. Adding the sprocket dropped my RPM's by about 500 across the range. I did a before and after run and this is what I found.

Stock 15 Tooth
1st Gear@ 20mph 6500RPM About 5900
2nd Gear@20mph 4500RPM 4000
3rd Gear @20mph 3750 3200
5th Gear @50mph 6500 Drop under 6000
6th Gear @50mph 5500 5000
6th Gear @ 60mph 7000 Drop under 6500

The Bike seems calmer because you are traveling at lower RPM's. I didn't notice any difference in acceleration in the lower gears but 5th and 6th gear accelerated a little slower...just barley noticeable. 1st gear is now slightly more usable and the need for a 7th gear is diminished slightly

.

Disclaimer: Obviously all our bikes are different so your results may vary. If you do plan on doing this and testing it out do it on a straight road with very little traffic and dont stare at you tach and speedo! I greatly recommend this mod

Edit: My little graph on top didnt come out like I wanted it too. The 1st rpm reading is stock and the 2nd is with the 15 tooth

Alex · January 12th, 2009, 04:50 PM

Umm, not to be a wise-ass, but you realize that the revs would change in every gear by exactly 14/15ths, right?

With the starting revs you posted, the new revs with the larger front sprocket have to be:

14-tooth......... 15-tooth
6500 (*14/15) = 6066.7
4500 (*14/15) = 4200
3750 (*14/15) = 3500
6500 (*14/15) = 6066.7
5500 (*14/15) = 5133.3
7000 (*14/15) = 6533.3

I realize the tach might not be telling you this exactly, but keep in mind that the tach is only accurate +/- 10% if you're lucky anyway. You changed the revolutions of the engine for a given speed by exactly 14/15ths, or about 7%. 7% may not seem like alot, but it does quiet things down on the highway a bit, and I appreciated the highway ride/comfort of the new gearing when we did the same mod on our '04. We've left the gearing stock on the '08 so far as Annie didn't like that the higher gearing made it slightly harder to start from a dead stop, especially if on a hill.

M-Oorb · January 12th, 2009, 05:21 PM

Yea I know what it would do exactly I was just posting what my bike was reading thats all but thanks for clearing that up.

Broom · January 12th, 2009, 08:43 PM

not everyone likes to do it the nerdy way, Alex.

kkim · January 12th, 2009, 08:45 PM

Quote:

Originally Posted by Broom

not everyone likes to do it the nerdy way, Alex.

bwahahaha....

Alex · January 12th, 2009, 09:18 PM

Quote:

Originally Posted by Broom

not everyone likes to do it the nerdy way, Alex.

I'm hesitant to imagine a community where using fractions is considered the nerdy way.

kkim · January 12th, 2009, 09:37 PM

Quote:

Originally Posted by Alex

I'm hesitant to imagine a community where using fractions is considered the nerdy way.

there you go again!!

Alex · January 12th, 2009, 09:40 PM

I know, I'm incorrigible!

January 12th, 2009, 02:56 PM	#1
M-Oorb ninjette.org sage Name: Matt Location: South East Florida/Rutgers University Join Date: Dec 2008 Motorcycle(s): 2008 250r (Fastest Color) Posts: 914	In case you were thinking about changing your front sprocket... Just finished changing my front sprocket. First I'd just like to say...if you are going to do this read and follow the DIY..I did step by step and the process was fairly simple and straight forward and worked well. On that note...I must stress that the nut the holds in the sprocket is verryyyyyy tight. I used a 15in breaker bar with a 2 foot piece of PVC pipe added for leverage with the bike in gear with the rear break on and PVC wedged in the back rim and it still took a lot of strength but it came. I swapped the stock 14 tooth for a 15 and left the rear stock.So my overall impression...Well my engine is pretty much stock save for the removed snorkel and 1 washer under each jet in the carb. Adding the sprocket dropped my RPM's by about 500 across the range. I did a before and after run and this is what I found. Stock 15 Tooth 1st Gear@ 20mph 6500RPM About 5900 2nd Gear@20mph 4500RPM 4000 3rd Gear @20mph 3750 3200 5th Gear @50mph 6500 Drop under 6000 6th Gear @50mph 5500 5000 6th Gear @ 60mph 7000 Drop under 6500 The Bike seems calmer because you are traveling at lower RPM's. I didn't notice any difference in acceleration in the lower gears but 5th and 6th gear accelerated a little slower...just barley noticeable. 1st gear is now slightly more usable and the need for a 7th gear is diminished slightly . Disclaimer: Obviously all our bikes are different so your results may vary. If you do plan on doing this and testing it out do it on a straight road with very little traffic and dont stare at you tach and speedo! I greatly recommend this mod Edit: My little graph on top didnt come out like I wanted it too. The 1st rpm reading is stock and the 2nd is with the 15 tooth

January 12th, 2009, 04:50 PM	#2
Alex ninjette.org dude Name: 1 guess :-) Location: SF Bay Area Join Date: Jun 2008 Motorcycle(s): '13 Ninja 300 (white, the fastest color!), '13 R1200RT, '14 CRF250L, '12 TT-R125LE Posts: Too much. Blog Entries: 7	Umm, not to be a wise-ass, but you realize that the revs would change in every gear by exactly 14/15ths, right? With the starting revs you posted, the new revs with the larger front sprocket have to be: 14-tooth......... 15-tooth 6500 (14/15) = 6066.7 4500 (14/15) = 4200 3750 (14/15) = 3500 6500 (14/15) = 6066.7 5500 (14/15) = 5133.3 7000 (14/15) = 6533.3 I realize the tach might not be telling you this exactly, but keep in mind that the tach is only accurate +/- 10% if you're lucky anyway. You changed the revolutions of the engine for a given speed by exactly 14/15ths, or about 7%. 7% may not seem like alot, but it does quiet things down on the highway a bit, and I appreciated the highway ride/comfort of the new gearing when we did the same mod on our '04. We've left the gearing stock on the '08 so far as Annie didn't like that the higher gearing made it slightly harder to start from a dead stop, especially if on a hill. __________________________________________________ Montgomery Street Motorcycle Club / cal24.com / crf250l.org / ninjette.org ninjette.org Terms of Service Shopping for motorcycle parts or equipment? Come here first. The friendliest Ninja 250R/300/400 forum on the internet! (especially Unregistered)

January 12th, 2009, 08:43 PM	#4
Broom Track Junkie Name: Jon Location: Dallas Join Date: Dec 2008 Motorcycle(s): '08 Ninja 250r Track Bike, DR350 commuter, KDX220 woods bike Posts: 602	not everyone likes to do it the nerdy way, Alex. __________________________________________________ Las Escobas -- Track Bikes Save Lives JonBroom.com

January 12th, 2009, 09:40 PM	#8
Alex ninjette.org dude Name: 1 guess :-) Location: SF Bay Area Join Date: Jun 2008 Motorcycle(s): '13 Ninja 300 (white, the fastest color!), '13 R1200RT, '14 CRF250L, '12 TT-R125LE Posts: Too much. Blog Entries: 7	I know, I'm incorrigible! __________________________________________________ Montgomery Street Motorcycle Club / cal24.com / crf250l.org / ninjette.org ninjette.org Terms of Service Shopping for motorcycle parts or equipment? Come here first. The friendliest Ninja 250R/300/400 forum on the internet! (especially Unregistered)

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January 12th, 2009, 05:21 PM	#3
M-Oorb ninjette.org sage Name: Matt Location: South East Florida/Rutgers University Join Date: Dec 2008 Motorcycle(s): 2008 250r (Fastest Color) Posts: 914	Yea I know what it would do exactly I was just posting what my bike was reading thats all but thanks for clearing that up.