Effects of changing sprockets


UselessPickles

New Member
Since power and torque are directly related through RPMs, I could theoretically get the torque info from a power chart, but the precision of the torque at lower RPMs would be pretty crappy. A high resolution SAE-corrected torque chart with a thin torque line would give me what I need (but not a photo of one, because the chart could be rotated slightly and warped by the camera lens, making it difficult to get accurate measurements). An original dyno run file is even better, because I can load it into DynoJet's viewer and export raw data in 100 RPM increments, rather than taking measurements from a picture.
 

linkgt

Member
Since power and torque are directly related through RPMs, I could theoretically get the torque info from a power chart, but the precision of the torque at lower RPMs would be pretty crappy. A high resolution SAE-corrected torque chart with a thin torque line would give me what I need (but not a photo of one, because the chart could be rotated slightly and warped by the camera lens, making it difficult to get accurate measurements). An original dyno run file is even better, because I can load it into DynoJet's viewer and export raw data in 100 RPM increments, rather than taking measurements from a picture.

If someone can give pickles the info that would be great. I'm curious to see top speed with +1 and exhaust mod+Power commander. I know that when I went +1 front, top speed was reduced for reasons people have mentioned here (Hp needed to overcome drag, etc)
 

UselessPickles

New Member
I'm curious to see top speed with +1 and exhaust mod+Power commander.
Probably not much higher than stock exhaust with +1 up front. Power of drag increases based on the cube of speed. The TwoBros dyno chart shows a 7.7% gain in peak HP. Best case scenario (if the shape of the HP curve near the peak happens to have shifted up in RPMs a certain amount), that could result in a 2.5% gain in top speed (cube root of 1.077 = 1.025), which would be an extra 3mph. Best case scenario is unlikely, so I predict a 1.5-2mph gain.

I know that when I went +1 front, top speed was reduced for reasons people have mentioned here (Hp needed to overcome drag, etc)
Top speed should increase (but barely; look at my comparisons). You probably saw a decrease in top speed because you were looking at your speedometer, which was about 6% optimistic at stock gearing, but nearly correct with +1 up front, which would give the appearance of about a 4mph loss in top speed. If you are comparing actual GPS speed before/after, then it was probably just a difference in wind or slope of the road that caused the decrease.
 

linkgt

Member
Probably not much higher than stock exhaust with +1 up front. Power of drag increases based on the cube of speed. The TwoBros dyno chart shows a 7.7% gain in peak HP. Best case scenario (if the shape of the HP curve near the peak happens to have shifted up in RPMs a certain amount), that could result in a 2.5% gain in top speed (cube root of 1.077 = 1.025), which would be an extra 3mph. Best case scenario is unlikely, so I predict a 1.5-2mph gain.



Top speed should increase (but barely; look at my comparisons). You probably saw a decrease in top speed because you were looking at your speedometer, which was about 6% optimistic at stock gearing, but nearly correct with +1 up front, which would give the appearance of about a 4mph loss in top speed. If you are comparing actual GPS speed before/after, then it was probably just a difference in wind or slope of the road that caused the decrease.
You could be right. Last time I tried to test top speed was late October and that day was a lot more windy than usual and also felt more drag as well. My buddy however seemed unaffected and got more ahead of me than he usually would, but now I'm guessing it's because of the hurt in acceleration of the +1 up front(causing the bike to take longer to get to top speed) instead of top speed actually decreasing.
 

mische42

Member
First of all, THANK YOU! pickles for doing these calculations...extremely informative (and I enjoy this stuff being an aeronautical engineer myslef).

After reading all of these posts and looking over the info, here is what I summarize.

Regardless of the gearing combination we are talking fraction of a second differences across the board and in all cases less that 5 MPH differences in speed. For a bike like the FZ6R and the typical experience of teh riders on them...my question is, is it really worth it for these fractional gains/losses??

My half cent would simply be, put a +1 on the front and be happy that your speedo and odometer are correct...anything beyond that just seems frivilous on this bike.
 
Y

yellowfz

What does -1+0 calculate out at if you do hard takeoff second gear rather than first (giving away secret)? :D This has always given me good results. Try it even with stock setup it works real well (Warning for experienced riders only).
 

UselessPickles

New Member
If you can launch faster on the FZ6R in 2nd gear, then you are doing something wrong. 1st gear gives you more acceleration, and not so much that it's unusable.

The only way a 2nd gear launch would be better is if 1st gear is so excessively powerful AND short that it's unusable because you redline very quickly while spinning tires uncontrollably. This has actually been reported to be true for one of those small almost-a-go-kart cars (can't remember if it was the Ariel Atom, or the T-Rex).

The FZ6R definitely does not suffer from this problem. As requested, here's some 1st and 2nd gear launch comparisons with -1/+0 sprockets:

1/4 mile (hard launch)
1st: 12.24s @ 104.6mph
2nd: 12.76s @ 104.5mph

0-60mph (hard launch)
1st: 3.62s
2nd: 4.23s

0-100mph (hard launch)
1st: 10.60s
2nd: 11.21s
 

Marthy

World Most Bad A$$ 6R
Elite Member

dste0395

New Member
So the most likely way you got to 145mph was by using -1/+2 gearing and looking at your speedometer.

Redline is at 11500rpm. You can't go faster than that. With stock gearing, that would be 138mph (but you can't get there due to drag). With -1/+2 gearing, you would be at 124mph (actual speed). An actual speed of 145mph is just impossible.

A stock bike has already been shown to have about 6% speedo error (+1/+0 sprockets are 6.25% taller than stock and seem to make the speedo accurate).

Stock gearing is 11.3% taller than -1/+2.

That gives a grand total of 18.3% speedo error with -1/+2 gearing, so your 145mph speedo reading would be an actual speed of 145mph / 1.183 = 122.6mph, which is very close to my simulated top speed of 122.9mph.
I am a complete NOOB when it comes to any of this. I am trying to change my speedometer (stock) on the FZ6R to the DL Digital Universal Speedo or something else. The dealer that is assisting me wants to know my stock ratios, do you have an answer for that? Can I assume it is (+1/+0) based on your information above?
 

Marthy

World Most Bad A$$ 6R
Elite Member

JSP

Super Moderator
I am a complete NOOB when it comes to any of this. I am trying to change my speedometer (stock) on the FZ6R to the DL Digital Universal Speedo or something else. The dealer that is assisting me wants to know my stock ratios, do you have an answer for that? Can I assume it is (+1/+0) based on your information above?

Think he may want this?

Primary reduction ratio 86/44 (1.955) Spur gear

Secondary reduction ratio 46/16 (2.875) Sprockets rear and front

1st 37/13 (2.846)
2nd 37/19 (1.947)
3rd 28/18 (1.556)
4th 32/24 (1.333)
5th 25/21 (1.190)
6th 25/24 (1.083)
 

dste0395

New Member
Speedometer Ratios

Do you all know our stock speedometer ratios? Yamaha cannot help me, they said if it isn't published in their service manual then they cannot get it.
 

Marthy

World Most Bad A$$ 6R
Elite Member

dste0395

New Member
Tell those idiot to go F%^$ themself! The speedo is about 5% off. Read the instructions on how to play with the speedo healer then use a GPS or phone tape on your fuel tank and go up or down to calibrate the speedo.

If they're going to rape you $80.00 +/hour to tell you there clueless... do it yourself my friend!
I am going to change the speedo myself but I need a new speedo, I don't want to use my original. I am trying to tell oldbikebarn what my stock speedo ratio's are so I can order the right replacement speedo. But no one seems to know what our stock speedo ratios are.

If it is as easy as what you say above I can do that, but I still need to know which magnetic speedo will work with my bike. That is why i may just do the DL Digital Universal and attach the magnets to the front wheel.

Another issue I am going to have is how to run the turn signals and rear brake light once I have replaced our stock console, but I can figure that out when the time comes.
 

Marthy

World Most Bad A$$ 6R
Elite Member

dste0395

New Member
Got it. Your speedo is a Hall effect sensor on the top of the gearbox. If Im right it read the speed out a gear. Remove the sensor and count the tooth on that gear with a sharpy and turn the wheel (in gear) That should be one if the gear that JSP mention.

Sent from my LG-P925 using Tapatalk 2
So If i get the Universal speedo Koso DL Universal Electronic Speedometer - Electrical - sportbike - Superbike Toy Store - 1.866.999.9823 and go with the old school front wheel sensor, then I can ditch the current speedo right?

If I ditch the current speedo then how do I control my turn signals and brake light, would that mean that the turn signals and brake light have to have independent wiring now?

Again, sorry, total NOOB at this stuff.
 


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