Yamaha R6 Forum: YZF-R6 Forums banner

1 - 6 of 6 Posts

·
2 wheels > 4 wheels
Joined
·
123 Posts
Discussion Starter · #1 · (Edited)
OK... so.... I get the point of going -1/+1 or -1/+2 for sprockets. All the bikes I have ever owned (2 so far), I changed to quick accelerating ratio. Although it feels great accelerating so fast, I want to rant about the pros & cons of this.

Pros:
1. Obviously quicker launch
2. Higher torque due to higher RPM
3. Higher torque due to overall gear ratio

Check the dyno graph. The gearing chart is for 15/49 ratio for a 2005 R6. When you go this route, you'll be at a higher RPM at any given speed than stock ratio. So as a result, you'll be demanding higher torque at any given speed (at a constant gear). Sounds like a win-win?
Screenshot_20210501-090321_Excel.jpg


Cons/counter arguments:
1. Besides other sportbikes (600cc +) or 7-digit $ supercars, you launch quicker than anyone on the road even at stock ratio. So why the need for higher acceleration?
2. Speedo healer hides the true engine mileage. At least on my 2005, mileage is calculated based on engine output speed. So tinkering with this, your display will show a significantly less number. For example, going from 16/48 to 15/49, my odometer will show ~9% error. Might not sound much, but it is significant.
3. Unless you're well on top of your maintenance schedule, this is skew your intervals. You'll have to maintain at 92% of the recommended intervals.
4. You'll lose top speed on a track. You'll top out at 92% of those with stock ratios (debatable. See EDIT)
5. Like most, if you run lower tire psi than recommended, this error will only get worse. And add to that tire wear.
6. Finally, the tension in the chain is directly proportional to the gear ratio. Running 15/49 instead of 16/48, your chain tension will accordingly be ~9% higher.

Now, if you go -1/+2 instead, the error is even larger.
There it goes! Now I'm crawling back to my basement.

** EDIT: your bike's top speed is mostly limited by aero drag. Let's say 150 mph is your top. One could argue that you'll be drawing higher torque at 150 than stock, and hence higher thrust forward into the air (if the power is linear). Might even gain 1 or 2 mph! But since the dyno graphs show a drop in HP after the peak, it's debatable for this bike.
 

·
Registered
Joined
·
2,741 Posts
Since I typically run lower/lowest necessary shift point for the desired acceleration on any vehicle, I'd probably only end up changing my shift points.

For me, it might result with additional shifting.
(there are a lot of folks here that seem to do little/no throttle control for hills - so they routinely loose 5 - 15MPH on short inclines)

Manual shifters often rotate way higher than is necessary.
8,000 RPM means that a piston moves up AND down, more than 133 times in a single second.
That means it takes just 0.0075 of a second for that up AND down motion.
Can anyone imagine the forces involved with that piston's directional changes alone?
(particularly on the exhaust stroke where it's being pulled instead of pushed back down)

As mentioned, this greatly reduces unnecessary wear and noise levels.
(note: I wear ear plugs)
 

·
2 wheels > 4 wheels
Joined
·
123 Posts
Discussion Starter · #3 ·
I can post some more pictures of my spreadsheet graphs tomorrow when I get to my laptop if anyone's interested, but...

Unless the bike is being tuned for a specific race track where you ought to be in a specific gear coming out of a specific turn, the only upside with going -1/+1 or -1/+2 is the first gear launch. Basically, you'll be in 3rd gear instead of 2nd, or 4th instead of 3rd. You can see the gearing graph shrink to left where the Nth gear of -1/+2 ratio coincides with N-1 th gear of stock ratio.

I'm a little obsessed with gear ratios lately. I just ordered 0/-1 ratio (putting hand where my mouth is). Stock is 16/48, so I'm going with 16/47.
 

·
Registered
Joined
·
2,741 Posts
Interesetingly, the preevious car had 5 geaers while the neew onee has 6 gears. Looking at the ratios, I realized that they basically added an eextra geear before "1". The final ratios are close, if not the same. But turbo boost is capped in 1st and 2nd gear because the torque simply isn't usable on a stock setup. (FWD, 205 or 215 tire)

Regular stunting (wheelie-ing) without roasting the clutch is another scenario where it may be beneficial. It's possible and with a tuned engine, easy on stock. But it's just much easier and less clutchestrophic with a gear reduction.

** Note - the keyboard just started malfunctioning two days ago and often duplicatese and/or places extra 'e' characters -- and are getting tired of correcting them LoL
 

·
2 wheels > 4 wheels
Joined
·
123 Posts
Discussion Starter · #5 ·
This attachment is a good one on chain dynamics. One of the takeaways is that the higher the # of teeth, the smoother the operation. Every time a link engages/disengages the sprocket, there is a small spike in the tension of that link. When a tooth is about to receive a roller pin, it lifts the link momentarily, and the pin slides into the teeth. Chordal rise, they call it. So a larger sprocket with more teeth has lower chordal rise - implying that a 16T is slightly less stressful on the chain than a 15T, and a 17T is better than a 16T, etc. (chapter 2).
 

Attachments

·
2 wheels > 4 wheels
Joined
·
123 Posts
Discussion Starter · #6 ·
Here is the comparison. As you get up to higher gears, it doesn't make any difference. Going "quick acceleration" gives you a quicker launch off. After that, you basically have 1.5th gear, 2.5th gear, 3.5th gear, etc.... At this point, you're only playing with gear ratios for track/corner suitability. No real advantage.

gearing-comp.png
 
1 - 6 of 6 Posts
Top