Geared Up 2B Chained & ConvertedPosted: March 20, 2011
After wrestling for over a week with the question of what to do about my final drive ratio and what sprockets and chain to get, I have finally made a decision and pulled the trigger. I’m glad this is over. I’m always stressing over price/value and which way to go. Should I go cheap or should I go for quality? It is true what they say about getting what one is paying for, but trying to strike a balance between going all out and keeping it reasonable and less painful on the bank is what creates an elevated risk for an embolism in the grey matter.
First, there was the gearing to consider. I’ve never been to the Nashville Superspeedway. I couldn’t find a decent track map online and the scarce info that can be gleaned off of message boards and various web sites is suspect at best; at least to me. Then there is the slight hangup I have about owning my solution and a tendency of not listening to people whose credibility cannot be verified. Not to mention that there is a bunch of contradicting info out there. And I’d rather mess up of my own volition than play the victim without a clue to somebody else’s BS. In short, I can deal with my own mistakes and their consequences. Nobody to blame but myself. That’s the way it should be. Since I don’t know jack about gearing and cannot yet distinguish the utter crap from the useful information, I have to be very selective about my sources.
I’ve learned this much in racing school:
- Gearing is track specific.
- The vast majority of stock street bikes are geared wrong. It is very rare for stock gearing to be correct for the race track.
- Navigate the race track using the top half of the gearbox, meaning gears four through six; the gears are closer together there and hence RPM variances are less, making it easier to find the correct gear for any given corner.
- You should be able to hit red line in sixth gear somewhere on the track, usually at the end of the longest straight.
- Gear your bike to always be in the optimum power band.
With that said, I know I am missing essential information. How long is the longest straight at Nashville Superspeedway? Or at least what is the average top speed attained on a liter bike? I suppose I could leave well enough alone and go there with my stock setup. But I don’t work this way. Now that I have learned about this neat little morsel of racing info, I have to try and apply it. I’ve been doing fairly well lugging through some corners or screaming around in others or on the straights. Yes, I’m lazy. My shift light rapidly blinks to inform me it’s time and all I can think of? “I’m almost there… almost… I can make it… I don’t want to upshift just now, because ah… right here I would have had to downshift.” Most of the time, I street shift anyway… I am nowhere near the power band… I tool around the track in fuel saving mode. That tendency has to stop. No wonder I suck at going fast in a straight line. By the time I get the Pirate into her sweet spot where she pulls hard, it’s time to get on the binders again and stuff her into the next corner, where I –yet again– get to go around all those people who just passed me in the straights. I would like to get to a point in my riding where I only pass people ONCE. Less work that way. Unless I’m lapping them… then twice would be good. 😉
And why am I always catching up with them in the corners? Seems to me that I shouldn’t be… but that is a different blog post altogether.
I have finally decided to just wing it and go with theoretical values and bring my top speed down to my personal best, which somewhat coincides with values flung around online.
Now, where exactly would my shift points be on the S1000RR? That’s determined by the power band. To be scientific about it, I would have to get the bike on a dyno and see where she’s got what. I don’t have the money for that, nor do I know where to find one of those around here. Lastly, I just don’t feel up to finding out at the moment. My bike is stock, properly broken in, and dyno figures are a look at estimated real-world performance. Dyno figures do not translate directly. Not that simple. I just make it easy on myself and look at a few stock dyno charts. 9.5 – 13K. Good, that kind of meshes with my subjective experience and perception. The red line is at 14.5K and the front wants to come up around 11K. Further, BMW suggests to bring the revs up to 9K for a proper race start. Good enough. Now, I have a range.
I plug in some values into an online tool called the Gearing Commander and am torn between running 16/46 or 16/47, which would be -1/+2 and -1/+3 from stock respectively. I don’t like even/even distribution on teeth, so I opt for the 16/47 choice which seems better on overall wear and gets me a theoretical 4 MPH closer to that red-line moment I’m supposed to have at some point.
But it isn’t over quite yet. Should I stick with the stock 525 setup or go with a 520 conversion? 520 is obviously lighter since it isn’t as wide. The first number denotes pitch, which is the distance between two pins; the second number is the width of the chain. After sitting on the fence for another day, not being able to make up my mind one way or the other, the deciding factor came in the form of my LSR meet at the Maxton Mile in May. Weight matters there, never mind that I’m not going to be running these sprockets, but I want to keep everything the same size, so I can swap stuff at the track if I really need to. Another monetary consideration, definitely.
I’m not fast enough yet to even consider tweaks such as weight reduction to the point of measuring my fuel, ripping unnecessary parts off my bike, or to be concerned about the minute differences in chain acceleration, tension, and sprocket sizes. I’ll get to that when it is necessary. Right now I have other concerns. 520 it is. Cheaper also, less materials involved. And most of the good price/value ratios can be found in that size, too.
After checking that I have the necessary adjustment room on the rear axle and hoping that I have the clearance required to actually run a 47-tooth rear, it is time to order two sprockets and a chain. Two more days are spent wrestling with compromise between price and value and I finally decide on the following and pull the trigger before I can change my mind three more times:
- Vortex Racing 520 16T countershaft sprocket
- Vortex Racing 520 47T rear sprocket
- RK 520 GXW XW-Ring chain (118 links, I will need to cut one)
This will give me a final drive ratio of 2.94 as supposed to the stock ratio of 2.59.
The theoretical top speed would be 159 MPH as opposed to 181 MPH with stock gearing.
Theoretical shifting speeds at 9,500 RPM: 56, 70, 85, 98, 108, 117 through the six gears.
Yeah, I’m going to have to wear a diaper to stay in the top three gears. =D But it should be an improvement over the stock gearing. Now, wish me luck so I don’t wad that shit.
My work here is done. Come what may. I will own it.