Make Your Bike's Gear Ratio Fit Your Riding
Years ago, I bought a 2002 KLR 650. I had ridden one up in Alaska and fell in love with its easy to ride, do anything ride-attitude. The KLR is like a great utility ball player that can play every position except pitch (unless it is one of THOSE games).
But the more you spend with something (or someone), little things that were once overlooked, tend to rise to the top – and then it is all you can think about.
Anyone in a serious relationship knows this. Some things cannot be changed, but others can be well, maybe, modified a bit.
With the KLR 650 I found that on the highway, the bike was really pushing itself to get comfortable at higher speeds.
If you have ever ridden a KLR you know just how unreal the pure brawny horsepower of this engine (designed in the Carter Administration) truly is… or is not.
Getting the revs to drop a bit from ‘about to explode’ to ‘just getting ready to explode’ would make it far more enjoyable on bigger roads, or while touring.
If your machine is chain-driven, there is one, relatively easy, way to accomplish this… and it works in reverse as well.
Changing your sprockets.
I will make this as simple as can be – as I know not everyone who rides a motorcycle has a total grasp on how things work. That’s okay, and this is why we have articles like this.
Please note – I am a shade tree mechanic at best, and that tree is probably an Ash and will fall onto the barn with the next big gust. That being said… we plunge on undaunted.
Many motorcycles have a chain. That chain is turned by the far smaller sprocket that is on a spline shaft coming from the transmission, that is transmitting (thus its name) power from the engine.
This smaller sprocket is called the Countershaft Sprocket, or CS in this article.
As this turns, it carries the motorcycle’s chain with it. The spinning chain is run along the far larger sprocket at the rear wheel. The Rear Sprocket, or RS this time around.
When this happens, the motorcycle begins to move forward.
This is called Drive, and the chain is a Drive Chain.
See even a kid from Queens can explain this.
So here is where it gets a bit mathematical. I know…math sucks, but stick with me on this.
I wanted the KLR to rev a bit lower when I was pushing it. (not actually pushing it…you know).
The bike came with a 15-tooth CS up front, and a 43-tooth RS.
When you divide the number of CS teeth into the number of the RS teeth you get what is called the Drive Ratio. In this case 15 into 43 leaves us with a ratio of 2.86.
That means the countershaft sprocket must turn 2.86 times for the rear wheel to spin once.
My answer for this KLR issue was to swap the stock 15-tooth sprocket for a slightly larger 16-tooth sprocket. I left the rear sprocket size alone. This made the Gear Ratio a bit lower, now 2.68. That might not seem like much – but it did on the KLR. Much less nervous, and far more rideable.
Let's talk about lingo and why things get confusing.
When someone says their bike has Higher Gearing (Taller) it means larger FS – more top-end, less acceleration from the start.
When you talk about Lower Gearing (Short) it is the opposite. Smaller FS, and quicker off the line, but less top speed and higher revving bike on the highway.
Here comes the weird math – the larger the Gear Ratio number (say 3.10) and that means the shorter gear. Quicker off the line, but at the expense of top end. A Shorter Ratio (say 2.8) means taller gearing - and better fuel mileage, an easier pace, lower revving ride at higher speeds.
All this recently came about when I could see that Shira was riding her Honda 919 around our northwest New Jersey backroads in second and third gears, and I kept finding my Kawasaki 900 Z up in third and fourth – usually because the quick-revving Z needed to be shifted more – if just to keep the noise down, as the backroads are not a race track.
Shira’s bike came with shorter gearing from the factory, with a 16 CS and a 43 RS. The Z had a 15 CS, and 42 RS.
I raised the CS by just one tooth, losing the 15-tooth and replacing it with a 16-tooth. That lowered my Drive Ratio from a 2.8 to a 2.6. Like the KLR it was not much on paper, but plenty on the road.
If you have not changed your chain and sprockets in a long bit, it might be a great idea to change both sprockets and chain during this gear ratio adjustment.
Better to have everything fresh and new – and if you have thought this out well enough – you might feel like you have a brand-new and far more fun to ride motorcycle.