The Gearing Change Pack
What a sprocket change does to your instruments, your servicing and your running costs — after the ratio is worked out
Every gearing calculator on the internet gives you the final drive ratio, the top-speed change and the acceleration change. This pack starts where they stop. Change the sprockets on a bike whose speedometer reads from the gearbox and the speedo is now wrong, permanently, in a known direction. That much is widely known and widely shrugged at — six percent, who cares. What is almost never said is that the SAME signal drives the odometer, so the error does not sit still at six percent: it accumulates for as long as you own the machine, and it lands in three places nobody connects to a sprocket. Servicing intervals are counted in the miles the odometer logs rather than the miles you rode, so an under-counting odometer stretches every interval silently. Any mileage limit is read off the same instrument. And the bike is advertised at the odometer's figure when you sell it. Whether any of that applies to you depends on where your speedo takes its reading from, which is why forum answers to the question contradict each other. The pack gives you a way to tell by looking at the bike, and it is the first thing it asks you to settle, because everything downstream depends on it and the cost pages do not. The other half is what the change costs to make and to run. The chain and both sprockets wear as a set, so the pack prices them as one — on a cost-per-mile footing, where a dearer set is often the cheaper one. It tests the tempting economy of replacing only the chain by computing how many miles that chain would have to last to have been the cheaper choice, which is a larger number than it feels like. And it shows what gearing down does to chain life, because a larger rear sprocket wraps the chain around a bigger circle and every link articulates more times per mile — a running cost the acceleration figure never mentions. Every table is computed from the same modules behind the calculators on RidePlanet, and every figure in it is arithmetic on figures you supply. No market data anywhere: no chain prices, no sprocket prices, no labour rates, no depreciation tables, no service schedules. The pack ends with a sheet of the eleven lines the whole thing runs on, so you can work it again on your own bike — and if you buy from a calculator page, your own figures arrive already worked.
What’s inside
- What the change actually does — the ratio, and the speedometer error it produces before any consequence is counted
- Which speedo you have decides everything — gearbox-driven or wheel-driven, and how to tell by looking at the bike
- Why an ABS ring counts as wheel-driven no matter what gearbox sits behind it
- The error does not sit still — the same percentage as miles, accumulating across the whole ownership
- Servicing is counted on the wrong instrument — what an odometer error does to every interval, in real miles
- What it does when you sell — which way the advertised figure is wrong, and who it favours
- The set is the unit — chain and both sprockets priced together, per mile, where a dearer set can be the cheaper one
- The false economy — how many miles a chain-only job must last to have been the cheaper choice
- Gearing down costs chain life — more articulations per mile on a bigger rear sprocket, and what that does to the set
- Your own numbers — the eleven lines the pack runs on, as a sheet to fill in, and the order to work through them
- Before you change your gearing — the questions to settle while the decision is still free
Run one of the free calculators first and buy from that page, and this sheet is computed from your own figures. Buy from here and the pack still arrives complete — the sheet simply has no numbers of yours to work from yet.
14-day refund, no questions asked. If the pack is not what you needed, email support@graburl.com and we refund you in full — you do not have to justify it or delete the file. Full policy.
$19.00 including any taxes · PDF, 11 pages · instant download, link valid 7 days and 5 downloads.
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