Rear sprocket change or overdrive 5th

Pete, I've used that spreadsheet before on a PC but can't seem to get it to work on an I Pad.

You have to have release 8 or higher and the official Microsoft Excel APP which also requires you to open a Microsoft "account". The spreadsheet needs more than just a reader because when selecting from the pulldowns, Excel is actually running, so Microsoft also requires that you use Excel from their version of The Cloud, which you will have access to when you open your account.

There is no charge for this benevolence from Mr. Gates, but I suspect they have something in mind for the future once they get us hooked, so grab it now while it's free!

Start by getting the Microsoft APP which shows up as the first available if you search for excel in the APPS box. The rest is easy.
 
I'm no math wiz, nor am I that savvy about physics and engineering, but if my love for motorcycles is helping me understand the concept behind swapping gears and sprockets; it's simple: by lowering the RPMs at a given MPH, it essentially reduces stress on the engine by better preventing over revving it. Additionally based on 2M's comment about his Chevy, lower RPM at a higher MPH allows more headroom for faster MPH at a higher RPMs.

Do I have the right idea, or how exactly does this all work? Why are we obsessed with keeping our RPM's lower at certain speeds?
 
I'm no math wiz, nor am I that savvy about physics and engineering, but if my love for motorcycles is helping me understand the concept behind swapping gears and sprockets; it's simple: by lowering the RPMs at a given MPH, it essentially reduces stress on the engine by better preventing over revving it. Additionally based on 2M's comment about his Chevy, lower RPM at a higher MPH allows more headroom for faster MPH at a higher RPMs.

Do I have the right idea, or how exactly does this all work? Why are we obsessed with keeping our RPM's lower at certain speeds?
Gearing is not only about comfortable cruising at a preferred speed on a flat road. It is always a compromise that has to allow for steep hills, heavy riders, passengers and luggage, strong headwind, acceleration, fuel economy and so on...
Now the comparison beteween a Chevy SB (which mostly is in a really low state of tune when stock) is "apples and oranges"
For any vehicle, the top speed will be the speed and rpm where the total drag+rolling resistance is equal to the power at that given rpm. If this occurs at peak HP rpm, the ultimate top speed has been reached. Raising the gearing further (smaller rear sprocket) will result in a LOWER top speed. Lowering the gearing (larger rear sprocket) will let the engine rev past its power peak, but at a lower speed than the ultimate top speed. Any change in the engines power curve, max HP, the aerodynamic drag of bike+rider, rolling resistance will require a corresponding change in gearing in order to reach the ultimate top speed for that particular condition.
I have a feeling that many here on the forum has a bit of what I would call "Harley Envy", and want the XS to chug along at too low rpm. Instead it would be better to focus on reducing vibration by means of lighter pistons and rods, crankshaft balancing or re-phasing, good carburetor synchronization, correct ignition timing, and so on. I am pretty sure the Yamaha engineers NEVER intended the XS to run with a 30/18 sprocket set. If an engine gives best peak power at say 7000 rpm, it makes little sense with a gearing that will not let it rev past 5500 in top gear.

-Just my 2 (mechanical engineering) cents
 
There are a lot of things people do to motorcycles that the engineers never intended. For me at age 59 the 18/30 gearing allows me to ride the bike. Most rides are on 2 lane roads with 55 mph speed limits. With that gearing I don't have to stop and let my hands come back to life every 15 min. I wouldn't even think about taking it on a 70 mph freeway and have the VStar 1300 for that.
 
The overdrive feature in my trucks (and many more cars) is just there for highway economy cruise.
There's no way they could top-out speedwise with that overdrive gearing.
In fact, you're warned to not use overdrive in hilly or towing conditions.

In all my highway cruises back in the 70s, I kept wishing for a higher primary drive ratio. With its low rolling and wind resistance, and final state of tune, it could've easily held 70 mph at 3500 rpm.

Then Ivan Hoey came out with his hi-ratio primaries. Wish I had that back then. But would be wishing for a granny gear for starts.
 
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