Bike Technology

[Mad4TheCrest]

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[Allred]

Mad4TheCrest wrote

Thought I'd start a new thread where we can share information or ask questions about motorcycle tech.

Here's my first contribution - a question:

Is there a downside to IMU controlled lean sensitive ABS?

I've noticed the updated MT-10 and XSR900 Yamahas both allow the rider to select between lean sensitive and standard ABS. Why would you ever want to turn off the lean sensitive feature?

Good thread.....and good question.

The only answer I can come up with is.....it has to be a legal thing, insisted upon by the company attorneys.

Because lean angle ABS operates by "straightening the bike up" in a case of loss of tire traction under lean, then that could be an equally dangerous situation in a (momentary) loss of grip.

You barrel into a corner at a lean angle calculated (by your brain) to take you around the corner with sufficient radius angle to make the corner, and at some point in the corner there is a momentary loss of tire grip on a part of the road, maybe the road surface has a tar strip there, or a small pebble, or even a really small collection of fine gravel, whatever it is you barely notice it, and 100% grip is retained almost instantaneously, but the lean angle ABS detects it and straightens the bike up slightly to "prevent you from falling off", despite the fact that that is not a likely conclusion. Now, the rider sees that the new angle approach to the corner has been compromised, and that the current lean angle is not sufficient to actually make it around the corner!!!!

All very unlikely, but to be safe, the manufacturers' lawyers say we need an on/off switch to put the onus on the rider, not us.  ????????


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[Allred]

Thinking of the inter-connected complexities of modern motorcycles I can't help but think how "antiquated" things were during my early motorcycling life, and yet they didn't seem so at the time.

It wasn't uncommon during my early motorcycling years to ride machines with manual ignition advance and retard. A lever controlled a wire cable that rotated the slip-ring inside the magneto, thereby advancing or retarding the ignition. (The slip-ring inside the magneto is a "stationary internal cam" that opens and closes the contact breaker points as they rotate within it) 

When starting the machine a rider had to be sure to check were the lever was placed to avoid kick-starting the bike while in the fully advanced position, as this would most definitely lead to the machine "kicking back", something that could at the least ruin your favorite riding boots, or worse tear a gash in your calf, or even crack your shinbone. Once the optimal position had been found it was safe to kick start the machine.  (this was a serious thing to be aware of, a kick-back from a 650 twin was bad enough, a kickback from a 500 single was worse, and something like a Norton 19S 600cc single was something to be very careful with!)

For a smooth idle fully retarded would be selected, for around-town in traffic riding somewhere around midway would be selected, and once out on the open road the lever would be pushed more and more advanced. It all seemed second nature, you soon learned not to kick-start in the fully advanced position, and if you tried to ride with full throttle in a retarded position the exhaust note would "bark" loudly at you to remind you to advance the ignition!

Bob-weight controlled, centrifugal, automatic advance and retard units took away the guesswork. Mounted directly on the end of the magneto shaft, the faster the magneto turned, the more the spring-loaded bob-weights would fling out, thereby advancing the rotating contact-breaker points and advancing the ignition timing. As the magneto shaft slowed, so the light springs returned the bob-weights towards their "rest" position, thereby retarding the ignition.

Coil ignition allowed for the bob-weight device to be much smaller as it could fit inside the distributor, or contact breaker points housing.

Now everything is computer controlled, and becasue the ECU can make decisions based on input from multiple sensor devices, it can ensure that the ignition timing is always in the optimal position.



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[Mad4TheCrest]

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[motogrady]

Hey.......going from tickling the Amal to pushing the choke lever on a Bing, now that was large😁

[Allred]

Here's something else that is related to advance and retard ignition systems...........many early two strokes had fixed ignition timing, i.e. no manual or automatic advance and retard, and because of this the ignition timing was set at a compromise between fully retarded and fully advanced, which meant that, if circumstances were just right and there was a "mis-fire", a kickback on the kickstarter, or spit-back through the carb on start up, it was possible for the engine to accidentally run backwards!!!!

I've only had this happen to me twice, and both times were with BSA Bantams. Because the engine timing of a two stroke is controlled by the piston, not a camshaft, the engine can run forwards or backwards, one obvious difference is when it "accidentally" runs backwards the ignition timing is now firing after TDC not before, so you can immediately tell that something is wrong by the sound and response of the engine. That is a good thing because you do not want to jump on the bike and put it in gear and try to set off only to be surprised that you are going backwards!

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[Allred]

Here's an interesting article from KC on ignition timing (bear with me, it's related to the manual advance and retard blurb above) 

https://www.cycleworld.com/story/blogs/ask-kevin/flame-speed-and-spark-timing/

If you read/scroll down to where he talks about how he found that retarding the ignition timing at max revs on his TD250Z produced more revs/power, in the '60s we knew from experience that if you were riding a machine with a manual advance and retard lever, like say a 1960 BSA A10 Road Rocket, if you very slightly retarded the advance/retard lever at max revs/speed the bike actually went a little bit faster. We weren't as smart as KC, and we didn't know quite why, but we knew it to be true!

(Be careful trying this at home, retarding the ignition too much at full throttle/max revs can blow a hole in a piston).

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