Gyroscopic effects
in [Motorcycles]
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From: High Plains Thumper on 9 Jul 2010 08:42 Mark Olson wrote: > Snag wrote: > >> Gyroscopic precession is what makes countersteering work . Those >> forces are significant enough to make a bike that weighs several >> hundred pounds lean into a turn ... > > Gyroscopic forces are significant in motorcycle wheels. And they > contribute to countersteering. But they are NOT *primarily* why > countersteering works. > > There have been plenty of peer-reviewed papers on how motorcycles > steer. The phenomenon is well understood by academics who have > studied it and almost unknown to the vast majority of riders. > > http://en.wikipedia.org/wiki/Countersteering#Gyroscopic_effects I suppose there is some effect, but just now in a rough calculation, a 15 inch back rim does 780 RPM at 65 MPH. Rotational velocity seems a little slow. However, as a teen I remember doing about 55 MPH (in a 35 MPH zone) going down a steep hill on a 10 speed bike with 27 inch rims, I did notice the gyroscopic effect on the front wheel on the downhill road bends. Just to think back then in the 1960's, we didn't wear bicycle helmets, AFAIK, those weren't even available, I didn't know they existed. -- HPT
From: ? on 9 Jul 2010 08:52 On Jul 9, 5:42 am, High Plains Thumper <h...(a)invalid.invalid> wrote: > Just to think back then in the 1960's, we didn't wear bicycle helmets, > AFAIK, those weren't even available, I didn't know they existed. I first became aware of motorcycle helmets during the cold winter of 1963. I thought that it would be nice to wear a helmet to keep my head warm, but the helmets at the base exchange cost about $12 and I couldn't afford the luxury...
From: Mark Olson on 9 Jul 2010 09:03 High Plains Thumper wrote: > I suppose there is some effect, but just now in a rough calculation, a > 15 inch back rim does 780 RPM at 65 MPH. Rotational velocity seems a > little slow. However, as a teen I remember doing about 55 MPH (in a 35 > MPH zone) going down a steep hill on a 10 speed bike with 27 inch rims, > I did notice the gyroscopic effect on the front wheel on the downhill > road bends. Motorcycle wheels despite their smaller diameter, are pretty heavy compared to bicycle wheels, so their gyroscopic forces are orders of magnitudes higher. Remember 16" front wheels? They were in vogue in the mid 80s as a cure for too much gyroscopic effect. I remember reading that roadracers had to develop significant upper body strength to steer their bikes on twisty courses due to the gyro effect.
From: Henry on 9 Jul 2010 10:36 tomorrow(a)erols.com wrote: > On Jul 9, 7:18 am, "Snag" <snag_...(a)comcast.net> wrote: >> CindiK wrote: >>> I know the angular momentum of the driveshaft in shaft-driven bikes >>> makes it impossible for them to wheelie. >> Bullshit > Yes, but it is vintage, classic, succinct, and comfortingly familiar > reeky traditional bullshit! Unlike your and twitbull's claim that "Left to it's [sic] own devices, a non-sidecar bike will fall right over. And this is equally true whether said bike is moving or at rest." That right there is some brand new reeky bullshit! <g> -- "Condemnation without investigation is the height of ignorance." -- Albert Einstein. http://911research.wtc7.net http://www.journalof911studies.com/ http://www.ae911truth.org
From: S'mee on 9 Jul 2010 11:12
On Jul 9, 3:10 am, CindiK <cindi.k...(a)gmail.com> wrote: > On Jul 8, 10:26 pm, sean_q_ <nos...(a)no.spam> wrote: > > > > > > > S'mee brought this up in another topic, but since > > it's likely to get buried there I thought it deserved > > a thread of its own. > > > Of course as a spinning object a motorcycle wheel is > > subject to gyroscopic effects. The question is, how much, > > and are they significant? > > > I can think of two gyro effects to consider: > > > (A) Because a bike leans in a turn, its wheels rotate > > (or pivot) about a horizontal axis through the contact patch. > > > (B) In a curve, the wheels also rotate about an axis > > vertical to the road surface. If you enter a turn northbound > > and come out heading east, both your wheels have been rotated > > 90 degrees to the right. > > > I'm pretty sure everyone here has at one time or another held > > a spinning toy gyroscope in their hand, given it a sudden > > twist and felt the "strange" reactive force. However, > > on a moving motorcycle changes don't happen that abruptly. > > The faster the bike (ie, the higher the rotational inertia > > of the wheels, which means the higher the potential for > > gyro effects), the more gradual the turns. > > > Well I don't have any metrics. My guess is that type (A) isn't > > all that significant, especially for me. My chicken strips are > > probably as pristine as the day the tire was made (I ride for > > pleasure, not because I've something to prove). > > > Type (B) causes a precessional torque on the wheel through > > a horizontal axis tending to force it back to the vertical. > > This can be demonstrated using the Right-Hand Rule > > on a left hand turn (the easiest case because all rotations > > are clockwise): > > > Point your right index finger away from you (the direction > > of travel) with your thumb pointing straight up. Your 2nd > > (long) finger points to the left, representing the axle(s), > > the axis of wheel spin. The Observer's POV is the place > > on your palm where these 3 fingers "meet". > > > The Observer (a fictional construct for purposes of clarity) > > looks along your long finger and sees the wheel spinning > > clockwise. Then he looks upwards along your thumb and sees > > the wheel *turning* clockwise. Ie, to the left from > > the rider's POV. According the Right-Hand Rule, > > the precessional gyroscopic torque acts on the wheel to rotate > > it clockwise about the axis represented by your index finger, > > resisting the force acting to lean the wheel over to the left. > > Steer to the right and the same gyro effect resists -- not > > the lean itself, but the rotation into leaning that direction > > as well. > > > BTW I just did a quick test and verified the above, using > > the handiest "gyroscope" I could lay hands on -- in this case > > an electric fan (it's been a hot day here). > > > Again, is this effect strong enough to be significant? > > I don't know. If anyone does I'd appreciate them > > commenting on it. > > > SQ > > I know the angular momentum of the driveshaft in shaft-driven bikes > makes it impossible for them to wheelie. Only in Oz does this not happen. |