storckm

Well, I finally bought a Yuba Mundo. The owner's manual, seventeen pages joined with a staple, seems to consist mainly of warnings, with a few cautions thrown in, among which I thought the following particularly interesting:

"Never carry other riders or packages" !!!

"When braking always apply stronger braking pressure to the rear wheel . . . . If the front brake pressure . . . is applied too strongly or quickly, the bicycle may flip forward." I find it hard to believe that a bicycle as long and massive as the Mundo could flip.

wahoonc

Generic manual? Cycling is extremely dangerous.

Aaron

badmother

You need two helmets to ride that thing .

We need pix!

MadCityCyclist

No, it's simple physics. If you brake the front wheel more than the rear, the rear wheel moves faster than the front wheel and try to move around it, especially if there is more weight on the back. It's like a car braking on ice and then fishtailing, or a rear wheel drive car going up a hill on ice and stepping on the gas, which results in fishtailing. Trust me on this, I'm an engineer. If you know anyone who is a professional truck driver they will tell you basically the same thing. With the big trucks, they cannot even maintain the same speed going up a hill on ice because they will fishtail (although moving at the same speed, power is applied to the rear wheels going up a hill to maintain a constant speed, and the power that the rear wheels have but the front wheels don't have means that the rear wheels try to move in front of the front wheels). On ice, big trucks have to use the momentum of the downhill run to carry them up the next hill so they don't have to step on the gas. It's basically the same principle with stopping a cargo bike, in less dire circumstances of course. The rear wheel can't have more energy than the front wheel or it will find a way to move ahead of the front wheel, which isn't good.

In the situation described in your owner's manual, I don't think they were saying the Mundo would flip over your head if that is what you were thinking. But there is a good chance that it will flip to your left or right side in the right set of circumstances. In less extreme circumstances you will likely experience this as the bike doing a "shimmy" from side to side when you stop.

storckm

Well that's an interesting explanation.

PDub62

I don't really agree with your assessment MadCity. Braking can't be compared to a car or truck driving on ice or up a hill; the physics are completely different. Braking results in a greater normal force on the front wheel and a lower normal force on the rear as a result of a moment about the center of gravity of the rider and bike. As a rider you can feel this when you brake; you'll feel your body pushing forward on the handlebars which translates down to the front wheel contact patch. This results in significantly higher traction on the front tire than the rear. As a result, the front wheel has significantly more stopping power then the rear which is why motorcycles and sports cars have such huge disk brake rotors on the front and relatively small ones on the rear - so they can take advantage of this stopping power. And this is why you can endo if you get on the front brake too hard. I'm not sure you could lift the rear wheel off the ground with a Mundo but it would be interesting to try. It would be more difficult on a Mundo than on a single bike because the center of gravity is located farther back from the contact point of the front wheel mainly because the bike itself weighs so much. If the bike was loaded up with cargo then the CG moves back even farther and it would certainly be impossible to endo since there would not be enough traction on the front wheel. Of course this all assumes that the bike is vertical (not turning) and the rider doesn't turn the handlbars; braking under those circumstances would certainly cause different issues.

By the way, later in the Mundo manual they do mention that braking too hard w/ the front brake could cause the rear wheel to lift off the ground so I think when they warn of flipping the bike they are referring to endo'ing.

Disclaimer: I too am an engineer (or enginerd depending on your perspective).

badmother

Your description of the truck on ice reminds me of driving a Volvo 242 on ice. Those were the days..

wahoonc

I had a 144 with studded tires...what was the problem?

Aaron

badmother

Ok, maybe I had a tendensy to drive on "not so studded tyres".

When I was young I used to go fast with my horse and a long low sledge behind it. Since it was lighthly loaded (me) it would fishtail a lot. Great times.

wahoonc

They came with the car from Michigan. Living in NC at the time they were a bit of a novelty.

First snow fall regardless of car I was always the first into the mall parking lot to have fun on the made to order skid pad.

Aaron

kevbo

On a loaded longtail or a tandem, it is often possible to skid the front wheel (almost certain to cause a crash) before the rear wheel lifts. On a half-bike the rear brake is only a backup on pavement, but with a long wheelbase you need to use it to stop in minimum distance.