Modern Vespa

Granted, the three wheels provide better dry-traction and cornering ability but if all three wheels are on a wet or slippery surface (rain or wet leaves) and you are going into a curve does it actually provide better traction than a 2-wheeled motorcycle? Anybody here know about wet traction, contact-patch, co-efficient theory?

Also, when I ride in the rain on two wheels I only use my rear brake to avoid losing front-wheel traction. I rode the MP3 and the rear-brake doesn't do much so I wonder whether applying too much pressure on the front brake in the rain would cause the bike to hydroplane.

I think there's another factor, beyond the contact patch mathematics: the geometry of having three points on the ground makes it much harder to have a front wheel slip out from under you. With only one front wheel, if it slips, you're on the ground before you know it. There's no recovery. With two front wheels, even if both slip, the bike doesn't have the same tendency to fold under in the front. I think this is key to the safety of the MP3, even more than the additional contact patch.

I haven't ridden in the rain, yet; but I have ridden in gravel and on a dirt fire road. On both situations, the MP3 handled better then my BMW K12LT and Harley Ultra. Also, transitions on uneven pavement e.g. new asphalt in one lane with old concrete in the other (2" transition ledge--no big deal!). Tar strips, uneventful! Leaving pavement over a dropoff to dirt, when leaving the highway to the shoulder of the road, no biggie! Steel draw bridges, crosswalk lines, wet sewer lids--No Big Deal!

The traction is VERY predictable, and the bike handles unbelievably good in marginal traction situations. This scoot is ALMOST idiot proof! As I've said before, the MP3 is a great beginner's bike, but in the hands of an experienced rider, this bike is the Stadevarios of scooters!

Sometimes common sense isn't correct. Hopefully, we have a Physics Grad Student among our MP3 alumni.

The three contact points of the MP3 would provide more STABILITY in high-speed turns on dry surfaces because of the geometry and also in situations where one of the front tires contacts a wet or slippery surface while the other front tire remains in contact with a dry surface. But I'm not discussing these situations; I'm interested in the actual physics when all three wheels are in contact with a wet surface - riding in the rain.

Best as I can figure it goes something like this:

We see race cars with wide tires and assume that the reason for the wide tire is to provide a large "contact patch" for additional traction when the reality is that it is the soft sticky rubber of the tires that provides traction via molecular friction, the tires are also designed to provide a controlled slide (actually lose traction), and the reason the tire is WIDE is due to shear stress at the tire surface (a soft sticky compound giving better traction is weaker in shear).

Thus, if all tires were made of the same compound and race car tires were not designed to exhibit a controlled slide; race cars would have narrow tires for better traction in turns BECAUSE the smaller the surface area contacting the ground the greater the contact pressure the tire has to hold it at that physical point without slipping (not addressing heat dissipation issues in racing tires). Case in point, rally cars in the snow have narrow tires.

Now, bear in mind we are talking wet traction and specifically riding in the rain: any car would benefit from narrow tires while driving on a wet surface for two reasons: [1] the smaller the surface area contacting the ground the greater the contact pressure the tire has to hold it at that physical point without slipping and [2] the increased pressure and reduced surface area makes it easier to drain or "unload" water from under the tire to prevent hydroplaning.

With reference to the MP3, the three points provide more stability on a dry surface due to the geometry but the reduced surface area of a conventional motorcycle with two wheels (two contact points) actually provides greater contact pressure in wet conditions and less chance of hydroplaning. In addition, a Vespa with the same 250 engine has half the weight and would exhibit a shorter stopping distance using only the rear brake with a decreased chance of hydroplaning and certainly less chance of hydroplaning compared to using the two front brakes on the MP3.

My 2-cents.

Regarding wet road performance of an MP3: vs a traditional 2 wheeled MC:

A car has much better braking performance on wet roads than any 2wheeled vehicle. the reason is more contact area with the road and if traction is lost it will slide and not slide out from under you. It seem that same analogy can be applied to the MP3.

Dudel's Quote:
"..........With reference to the MP3, the three points provide more stability on a dry surface due to the geometry but the reduced surface area of a conventional motorcycle with two wheels (two contact points) actually provides greater contact pressure in wet conditions and less chance of hydroplaning. In addition, a Vespa with the same 250 engine has half the weight and would exhibit a shorter stopping distance using only the rear brake with a decreased chance of hydroplaning and certainly less chance of hydroplaning compared to using the two front brakes on the MP3."

Not correct. Hydroplaning has nothing to do with braking. It has to do with the surface contact patch of the tire and it does not matter if it is one tire contacting the road or 8. Again an MP3 will have better "real world" braking stability and shorter stopping distance that any 2 wheeled vehicle whether on dry or wet surfaces.

Wow, all this technical stuff is giving me a pain behind my right eye--Is that bad? All I can say is that my "seat of the pants" experience is that this scoot sticks like glue on every surface I've ridden on, to date, with the EXCEPTION of rain slicked streets, which I haven't ridden upon.

While I still had my Harley, I was able to ride the same terrain back to back with both the Harley and MP3, and as far as stability and confidence inspiring handling, the MP3 won, hands down! That's my $.02, for whatever it's worth!

I cannot answer Dudel's question in the manner he hath requested, but I can say that I have ridden in the rain on the mp3!
I rode about 7-8 miles to work in a downpour. I had to put my clothes in the dryer at work
It is miserable riding in the rain with the wrong gear
First I have never ridden a 2 wheeler in the rain
Second I would describe myself as a novice rider (1400-1500 miles on a 2/3 wheeler)
Third I made it to work safely albeit slowly
The mp3 did not seem to slide around in the rain very much although I was EXTREMELY cautious when approaching any turn. When approaching stops I never felt any sliding but I was not trying to lose/test traction.
So the bottom line is that the bike seems to work in the rain.
Next time it rains perhaps I will do some parking lot testing

I've have riden both my Mp3 and my previous Scooter a Piaggio B500, in some pretty heavy rain (which is most of the time over here) and I found the Mp3 is a lot safer. The B500 had a linked brake system so which ever lever you used it would put equal amount on both the front twin discs and the rear single, but i still found on a couple of occassions a bit of rear wheel twitch, and also slide in the wet on white lines and man hole covers.
I was also very aware when riding in heavy rain, and tried to give plenty of time when braking. But the Mp3 handles the wet very well, the slipping on line etc has gone and it stops very well, even in the heaviest of rain, on a couple of nights I had to pull over to the side of the road cause the rain was so heavy, i could actually see where i waqs going.
I've also hit a patch of diesal whilst taking a right bend, the sensation of sliding left was weird, but i stayed upright, on two wheel I would have been on the floor.

Still waiting for a physics alumni ?

I ain't that - but I have riddent the MP3 in the rain on numerous occasions (I'm on the "wet" west coast!) and I know it's superior to my GTS in the rain.
Traction on cornering is undoubtedly better and the braking is superior.

What more can I say. I don't have any formulae to prove it - I know it.

But I've only been riding for five years and I'd like for a more experienced rider to pipe in!

Di

I'd say it's infinitely better, safer and more controllable in the wet. I tried as hard as possible to make it let go whilst doing multiple laps of a roundabout in the wet and came away unscathed.

I think we're actually in agreement -- I'm dismissing the notion of increased contact patch, because my sense is that distributing the weight of the bike among three points lessens the size of each contact patch. I think the MP3s advantages come from the geometry, not the contact patch.

I have actually gotten both front wheels to break loose on the MP3. I was turning through an intersection (standard 90° surface street left-hand turn), leaning hard and going too fast. Both front wheels went over a large manhole cover, and the whole front end skidded sideways for a few inches, until one of the wheels hit the edge of the manhole cover, at which point the slide stopped abruptly. The whole incident was over before I really knew what was happening, and I continued on through the turn going "Huh. That was interesting."

So it looks like the tendency would be to understeer?