While I have not ridden mine in heavy rain yet, I don't think it would be a problem. Yamaha has been making e-bike systems for more than 25 years; surely they have learned a thing or two about making their equipment stand up to weather. Now, is it safe for you to ride in heavy rain, that is another matter.
I was caught in a downpour then steady rain a couple of weeks ago. It rained on me non-stop for my 18 mile ride home from work. Temps were around 45F. I had a rainshell top but no foot protection and my pants were not water proof. Got home with shoes/feet soaked, legs soaked and cold, top and head warm and dry. No issues for the bike, it ran fine, but I had to clean it. Everything booted up fine after the cleaning. This was on my Haibike. I've been told (by my LBS) that Bosch says you can do just about everything except submerge the components (ie you don't want to ride through that river on your eMTB).
Edit: sorry but just noticed you posted about Yamaha not Bosch so disregard my response. I would think they would be similar in ability to handle the inclement weather.
Don’t immerse the motor compartment under water (e.g. ride in a huge puddle). Once user here had 28,000 kilometers and shot his Yamaha drive like that (can’t remember which thread).
I’ve ridden in the rain. Doesn’t seem to have any effect on my Yamaha, but these are brief showers. I avoid prolonged riding in the wet. Many e-bikes go ballistic in the rain. A well known example: Stromer ST1. If I had that bike I would never ride in the rain.
One thing you should be careful about is that the brakes have a greatly reduced efficiency in the wet. You might find yourself unable to stop in heavy rain if the calipers are filled with water. This has happened to me several times.
After getting caught in sustained downpours Wednesday evening, 12 miles from home (leaving me soaked through to tshirt and my shoes squished out water when I got home) -- I wrote to the guys who made my bike (not a Haibike, but this thread seemed appropriate) and asked about the risk of exposing the bike to soaking rains like that. (I was feeling anxiety during the rain ride, wondering "am I destroying my bike now?"---otherwise it could have actually been a delightful rainfall to just enjoy riding in, given the hot muggy temperature at the start!)
Anyway -- they wrote back basically assuring me I was okay -- short of submerging parts/motor/battery, or hardy pressure washing.
So does that IP67 standard basically support this -- that the bike can "take it" -- any amount of rainfall, without risk to electronics? (I realize the "7" refers to water resistance for supposedly, 30 minutes submersion to 1 meter -- I obviously won't submerge any of my components, ever.)
I'd love to simply know that yes, essentially, other than my personal skin soaking, I can ride the bike in a summer downpour without fear of ruining/damaging the onboard electronics. (I don't actively seek to start new rides in the rain -- I'm really talking about getting caught in a deluge and not having the option to find shelter and wait it out...)
Exerpted from their reply to me: Our connectors and wiring are tested to IP67 standards. Rainfall should not hurt any of the electrical components on the bike. Where we have seen some issues is when customers use a pressure washer (over 20 psi) to clean their bike. I would make sure the charge port cover has the rubber plug installed and you should be good to go!
I had gotten into a downpour shortly after I received my XDuro Trekking RX and nothing happened. However, I noticed a few weeks later, when I happened to take off the Intuvia head-unit as I was going into a store and locked my bike that there was some corrosion around the row of contacts between holder and head-unit. Now I just make sure to dry off that area after any ride in rain or heavy fog, which fortunately doesn't happen all that often in San Diego.
Most engines are water resistant for at least 2 years unless water pressure machines are used. The most serious problem is immersion in water, although it does not affect the motor, it will certainly affect the system of connections and sensors, including the terminals. of battery in open battery systems that is not built-in chassis or frame.
Wearing a waterproof jacket with a hood and pants requires very little space and wearing waterproof boots even in winter is not a problem ... Goretex gloves in neoprene. I went to work with this same thing with 0º Celsius, just wet my face.