Ebike Chainring Size
 

I own a 2022 Giant Fast Road EBike. I'd like to swap out the 'stock' chainring (42T) for something with more teeth (say 50 or 52T). My goal would be to enhance the torque I can generate and thus my speed.

Any reason not to do this?

If you go to a bigger chainring, the torque you can create will be LESS.

Unless you mean - but isn’t saying - that you’re spinning out and can’t add any effort b/c of that.

Every bike I have motorized, I had to increase the chain ring size. Otherwise you're ghost pedaling and there is absolutely no resistance, not to mention no exercise because you simply can't spin that fast. A lot of e bikes are set up with traditional gearing and they just add a motor, not taking into account you need higher gear inches to actually use it like a bike with just some assist..

I left the 46T chainring on my bike but changed out the cassette that was 11-42T with one that is 11-34T. I get more options in the higher gears with this cassette. When I raced I had a bike with a 60T chainring so I could pedal even on steep downhill sections.

Ghost pedaling is a good description of what I'm doing using maximum motor power.

Swap the chainring up front to a larger size, and put an 11-28 (or 11-34) freewheel on the rear. This will increase the ability to pedal and keep cadence with the motor. I swapped the 14-28t freewheel on my qualisports dolphin for an 11-28t, and now I can get it up to 23mph on level 5 AND PEDAL THE WHOLE TIME!

That's incorrect. A larger chainring allows more speed, and a SMALLER freewheel/cassette/cog on the back will also allow you to reach higher speeds.

Switching to a smaller flywheel might help you drive at higher speeds while still pedaling, increasing overall speed.

You should pick a single thread and post that cross posting is frowned upon here. I would ask the mods to merge your threads or delete a thread.

Bikes don't have "flywheels"

You can increase speed this way, but you will be decreasing usable torque.

Here is an update.

I tried to call Giant and see if they would offer any advice.
They don't talk to consumers and said to call their retail shops.

I called 2 shops that sell Giant eBikes locally. One said I can use whatever size chainring I want but had no specific advice on what might be best.
The other shop said I could only use specific Giant eBike chainrings designed to work with a Yamaha motor.

Thoughts?

From the picture on Giant's site it looks like a 104 bcd chainring. You need to measure (see sheldon brown) to see if that's correct. If so, you should be able to use any "104" chainring (obviously that doesn't rub the frame). I changed the chainring on my Yamaha-equipped Haibike in that way.

Thoughts? Find a suitable compatible chainring and swap it out. See if the gearing is high enough for you. Just remember that the chain might need to be lengthened.

Now, for your viewing pleasure, here's the Sheldon Brown page with the gear inch calculator. It's a handy page to favorite/bookmark: https://www.sheldonbrown.com/gear-calc.html

To clarify, which dealer is correct?
Must I use a special chainring for Yamaha motors and/or Giant e-Bikes?

Considering the conflicting information from 2 different dealers it sounds like a judgement call. I provided you with information, do as you see fit. Upgrades can be made, it's up to you to decide whether you're up to the task. Ball is in your court. 👋👋👋

BTW, just for information, I used a regular four bolt design, 104 bcd chainring on my bike (which is a 2017 Haibike hardtail with Yamaha mid-drive). It would seem that the worst that could happen if you purchase one and it doesn't fit for some reason, you could just return it. Place the existing chainring and the new one side by side and compare.

In regard to the "worst that could happen," could I damage the motor in any way using a larger chainring? Maybe overstress something?

I would think you'll be OK as long as the motor doesn't get too hot. You can measure this qualitatively on a geared motor by putting your finger on the motor; as long as you can hold it there for 10 seconds, the "experts" say you're OK, that is the internal temperature of the motor is below 180 degrees or so (possibly your system has a temp sensor that will shut it off automatically). However, you'll probably be able to sense if the motor is lugging.

Here's a quote from the OP:"My goal would be to enhance the torque I can generate."
If bigger chainrings gave more torque, why does going to a smaller chainring make climbs easier?
A bigger chainring will only let a rider apply more torque if the current chainring has the rider spinning out, a scenario I mentioned in my reply.

A larger chainring and smaller cog in the rear increases speed. The OP states in their initial post they want to increase SPEED.

If you're going to quote something or someone, quote the entire line so it shows the actual discussion. I recently changed a cheap 14t-28t freewheel to a 11t-28t freewheel. The smallest cog (14t to 11t) allows me to reach higher speeds. Next, chainring. I swapped a 48t chainring for a 52t. It allows me to reach higher speeds. It does also provide more torque. BOTH TOGETHER increased the speed I can achieve. Apparently you have something confused. And the OP, as stated, is indeed interested in SPEED. If anything has changed since my previous post, who knows. Otherwise, you're WRONG. And chopping up someone's sentences won't change that.

PS - going from a smaller to a larger cog (gear) in the rear makes climbing easier. If you swap a 28t to a 32t rear cog you'll decrease speed BUT enable better climbing ability.

PPS - check out Sheldon Brown's Bicycle Gear Inch Calculator and play around with the settings. It'll give you a better idea of what size cogs and chainrings will get you: https://www.sheldonbrown.com/gear-calc.html

Your speed may be limited by wheel RPM. My Bafang mid-drive is, it has a magnet mounted to the rear wheel and a sensor on the chainstay. There is an easy hack that might work: mounting the magnet to the crank arm and moving the sensor. Still, with a 30t chainring I suspect that you would spin out if using e-assist.
What's your current top speed with throttle?

1. My Giant has an unhelpful setup. The sensor is built into the chainstay so if I move the magnet there will be nothing for the sensor to read.
2. It's a 42T chainring not 30. Would I spin out at 42T?
3. My fastest speed to date was 28 mph with maximum pedal assist. (The bike lacks a throttle.) The assist is significant up to 19 mph and then drops to very little between 20 to 27 mph.

Good thing you can't move the sensor since most OEM systems can detect that and in some (all) cases shut down your motor. An acquaintance derestricted one of the first Bosch bikes (he sold Felt ebikes), but they "fixed" the system to disallow the mod.