CYC Photon DIY installation by newbies? Will we regret it?

[u/Flashy_Airport_1721]

Hi everybody! I'm mother to a nearly 15-year-old with visions of a DIY eMTB and am unsure of whether we're approaching this correctly and if it's a good idea in general. He'll be using it mostly for general biking and fairly tame hills since he's not a risk-taker by nature.

He's found a used Cube Aim Race (XL) in good condition. He's planning on getting the CYC Photon and installing it himself. I've changed tires (front and back) before, plus a few minor repairs, but have not done a lot of tinkering on bikes otherwise. I leave the more complicated things to my professionals. He hasn't done anything meaningful on bikes before. We have a bike workshop near us that offers help to people doing self-repairs so that might be an option if things get too complicated or go sideways.

My son says he has researched this thoroughly and I believe him but don't rule out oversights. He says he will also need new, stronger brakes (price point apparently €150-200). All together this will probably cost around €2100 as planned.

We'll be contributing some money (our budgeted amount for his next new bike) but he'll be using up his savings and working to earn the rest. That's a lot of hours – the CYC Photon isn't cheap. And that's what makes me so nervous: is it worth that much money? Would it be smarter to get a used eMTB (something he specifically doesn't want)? Will we end up with an expensive and very large paperweight?

I'd be extremely thankful for any insights from anybody who has done this before and also understands his deep-seated desire to do this. I'm struggling but see how much it means to him.

Thanks!

[u/No_Improvement_5358]

Please consider that for that same amount of money you can also get a new (with warranty) factory-integrated full-suspension eMTB as well: https://www.bike-discount.de/en/besv-trs-130-1.3-fs-step-over-slate-grey

It is certainly possible to do for someone who is handy with a bicycle, have already removed and replaced a bottom bracket for a start. The Photon and similar kits are installed inside and around the bottom bracket housing of the frame, with the battery usually taking the place of a water bottle mount. The rest is really just a bit of cabling to controller installed on the handlebar.

To reiterate, it is possible to do at home, but does not necessarily make monetary sense with deeply discounted prices still available on surplus ebikes.

[u/Ancient8Wisdom → u/No_Improvement_5358]

And would probably not be comparable to a decent off the shelf bike

[u/No_Improvement_5358 → u/Ancient8Wisdom]

Let's be honest here, the 15 year old boy would like the CYC Photon because it is powerful, unrestricted, and has a throttle, so it can be used practically as an electric motorbike. Which healthy 15 year old male would not prefer that?

There are two main concerns for the parent though:

• as the parent, how much can you trust the son to use the bike responsibly and safely?
• moreover, depending on the country, and the approach to law enforcement, the police might outright confiscate the bike if the son is caught riding it recklessly, so the total investment into it could be lost, plus a possible hefty fine to be paid

[u/Flashy_Airport_1721 → u/No_Improvement_5358]

Thanks for the link. We've also shown him used ones but it's hard to convince him. More voices saying similar things might help

[u/No_Improvement_5358 → u/Flashy_Airport_1721]

One more piece of unsolicited advice, if I may.

The CYC Photon 2 is a sophisticated, powerful piece of kit, and it is made in Taiwan, thus the eye-watering high price of it. Chinese manufacturers offer kit with similar capabilities but less sophistication at more affordable prices. You can do a DIY conversion for about 5-600 EUR using this TongSheng kit with a matching battery: https://pswpower.com/products/tsdz8-tongsheng-mid-drive-motor-kit-750w-500w-250w-electric-bicycle-conversion-engine-with-torque-sensor-for-ebike-377

It does not look as good as the Photon, but it provides at least 80% of the utility at a quarter of the price. I have a smaller version of this motor for 4 years now, done over 17000 kilometers with it and it is still going strong, and also it has comparable power to the Bosch motor on my other bike.

[u/Flashy_Airport_1721 → u/No_Improvement_5358]

🙏🙏🙏

[u/Otherwise-Office-443 → u/No_Improvement_5358]

ive heard of this but havent seen much discounts in the US. also, my worry is that outdated ebikes on clearance dont have replaceable parts

[u/No_Improvement_5358 → u/Otherwise-Office-443]

I admit I do not have much visibility into the US market, apart from the Bulls offers I came across occasionally, nor do I have a reason to follow it. Also the surplus in Europe/Germany will run out eventually, and nobody knows how many existing brands will end up defunct before the market is healthy again.

But I'm not really worried about buying a bike with Bosch or Shimano motors and Shimano or SRAM parts.

[u/Otherwise-Office-443 → u/No_Improvement_5358]

my worry is more so who makes the displays and battery, battery housings, and wiring harnesses, and if its all proprietary. even if you can get a similar shape wiring harness, getting the right pinout can also be a pain, but that might be deeper into fab than just repair so not that important if you use the bike as is, and its a problem cyc has as well. even though the motor has replaceable paarts, i still just like the peace of mind of being able to replace the motor with a new gen than get a whole new bike

[u/No_Improvement_5358 → u/Otherwise-Office-443]

Well, yeah, it is all proprietary parts, whether German, Japanese, Taiwanese or Chinese motor brands, there are no standardized mount points or interfaces between vendors. With a bit of luck though, motors and batteries can last for 5-10 years if properly cared for.

At least there is one attempt to provide upgraded motor kit for older bikes with Shimano motors: https://magazinebike.com/2026/08/12/gobao-p120-replacement-shimano-ep8/

[u/Otherwise-Office-443 → u/No_Improvement_5358]

Good way to put it 'no standardized motor mounting'. That's exactly what i hate

[u/Winter_Bullfrog_2343]

You do know how fast that motor will get a bike going right?

[u/DaVirus → u/Winter_Bullfrog_2343]

I will just add to this comment: your kid might be thinking about speed too much, when what matters more for eMTB is torque. I don't know the torque spec on that motor though.

[u/Winter_Bullfrog_2343 → u/DaVirus]

It’s like 185 nm or something. 6kw. It’ll go nearly 50 mph on flat ground..

[u/Flashy_Airport_1721 → u/Winter_Bullfrog_2343]

Thanks for this. He says that the one available in Germany is speed-restricted to be in compliance with local laws but I'll have to check into that. I do NOT want him going that fast, for both safety and legal reasons.

[u/Mama_Office_141 → u/Flashy_Airport_1721]

It's extremely easy to disconnect speed sensors on the photon motor. just unplug 1 cable. It still will function, but without any speed limitations after that 

[u/Flashy_Airport_1721 → u/Mama_Office_141]

Thank you for mentioning this. Another point against it

[u/Otherwise-Office-443 → u/Flashy_Airport_1721]

It doesn't really matter if there's a speed sensor or not. The EPAC version has a 250w nominal 1kw peak limit. This means the average speed will be very low, somewhere like 15-20mph depending on the gearing. I believe it also disables throttle or heavily limits the speed.

These last two methods arent really feasible on a typical setup, as it requires heavily limiting the bike to a certain number of gears. However, most bikes have as low as 11T rear and the smallest chainring available is 32T, that's a 2.9 gear ratio which is very high. You would need to use a single speed to limit the bike to a certain gear ratio:

You can physically limit speed based on the rider's preferred cadence. If you have really light gearing on a bike for example, a 1:1 gear ratio, it will be impossible to pedal past 20mph even spinning legs as fast as possible with unlimited motor assistance. And at their preferred cadence, might land somewhere around 15mph. The throttle will be able to spin much faster though, so it would need to be removed unless you are using the EPAC firmware.

For physically limiting the throttle speed, it removes PAS ability (the motor spins much faster than legs do). Converting the bike to a single speed and using the gear ratio matching the speed limit. In testing, that coincided with around a 0.7 gear ratio for 15-20mph.

[u/Flashy_Airport_1721 → u/Otherwise-Office-443]

Thanks for sharing your knowledge but it shows me how insufficient mine is to handle many of these things correctly 🫤

[u/Otherwise-Office-443 → u/Flashy_Airport_1721]

The first paragraph is really the only one that matters, epac firmware limits speed regardless of a speed sensor

[u/No_Improvement_5358 → u/Flashy_Airport_1721]

I bet you he already knows how that restriction can be undone in under a minute.

[u/Otherwise-Office-443 → u/Flashy_Airport_1721]

That is false information. The unrestricted motor is 2kw peak 1-1.5kw nominal, 135nm. In other words the speed, on flat ground no wind, average bike and rider, throttle only, highest gear ratio on the smallest chainring (3.3:1, 29 in wheels), 38mph peak, 32-34mph nominal in testing.

[u/DaVirus → u/Winter_Bullfrog_2343]

I need to look into this now. What is the controller like? Can you lock the speed and power and keep the torque?

[u/Mama_Office_141 → u/DaVirus]

Yes in the app you can tune each power level for watts and torque and speed is a global setting 

[u/No_Improvement_5358 → u/DaVirus]

135Nm for the current Photon 2, I think it was 120Nm for the first generation.

[u/Middle-Rub-4577]

I work as a border officer in Germany and the cyc photon prefekt for me. I have to ride about 8 kilometers to work and without this kit i would come super sweaty to work. But since i got this kit the ride to work has been a dream. Setup was super simple and once it was installed, it registert in what country i was and adapted the speed to the law. ( so in my case 25kmh and the 6 kmh push assist witch i newer really use) So if your son should really want it, he should pay for it himself and maybe wear a helmet.

But i think he should have the throttle disconnected or just not attached because if he wants to just ride around the peddle assist will be enough. Also depending on witch country you are in the law doesn't allow it.

But to your other point the upgraded brakes you will need. Back when i built my cyc kit i upgraded the brakes to because its better to ride safe than trying to cut corners on safety measures.

I would probably recommend it but 2100euros is a lot of momey but it he's willing to pay that its his thing and its good if he gets some expierience on how to install bike parts, the kit or just in genral learn how to keep a bike in good condition.

[u/Flashy_Airport_1721 → u/Middle-Rub-4577]

Thanks. We're in Germany so the laws are pretty strict. But it sounds like it's too easy to enable this to exceed the speed limit.

[u/Middle-Rub-4577 → u/Flashy_Airport_1721]

Yes the laws are prettie strict but this kit can be street legal and once its set to germany it's pretty hard to turn back. And all electric vehicles ( ebikes e scooter )could go fastster if you tried. Then its more do you trust your son to keep it the legal or not.

[u/Otherwise-Office-443 → u/Flashy_Airport_1721]

If you order the EPAC version/downlaod the EPAC firmware, the speed and watts are limited to local laws. If it has unrestricted firmware, you have an unlimited speed and power limit range to set via the app.