Sounds like V-brake is the best way to

[BarelyAWake]

... too much tech and to much hype with fancy brakes ......

The last four or five Vbrake conversions I've done did not cost more than $2 worth of welding rod, grinding wheel and electricity.
If you want the best possible Vbrake, Koolstop pads are under $20
I'll put a properly adjusted vbrake with Koolstop pads against ANY disc brake setup retailing for under $250.
I'm fat and fast and they last fine for me. Pads are cheap and easy to find, adjustment is simple, and they are very reliable and damage resistant. Discs bend easier than rims.
But it's a personal choice in the end.
I'm a cheap bastard.

If bosses/mounts for rim brakes can be welded, the same can be done for disc calipers - it's actually quite easy. With the wheel & rotor in place, clamp the caliper on the rotor using it's own pads & the inner adjustment setting (floater pad), this sets the caliper exactly where it needs to be for perfect alignment - tack the adapter plate, remove all components, weld, paint, reassemble & done. The cost in welding materials is likely identical.



If we're down to counting pennies, it's going to be hard to warrant one over the other on cost alone...

As a brand-name entry level AVID BB5 disc set front & rear complete can be had for $48 which at $24ea, including pads & rotors is pretty tough to beat (Shimano is even cheaper, but I like AVID): http://www.amazon.com/AVID-Mechanical-Brake-Front-160mm/dp/B00BOJ60O6/ ...replacement pads are usually $12-$14, as are rotors - of which both seem to have better longevity then rim brakes under both adverse & normal riding conditions.

Which leaves the hub - admittedly the primary upgrade cost difference between rim & disc, yet even still disc hubs don't need be expensive, here's a Shimano 36h disc hub for $18: http://www.amazon.com/Shimano-Deore-M525A-Front-Black/dp/B007A8LHRK - don't wish to build a wheel? Upgrade to a nice Weinmann double wall aluminum rim complete w/stainless spokes & six-bolt disc hub for $50 http://www.amazon.com/Wheel-Master-Weinmann-Front-Release/dp/B0040DRGOG ...again, there's even cheaper - but why replace a rim w/o upgrading it's safety? Sure, if we're comparing the absolute cheapest of ebay or what can be scrounged from the recycling bin there's probably a few bucks here and there to be "saved" one way or the other, but neither example would do that brake system any justice... heck, I've a set of discs, calipers & wheels in my scrap pile - but I can't use "free" as an example & still be fair.

As for adjustment, complexity, stopping power, squeal & damage I believe the reason there's always controversy regarding disc vs rim brakes is an oft overlooked truth & that is both rim & disc brakes are essentially the same thing, the work on the same principals in almost exactly the same fashion. The primary and most troublesome difference is rim brakes use the rim for a rotor. While this gives excellent leverage given the diameter, the "rotor" (rim) is likely aluminum, an alloy not known for wear & chafe resistance, consequently the pads need be a softer compound to reduce damage - if they're not ("preformance" pads), rim wear is exacerbated. While it's conceivable you could bend a disc rotor somehow, it's highly unlikely. Bending and/or wearing out an aluminum rim isn't - so your "rotor" replacement is your rim, not a $12 disc. I've not yet ever needed to replace a bicycle rotor due to wear or damage, the same can't be said of rims unfortunately.

Stainless steel disc brake rotors may be smaller in diameter - but with the mechanical advantage of a cam, greater pressure can be applied with larger, harder pads & gripping surface, which is often slotted/ported for cooling & water displacement. Disc brake mechanicals and their adjustment are the same or less complicated as it's the same cable actuation from the lever with one small adjustment wheel for the inner pad - you needn't worry cable splitter/saddle balance or arm return tension as with rim brakes. All brake types can squeal, pad adjustment/dressing is required regardless.

So all in all they're roughly equal, except wear rate & reliability in wet conditions - as I like needing to replace/adjust things as little as possible & I really like stopping in the rain/ice/snow as much or more as in good weather, it's discs for me lol

Run whatever brakes you prefer, but if considering a new bike build I'd look for disc mounts, if for no other reason then the possibility of later upgrade. I believe rim brakes are still not uncommon on bicycles for two reasons, they can weigh less in a world obsessed with ounces and HPV bicycles are unlikely to need much more then what rim brakes can provide - should you add in the additional speeds, weights & distances of motorization, discs while not mandatory are an elementary upgrade in my opinion... there's a reason our motorized brethren on mopeds, scooters & motorcycles aren't trying to stop with rim brakes, they went to disc & drum long ago.

 

[Citi-sporter]

I think building the propulsion system to be sanely capable of use with the extant pedal drive and braking available for that particular bike is an honest approach.

I tend to view MB's more as MAB's with a focus on slower speeds, cruising at 15 to 20 mph seems fast enough to me.

I already own two small motorcycles.

I'm actually riding the MAB to get some exercise and have some additional engine help against our gale force summer winds. V-brakes or canti's seem more than capable if the bike is modestly powered and light.

 

[BarelyAWake]

I think building the propulsion system to be sanely capable of use with the extant pedal drive and braking available for that particular bike is an honest approach.

I tend to view MB's more as MAB's with a focus on slower speeds, cruising at 15 to 20 mph seems fast enough to me.

I already own two small motorcycles.

I'm actually riding the MAB to get some exercise and have some additional engine help against our gale force summer winds. V-brakes or canti's seem more than capable if the bike is modestly powered and light.

Mongo, my daily rider beater/commuter pretty much fits that description w/a whopping 1.3hp electric... but it's not only speed, it's mileage & thus maintenance & wear which equates to reliability that's a concern. Motorized, it's likely you'll not only ride faster, but far farther then you'd normally pedal - in the almost three years and well over 6000 miles I've beaten Mongo I've adjusted my brakes three times (once each spring, regardless of need) and replaced the pads once, just the rears & that was my fault, I'd spilled chain lube all over them like a dolt & didn't trust them anymore;



The same conditions & riding style with just a bit more distance & speed (two stroke) resulted in this with rim brakes;

Will that happen to you? Not if you ride in "average" conditions for "normal" distances and are attentive to your maintenance, repairing/replacing what needs be when it needs it - including the rim when it's worn. Are rim brakes "good enough" under those circumstances? Sure, provided they're not wet or packed with ice they stop great...

...but isn't reduced maintenance/increased reliability a good thing? Is "good enough" good enough when it comes to braking?

Rim brakes do stop a bike well, they're common and not particularly difficult to maintain and if that's what the bike has already, if it's not a priority to upgrade anything - there's nothing wrong enough with them to consider anything else... but it's been proposed that they're somehow "better" then discs, that's the thing I just can't agree with is all

 

[greaser_monkey_87]

I'm planning to lace a 6" motorcycle drum to a 24" front wheel and run an Odyssey 1999 bmx brake in rear. I expect more than adequate stopping power with the mondo front drum, the bmx brake is simply to slow the rear wheel enough that I'm not attempting to use only a front brake while the rear wheel is still under engine power. I plan on operating both with a dual pull lever with built-in brake light switch.

 

[maniac57]

I only meant better in the sense they are easier to fit on most any build and cheaper than almost any disc setup.
ALL you concerns about rim wear are valid if you ride in dirty conditions.
In normal use on streets the Vbrakes are nowhere NEAR this hard on rims.
I've been riding for well over 40 years and I have see this happen exactly twice.
BOTH times the rider was dealing with lots of sticky abrasive mud with a lot of sand in it.
Slush can also do this since you have less effective brakes and therefore use them more and harder.
On 99% of the typical motorized bicycle builds I have seen, this kind of problem simply does not happen unless the rim is VERY high mileage.
Keep in mind I recently sold one of my personal rides with over 10k on the same wheels.

 

[greaser_monkey_87]

Drums really aren't that difficult to install. Assuming you aren't lacing the drum into the wheel yourself, which I would not count as adding to the difficulty because there are complete wheels available with drum hubs, install the wheel just like any normal wheel. You may need to come up with a way to mount the brake arm if your fork doesn't have a tab. You can weld a tab on or make a bracket, as I've done. It's a lot easier than you make it sound. Usually no welding required.

 

[BarelyAWake]

I only meant better in the sense they are easier to fit on most any build and cheaper than almost any disc setup.
ALL you concerns about rim wear are valid if you ride in dirty conditions.
In normal use on streets the Vbrakes are nowhere NEAR this hard on rims.
I've been riding for well over 40 years and I have see this happen exactly twice.
BOTH times the rider was dealing with lots of sticky abrasive mud with a lot of sand in it.
Slush can also do this since you have less effective brakes and therefore use them more and harder.
On 99% of the typical motorized bicycle builds I have seen, this kind of problem simply does not happen unless the rim is VERY high mileage.
Keep in mind I recently sold one of my personal rides with over 10k on the same wheels.

Defo, you made that clear a couple few posts back;

IF you have the means, discs are the way to go. BUT!
MAKE sure they are decent brakes. The wallyworld discs are all looks, no real performance.
ESPECIALLY on a motorized bike.
...My bike does not get ridden in wet or nasty conditions, so rim brakes are my choice for budget and ease of replacement/adjustment and low initial cost.

I jus' wanted to make all the pros/cons as clear, I've been called "worst case scenario" before lol

 

[mew905]

Only if you BUY them. Scrounge them and the price is free.
The last four or five Vbrake conversions I've done did not cost more than $2 worth of welding rod, grinding wheel and electricity.
If you want the best possible Vbrake, Koolstop pads are under $20
I'll put a properly adjusted vbrake with Koolstop pads against ANY disc brake setup retailing for under $250.
I'm fat and fast and they last fine for me. Pads are cheap and easy to find, adjustment is simple, and they are very reliable and damage resistant. Discs bend easier than rims.
But it's a personal choice in the end.
I'm a cheap bastard.

How bout a 255mm disc with shimano hydraulics for $150? How would we quantify a test like that?