Bicycle Disk Brakes - how powerful ?

Ok, my toy project is a two person PVC NEV (neighborhood vehicle) that can hit 25+Mph with 1 rider.

http://endless-sphere.com/forums/viewtopic.php?t=2493&start=15
(Scroll down for a neat picture)

Don't know what it will do with two, but it won't be 25Mph for sure with only one motor.

Issue is, the stock BICYCLE caliper brakes don't hack it... even adjusted tight, with good shoes and everything just right, they can't haul the 350#'s to a stop quickly... not even close to the limit of the tires, I have yet to skid a tire...

A Brake upgrade is desperately needed... I know I can get Hub motors with the plate adapter for disk brakes, but then what... what size (6" or 8") and who's stuff? Will I get better performance if I use one companies calipers and another companies controls if they even will fit?

Over the winter I will be rebuilding it to fix some first gen mistakes, put the wires on the inside, have a place for a 50Ahr LiPo4 pack and hopefully add a second Phoenix Racer Motor & controller, so it would be a PERFECT time to add real brakes....

Ideas PLEASE !!

Esteemed member Lowell might have the most stopping power (he needs it.) Search for his stuff and you'll see some heavy-duty gear.

Check with Justin at ebikes.ca , i noticed new adapters now available that conform to the american standards:

http://www.ebike.ca/

Disk brakes are excellent, entirely worth the hassle that they can sometimes be to install.

I have made my 4 series motors and an X5302 work with disk brakes on my Norco, 8" disks.. from 40 km/h to 0 in very little time, no fade.

The disk diameter is not as big a deal as caliper and pad quality, mechanical ( cable operated ) disks are fine, hydraulic are more serious and expensive.

I have friends that weight well over 220lbs and they never have trouble stopping their bikes. Assuming you weigh less than 200lbs, 2, 6" disc's i think will work, but 8" is obviosly better. Considering prices are dropping, just pay the extra $50 or so, and be safe. The last thing you want is to end up in the hospital because you wanted to save 50 dollars.

Dirt bike brakes would probably fit the bill. With mountain bike stuff, you pay extra for lightweight that you don't need.

yeah go for the 8" and choose some good pads. I'd also reccomend hydrollic brakes - i find them a lot better than the mechanical (ie cable based) brakes.

Why get an 8" rotor when you can have a 9"? http://www.pinkbike.com/buysell/247789/

Hmm... that might come in handy when trying to put a rear disk on a hub motor. The extra diameter might give enough clearance for the caliper.

Justin at Ebikes.ca has an adapter that can be put on hub motors, but requires drilling and tapping.... $60

Then you need to add the disk and stuff to go with it... but for some it may be the ticket....