Disc brake on a minibike

#8
Disc brake install complete along with a home built hub assy. The original rear wheel was corroded beyond repair. This minibike is a trailblazer from 1970 or 71. There was no rear brake on the rear wheel. What did they use for a rear brake.. Now to find a motor for this minibike. A tecumseh h50 would be a good choice.
 

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#9
Here's mine: Brake caliper is an Avid BB7 Road SL. Rims are UMI Goped polished aluminum, fitted with Skopod adapters, which allowed for easy mounting of the brake disc. The brake disc (believe it or not) has "not" been chromed, but only polished. (some kind of high-end metal there, that's for sure) On the backside is an aluminum polished sprocket which has also been mounted utilizing another Skopod. Only glitch was the sprocket had to be drilled to match the 6 bolt bicycle disc holes. Tire looks a little "square" because I never keep these fully inflated when not in use.
Now all I gotta do is build a bike to fit. (ha) IMG_3751.JPG
 

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#11
This is how I install a bicycle disc brake on a older minibike. Machine a hub to attach the rotor to the wheel hub and build a bracket to hold the caliper. This bracket centers on the axle spacer so it requires no slots for adjustment. And lots of stopping power.
One a bicycle disk brake isn’t wasn’t designed to stop a hundred something pound rolling chunk on steel,and aluminum .
 
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#12
One a bicycle disk brake isn’t wasn’t designed to stop a hun something pound fooling chunk on steel,and aluminum .
They are used on ebikes which can weigh as much as a minibike. Besides that, the brakes would be much more effective on a small OD minibike wheel/tire than on a much larger OD bicycle wheel/tire due to the greater force multiplication (leverage) that the bicycle wheel/tire would have over the brake.
 
#13
Here's mine: Brake caliper is an Avid BB7 Road SL. Rims are UMI Goped polished aluminum, fitted with Skopod adapters, which allowed for easy mounting of the brake disc. The brake disc (believe it or not) has "not" been chromed, but only polished. (some kind of high-end metal there, that's for sure) On the backside is an aluminum polished sprocket which has also been mounted utilizing another Skopod. Only glitch was the sprocket had to be drilled to match the 6 bolt bicycle disc holes. Tire looks a little "square" because I never keep these fully inflated when not in use.
Now all I gotta do is build a bike to fit. (ha) View attachment 291066
While that may look pretty, the rotor has been way over-polished, the friction surface of the rotor is not flat, the contours around the slots and edges are clearly visible in the photo, only the high spot would contact the brake pads. Also, a polished surface would reduce friction until it becomes scuffed from use. There's a reason why brake rotors are machined flat (for maximum and even contact in case it isn't obvious). Polishing the center would be fine but I wouldn't polish the friction surface.
 
#14
Charles: From your comments, I suspect you believe some material was removed from my brake disc as a result of polishing. That's not the case! The "contours" of which you speak are exactly as they were prior to polishing. It is my understanding that these contours are "rounded" in such a fashion so as to prevent sharp edges from damaging the brake pads; at least that's how I remember it. I have to say, these discs must obviously be made of a fairly hard alloy. Believe me, it would take more severe grinding than the polishing we did to change the configuration of this disc. As to the reduction in braking efficiency resulting from the polishing?.........IMHO, the difference may not be as noticable as we think; particularly after a short period of use.
Further (and in contrast to the above), I definitely agree with your view as to how much more effective these calipers could prove to be; especially when used on the small diameter wheels (as opposed to the large diameter bicycle wheels) that we generally see on a mini bike.
All the best, Henry

P.S. BTW, my middle name is Charles (ha)
 
#15
Charles: From your comments, I suspect you believe some material was removed from my brake disc as a result of polishing. That's not the case! The "contours" of which you speak are exactly as they were prior to polishing. It is my understanding that these contours are "rounded" in such a fashion so as to prevent sharp edges from damaging the brake pads; at least that's how I remember it. I have to say, these discs must obviously be made of a fairly hard alloy. Believe me, it would take more severe grinding than the polishing we did to change the configuration of this disc. As to the reduction in braking efficiency resulting from the polishing?.........IMHO, the difference may not be as noticable as we think; particularly after a short period of use.
Further (and in contrast to the above), I definitely agree with your view as to how much more effective these calipers could prove to be; especially when used on the small diameter wheels (as opposed to the large diameter bicycle wheels) that we generally see on a mini bike.
All the best, Henry

P.S. BTW, my middle name is Charles (ha)
Must be a stamped rotor that wasn't machined (probably a cost cutting measure), stamping often results in rounded edges on one side and sharp edges on the other. It looks like some parts I've seen that were over-polished on a buffing wheel, a buffing wheel and compound can remove a lot of material and can remove it unevenly if not done properly. I assumed that was the case here, my bad. The rotor is probably made of stainless steel, most stainless alloys are pretty hard.
 
#18
Lizard: Those Skopod adapters were made for the UMI Goped wheels and were engineered to match both the wheel hole spacing as well as the standard 6 bolt bicycle brake disc pattern. These made putting a brake disc on a Goped a pretty simple job. BTW, those Skopods didn't only fit the UMI wheels, but fit many of the other standard Goped wheels that were being manufactured at the time. They came from DDM Racing out of Draper, Utah. As far as mounting goes: Since I used the Skopods on both sides, I had some cutom polished stainless steel bolts made that run completely thru, from one side to the other. In other words; the bolts hold both Skopods together against the rims. These bolts came from a company called Southwest Stainless in Lake Havasu City, AZ. I think the people who owned this company have since sold out and retired. Nothing "cheap" about me.......eh? (ha)
 
#19
Sorry, but as a postscript to the above: Just take a look at a closeup of the brake disc pic and you will see the polished allen head fasteners, behind the disc, that I'm talking about. And BTW, the wheels look a helluvalot better in real life than they do in these pictures.
 

Lizardking

Well-Known Member
#20
Lizard: Those Skopod adapters were made for the UMI Goped wheels and were engineered to match both the wheel hole spacing as well as the standard 6 bolt bicycle brake disc pattern. These made putting a brake disc on a Goped a pretty simple job. BTW, those Skopods didn't only fit the UMI wheels, but fit many of the other standard Goped wheels that were being manufactured at the time. They came from DDM Racing out of Draper, Utah. As far as mounting goes: Since I used the Skopods on both sides, I had some cutom polished stainless steel bolts made that run completely thru, from one side to the other. In other words; the bolts hold both Skopods together against the rims. These bolts came from a company called Southwest Stainless in Lake Havasu City, AZ. I think the people who owned this company have since sold out and retired. Nothing "cheap" about me.......eh? (ha)
The question was for @Luke135 but good to know about your setup. Your wheels are nice!
 
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