203MM Avid BB7 on sale $39.99

[Sturdly]

If you need a large rotor (203mm) disc brake Beyondbikes has them on sale for $39.99. Best price I have ever seen for these front and rear.

http://www.beyondbikes.com/bb/Items.asp?Cc=CM%2DBRA%2DCAB

I am not affiliated with them but have bought from them before and service was good.

FYI bargain hunters.

 

[HornetB]

Thanks for the link.

Do you happen to have any experience with these brakes or have one in hand? I'm particularly interested to hear how wide the caliper is on the inside of the brake disc. I've seen these 203mm rotors put onto front motors like the WE (Dirtdad-but he used a Gustav), the clincher is how wide the inside caliper is. Do you happen to know if this caliper would be narrow enough to clear the hub motor if it was the disc was bolted to the motor?

Thanks again for the link. HB

 

[Sturdly]

At the adjusting screw, it's widest point, about 11/16th of an inch approximately 3 1/2" from the axle center. Will it fit depends upon application, no problem on a BMC, Ezee or Bafang hub motor. I just got some for my Kona Blast upcoming winter upgrade, but its a BB drive and it will remain so or get one of the three motors I mentioned.

 

[swbluto]

:|

Something seems fishy. They have the "Cable Actuated (203mm Rotor) BB-7", which's description states rotor and caliper, for 39.95 while the "Cable Actuated BB7 160mm & 185mm" is for $47.95 in the title but $41.95 in the description. I can't seem to tell, as explicitly, if the caliper is included with the latter but they come with the disc tabs.

This price difference isn't making sense. Don't more effective (larger)rotor+caliper kits go for more?

But it seems like a really good deal. I got my 160mm front for 49.99, shipping included. With this place's shipping(to my locale, anyways), it seems like the 203mm disc brake would cost 49.94 which is still pretty good.

 

[ngocthach1130]

Argh i just bought BB5 for 49 about a few month back. Blast it all.

 

[marvingalaxy]

I'm new to bike disk brakes. I have front ~150mm brakes on my generic MTB. How can I determine which brakes will fit? Is there any type of standard for front disks?

 

[Sturdly]

Argh i just bought BB5 for 49 about a few month back. Blast it all.

It gets better, promo code VEGAS gets an additional 10% off of that price.

 

[Sturdly]

I'm new to bike disk brakes. I have front ~150mm brakes on my generic MTB. How can I determine which brakes will fit? Is there any type of standard for front disks?

Standard 6 hole 41mm spacing for mounting rotors. Calipers on forks mostly 51mm standard, some post mount. If the caliper and rotor are sold as a set an adapter or spacer is included if not, one will usually need to be purchased. Different sizes of caliper adapters are used for rotors measuring 180mm or 203mm, 160mm is standard and no adapter is needed.

Basically you can make any size rotor fit if there is clearance, have a 41mm spacing of the 6 bolt holes on your front hub, and use the correct size caliper adapter.

 

[andys]

I got those brakes from them and they are very strong-stopping power is noticeably better than with the 160mm rotor. Took about 50 miles to bed in fully, but now they stop on a dime with terrific modualtion. You need to have a strong fork to run those on the front, as they generate a lot of force on the crown. They were really designed for downhill bikes with dual crown forks, but they seem to be OK on my 32mm sanction Rockshox Reba. I wouldn't run them on a department store front fork!

Caliper clearance shouldn't be an issue.

 

[Link]

Basically you can make any size rotor fit if there is clearance, have a 41mm spacing of the 6 bolt holes on your front hub, and use the correct size caliper adapter.

So if I have a 160mm rotor now, I can get an adaptor to fit a 203mm disc?

(LOL, so much I know about ebike parts, so little about normal ones. )

 

[Sturdly]

Yup, some examples here .......http://shop.ebay.com/items/_W0QQ_nkwZ203mmQ20discQ20adapterQQ_armrsZ1QQ_fromZQQ_mdoZ

 

[Link]

Awesome. New brake in my future.

 

[swbluto]

Yay, now I know I can "adapt" without buying a whole new set!(Not that I didn't know it if I thought of it, but I didn't think of it. )

But... ummm.... how much more stopping power does 203mm really provide? It seems like it'd only have 203/160 as much torque as 160 so, yeah, there'd be some increase but it doesn't seem like a whole lot in physical terms. Well... I guess disc fade would be reduced from the increased thermal mass so it'd be noticeably more effective in extended braking situations. And for our high-speed applications(Although they explicitly states something along the lines of "This isn't meant for a motorized vehicle". :lol: .).

(The bicycle is classified as a vehicle in few states.)

 

[docnjoj]

Prolly be a lot more powerful. Not only is the mechanical advantage better, but the swept area in much greater! If I needed new rotors, this might be the way to go! My 6inch ones stand me on my face (or noseboom) at 10-15 mph stops. Maybe I dont need to do frontflips!
otherDoc

 

[Sturdly]

Yay, now I know I can "adapt" without buying a whole new set!(Not that I didn't know it if I thought of it, but I didn't think of it. )

But... ummm.... how much more stopping power does 203mm really provide? It seems like it'd only have 203/160 as much torque as 160 so, yeah, there'd be some increase but it doesn't seem like a whole lot in physical terms. Well... I guess disc fade would be reduced from the increased thermal mass so it'd be noticeably more effective in extended braking situations. And for our high-speed applications(Although they explicitly states something along the lines of "This isn't meant for a motorized vehicle". :lol: .).

(The bicycle is classified as a vehicle in few states.)

Some hub motor applications will simply not allow the use of a smaller diameter rotor due to interference with the caliper. So even if a smaller rotor will supply enough stopping power it physically will not fit. If a larger unit has too much stopping power at lock up maybe you could just not squeeze the lever so hard.

 

[Link]

Seems they're sold out of front sets. Cheapest I could find the whole brake/adapter/disc setup elsewhere was over $60.

 

[ngocthach1130]

Yes, if you're locking up your wheel or doing stoppy often now, you need to learn to modulate your braking. Those 203mm will add a lot of stopping power. They also solve a lot of side clearance problem when dealing with mounting disc brake on 4 series crystalyte motor. Link, those adapter aren't cheap. 203mm rotor and 203mm adapter on ebay is 40 bucks per set.

 

[Mark_A_W]

Just be careful on regular forks boyos - you really need triple clamps to be running a 203mm disc. You can tear the staunchions out of the crowns..

 

[John in CR]

Yay, now I know I can "adapt" without buying a whole new set!(Not that I didn't know it if I thought of it, but I didn't think of it. )

But... ummm.... how much more stopping power does 203mm really provide? It seems like it'd only have 203/160 as much torque as 160 so, yeah, there'd be some increase but it doesn't seem like a whole lot in physical terms. Well... I guess disc fade would be reduced from the increased thermal mass so it'd be noticeably more effective in extended braking situations. And for our high-speed applications(Although they explicitly states something along the lines of "This isn't meant for a motorized vehicle". :lol: .).

(The bicycle is classified as a vehicle in few states.)

It seems like a great price, but the "isn't meant for a motorized vehicle" is concern, especially when from the pic it looks like only 4 relatively thin spokes from the braking surface to the hub. I'm looking at greater mass to stop at double the typical speed, so it's will see far higher temperatures and forces than the designed use. Will these disks hold up? Has anyone ever broken a brake disk with their ebike? That would seem to be a pretty nasty incident I never want to encounter.

John

 

[andys]

Guys run those 203mm disc on downhill mountain bikes that go as fast as an e-bike and weigh nearly as much. If they can stand up to that kind of abuse,I am not worried about a failure slowing down my e-bike under normal use. I like my Avid BB7 203mm set up, and it has much more stopping power than the 160mm disc set up I run on a regular bike, and is way stronger than even the very best rim brakes.(plus you are not wearing out the rims which can cost way more than a new rotor)

The 203mm set up was overkill for my regular leg powered bike-it was more brakes than I'd ever need for the way I ride, and it weighs more than the 160mm rotor set up (which of course means little on a motor powered bike).

 

[swbluto]

Guys run those 203mm disc on downhill mountain bikes that go as fast as an e-bike and weigh nearly as much. If they can stand up to that kind of abuse,I am not worried about a failure slowing down my e-bike under normal use. I like my Avid BB7 203mm set up, and it has much more stopping power than the 160mm disc set up I run on a regular bike, and is way stronger than even the very best rim brakes.(plus you are not wearing out the rims which can cost way more than a new rotor)

The 203mm set up was overkill for my regular leg powered bike-it was more brakes than I'd ever need for the way I ride, and it weighs more than the 160mm rotor set up (which of course means little on a motor powered bike).

Are these downhill segments on asphalt and are they stopping to a complete stop from 40-0 with the same type of deceleration as an emergency stop that a car would? The friction between rubber/asphalt is faaar higher than rubber/dirt, so the brake would heat up far more quickly and probably to a greater extent as these "down-hillers" are more likely, it seems, to lock up their brakes in dirt/not-quite-asphalt environments.

And, yeah, there's a significant difference between lower speeds and higher speed energy that needs to be dissipated as kinetic energy = .5*m*v^2, where m is the mass and v the velocity. The energy difference between 40 mph and 20 mph is a factor of four, so the same disc brake stopping to a complete stop at 40 would heat up about four times as much as one stopping from 20 mph. Add on the weight of a typical ebike going 40 and you're looking somewhere about 4.5-5 times the amount of energy to dissipate than "normal" braking. But... I'm guessing these down-hill brakes were possibly designed from stopping from 30-25 mph on asphalt, so it seems a "normal" hi-speed e-bike would have somewhere near twice the amount of the energy demands which might be risky.

But, yeah, there's more to the disc brake then just the rotor to consider. There's also the ... ummm... crown(?), stanchions and tabs.

Despite these safety warnings, I still use 160mm fronts on my e-bike and I typically travel at 25-30 mph. I just make sure I don't get into any surprise emergency situations. :wink: (Yeah, I know, it seems risky.)

 

[Sturdly]

The energy difference between 40 mph and 20 mph is a factor of four, so the same disc brake stopping to a complete stop at 40 would heat up about four times as much as one stopping from 20 mph. Add on the weight of a typical ebike going 40 :wink: (Yeah, I know, it seems risky.)

Typical ebike going 40mph?

 

[swbluto]

The energy difference between 40 mph and 20 mph is a factor of four, so the same disc brake stopping to a complete stop at 40 would heat up about four times as much as one stopping from 20 mph. Add on the weight of a typical ebike going 40 :wink: (Yeah, I know, it seems risky.)

Typical ebike going 40mph?

The intended semantics of that was "a typical ebike that goes 40" / "a typical 40mph e-bike", not necessarily that a "typical ebike" goes 40. We do have a few of those around here and my polling suggests that 1 out of 2 to 4 e-bike users have the 40 mph e-bikes, so it's common enough to be a concern.

 

[John in CR]

I was really just trying to find out if anyone's heard of a heat related failure, since I'm sure I'd be exceeding the design specs by far more than a factor of 4. That seems to pose significant risk. One of my employees is a downhill racer and tells me the main thing is to almost never use your brakes, and with 2-3minute runs it's hardly comparable.

For now I think I'll pursue plug brakes to take most of the load off of my V brake front that's putting off a ton of black dust. Regen braking should become the standard soon anyway, so we'll only need mechanical brakes as backup and for very low speed braking assistance.

John