Disc brake compatibility - 180mm rotor, front vs rear

[ciaran.mooney]

Hi,

I have an electric Radwagon 4 cargo bike which has single piston mechanical disc brakes front and rear both operating on 180mm rotors. They are barely adequate at braking and require constant adjustment. So I'm planning on swapping them for some dual action mechanical calipers.

As the bike is electric I don't really want to go to the expense of ebike specific hydraulic brakes so I'm sticking with mechanical for now. I'd like to keep the original 180mm rotors as I'd rather have bigger rotors than smaller ones plus it keeps costs down. I would be willing to buy new ones if that's necessary.

Disc brakes are a bit of a new world to me and I can't figure out what would be compatible. Most sets seem to come with a front/rear combo of different rotor sizes. I'm also unsure if the front/rear calipers are interchangeable with the difference being the rotor itself. Is this the case?

[531colin]

Exact model number and type of brake callipers and levers will be asked by someone who knows about this stuff.
What pads are you using?
Are you using compression less cable outers and are the cables above reproach?
Rotors will usually fit front or back.
I’m sure you will be advised to go hydraulic; are brake levers separate or combined with gear shifters?

[Brucey]

...I have an electric Radwagon 4 cargo bike which has single piston mechanical disc brakes front and rear both operating on 180mm rotors. They are barely adequate at braking and require constant adjustment. So I'm planning on swapping them for some dual action mechanical calipers......

IMHO if you do that,the brakes will still need frequent adjustment plus they are unlikely to work much better than the brakes you already have.The only people that think dual actuation automatically means improved performance are people who don't really understand how brakes work.

[rareposter]

As the bike is electric I don't really want to go to the expense of ebike specific hydraulic brakes so I'm sticking with mechanical for now. I'd like to keep the original 180mm rotors as I'd rather have bigger rotors than smaller ones plus it keeps costs down. I would be willing to buy new ones if that's necessary.

Do the job properly and buy full hydraulic.

What'll happen is you'll buy dual action mechanical, they'll still be rubbish, they'll still need loads of adjustment and you could save yourself a lot of time, effort and money in the long term if you just get decent hydraulics.

They don't need to be expensive - you can pick up Shimano Deore brakes for <£100 the pair.

Frankly it should be illegal to sell e-cargo bikes with mechanical discs, they don't have the power to stop the extra weight. My e-cargo has some massive Magura 4-piston hydraulics on there - the sort of thing that 10 years ago would have been seen as the sole preserve of DH race bikes!

[mattsccm]

Just buy some cheaper hydro brakes. Damn site less fuss and cheaper than any decent cable ones. Low end Shimano, lower than Deore even or something like Clarks will be great.

[Brucey]

clarks hydro discs are very inexpensive, but I don't know how readily they would fit your machine. The usual arrangement (eg. with IS discs and mounts) is that you can use a 'rear' caliper at the front, provided the disc is 20mm larger. So, if you buy a 160mm rear brake, it should work at the front with a 180mm disc In practice you will probably have to buy at least 1 front and 1 rear brake, just to get the correct master cylinders. It is not very difficult to bleed brakes or make up longer lines; it is also possible to use readily available and inexpensive citroen LHM type oil in most hydraulic systems designed for 'mineral oil'. Finally I feel I should mention that it doesn't cost much to buy a set of +20mm adaptor brackets, and therefore fit calipers originally meant for 160mm discs with 180mm discs instead. In fact, this is almost certainly how your extant calipers are mounted, so you may already have a set of +20mm adaptors you can re-use.

If you don't fancy doing the work yourself, there is nothing to stop you from buying all the bits and then using the LBS for making up the longer hoses, bleeding etc.

[ciaran.mooney]

My main worry is just dropping £100+ on a brake set only to find they won't fit or be compaitable in some stupid way (ie 160 mm caliper on 180mm rotor). From what you've said Brucey I'll take a closer look at what is currently fitted.

Quite happy with fitting, bleeding and setting up that doesn't faze me.

It doesn't seem to be a simple task sourcing ebike specific hydraulic brakes. Sure there are lots to choose from of regular brakes but the levers are ebike specific. They cause the motor to cut out when they are applied, which is a feature I would very much like to keep.

Searching Google gives results that fall into two categories, either they are reputable brands from sketchy looking suppliers, or sketchy brands on Amazon/Ebay. I tend to buy from SJS a lot but it seems this isn't quite their market.

Clarks HD M3000 and Tektro HD E350 both seem suitable. If anyone can see these on a retailer they are familiar I'd appreciate being told.

[TheBomber]

The best disc brakes I’ve ever used were BB7 MTNs with matching Speed dial levers, compressionless cables and 200mm rotors. Had them on a tandem where they gave oodles of stopping power and were very easy to live with. That BB7 setup will almost certainly cost more than hydros though, so consider your motivations for wanting mechanical. The callipers were the same f&r, they just sat on the appropriate adapter depending on the frame and fork mounts.

As for dual pistons - if you want to squash a lump of bluetack you could place it between thumb and finger and squeeze, or put it on the table and just use your thumb. Is one easier than the other?

[rareposter]

It doesn't seem to be a simple task sourcing ebike specific hydraulic brakes. Sure there are lots to choose from of regular brakes but the levers are ebike specific. They cause the motor to cut out when they are applied, which is a feature I would very much like to keep.

The motor cuts out when you stop pedalling so surely the brake thing is largely irrelevant?

I'm fairly certain my e-cargo bike just uses normal hydro discs, there's nothing clever in there to cut the motor when applied (at least I don't think there is...)

[Brucey]

I would say that it ought to be possible to graft a microswitch onto almost any conventional lever to give the required functionality.

[Mykidsdad]

Got the same bike, brakes are OK, but here's a Reddit thread suggesting a replacement hydraulic set:
https://www.reddit.com/r/RadPowerBikes/ ... e_upgrade/
They recommend a Magura set, a quick web search indicates the brakes have cut off switches (actually not just cut off, activates regen to charge the battery!) and there are distributors in the UK.

[Airsporter1st]

As for dual pistons - if you want to squash a lump of bluetack you could place it between thumb and finger and squeeze, or put it on the table and just use your thumb. Is one easier than the other?

My ebike-specific dual piston brakes have both pistons on one side - so two thumbs and a table.

[Brucey]

the other thing which occurs to me is that it might be possible to retain the levers you have right now, by using a cable-operated hydraulic system. The snag is that these are all configured to work with 'road' pull levers. So if you were to try TRP HyRd calipers for example, you would have to increase the system MA somewhere, either in the lever or the caliper. Some levers can be converted easily to high MA, short cable pull, but others can't. Perhaps a longer lever can be arranged in the caliper somehow.

[PH]

An alternative idea - Swap the front brake for a hydraulic and leave the rear mechanical. Most of your stopping power comes from the front brake and you'd still have the cut-off on the lever for the rear.

[ciaran.mooney]

Thank you all for your input.

I have pretty much decided to go the whole hog and fit hydraulic.

I very much want to keep the e-bike specific levers, this bike is used by my girlfriend to carry children around and I don't want her to have a learning curve with 2 bickering children. I have used the bike at low speed manoeuvrers and very much appreciate the motor override the brakes provide.

Fitting cable operated hydraulics was considered but I couldn't find any at a reasonable price.

I even considered getting ebike specific hydraulic levers and combining them with off-the-shelf calipers. There's nothing special about the calipers themselves just the lever. Again, lots of no name results from Amazon and Ebay but nothing I would trust.

Looking at the Reddit post I've managed to find the calipers mentioned - Magura MT5e - from a supplier I've heard off - Bikeinn.

https://www.tradeinn.com/bikeinn/en/mag ... 36813257/p

Its only a single caliper but I can fit it and see how it goes before moving onto the other.

I have had a look at my calipers, they look identical and there appear to be no adapters.