Front Caliper Dimensions?

[VAG944]

I don't understand why everyone is worried about the caliper so much? It is radial mounted and although not a mono block it is 4 piston. It's not the weak link, in fact it is probably the best part of the whole system.

I'm going to see what the brakes are like first. If the brakes aren't up to the whole 44hp of pumping thunder, then I'll do pads, rotor to the 320mm, then the master and lever after that I'll just buy a Moto3 bike because I'm awesome!! LOL

 

[guzz46]

I am chilled out, I don't know why you think I'm not, you previously said owning a ZX10 doesn't prove you know how to ride, so I simply explained that he did.
In your original post you said "Nearly all of the thorough reviews have stated that the brakes are one of the bike's weak areas"
My original reply was in regard to that, but it sounds like you've already decided that the brakes are crap, and aren't interested in anyone's opinion besides certain motorcycle journalists, so I'll leave it at that.

 

[a_morti]

Hi all!

I'm sorry to bring up a zombie thread but google brought me here.
I am using an RC390 front caliper on my Grom 125, using an adapter from SteadyGarage.
The bolt centres are 80mm. There are various other calipers available in this size if you aren't happy with stock. Aprilia RS125, Derbi GPR125, various "bling" feign and RRGS calipers usually used by the Ruckus boys will also fit.
The pistons are approx 28mm diameter, both pairs are the same. They are made of aluminium.

To the guy who wondered where to get extra mounting bolts from - m8x1 is a weird "fine thread" size, so you will have a hard time in USA. I do have two used bolts here that I don't need. They are with me in europe so shipping can take a while but it only costs a few $. Let me know if they are useful.

I have a question - what size diameter front master cylinder is the RC equipped with? If it's a brembo copy lever with the same leverage ratio, I would expect it to be 12mm for best performance since 13mm is equipped on bikes with a single goldline caliper (30/34mm pistons). If the MC is too small you'll have a spongy lever, or too large and you'll have a wooden lever.

Also, what pads have been found to work well for road use? The pads in my caliper won't hold for very much longer.

Thanks,
morti

 

[a_morti]

Hi all!

I'm sorry to bring up a zombie thread but google brought me here.
I am using an RC390 front caliper on my Grom 125, using an adapter from SteadyGarage.
The bolt centres are 80mm. There are various other calipers available in this size if you aren't happy with stock. Aprilia RS125, Derbi GPR125, various "bling" feign and RRGS calipers usually used by the Ruckus boys will also fit.
The pistons are approx 28mm diameter, both pairs are the same. They are made of aluminium.

To the guy who wondered where to get extra mounting bolts from - m8x1 is a weird "fine thread" size, so you will have a hard time in USA. I do have two used bolts here that I don't need. They are with me in europe so shipping can take a while but it only costs a few $. Let me know if they are useful.

I have a question - what size diameter front master cylinder is the RC equipped with? If it's a brembo copy lever with the same leverage ratio, I would expect it to be 12mm for best performance since 13mm is equipped on bikes with a single goldline caliper (30/34mm pistons). If the MC is too small you'll have a spongy lever, or too large and you'll have a wooden lever.

Also, what pads have been found to work well for road use? The pads in my caliper won't hold for very much longer.

Thanks,
morti

Sorry, scratch all the above. The ByBre caliper is wider than a normal 80mm radial caliper. I think you'll be stuck with it, or anything designed specifically as a replacement.

See here for pics.

ByBre 4 pot 80mm Radial Caliper (Steady Garage PH80 Bracket)

 

[ray]

With quite a few miles with the RC, I can honestly say that the weakest point of the bike is indeed the Brakes. Pretty much no feel to it and needs to be squeezed hard. I am trying to get my hand on a certain Master Cylinder and work my way from there. Hoping to get it sorted before I hit the tracks,.

 

[guzz46]

With quite a few miles with the RC, I can honestly say that the weakest point of the bike is indeed the Brakes. Pretty much no feel to it and needs to be squeezed hard. I am trying to get my hand on a certain Master Cylinder and work my way from there. Hoping to get it sorted before I hit the tracks,.

I wonder if the yankee bikes have different pads? my front brake's awesome, even coming from my husky sm610 which has brembo's, the RC 390's brakes don't feel lacking, they just have a more progressive bite compared to the brembo's on the husky.

Have you disabled ABS?

 

[ray]

Honestly, I haven't tried with the ABS switched off. Damn thing switches back on at every startup. Will give it a go even though I don't expect it to make a difference. Even I was kinda surprised at how the brakes performed and had to check with other riders who all agreed to the same!

 

[guzz46]

Honestly, I haven't tried with the ABS switched off. Damn thing switches back on at every startup. Will give it a go even though I don't expect it to make a difference. Even I was kinda surprised at how the brakes performed and had to check with other riders who all agreed to the same!

You can permanently disable it by disconnecting the rear ABS sensor cable, it connects up by the rear brake reservoir, it may make a slight difference, but I suspect it maybe something else, like the brake pads maybe? have you taken them out to see what they are? the MCN guy reckoned he had to use the rear brake to help slow him down, which I find a bit odd, because I have to slide back in the seat to try and keep the rear on the ground under heavy braking (front only) on my RC.

 

[ray]

Nice! I thought the only way was to remove the ABS fuse. Will give it a go with ABS turned off. The pads will mostly be what the CBR250/300 has, these are pretty standard ByBre's for the smaller bikes. Will compare them soon and I suppose even the YAMAHA R3 will have the same ones.

Was discussing with a friend and we came to the conclusion that its moist probably not the pads to be blamed, I am trying to get my hands on a used Daytona/Dragex front brake reservoir for the Yamaha R15's to test with.

 

[guzz46]

Nice! I thought the only way was to remove the ABS fuse. Will give it a go with ABS turned off. The pads will mostly be what the CBR250/300 has, these are pretty standard ByBre's for the smaller bikes. Will compare them soon and I suppose even the YAMAHA R3 will have the same ones.

Was discussing with a friend and we came to the conclusion that its moist probably not the pads to be blamed, I am trying to get my hands on a used Daytona/Dragex front brake reservoir for the Yamaha R15's to test with.

I tried removing the ABS fuse, but it disables the speedo, personally I would try changing the pads first, to some sintered metal pads, if it doesn't already have them, it would be the cheaper and easier option.

 

[a_morti]

I was thinking about this... it sounds like there's a 20mm bigger disc available for the rc390. In that case you just need a 10mm slab of alloy, drill two 8mm holes at 80mm centres then two more holes at either 100mm (brembo) or 108mm centres (Tokico/nissin) and you have an adapter for a full size radial caliper. That bigger caliper would sort out the ratios problem, the 10mm thickness would build it out for a bigger disc, and give you a full size caliper with bigger pads (more friction area).

If any of you are good at CNC I can imagine it'd be a fairly easy project.

 

[emeglasson]

I just picked my 390 up (I'm in the US) and I would concur that the front brake is the weak link on the bike. I've had several other bikes with much better 'bite'. I'll be upgrading my front brake system piece by piece and will report on what I find each step of the way. Mind you, my feedback will be purely subjective based on what I 'feel' on the bike. It seems the 320mm disc is not available at this time. My dealer said it is noted as discontinued through KTM. So, it may be tough to get a hold of one. I'll start with EBC pad upgrade, then try the wave rotor from KTM, then I'll install a new radial master cylinder with good fluid. I just ordered a 16mm radial unit from Braking. But it was a wild guess on the proper size required. If anyone has a definitive knowledge on the proper size, I'd love to hear from them. Thanks.

 

[ToraTora]

An Update!

It's funny how things work--I had forgotten about this post, and missed the info from a_morti, and others. Hah! But thanks to Guz and his insistence that I called his brother something disparaging I had to revisit.

Morti! Such great info. Too bad I was so slow at picking up on it. Also so sad that these are 80mm. I have a 2005 Derbi GPR with the same spec, and well I suppose we are SOL with regards to getting a nice Mono-Block Brembo for these bikes. But lets see what kind of things we can bring to this thread.

Morti has measured the center to center of the ByBre front caliper, and found them to be 80mm.

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So what is available in a front caliper mounting at 80mm? There's not much, although now that the RC, and the Duke are running 80mm mounts we just might get lucky.

R6--These guys make some superb scooter parts. They have a caliper with amazing fit and finish. I bought one of these for my GPR, only to find that the mounting bolts were smaller. Now I could have drilled out the holes, or used inserts on the forks, but for brakes that's one place I don't like to screw around. So I gave the caliper to one of my scooter friends.

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The 2005 to ~2011 Derbi GPR50s came with a caliper that should fit, but you probably wouldn't want to employ it, as there's hardly enough power there for the fifty.

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Interestingly though Derbi built the same bike with a Yammie 125cc stroker engine. On this they fitted an AJP caliper that is much nicer than the one fitted on the fifty. These are probably slightly nicer than the ByBre, but not worth the effort to exchange one. With the proper master I found this caliper to be excellent on the fifty. I don't think I'd like it all that much on a bike weighting over a hundred pounds more though...

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You might read some bits about the Aprilia RS125 being fitted with similar hardware. This would be incorrect. The RS125 was a completely different animal. The 2006 and later RS50s were effectively Derbi's with slightly different plastics. Those will be the same, and later when they changed to the RS4 that too was mostly a Derbi, and the 125 four stroke version had the same forks, and a similar caliper. So you could source from those as well. But again, probably not anything worth writing home about compared to the stock ByBre.


In Morti's thread over on the Grom list there was mention of the Discacciati caliper. This looks promising. But that's all the information I have on it so far.

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[SHOW SCARECROW]

Do not the caliper fixed than not need to be involved in the radial mount
It will function in a sufficiently high performance even on older caliper of Brembo
I think the radial mount of 80mm pitch's easy to change to 40mm axial mount

 

[TZMike]

I think the radial mount of 80mm pitch's easy to change to 40mm axial mount

now there's a novel solution I had not considered. that would actually work very well. just needs an adapter plate to mount a non-radial caliper of whatever center distance one might want. the braking performance can only be improved. Bravo!

 

[gbabyracing]

Why not try different pads and brake fluid first. A change to EBC FA606HH and Motul RBF600 fluid was an improvement for us for sure. The stock pads were so uneven that they would take an eternity to bed in. (variable quality pad probably explains why some feel the brakes are fine) Eliminating the ABS unit using Commonwealth Motorcycles brake line kit was another huge improvement to eliminate fade issues. (we still had fade issues after extended hard race braking use so we did the line upgrade - much better now) I did a quick test on SBS SuperBike sintered pads just received from SBS and they also look to be an improvement as well (more extended testing on these tomorrow).

 

[ToraTora]

Yeah there are lots of alternatives, and yes better pads, better lines, etc will all make improvements, although not on the same level as a caliper improvement. As for feel, the stock master replaced with an RCS would make a huge improvement.

 

[chevaliernoir]

In Morti's thread over on the Grom list there was mention of the Discacciati caliper. This looks promising. But that's all the information I have on it so far.

I found them now in Europe, and even at a descent price now.
For exemple here at 171 € (~190 USD)
But the design is 2 pistons and not 4 pistons...

2 pistons 34mm = 18 cm²
compared to ByBre today :
4 pistons 28mm = 25 cm²
-> we would need a really small pump to drive this Discacciati caliper...

Let's check the offset then try?

 

[SHOW SCARECROW]

A high-performance caliper exists even for old parts
Brembo's racing calipers are easy to obtain
If you design the caliper support with high rigidity, it will not cause problems

 

[ToraTora]

I found them now in Europe, and even at a descent price now.
For exemple here at 171 € (~190 USD)
But the design is 2 pistons and not 4 pistons...

That looks similar to either a rear caliper, or a 125GP/Moto3 dual caliper setup. I don't think you'd want to run that on the front of these bikes. The one I linked is a four piston caliper.

A high-performance caliper exists even for old parts
Brembo's racing calipers are easy to obtain
If you design the caliper support with high rigidity, it will not cause problems

If you know of one with the proper dimensions I'd like to see it. My extensive research had turned up empty handed. But I'd be quite happy for you to have discovered something! And I don't mean a glommed on axial caliper.