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Discussion Starter #1
I've got no interest in this company, but found a deal I couldn't pass up last night - Carpimoto (Italy) is selling Brembo 4P-30/34 40mm calipers for 55% off right now and the shipping price to the USA is VERY fair:

https://www.carpimoto.com/en-US/42408_20516589-Brembo-P4-30.htm - Titanium/Red
https://www.carpimoto.com/en-US/4292_20516568-Brembo-P4-30.htm - Gold/Silver

You'll need an adapter bracket, but these are available from about a dozen different companies on WeBike. For what it's worth, the price on these right now is better than the 2P calipers normally retail for!
 

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Discussion Starter #3
Gonna try it with stock before I change it out. Given the fact that Takegawa sell 4P/2P bracket kits and don't suggest a Brembo radial master, I suspect it will be decent as-is. Worst case, I swap the stocker back until I get a radial.
 

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You'll get a longer travel and softer lever, but lots more power.

here's something to consider


the two pistons in the stock caliper are 25.3mm, this gives you a total cross sectional area of 1005 mm^2
the four pistons in the p4 30x34 are obviously 2 x 30 and 2 x 34 which gives you a total cross sectional area of 3227 mm^2



put simply, this means you'll have 3 times the lever travel but 3 times the braking pressure.


this is far from ideal, and will likely produce a poorly performing system.
 

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for reference, i have this exact caliper matched with a brembo 16x16 master. i wouldn't want the brakes to be any touchier. with the stock grom 12.7mm master i suspect they may be a little too crazy.
 

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Discussion Starter #6
I did the math on it - as you mentioned, stock master is 1/2". Front pistons (2) are effectively 1" each.

Using the upper limits:

Front piston area = ~1010 mm^2
Master piston area = ~126 mm^2

Roughly 8:1 ratio - this is why the stock front on the Grom feels firm at the lever, not very grabby at the rotor, then suddenly locks as you increase pressure. Part of this is the garbage uF of the stock pads, too.

You can't exactly compare opposed piston calipers to the stock calipers like that, either. Opposed piston calipers work well with a much higher ratio (roughly double), generally speaking. This means you can get away with a smaller master.

The Brembo has a front piston area = ~3230 mm^2

This produces a ratio of 25.6:1. I had a target of 24-25:1 so I'm pretty happy with the initial math. The lever ratio isn't exactly wonderful on the stock bike, however - I'll report back once it's all mounted up.

Your ratio using the 16 mm master is 16:1 which should be more-or-less identical to the stock brake feel (though the lever ratio is probably different). In your last post, you have it backwards in that by using the stock master, you'll be making it less 'touchy' by giving the rider more travel/feel to the lever.
 

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It'll be more touchy because you get more braking for less effort.

This is just a matter of semantics.


Keep in mind as well the Grom weighs half what most bikes do. So while 25:1 is a nice number on a 1000cc superbike, it is less desirable on a 220lb scooter.

As I said with all considerations I'd be concerned about a 1/2" bore master on a large caliper like that. But it's your bike not mine.
 

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Discussion Starter #8
Fair enough - it'll all be clear in a few laps around the block afterwards if I've got more money I need to spend.

It'll be more touchy because you get more braking for less effort.

This is just a matter of semantics.


Keep in mind as well the Grom weighs half what most bikes do. So while 25:1 is a nice number on a 1000cc superbike, it is less desirable on a 220lb scooter.

As I said with all considerations I'd be concerned about a 1/2" bore master on a large caliper like that. But it's your bike not mine.
 

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make sure you report your findings. brakes aren't discussed in detail nearly enough. especially when it comes to pairing masters and calipers appropriately.
 

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Thanks for the heads up on this deal. Decided to get one as well. M in SC says he has great results with the stock MC and this caliper.
 

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you cannot put the caliper over the rotor if the rotor is mounted to the wheel. whether the wheel is on or off the bike is irrelevant.
 

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Discussion Starter #15
Interesting... I guess I'll find out soon enough. Where is the issue of clearance? If the pads are removed, is it any better?
 

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For anyone who purchases one of these and wants to mount to 14-15 Grom I have the mount for sale $40 shipped to any US state.

6C177401-D386-4D56-9207-20D242905897.jpeg
 

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Shipping on these calipers was insanely fast...from Milan to San Diego in two days via DHL.

Can't wait to mount them up!
 

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Caliper went on without any drama. Unsure why Wibbly had to remove his rotor. The caliper just barely makes it's way in, then the mount. Plenty of clearance to achieve it all without removal of anything except stock caliper and mount.
 

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I stand corrected. Wibbly is correct - once you bleed the system, there is no room for the caliper to escape. I ended up taking three rotor bolts out, loosening the fourth, and that gave me plenty of clearance to remove the caliper.
 

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Discussion Starter #20
I stand corrected. Wibbly is correct - once you bleed the system, there is no room for the caliper to escape. I ended up taking three rotor bolts out, loosening the fourth, and that gave me plenty of clearance to remove the caliper.
What if you wobble it to compress the pistons, then remove the pads? The pads can be removed from the back of the caliper, correct?
 
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