Street Twin Brakes

Hydraulics is all very similar to a set of levers and leverage ratios.
What is the diameter of the standard master cylinder?

A 2 pot to 3 pot conversion will need more fluid volume movement for the same caliper piston travel.
A smaller master will provide more lever travel and an increased leverage ratio i.e. easier to apply more pressure, but, this may be at the risk of the lever coming to the bars.

HH pads in a standard Nissin 2 pot caliper provide a nice upgrade to OE.

 

So going from a diameter of 11mm to 14mm will push more fluid for the same stroke however, the leverage ratio will have now gone down so more force will be required. This may improve feedback if the current combination is too grabby for example.

It all depends exactly what you're after?

Better brakes is a very ambiguous term and everything is a compromise.

Think the above through and try to describe, as specific as you can, what you want to actually achieve?

 

So is it a straight fit from the older CB1000R abs model?

Here's mine from 7 years or so ago.

 

After reading through this thread am I correct in assuming the front 3-pot calliper from a Honda CB1000R is the same as fitted to the Bonneville Scrambler? Therefore either is a direct fit on the Street Twin (or Street Cup)?
I'm asking because a used CB1000R calliper might be a bit cheaper than a brand new Scrambler calliper imported from Italy.

RevPaul, when you get round to fitting the 3-pot please let me (us) know your opinion. Perhaps you could put on an extra pair of thermals and get in that garage soon, before I forget all about this potential upgrade, which tends to happen at my age

 

T

@beerkat be aware the older CB1000R was offered with two different front brake setups.
Without abs and with.

Without abs - radial calipers were fitted with m10 bolts but I can't remember the manufacturer. Looking at owners viewpoints as I used to be on a Honda forum, these were the inferior option quality wise.

With abs - these are what we are interested in here and were made by Nissin. These were not radially mounted and held by m8 bolts..

On a fairly recent search a nice pair ........were going for £450 secondhand

 

The switch to a 4 pot Brembo front caliper from 2019> on the ST and SS was accompanied by a larger 12.7mm master cylinder. Can't comment on the braking performance of earlier bikes but you can practically stand the thing on it's nose using two fingers with the Brembo setup.

 

I have just got a cb1000r caliper from ebay for my street twin. The piston surface area of a standard 2 piston caliper of a Gen1 Street Twin is 1145.2 Sq/mm. The Honda caliper comes in at 1361.9 Sq/mm. So the Honda caliper is an improvement but, at first glance, not much compared to the Brembo fitted to the Gen2 Street Twin. Although I'm no expert in this field, I can see why the standard master cylinder still works well.

However, I paid £60 for my caliper and it's mounting bracket from a breakers. I also have an ebc floating disc for a Street Cup coming at about £150. I never thought the standard front brake was as bad as some would suggest in the first place so £210 and a bit of brake fluid for a simple brake upgrade seems dirt cheap to me. Should match nicely my full stage1 engine/airbox, decat and straight through V&H performance upgrades. 2820 Hagons with 8.5n/mm front springs compliment.

Thanks for the idea mate, nice one - the brake upgrade was the last thing on the list and I was gagging at the £650 Brembo kit cost.

 

I'm not sure I'm following your reasoning and understanding of engineering, but if you're happy then that's all that matters.

Greater ( presumably your measurements are external) surface area is only one part of the equation, master cylinder volume and the ratio to caliper volume need to be correct to provide adequate leverage WITHOUT excessive travel.

When people use words like " improvement" I usually smile as there is no such thing as a free lunch.

 

Agree. I make the assumption that, for the caliper, larger pistons equals force applied evenly and with potentially more power/friction. I'm no expert on this but my logic is if there wasn't an advantage performance bikes and cars would have 'basic' breaking solutions.

I'm a mechanical engineer and not a hydrolic or brakes expert - far from it! My surface area calculations based on the piston sizes was the only way my amateur mind could compare the 2 calipers in question and start rationalising the choices and try and understand the limits of the standard master cylinder. I'm sure there is an equation that links the hydrolic pressure pushed by the master cylinder, volume of the fluid pushed, size of the pistons, temperature (and maybe other factors) to the 'grab' of a braking system. Feel, as has been said is subjective and a matter for personal taste. For me it is about how quickly I can stop. The feel, well, I'll get used to that.

My major problem is I can't be bothered to do this deep research myself!! So, like most who use forums, I build on the experience of others and try to make sense of it. Anyway, if our friend above says his lever action is adequate that is good enough for me to give it a go. I do have a 14mm Triumph master cylinder in the shed but I suspect/guess it will be a hard pull. Anyway, based on my lack of knowledge it's trial and error! Fortunately I have the time.

 

The glossy spots is wet satin hammerite. £60. Pistons look good and clean. Floating disc, HH disc pads and 14mm master cylinder repair kit (for T595 M/C I have in the shed) in the post.

 

After 2 days of reading ratio tables, playing with master cylinder calculators, finding formulas linking piston surface areas with just about everything else that moves on a vehicle I recon the ideal master cylinder is the 12.7mm bore for a 3 pot Nissen caliper.

The optimum size may well be a bit less but given the sizes commonly available in the market (11mm, 12.7mm, 14mm, 16mm, 17mm etc) with suitable brake light switches, look, and a 'standard' lever length I'm going for a 12.7mm bore - basically the master cylinder for the 4 pot Brembo equiped gen2 LC 900 is the one. I'm expecting the lever to have slightly less travel and require a bit more effort than the standard braking system but close.

And of course it's obvious. The 14mm bore supports twin disc, mostly 4 pot caliper fits. 11.7mm does the 2 pot gen1 single disc twins. The 3 pot Nissen has about 20% more piston surface area over the standard twin pot caliper. Working the maths a 12mm may be a ideal pairing but the maths is significant as there is so much to consider including disc size, weight of the machine, momentum etc.. Anywa, as a 12mm isn't available except for custom application such as bespoke racing kit it is the 12.7mm Triumph master cylinder.

I got a second hand one tonight. Given I was going to use a 14mm, off a T595, master cylinder I had in the shed (free) is the whole endeavor worth it over buying a kit?

Floating 310mm EBC Street Cup floating disc = £150
Used 3 pot Nissen Honda Caliper = £60
12.7mm used Triumph Master Cylinder = £85
Second hand but unopened EBC HH pads = £23

Total = £318

That, assuming all work well and the Master cylinder does not need a repair kit, gets you an upgraded braking system that is unlikely to stop you quicker (for want of a better expression) than the 4 pot brembo kit we all have seen. Is the Brenbo upgrade more reliable in the long term? Who knows? Will the kit look better? To me yes - it will all be new and unmarked and have Brembo written on it if that matters to you.

As I write I'm undecided if I would do this again on any future bike. If I fit my solution and it bleeds up easy and works well it make my Triumph a bit more 'mine' and a bit more unique and have a more powerful front brake over standard. I guess I will be happy and forget the fact that I could have saved for another month or two and got a better solution.

I will fit my solution next week now and post the 'on the road' assessment if anyone is interested.