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post #1 of 13 (permalink) Old 12-14-2006, 09:45 PM Thread Starter
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Master Cylinder Bore Size

To my knowledge the SP2 has a 17.5mm bore front brake master cylinder and the earlier SP1 has a 19mm bore front brake master cylinder which seems a backward step to me. Does anyone know why this is ?
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post #2 of 13 (permalink) Old 12-16-2006, 12:11 AM
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Different length of stroke, perhaps?

Along these lines, does anyone have any recommendations on bore vs stroke for a radial aftermarket master cylinder?
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post #3 of 13 (permalink) Old 12-16-2006, 12:19 AM
 
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Originally Posted by MyRCRocks
Different length of stroke, perhaps?

Along these lines, does anyone have any recommendations on bore vs stroke for a radial aftermarket master cylinder?
Bigger bore = shorter stroke

All depends on the feel you want.
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post #4 of 13 (permalink) Old 12-16-2006, 12:39 AM Thread Starter
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So I guess Honda's intension in reducing the bore diameter on the later SP2 was to increase feel by having a longer stroke. Would that make sense ?
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post #5 of 13 (permalink) Old 12-16-2006, 12:49 AM
 
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Originally Posted by SP2rider
So I guess Honda's intension in reducing the bore diameter on the later SP2 was to increase feel by having a longer stroke. Would that make sense ?
Would make sense however it appears that the brake calipers were also different SP-1 versus SP-2.

Anyone know if its due to bore size of caliper pistons? They do have different part #s.

If yes, that could account for change in m/c size.
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post #6 of 13 (permalink) Old 12-17-2006, 04:39 AM Thread Starter
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According to the Honda Press Pack for the SP2 at launch Honda quote the following "The new front brake master cylinder features shorter-stroke operation for more linear and responsive braking control. The two comact 4 piston front calipers were also found to run cooler than expect in most applications, so the insualtor backing material was removed from their pads for a slight reduction in unsprung weight."

You are correct when you say the calipers are different between the SP1 & 2 the major difference being piston diameter as follows:

SP1 34mm & 32mm pistons
SP2 32mm & 30mm pistons

So in summary the SP2 has a smaller piston size and stroke on the master cylinder and subsequently smaller pistons on the calipers which all makes sense to improve the feel which was Honda's intention. But what would be very very interesting would be to try a SP1 master cylinder (same size bore as Brembo upgrade item) with twin braided front lines which would beneift from the increase in master cylinder piston diameter working on the standard SP2 calipers. Anyone ever tried this or got any opinion on it as it sounds like a worthwhile upgrade, plus has anyone ridden SP1 and SP2 back to back to compare the difference in braking ?
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post #7 of 13 (permalink) Old 12-17-2006, 05:03 AM
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Think in terms of gear ratios, ie:32mm x 2 caliper bores / 19 mm master vs 32 mm caliper bores / 17.5 mm master. As long as you don't bottom the smaller master it will generate more force at the caliper for equal input at the brake lever. :twocents Nemo

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post #8 of 13 (permalink) Old 12-17-2006, 10:37 PM Thread Starter
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Originally Posted by Nemo
Think in terms of gear ratios, ie:32mm x 2 caliper bores / 19 mm master vs 32 mm caliper bores / 17.5 mm master. As long as you don't bottom the smaller master it will generate more force at the caliper for equal input at the brake lever. :twocents Nemo
I m not sure your right in what you say. In my opinion the larger master cylinder will move a greater volume of fluid for the same input at the brake lever and this increased volume of fluid acting on the same size calpier piston will develop more force at the caliper.

What are you on about gear ratios ? there is no direct relation between gearing and hydraulic pressure you have totally lost me on that one.
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post #9 of 13 (permalink) Old 12-17-2006, 10:56 PM
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Most people run a Brembo 19x18 forged master cylinder and some runb the Brembo billet 19x16 both are a lot better then stock for any RC51.


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post #10 of 13 (permalink) Old 12-17-2006, 11:45 PM Thread Starter
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Most people run a Brembo 19x18 forged master cylinder and some runb the Brembo billet 19x16 both are a lot better then stock for any RC51.
I have searched the internet high and low but cannot find anywhere what the second number means apart from its a ratio which I guess is most likely piston bore to piston stroke ratio but just can't find a decent explanation anywhere. Does anyone know what the ratio refers too ? as I dont want to just blindy upgrade to something I dont know what it is just cos others say its good. I would rather have a understanding of what I m buying and why it should improve things so I can assess whether I think the upgrade is worth while.

Out of interest I found this on www.harris-performance.co.uk so in there opinion and these guys have run motogp teams (WCM) they suggest 19/20 for the rc as it doesn't have brembo calipers.


16 ratio - The least popular although can be good for supermoto and 125 to increase feel. Easiest to pull with most feel.

18 ratio - Used by almost every works rider using Brembo brake calipers. Best combination of feel and travel. 20 ratio - Most popular for bikes without Brembo race calipers. Harder to pull with least travel
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post #11 of 13 (permalink) Old 12-18-2006, 12:12 AM
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Just give me a call and I will explain it to you (619) 444-9325


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post #12 of 13 (permalink) Old 12-18-2006, 02:24 AM Thread Starter
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Just give me a call and I will explain it to you (619) 444-9325
Thanks for the offer of help but as I m in England the international call will be too much money, plus I m in work and the international call will be blocked. If you could put a brief explaination together and post it on here that would be great or alternatively provide a link to another site that has the info maybe.

Cheers
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post #13 of 13 (permalink) Old 12-19-2006, 01:10 AM
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Quote:
Originally Posted by SP2rider
I m not sure your right in what you say. In my opinion the larger master cylinder will move a greater volume of fluid for the same input at the brake lever and this increased volume of fluid acting on the same size calpier piston will develop more force at the caliper.

What are you on about gear ratios ? there is no direct relation between gearing and hydraulic pressure you have totally lost me on that one.
I'm not a hydraulics engineer, but I've run and maintained hydraulic machines for years. Having said that, I'll state that your brakes are a hydraulic system. The pressure comes from your hand squeezing the lever which moves the master cyl. piston. A smaller piston displaces less fluid for a given stroke and therefore will have to travel farther to move as much fluid. Since the piston will have to travel further to move as much fluid so will the lever = a change in RATIO hope this helps, Nemo

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