Rc51 (Sp1/sp2) Forks Vs. Cbr1000Rr Forks

[JZH]

I've been commuting to work in London a few days a week and, though my "hot rod" FP is holding up, I've pretty much decided that I need another VFR... 

So, why not the exact same year and model I already know and love? 

 

And that means mods! 

 

So, do I go down the "tried and true" path to USD enlightenment?  Or do I really push the boat out, throw caution to the wind and experiment with another variety of early 21st Century Showa forks?

 

I have a set of 1000RR forks (I think they're usable), but when I took them apart years ago I recall thinking they seemed like cheapo imitations compared with the obvious quality of my SP1 forks.  But are they really worse?  I'm curious if anyone knows the answer to that?  Do the radial brake calipers make up for any difference?

 

(I've noticed that Honda has helpfully manufactured both a CBR954RR and a CBR600RR in the VFR's lovely PB-215C Candy Tahitian blue, so I can easily fit a matching mudguard--how convenient!)

 

Cheers,

[CornerCarver]

I recently acquired a 2008 and I think I am going to the leave the second (or is it third?) generation LBS system intact and go with a set of cartridge inserts from Traxxion for the forks.

I would be more inclined to experiment with various newer USD options to lose the LBS if I weren't so anal about finding a set of triple clamps with with VFR offset in USD dimensions.

That being said, I do not know the answer to your question on real or perceived quality differences in the Showa offerings.

[Mohawk]

I'd go for some Showa BPF forks, regardless of manufacturer, I think they all use them now & they are he best sick design forks you can get.

I see you like the best bike in the very best colour ;)

[BiKenG]

Be aware that the 2008-> 'Blade (that has BPFs) reduced the fork width from 214 to 204. The front wheel was 5mm narrower than previously and the disc offset was also 5mm less so the 10mm fork width change was shared between the wheel and the discs.

The SP-1 and 2 (RVT) and 'Blades (prior to 2008 with USD forks) use the same 214 width and front wheel and disc mount dimensions (but with axle diameter differences), but the BPF from the later 'Blades will be a problem to fit due to the different widths noted above. Nothing's impossible, but one would need to be aware of those differences.

I believe the 204 width is used on the CBR600, so if you used the 600 yokes, then the late 'Blade BPFs with wheel and discs might be a good fit as long as they clear the frame. Unfortunately, all 'Blades use a rather short fork, a good 2" shorter than e.g. the RVT which may not then provide the desired steering geometry. As I said, nothing's impossible, but always helps to know these things beforehand.

[BiKenG]

On the subject of RVT forks, they are a useful starting point as they are long enough for use on many other bikes. But no radial caliper mounts. You can still get adapters for these (or make a hybrid with CBR1000RR lowers as I did for an SP-2, but that's another long story) or stick with the axial brakes of the RVT. Here's the thing:-

Radial mount callipers are no better than axial mount. All that talk of better load distribution is bunkum. The reason they were introduced in racing is because with radial mounting it's easy to change the disc diameter and just space the callipers accordingly. I know some will view this as heresy, but that's the way it is, pure and simple. So don't dismiss axial mount calipers due to any misguided notions of their efficiency. If you want radial mounts for the bling factor, fine, just don't kid yourself about how they work.

Similarly, radial master cylinders (a nonsensical description in any case) are used as it allows for greater mechanical leverage. The braking power available is solely due to this mechanical advantage at the lever, the relative diameters of the master cylinder and calliper pistons and the diameter of the disc. How they mount and work and in which direction is irrelevant. And don't kid yourself that fitting a Brembo master cylinder will automatically improve your brakes. It may, but it may not. It depends ONLY on the physical dimensions of the lever and the piston. I've read so many times how such a change really improved the brakes, but a simple calculation revealed they actually just ended up with a harder brake feel which they 'believe' is better, but in fact they have reduced their actual braking power. Not knocking Brembo, they make good kit, as do Nissin and Tokico etc. The main difference is Brembo sell to the aftermarket. But forget the name, just make sure you choose the right dimensions. Anyway...

For many years Honda used Nissin axial mount calipers, e.g. on the RVT etc. These are VERY GOOD callipers, but not all the same size piston, whereas all radial mounts Honda have used are 30/32mm pistons. The SP-1 were 32/34, same as for the RRW and RRX 'Blades (just different colours). The SP-2 changed to the now ubiquitous 30/32 and same as the 954 'Blade. The 929 'Blade was odd with 30/34 pistons and the CBR600s? I've no idea. The point I'm making is that although they may look the same, they may not be. They're all very good callipers and will work, but unless some thought is given to the disc size and especially the master cylinder piston size, you may not achieve optimum braking. Don't forget, the harder the brake, the less actual braking force is available and the corollary of that is that softer brakes means greater braking force is available. Obviously there are limits in practice and using harder lines can reduce the softness, so you are able to achieve great braking yet not too soft.

One last point about OEM brake lines. Any expansion of the brake hose during braking does NOT reduce the pressure and hence braking force as is often thought. What is does cause is greater lever travel. So soft lines that then expand under braking can allow a lever to come back to the bars. What you want is to maximise braking force, while not allowing the lever to move too far. As with so many things, it's a compromise. Honda want to provide good brakes, but make it hard to lock the wheel and on the whole they do a pretty good job. But it's always possible to tweek them for personal preference.

Finally, the VFR800 (well, most of them) use a 1/2" master cylinder which is too small for most of the callipers I mention above. Terrific force available, but too soft and tend to come back and hit the bars. However, the very common 14mm master cylinder works very well with the SP-1's or CBR900RRW/X's 32/34 callipers. I've used that combination on many RVTs and they're stunning brakes. Any of the other smaller piston callipers will work, but not as well.

Happy braking.

[JZH]

Be aware that the 2008-> 'Blade (that has BPFs) reduced the fork width from 214 to 204. The front wheel was 5mm narrower than previously and the disc offset was also 5mm less so the 10mm fork width change was shared between the wheel and the discs.

The SP-1 and 2 (RVT) and 'Blades (prior to 2008 with USD forks) use the same 214 width and front wheel and disc mount dimensions (but with axle diameter differences), but the BPF from the later 'Blades will be a problem to fit due to the different widths noted above. Nothing's impossible, but one would need to be aware of those differences.

I believe the 204 width is used on the CBR600, so if you used the 600 yokes, then the late 'Blade BPFs with wheel and discs might be a good fit as long as they clear the frame. Unfortunately, all 'Blades use a rather short fork, a good 2" shorter than e.g. the RVT which may not then provide the desired steering geometry. As I said, nothing's impossible, but always helps to know these things beforehand.

All good stuff, Ken, which I agree with. Just a query on the change from the '07 to '08 'Blades: My data says the disc offset increased from 12.5mm to 15.25mm, but I don't know where I got those dimensions...

I think I now have almost all of the data for brake calipers for most sportish Hondas of the last 25 years. The F4-on CBR600s had 34/32 pistons and 5/8" masters; the early 600RRs had 32/30 pistons and 11/16" masters (this is what I have purchased for the above "soon-to-be" VFR). As you say, there is no way to tell from the outside which size pistons are used in similar-looking calipers, so I will measure them before I install them. I think F4i calipers are black, and I know I have a set of silver ones somewhere, but all the rest are gold.

I would consider the more advanced BPF forks, but the shorter length would be a problem. Besides, I already have a complete SP1 front end I could use for this bike...

Ciao,

[Rush2112]

Great Info!

Thanks for sharing guys!

[Veefer800Canuck]

Consider the overall length is my suggestion.

The newer BPF forks are better no doubt, but check their overall length and think about possible fouling at full compression of the tire/fender and solid bits of the motorcycle.

[BiKenG]

... Just a query on the change from the '07 to '08 'Blades: My data says the disc offset increased from 12.5mm to 15.25mm, but I don't know where I got those dimensions...

I think I now have almost all of the data for brake calipers for most sportish Hondas of the last 25 years. The F4-on CBR600s had 34/32 pistons and 5/8" masters; the early 600RRs had 32/30 pistons and 11/16" masters (this is what I have purchased for the above "soon-to-be" VFR). As you say, there is no way to tell from the outside which size pistons are used in similar-looking calipers, so I will measure them before I install them. I think F4i calipers are black, and I know I have a set of silver ones somewhere, but all the rest are gold.

I would consider the more advanced BPF forks, but the shorter length would be a problem. Besides, I already have a complete SP1 front end I could use for this bike...

Ciao,

My memory indicates that the disc offset (width) reduced and thinking about it again, from first principles it would need to be less to suit the '08-> narrower forks. I can check to confirm as I have both types here, but I'm very sure the offset was reduced.

Apparently the narrower fork spacing helps reduce the frontal area and hence wind resistance of the bike and also some steering inertia. But the frame needs to be designed to suit really as otherwise the narrower forks with fat USB legs can hit the frame. Not only that but the bottom yoke design can also impact on what fits what. Try to fit a flat CBR lower yoke on an RVT and it'll hit stuff. That gull wing bottom yoke is like that to clear things like the oil cooler, rad etc. Fortunately for us, these variations mean there's probably something out there that will fit almost anything we want.

I didn't realise the 600 ever used the 32/34 calipers, but I never had anything to do with the 600s. The 11/16" master cylinder is one of the crossover type. The lever design is such that they are virtually the same ratio as the later radials, so for all those the leverage calculation would be the same. But they are all very different from the earlier master cylinders, such as on the early 'Blades, VFR800, Firestorm, RC45 and many others. You simply cannot compare the piston size. The old style 14mm master cylinder is roughly equivalent to a 19mm in the new style (and also radials) with the longer levers.

For the RRW/X 'Blades with the 32/34 calipers, Honda used a 5/8" master cylinder (old style of course). These brakes were an improvement on the earlier 27/30 calipers with 14mm master cylinder. But as we know, the 14mm master cylinder works great with those 32/34 calipers. However, I do like very strong brakes and accept that it is possible to squeeze too hard in an emergency, something Honda have always been very keen to avoid. They try very hard to make good brakes.

Most of you won't remember the first disc brakes that simply did not work in the wet and I mean really did NOT work. Most bikes combined front discs with drum rears so you at least had some braking in the wet. The situation came to the attention of the government (Department of Transport) who thought new legislation was necessary to eliminate the problem. Fortunately they did discuss their 'Wet Weather Braking' proposals with the industry first. Honda was adamant that legislation was NOT necessary and that the notion of the problem being due to the stainless discs used was misguided and far from the truth. The oft recommended cast iron discs were not in fact the solution which in fact would be found in new better pad materials, about which they were researching and working very hard to come up with the real solution. Honda requested strongly that the DOT just hold off from introducing any legislation until the problem was really solved with new pads.

The rest as they say is history. New pad materials were developed and legislation was avoided and now years later, we don't even think to mention wet weather performance of disc brakes, it's simply not a consideration. Now that's progress.

What does puzzle me though is that Honda's main brake supplier is Nissin, hardly a surprise as they are wholly owned by Honda, but the brakes they use on the top of the range bikes are from Tokico who I believe are not similarly owned by Honda. Nissin do make radial calipers, but Honda don't use them. Odd.

[Mohawk]

Honda did use Nissin, but Tokico's are cheaper. Nissin may be owned by Honda, but they operate as a seperate company, and as required by most countries competition laws, wholly owned companies can NOT give discounts to associate companies, so Nissin sets their prices & Honda or anyone else can choose them or not.

A bit like the wet weather braking, I remember when you stripped any Japanese bike in the 70/80's EVERY part had "Made in Japan" stamped on them, you rarely see that these days with the worldwide supply chain ! With a lot of Japanese bike parts being made in their south east asia factories, where labour costs are greatly reduced.

[BiKenG]

I know what you're saying about pricing, but other manufacturers use Nissin radials, like Kawasaki, Triumph and no doubt others, so were they offered cheaper prices? Also, Honda injection systems are always Kei Hin are they not. It's no big deal, but I'm just curious as to how these things come about.

However, back on topic, it would be interesting to compare trail figures between original, RVT and CBR forks, with flat and gull wing top yoke with the latter two. That would give us a good idea of what to expect. Has anyone done this? Otherwise I might have a go.

[Mohawk]

Well IIRC the yokes provide the offset, the offset determines trail, online resources show the following values for the various bikes

SP1 (RC51A) - With 24.5 degrees of rake and 100.5mm (3.96 inches) of trail

SP2 (RC51B) - With 23.5 degrees of rake and 94.6mm (3.7 inches) of trail

CBR954RR 2002-2003 - With 23.8 degrees of rake and 97mm (3.8 inches) of trail

CBR1000RR 2004-2007 - With 23.3 degrees of rake and 102mm (4.5 inches) of trail

CBR1000RR 2008-2015 - With 23.3 degrees of rake and 96.2mm (3.8 inches) of trail

Have fun.

[BiKenG]

Wow, you got all that from memory?

However that's not the whole story. You need to indicate the fork/yoke offset in each and also what trail would you get when fitted to a VFR800 as the different lengths of forks would affect the rake and hence the trail for any fork offset.

[BiKenG]

...I have a set of 1000RR forks (I think they're usable), but when I took them apart years ago I recall thinking they seemed like cheapo imitations compared with the obvious quality of my SP1 forks. But are they really worse? I'm curious if anyone knows the answer to that? Do the radial brake calipers make up for any difference?

I would disagree that the forks are of any difference in quality. They're basically all the same apart from the adjusters getting moved around. I've even made hybrids of the SP-2 and 'Blade versions to get radial caliper mounts on an SP-2. The forks caps/adjusters at the top are in fact the same, just different colours.

As for radial calipers being better, I'm going to repeat myself here, no, there's no difference in braking performance. The advantage of the radial mount is allowing the use of different disc sizes with just different spacers, that's all. It's the design of the caliper that is important, not which direction the mount bolts go. The common Nissin axial mount is a very good caliper and with a correctly matched master cylinder will provide at least as much brake performance as the radials. However if you want the bling factor of the latest technology in braking and easy disc size selection, then go for radials, but it's harder to find suitable forks as the RVTs were all axial mount. But if you do opt for radials, don't kid yourself that you're getting better brakes.

Nearly forgot, it is still possible to find adapters to fit radial calipers onto RVT forks. This is ideal as you end up with radial calipers on the long RVT forks. The only trouble is those forks are getting harder to find.

Another option is the Ohlins 'std' Road & Track forks which are even longer and designed to accept any caliper mount you want. But last time I checked, getting those adapters made was simply too much and when added to the cost of the forks, more than the VFR800 was worth.

[JZH]

The 11/16" master cylinder is one of the crossover type. The lever design is such that they are virtually the same ratio as the later radials, so for all those the leverage calculation would be the same. But they are all very different from the earlier master cylinders, such as on the early 'Blades, VFR800, Firestorm, RC45 and many others. You simply cannot compare the piston size. The old style 14mm master cylinder is roughly equivalent to a 19mm in the new style (and also radials) with the longer levers.

Ken, do you happen to know the difference in the lever ratio? I hadn't actually noticed before you mentioned it, but the "crossover" masters, as you call them, are noticeably different in outward appearance, as the orientation of the master cylinder piston is different (in-line with the clip-ons on the older masters, angled on the crossovers). I think from what you're saying, is that there are three OEM NISSIN lever ratios used by Honda on its sport bikes: straight, crossover and radial, or possibly just two: early (straight) and late (crossover and radial)?

Cheers,

[BiKenG]

Yes, I measured them all once I realised Honda were introducing higher ratio lever designs. I just measured to the end of the lever, but of course you never pull at the very end. However where you place your hand is likely to affect them all roughly the same, so I ignore that and just use the full lever length to provide the comparison.

• Master Cylinder = lever for hand / lever to piston / ratio / lbs/sq" pressure
• Original (1/2",14mm etc) = 170 / 25 / 6.8 / 4.417
• Crossover (17.50, 11/16" etc) = 190 / 20 / 9.5 / 3.950
• Radial type (17.50) = 200 / 20 / 10.0 / 4.158

As you can see the crossover lever is very similar length to the radial one. It was Honda's attempt to increase the mechanical advantage of the master cylinder until they changed to radial type. The effect of varying the mechanical advantage is basically the same as changing piston sizes to change hydraulic advantage. So why increase one and decrease another to end up with the same overall advantage? This is something I've not fully figured out.

The biggest problem with hydraulics like this is free play. For the greatest braking force you need the actuating lever (at the hand) to move as great a distance as possible (that's what translates to power in the caliper), but obviously limited so the lever doesn't come back to the bars. It's always a compromise and any free play has a big impact on these limits. I'm thinking that mechanical advantage creates less free play than hydraulic advantage since to gain the latter you need large pistons in the caliper. But the pistons have to 'pull back' from the disc surface once pressure is removed. Not a lot, but enough to not cause wear to the pads. This 'pull back' is effected by the seals and the required distance will be a constant, i.e. not affected by the piston diameter. So a large caliper piston causes greater push back of fluid when released and this requires more lever movement to take up this 'slack' again the next time the brakes are applied. However, simply changing the lever ratios causes no such problems. You just get the greater advantage with no additional free play. Hence the move to greater mechanical advantage at the expense of hydraulic advantage.

This is just my supposition, but it makes sense to me. Whatever the reason, it is the way master cylinder design has been going. The name radial as applied to a master cylinder is a nonsense really, but the perpendicular orientation of the cylinder does allow the better lever design as the figures above show.

Overall braking performance is also dependent on disc diameter, so any overall calc should also take that into account, however it makes NO difference to lever feel. So rather like longer master cylinders lever ratios. it's higher performance for no disadvantage in additional free play. But, larger discs are heavier and create greater gyroscopic forces, so there is a downside.

I've been looking at the use of a 1/2" master cylinder with 30/32 calipers. The feel will be somewhere between that of a 14mm with 32/34 calipers (very good) and that of the 1/2" with 32/34 calipers (not good, way too much lever travel). However, it's closer to the former than the latter, so it might work well. You would definitely need hard lines, but I think it would be just acceptable. Unless anyone has already tried this, I'll have to, just to find out as I want to use it on my VFR800 project.

[JZH]

Interesting. I have gone through and identified which OEM master cylinders are of this "crossover" design, and as far as I can tell there were only a few models originally equipped with them. Specifically, we're talking about:

2003-06 CBR600RR3-6, 11/16" OD (used with 310 discs and, interestingly, the same master cylinder was used with the '03-'04's axial calipers and the '05-'06's radial calipers--each of which had 32/30 pistons)

2000-01 CBR900RRY-1, 3/4" OD (used with 330 discs, 34/30 pistons)

2002-03 CBR900RR2-3, 11/16" OD (used with 330 discs, 32/30 pistons)

2000-01 VTR1000SP-1, 3/4" OD (used with 320 discs, 34/32 pistons)

2002-06 VTR1000SP-2, 11/16" OD (used with 320 discs, 32/30 pistons)

NISSIN actually sells two types of aftermarket brake master cylinders, the conventional one and one they call "semi-radial", which has the master cylinder/piston angled somewhat towards the perpendicular (no doubt the same angle they used for the "crossover" masters on the above bikes).

Good luck with your tests! I'm probably going to use 320 discs with my CBR600RR3-4 master cylinder and calipers, as I've already got a pair I can use.

Ciao,

[BiKenG]

Hey JZH, where are you when in London? I'm only just west of London. Call in sometime.

[JZH]

I'm near Greenwich, so not too far away. I sometimes ride out your way, so I'll get in touch next time I'm out that way.

I was looking further into the "Big Piston Forks" issue and it looks like this was a change Honda made in 2012 on the 1000RR and in 2013 on the 600RR. (This may explain the disc offset anomaly mentioned several posts above, if the change to 204mm fork spacing also actually occurred in 2012.) Extra bling (for anyone who gets close enough to see the fork caps!), but of no real practical benefit on the road. Still, I'm intrigued about possibly swapping "USD" fork lowers onto an otherwise stock set of SP1 or SP2 forks.

Both the 2005 Fireblade and 2012 VFR1200 had front mudguards in PB215C blue, which is the same blue as the RC46's blue, which is nice. Both 214mm fork spacing, too, so the mudguard would fit onto 1000RR forks (or any other USD forks with Showa radial caliper bottoms) held in SP1 yokes/triples and use the SP1 wheel w/o spacers.

Ciao,

[BiKenG]

Yes sorry, forgot to mention the BPFs. You're right their introduction on the 'Blade coincided with the change to 204 fork spacing, but not related.

Sounds like you have the same colour as Mohawk's.

Be careful with mudguards, they're not all the same. CBR1000 prior to 2008 used a double mount at the front, whereas the RVT, along with 929 and 954 (I think) use a single mount in front and the other behind the fork leg. So not completely interchangeable. On the 2008-> 'Blade with the narrow fork the mount points mimic those of the RVTs, but of course narrower, so no swapsies there.

I was going to use a CB1000R mudguard on the eVo4, but then decided to use Ohlins forks made for the Kawasaki ZZR1400 and it was simplest to use a mudguard to suit that. I don't like that OEM mudguard, but found a beautiful Carbon one in a better style from Japan. Expensive though.

I would choose what you like and fits and then worry about colour later, repaint if required. Don't base your whole project strategy on what's already available in your chosen colour. But handy if it does all come together like that, I agree.

[JZH]

Chooseing mods to suit existing OEM mudguards is possibly cart-before-horse, but I do get enormous satisfaction from being able to do unusual things with OEM parts! Besides, I hate painting.

Ciao,

[BiKenG]

... I do get enormous satisfaction from being able to do unusual things with OEM parts! Besides, I hate painting.

Ciao,

I'm with you on the painting and also using OEM parts on different bikes and coming up with interesting variations. Here's one I did (a lot) earlier:-

https://www.dropbox.com/sh/rz8w3fc6297btu3/AAD3zXlm3WSWvLIhFTVX78zha?dl=0

[Terry]

Interesting. I have gone through and identified which OEM master cylinders are of this "crossover" design, and as far as I can tell there were only a few models originally equipped with them. Specifically, we're talking about:

2003-06 CBR600RR3-6, 11/16" OD (used with 310 discs and, interestingly, the same master cylinder was used with the '03-'04's axial calipers and the '05-'06's radial calipers--each of which had 32/30 pistons)

2000-01 CBR900RRY-1, 3/4" OD (used with 330 discs, 34/30 pistons)

2002-03 CBR900RR2-3, 11/16" OD (used with 330 discs, 32/30 pistons)

2000-01 VTR1000SP-1, 3/4" OD (used with 320 discs, 34/32 pistons)

2002-06 VTR1000SP-2, 11/16" OD (used with 320 discs, 32/30 pistons)

NISSIN actually sells two types of aftermarket brake master cylinders, the conventional one and one they call "semi-radial", which has the master cylinder/piston angled somewhat towards the perpendicular (no doubt the same angle they used for the "crossover" masters on the above bikes).

Good luck with your tests! I'm probably going to use 320 discs with my CBR600RR3-4 master cylinder and calipers, as I've already got a pair I can use.

Ciao,

Yes, I measured them all once I realised Honda were introducing higher ratio lever designs. I just measured to the end of the lever, but of course you never pull at the very end. However where you place your hand is likely to affect them all roughly the same, so I ignore that and just use the full lever length to provide the comparison.

• Master Cylinder = lever for hand / lever to piston / ratio / lbs/sq" pressure
• Original (1/2",14mm etc) = 170 / 25 / 6.8 / 4.417
• Crossover (17.50, 11/16" etc) = 190 / 20 / 9.5 / 3.950
• Radial type (17.50) = 200 / 20 / 10.0 / 4.158

As you can see the crossover lever is very similar length to the radial one. It was Honda's attempt to increase the mechanical advantage of the master cylinder until they changed to radial type. The effect of varying the mechanical advantage is basically the same as changing piston sizes to change hydraulic advantage. So why increase one and decrease another to end up with the same overall advantage? This is something I've not fully figured out.

The biggest problem with hydraulics like this is free play. For the greatest braking force you need the actuating lever (at the hand) to move as great a distance as possible (that's what translates to power in the caliper), but obviously limited so the lever doesn't come back to the bars. It's always a compromise and any free play has a big impact on these limits. I'm thinking that mechanical advantage creates less free play than hydraulic advantage since to gain the latter you need large pistons in the caliper. But the pistons have to 'pull back' from the disc surface once pressure is removed. Not a lot, but enough to not cause wear to the pads. This 'pull back' is effected by the seals and the required distance will be a constant, i.e. not affected by the piston diameter. So a large caliper piston causes greater push back of fluid when released and this requires more lever movement to take up this 'slack' again the next time the brakes are applied. However, simply changing the lever ratios causes no such problems. You just get the greater advantage with no additional free play. Hence the move to greater mechanical advantage at the expense of hydraulic advantage.

This is just my supposition, but it makes sense to me. Whatever the reason, it is the way master cylinder design has been going. The name radial as applied to a master cylinder is a nonsense really, but the perpendicular orientation of the cylinder does allow the better lever design as the figures above show.

Overall braking performance is also dependent on disc diameter, so any overall calc should also take that into account, however it makes NO difference to lever feel. So rather like longer master cylinders lever ratios. it's higher performance for no disadvantage in additional free play. But, larger discs are heavier and create greater gyroscopic forces, so there is a downside.

I've been looking at the use of a 1/2" master cylinder with 30/32 calipers. The feel will be somewhere between that of a 14mm with 32/34 calipers (very good) and that of the 1/2" with 32/34 calipers (not good, way too much lever travel). However, it's closer to the former than the latter, so it might work well. You would definitely need hard lines, but I think it would be just acceptable. Unless anyone has already tried this, I'll have to, just to find out as I want to use it on my VFR800 project.

Thanks to you both for interesting posts. I confess I'd never considered the lever ratio but I can see how a mm or two would make a substantial difference to the pressure applied and lever travel.

As I understand it, keeping the caliper piston diameter down also narrows the swept area of the disc which can minimise differences in temperature from the outer to inner edge of the disc and hence distortion. From here I assume the designer picks the largest master diameter that will minimise the lever travel moving the pads back to the disc, but small enough to provide enough mechanical advantage for the human hand.

I have experienced the 14mm master 27/30 combination on my VTR, and did not like that much at all, as it had a real servo effect where brake force increased disproportionately to squeeze, feeling initially a bit dead then having too much bite.

I have a 5/8 mm master with 32/34mm callipers on my VFR and IMO this has too much mechanical advantage (I use EBC HH pads). I much prefer the 11/16 master and 30/32mm combination (from a CBR954) that I now have on my VTR1000F. Plenty of power with the that, and more linear and controllable. Based on my experience, that combination feels like the sweet spot.

[BiKenG]

Good point about the small caliper pistons allowing narrower frictional areas on the disc. Brembos latest and greatest bike caliper is the M50 which is 30/30 and the designer said he deliberately kept it small to reduce weight, so that's another advantage of smaller caliper pistons.

A few mm on the end of the lever where your hand operates would make little difference, but that same change in the other end of the lever, where it pushes on the piston, would make a very large difference as even 2mm would represent a large percentage of the overall length.

I think the 27/30 calipers would work well with a 1/2" master cylinder, but I'm surprised you had a problem with a 14mm and 32/34 calipers. I found that worked extremely well. But I always use OEM pads. Any pad material that bites harder will wear faster, both the pad and the disc and the latter can be very expensive, although to be fair, Honda have massively reduced the cost of their discs over the years.

[Mohawk]

From all the research I have done the best hydraulic ratio for a bikes front brake system should be in the 30-35/1 range, so 33/1 is as close to perfect as possible. Feel can be adjusted by the mechanical lever ratio !

Anything lower than 30/1 is usually too stiff at the lever, anything higher than 36/1 is usually to spongy.

Here's some number to demonstrate. With my setup, a gentle tickle allows perfect modulation of the braking effort all the way to the apex, but a stronger pull will invoke a stoppie ! Remember most brakes are 4-pot, so 8 pistons, many people for get that when calculating :)

P1 P2 M/C Kens Proposed setup
30.00 32.00 12.70 Dia
15.00 16.00 6.35 Radius
706.50 803.84 126.61 Area
2826.00 3215.36 47.72 8 pistons = Ratio 47.72/1 (will be too soft, lever will hit bar)


P1 P2 M/C My current setup
30.00 34.00 15.87 Dia CBR600F4/i M/C + CBR929 Nissin Calipers
15.00 17.00 7.94 Radius
706.50 907.46 197.71 Area
2826.00 3629.84 32.65 8 pistons = Ratio 32.65/1 (Perfection :)


P1 P2 M/C Comparison-1
30.00 32.00 15.87 Dia CBR600F4/i M/C
15.00 16.00 7.94 Radius
706.50 803.84 197.71 Area
2826.00 3215.36 30.56 8 pistons = Ratio 30.56/1 (CBR600F4/i STD setup = very good)


P1 P2 M/C Comparison-2
30.00 32.00 14.00 Dia
15.00 16.00 7.00 Radius
706.50 803.84 153.86 Area
2826.00 3215.36 39.27 8 pistons = Ratio 39.27/1 (Too soft)


P1 P2 M/C Comparison-2
27.00 30.00 12.70 Dia
13.50 15.00 6.35 Radius
572.27 706.50 126.61 Area
2289.06 2826.00 40.40 8 pistons Ratio = 40.40/1 (Too soft)

[BiKenG]

Hmm, figures ok (ignoring effect of lever ratios as you quote all old style master cylinders), but conclusions are not correct. E.g. I can categorically state that a 14mm master cylinder with 32/34 pistons is EXCELLENT. So it is certainly not too soft with smaller caliper pistons.

Of course, it does also depend on what you are looking for in a brake, but I've never had brakes that are too fierce and that wasn't combined with too much lever travel so they hit the bars and had to be pumped to make them work. So I look for the strongest brakes I can get, with a lever that works well and doesn't hit the bars and the above example fits that requirement very well.

If you instead use a 5/8" master cylinder, yes they're still good, but not AS good as with a 14. And IMO combining the 5/8" with smaller caliper pistons just makes you work harder to pull the brakes as you will simply end up with harder brakes and less lever travel but also less ultimate braking force available. Why would you want that?

Chris (Mohawk) knows the type of riding I enjoy in the Alps etc and the 14mm-32/34 setup has worked very well there for many years. No complaints whatsoever, from myself or others using the same setup. I'm not using it now as I have a different bike with a different setup, but I would have no hesitation in recommending it to anyone else. You should try it.