Re-engineered V11S rear brake interest?

[GTM®]

For those who own V11 Sport variants... tired of having your rear brake rendered useless after a few turns in the twisties?
I'm looking to see if there is any interest in a rear brake kit that would upgrade the system including the rear master cylinder, caliper (to a 4-piston variety) and either a modified stock bracket and stay pin or one CNC'ed from scratch?
This will also finally resolve the premature bearing failure as well.
The kit would likely be ~$600 USD.
Mock-up (using used parts) on my LM track bike;

 

[Belfastguzzi]

I'd be interested, if I hadn't just bought another bike, as my V.11 caliper melted.
I think that part of the problem is the low upside-down position that these things are mounted in.

So I can't afford it just now. In the longer term I'd be interested.

 

[GTM®]

It's not the mounting position that's the problem, it's that the caliper and master cylinder are too far undersized for the 280mm rear rotor and weight of the bike.

 

[pauldaytona]

undersized? I had 2 times one failing, and what heppens is that the disk gets red glowing. A piston that is undersized can't do that.
What I noticed, is that the brembo caliper doesn't have any dust seal, the ealier version as mounted on the daytona did have that, and never had a problem. They look the same outside, but the dust seal is missing. Cheap manufacturing.

But after that I took I ral cailiper: PVM 4 piston, very expensive. And look what it did to a new braking wave disk:

I even have a picture of that, look at the disk:

 

[GuzziMoto]

I gotta say, I don't follow your logic, Todd. It sounds like you are suggesting that the caliper is too small and that causes brake fad. That does not make sense to me. Brake drag caused by a crappy caliper could cause fad, but I don't see how an undersized caliper could.

 

[GTM®]

My logic is simple... aside from the problematic rear bearing issue and improper caliper alignment on the stock bracket, the rear brake can be easily rendered useless in a few corners. The post on the meltdown above, is one of many I have heard of and witnessed over the years. I am not sure why Guzzi chose such a small caliper and m/c for the Sport line. The 282mm rear disk can be fully benefitted by a larger caliper. Stock m/c on my LM is 11mm. The California's use a 2-piston caliper (shown above) and a 13mm m/c that works brilliantly, no matter that I throw at it, even on the track.

 

[GuzziMoto]

What I don't understand about your logic is that caliper size has little to do with fade. If the caliper sticks, as I believe the stock caliper can be prone to doing, that can cause drag which can lead to fade. But the size of the caliper does not have much effect on fade in my experience. A 4 piston caliper on the rear is much larger then I have ever needed. I have not had a problem with the stock set up, but I try to keep it reasonably clean and working correctly (a task made harder by the mounting position/location) and neither my wife nor myself is a big user of the rear brake.
I am not saying that you should not improve the stock rear brake set up, I just don't understand why you are associating brake fade with caliper size.

 

[guzzi jon]

I experienced rear brake pedal go missing on my Kawasaki ZX-9R, my 02 Lemans and Ed's/Chucks Quota after going down some twisties and trail braking. With Ed's Quota and my ZX-9R, the problem was water in the brake fluid, its hydroscopic and absorbs water over time. Ed's quota may be worse as Roger ran out of brakes and ended up stuck in the mud running off the track when the brake failed. If the caliper is not up to the job, and heats up, the braking feel can go away, if you have any water in your brake fluid (its over six months old), your brakes will dissappear. I have experienced this on several bikes with several brands of braking systems.... poor fluid was a common demoninator, but on my bikes that have never had a problem, adequate calipers and discs were not near as likely to give up due to poor maintenance. When you are going into a corner hot, and you press the rear pedal and it goes all the way down without any slowing, well, you can guess the rest, the best outcome is an expensive cleaning bill for you leathers. As for my Lemans, changing out the fluid and adding new pads eliminated the problem, the Quota, it could not be cured, the caliper and MS are simply not up to the task of aggressive rear braking..... (New pads are thicker and take longer to heat the brake fluid in the calipers as well) EBC HH's worked for me

 

[motoguzznix]

The problem is the small brake pad area of this caliper given by the small pistons. On my V11 the rear brake pads never lasted longer than 5000 km, no race track use.

A four pin calipper wold double the pad area and thus reduce the heat generated during braking. For the eaqual braking performance the disk would get less hot.
Less brake pad wear would be the other benefit.

Therefor I think Todds idea is the correct way to solve the problem.

 

[GuzziMoto]

The problem is the small brake pad area of this caliper given by the small pistons. On my V11 the rear brake pads never lasted longer than 5000 km, no race track use.

A four pin calipper wold double the pad area and thus reduce the heat generated during braking. For the eaqual braking performance the disk would get less hot.
Less brake pad wear would be the other benefit.

Therefore I think Todds idea is the correct way to solve the problem.

Except that the temp of the disc would not likely reduce. You would still have the same amount of energy (heat) being input into the same amount of disc. For a given amount of reduction in speed there is a given amount of heat produced. The temp of the brake pads might go down slightly as the increased mass of the pads would diffuse the heat that the pads absorb during braking slightly. But the disc temp is typically what is the determining factor in brake fade, not pad temp. When the disc over heats the brakes fade. More of the heat from braking goes into the disc then the pads, and the discs greater mass is part of the equation. If the pads got as hot as the discs, over 800 to 1000 degrees, the fluid in the caliper would have long since boiled (most brake fluids can't handle more the mid 500's). You would likely see increased pad life by increasing the size of the pads, but that is not the same thing as resistance to fade.
Todds mod may improve rear brake feel for people who use their rear brake that much, but unless it reduces brake drag I don't see how it could reduce fade. Cleaning your caliper and making sure the brake is set up correctly could accomplish that as well.
Upgrading to higher quality calipers and master cylinders has more effect on feel of the brakes. Upgrading the disc has the most effect on fade, although it can have an impact on feel with a switch in disc material.

 

[GuzziMoto]

The problem is the small brake pad area of this caliper given by the small pistons. On my V11 the rear brake pads never lasted longer than 5000 km, no race track use.

A four pin calipper wold double the pad area and thus reduce the heat generated during braking. For the eaqual braking performance the disk would get less hot.
Less brake pad wear would be the other benefit.

Therefore I think Todds idea is the correct way to solve the problem.

Except that the temp of the disc would not likely reduce. You would still have the same amount of energy (heat) being input into the same amount of disc. For a given amount of reduction in speed there is a given amount of heat produced. The temp of the brake pads might go down slightly as the increased mass of the pads would diffuse the heat that the pads absorb during braking slightly. But the disc temp is typically what is the determining factor in brake fade, not pad temp. When the disc over heats the brakes fade. More of the heat from braking goes into the disc then the pads, and the discs greater mass is part of the equation. If the pads got as hot as the discs, over 800 to 1000 degrees, the fluid in the caliper would have long since boiled (most brake fluids can't handle more the mid 500's). You would likely see increased pad life by increasing the size of the pads, but that is not the same thing as resistance to fade.
Todds mod may improve rear brake feel for people who use their rear brake that much, but unless it reduces brake drag I don't see how it could reduce fade. Cleaning your caliper and making sure the brake is set up correctly could accomplish that as well.
Upgrading to higher quality calipers and master cylinders has more effect on the feel and power of the brakes. Upgrading the disc has the most effect on fade, although it can have an impact on feel with a switch in disc material.

 

[GTM®]

Michael, only thing I can add is this is the OEM set up on the Jackal, which sees a good deal of hard riding in the local canyons and on the track, and I have zero brake issues. When on the track I do ~300 miles/day, 40 minutes per hour on track, on average. 1/3rd of those miles are run pretty hard all things considered (it's a track day, not a race day).

 

[GuzziMoto]

Don't get me wrong. I am all for making improvements to bikes. I am just questioning the hows and whys. It may be that your mod has less fade then the stock set up, but I would expect that if it does it is for reasons other the the size of the brake pads.
My Daytona has almost the exact same rear brake set up as my wifes V11 except that the Daytona mounts the caliper at the bottom which is may the worst spot to put the caliper. Neither bike is prone to brake fade, and that includes recently when my new front brakes (that came with the GSXR front end) acted up and I rode the rest of the way using only the rear brake. I don't usually use it that much, which may explain me not having issues with the rear brake. Or it could be some other reason.
Any way. I do think upgrading your brakes is a good thing, But the rear brake caliper on the V11 is not in my experience inherently flawed, although the bleed is in a bad location and it is hard to keep clean due to the mounting. But this just means that to properly service it you need to remove it from the bike.

 

[Rafael]

Except that the temp of the disc would not likely reduce.

I think the larger pad will reduce the peak temperature during hard braking by allowing the heat to be disbursed over a larger area of the rotor allowing to cool and maintain a lower temp. The formula for calculating heat is probably more complex than a unit of heat is equal to a unit of friction in a situation where two different designs are being compared. The pressure required for the equivalent braking will change with a different pad size. Imagine if the original pads were 1/4" wide, they'd reach a high temp faster.

Anyway, my question is what makes an opposing 4 pot caliper better than a 2 pot (same side) floating caliper for the rear. If a 2 pot floater is used, can the original MC be kept? It be cool to see test results for the redesigned set up.

thanks, Rafael

 

[GuzziMoto]

The swept area of the rotor does not change. The mass of the disc does not change. Yes, larger pads could run a little cooler then smaller ones, but that is just the pad temp not the disc temp. Larger pads, having a larger surface area in contact with the disc, are also capable of putting more heat into the disc (more surface area too apply said heat into the disc). But that may not be that important as it would likely be more heat but over a shorter time, so it should balance out.
The pressure at the lever required does not really change with larger or smaller pads until you are applying large amounts of force on the brake lever. At small levels of braking the force required should not change much. Larger pads simply spread the clamping force of the caliper out over a larger area. There may be a small change in pressure required but I would not expect a large change. The big change comes from changes in the amount of fluid it takes to displace the pistons on one side of the caliper compared to the amount of fluid the master cylinder displaces. A two piston floating caliper can require the same size master cylinder as a matching four piston caliper with equal piston sizes, but a two piston opposed caliper with the same sized pistons would not.
Do you suffer from rear brake fade?

 

[Rafael]

Nope, no rear brake fade; mostly touring. Just thinking about friction and the heat it generates. There's nothing like an actual test though. I agree about the rotor being a fixed factor, but I suspect that an increased pad size would increase the area that the heat is transfered into the rotor allowing it to cool more quickly, but that might be negligible. Waiting for test results on the V11S...

 

[GuzziMoto]

Oh, and as far as the reasons to use an opposed piston caliper over a floating caliper. The opposed piston caliper would usually have better feel all else being equal as the floating caliper tends to have more inherent flex. Opposed piston calipers tend to be more rigid and that equates to better feel. But that is a generalization and not all floating calipers would have more flex.