Bigger Brakes?

[Stephen.G.Fiddes]

I'm probably going to receive some flack for coming up with this idea, try not to flame too much guys... And PLEASE correct me if any of my thinking is wrong on this... (Really hoping for BDF to chime in)

I've done some searching around, and can't find much as far as larger rotor conversions on Motorcycles, except in the motocross world.  To me it makes sense, especially on these heavier bikes.  If you look at Moto GP Rotors they are HUGE compared to street rotors.  They're definately a larger diameter, but also have more surface area.  I understand their brakes probably cost as much as our bikes, but physics says that a similar thought process could (and should) be applied to the street...

Brakes work in a similar fashion to a breaker bar... The longer the breaker bar, the easier it is to bust a nut loose (Easy boys!).  The larger the diameter of brake rotor, the more stopping force can be applied (per percentage of effort put into the brake lever).

The larger rotors should also be able to stay cooler as they have longer to go around, and there is less friction needed to get the same amount of stopping power...

Also with that less friction, there should be less pad wear increasing the usable life-length of the pads.

I understand that it would also be easier to lock up the wheels, but with ABS, that shouldn't be an issue (unless of course the difference in required pressure would throw the ABS computer off...?)



Again this is all theoretical, but I don't see why it wouldn't work... I'm looking for someone to either prove me wrong, or confirm my thoughts and wonder why there aren't 320 mm rotors for our bikes. (Cause there is room for the calipers to be spaced out 5mm...)

[Racer Boy]

I haven't ever heard of anyone complaining that the brakes needed to be upgraded on C14's (unlike C10 brakes, which are barely adequate for brisk street riding).

The larger the rotor, they heavier they are. Unsprung weight is a bad thing, even on a heavy bike like the C14.

Larger rotors don't run cooler because they take longer to go around, because they don't take longer to go around. They spin at the same rate; think about it a bit and you'll understand. Larger rotors can run cooler because they have more mass, which doesn't get as hot, all things being equal. The fact that they have more surface areas may also play a small part in that.

Are rotors larger than 320 mm commonly available? In my opinion, Kawasaki really did do a good job on the brakes for the C14. I'm sure that if you do trackdays (which I'm sure wasn't part of the intended usage for this bike) the brakes might need some help, but for street riding, they are awesome.

[Stephen.G.Fiddes]

I haven't ever heard of anyone complaining that the brakes needed to be upgraded on C14's (unlike C10 brakes, which are barely adequate for brisk street riding).

The larger the rotor, they heavier they are. Unsprung weight is a bad thing, even on a heavy bike like the C14.

Larger rotors don't run cooler because they take longer to go around, because they don't take longer to go around. They spin at the same rate; think about it a bit and you'll understand. Larger rotors can run cooler because they have more mass, which doesn't get as hot, all things being equal. The fact that they have more surface areas may also play a small part in that.

Are rotors larger than 320 mm commonly available? In my opinion, Kawasaki really did do a good job on the brakes for the C14. I'm sure that if you do trackdays (which I'm sure wasn't part of the intended usage for this bike) the brakes might need some help, but for street riding, they are awesome.

I don't think you could fit bigger than 320 on it...

The purpose would mainly be to reduce pad wear (due to the extra weight, these bikes burn through pads pretty quick, and they're the same pads the ZX-10 uses... Especially 2-up), and less heat buildup to prevent warping (which is a known issue)

[maxtog]

To me it makes sense, especially on these heavier bikes.

I can't imagine it would be worth the cost/complexity.

If you look at Moto GP Rotors they are HUGE compared to street rotors.

They are also going much faster than people on the street (or I certainly hope so) and are using the brakes more often and for longer periods, requiring more heat dissipation.  Braking capacity beyond what the tires can grab is usually (but not always) a waste.  And the excess also comes at a price- dollars, total weight, unsprung weight.

The larger rotors should also be able to stay cooler as they have longer to go around, and there is less friction needed to get the same amount of stopping power...

First part yes.  Second part no.  Friction is what stops.  Brakes are converting mechanical energy into heat through friction.  That energy conversion is the same for a set mass declaration over time, regardless of the size or types brakes.  Larger surface area for that friction will increase potential stopping power.

Also with that less friction, there should be less pad wear increasing the usable life-length of the pads.

There is the same amount of friction, it is just spread over a larger area.  If the pads are larger, they will last longer (assuming the same composition); otherwise the life should remain similar.  If the rotor is larger, it MIGHT tend to extend the life of the pads, but probably not under typical street conditions.

I understand that it would also be easier to lock up the wheels, but with ABS, that shouldn't be an issue (unless of course the difference in required pressure would throw the ABS computer off...?)

Once you reach the limit of the tires, no additional braking force is useful (unless we are talking about extended use with heat fade and such).

[Stephen.G.Fiddes]

Maxtog: 

Pretty sure I did a horriffic job of explaining my thoughts the first time... lol

Obviously I know GP bikes are going faster and braking harder for longer, but they also have special pads that cost money and they have money and blah blah blah...

To go back to the breaker bar, if you try to remove the front engine bolts to mount the Canyon Cages, and do that with a ratchet, good luck... But if you use a breaker bar, applying less force, you can get more torque against the bolt...

Therefore, (in my head) the braking force required at the caliper/pad/rotor relationship *SHOULD* have to be less, in order to have the same amount of traction usage at the tire

310mm:  70% applied at the brake lever, 95% traction used at the tire on a given surface
320mm:  60% applied at the brake lever, 95% traction used at the tire on a given surface
Disclaimer: ^^ made up numbers in my head

Because you don't have to pull the brakes as hard, that would use less pad and rotor...


Like I said, I could be completely off base on this... And most likely am... But the thought crossed my mind.    The only real advantage/ purpose would be to save brake wear. The next question would of course then be the first point you brought up, is it enough savings to justify any kind of cost? Who knows... 320MM Rotors can't cost that much more, and a spacer for the caliper would be easy enough to machine up (and I'm pretty sure they already exist...)

[gPink]

Some good info in this thread if you dig down deep enough.

http://forum.cog-online.org/index.php/topic,47664.30.html

[martin_14]

Stephen,
your logic is ok, but as Max pointed out, once your braking system can lock up the wheels, there's nothing you can do with extra performance from the brake system. Except...
The brake system is not only made to brake, but to brake repeatedly. So, just like a sports car has wider tires to deal with more power (and change the saturation characteristics of the vertical vs. lateral load, but that's another story), the real deal with mounting an over-dimensioned brake system is to fight fading. Just like one of the real reasons to mount wider tires is to increase longevity and deal with heat.
Porsche did an amazing study in the '90s where they proved once and for all that, just like we learnt in school, the contact area means squat to the braking performance. With one caveat: once. Since in the real world you have more than just the applied force and the coefficient of friction, heat and hence fading will start decreasing the performance, and that's where it's better to built-in some safety margin in the system.
I came to the limits of the braking system in this Kawasaki more than once, and I mean lever-to-the-grip braking, where the bike was well under-performing in the brake department and had to back off. Granted, I was chasing (and keeping up with) sports bikes in the best Italian passes, but after half an hour of extreme driving the brakes were toast and remained like that for the rest of the morning. Only after lunch I could grab a handful again.
Steel brake lines, thicker discs (heat resistance and dissipation), better pad/brake fluid thermal isolation... all would help.

[B.D.F.]

Gee, you make it sound like I am the guy who will come along and pi$$ on everyone's 'wrong thinking'. :-)

Actually what you propose is interesting and has several facets I think that would require some thought and testing to prove one way or the other.

But just going by logic and a couple of 'rules' (physics), to accomplish the same braking, the same amount of energy must be generated (not exactly right but very close for our purposes). So a larger rotor would take the same energy but spread it through more material, which would mean a lower peak as well as average operating temperature (same amount of heat, more area, equals less temp.). So the system would run cooler. How much I don't know and probably not enough to justify the cost / weight but still, it should work.

As far as brake pads lasting longer, I think that would be a wash either way or again, extremely close. Same pad size, same braking effort used will consume the same amount of pad (or very close). Your thinking is correct I believe regarding the lower force of the pad due to the increased radius.... but, the rotor would have to have a higher surface speed also (same wheel RPM, larger dia. rotor equals higher rotor surface speed). I think the lower pressure and higher speed would equalize.

As others have pointed out, this would increase unsprung weight. Again, enough to notice in the 'real world'? Probably not.

Sorry no definitive answers or even complete thoughts on whether this would be an effective improvement or not. I believe actual testing would be needed, and then with some lab. equipment, to know if it was an worthwhile change or not.

As I said though, interesting line of thinking IMO.

Brian

I'm probably going to receive some flack for coming up with this idea, try not to flame too much guys... And PLEASE correct me if any of my thinking is wrong on this... (Really hoping for BDF to chime in)

I've done some searching around, and can't find much as far as larger rotor conversions on Motorcycles, except in the motocross world.  To me it makes sense, especially on these heavier bikes.  If you look at Moto GP Rotors they are HUGE compared to street rotors.  They're definately a larger diameter, but also have more surface area.  I understand their brakes probably cost as much as our bikes, but physics says that a similar thought process could (and should) be applied to the street...

Brakes work in a similar fashion to a breaker bar... The longer the breaker bar, the easier it is to bust a nut loose (Easy boys!).  The larger the diameter of brake rotor, the more stopping force can be applied (per percentage of effort put into the brake lever).

The larger rotors should also be able to stay cooler as they have longer to go around, and there is less friction needed to get the same amount of stopping power...

Also with that less friction, there should be less pad wear increasing the usable life-length of the pads.

I understand that it would also be easier to lock up the wheels, but with ABS, that shouldn't be an issue (unless of course the difference in required pressure would throw the ABS computer off...?)



Again this is all theoretical, but I don't see why it wouldn't work... I'm looking for someone to either prove me wrong, or confirm my thoughts and wonder why there aren't 320 mm rotors for our bikes. (Cause there is room for the calipers to be spaced out 5mm...)

[Rembrant]

[Steve in Sunny Fla]

Having done larger rotors on my c-10 but maintaining the stock calipers, I can say the OP's assertion that the rotor diameter increase will result in better braking is spot on. Stock front rotors on a later model are 300mm, I installed 320's from a zzr1200 and the increased braking was very obvious. Less effort at the grip to achieve the same level of stops.

  As far as pad wear, well, when your brakes work better you might ride faster, and stop harder, so I can't say the pads lasted longer  Steve

[VirginiaJim]

I'm trying to understand this but I think I'm missing something here.  If you leave the stock calipers on with the stock pads and increase the rotor diameter, how is that going to help anything?  The pad surface area on the rotor stays the same.  They (the pads) don't have a clue that you've changed the rotor.  I could understand that if you upgraded the calipers as well with larger pads but I'm not seeing the connection..

[jimmymac]

You've got ZX14 brakes, the best in the business, on the Connie. If you're worried about pad wear, ride in a lower gear. The Connie's brakes are the best thing on the bike.

[VirginiaJim]

I totally agree.......when they aren't pulsing or warped.

[gPink]

Here in the midwest flatlands I find it easier to out ride my brain than the brakes.

[Rembrant]

I'm trying to understand this but I think I'm missing something here.  If you leave the stock calipers on with the stock pads and increase the rotor diameter, how is that going to help anything?  The pad surface area on the rotor stays the same.  They (the pads) don't have a clue that you've changed the rotor.  I could understand that if you upgraded the calipers as well with larger pads but I'm not seeing the connection..

The gain would be in moving the calipers outwards by 5mm. For a 10mm increase in rotor OD, you'd have to move the caliper out by 5mm.

This is a really common mod for the track guys....just about everybody with an older sportbike bike is running newer (larger OD) rotors, with calipers spaced out (at least with the bikes from the early to mid 2000's and up that have factory radial mount calipers).

The spacers are available pre-made in various sizes and have been available for a long time...or people simply make their own. The difficult part is in finding longer caliper mounting bolts...they're available, but you usually can't get them at the local fastener shop or hardware store.

I did a radial swap a few years back...installed a set of black Tokico calipers from a 2007 ZX10R on my 2002 ZRX1200R. The adapter brackets I bought came with a few different caliper spacers to get everything set correctly with the rotor OD.

As a stand alone mod on a newer C14 for street use...I would never even bother with it for the little gain (perceived or otherwise) there would be. On the other hand...IF you had to replace your front rotors anyway and had no warranty...I guess you could bump up to the next size and space out the calipers...if you wanted to. Personally, I would never bother...I find the stock C14 brakes to be fantastic. In fact, the stock calipers on the C14 are highly sought after by the guys with the older Kawi track bikes...2007 and older ZX10R, and 2006-older ZX6R.

JMTCW,
Rem

[Rhino]

I'm trying to understand this but I think I'm missing something here.  If you leave the stock calipers on with the stock pads and increase the rotor diameter, how is that going to help anything?  The pad surface area on the rotor stays the same.  They (the pads) don't have a clue that you've changed the rotor.  I could understand that if you upgraded the calipers as well with larger pads but I'm not seeing the connection..

Larger diameter means more leverage as well as greater rotor surface area for cooling. All that said, I agree with with everyone else that the brakes on the C14 will stop this beast on a dime. The issue would be on a track and continuous hard braking. Brakes turn kinetic energy into heat. Got to get rid of that heat some how. Bigger rotors is the way to go for that.

[B.D.F.]

Everything you said was exactly right Jim as far as just changing the rotors. But in addition, he is talking about spacing the calipers out farther away from the axle to use the outer part of the new, larger rotors. So the area the pads actually contact is larger in diameter. The calipers and pads remain the same but they use a different, larger swept area of the new, larger rotor.

Brian

I'm trying to understand this but I think I'm missing something here.  If you leave the stock calipers on with the stock pads and increase the rotor diameter, how is that going to help anything?  The pad surface area on the rotor stays the same.  They (the pads) don't have a clue that you've changed the rotor.  I could understand that if you upgraded the calipers as well with larger pads but I'm not seeing the connection..

[Rembrant]

...and a spacer for the caliper would be easy enough to machine up (and I'm pretty sure they already exist...)

Yup...they're all over the place...you just have to search for other Kawi models...

These are 10mm spacers I think...

http://www.moto-racing.co.uk/prod/ZX10SpacerKits

Rem

[Stephen.G.Fiddes]

Gee, you make it sound like I am the guy who will come along and pi$$ on everyone's 'wrong thinking'. :-)

Ha, no I value your opinion, experience, and knowledge.

Actually what you propose is interesting and has several facets I think that would require some thought and testing to prove one way or the other.

But just going by logic and a couple of 'rules' (physics), to accomplish the same braking, the same amount of energy must be generated (not exactly right but very close for our purposes). So a larger rotor would take the same energy but spread it through more material, which would mean a lower peak as well as average operating temperature (same amount of heat, more area, equals less temp.). So the system would run cooler. How much I don't know and probably not enough to justify the cost / weight but still, it should work.

As far as brake pads lasting longer, I think that would be a wash either way or again, extremely close. Same pad size, same braking effort used will consume the same amount of pad (or very close). Your thinking is correct I believe regarding the lower force of the pad due to the increased radius.... but, the rotor would have to have a higher surface speed also (same wheel RPM, larger dia. rotor equals higher rotor surface speed). I think the lower pressure and higher speed would equalize.

Brian

Brian this is exactly what I was looking for. Especially the last sentence.  I knew I was missing something in my logic.

So now the only REAL gain would be slight heat dissipation which MIGHT help with warping, but no guarantee (unless you had a round rotor instead of the contoured like we got stock on the bike.)

Unless of course you were to go completely aftermarket and at that point you're talking some coin far beyond any money saved on the other end...

[Stephen.G.Fiddes]

Now I'm seeing that someone has done 330mm brakes... through this link someone else posted...

http://forum.cog-online.org/index.php/topic,47664.30.html

Again, not looking at braking power, as we can lock them up with the stock brakes... Now looking at heat dissipation and pad life...