Brake upgrades and unsprung weight

[jetmechmarty]

We were discussing this bike recently and the replacement brake rotors were noted. I was prompted to weigh the stock brake rotors.
The stock brake rotors weigh 6 pounds plus 12 ounces each! That is a lot of unsprung weight hanging on the axles!

here’s what really happens to the unsprung mass. When you ride over bumps and surface imperfections in the road, these cause tyre compression—which induces a force on the unsprung weight. Every time you hit a bump, the wheel assembly is accelerated upwards, decelerates to a stop, and then accelerates downward until it reaches equilibrium. If the wheel can’t accelerate fast enough, shock is transmitted to the body, which may upset the balance of the bike.

Consider also that our heavy brake rotors are rotating mass. All that rotating mass works against you when you are trying to accelerate or decelerate. The internet is full of information on this subject if you care to research it.


I believe this is the rotor on the bike pictured at the top of the page. It's an EBC rotor that weighs in at 4 lbs 4 oz. That saves five pounds of unsprung weight off the front axle!


Here's a 3 lb 6 oz Brembo rotor that is available for the XS1100.


This EBC rotor weighs just 2 lbs 15 oz.

Use of these rotors will likely involve spacers and different pad compounds, the latter more easily found for the standard than the Special. It's also going to take lots of love because these upgrades don't come cheap.

For proper parts from an expert, I recommend Michael Morse at 650 Central.

[IanDMacDonald]

It seems we're all on a brake kick at the moment. I think "TheRev" has something good going with his setup, but I aam doing some reading on the UK site and was surprised to read them dissing the blue dots in comparison to the Brembo units. Not sure $300, $400, $500 is worth it for a front brake upgrade alone.

[jetmechmarty]

Not sure $300, $400, $500 is worth it for a front brake upgrade alone.

Around here the roads are mostly as smooth as glass. I took a beating at XS East in WV. I expect the heavy springs I installed make it worse than with stock springs.

Whether it's worth it depends upon how deep your pockets are, how much you ride the bike and what you've already done to it, and whether or not you have aspirations of owning a newer motorcycle. Knocking a few pounds of unsprung weight off the XS1100 would probably go a long way towards its transformation.

I have invited this discussion not having done these modifications. I have done suspension work that transformed the ride dramatically. I've drawn inspiration from bikes posted on here recently. I'm not sure if I'll go this way or not.




Right now, I'm mostly interested in the unsprung weight side of this equation. I understand there are master cyl/caliper mods to improve performance, but I mostly view that as a separate issue at this point in time.

[MaximPhil]

Hi Marty,
While the topic is unsprung weight, so far Rotors seem to be the area discussed. I have always thought that one should have only one "floating" component to brakes. Is installing a floating rotor with existing floating caliper a good idea ?

Having been wrong before once more will not bother me
Phil

[Mathh]

With a bit of fantasy and elbow grease you can fit anything. The last set I installed was this week and were a 1980s' magnesium PVM 18" front wheel with Yamaha Brembo discs and 1980s' Ducati 851 Brembo calipers ... All in a standard fork.

[natemoen]

With a bit of fantasy and elbow grease you can fit anything. The last set I installed was this week and were a 1980s' magnesium PVM 18" front wheel with Yamaha Brembo discs and 1980s' Ducati 851 Brembo calipers ... All in a standard fork.

Pics and details please!

[jetmechmarty]

Hi Marty,
While the topic is unsprung weight, so far Rotors seem to be the area discussed. I have always thought that one should have only one "floating" component to brakes. Is installing a floating rotor with existing floating caliper a good idea ?

Having been wrong before once more will not bother me
Phil

Phil, I'm glad you brought that up. I really don't know the answer. I did find this after a quick search:

Floating rotors dont actually float to center the caliper, they are just multi piece to reduce warpage.

I don't know if the statement is true or not. I assume the rotors I posted are OK since someone I trust is selling them to mix with the same caliper that the XS1100 standard wears.

With a bit of fantasy and elbow grease you can fit anything. The last set I installed was this week and were a 1980s' magnesium PVM 18" front wheel with Yamaha Brembo discs and 1980s' Ducati 851 Brembo calipers ... All in a standard fork.

Mathh,
You are obviously gifted beyond most mortals! I think I am pretty good at figuring out how to fix stuff the way the original engineers intended. I struggle to get out of that box.

[rover]

unsprung weight

These wheels are REALLY heavy. Replacing them with super light or even spoked wheels would greatly reduce the unsprung weight and the rotating mass.

[jetmechmarty]

I have some XS650 wheels with steel rims. I don't know how much they weigh, but I guess it's close to the same as the cast wheel. The XJ/Virago wheels look like they weigh less. True?

[Mathh]

Hi Marty, it is all about taking the step to try it. I've been reading on this forum for quite some time now and the questions about upgrading brakes have appeared ever since. People here often ask for drawings to make adapter plates, but when you are in the proces of upgrading your brakes it really is not a lot of extra work to get out your forks with wheel and brakes, lay them on their side on the floor, put the parts you want in their place and draw a template on cardboard or wood to check how the adapter plate should look. You can even make ally plates by hand using a saw and or file. Difficult ones can be brought to someone with a milling machine for the final touch. Everything step by step, thinking logically, measuring everything correctly, drilling the holes as late as possible and making sure the calipers are running free from the discs and wheel. Common sense and patience is the most important. And who cares if you have to try two or three times before the end result is acceptable?
If you have done it more than once you don't even need the cardboard template anymore

I' ll post some pics of brake upgrades I did in the past. I always installed brakes that I wanted to have, not which ones fitted the easiest. And always used second hand parts, not new ones. Much cheaper than buying aftermarket replacements. And with the money you keep in your pocket you can buy a couple of bottles of beer for the guy with the milling machine.

[XS1100carbon]

Floating rotors

I've been told the floating rotors came from racing. The reason being to separate the outer rotor heat from the hub and bearings. Sounds reasonable. The weight reduction is nice too.

[jetmechmarty]

I just put a front wheel with worn out tire on the scale. It comes in just under 40 lbs. In the case of John and the Enterprise, the 5 lbs shaved off by those aftermarket rotors is significant.

[fredintoon]

I just put a front wheel with worn out tire on the scale. It comes in just under 40 lbs. - - -

Hi Marty,
don't remember the numbers because it was several years ago but one time I weighed two XS650 front wheels (same wheel as on XS750/850/1100) against one another. Within the accuracy limits of a bathroom scale the aluminum-rim wire wheel and the 7-spoke cast wheel weighed exactly the same.

[jetmechmarty]

Fred,
Did you weigh them with tires on them? One of those wheels would would have included a tube. The easiest place to shed rotating mass is the brake rotors.

[trbig]

Easiest way to shed strength is use spokes..

I was about to make some crack about saving 5lbs on rotors, then adding 6lbs worth of 4 piston Brembo calipers.. But it's still getting rid of the rotating mass weight and would be OK. Besides, XS11's would look cool doing one-finger stoppies!