[alex spencer]

how much does a caliper half for a hope E4 cost? i need one to put my front disc upto 205mm as the 185mm can't stop me fast enough, so i'm going to get a rear 185mm system (hopefully without a rotor) and i'll stick the front rotor i have now on the rear and get a new rotor and caliper half for the front.

oh yeah, will a 205mm E4 on the front rip the disc mount off my 2000 JR t's?

 

[KonaDude]

I don't have a price on the half calipers. Drop by your local bike shop and they'll probably look it up for you.

As far as ripping the disc mount off, it's not likely. Using a larger rotor puts less load into the caliper.

 

[alex spencer]

thanks, i'll try to find out the price at my lbs.

and thanks for the adive on the disc size thing, i just don't want to rip the disc mount off when i'm trying to stop.

 

[Brian HCM#1]

Originally posted by alex spencer
how much does a caliper half for a hope E4 cost? i need one to put my front disc upto 205mm as the 185mm can't stop me fast enough, so i'm going to get a rear 185mm system (hopefully without a rotor) and i'll stick the front rotor i have now on the rear and get a new rotor and caliper half for the front.

oh yeah, will a 205mm E4 on the front rip the disc mount off my 2000 JR t's?

I usally charge $65-$70 US for the caliper halfs. I'm supprised for what you said about the 185mm rotor. I ran that for years without any problems on my DH bike. Now i'm running a 205mm in the front and its even better. You need the #8 caliper half for the front for a 205mm and a #8 caliper half in the rear to run a 185mm. If you need the complete system for the rear you'll get everything. I think buying the caliper and lever seprate would be more expensive + you'll have an extra rotor laying around. As far as the Jr. T I'd ask Hope. I don't think there would be a problem.

 

[alex spencer]

i think it doesn't stop me too well because i'm 250 pounds, and go far too fast, i'm going to try to get a rear brake without the rotor as it will be cheaper, i've emailed marzocchi, windwaves (uk marz importers and mbuk, to see what they say, thanks for the info.

 

[Dog Welder]

Yes, according to Marzocchi, and a number of other people whom I have asked this...if you are running a QR DO NOT USE a 200mm rotor. They have developed stress fractures near the brake mount. I have a 01 JrT and I've also noticed that the QR doesn't do a good job of holding the wheel in place when I lay on teh front brake. To make it hold the wheel in place I've had to REALLY torque down on the QR. But if you torque too much you stand the possibility of snapping at the stancions. If you want to run a big rotor Marzocchi recommended that you have something with a 20mm axle. Oh yeah the warranty is void if you do run a large rotor. They told me this because I tried to do the same thing.

 

[KonaDude]

Marzocchi's silly.

Considering they have the exact same disc mount on the regular axle forks as they have on the QR.20 forks (which are supposed to use 8" rotors) they're just full of it.

yes, Marzocchi's had a few disc tabs break. But the fact remains that 8" rotors put LESS force into the caliper than a 6" rotor.

hm.

 

[Dog Welder]

Hey Kona Dude...how do you reckon that? An 8 puts less stress than a 6? Its all in the leverage ain't it? If I have a 8in lever it is easier to put more force on an object than a 6in lever. Plus you got to figure what would Marzocchi gain from telling me otherwise. It they don't break on the majority of the forks they make then you'd figure that they wouldn't have a problem with me running the 8.

 

[gravity]

Originally posted by Dog Welder
Hey Kona Dude...how do you reckon that? An 8 puts less stress than a 6? Its all in the leverage ain't it? If I have a 8in lever it is easier to put more force on an object than a 6in lever. Plus you got to figure what would Marzocchi gain from telling me otherwise. It they don't break on the majority of the forks they make then you'd figure that they wouldn't have a problem with me running the 8.

an 8" puts less stress than a 6" on a fork cos its the fork applying leverage to the rotor, not the other way around. so the fork has more leverage therefore less load per distance traveled than with a 6" rotor.
the theory here is that if you need say 50kg of force to move something one metre, no matter how you do it 50kg of force must be applied. by using a longer lever, you push a greater distance on the lever, but with less force-to-distance ratio. eg if you have a lever one metre long on the load side of the pivot and ten metres long on the force side (the side you are pushing on) you have to move your side ten metres to move the other side one metre, but as you need a total force of 50kg to move it that far, it needs 5kg of pressure per metre, continued for ten metres (10x5=50). here the ratio is 10:1 of distance vs mass. compare this to when the lever is one metre long on each side of the pivot, you must apply 50kg/metre of pressure to move it a metre, as the ratio is 1:1.
as the force that the brakes are acting against is the momentum of the frame/bike/rider, not the spinning wheels, therefore the f/b/r is applying force to the wheel through the disc, not the other way around.
i hope you followed that dog welder!

 

[alex spencer]

it does make sense, but i've got replys from marzocchi who say its a no-no and windwaves the uk importer who say its fine as long as its set up right, which i can do.

 

[Dog Welder]

How do you set it up right? Do you mean just the installation part? Hey Alex keep me posted...if it works for you I'll try it also.

 

[Micro-Sanjay]

DH4s (enduro) rule...I own a prehistoric set. 12th from the original production run and still works. I have replaced the half caliper on my rear so I can ran the bigger rotor (since I warped the 6" rotor so quickly like it's noone's business). A week into the ride, the caliper just yanked itself out of the tabs ripping the threads in the bolt holes. A couple of my racing buddies with exact setup have had this happen. They said it's due to the added sheer power produced by the 8' rotor setup. I think it's just the soft and shallow alum thread on the caliper bolt holes. Regardless, my rear caliper is running one hole with a bolt and nut setup.. Is this related to the thread anyways...I'm sleepy...

Corporate racer:
Ozzer

 

[gravity]

ozzer, you better change that sig before RM sees it...... he'll crack it big time!

 

[KonaDude]

The deal is: Your wheel has approximately a 26" diameter. 13" radius. The 6" rotor has a 3" radius.

13/3 = 4.33.

So, a force applied to the outside radius of the wheel is multiplied by 4.33 at the outside of the rotor.

An 8" rotor has a 4" radius.

13/4 = 3.25.

So a force applied to the outside radius of the wheel is multiplied by 3.25 at the outside of the rotor.

So, the load DIRECTLY into the caliper is lower for a given braking force. Average loading will be lower since the traction limit of the wheel remains the same with either rotor attached. What changes is the power of the caliper required to do that work.

The load into the mounts is obviously different, since we have the adapters or caliper shapes that can act like levers and multiply force again. So, you may reach back up to what a 6" rotor has in leverage on the mount, but it is implausible that the forces would peak any higher than that.

Any stories like: "as soon as my buddies upgraded to 8" rotors, their tabs snapped" are moot, considering the tabs may have gone at the same time with the previous setup. There is no way to prove that the upgrade to 8" rotors did it.

Again, take a look at Marzocchi's disc mounts for the regular axle forks and compare them to the disc mounts for the QR.20 forks. They are identical. Case in point.

 

[gravity]

KD sure knows his stuff!

 

[taylor]

I think that Marzocchi is worried about the added force ripping the axel out of the dropout or breaking the dropout tang itself,unless of course it is a QR20...............I think.........?

 

[Shibby]

right on KD, rotecguy, gravity...

just a supplement to what you said:

i like to think about it in terms of "work" (=force*distance). a larger rotor allows the caliper to apply the same amount of force, but since the circumference of the rotor is larger, distance is larger, thus the amount of work done on the wheel per revolution is larger.

bigger work = bigger (kinetic) energy change.

as for the torque and leverage and stuff on the caliper and tabs, i think it's actually debatable. since you have to hang the caliper further out away from the fork leg to be in the proper position for an 8" rotor, there is a greater twisting force applied to the tabs (toward the rotor) due to the greater leverage created by the larger adaptor.

i'm tired. just spouting my (amateur) physics...

 

[KonaDude]

Originally posted by Shibby
right on KD, rotecguy, gravity...

just a supplement to what you said:

i like to think about it in terms of "work" (=force*distance). a larger rotor allows the caliper to apply the same amount of force, but since the circumference of the rotor is larger, distance is larger, thus the amount of work done on the wheel per revolution is larger.

bigger work = bigger (kinetic) energy change.

as for the torque and leverage and stuff on the caliper and tabs, i think it's actually debatable. since you have to hang the caliper further out away from the fork leg to be in the proper position for an 8" rotor, there is a greater twisting force applied to the tabs (toward the rotor) due to the greater leverage created by the larger adaptor.

i'm tired. just spouting my (amateur) physics...

I may not have made it clear, but when I used leverage, that leverage was on the caliper. A caliper using an 8" rotor will see about 25% less force than one mounted to a 6" rotor, BUT you are right about the adapter. It has leverage on the mounts, and therefore will increase the force put into the fork/frame again. Whether or not this increase allows the force to surpass what a 6" rotor applies I do not know, but I do agree with that, and I meant for it to be clear in my last post on this topic.

A viable concern could be the dropout tangs ripping off. When you put on a disc brake, you are trying to rip the wheel out of the dropout, and if you put more load into the wheel (which you do as the 8" rotor is further from the wheel's center), it will also load the dropouts more. So that is a consideration. That explains why Marzocchi's disc tabs don't change between QR.20 and non QR.20 forks, but obviously the dropouts do. Take a look at a Monster T, those disc mounts are NOT at all beefy, but the leg and axle mounts are, so this concern might be the one that makes the difference.

Cool!