3C disc brakes.

V

Vince

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After a comment from a trusted source I just measured my 280mm std cast iron discs on my 3c. It has a couple of 4-spot callipers fitted. They measured at the left disc 5.6mm and the right disc at 5.4mm. From what I can find minimum size is 5.8mm so mine are well undersized and need replacing ASAP. So I guess I need some new discs, probably floating and stainless and I want to stick to std 280mm. Who sells these in Oz? And I guess pads that work on Stainless discs.
 
I looked at some specs for discs for sale and found something odd. New standard discs are 6.75mm thick, but floaters are sold at 5mm thick. Same material, stainless. If my std cast iron discs are undersized at below 5.8mm and could allow a seal to come out or warp a disc then how can floating discs be ok at 5mm? I get they don't warp but is there any other safety effect at running undersize cast iron discs, especially with 4 spots? Thanks, Hooksy I will check them out.
 
New Metalgear stainless rotors are 6.56mm thick
Just measured 3 new rotors from them on an 81 Jota I am building
 
I think you will need 5mm to clear P4 calipers with std pads. only seen these with the later brembo carriers and 9 bolt disc rotors.


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Are they floating or Rigidly mounted? From what a saw floaters are 5mm, that's petty thin. Floaters are almost twice the price of rigidly mounted as well. With some thinking time, floaters are very sexy but unless you're hammering the brakes to the max, and that's unlikely on the road with limited high speeds and hard braking there's probably overkill. In more than 30 years of use, I have never warped a Laverda disc anyway. The ones in use are my second set, I wore the first set out thickness-wise.
 
Vince said:
I looked at some specs for discs for sale and found something odd. New standard discs are 6.75mm thick, but floaters are sold at 5mm thick. Same material, stainless. If my std cast iron discs are undersized at below 5.8mm and could allow a seal to come out or warp a disc then how can floating discs be ok at 5mm? I get they don't warp but is there any other safety effect at running undersize cast iron discs, especially with 4 spots? Thanks, Hooksy I will check them out.
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Absolutely no way a 5mm disc would allow a seal to pop, Vince. not that I'm suggesting you get some - I ran a std 280mm with an 08 caliper on my Kwaka rear spoked disc hub, zero probs - was worn out at under 5mm but never under stresses approaching what a front disc sees.
 
Just another note :-) the problem with disc thickness is the loss of heat dissipation. if they get too thin they over heat and warp, i have seen them trued up but they warp again pretty quick. I doubt its a structural thing, its more likely to warp long before it collapsed..
That said its brakes and i am not offering any factual advice on a safety issue like this. :)
 
Hey Vince, your not likely to have any dramas with you current discs riding the roads.
If your at a track day on a short circuit......they may get a little hot!

If they aren't warped leave em alone.
 
The way I ride, The Pace, involves minimum braking. If you maintain corner speed and don't accelerate between corners the brakes bearly get used. But it's good to have em if you need em.
 
Vince said:
The way I ride, The Pace, involves minimum braking. If you maintain corner speed and don't accelerate between corners the brakes bearly get used. But it's good to have em if you need em.
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In that case Vince, floating discs are more or less a waste of money. With disc diametre, pad area and friction coefficients being the same, a floating disc will not offer one iota more stopping power over a rigid item. Simply chucking excess cash at a bike will not necessarily make it any better or more rideable. May enhance street cred though... ;)

Floating discs offer an advantage once brake performance exceeds the heat transfer capabilities of the hub and carrier, ie, heat remains in the disc long enough to cause warping, especially the case with larger, thinner discs. Floaters often actually impair heat transfer through their minimal contact areas to the carrier/hub, but they (should) then allow the discs to wobble around and not cause any judders once they are warped. That at least is the theory, owners of Zane Laverdas and '90s Ducatis fitted with floating Brembo discs can tell different stories! I remember especially bad cases of warping on the early 340mm Buell single front discs, these didn't stand up to more than 2 laps of a race track. They would be dished to the point where the caliper could no longer be removed from the disc!

The France Equipment stainless discs that Paddy has posted offer excellent results when paired to suitable pads, loads better than the cast iron Brembos were ever capable of, especially in the wet! I've supplied quite a few of these, customer feedback is 100% positive! Reckon your locally available Metalgear items will be much the same.

piet
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