Fancy a conversion to cast iron discs, anyone done this?

[Oddjob]

In order to improve braking performance I was investigating have the OE discs drilled or slotted or both. Current cost to drill them is about £100 a pair. Can't find anyone to slot and drill them yet.

However whilst I was investigating I spotted some cast iron discs in Australia, yeah, other side of the world, postage etc won't be cheap but they should perform miles better than standard discs and they are drilled with a decent pattern of holes as well. Cost around £270 for a pair including postage but maybe import duties on top. You need to remount the discs on original carriers though, which is something I've done before so doesn't bother me.

I was wondering however IF cast iron discs were also available in the UK and if anyone has tried them before and if so what was you're findings, worth it or not.

I do remember they were available back in the day but searching for them gives no results in the UK.

[Bryanj]

Yes Ken they were available in late 70's and came with small bolts with nylock nuts to fit them to the carriers, fitted one to the 500 i had at the time and from memory it made little if any difference in the dry and worked too well in the wet, locked up and came off when the ubiqutous little old lady walked off the kerb in front of me going to Skellerns in Worcester for an urget parts run when it was heavy rain and lots of standing water.
Then went to twin stainless using 2 500 sliders so one caliper in front and one behind with a cut and shut mudguard bracket plus GL 1000 master and found it better.
Just what i found in the day mate

[Oddjob]

So being honest Bryan. How much of the rain comment was due to the tyre compounds of those days? I mean if they were the original Bridgestone tyres they'd let go in the rain just banking the bike over, worse tyre I've ever ridden on, scared me to death, hated them with a vengeance and to this day I still refuse to fit any Bridgestone tyres as the memory is not a good one.

I have the twin disc setup now and have done since the 70s, even with undrilled discs I found them adequate, in the wet not great if I'm honest. But in the dry I could really stop in comparison to the single disc, saying that I had updated to braided lines and fitted a bigger MC.

[Bryanj]

I was on TT 100 at the time Ken, it felt to me like the brake just locked in comparison to the stainless but there was about 3 inch of water on the road at the time and it was on a corner, as a single disc it just did not seem an improvement in the dry, where twin did, but too much in the wet. At least it was on the way to Skellerns so i just added the headlamp bracket and handlebars to the list of bits i needed!
This is all from a very Guinessed, adled, aged brain mate so i cant be 100% on any of it

[Oddjob]

I think I'll give it a miss then Bryan.

At least I found a nice pattern for the holes, I've found someone in Scotland who can drill them to your pattern.

[McCabe-Thiele (Ted)]

I've seen a disc snap off the centre boss  due to a seized caliper on one side.

[JezzaPeach]

I had a cast iron disc in the ‘70’s. It was great most of the time and didn’t fade on long descents, but in the wet, ZERO braking!!! So I switched back to the original. Fast forward a few decades, EBC pretty good but now about to try the SBS ceramic ones.

[McCabe-Thiele (Ted)]

I had a cast iron disc in the ‘70’s. It was great most of the time and didn’t fade on long descents, but in the wet, ZERO braking!!! So I switched back to the original. Fast forward a few decades, EBC pretty good but now about to try the SBS ceramic ones.

I'm quite impressed with the Bembo carbon/ceramic pads + not cheap but they felt good.

[philward]

I had a cast iron disc in the ‘70’s. It was great most of the time and didn’t fade on long descents, but in the wet, ZERO braking!!! So I switched back to the original. Fast forward a few decades, EBC pretty good but now about to try the SBS ceramic ones.

I'm quite impressed with the Bembo carbon/ceramic pads + not cheap but they felt good.

Thats good to hear Ted, got some on watch on eBay ready to buy for 500 and 750

[Lobo]

Funny old thing, but I was up at Lindsay’s place (engine builder / anything automotive) and there on the floor was a Honda wheel he’d put drilled cast iron discs onto, as he prepped a race / bored out ‘750. Very labour intensive he told me, working out the drill pattern with compasses and cardboard template…. which was then used to mark up the disc.

Fundamentally, the holes are indeed to improve wet performance, as they give the water somewhere to go, plus increase surface area for cooling. On the downside there is less surface area for the brake pads to act upon.

Cast iron apparently conducts heat far more efficiently than stainless, and so these discs can be significantly thinner - if the SS discs were of similar thickness they’d warp / dish & seize.

And then there’s the rust…😱.