Best Front Brake Rotor for Vintage Racing

[rlloydm]

Hey Folks,

Here's the deal - I'm racing with AHRMA these days and looking to do some tinkering over the coming off-season to bolster my mechanical advantage come next year.

The stock front brake rotor is a boat anchor, even drilled like mine. I have a Grimeca (Lockheed copy) caliper that I'll be using, so I have to make a caliper adapter anyway. As I see it, the sky's the limit for rotors as long as I play by the rulebook. I have a lathe and can turn an adapter if the offset needs to be adjusted outwards.

So... What's the best fixed rotor with an RD350 hub bolt pattern? I have looked and looked and can only find floating rotors, which are not allowed per the rulebook. Something larger and much thinner than stock would be ideal.

Thanks in advance!

[rlloydm]

For example - what are these?





Asking the hive mind here because I can't find diddly

[BlueR32]

Bike # 54 was featured in Iron & Air magazine in 2014. The build details are attached. Front rotors are "modified Honda 600 discs"

[DesmoDrew]

   Front brake on my AHRMA F250 Yamaha.  TZ500 front disc (thinner and MUCH lighter than an RD or XS disc) on XS650 carrier.  Grimeca caliper with homemade caliper hanger.  Forks are RD350, but swapped sides to better route the brake line and move caliper to back of fork (aesthetic benefit only).  RD350 hub, so everything is Yamaha and bolts right up without having to figure out any spacers or adapters.

[teazer]

I had two of those disk/carrier combos on my TZ and swapped them out for a single stock TZ type when I sold it.  They are still gathering dust here somewhere.

BTW I have seen a few floating disks on RDs over the years with modified mounting bolts but the rider had to be careful to lightly apply the front brake in tech.

[rlloydm]

I had two of those disk/carrier combos on my TZ and swapped them out for a single stock TZ type when I sold it.  They are still gathering dust here somewhere.

BTW I have seen a few floating disks on RDs over the years with modified mounting bolts but the rider had to be careful to lightly apply the front brake in tech.

Hey if you'd like to lighten your load a bit, I'd love one of those carriers for the disc that I'm working on buying from DesmoDrew. PM me with details if you're interested in parting with it and can lay hands on it.

I wish I could make the 996 disc that i have laying right here work. I machined a spacer for it any everything before I realized that I can't read and that floating rotors are against the rules.

[oxford]

Probably not what you are looking for but I thinned and drilled stock RD rotors for my street bike.

[Hawaii-Mike]

The top picture shows a "Hole-ee" brake disc that used to be sold by Racer's Supply.

[Hawaii-Mike]

Here's a Hole-ee disc mounted on my H2.

[m in sc]

i HAD ONE OF THOSE FOR AN s2.  i wonder if i still do. it was light as hell too.

[bitzz]

Being in the same boat, except with VRRA, the "best" I found was a TZ250/350 or 750 disc (the carriers are different looking, dimensions are the same).
Rare as unicorn tears. There's usually one on ebay for stupid money.
The TZ discs are 296mm x 5mm thick (I'm gonna keep saying 296, but it might be 298. I don't remember. I'm old)
There's a XS650 disc that's similar, you have to turn the disc down
Honda CB750 had a 296mm disc, you have to enlarge the center hole, but everything else lines up... but it's discs are stainless... and about 1/2" thick and they're riveted to the carrier... and you might have to reverse them (they're counter bored on one face)... I don't remember....
I was looking at buying a 320mm spin cast disc, about $80 IIRC and was going to make my own discs....     (arguably spin cast steel discs will be the most efficient metal to use).
Then VRRA changed the rules to allow floaters, so making my own went no where.

While looking at making discs I found you don't want to drill holes in a solid mount discs. For a few reasons:
The loss of mass will promote warpage
The tiny bit of weight  you save is traded for swept braking area.
... and the ORIGINAL reason they drilled brake rotors was when the pads heated up, they would build a boundary layer of gas on the surface of the rotor, reducing brake efficiency and the holes gave the gas somewhere to go. They changed the pads and they don't do that anymore.
You DO want to cut "some" radial slots, to give the disc somewhere to expand to. I think Spondon used to slot their discs. (I say "some" cuz you're on your own trying to figure out how many and how big, but the slot has to go across the whole swept width)
I have a 296mm disc that someone thought making swizz cheese holes in it would be  a good idea, you can have  it if you want... but it doesn't stop very good.
I ended up using a disc off a FJ and a spacer. EBC has a part number for a floater disc... but they won't sell me one, or three, for some reason.
... if you want to go NUTS, the 320mm discs off a Ducati SS bolts on
... and I'll tell you the stock steel RD caliper is more rigid than your Gremica
Hey, you asked... So my answer is: a disk that looks a lot like a TZ disc and a RD caliper. The stock master is fine... but the round 1/2" Honda one is better (the one that looks like the period Brembo 1/2") ... and use QUALITY DOT4 fluid... and bleed it every other outing.

[Plasticman]

I have a '82 GPX1100 front rotor on my RD400.

[teazer]

I know the question related to the rotors but has anyone tried an Aluminum replica RD caliper with aluminum pistons?  That's what we use on our RD350 drag bike and it works well.  My concern was that the pistons would expand more that stock steel ones and bind in the bores, so I had a poofteenth machined off the pistons to provide extra clearance.

That combo is lighter than a stock RD and probably as stiff as a TZ aluminum caliper.  No idea how that would work on an AHRMA racer but i am guessing that the lighter weight would more than compensate for any other shortcomings.

Stock RD caliper complete is around 1540 gms.  TZ alloy is around 890gms.  Brembo P108 is around 1,000 and Brembo goldline 4 piston is 720 with Ti bolts. RD Al replica caliper with pads is around 940gms but I think that was with steel pistons and I am not taking it off to measure it, but thanks for asking.  get some Ti hardware and call Economy to order a stock looking caliper.

With a larger diameter disk rotor, you probably need TZ or TX/XS fork sliders to move the caliper away from the axle.

[oxford]

I know the question related to the rotors but has anyone tried an Aluminum replica RD caliper with aluminum pistons?

I have them on the above picture I posted.  Re-pop aluminum calipers from Economy and pistons from Eric (202wagon).

I knew I was going to take a hit on weight with the dual disc so I tried to lighten things up as much as I could.

[Hawaii-Mike]

Teazer I admire your brake discs!