Single or dual front discs?

[gavinnz]

Back in the 1970's putting a second disc and caliper on the front was the way to go... most standard brakes were pretty crap back then so I can see why it was done.

But doing up a 1970's bike NOW I am wondering if the second disc could in some ways be a backward step?
Bike will be about 130kg and I am about 100kg and the bike will be able to do around 200kmh.

Using 1970 reproduction bits, I could fit a new AP Lockheed 2 piston caliper and a good 280mm single solid mounted disc... (280 solid mounted not 300 floating for the look) and with a good master cylinder ratio and braided line and top pads I am starting to think that it would be enough brake to overcome front tyre grip? (90/90/18)

Would a second disc just add weight and harm the handling with no advantage?

Double discs would generate lower temperatures and cool faster than a single unit stopping at the same rate and so it would not fade as fast in racing.

What's the "best" material for discs on the track? I am from the 1970's so I still like cast iron discs... but I have no reason to think that other than past use.

At the end of the day I think twin discs look better so I expect I will end up going that way... :)

Anyhow... just thinking out load really...

Regards
Gavin

[AllanB]

I'd do yourself a favour and find a late model disk, calliper and master cylinder that you could adapt to the bike. The modern stuff is vastly superior to anything out of the 70's.

[Kickaha]

I'd do yourself a favour and find a late model disk, calliper and master cylinder that you could adapt to the bike. The modern stuff is vastly superior to anything out of the 70's.

Maybe, but the AP lockheed or the F08 Brembo from that era with the right pad compound and master cylinder are very good

Single disc with an AP caliper and good pads would easily be enough for a 130kg bike

[ellipsis]

...you mentioned track in your post...if you mean to race it you should check out PC rules relating to the era...(if not, carry on)...

[98tls]

I'd do yourself a favour and find a late model disk, calliper and master cylinder that you could adapt to the bike. The modern stuff is vastly superior to anything out of the 70's.

Gotta be careful though mate theres some later model stuff thats just shite ie believe it or not older Hayabusa calipers,i tried some on the S simply because they bolted on and no matter what i did they didnt compare to the original 4 pots,that said the radials that came with the gixxer forks are a revalation.

[FJRider]

Would a second disc just add weight and harm the handling with no advantage?


Double discs would generate lower temperatures and cool faster than a single unit stopping at the same rate and so it would not fade as
fast in racing.


What's the "best" material for discs on the track? I am from the 1970's so I still like cast iron discs... but I have no reason to think that other than past use.


At the end of the day I think twin discs look better so I expect I will end up going that way... :)


Anyhow... just thinking out load really...


Regards
Gavin

Make up your mind what you want to ask ...

I owned a 70's CB750 (F1) and fitted a twin disc set-up. It helped immensely with stopping ability. It had 70's era disc's and did the job well as could be expected at the time.

Unless you are racing ... or looking hard for stopping power ... 70's era disc's will be ok.

Many similar bikes running single disc's seem to get by ...

[Akzle]

make sure to get cross drilled lines.

and wave rotors.

[koba]

I'd go single and see how it goes, could go double later if left wanting.

I had the chance to do a direct back-to-back comparison on my bucket (not a 200kph bike!) single has PLENTY, even braking hard with a hot front slick.
I could feel the extra weight of twin discs, could feel it's affect on front end grip; I went slower.

[gavinnz]

I'd do yourself a favour and find a late model disk, calliper and master cylinder that you could adapt to the bike. The modern stuff is vastly superior to anything out of the 70's.

I agree with what you are saying, but I want it to look like it was built in the 1970's and I want to conform to Post Classic pre 82 rules just in case I decide to race it.

Regards
Gavin

[gavinnz]

Maybe, but the AP lockheed or the F08 Brembo from that era with the right pad compound and master cylinder are very good

Single disc with an AP caliper and good pads would easily be enough for a 130kg bike

Interesting.... what disc material would you think was best?
Regards
Gavin

[gavinnz]

I'd go single and see how it goes, could go double later if left wanting.

I had the chance to do a direct back-to-back comparison on my bucket (not a 200kph bike!) single has PLENTY, even braking hard with a hot front slick.
I could feel the extra weight of twin discs, could feel it's affect on front end grip; I went slower.

Great! The man who has been their and done that!! :)
Thanks for your comments.
How did the extra weight of the second disc and caliper effect the feel of the bike? I would be interested in more detail on your findings.
Regards
Gavin

[koba]

Great! The man who has been their and done that!! :)
Thanks for your comments.
How did the extra weight of the second disc and caliper effect the feel of the bike? I would be interested in more detail on your findings.
Regards
Gavin

It's not likely to be totally relevant to your situation...

But, I found with twin disks the front tyre was less responsive to small surface changes under it's heaviest loads, i.e. hard on the picks or at full lean.

I had more confidence, therefore more speed, with the single.

[Kickaha]

Interesting.... what disc material would you think was best?
Regards
Gavin

I like cast with either Galfer green pads or Ferodo CP211 although I think that has been replaced by CP1

[Grumph]

Early disc brakes can be upgraded significantly with the right size mastercylinder and modern pad materials...if available for that caliper.

early single calipers often used very conservative cylinder sizes - On kawa Z's for example, going from a 5/8 m/c to a 14mm one improves power and feel immensely. If you're using OE stainless discs then an organic pad helps too.

For race use discs can be thinned as well - period stainless i don't take below 5mm thickness. Given they're often 7mm that's quite a weight saving. Drilling helps too.

[FJRider]

But, I found with twin disks the front tyre was less responsive to small surface changes under it's heaviest loads, i.e. hard on the picks or at full lean.

I had more confidence, therefore more speed, with the single.

Twin disc's would put more weight on the front tyre under heavy braking ... as the extra braking ability should do (and be expected to) ...

Thus with the more down pressure on the front tyre ... less "response" would be expected. The loss of confidence is your issue in your head. The lesser "response" of the front tyre does not indicate any lesser grip (read stopping power) of the front tyre.

Unless of course ... your front tyre quality is suspect.

[koba]

Twin disc's would put more weight on the front tyre under heavy braking ... as the extra braking ability should do (and be expected to) ...

Thus with the more down pressure on the front tyre ... less "response" would be expected. The loss of confidence is your issue in your head. The lesser "response" of the front tyre does not indicate any lesser grip (read stopping power) of the front tyre.

Unless of course ... your front tyre quality is suspect.

These two are also at play:

http://en.wikipedia.org/wiki/Unsprung_mass

http://en.wikipedia.org/wiki/Gyroscope

In my (really irrelevant) example the bike was measurably faster on track with a single disk BUT it still had plenty enough braking power for the task at hand.

(It was then about 170kg with me on it - braking from around 90kph to about 40kph, the situation may well be different on any other given example.)

I've ridden bikes with not enough brakes, you can tell pretty quick, which (If easy enough) is why I'd plan to start with one and add another if required.