F/ Disc brake hub centralised?

SteveA said:

Thanks for the drawing, which eloquently illustrates my point. It has a 280mm disc (11.023622047 inches)

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271.7mm/10.7" (I checked and they are) not quite the full 11.0".

SteveA said:

Thanks for the drawing, which eloquently illustrates my point. It has a 280mm disc (11.023622047 inches)

Click to expand...

Dimension 140mm relates to the outside of the caliper piston. It's obviously outside of the brake disc.

Edit: Wrong assumption. Why is there a dimension of the screw plug?

- Knut

mdt-son said:

Dimension 140mm relates to the outside of the caliper piston. It's obviously outside of the brake disc.

- Knut

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I don't think the pistons overhang the disc...


The other dimension given is 90mm but the piston isn't 50mm diameter, it's 44.4mm, 1 3/4". The screw plug is 50mm.

SteveA said:

Yes, but as British chaps, instead of saying 'unsafe' we might state: 'it isn't as safe as it might be'. Very little is.

A solution might have been moving the fork legs further apart and allowing the hub and rim to run central. But that might have been seen as 'overengineering'.

Certainly expensive, and possibly ugly?

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I see it *slightly* differently:
Sub-optimal from a load distribution perspective, mitigated by heavier gauge spokes on the disc side; hence as safe as previously, IMHO - it has to be.
Bicycle wheels have been this way since the derailleur was introduced; the dishing is so severe the drive side spokes have very little offset at all: Drive side spokes go 'ting!', opposite side spokes go 'dung', so to speak. Makes truing up interesting.

Every safety related/safety critical application must have an analysis done, and I'm presuming this has always been true of vehicle braking systems.
Granted, it wasn't re-stressed to accommodate 4-pot calipers & 14" discs (who knew?!), but it was definitely re-stressed.

L.A.B. said:

http://www.classicbike.biz/Norton/Repair/70up_Commando/70upCommando.pdf

271.7mm/10.7" (I checked and they are) not quite the full 11.0".

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I just measured the disc in my photo: 278mm (10.94488") This disc pad track was cut from a pattern Commando part rather than an AN part.

And a Dick Hunt supplied cast iron Seeley Disc: 279mm (10.98425")

OK, so neither are 279.4mm, but neither are 254mm!

The other disc I have is also a Dick Hunt Seeley item, but with alloy carrier, but it's on the bike and in another workshop, and it's raining.

SteveA said:

I just measured the disc in my photo: 278mm (10.94488") This disc pad track was cut from a pattern Commando part rather than an AN part.

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I doubt a 278mm diameter disc, pattern or not, would fit in my Commando's front caliper as there's barely 2mm clearance as it is.

L.A.B. said:

I doubt a 278mm diameter disc, pattern or not, would fit in my Commando's front caliper as there's barely 2mm clearance as it is.

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You mean the person who made this disc and carrier for me lied to me when he said it was cut from a Commando disc?

I confess I didn't physically see it before it was cut. I had always assumed it was sourced from India! But it has survived several seasons of heat cycles. I changed it because the replacement became available at a good price, and the pad track is from PFM and proved to be marginally thicker. In use, I didn't have any other concern.

I never understood the need for this extreme offset.
There is plenty of clearance between the spokes and the caliper.
I can't help but think that when braking hard (with a decent front brake..) the extra tension on the 'loose' LH spokes, makes the rim shift to the left.
Maybe with an insignificant amount, but I don't like the Idea.