Ridgeback Panorama Deluxe

[gaz]

Braking stresses in wheels were discussed here: viewtopic.php?f=5&t=94181&p=866973

[bretonbikes]

I won't bore anyone further on that then...

Has anyone on here had a fork collapse mid-forkblade when braking? I'd be very interested to see if this is an issue.

In my experience forks only ever fail (in accidents of course) by bending around the joint of crown and headtube, or (especially on unicrowns) at the very top of the fork. These fail points are the same for disc or rim brakes. Yes, some of the forces acting down the fork blades are different with the two brake types (especially the tendency to try and level the wheel from the dropouts), but I would contend that the major forces capable of damaging a fork are the same.

[Brucey]

...Has anyone on here had a fork collapse mid-forkblade when braking? I'd be very interested to see if this is an issue.

In my experience forks only ever fail (in accidents of course) by bending around the joint of crown and headtube, or (especially on unicrowns) at the very top of the fork. These fail points are the same for disc or rim brakes. Yes, some of the forces acting down the fork blades are different with the two brake types (especially the tendency to try and level the wheel from the dropouts), but I would contend that the major forces capable of damaging a fork are the same.

yes it is an issue; you certainly can't just nail a disc mount onto a fork meant for rim brakes, the loads in the fork blade with the caliper attached are completely different. The local bending moment at the fork tip can be about x5 vs a rim brake, and if the fork is not well designed it can easily fail near the caliper mount. There have been several fork recalls for this exact problem and it is unwise to assume that a disc fork cannot or will not fail in this area- it is commonplace that it does exactly that.

If the caliper mount is well engineered (i.e. mounted on a reinforced fork blade) then the fork should then perhaps fail in the usual places (crown area, and/or steerer) in the event of a frontal overload. Many don't do this though.

Any reinforcement in the fork will undoubtedly make the fork stiffer and the bike will ride less well as a consequence. If the fitment of disc brakes produces a more powerful brake (as it sometimes does) then the whole front end of the bike needs to be built stronger and this again can affect ride quality.

I have estimated that in a traditional touring bike about 1/3 of the fork tip deflection may occur because of flex in the top tube and down tube near the headstock; anyone who has ridden an otherwise identical pair of gents and mixte framed machines will be able to testify that the mixte machine will have a much softer front end; this is because the mixte frame is about half as stiff in bending near the headstock.

cheers

[bretonbikes]

...Has anyone on here had a fork collapse mid-forkblade when braking? I'd be very interested to see if this is an issue.

In my experience forks only ever fail (in accidents of course) by bending around the joint of crown and headtube, or (especially on unicrowns) at the very top of the fork. These fail points are the same for disc or rim brakes. Yes, some of the forces acting down the fork blades are different with the two brake types (especially the tendency to try and level the wheel from the dropouts), but I would contend that the major forces capable of damaging a fork are the same.

yes it is an issue; you certainly can't just nail a disc mount onto a fork meant for rim brakes, the loads in the fork blade with the caliper attached are completely different. The local bending moment at the fork tip can be about x5 vs a rim brake, and if the fork is not well designed it can easily fail near the caliper mount. There have been several fork recalls for this exact problem and it is unwise to assume that a disc fork cannot or will not fail in this area- it is commonplace that it does exactly that.

If the caliper mount is well engineered (i.e. mounted on a reinforced fork blade) then the fork should then perhaps fail in the usual places (crown area, and/or steerer) in the event of a frontal overload. Many don't do this though.

Any reinforcement in the fork will undoubtedly make the fork stiffer and the bike will ride less well as a consequence. If the fitment of disc brakes produces a more powerful brake (as it sometimes does) then the whole front end of the bike needs to be built stronger and this again can affect ride quality.

I have estimated that in a traditional touring bike about 1/3 of the fork tip deflection may occur because of flex in the top tube and down tube near the headstock; anyone who has ridden an otherwise identical pair of gents and mixte framed machines will be able to testify that the mixte machine will have a much softer front end; this is because the mixte frame is about half as stiff in bending near the headstock.

It's OK I'm here to be educated;-) I can see that in that very local area in effect between the disc and the drop-out the forces are very high for that short distance and as I mentioned the structure of the mount itself - being essentially solid will act as a knee at the point where it ends and the fork becomes 'on-it's-own' - but as for the whole front end of the bike needing rebuilding I don're really see it - you can lock the front wheel with ease on a V-braked bike - the limit is the adhesion of the tyre - therefore you could have brakes 10x the power but the maximum force through the front of the frame would never exceed that needed to lock the front wheel or pitch you over it - or am I missing something?

[Brucey]

no I don't think you are missing anything except perhaps that I made that comment with the caveat

'If the fitment of disc brakes produces a more powerful brake (as it sometimes does)....';

as you point out it often doesn't.

cheers

[NATURAL ANKLING]

Hi,
Colour I like
48 chainwheel on the front is overgeared for type of bike.
I remember my Raleigh coming with 46 /11 and I could never get above 14-15 on the cassette.

Who really powers above 48 / 12 (108") let alone 48 / 11 on the flat with a 15 - 18 kgs bike with minimum accessories
Despite the drops its no sportif wanabee racer.

[bretonbikes]

no I don't think you are missing anything except perhaps that I made that comment with the caveat

'If the fitment of disc brakes produces a more powerful brake (as it sometimes does)....';

as you point out it often doesn't.

cheers

OK ta;-)

It's odd really. In the car world - let's say someone put better than standard tyres on their VW so upped the stopping power of their car - then the car had it's front suspension ripped out under emergency braking. Can you imagine the headlines... Yet over the years we've had batches of tyres blow-out, dodgy brakes, brake cables than snap under normal use (all these have happened to my hire bikes in 25 years) - and not a whimper from manufacterers or the authorities. Latest one are our Dawes tandems - A couple of the tyres fitted blew out after a couple of weeks touring. Obviously I inspected them all and most of those on the front that hadn't failed were showing signs of failure. Contacted Dawes and they didn't even reply. If that had been a car manufacturer and 50% of a batch of tyres were blowing out it'd be national news and a massive recall.

How tolerant we cyclists are...

[Brucey]

if you have reason to believe that a product is faulty and the manufacturers are ignoring evidence of this then you should contact VOSA directly

http://www.transportoffice.gov.uk/crt/doitonline/bl/help/voluntaryrecallsystem.htm

In these days of internet forums and social media it ought to be easy enough to identify if there is a common problem or not, and alert those responsible accordingly.

cheers

[bretonbikes]

if you have reason to believe that a product is faulty and the manufacturers are ignoring evidence of this then you should contact VOSA directly

http://www.transportoffice.gov.uk/crt/doitonline/bl/help/voluntaryrecallsystem.htm

In these days of internet forums and social media it ought to be easy enough to identify if there is a common problem or not, and alert those responsible accordingly.

cheers

Bit unfair to target Dawes - they are far from alone, things like this happen to me with batches of bikes or spares all the time. A problem will flag up with a couple of hire bikes then I'll investigate the rest of the fleet and find others ready to fail. A complaint would probably lose me my trade account. Bike shops will rarely be having the same experience (i.e. say 30 identical bikes running in parallel) so probably don't flag up these things in the same way. I get 'batch' failures of all sorts of things that are less life critical - panniers, tents (zips and poles) etc and I've yet to find any manufacturer who had any interest in my feedback.

The worse was 23 years ago when I led my first trip to the Pyrenees. At the top of the first col I checked every bike's front brake by pulling the front brake on as hard as I could on everyone's bike - 14 in all - (in those days you'd need to coming down a col!) - three front cables snapped - the nipples just pulling out. These 'Indeca' cables were supposed to be quality. I had three spare cables with me, we all descended very gingerly and I stripped out all the cables that night...

[Brucey]

that is the stuff of nightmares. Good thing you had the presence of mind to check everyone's bike.

A chum had a new cable fail similarly and he was unlucky enough to have a prang as a result. The brake cable manufacturer paid for a new bike and would have been liable for any serious injuries too.

Fortunately such problems are not that commonplace.

If you suspect that the same product is sold in the USA then one approach is to alert the CPSC in the USA to the problem. This may or may not result in a product recall there, but if it does, any manufacturer will be seen to have behaved negligently if they do not similarly recall the product in other markets. Cable recalls can and do happen when people report that there is a bad batch out there.

cheers

[rmurphy195]

With disc brakes all the braking force has to transfer through the spokes to the rim. Yes the tire has the same braking friction whether rim or disc brakes.

Surely that's the same with rim brakes?

[Brucey]

With disc brakes all the braking force has to transfer through the spokes to the rim. Yes the tire has the same braking friction whether rim or disc brakes.

Surely that's the same with rim brakes?

the additional spoke loadings when braking are considerably more severe in disc braked wheels than in rim braked wheels. It'll vary with the service conditions of course but I have estimated that they can easily add +10-25% to the fatigue loadings in the spokes of a typical disc brake wheel.

cheers

[yostumpy]

Well I've just pulled the trigger on one of these, last one in 60cm flavour. Amazing price,@£999,and thanks for the link, you saved me at least£400, I've seen it discounted else where at £1395, but also still on sale at other on line outlets at the full £1699. So its a genuine bargain. Hope we get on well.

[reohn2]

To all the don't do it disc brake naysayers.
I've four bikes(two tourers,one MTB and one tandem)all with mechanical disc brakes(BB7)all brake fantastically well(and here's the important bit)wet or dry.No more wet weather squeeze and hope,it's a matter of squeeze and they work,just like when they're dry,we've toured on the tandem in fairly hilly North Wales without the brakes disintegrating or warping rotors.
I'd recommend mechanical discs to anyone touring,and pads last far longer than any rim brake pads,whilst not wearing out rims into the bargain
Touring bike forks capable of carrying front panniers aren't springy 531C affairs,discs or not,they're built to stand the strain of hard graft and loaded panniers,so won't be boinging much anyway.
The comfort comes from quality,supple wide tyres run at the correct pressures for load,so don't be fooled by thinking a disc brake fork will be any more harsher than any other touring bike,just buy the 37mm Vittoria Hypers and wonder at why you didn't know this level of comfort was possible and also now understand that good wide tyres roll just as good as narrow HP ones ,along with the disc brake wonderment of being able to actually stop predictably,even loaded,in the piddling down rain,that's been the feature of the UK for the past couple of months

The bike in the OP's link looks like a bargain,well equipped and well priced,should be a good buy .

Another point about discs,sintered pads last longer if riding in continually bad wet/mucky weather,but don't stop quuiittee as well as organics,though there ain't much in it.
TRP Spyre/Spykes are good stoppers,I had them on my MTB from new but swapped them over to BB7's due to squeal in mucky conditions when they got hot.
Bear in mind I'm talking reeaalllyyy boggy wet muckyness.
They ate the standard organic pads in short order and whilst the sintered pads lasted longer I couldn't totally eliminate squeal.
TBH on a touring machine I'd envisage that kind of problem to be minimal.

Edited for clarity.

[Rich_Clements]

Another point about discs,sintered pads last longer if riding in continually bad wet/mucky weather,but don't stop quuiittee as well as organics,though there ain't much in it.
TRP Spyre/Spykes are good stoppers,I had them on my MTB from new but swapped them over to BB7's due to squeal in mucky conditions when they got hot.
Bear in mind I'm talking reeaalllyyy boggy wet muckyness.
They ate the standard organic pads in short order and whilst the sintered pads lasted longer I couldn't totally eliminate squeal.
TBH on a touring machine I'd envisage that kind of problem to be minimal.

Edited for clarity.

Just swapped out the original pads from the TRP's and gone sintered, will let you know how I get on. The originals lasted 1300 miles quite a lot in the wet.

I also put 32c Hypers on the bike and its a completely different bike wow!