Currentley have a 180mm diameter rotor on the front with a BB7 caliper. This is fine most of the time but occasionally I get cramp in my hand on long decents and on a couple of occasions have almost run out of brakes on high speed fully loaded decents ( when I knew I should have been going slower but was having too much fun). Is it worth increasing the rotor diameter to 203mm? Are larger rotors more vulnerable to warping?
I realise that going to a hydraulic system would give me more power but cost and luddite tendencies preclude it

It will increase power but pad / cable choice could also*.

*yes, it's debatable whether those two things actually increase 'power' in the true sense as they aren't effecting mechanical advantage but you know what I mean

Whilst I understand the maths it did not make a noticeable difference for me ( but I was not running out of brakes anyway) .
It's certainly the cheapest fix

Go for it. I think a 203mm rotor is great for BB7’s and didn’t much like it when new forks forced a downsize to 180mm.

Yup. Bigger is always better for brakes - bigger mechanical advantage so more power for a given pad pressure, more heat dissipation so less chance of warping or fading, less disk wear, looks cool. Avid do a +60 bracket so you could even go for a 220 disk

BB7s will likely be the weakest link in the system, if they're not perfectly set up they're not great (and any pad wear will cause them to revert to less great)

In the end in the same situation I spent far too much money and time before getting a Juin Tech R1, sticking it on the front and never having any more issues....

AlexGold wrote: ↑Mon Feb 07, 2022 6:26 pm BB7s will likely be the weakest link in the system, if they're not perfectly set up they're not great (and any pad wear will cause them to revert to less great)

In the end in the same situation I spent far too much money and time before getting a Juin Tech R1, sticking it on the front and never having any more issues....

Aren't cable operated hydraulics just combining the worst of both worlds?

woodsmith wrote: ↑Mon Feb 07, 2022 6:46 pm Aren't cable operated hydraulics just combining the worst of both worlds?

Not at all. I know where you’re coming from and used to think the same. I used BB7 for many years and rated them highly but started to get fed up with the fiddly set up and rub I was often left with.
I got a set of Juin Tech hybrids not expecting much and have now got a set on all 3 of my disk brake bikes.
The set up is a doddle, performance is good and quality is great.
I think they are actually the best of both, not worst of both. You retain an easily field serviceable cable and adjustable bite point from cable disks and gain the even pad wear and snappy return from hydraulics.
As a closed system they need no bleeding.
My oldest set are now two years old and have seen regular use and have had no issues.
My only worry is they take an old design XTR pad that I’m concerned will become hard to find. I have bought up a good few years supply to keep aside.

woodsmith wrote: ↑Mon Feb 07, 2022 12:27 pm I get cramp in my hand on long decents

Perhaps also worth trying training your grip strength with a powerball and theraputty.

This and a larger rotor (and more powerfull pads) should make quite the difference.