Discs on a road bike - yes or no?

JonEdwards

I think overall it would be a positive thing.

Properly designed road brakes would be only negligibly heavier than calipers. Look at the mtb world - even the most weightweenie of xc racers are on discs now, as they weigh the same as V-brakes. Any weight increase would be offset by being able to use lighter rims - carbon clinchers wouldn't have to be so overbuilt for starters! I reckon a 140mm front, 100mm rear disc, 2 piston setup would offer more than enough braking for road use.

All the technology for mounting already exists, and the stresses involved are already understood, so once the braking system itself existed, slapping mounts onto the frames and forks and modifying hubs is very easy to do.

I wouldn't go racing out to buy a disc road bike, any more than I've raced out to buy DI2 or carbon rims, but if I was looking to buy a new bike anyway and properly sorted discs were available it would be a no brainer to use them.

rolf_f

MaxwellBygraves wrote:

But MTB discs are to be used off road. You may as well compare a cars disc brakes and say 'no they're too powerful for road bike use'.

I've no issues over things like their power - I am quite happy with the power of both my road bike brakes and my MTB brakes on road (in dry conditions, there is little difference). What annoys me is the sticking and squeakiness which is less noticeable off road but still annoying. It doesn't alter the facts that things like tolerances and complexity are rather greater than a simple caliper so I think I'd tend to stick with calipers.

JonEdwards

What annoys me is the sticking and squeakiness which is less noticeable off road but still annoying

That's dependent on the manufacturer and the exact leverage ratio they use. Avids (amongst others) run the pads very close to the disc. Hopes sit the pad a bigger distance from the disc (designed for muddy UK riding).

Shimano use a variable ratio (servowave) so that the pads can sit a long way out, but you still get loads of power once the lever is pulled in a long way.

All solvable issues, and actually, mostly down to setup and maintenance.

armymankin

the simple word is; Yes--- if you are going to brake VERY FREQUENT that develop heat problem. otherwise, you are paying a technology that you dont need.

Disc brakes are powerful in reality but less efficient (compare to calipers on bikes or drum brakes in cars) in physics terms.

I am no expert, but my research tells me Disc Brakes are invented to overcome overheating to the wheels that cause problem of tyres air pressure due to frequent braking, by having the contact units set aside from the rim. Racing cars + mtb tend to use them as there is a lot of braking involve on their course.

And of coz, there are lots if benefits of disc as it brakes better in muddy terrain as the rim tends to coated with mud and dirty which affect the braking contact.

Paul E

They don't need to be anywhere near the power of mtb disc brakes, When I had an mtb the brakes never needed to be bled (avid's) and the power and control they gave were awesome.

On road you could reduce the diameter of the discs and run smaller calipers.

As others have said the weight if any would be offset with not having to have heavy braking tracks on the edges of the rims where you really don't want weight anyway to the effects would be magnified and more than cancel out any weight gains.

The only time the brake pads wore out on me was when I rode in wet weather and the mud made a grinding paste but even then it wasn't too bad.

If I had the choice I would go for discs anyday.

gilesjuk

MaxwellBygraves wrote:

But MTB discs are to be used off road. You may as well compare a cars disc brakes and say 'no they're too powerful for road bike use'.

Do they not work when you're on the road?

Sure, you will skid if you pull them on hard but then you just do what I do and pull them on in pulses like ABS.

gilesjuk

armymankin wrote:

I am no expert, but my research tells me Disc Brakes are invented to overcome overheating to the wheels that cause problem of tyres air pressure due to frequent braking, by having the contact units set aside from the rim. Racing cars + mtb tend to use them as there is a lot of braking involve on their course.

And of coz, there are lots if benefits of disc as it brakes better in muddy terrain as the rim tends to coated with mud and dirty which affect the braking contact.

Not quite, drum brakes suffer from huge brake fade due to the drum expanding when it gets warm and the gases having nowhere to go.

From Wikipedia:

"When the drums are heated by hard braking, the diameter of the drum increases slightly due to thermal expansion, this means the brakes shoes have to move farther and the brake pedal has to be depressed further."

In a disc system the disc expands outwards making the compression force harder and there's holes in the discs (on bikes anyway) to allow the gases to escape.

Of course, with rim brakes the drum brake fade problem doesn't occur, but you're still wearing out your rims.

Paul E

Drums are terrible, I had them all round on my first mini and they were lethal, next one had front discs, a huge improvement.

rolf_f

JonEdwards wrote:

What annoys me is the sticking and squeakiness which is less noticeable off road but still annoying

That's dependent on the manufacturer and the exact leverage ratio they use. Avids (amongst others) run the pads very close to the disc. Hopes sit the pad a bigger distance from the disc (designed for muddy UK riding).

Shimano use a variable ratio (servowave) so that the pads can sit a long way out, but you still get loads of power once the lever is pulled in a long way.

All solvable issues, and actually, mostly down to setup and maintenance.

Taaa for that - useful to know. I suspect I'll replace the Avids with Shimano. I'm pretty fastidious with maintenance but the Avids have totally beaten me! Currently, the pads are locked onto the discs!

mcj78

I'd certainly like to see disc brakes on road bikes - currently contemplating buying a Genesis cdf to use as a road/commuting bike as i'm fed up with hearing that horrible grinding crunching noise that tells you your nice shiny new rims are being chewed away every time you touch the brakes & when you commute every day in all weathers, this happens alot - currently chewing through a nice set of RS20s & not sure if it would ever be financially viable to replace the rim once they're worn due to fairly unusual spoke count / layout.

Don't really understand why people are getting hung up of hydraulics though - any cable disc brake i've used have been perfectly adequate on a MTB & if anything would have to be "restricted" via smaller rotor for use on a road bike with thinner tyres. Why not smaller, lighter cable operated discs (preferrably highly polished, with a choice of anodized alloy / ti hardware to match the rest of your bike)

Perhaps those wanting discs are the sort of folk who ride mainly in town & cities with lots of stop-start cycles due to traffic lights etc. - hammering on the brakes every couple of hundred metres in shitty weather tears through rims & pads at a fair old pace, not to mention the reduction in braking efficiency the weather causes. Maybe high end road bikes that only see beautiful sunny days don't really need discs, but for the majority of folk cutting around town, riding in all weathers, I can't see a negative side to them - you only have to have a look through the commuting threads (or on the roads) to see how many folk are interested in disk equipped CX bikes these days for that purpose - even many of the flat-bar hybrids are starting to spec. discs as a feature, & the some of the folk buying those are probably wishing after a few months that they came specced with drop bars.

Sign me up!
j

zn533

I've only once used discs on my friend's MTB (it wasn't a super-duper one) and they were really lovely. Effortless power and usable modulation compared to my Shimano 105s with Koolstops. I do wonder if high end calipers are as good? Never tried Dura Aces, Reds or Records.

I'd agree that you'd only need them on the front wheel of a road bike though.

mcj78

zn533 wrote:

I'd agree that you'd only need them on the front wheel of a road bike though.

If the technology's there, why not both wheels (plus it looks better than 1 disc & 1 caliper ) - when discs first appeared on the mtb scene, the reason some folk had discs on the front & a V or magura on the rear was down to fork manufacturers starting to spec disc mounts on forks before many of the big bike manufacturers started putting disc tabs on all frames (also - lots of folk upgraded forks before frames), ergo it was relatively easy to upgrade to a front disc (new wheel & brake) but not the rear as you'd need to find some form of adaptor - plus the front brake does most of the work, so it wasn't really imperative that the rear was also upgraded. Once frame manufacturers started putting disc mounts on frames, folk soon upgraded the rear brakes to discs too - I remember plenty of bikes being marketed as "disc ready" but came as standard with V's :roll:

j

The Spiderman

Really can`t understand why it hasn`t been done before on road bikes.My MTB has dual control XT brake levers where the gear shifters are integrated into the brake levers in a similar way to a road bike.

This set up has been trouble free for 5 years now,no rubbing,no buckled rims to worry about.

Pad changes are quick,no wear on the rim to worry about,just consistent effortless braking.

I`m sure the calipers and discs could be downsized.Even my relatively small 160mm rotors on my mtb would be complete overkill on my roadbike.

If the rim didn`t need a braking surface,I`m sure they could be made a little lighter too.

As said before if discs were optimised for road bikes I reckon in time the weight difference wouldc be neglible.