Is bigger better? 180mm disc brake rotor spotted on Tour de France bike

As we hit the third rest day, Team Bahrain Victorious has so far found a stage win at this year's Tour de France elusive, but could it have found a solution in the use of a huge 180mm front disc rotor.

Fred Wright has come closest to a stage victory, finishing second on Stage 13, but many Bahrain Victorious riders have only been noticeable by their absence. Even Matej Mohoric doesn't appear to be his usual self and it's been down to Tom Pidcock of Ineos Grenadiers to impress on the descents. 

But Bahrain Victorious has a new weapon in its armoury. We spotted one of their bikes just before the start of Stage 14 fitted with a huge 180mm front disc rotor.

Typically in the pro peloton, we see riders and teams opting for a 160mm disc at the front and a 140mm disc at the rear. This is often what bikes get sold with as standard and seems to strike a good balance between braking power, heat dissipation and weight.

We do sometimes see smaller riders using a 140mm disc at both the front and the rear as their lower mass means they don't need as much braking power and are less likely to overheat a rotor even on the Tour's long descents.

> How fast!? We analyse Tom Pidcock's stage-winning Strava file

Many teams like all their riders to be using a consistent brake rotor size as it makes wheel swaps much simpler – any rider can have any wheel off the roof of the team car. Using 160mm and 140mm rotors also makes it more likely that the neutral service will be able to help the rider in an emergency. This year neutral service is provided by Shimano which has taken over from Mavic.

> Did disc brakes get Pogacar dropped?

Shimano also supplies Team Bahrain Victorious, using the Dura-Ace R9200 12-speed groupset at this year's Tour. The groupset uses M900 Ice-Tech Freeze rotors borrowed from the brand's XTR top-of-the-range mountain bike (MTB) groupset.

Being designed for mountain bikes, there are some huge sizes available but Shimano only sells 140 or 160mm for road use. Both of those options feature four arms connecting the braking surface to the centre lock whereas the one pictured on the Bahrain Victorious bike clearly uses five as found on the 180mm+ rotors.

> Review: Shimano Dura-Ace R9200 groupset

The move to the MTB rotors comes after complaints of the older style Dura-Ace discs warping when hot and then rubbing on the pads. In my experience, it is a definite improvement and when combined with the additional 10% pad clearance of the latest callipers, it does almost eliminate the problem with a good set-up.

> Chris Froome STILL has disc brake problems

So why would anyone use a bigger rotor? Well, we've been asking ourselves the same question as this change to 180/160mm rotors is likely costing the rider 60-70g when compared to a 160/140mm setup.

We do often see huge rotors used on mountain bikes because they provide greater leverage and torque to stop the rotation due to the fact that they are further away from the rotating axle (the hub). In plain English, that means more braking power but as the limiting factor in road riding is usually the tyre's contact with the road, is that not a bit unnecessary?

Zac Williams/SWPix.com

Well, we think yes but the unknown Bahrain Victorious rider was clearly quite set on the idea as the bike requires a different calliper mount and adds the risk of not being able to find a spare wheel if he punctured. Bigger rotors do also have a larger braking surface to dissipate heat which means more consistent braking performance even after multiple heavy braking zones as is typical of a hairpin descent, for example.

> Everything you need to know about disc brakes

Zac Williams/SWPix.com

From previous races, we know that Bahrain Victorious aren't afraid to buck the trend and try something new. For example, at Milan-San Remo, Matej Mohoric used a dropper post on his way to victory. Is there anything we can't steal from the mountain bikers? Dropper posts, fatter tyres, tubeless tech and now big discs. What do you think is next!?

> UCI confirms that Mohoric's dropper post was within the rules

Let us know your thoughts on 180mm discs and what mountain bike tech we roadies will steal next in the comments below...