Idiots' Guide to Road Disc Brakes

[Andy_R]

Me again! I have installed the Spyres (160 front and 140 rear) and all is well except that I am slightly nervous about the minuscule clearance between the front brake and the spokes. Although the whole unit can be adjusted laterally, I don't have any leeway when it comes to moving it outboard, or the rotor will be rubbing the brake pad. I'm thinking that swapping in a 180 rotor on the front might be an option - the Spyres came with two different mount adapters, and the ones I'm not currently using appear to be meant for a 180 front or a 160 rear. However I don't think Spyre supply 180 rotors. Is there anything I need to know about rotor compatibility, or are all 180 rotors essentially the same barring the mount type?

How much clearance exactly (or inexactly) between the caliper and the spokes (ish). Rotors are pretty much interchangable so a Shimano 180 rotor will do the job (in the interest of fairness, other 180mm rotors are available)

 

[Andy_R]

You will not need bigger rotors on a road bike - 140s or 160s at most. You get less clearance too if you use the centre lock/6 bolt adapters

That's why the OP wants to use a 180 - to move it away from the centre of the wheel which means it's further away from the spokes laterally

 

[theclaud]

How much clearance exactly (or inexactly) between the caliper and the spokes (ish). Rotors are pretty much interchangable so a Shimano 180 rotor will do the job (in the interest of fairness, other 180mm rotors are available)

There's about 1mm with the 160s.

 

[theclaud]

You get less clearance too if you use the centre lock/6 bolt adapters

I'd not thought of that. I could get a 160 centre lock rotor. How much difference do you think it makes in mm??

 

[Yellow Saddle]

Me again! I have installed the Spyres (160 front and 140 rear) and all is well except that I am slightly nervous about the minuscule clearance between the front brake and the spokes. Although the whole unit can be adjusted laterally, I don't have any leeway when it comes to moving it outboard, or the rotor will be rubbing the brake pad. I'm thinking that swapping in a 180 rotor on the front might be an option - the Spyres came with two different mount adapters, and the ones I'm not currently using appear to be meant for a 180 front or a 160 rear. However I don't think Spyre supply 180 rotors. Is there anything I need to know about rotor compatibility, or are all 180 rotors essentially the same barring the mount type?

Front wheels designed for disc brakes require a very specific lacing pattern to address the problem of small clearance between brakes and spokes. If you have the right design in cross-overs etc, the spokes will pull away from the brakes when you apply brakes. If you have the wrong design, the spokes will move into the brakes.

You can post a few pictures of the hub area of your wheel showing detail of the spokes and I'll have a look for you. Otherwise, identify (on the left side of the front wheel) the pulling spokes. Isolate one spoke at the hub, with your finger and run your finger outwards to where that spoke crosses another. If the cross is over the pushing spoke, you are ok. If the pulling spoke crosses under the pushing spoke, you are not OK.

It is totally irrelevant on the rear because that brake cannot generate enough force without the wheel locking up and skidding.

 

[theclaud]

Front wheels designed for disc brakes require a very specific lacing pattern to address the problem of small clearance between brakes and spokes. If you have the right design in cross-overs etc, the spokes will pull away from the brakes when you apply brakes. If you have the wrong design, the spokes will move into the brakes.

You can post a few pictures of the hub area of your wheel showing detail of the spokes and I'll have a look for you. Otherwise, identify (on the left side of the front wheel) the pulling spokes. Isolate one spoke at the hub, with your finger and run your finger outwards to where that spoke crosses another. If the cross is over the pushing spoke, you are ok. If the pulling spoke crosses under the pushing spoke, you are not OK.

It is totally irrelevant on the rear because that brake cannot generate enough force without the wheel locking up and skidding.

Thanks. They are Shimano factory disc-specific wheels, so it would be odd if they were laced in such a way as to be unsuitable for discs, and the Spyre calipers don't seem especially bulky. Herewith images:

On the plus side, although I've not had a reply from Planet X, the fork is recessed on the interior of the rotor-side blade, and this recess appears to be large enough to accommodate a 180mm rotor...

 

[Yellow Saddle]

Perfect. The inbound spokes (heads outside, elbows inside) are the pulling spokes when braking and go over the pushing spoke. This means the spokes move inwards under heavy braking and the wheel itself will not do anything to decrease the spacing. A fork also flexes under braking but not in the plane that affects the spacing. You are good to go on any sized disc. Now it is just up to you to examine the brake caliper's construction and convince yourself there is nothing that will make the silver disc I can see in the photo move towards the spokes. I can't picture it's function.

 

[theclaud]

Perfect. The inbound spokes (heads outside, elbows inside) are the pulling spokes when braking and go over the pushing spoke. This means the spokes move inwards under heavy braking and the wheel itself will not do anything to decrease the spacing. A fork also flexes under braking but not in the plane that affects the spacing. You are good to go on any sized disc. Now it is just up to you to examine the brake caliper's construction and convince yourself there is nothing that will make the silver disc I can see in the photo move towards the spokes. I can't picture it's function.

Thanks. That's not a disc as such but the pivot end of the moving arm which is pulled by the cable. It doesn't have any lateral movement. I'm going to try the 180 discs...

 

[Smokin Joe]

Ah, right. I've sent them a query by email. The mount adapters came with the Spyres, so I'm assuming that it's not wildly unconventional to use a 180mm on a road bike? They are steel forks, and quite rufty-tufty in appearance, although I've no idea how one would go about a precise assessment of their tolerances. I have a friend called Dr Evil who might have an opinion on it...

Let us know if they reply. I emailed PX a week and a half ago with a query on jersey sizing. Apart from a reply saying they'd received it, zilch

 

[theclaud]

Let us know if they reply. I emailed PX a week and a half ago with a query on jersey sizing. Apart from a reply saying they'd received it, zilch

They replied today, although it's not helpful. Some guy blandly 'recommending' 160s, although I have told them I already have an issue with 160s...

 

[theclaud]

Well I put a 180 on the front, and thought I might as well stick the 160 on the back to balance it out a bit. The 140 was an extra thrown in by the nice man at Freeborn Cycles, so I now have a spare 160/140 set in case I decide to build another disc road bike (!). So I now have a bicycle that I don't think is going to kill me suddenly by destroying my spokes on a descent. Which is nice. I'm pleased with it, and all being well will take it on the Fridays Tour de Normandie. This, in case anyone is interested, is what it cost and where it came from...

PX Kaffenback Frame & Fork 160.00
PX Midge Bars 24.50
PX Superlight Seatpost 15.00
PX Headset Spacers 4.00
Shimano RX05 Disc Wheels (Merlin) 120.00
Schwalbe Durano 28mm x 2 (Merlin) 46.00
Schwalbe Tubes x 2 (Merlin) 8.50
Seat Clamp (Quella) 5.00
TRP Spyre Road Disc Brakes x 2 (Freeborn Bikes) 93.50
Centre Lock Adapters x 2 (Freeborn) 22.00
Sora 9 Speed STI Shifters (St John St Cycles) 55.50
Shimano A530 Pedals (Ribble) 29.00
FSA Mega Exo Compact Chainset & BB (gift) 90.00
FSA Omega Stem 80mm 27.00
FSA Orbit Headset (CRC) 25.00
Sora Rear Mech (CRC) 16.00
Ritchey Barrel Adjusters (CRC) 5.50
Kore Brake Cable Kit (CRC) 11.00
Clarks 180mm Disc Rotor (CRC) 5.50
SRAM Cassette and Chain (CRC) 23.00
Cable Guide (CRC) 2.00
Sora Front Mech (Wiggle) 11.00
Alloy Bottle Cage (Wilko!) 3.00
Gear Inners x 2 (Wilko) 2.50
Bike Ribbon Bar Tape 6.00
Caps, Ferrules etc 2.00
Bontrager Disc Rack (Evans) 25.00
TOTAL: £835.50
Gifts: £500
Stuff from spares box: £33
Immediate cost to me: £302.50. Which I think is a bargain.

 

[Smokin Joe]

Nice.

No mudguards though?

 

[TheDoctor]

Nice bike, TC!!
*applauds* and *approves"

 

[theclaud]

Nice.

No mudguards though?

Yeah might do . Unsure about which to get, and they are not easy things to get excited about. If I get time I will pop into my LBS and if he has some that fit the bill I will go for it. Astute observers might also notice that I didn't list a saddle. I'm keeping my eye out for something similar to but cheaper than the Specialized Ruby I have on my road bike, which I have swapped over for the moment. If I can't find anything I might use a Charge Ladle from a little-used bike.

 

[theclaud]

Brooks B17?

Absolutely not.