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Old 09-28-11, 10:28 AM   #1
Buggington
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160mm to 180mm rotors?

Hi all

Interested in upgrading my brake system a bit, but I don't have the money to go for the full monty and get a hydraulic system, so I'm gonna stick with my cables.

I want to change the rotors, because apparently the braking force increases by 20% for every 20mm, but do I have to change the callipers if I do this?

I also had something else I wanted to ask, but I forget what it was. I'm sure it'll come to me later

Thanks
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Old 09-28-11, 11:35 AM   #2
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no, but you have to change the caliper frame mount adapter, and you really have to make sure that you have the clearance on your fork (often the fork tapers in on non-MTB forks, so adding an additional 10mm to the "top" (20mm total diameter increase) means the rotor may rub on the inside of the fork).

also make sure that you have the newer front fork forward-facing dropouts that are safe for large rotors. the old ff dropouts may not be safe with the increased force of the larger rotor. I know on my '08 Salsa La Cruz this is the case---a 180mm rotor both rubs, and under extreme braking the 180mm will begin to torque the wheel out of the dropout, which is not good. (I run BB7s.)

you'd probably be better off finessing your current 160mm set-up: low friction compressionless cable housing, etc. with a 160mm i can still endo without problem, although the 180mm definitely makes endos a little easier. but for useful real-world braking, i'd bet it's more or less a wash in terms of practicality, which means it's a loss in terms of cost-benefit.
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Old 09-28-11, 11:41 AM   #3
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Or the casting for the lower leg, on a suspension fork,
only has clearance for a 160 . [I have one, like that]

but you can measure your fork to assess if it has another 10 mm of radial clearance.
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Old 09-28-11, 12:02 PM   #4
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So I have post type mounts on my Suntour XCM V3's, so that means I'm ok on that one, right? I think I have reasonably square forks.

Pwdeegen - what do you mean torque the wheel out? I know when I start to brake hard on the front with steering fairly tight I do get the wheel bend out slightly. Is this what you mean? And do you mean I basically need an adaptor that can add 10mm to the calliper?

I'm pretty sure that I can get 180mm in there. But overall, pwdeegen, you reckon it's not worth it?
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Old 09-28-11, 12:08 PM   #5
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The only change in addition to the rotors will be the adaptor which goes between the fork mount, and the caliper. this is assuming that your fork will take a larger disc.

Would suggest you don't bother with the rear, as most of the braking is done on the front. As you are keeping cable, and not going Hydraulic, even putting 203mm rotors on will never bring the braking performance up to an equlvilant Hydraulic setup.

What are you using this on?, if an MTB, off road, this would be a reasonable upgrade, if a commuter bike, not sure that you will see much benifit over the 160mm you have already. Have you looked at the cable housing, maybe replacing the current housing with Gore Ride-On cables or similar.
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Old 09-28-11, 12:12 PM   #6
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For the Forks you have, a very quick google search shows they can take a 185mm rotor max http://www.srsuntour-cycling.com/dst...+V3+26%27.html

For the 'torque' the wheel out, not an expression commonly used in the UK in this context, but with the fork you have, this won't be an issue, if the QR is correctly done up.
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Old 09-28-11, 12:42 PM   #7
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So what does torquing out a wheel do? New words here

I do take my MTB off road quite a bit - there were times when going down some long, steep hills where I felt the brakes just weren't quite strong enough - I needed a huge amount of effort at the level to stop, and I only weigh 110 pounds!

I also commute, but down some evil hills too - so hopefully I'll see the difference there too.

The QR leaves an imprint in my palm for a few seconds. This right?
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Old 09-28-11, 03:19 PM   #8
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The QR leaves an imprint in my palm for a few seconds. This right?
If you doing that, it should be tight enough.

if you are only weighing in at 110lbs / 50Kg, even 140mm rotors should stop you fine have you looked at the state of / type of pads you are using?

If it's the G4 bike you have in your sig, would be carefull about spending too much money on it, as it's a fairly low end bike, which could end up being a money pit very quickly.

Last edited by jimc101; 09-28-11 at 03:22 PM.
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Old 09-28-11, 04:38 PM   #9
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by "torquing out" i mean that on downward facing front dropouts, there may be enough rotational force generated by a braking disc rotor to literally force the wheel out of the dropout, effectively dropping you in a painful way. with forward facing dropouts, the rotational force actually pushes the axle back in. a larger rotor increases the leverage/force.

someone with a better handle on physics can describe this in the appropriate way, or here is a link to that approximates it:
http://www.ne.jp/asahi/julesandjames...quick_release/

@jimc101 is right: @101# a 140mm that is adjusted properly should generate enough friction/stopping power to flip you over (end-over, i.e., endo). a larger rotor makes it easier to do this. however, if you do ride the brakes down a long section of hill, it's possible to overheat the rotor and experience brake-fade or even failure. this is very uncommon for most bicyclists. a larger rotor will increase surface area and thus help dissipate heat better, reducing the chances of this. chances are though, a combination of better rotor or new pads will make the same difference.

for my part, i did notice a major difference in stopping power with a 180mm over a 160mm. that is, it was easier to brake harder. in that same vein, it was harder to brake softer since the slightest increase in force on the brake lever made more of a difference on the larger rotor.

for me, the switch to 180mm wasn't practical. i singletrack on my 160s just fine, but i also don't bomb down the mountain with a dragging front brake. if you do a lot of that sort of thing, 180mm or larger could be useful.
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Old 09-29-11, 12:34 AM   #10
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Hmmm... It is rare that I have to brake gently, as stupid as it sounds, I only ever tend to brake when I have to stop, so I don't think small increments in braking really bother me too much, though I guess this is an advantage of the hydraulics.

Hopefully I won't torque out - I've never heard of that before, and it sounded like that was the only case of it...

My current setup is 160mm rotors, as you've probably gathered, with the original cables and pads that came with the bike. The pads still have 2-3mm left on them, but I don't know what is was when they were new. I often go over the rotors and pads with disc brake cleaner about once a month.

Yes, I'm aware the bike could well become a money pit, and it slowly is, but I couldn't afford a better bike when I bought it, so upgrading bits is about the only way I can do this all. What in particular suggests its a low end bike, out of interest?

Thanks for all the help XD
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Old 09-29-11, 02:03 AM   #11
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What in particular suggests its a low end bike, out of interest?
From what I have found via Google, the retail for the Landrover G4 is aroun 270, this isn't much when you have a suspension fork, and disc brakes.

The link in your sig, shows the bike with low end parts, the disc brakes are no name, and when the pads are worn out, it may well be the case that the whole system needs to be replaced as spare pads are unavailable.

In your case; and any involving a low end bike, it is not normally worth upgrading, except for fit purposes, as you will still be stuck with a heavy frame, and the cost will be more than replacing the whole bike.
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Old 09-29-11, 09:04 AM   #12
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...I often go over the rotors and pads with disc brake cleaner about once a month...
Pad material transfers to the rotor increasing performance, cleaning the rotor removes beneficial compound residue. The time to aggressively clean rotors is after swapping to a new pad compound.

I suggest a try at resurfacing the pads and rotors, followed by a proper bed-in process, before replacing hardware. It may be the type of brake use causes the pads to glaze. If performance improves after servicing and declines shortly afterward, consider a different pad, and possibly a larger rotor to handle the heat. To resurface, lay a section of 600 grit sandpaper down on a flat surface with the abrasive side up, place the pad friction surface down on the sandpaper, sand lightly until no striations can be seen on the pad, do not touch the pad's friction surface (or sandpaper) with fingers, or wipe with anything. Lightly use a finer grade sandpaper on the rotor's swept area; the goal is not to smooth completely, only to remove contaminates, and small ridges. Next use the brake cleaner on a clean, uncolored paper towel to wipe the rotor, not the pad. Different pad compounds require variations in bed-in technique, I suggest a light bed-in of 6 near stops from a running pace for the front and rear separately, followed by a cool off period where the brakes are unused.
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Old 09-29-11, 09:28 AM   #13
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When a_ rear of left fork disc caliper_ is braking, there is a CCW force
rotating around the caliper as a torque center ... and an open bottom.

I've seen builds that reversed that , put the caliper front right ,
then the torque, braking, tended to push the axle more firmly into the dropout.
But mass market has kept the brake on the back of the left fork-blade.

Last edited by fietsbob; 09-29-11 at 09:31 AM.
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Old 09-29-11, 12:12 PM   #14
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When a_ rear of left fork disc caliper_ is braking, there is a CCW force
rotating around the caliper as a torque center ... and an open bottom.
Pretty much the only time when lawyer lips come in handy.
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Old 09-30-11, 02:53 PM   #15
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Originally Posted by jimc101 View Post
From what I have found via Google, the retail for the Landrover G4 is aroun 270, this isn't much when you have a suspension fork, and disc brakes.

The link in your sig, shows the bike with low end parts, the disc brakes are no name, and when the pads are worn out, it may well be the case that the whole system needs to be replaced as spare pads are unavailable.

In your case; and any involving a low end bike, it is not normally worth upgrading, except for fit purposes, as you will still be stuck with a heavy frame, and the cost will be more than replacing the whole bike.
I think the LBS say that I can get spare Fibrax pads - I'll have to check this soon. And I think I paid about 350 for it. It's a nice bike, feels much better designed than my dad's carrera, which is a pig to ride. I don't really notice the extra weight - it still feels nice to ride. There are a few things I'd like to do, one of which is make it stop better, and another is to upgrade to a 48 tooth chain ring. The 42 is driving me nuts! And what do you mean fit purposes? I'm confused

Quote:
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Pad material transfers to the rotor increasing performance, cleaning the rotor removes beneficial compound residue. The time to aggressively clean rotors is after swapping to a new pad compound.

I suggest a try at resurfacing the pads and rotors, followed by a proper bed-in process, before replacing hardware. It may be the type of brake use causes the pads to glaze. If performance improves after servicing and declines shortly afterward, consider a different pad, and possibly a larger rotor to handle the heat. To resurface, lay a section of 600 grit sandpaper down on a flat surface with the abrasive side up, place the pad friction surface down on the sandpaper, sand lightly until no striations can be seen on the pad, do not touch the pad's friction surface (or sandpaper) with fingers, or wipe with anything. Lightly use a finer grade sandpaper on the rotor's swept area; the goal is not to smooth completely, only to remove contaminates, and small ridges. Next use the brake cleaner on a clean, uncolored paper towel to wipe the rotor, not the pad. Different pad compounds require variations in bed-in technique, I suggest a light bed-in of 6 near stops from a running pace for the front and rear separately, followed by a cool off period where the brakes are unused.
Wow. That's a lot of technique, thanks! I will be paying attention to that - it's possibly contaminants that are hindering the performance, though the 180's will surely make a big difference. This sounds stupid, but I've noticed the rotors do seem to be going more grey (pic attached, ignore the rust, it's now been painted over ) - might this be contaminents?

Quote:
Originally Posted by fietsbob View Post
When a_ rear of left fork disc caliper_ is braking, there is a CCW force
rotating around the caliper as a torque center ... and an open bottom.

I've seen builds that reversed that , put the caliper front right ,
then the torque, braking, tended to push the axle more firmly into the dropout.
But mass market has kept the brake on the back of the left fork-blade.
I think I'm right in saying there was a design by Scott which had a disc on either side, one on the back left and one on the front right.

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Originally Posted by leob1 View Post
Pretty much the only time when lawyer lips come in handy.
True that

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Old 09-30-11, 03:22 PM   #16
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You have a ISO mount on that fork, so a different adapter is what you get,
and the disc.
good time to replace the pads too.
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Old 09-30-11, 03:55 PM   #17
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And what do you mean fit purposes?
Longer / shorter stem, i.e. so the bike fits you.

Would look at that adjustor screw on your disc, it's backed way out. is there much thread holding it in?
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Old 09-30-11, 04:25 PM   #18
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Funny enough this post answers both those points - I've changed the fork since then, so I now have a post mount, but I will have to get hold of an adaptor to mount it further away. And since the bike went in to have the forks done the cable was re threaded, so there's a whole load more cable available so the adjuster down there is wound all the way in now. Is it REALLY bad to have it a long way out then?
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Old 09-30-11, 04:38 PM   #19
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really bad, because if that screw came out (on account of having so few threads holding it in place) you would have NO braking from that front brake. avoid turning into the human battering ram.

@fietsbob: you're right. i'd forgotten about the left-front-mounted-brake fork. fwiw, bunches of people sell forward-facing dropout forks now.
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Old 10-02-11, 01:55 AM   #20
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avoid turning into the human battering ram.
Will do! that adjuster has been wound in for several months now - no battering ram here
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