Min. Brake Disc for MOT

Hasujek · Two Stroke Sniffer Joined: 16 Nov 2016 Karma :

Hi, I am preparing my CBR125 for MOT and been told by a garage that my rear disc is below the limit (3.5mm?). Checked myself and the corner of it is 3.6mm but it's more worn on the inside, roughly about 3.3/4mm. My question is what is the minimum for the MOT as can't find anywhere on internet. I am selling the bike soon and don't want to spend ££ on new disc.

Beehive Bedlam · World Chat Champion Joined: 28 Oct 2013 Karma :

Should be stamped on the disc.

I wouldn't sweat it at the very worse you would get an advisory he would be a royal cunt to fail it on a worn disc.

Monkeywrenche... · Nearly there... Joined: 27 Mar 2015 Karma :

The limit for mot is what the tester regards as "excessive", for the purposes of the test that would be so worn that failure is imminent. things stamped on it or makers specs are irrellevant.
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stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Minimum varies for each disc. Even between brands for the same model. It's marked on the disc.

Excessively worn brake disc is a fail.

It's a numbers game. The only way it ought to pass if it'sthinner than the markings is if the tester doesn't notice. You could chance your hand and change the disc if it fails. many places do a free retest within a week (but not all of them so check).
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Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

Gamble on a used disc = £15
Throw in a new Chinesium disc = £25 (last one on eBay) then £35
Cost of retest = £0 or £15 or £30 if you prevaricate.

There's no obviously right answer since we don't know how strict your MOT tester is, or what condition the rest of the bike is in - it might well fail on something else.

Do you feel lucky, punk?
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

It's a safety item, it's not worth the risk. The minimum thickness on the disc is really the minimum thickness of the disc. If you want to ride the bike like that, it's your own risk, but I wouldn't ever sell a bike in that state as roadworthy.

As an aside, I don't recall ever in my nearly 20 years of riding having worn a disc past the wear limit. I've warped a few, and I've scored a few, and I've had things like theft attempts that damaged discs, but I've never worn it to death like that.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

Ste · Not Work Safe Joined: 01 Sep 2002 Karma :

Wearing the rear brake disc below the minimum limit on a CBR125 must have taken some effort! Laughing

Hasujek · Two Stroke Sniffer Joined: 16 Nov 2016 Karma :

Ste · Not Work Safe Joined: 01 Sep 2002 Karma :

Hasujek · Two Stroke Sniffer Joined: 16 Nov 2016 Karma :

Rogerborg · nimbA Joined: 26 Oct 2010 Karma :

You actually did the A1 tests? Good chap (or lady-chap). Thumbs Up

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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

Chris45 · Nitrous Nuisance Joined: 23 Oct 2016 Karma :

Most disks have the min thickness stamped on them. 4.5 mm is a norm and that's the disk, not the rim, so if the tester has failed it on that point you need a replacement.
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Honda CG125>Suzuki GT185>Honda CB 250N>Suzuki GSX400>Honda CX500B>Kawasaki GPZ305> Kawasaki GPZ550>Kawasaki GPZ500S+BMW 650GS

Hasujek · Two Stroke Sniffer Joined: 16 Nov 2016 Karma :

kramdra · World Chat Champion Joined: 28 Oct 2010 Karma :

Most honda's share the same disc setup, maybe not on a 125 but almost all 4 bolt rears are the same part, so plenty of almost unused ones on ebay.

The min limit might seem silly, 4.5mm (on mine) is a lot of metal, however it is very common for them to crack (unsure if disc lock or weakness from drilling, Ive got two in the spares box that came with bikes).
At 80k miles I changed on the cbr6 and it was well under the min at 3.3mm. I think the new one was 5 or 5.5mm, much less than I expected.

RhynoCZ · Super Spammer Joined: 09 Mar 2012 Karma :

uberkron · Crazy Courier Joined: 12 Nov 2012 Karma :

Mr rhyno.

My scooter eats a brake disc each 30,000km.

My Toyota car gets 100,000km to a set of discs.

W203 Benz with v6 I get 80/100,000km.

I've been replacing front disc on mum's Virago every 30/40,000.

Can I buy your invincible discs?
Maybe I'm just an idiot for machining the discs when I change pads?
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i ride a zip 50 2smoke. It overtakes a hundred times a day.

Hasujek · Two Stroke Sniffer Joined: 16 Nov 2016 Karma :

RhynoCZ · Super Spammer Joined: 09 Mar 2012 Karma :

uberkron · Crazy Courier Joined: 12 Nov 2012 Karma :

Because my brake lathe cost alot and I find the brake pads work well when not riding on the glaze of past pads.

I don't warranty a brake job if rotors aren't replaced or machined.

Neither will my suppliers of brake pads.
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i ride a zip 50 2smoke. It overtakes a hundred times a day.

RhynoCZ · Super Spammer Joined: 09 Mar 2012 Karma :

RhynoCZ · Super Spammer Joined: 09 Mar 2012 Karma :

uberkron · Crazy Courier Joined: 12 Nov 2012 Karma :

Oh. I make my living running a workshop, so there's more to my trade than just spending as little as possible.

I understand for the home mechanic it is different.
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i ride a zip 50 2smoke. It overtakes a hundred times a day.