This might be a dopey question : Rear disc minium thickness

[StewMcGrew]

My rear disc is currently at 4.40 mm (a slight lip) and the BMW guys are telling me that it needs replacing as the service level is 4.5mm. Now the rear comes new with only 5mm on it and the fronts come with 4mm on it from the factory.

Does the rear disc really need replacing or would I get another set of pads through it?

 

[Smug]

So long as it is not warped then I wouldn't change it.

 

[JJH]

No do not replace it. JJH

 

[StewMcGrew]

Thanks guys. I thought it was just BMW pulling a fast one. I need new pads as well, as I have a 2012 hexhead, what pads can I use?

I see there are different types:-

HH - only use if HH allround
Ferodo ST - only on stainless steel discs.
Organic - I've used this compound on my moutain bike and wore them out in day on wet trail.

Any advice would be appreciated.

Thanks

Stew

 

[Sgt Bilco]

You will get a multitude of opinions on pads but I use Ferodo's from Steptoe of this parish and available at www.gsshop.biz. Never had any issues with them and I get great pad life and stopping power.

 

[Bendy toy]

I have HH all around. Organics lasted less than 4000 in the back brake with resultant damage to the disc.

My rear disc got well below its official minimum thickness. The MOT tester said he looks for signs of cracking at the drillings through the disc. Mine was about 3.5mm maybe less when I changed the disc. No signs of cracking though.

I suspect BMW have a light wear limit because the back brake gets so heavily used by default.

 

[AlexG]

To be fair to the BMW guys...the Haynes manual states the service limit of the rear disc is 4.5mm (which I assume is direct from the BMW specs).

Presumably BMW have set the limit at 4.5mm for a reason.

At 4.4mm I probably would not replace the disc, but I honestly cannot think of a sensible reason why not.

 

[Lord Snooty]

I think it is just BMW being ultra cautious in order to avoid litigious action by Merkins and compo chasing lawyers

 

[Smug]

Could it be something to do with them costing £200 a throw plus fitting?

 

[Bendy toy]

I think it is just BMW being ultra cautious in order to avoid litigious action by Merkins and compo chasing lawyers

I'm sure this is spot on. A disc developing cracks suddenly becomes an unknown quantity so the manufacturer will want to stay well outside that risk. Add that the GS over uses it's rear disc it's easy to see why BMW are taking no chances. A lesser cost option (for BMW and us) would have been larger diameter disc on the back wheel. But that would be too easy (and spoil the lines of your awesome steed).

 

[Watty100]

Had the same thing from the dealer when my bike went in for its 24k service. (the last time it saw the inside of a dealership)

It looked fine and I measured it at 4.5mm so left it well alone.

Finally changed it with over 60k on the clock, it was virtually see-through by then....

 

[sanensafe]

I also had the same story from the service department for the last 2 BMW services. Spoke to the Brembo guy at the bike show. He tells me they supply the BMW discs with 5mm. If you get the Brembo item they have 5.5mm. You decide but as the Brembo item is less expensive it's a no brainer for me.

 

[Bendy toy]

I also had the same story from the service department for the last 2 BMW services. Spoke to the Brembo guy at the bike show. He tells me they supply the BMW discs with 5mm. If you get the Brembo item they have 5.5mm. You decide but as the Brembo item is less expensive it's a no brainer for me.

You rebel you. Just think of the increased unsprung weight.