Front disc thickness?

[rustychain]

I measured the front discs on my 1150GS (2001) yesterday and they are down to ~4.5 mm.

According to the BMW repair manual they should be 5.0 mm when new and need replacing at 4.5 mm.

Replacement Galfer discs are 4.5 mm thick new. I'm not clear why a reputable manufacturer doesn't meet OE spec?

Avoid and get Brembos or EBC?

 

[Smithmas]

On my last service (Wollaston Northampton) they sent the inspection video - recommended minimum was 4.5mm for the rear discs and on the front was 4mm

 

[sproggy]

BMW’s recommended thickness is for their own discs, not for the bike irrespective of disc manufacturer. I don’t see anything wrong with new Galfer discs being 4.5mm - that’s how they’ve designed and manufactured them. Probably superior design or materials (or both) to the OE ones.

 

[rustychain]

Thanks both and that's a good point you raise sproggy.

 

[Paul Young]

There must be some correlation between disc and pad thickness as no two brands of either are likely to be identical. Galfer may use thicker back plates for their pads so any difference is made up for.

Personally, I have an R1100R alloy front wheel with the bigger fully floating discs, mounted on alloy carriers. To replace the OEMs when they got to 4.5mm, I fitted Tsuboss wavy discs to the original carriers. They’re as thick or thicker than OEM and work well with whatever pads have fitted.

 

[rustychain]

I've done some more digging - the Galfer wear limit is 4mm.

Those Tsuboss discs look good value @Paul Young, are you happy with their performance?

 

[theoneandonly]

RIGHT . THERE IS NO MINIMUM THICKNESS FOR AN MOT INSPECTION

it is testers discretion ,

all the suckers that listen to their BMW garage , when they suck their teeth and stiff you £ xxx cos your discs are "worn out " @ 3.95 mm .

my MOT tester looks for cracks and flex.

my 1150gs got new discs @ 75k miles ...and i live in London , and i'm not gentle on the brakes.

if you are changing those , you evidently have too much money in your pocket ( strange for a Yorkshireman ) so you can post down your " worn out" discs to me for free and i'll use them for the next 3-4 years.

 

[rustychain]

RIGHT . THERE IS NO MINIMUM THICKNESS FOR AN MOT INSPECTION

it is testers discretion ,

all the suckers that listen to their BMW garage , when they suck their teeth and stiff you £ xxx cos your discs are "worn out " @ 3.95 mm .

my MOT tester looks for cracks and flex.

my 1150gs got new discs @ 75k miles ...and i live in London , and i'm not gentle on the brakes.

if you are changing those , you evidently have too much money in your pocket ( strange for a Yorkshireman ) so you can post down your " worn out" discs to me for free and i'll use them for the next 3-4 years.

I always love to see your responses @theoneandonly. Are you sure you don't have some Yorkshire heritage with all your straight talking?

I measured them myself so no dealers involved. Are you saying there's no safety issues if a disc is worn beneath the manufacturers specification?

I was concerned that below the specified thickness the discs could fail under heavy braking due to the lack of structural integrity. I am happy to be corrected as I'm no expert in this area. There must come a point where a disc is just too thin to be safe?

You're 100% right, I am a tight Yorkshire man. However, when it comes to safety critical things that might mean I end up in a wheel chair/morgue I'm quite happy to spend! (as painful as that is...)

 

[Steptoe]

I remember a few years ago I had a despatch riders K100 (told you it was years ago) in for servicing.
The front discs were like a biscuit tin he told me not to fit new discs as they still had a few miles left in them

 

[theoneandonly]

my previous post quoted my MOT tester
he/they check for cracks between the holes and can you flex it . either is a fail with them .
i worked in an MOT station and my boss wrote an advisory for worn discs , ( i never let him MOT my bike again )
i have run discs down to about 3mm thick , before replacing them ( yes i used to be a courier , at the same Co. as Steptoe.)
yes as a mechanic , i have seen discs like round razors , yes i am careful( read tight) with mine and other peoples money , no i'm not from Yorkshire , but lived briefly in Northallerton when i was very small .
maybe something rubbed off on me then .

the min thickness stamped into discs is so that if you have is refinished/ground , that is what they think it should be .

driving with thin discs , a copper may consider that you are " maintaining in a poor condition " and give you a ticket.

last week i saved a punter from spending the £1k on new discs and calipers a shop said he needed ....what he needed was a disc , just 1 , a caliper clean and new seal kit and pads .

 

[Riceburner]

@theoneandonly : which caliper/pad/disc combo are you running that is preventing the discs "lipping"?? I'm not sure I've ever had a bike that didn't lip the discs as they got worn, which is what (ime) most MOT testers use as their gauge of whether a disc is worn or not.

 

[theoneandonly]

@theoneandonly : which caliper/pad/disc combo are you running that is preventing the discs "lipping"?? I'm not sure I've ever had a bike that didn't lip the discs as they got worn, which is what (ime) most MOT testers use as their gauge of whether a disc is worn or not.

i do Guzzi's , std discs and ferodo pads . my BMW's run std discs and ferodo pads
NOT ST pads, std platinum

when they get a bit of a lip i....have the wheel spinning freely . and take an angle grinder to the lip. do it properly , and the wheel will spin with the grinder and you end up with a bevel on the outside edge of the disc . do inside and outside . THEN when tester/copper has a quick feel they can only feel the thickness.

 

[Paul Young]

I've done some more digging - the Galfer wear limit is 4mm.

Those Tsuboss discs look good value @Paul Young, are you happy with their performance?

I’ve been perfectly happy with them.
I did have an issue with a binding caliper and that warped my first pair. My friend is brilliant at stripping and refurbishing calipers so I sent them off to him and they came back working better than new. Fitted a new pair and they’ve been brilliant. Size matters though, and the bigger floating discs are an improvement on the standard 1150 items.

The pads are Kyoto ones from eBay, I think.

 

[Wrigsby1]

I change discs when they are quite worn and have never had a crack etc even though the old K discs started thin and cracked more easily ... BMW will have a limit due to liability as well and .25mm on either face would not be noticed by many riders and many people in the trade... The most important thing is you are happy with your brakes and that will obviously be very subjective...

 

[AdrianS]

What’s the heat dissipation like with thin discs compared to new ones? I thought discs were changed due to excess heat possibly distorting them, as well as for safety regarding strength.
Must admit with car discs, I change mine every pad change ( usually around 50,000 miles).