When some stupid motorist or pedestrian suddenly gets in the way, you want to have all possible braking that is available.

Some manufacturers/maintenance staff manage to blend the two types of brakes (dynamic and hydraulic) well, others don't.

Regards,

> On 23 May 2017, at 2:57 pm, 'Noel Reed'noelreed10@... [TramsDownUnder] TramsDownUnder@...> wrote:

>

> Matthew Geier wrote -- There have been trains fitted with disc brakes as their primary braking system also having clasp brakes fitted to 'clean' the wheels. Usually it's for track circuit reasons, not to rub wheel flats off.

>

> ....................................................

>

> The Budd railcars including those once in NSW had disc brakes and also ‘shunt shoes’ [for track circuit purposes] resting on the top of wheel treads. These railcars also had anti-slip braking equipment.

>

> Non powered tram wheels don’t slip with acceleration but can easily collect track debris [leaves]. If an articulated tram does not need all wheels powered, why do they need wheel brakes on the non powered wheels ? Wouldn’t track brakes provide sufficient stopping power ?

>

> Noel Reed.

>

>

>

>

>

> From:TramsDownUnder@... [mailto:TramsDownUnder@yahoogroups.com]

> Sent: Tuesday, 23 May 2017 2:28 PM

> To:TramsDownUnder@...

> Subject: Re: FW: [TramsDownUnder] Leaves on Melbourne tracks

>

>

>

>

>

> On 23/05/17 14:16, 'Noel Reed'noelreed10@... [TramsDownUnder]

> wrote:

> >

> >

> > Would several runs with abrasive brake shoes solve the ‘wheel flat’

> > problem without needing the wheel lathe ?

>

> The problem is they have disc brakes, not wheel clasp brakes.

>

> If they had clasp brakes, that would work - and normal brake shoes will

> tend to rub off small flats, although not as rapidly as putting a hard

> cast iron shoe on does.

>

> When a disc brake causes a wheel flat, the resulting damage is amplified

> over time instead of being rubbed out by the brakes.

> The railways discovered this the hard way too.

>

> Also why a functional wheel slide protection system is now so important,

> something it appears, Siemens have never quite got right on the D2 class

> trams.

>

> There have been trains fitted with disc brakes as their primary braking

> system also having clasp brakes fitted to 'clean' the wheels. Usually

> it's for track circuit reasons, not to rub wheel flats off.

>

>

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>