DI.R.T. (note the weird placing of the full stops) stands for DIrect Response Technology. The DI.R.T. designs were extremely innovative, with two composite knuckles, a composite outer parallelogram plate and a composite inner pulley cage plate. That's a lot of composite for the time, and it made these derailleurs fiendishly light. They also had a pretty straight cable run and a groovy curvaceous look. Finally they were Shimano compatible - which gave SRAM something to offer the majority of the market, while it gradually built the population of riders using its proprietary 1:1 actuation.
Did they change gear well? I would say that they did - although many home mechanics, who were not used to the straight outer cable run, were not careful enough about the length of outer cable required. Get this right and these gears worked well, possibly very, very, well. Get it wrong and they were dogs.
Were they a commercial success? Possibly not. They acquired a reputation for being fragile, with numerous macho dudes claiming on the, then newly fashionable, internet that they had smashed their DI.R.T. derailleurs to pieces in this way or that. I have to say that I didn't notice more smashed DI.R.T. derailleurs than smashed Shimano derailleurs, so I am mildly dubious about this claim. I do think that the DI.R.T. derailleurs looked fragile, and that plastic and pressed aluminium possibly does not look as comforting as polished or anodised aluminium forgings.
Most of all these derailleurs were not cheap (particularly the higher end ones). The biggest downside of the DI.R.T. derailleurs was that it was hard to convince customers that a plastic and pressed aluminium derailleur was a luxury item that should cost as much as one constructed of polished or anodised aluminium forgings. These derailleurs were no only light in weight, they were also light on Bling.
Despite this history, and despite the fact that it does not chime with SRAM's foundation myth, it might be true to say that there is more of the Sachs DI.R.T. DNA in, say, a SRAM X-0, than DNA from SRAM's own, contemporary, SRAM ESP 900.
This is a, slightly battered, example of a SRAM Plasma. I think it is a relatively late version.
The scars on this derailleur point to some of the disadvantages of the DI.R.T. designs discussed above. The straight outer cable run leads to an exposed extension to the parallelogram at the back of the derailleur that can easily take a hit - and in this case has done so. The composite b-knuckle has suffered a dose of road-rash, as is also common with many derailleurs with metal knuckles - but it somehow seems more serious here. And the composite inner pulley cage plate has suffered some aggressive cuts at the hands of the chain. This is, probably, not as serious as it looks - but it certainly made me pause for thought.
The SRAM Plasma was the top model in the SRAM DI.R.T. range. It weighed in at an impressive 207g and featured:
That's quite a lot of Sachs branding for a SRAM product. Note also that the tension pulley is branded 'Sachs', but I don't know of a Sachs derailleur with orange pulley wheels - so these must have been manufactured specially for this derailleur.
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