Safeway

I am buying a new set of rotors for a race wheel set. I see that there are two versions of the IceTech rotors available. The only visual difference is the spider. The SS has a solid and more angular spider, and the A-SS has holes and a more curvaceous spider.

I can't find any documentation on these rotors. Is one newer? Is the A-SS a "Revision A" of the SS?

Shimano 140mm OD SM-RT99-SS:



Shimano 140mm OD SM-RT99-A-SS:

wschruba

Typically, convention has that more complicated names are later productions. But that's not what is going on here.

I'd chalk it the different look up to an engineering revision (a more gradual curve on the spider). Anytime you see something that looks almost identical, it's usually because a failure mode was identified post production, and minor changes were made to improve the part. A good example is the difference between first generation and second generation derailleur clutches. Changing the radius on the part stopped them from breaking. I know of no such issue with the brake rotors.

That said, that's not what the letter is designating; A=140mm, S[mall]=160, M[edium]=180, L[arge]=203

So, Shimano's part designation for that particular item would be SM [designation small part]-RT99 [the model] A [the size of the item].

You can use this to find out more information on pretty much any item, or how to find the name of a part you are unfamiliar with.

cobba

'A' is the new model that weighs 0.5gm less then the old model

Specs: https://productinfo.shimano.com/#/spe...L/Disc%20Rotor

140mm is SS not A

https://productinfo.shimano.com/#/com...460&acid=C-460

Safeway

wschruba, cobba: Thank you for this information! Picking up a set of the A-SS now.