I've always thought the Simplex SX610 was the the econo version of the SLJ 6600 (T/SP versions). However, the SX610 has a max wrap and max cog size of 28 teeth, while the SLJ 6600 has a max wrap of 22 teeth and a max cog size of 24 teeth, according to Velobase catalog scans. Why the difference? Is the pulley cage a bit longer? The parallelogram travel a bit wider?

At first I thought you must be mistaken, but since the '84 catalog scan on Velobase came from me, I dug it out and sure enough, there it is. In the photos they definitely look like they have the same cage length and geometry.

If you look at the "Gold Range Touring" derailleurs, there's no difference in capacity between the straight parallelogram 5500 GT/SP and the drop parallelogram 6600. Why wouldn't the same be true for the 5500 and 6600 T/SP?

I think the capacity shown for the 6600 T/SP is either a typo, or a bit of fiction designed to let the consumer know that this is their serious "racing" derailleur. I wouldn't be afraid to try one with a 28t cog.

I can not give much on gear capacity but of the half dozen or SX series I have come across 4 where in peices not in one functioning unit . As for the deference in capacity the SX DR's have signifcantly longer pulley arm almost a fulll inch longer than most Simplex stuff.

Simplex derailleurs from this era came in three cage lengths:

CP - short, T - medium, and GT - long.

The /P or /SP designated whether the derailleur came with a mounting plate or not. So for instance, a GT/SP derailleur was a long cage derailleur without a mounting plate.

That question crossed my mind, too!

That's interesting, given Simplex's late move to the dropped parallelogram. I do hope it actually has a little larger capacity than advertised. Thanks for your comments SuperLJ!

My SLJ 6000 handles a 28t cog just fine.

There you go SlowRoller, the SLJ6000 is the same as the 6600, just a couple of years older.

My SLJ 5500T will handle the advertised 30t cog no problem (I had it set up as a half-step for a time), but I'm currently running it with 50/36 chainwheels and a 14-24 freewheel for a total of 28 (two below what's recommended) and it's probably a little more than maxed out capacity-wise.

Thanks, SLJ and Grand Bois. I may have to mount it and give it a shot.