So I made a quick simple image guide on how to quickly and easily determine if FD calipers are the standard brakes aka "16inch" or the larger ones aka "17inch". The larger "17inch" ones came stock on Spirit-r (red) and some RZ/RS models (non-red). The two caliper looks similar, but are NOT the same. They are actually two different models of calipers, they are dimensionally different.

So if you ae buying used FD calipers or you are just not sure which calipers you have on your FD, here is a simple guide which will help you determine if they are the smaller standard ones or the larger "17inch" ones.

(16inch and 17inch nick names for these calipers come from Japan, because FD's with stock 16inch rims came with smaller calipers and obviously the larger caliper could no be used on FD's with 16inch rims, so hence the nick name "17inch")

 

Looks like the pistons are different sizes too or is it the pic?

 

They are different. Staggard sized

I know this is a VISUAL difference but if you measure the opening where the pads go, the 17in calipers is huge compared to 16. The regular 16in calipers comine at ~68-70mm depending how you measure. 17in calipers come in wayyy larger at a number I can't remember right now

 

Easiest way to tell is the pistons if you can only look at a picture, the 17s has 1 large and 1 small piston, while the 16s are 2 equal size pistons.

 

Yes the pistons are different as well. However, I noticed a few people lately asking whether they have standard or larger calipers, so in the case the calipers are installed on the car, and you cannot see the pistons it is useful to know about the 4 indents (which the larger calipers lack). Or if you are buying used calipers online, and want to make sure you know what you are buying, the guide above is just a quick way to tell the difference so fellow FD owners don't get screwed over.