Kontact, really like your posts in general (I learn a lot from them) so I'm not trying to start any battles here. But your response in this case is a little simplistic I believe. I could be full of it but Shimano compatible freehub body widths are not all the same. Yes, the Shimano 11s road freehub body is 1.85 mm wider than the Shimano 8/9/10s bodies (which were same for road and MTB) so an 11s road cassette fits exactly but an 11s MTB cassette must be fitted using an 1.85mm spacer. The Shimano 11s MTB freehub body is the same width as the Shimano 8/9/10s body so an 11s road cassette will not fit (about 1.85 mm to wide) but an 11s MTB cassette will fit with no spacer. Why? Because the largest cog on a Shimano MTB cassette is mounted on a spider with other cogs, and this largest cog overhangs the inside of the freehub body. But wont this interfere with the spokes? No, the monster 11s large cogs have such a large diameter that the chain and RD will not touch the spokes. Why didn’t Shimano make 11-speed road cassettes compatible with Shimano 8/9/10s hubs? The smaller large cogs of road-oriented cassettes, even with a 28 or 32 tooth large cog, would interfere with the spokes if fit on a 8/9/10s Shimano freehub, Notice that I have not said anything about any other manufacturer's hub (or cassette). This of course is completely off topic to the OPs question but just indicative of the non standardization we are dealing with. And it ain't getting any better in the near future,

You're correct - I forgot about the MTB version.

I don't think any of the discussion about overhang or not really matter in terms of why the Xtender does or doesn't work on a Shimano cassette.

Anyone who wants to measure the overhang just needs to put a straightedge over the back of their removed cassette. That will end any sort of debate.

Boy that is an informative post and a very helpful explanation, thank you. And now I better understand why an experienced chap on YouTube said that when putting a mtb cassette on your road bike, you have to put a spacer on first. I'm just about to replace my 11-32 with an 11-42. Would that qualify as needing such a spacer EggMan? I'd have to order one wouldn't I? I thought I was now ready to slap it all together, but looks like I might not be there yet.

Based on the info you are providing, I assume your current 11-32 is an 11s road cassette and the proposed 11-42 is an 11s MTB cassette, So yes you should purchase a 1.85mm spacer like what you can find at https://www.universalcycles.com/shopping/product_details.php?id=61155&category=503about

If you end up not needing it you can possibly return it or be out $6. A LBS should also have a supply of spacers. So if you slide the new cassette on your hub, and find you need a spacer, you could just run down to your LBS and they could fit the correct one on. I think the spacer goes on first, then the cassette. Good luck and hope you get the gearing you want.

You're right I will need the spacer when converting from 11-speed road to 11-speed mtb cassette, and the spacer goes on first. Your post prompted me to asked around and it was confirmed a couple of times.

The 11-32 cassette is Shimano 105 11-speed and the 11-42 is a Sunshine mtb cassette.

I'll have the tools tomorrow to do the job and will use the local bike shop for the part. Thanks a lot.

I thought I'd let you know how I got on for your information. When I took the 11-32 Shimano 5800 cassette off, it turned out I had a good half dozen or so spacers to work with lol. Every cog but the big three were separate, the last three (25-28-32) being riveted together on what I assume is a spider.

It turned out that a spacer was not required for the 11-42 Sunshine mtb cassette. Just like the 11-32 Shimano 105 cassette, the Sunshine's big cog was also housed on a spider. Therefore I assume the freehub that came with my Giant Contend is such that a spacer is not required when a spider houses the big cog.

I assume that with a typical road cassette, the biggest cog is not housed on a spider? In that regard perhaps this particular 11-32 Shimano 105 cassette is an atypical example of a road cassette.

When I tried using a spacer on the 11-42 cassette, the 11-tooth cog would not slide onto the freehub splines. The stack (total cassette width) of the 11-42 Sunshine cassette is exactly the same as the stack of the Shimano 105 11-32 cassette.

Interesting. When you had the cassettes on their side on a table, did both the largest cog and spider rest on the table. If so, then the largest cog is not "overhanging the inside of the free hub".

I took photos of the backsides of the big cogs, but I'm having trouble sending the photos. Both the 11-32 and 11-42 are the same in this regard. When placed flat on the table, only the big cog contacts the table, the spider bit is recessed by about 2 millimeters. Come to think of it, that distance could be the width of a spacer, 1.85mm.

So this must mean that the big cog is indeed overhanging the inside of the freehub, I assume by 1.85mm. And if I understand right, that should require the use of a spacer. But, as I said, for some reason the spacer results in both cassettes not fitting.

​​​​​​​I can only think that the hub dimensions themselves aren't typical. I've been told that they're probably Formula hubs, but I'm not 100%. Do mtb hubs typically require spacers for a mtb cassette? If not, then it might be resembling a mtb hub.

I fixed my photo-sending problem. The first is the 11-32 Shimano 105 5800 cassette (25,28, 32), and the second photo is the 11-42 Sunshine mtb cassette (15 - 42, with 11 and 13 loose):

https://cimg6.ibsrv.net/gimg/bikefor...89533dd1af.jpg
https://cimg0.ibsrv.net/gimg/bikefor...4054bed296.jpg

Say your later post with pictures but couldn't see how spider in relation to the large cog. Who knows what the freehub length is that Giant uses on your bike. Not needing the spacer would suggest its a hub designed for 11s MTB, which supposedly is teh same width as 8/9/10 speed freehubs. From what I am told (but have not conformed for myself) is that the road freehub is 1.85 mm wider than the older 8/9/10 speed freehubs. Not needing a spacer for either hub says the 11-32 105 cassette is overhanging (as you state above) the inside of the freehub. This is counter to what I have read for "road cassettes". Bottom line, I am glad it is working for you, and the rest of us (or most of us) are just repeating what we have read elsewhere and no longer have any idea what is or is not compatible. As I said, wait until the new Shimano 12 speed is in circulation with its new hub configuration. Truly the big 3 are saying their system is best, at the expense of the consumer have to lock into a standard.

Hope you like the new gearing.