On the few attractions where you have to transfer, I have always been able to get a plus sizes chair that works for me. They usually have both sizes available, unless they are in use, in which case they might suggest you come back in a little bit or be able to find one for you. Just a note that sometimes they keep the wider chairs in a separate spot so that those that actually need the wider chairs can get them, in those cases you need to ask the CM for them. The width is the same as the wide chairs you can rent at the front of the park.
Additionally, it should be noted that the following attractions will initially say you need to transfer to a regular wheelchair for the queues, but they do have an alternate entrance that
ECVs can be taken through if the wheelchair won't work for you:
- Buzz
- Tower of Terror
- Rockin Roller Coaster
- Test Track
- Star Tours sometimes will tell you this, but does have an alternate available
Please note that the alternate entrances at these attractions will generally skip any applicable preshows, although many of the preshows aren't being used right now anyway.
Also, Haunted Mansion normally doesn't allow ECVs through the queue, but is currently using an alternate entrance that does.
Pirates does have an alternate entrance, but I haven't seen it used in many years as it does involve being escorted backstage. I do know it exists because I have used it before Pirates got FP.