I can't quite remember when the generation for the Madone changed and clearance is both tire and rim specific. I have the first gen with the Isospeed decoupler and HED Jet+ (21 mm internal width). I have 25mm 5000TLs and there is still a ton of room. Something taller and wider, like the 4000 might be tight in a 28

I'm 99% sure you can get 28's in there but there won't be a lot of clearance. I had one and considered putting 28s in, and had a buddy who did, he just had to steer clear of wet gravel or stuff like that on bad days.

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Raf
http://www.shutuplegs.org

I ran GP4000 in 28 that measured about 32 on a 21mm internal rim. They didn't work on a 19mm rim as they became too tall.

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24 Hour World TT Champs-American record holder
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