Another cassette/chain question

[chillyuk]

I have mentioned elswhere my recent Ebay road bike I picked up last week. I ordered a new 7 speed freewheel from Ebay, but now realise that I have clanged. My existing freewheel is a 24 or 25 tooth bottom gear, but I have ordered a 28 bottom toothed one. In itself it isn't a problem as I am also changing the chain at the same time. My only worry is wether the gears will clear the freewheel. On the chain front I have seen three different methods of measuring the chain length needed. One is to go small to small sprockets then tension the chain till it just clears the jocky wheel cage, then there is the large to large plus one link and then one went large front and small back and tension the chain until the jocky wheel cage is vertical. Normally I just measure the old chain against the new, but as I am not replacing like for like that wont work, so what is the best way to get the right chain length. Advice gratefully received.

 

[HLaB]

I don't how gospel this is so check, but I believe most tripples have a long cage; hence if its a tripple worry no further. Doubles on the other hand are short cages and I think the accommodate up to 27t so it could be a problem.

The last time I changed the size of my set up I adjusted the length of the chain using the guide on bike tutor. IIRC you wrap the chain around both the large front chain ring and large cassette (free of al dérailleurs) and when the chain overlaps by a link, thats the length you need. Anyway check out his video :-)
PS It done the trick on my bike :-)

 

[youngoldbloke]

I have used this chain length and found it very accurate.

 

[chillyuk]

The freewheel arrived today. I have just fitted it and it all works fine even with the extra teeth on bottom gear. Chain can wait until tomorrow, I am knackered after trawling round Tesco with my wife!