Chain wrap, total capacity and cassette replacement

[rockyraccoon]

I've checked several websites and I thought I'd post here to double check with you guys.

My idea is to replace my 8 speed cassette (13-26) for an 11-28 cassette. I'm wondering whether the RD would couple with the change. The reason why is because I have a compact now (50/34) and with an 13-26 cassette I don't have as much gear on top end as I used to with the double. I cannot exceed the 20 mph down hill by moving the pedals.

According to sheldon brown it is possible to exceed Shimano's recommendation by a few teeth, but not a lot.

Shimanos recommendation for my 8 speed Rear Derailleur 2300 is:

Total capacity: 35 teeth or less
Front chainwheel tooth difference: 22 T
Largest sprocket: 26 T
Smallest sprocket: 12 T

According to my calculations

(50+28) - (34+11) = 78 - 45 = 33

or another way of calculating it

(50-34) + (28-11) = 16 + 17 = 33 teeth of wrap capacity from the RD

The total capacity of the rear derailleur 2300 (according to shimano) is 35 teeth or less, therefore could I say that it should be ok to replace my cassette and keep my RD!?

 

[Herzog]

The total capacity of the rear derailleur 2300 (according to shimano) is 35 teeth or less, therefore could I say that it should be ok to replace my cassette and keep my RD!?

Yep, it'll be fine

 

[bobones]

I have a bike with an 8 speed 11-28 cassette and 2300 RD with 50-34 compact up front and it works just fine. I'd recommend a SRAM PG-830 cassette which you can pick up on the net for a decent price. It might be an idea to replace your chain if you've had a fair bit of use of your old one although if you haven't used it much then your current chain should be the correct length anyway.