Gear Ratio Advice URGENT!
bmxboy10
Posts: 1,958
Just a quickie, what real difference is there likely to be between a 12-25 with 36/52 Chainset compared to a 11-28 with a 34/50 Chainset which is what I have now? I am also used to a compact with 12-25. I am concerned about hills not top speed!
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According to the ratio chart I feel I ought to stick with a compact which is a PITA as PBK have full Ultegra Groupsets for £417!0
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36/25 = 1.44
34/28 = 1.21 (what you have now)
34/25 = 1.36 (what you've also used)
That is, each revolution of the pedals will turn the back wheel either 1.44, 1.21 or 1.36 revolutions in the lowest gear of each setup. I would call 1.44 significantly different to 1.21. The main question is why are you considering the change if you're "concerned about hills not top speed"? The smaller chainring will obviously give you the lowest gears so if you're concerned about having low gears for getting up the hills that's the better choice. If you find you never need the smallest gear on your current setup then maybe the 52 & 36 chainrings would be fine. The only real compromise with the 34t chainring is a maximum big chainring size of 50 teeth. If you don't need more than 50 teeth then why consider changing?
Incidentally a 25t sprocket with the 36t chainring is equivalent to a 23.6t sprocket with the 34 chainring. (obviously you couldn't really have 0.6 of a tooth!) So see how many teeth are on your current 2nd and 3rd largest sprockets, pick the closest and go up your steepest hill to get an idea if you'll be okay with 36/25. Depending on how many sprockets are on your cassette your 2nd biggest is probably either 24t or 25t. A 24t with 34t front will be fraction easier to turn than a 25 with the 36t but it'll give you a good idea.0 -
solboy10 wrote:According to the ratio chart I feel I ought to stick with a compact which is a PITA as PBK have full Ultegra Groupsets for £417!
The chainrings are interchangeable (all 6800 chainsets are 110bcd). So you could just buy a standard and swap the rings.Red bikes are the fastest.0 -
Depending on how many sprockets are on your cassette your 2nd biggest is probably either 24t or 25t. A 24t with 34t front will be fraction easier to turn than a 25 with the 36t but it'll give you a good idea.0
