Hi,

Just completed my first Duathlon of the year and came across an interesting issue. The course I had to ride was completely flat and I found myself totally under geared as I have my bike setup with a Shimano 7950 compact 50/34 chainset (use it as it's very hilly where I live and train).

So the big question is, what are my options as it looks like I can't easily change the 50/34 ratio to something bigger without the chainset looking odd. Should I just buy a non compact Shimano 7900 chainset or are there better/lighter options I could consider as I don't mind changing the pressfit bottom bracket at the same time? Guessing the bottom bracket will have to be a Shimano pressfit as I've tried looking around and ended up totally confused within 5 secs.

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Regards

Portia Baines

What cassette were you using? 50-11 is slightly taller gear than 53-12, so that should give you all the top end you need... For really flat terrain, 11-21 would be ideal (straight block cassette, allowing equal spacing between gears), or 11-23 is a good option. Personally, I'm not a big fan of the 34, swap that for a 36 and you still have a useful compact, but much better shifting.

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"Suddenly the thought struck me; my floor is someone elses ceiling" - Nils Ferlin

While I'd be a little surprised that a 50 was holding you back, as a 50/12 at 90rmp is 30mph, maybe just pick up some Praxis 7950 52/36 rings and get a 11 tooth cassette:
http://shop.praxis-works.com/Compact-DA ... oductId=32

Sound advise, but if you're keeping 30MPH, then call Praxis as I'm certain they will sponsor you.

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"Suddenly the thought struck me; my floor is someone elses ceiling" - Nils Ferlin

Hi and thanks for the replies.

The cassette is currently a 11-28 so I'm guessing that could be changed also.

If I was to change the whole chainset what would be some good non-compact alternatives? What gear ratios are more normal for time trial bikes? Is there anything lighter than the 7950 which will easily fit?

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Regards

Portia Baines

BB86 is probably the most "limiting" standard as you have to run a ~86mm length spindle and ideally a 24mm diameter spindle. There are some "hacks" to allow the use of 30mm spindles, but you'll use a smaller bearing with potentially shorter life span.

Dura Ace 7900 in a standard is a good bet, all things considered. Its on sale lots of places, good shifting, stiffness and decent weight.

Fairwheel bikes carries all usual more "exotic" options like Lightning, Clavicula...

I'd be interested to see some of the maths involved here. You say 50-34 with 11-28 is too low for you, but as noted 50/11 is 32mph at 90rpm. When you feel that the current chainset is under-geared, are you at the top gearing? What's your target cadence? What's a regular cruising speed for you?

I run 54/42 and 11-25 cassette and it works well. On a drag-strip course with a tail wind/slight downhill then 50*11 is not enough.

Having said that the last TT I did I was passed by Alex Dowsett like I was standing still...

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