Bigger gears for TT's than road racing?

flyingelephant
flyingelephant Posts: 121
edited July 2009 in Road buying advice
I do road racing on a 50/36 front and 11/23 rear cassette. Having recently changed groupsets from 53/39 front and 12/25 cassette. I used this for TT's road racing and tri's on a road bike. I'm happy with both these setups.
BUT, I now have a tri/TT specific frame. Should I use the same gear ratio, or something bigger like 52/39 front and 11/23 cassette.
I'm not changing out the cassette. Just the chainset. So the choices are with a 11-23 cassette:
Chainset
53/39
52/39
50/34

I guess I could change the 34 inner to a 36.

HELP!
A Devonian in Norway

Comments

  • redddraggon
    redddraggon Posts: 10,862
    Depends on your strength, the courses, the cadence you like, etc etc with respect to keeping the straightest chainline for the longest amount of time.

    So you're in the best position to answer your own question to be honest.
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  • Pokerface
    Pokerface Posts: 7,960
    You can even change out the inner chainring to a more TT-specific gearing of 42.

    I took an old compact crankset I had, and am now running a 52-42 for TT's on it.

    Experimentation may be the key. And as RD says - depends on the type of courses you use.
  • huuregeil
    huuregeil Posts: 780
    When you ride a TT:

    Is 50-11 too small?
    Is 36-23 too big?

    Decision made - it's not rocket science!
  • chriskempton
    chriskempton Posts: 1,245
    Have you still got the 53-39? If you do, bung that on your TT bike and leave your road bike as is.

    A compact on a TT bike gives too big a jump on all but the hilliest courses. If you're only riding fairly flat courses you'll probably never use the inner ring anyway.
  • redddraggon
    redddraggon Posts: 10,862
    huuregeil wrote:
    When you ride a TT:

    Is 50-11 too small?
    Is 36-23 too big?

    Decision made - it's not rocket science!

    You shouldn't concentrate on the gearing extremes. It's all about mechanical efficiencies. If you are ending up 50-11 on a flattish course your gearing is all wrong IMO.

    You've not got a very straight chainline and smaller sprockets take fractionally more power for the chain to get wrapped about.

    OK, the difference is negligible but if the OP is deciding on chainrings for the TT bike, why go for something less than perfect?
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  • huuregeil
    huuregeil Posts: 780
    redddraggon wrote:
    huuregeil wrote:
    When you ride a TT:

    Is 50-11 too small?
    Is 36-23 too big?

    Decision made - it's not rocket science!

    You shouldn't concentrate on the gearing extremes. It's all about mechanical efficiencies. If you are ending up 50-11 on a flattish course your gearing is all wrong IMO.

    You've not got a very straight chainline and smaller sprockets take fractionally more power for the chain to get wrapped about.

    OK, the difference is negligible but if the OP is deciding on chainrings for the TT bike, why go for something less than perfect?

    Sure, I'm well aware of that. But given the OP's initial question, it seems that's a step too far for him/her now - e.g. if a TT gearing question is framed simply in terms of chainring sizes as the only variable, then the best thing is probably to stick whatever on (subject to not running out of gears etc.), do lots of TTs, and then refine it from there. In that, at the end of the day, it's a personal thing (strength, cadence, course profile) and trial and error/experience is the only guide.
  • flyingelephant
    flyingelephant Posts: 121
    Yep, looked at Sheldon Brown for ratios. Most courses are rolling or hilly. RPM is about 75 to 95 on 175 cranks. I aim at mid/upper 80's to low 90's RPM.
    If I'm happy with a 50 and 11-23 in road racing and not spinning out, On a TT bike would it be better to go 52 with a 11-23. Never having ridden a TT bike I have no way of knowing if going bigger is better. But when using a road bike on TT's 50 and a 11-23 cassette is OK. On a TT bike I am wondering if a 52 front with a 11-23 would work better, never having tried a TT bike before, and not wanting to buy and try, buy and try again and agian waisting money on chainrings..Cheers
    A Devonian in Norway
  • SBezza
    SBezza Posts: 2,173
    My road bike is a compact, but my TT bike is a 53/39 and I have no issues with the difference, I just spin more on the road bike, then again as I don't race on it the gearing is more than adequate.

    I have an 11-23 cassette, and even with the 53 chainring, I am in the 11 some of the time, so will be getting a 54 chain ring to get the chain line better as mentioned above. I would suggest you will end up spinning quite a bit in a TT if you use a compact, so would suggest either of the 2 standard size chainrings.
  • aracer
    aracer Posts: 1,649
    I would suggest you will end up spinning quite a bit in a TT if you use a compact
    What, with a 50/11? :shock: Is your real name Alberto or Bradley?
  • SBezza
    SBezza Posts: 2,173
    aracer wrote:
    I would suggest you will end up spinning quite a bit in a TT if you use a compact
    What, with a 50/11? :shock: Is your real name Alberto or Bradley?

    I have had cadences of 110+ in 53/11 on a TT, they do go downhill as well ;), with a 50/11 I would either not go as fast, or have to spin even faster
  • chriskempton
    chriskempton Posts: 1,245
    +1

    50-11 @ 100rpm = 34mph. Lots of us everyday testers exceed that with a tailwind, let alone downhill. Like Bezza says, there's faster bits and slower bits in most 25mph average rides. No ones saying they're Bradley or Alberto.

    50 not big enough.
  • eh
    eh Posts: 4,854
    I'd go 53/42 if I had the option you don't need really low climbing gears on a TT frame.

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