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Thread: Road Frame Size

  1. #1
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    Road Frame Size

    I started cycling again 2 months ago after a 6 year hiatus. I put 2600 miles on my 58 cm road bike back then and never thought anything of the fit. When I started up again, I realized just how stretched out my upper body was, so I swapped my 110 mm stem for an 80 mm version. That has made a big difference, but I don't think I'm satisfied yet with the fit. I am 5'10". I'm thinking about swapping my traditional geometry road frame with a 54 cm semi-compact frame. My current TT length is 57.1 cm. The frame I'm looking at has identical head and seat tube angles with an effective TT length of 55 cm. The only other difference is the BB is 1.2 cm higher on the new frame than my current one.

    Do you think this is a worthwhile venture? I don't think I want to reduce the stem length any more. Would I notice the higher BB and corresponding higher center of gravity? Thanks!

    Alan

  2. #2
    Senior Member Road Fan's Avatar
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    Higher BB/higher CG is a bit of a religious issue. Personally I think I like the feel of a lower BB, 7.5 to 8 cm drop. But one of my best bikes ever, a 1980 Woodrup, had a 6.5 cm drop. It seemed a little toppley when I rode it, but it worked well on a long tour.

    A 3 cm reduction in reach is rather drastic. Are you sure you didn't back up too far? Considering this your idea to just buy an arbitrarily shorter frame is a shot in the dark. Is there any way you can try out a friend's bike first?

    Another consideration in shortening the TT is toe overlap. On your current bike, how far are you from toe overlapping the front wheel? It'll rarely happen at speed but it could happen at low speed when the bike is less stable. If you are not practiced in how to react, you may go down.

    Then again, some people are never bothered if the toe interferes with the front wheel.

    Ultimately, the requirement for frame sizing is that it must enable proper bicycle fitting - the actual placement of the contact points. It's preferred to have the correct fitting locations not at the extremes of the positions for bars and saddle that can be achieved with a given frame. I'd say that if you have confidence that these conditions are met with your new frame and cannot be met with your old frame, then go for the new one and see what happens.
    Last edited by Road Fan; 06-29-13 at 06:23 PM.

  3. #3
    coprolite fietsbob's Avatar
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    center of gravity can be improved with more setback.. distance rearward from plumb line thru the BB axis ..

    may be a seat post change, saddle adjustment on the seatpost or a frameset with a lower angle seat tube.

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    Thanks. The reason this came up was that I actually rode a smaller bike 56cm bike for a short while when I started back up. It was actually very comfortable for me so when I switched back to my normal bike it felt huge. I measured the reach between the two and it was different by about 2 inches! So my 30 cm change was actually less than I tried out between the two bikes.

    I'll have to pay attention to toe overlap and see how close I am to that being a problem.
    Alan

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    Quote Originally Posted by fietsbob View Post
    center of gravity can be improved with more setback.. distance rearward from plumb line thru the BB axis ..

    may be a seat post change, saddle adjustment on the seatpost or a frameset with a lower angle seat tube.
    My saddle has been pushed up as far as it will go. I never fitted the bike according to my knees and pedal spindles. I would assume my saddle ended up that far forward due to a reach problem.

  6. #6
    coprolite fietsbob's Avatar
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    Well a shorter than standard top tube length gets you out of the off the shelf bike frames .
    ready for a made to measure custom?

  7. #7
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    My opinion, based on what you've said, is that probably the 54cm frame will work well. Road Fan's points are right on, and given your seat is slammed all the way forward on the 58cm, and that the 80mm stem is still a bit off feeling, I think dropping down to a 550TT from a 571TT/80 stem combo will work better, my guess with a 110mm stem. The reason being that the shorter wheelbase will put you further back over the BB and make the bike feel more centered, which I think is what Fietsbob was getting at.

    i share Road Fan's uncertanty, but it does sound like most of your height is in your legs, so I say go for it! I'm of the opinion that's it's more difficult to fit and more unpleasant to ride a too big frame than a too little one. Also, the semi-compact frame should have a moderate height head tube, so that you'll be able to dial in the right amount of bar drop.
    Chaad--'95 DeKerf Team SL, '02 Lemond Buenos Aires, '05 Novara Buzz, '73 Schwinn Collegiate, '06 Mountain Cycle Rumble, '09 Dahon Mariner D7, '12 Mercier Nano, '12 Breezer Venturi

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