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    • CommentAuthorShady John
    • CommentTimeOct 21st 2018
     
    gottobike:Question for all you bicycle frame design experts and industry pros:
    If the steep seat tubes (74 degrees or more) and slack head tubes (71 degrees or less) we see on the smaller frame road bikes are so great, why not just continue that geometry into the larger sizes?

    The road frames that handle well and I am able to get comfortable on have 73/72 degree tubes and bb drop ~72mm. For 700c designed bikes, this geometry is only available in larger sizes. Seems it would be cheaper to maintain this fantastic 74/71 geometry promoted by the bicycle industry across all frame sizes instead of having to refixture for the smaller sizes.

    Example:
    Trek has a great new Checkpoint with ~73/72 degree geometry in 56cm and above:
    https://www.trekbikes.com/us/en_US/bikes/road-bikes/checkpoint/checkpoint-alr-4/p/22628/

    However, this quickly erodes to an unrideable ~74/71 geometry in smaller sizes.


    The smaller size frames should have more slack head angles to avoid toe overlap, and also have more trail in the fork to compensate (and increase front-center to additionally help with toe overlap). This is a design compromise dictated by keeping the wheel size constant (700c) as you decrease the frame size. The proper design change for smaller road frame sizes (e.g. 43 cm c-t) is to use 26" or 650c wheels and use "normal" frame geometry. There were many such bikes available in the early 2000's, but these had all but disappeared by 2013. Cost saving measure as far as I can tell.

    I had a whole set of links for the question of 650c vs 700c for small road bikes--I can dig these up if interested.
    • CommentAuthorgottobike
    • CommentTimeNov 6th 2018
     
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