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Frame Sizing

redstuartredstuart Posts: 12
edited October 2010 in Road beginners
Hi,
I'm new here and this is my first post. I've been commuting to work on a 15 year old MTB for the past year and have finally decided to upgrade to a proper road bike.

Having spent a good long while researching, I bobbed down to my local LBS where I did a few test rides.

My decision basically came down to a choice between the Giant Defy 2 (2010) and the Specialized Allez Elite (2010). Both come with Tiagra groupsets and pretty much comparable frames etc (there's lots on here about both bikes).

I've decided I prefer the Giant Defy 2, but having read up on frame size am a little concerned I may have done this because the one I tested had a smaller frame.

My MTB only has an 18" (45cm) frame for throwing around trails and the like. I tested the size M Giant which has a 50cm frame which felt great. I'm concerned as the general guidelines seem to suggest someone of my height (5'10" - 31" inside leg) should be going for a 54-56cm frame? I don't want to go for a small frame because it feels good in the short term if it's not what I should riding in the long term. The M/L Giant Defy is 53.5cm so is more in my suggested size range.

Any help would be much appreciated.

Posts

  • John.TJohn.T Posts: 3,698
    Manufacturers all seem to measure their frames differently. I am 5'11" with about a 32" inside leg. I ride a 56cm Trek 5.2 Madone. In the most important measurements (especially on a sloping TT frame), the TT and head tube length, this falls between the M and the M/L Defy. Saddle height is not a problem as you can get long seat posts if needed. Saddle position is set by how far behind the BB you need it and would be the same on either size. The factors you need to look at are reach (which can only be adjusted by stem length which on a road bike should be between 100mm and 130mm. More or less will affect the bikes steering response.) and bar height. Bar height can be adjusted by spacers under the stem but it is not normally recomended to exceed 50mm of these. You can also 'flip' the stem over to raise the bars but this does not look so good. Providing you can get comfortable on the smaller frame within these limits I would go for that. It is easier to make a small framed bike bigger than vice-versa.
  • John,

    Thanks for your advice. I'm heading back down to the shop tonight to have another look but I have cleared up in the meantime the discrepancy on frame size with the Giant, in that the Defy has a Compact frame with a sloping top tube, making the measured size smaller than the effective size, which is more like the 54cm or so that I thought I needed.

    I'm going to get the guys at the shop to play around with the stem and handlebar setup for me to make sure it's exactly to my spec before I ride off.

    Thanks again - I hadn't considered there was so much that could be adapted / specified.
  • ride_wheneverride_whenever Posts: 13,279
    Generally you size up when going from mtb to road bikes as you don't need to be able to ride the bike, only sit on it and pedal. There are no worries about being able to move around the bike to negotiate obstacles and you never hang off the back for stupid descents!
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