Sizing Surly Trucker vs Trek 520

[Doug.ftc]

We're looking for experience with sizing on Surly Trucker vs Trek 520. We're looking for a bike for my wife for a fully loaded tour we're planning later this year, hoping to buy used to stay within our budget. Yesterday she rode the Trek 520 in both 51 and 54cm sizes. The 54 was a really good fit while the 51 was clearly too small. However we've been unable to find any Truckers in our area that she can test ride. So wondering if you know how that Trek size might cross over into the Surly geometry?

Other clues:
* She's about 5'8"
* Pubic bone height / "true inseam" = 81 cm
* Effective top tube length for her road bike which is a great fit = 53.5 cm (measured per Surly diagram)

Looking at the Surly geometry charts, she should be in the 50/52/54 range but hard to be confident without getting on the bike.

Thanks in advance for any info you can provide!
Doug

[RussSeaton]

Not really sure what your problem here is.  Your wife rides a road bike that fits perfectly now.  It has a top tube of 53.5cm.  Guessing the Trek she rode had a top tube of about the exact same length.  Give or take a half centimeter.  Find a Surly with the exact same top tube as your wife's current 53.5cm and/or the same as the Trek.  Trek and Surly have about the same frame.  Same seat and head angles.  Same everything more or less.  Just different paint.  So if one fits, the other will fit too.  And your wife's current road bike has 53.5cm top tube.  So you know any bike you buy should be very, very close to that.  53 to maybe 54cm.  Pretty sure Trek and Surly publish frame dimensions for all their bikes.  And your wife's current bike has the frame dimensions online somewhere.  Find a size that matches.  I am assuming all the bike makers use decent tape measures to measure their bikes.  Tape measures are not off by 5cm.  And the bike makers have robots and jigs to make their bikes to the same size every time.  No random size frames made.  All 54cm frames are made the same size and all are measured correctly.  Maybe an assumption.

[DaveB]

Yesterday she rode the Trek 520 in both 51 and 54cm sizes. The 54 was a really good fit while the 51 was clearly too small.

If she rode the Trek and it fit well, why not just buy it? 

[Doug.ftc]

Update that might help someone else . . .
We found a 52cm LHT she could test ride today, which also fit very well. So two good candidates as we continue our search for a used bike that fits our budget.
Doug

[walks.in2.trees]

Update that might help someone else . . .
We found a 52cm LHT she could test ride today, which also fit very well. So two good candidates as we continue our search for a used bike that fits our budget.
Doug

I used the bike fit calculator ... But I used the results as a general idea for the fixed lengths, keeping in mind the idea that I could adjust the other dimensions (seat position and height) to a limited extent to find an exact fit.

54" was actually where I landed too, myself being 5'-7" and after a few months that's still comfortable for me though I haven't been on any rides longer than an hour so far.
so I'd say, you're in the ballpark.

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[walks.in2.trees]

Update that might help someone else . . .
We found a 52cm LHT she could test ride today, which also fit very well. So two good candidates as we continue our search for a used bike that fits our budget.
Doug

I used the bike fit calculator ... But I used the results as a general idea for the fixed lengths, keeping in mind the idea that I could adjust the other dimensions (seat position and height) to a limited extent to find an exact fit.

54" was actually where I landed too, myself being 5'-7" and after a few months that's still comfortable for me though I haven't been on any rides longer than an hour so far.
so I'd say, you're in the ballpark.

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Oh... And I did notice there can be some significant dimension swings in the frame geometry between different frames, so I wanted you to know that asking about it wasn't a waste of time... It seemed like some folks were aluding that it was.... The top tube is NOT the only fixed dimension on a bike frame.. The entire shape of the triangle controls how far you are from the pedals and how far you'll need to reach, how far you'll need to bend, how much weight is supported by your arms and back... And the top tube length alone doesn't tell that whole story.

I found too, that with a little research I could find the dimensions of the frames that I was considering... Sometimes it meant going to the manufacturers website... So you probably can as well

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