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Trek sizing question(5 posts)

Trek sizing questionoddi
Sep 25, 2002 4:17 PM
I posted a few days ago w/ my measurements. At the time I thought I was 5'10" w/ a 31" inseam, which others told me was short for my height. Well it turns out I took the measurement incorrectly, not pressing hard enough into my groin. So my inseam is actually 32.75", which I hope seems more normal. Based on this I think my correct frame size would be 56 C-TT or 54 C-C. I'm looking at Trek bikes but have been told their measurements are C to the top of the seat tube. So a 56 from them may actually be only a 54 measured C-TT. I'm wondering if I'm supposed to take that into account, or does Trek really want someone who rides a 56 C-TT to ride one of their 56, which would be a smaller frame. I guess the issue at hand is top tube length. So, given a 56cm frame in Trek's sizing, would they size their top tube length like a 56 cm from another manufacturer using the C-TT system, or more like a 54 cm using the C-TT. Sorry if this question sounds confusing, or if the answer is obvious. Thanks for your help.
re: Trek sizing questionbriko51
Sep 25, 2002 4:33 PM
pretty sure trek (and most frame builders) measure top tube length from center of seat tube to center of the head tube. that princible basically holds true for all standard geometry frames. compacts usually have a "virtual" top tube length which is a horizontal measurement from center of seat tube to center of head tube (since they are sloping top tubes) trek also has a "virtual" length listed, but i think this is just because the carbon frames have a lot of sloping angles and such between joints of seat tube/top tube/etc.

honestly i would just measure the bike by the TT length. you can always adjust the height of the seat post to compensate some small errors of calculation relating to the seat tube length.

best way to see is to test one out at a LBS...maybe not even ride it but maybe a local shop as a few size for you to sit on to get a feel for the size you need...

good luck!
re: Trek sizing questiontrout_bum
Sep 25, 2002 7:09 PM
Just went through the sizing thing myself recently - not on a trek though. Here's some things to keep in mind, not discounting the possibility of researching LBSs and finding one with a great reputation with sizing expertise-(this can be more difficult than you think! Ask around.)

For size/Seat Tube length you want to make sure the drop from the top of saddle to the top of the handlebars when you set your saddle height is not too great or small for your riding style(multiply your cycling inseam by .883 to get saddle ht. for starters). There are many different opinions on this but a "normal" range seems to be from 1-3in. Also allowing for appropriate standover clearance. I think Treks have a seat tube which extend 1-2cm above top tube so I think this is what people are referring to when they say "Treks run small" in that a 56cm Trek will actually fit more like a 54cm with regards to saddle to bar drop.

However, keep in mind your top length. Here's where an expert sizing will be most useful. Keep in mind that you want to pick a frame with a top tube length that lets you run a stem length that's within an acceptible range for a given frame size for best handling (usually 90-120mm). This may mean sometimes that you may want to look into other manufacturers geometries to get an ideal fit even though you had your heart set on another bike.

It wouldn't hurt to run through the fit forms on www.wrenchscience.com, www.coloradocyclist.com before visiting the bike shop for a fitting. These will give you a BALLPARK idea of what size you should be riding if you follow the measuring instructions to the letter. This way you will be more informed before heading off to the shop.

Good Luck
re: Trek sizing questioncastrello
Sep 28, 2002 12:24 AM
Interesting.

As you may have read Im going trough the same thing, choosing between a 58 or 60 cm CAAD 5. I know that I´m now in the ballpark (using the sources you mention). However, both of these sources recommend a size 60, and it has a 2 cm longer top tube than my old bike. I know Ill have to test ride, but apart from that what can I do? My heart tells me size 58 (I´d rather have a bike that´s 1 cm too short, than too long) but my mind tells me size 60 (I could cope with the shorter top tube by changing the stem or whatever, but if the drop to the bars is too steep I would suffer for real).
Test Ride Different Sizesms
Sep 26, 2002 5:39 AM
There have been a number of posts about Trek sizing differing from other manufacturers. I'm just under 6'0" (5'11 3/4" to be exact), with a 32" inseam. I ride a 58cm Trek. Before I settled on the 58cm, I test rode both a 56cm and 60cm. Notwithstanding all kinds of measuring devices and formulas, I still think that the best way to make sure that you have the best size is to do a test ride.