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Road bike sizing


RossW
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Hey everyone,

 

 

 

With winter up and coming I am looking at getting a road bike - my first! Having the road bike means more training to me with help of street lights etc ... But this is not why I am here.

 

 

 

My question is on how to decide what size bike I need. I have heard that one should measure your inseam and multiply by a fraction.

 

 

 

Inseam : 74cm

 

 

 

Now what size bike should I be looking at? Seen a good couple here recently for really good prices so would like to strike while the iron is hot.

 

 

 

Thanks everyone :)

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Guest Boytjie

(1) Road and Track Bike = Inseam (cm) x 0.65  (2) MTB = Inseam (cm) x 0.56

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Forget about inseem measurement. Look at top tube or virtual top tube lengths. You road bike will be about 20-30mm shorter then you MTB.

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@Mampara: My Santa Cruz has a 58cm top tube so I need to ask people for a 55cm top tube on road bikes? Would this not correspond to a XXcm seat tube which people may be more used to?

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It sounds like your SC is a M. Mine was L had a top tube of 595mm. I had a bike with a tt of 56 (100mm stem) and now 57 (90mm stem). A 55cm top tube will be M in Giant sizing and S in Raleigh. Remember, the inseem measurements were used on traditional straight top frames and now converted to compact frames.

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You are spot on, it is a M :) What is a compact frame? Do you therefore get two or more types of road frames? As you can see, I'm pretty new to this road thing.

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A compact frame is the new kind of frames like MTB frames where the top tubes slopes and is normally sized in S,M,L etc. The old school sizing has horizontal top tubes and are much easier to get fitted as there is basically a size every 2cm and in some cases even every 1cm.

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@Tankman - Thanks for the link. Shows I need a C-C of 54cm and top tube of 52cm for an Eddy fit. Will start using the TT as reference for fit because of the compact frames potentially confusing me.

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You will never find a bike with 54 seat tube and 52 top tube. And a 52 top tube is like a XS in compact sizes.

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That's not good news! I guess I'm looking for a 54 C-C then rather than a 52 top tube. I'll have to see what pops here and also go try sizes at LBS ...

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That's not good news! I guess I'm looking for a 54 C-C then rather than a 52 top tube. I'll have to see what pops here and also go try sizes at LBS ...

 

 

 

Okay, now you have to decide is that 54 seat tube traditional or compact size. It sounds good for traditional which will give you about a 54.5-55cm top tube. If you get a 54 compact it will be about a 60cm top tube.

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Ha ha ha, this is getting more and more complicated by the minute!

 

 

 

I see Trek offers a 53.5cm seat tube and it has a 55.7cm effective top tube. Seems this is traditional sizing rather than compact? Madone range... Which is labeled as a 56cm (S)

 

 

 

The Eddy Fit (cm)

 

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Seat tube range c-c:   54.3 - 54.8

 

Seat tube range c-t:   55.9 - 56.4

 

Top tube length:       52.0 - 52.4

 

Stem Length:           9.5 - 10.1

 

BB-Saddle Position:    69.4 - 71.4

 

Saddle-Handlebar:      51.0 - 51.6

 

Saddle Setback:        6.1 - 6.5

 

 

 

 

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Top tube length is much more important should be your deciding factor.

There is nothing more you can do if you top tube is to long or to short than a 2-3cm adjustment with a stem.

 

You can however increase or decrease you seat tube quite drastically, so forget all else and focus on the top tube, even with a compact frame - just draw an imaginary straight line from top tube to seat post.

 

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