Bike Size (frame size or top tube?)

TheTubes

I'm looking to buy my first road bike.
From all the reading I've done I think im looking for a bike that is 54/55cm (I'm 5'9").
I'm looking at a GT GTR Series Four on CRC.

The bike is available in 50/54CM (M/L).
I assumed the 54Cm would be the one I'm looking for but then I looked at the sizing chart.
The frame size is 54 (L) but the top tube is 57.6cm, the top tube on the 50CM (M) is 55.5cm.

I'm just wondering if its the frame size or top tube I should be looking at given that its the top of the inside leg that I was told to use to work out the bike size?

Also, is that bike ok? I read here that Shimano Tiagra drivetrain is the minimum to go for so I'm guessing that the rest of the spec should be of the same level...

Lumen

In principle, frame size is based on seat tube length, although it's more complicated than that depending on geometry.

So 54cm frame = 540mm seat tube (see the table on the link you posted).

TheTubes

so its the frame size i should be looking at and not worry about the top tube measurement?

Ok, 54cm should be ok so?

scottreynolds

Lumen wrote: »

In principle, frame size is based on seat tube length, although it's more complicated than that depending on geometry.

So 54cm frame = 540mm seat tube (see the table on the link you posted).

Oh yes -- its a sloping frame as well so the sizing is different. I'd say M is the correct size.

TheTubes

scottreynolds wrote: »

I'd say M is the correct size.

I just noticed a typo in my original post, I said the 54cm was M, its L. THe 50cm is M.
Fixed. oopsie

blorg

TheTubes wrote: »

so its the frame size i should be looking at and not worry about the top tube measurement?

Ok, 54cm should be ok so?

It's a bit more complicated, bikes are measured on the seat tube measurement (or often effective seat tube on compact frames.) However top tube is arguably more important as it largely dictates how stretched out you will be on the bike. But the two are generally proportionate, e.g. bikes in a given size tend to have similar effective top tube lengths.

Note also that top tube is almost always measured as "effective" top tube, e.g. the length the top tube would be if it was horizontal rather than sloping.

Lumen

Geometry chart:

scottreynolds

TheTubes wrote: »

I just noticed a typo in my original post, I said the 54cm was M, its L. THe 50cm is M.
Fixed. oopsie

I think I still vote M. Perhaps call them up and see what they say. I'm 5'10 and I think I would fit it -- althouh as I am not buying it I can't really help. In fact ring GT in the US they are more likely to answer the phone than CRC.

TheTubes

emailed both, CRC replied

A 50cm bike would be suitable for a range of 28 to 32inches.
A 54cm bike would be suitable for a range of 30 to 34 inches.

Will measure again when I get home just to be sure.
Will prob order on monday, looking forward to it

No1 said the bike was rubbish or a rip off so I'll take it that its an ok spec/value (for a beginner) ? :pac:

Thanks for all replies.

short circuit

You might want to rethink the bike .... the chainrings are oddly sized ... neither double .. nor compact ... seems to be designed for someone who always cycles on inclines between -3% and +3% ...

scottreynolds

short circuit wrote: »

You might want to rethink the bike .... the chainrings are oddly sized ... neither double .. nor compact ... seems to be designed for someone who always cycles on inclines between -3% and +3% ...

Freewheel - Shimano HG-50 8 spd 12-25
Crankset - FSA Varo Compact crankset, 50/39

short circuit

scottreynolds wrote: »

Freewheel - Shimano HG-50 8 spd 12-25
Crankset - FSA Varo Compact crankset, 50/39

Exactly ... I would have expected a 53 or 52 with a 39 ... or a 34/36 with a 50. Its neither here nor there ... doesn't go high enough ... or low enough.

blorg

short circuit wrote: »

Exactly ... I would have expected a 53 or 52 with a 39 ... or a 34/36 with a 50. Its neither here nor there ... doesn't go high enough ... or low enough.

It's almost certainly a typo, the picture clearly shows a 34 inner ring (you could clarify to be sure) and it is FSA Vero while they have Varo. CRC has a few typos like that about their site.

Lumen

I have the brochure in front of me. For the "GTR Series 4" it says "FSA Vero Compact 50/39".

blorg

It's a typo CRC just copied then I reckon. I do not believe that a 50/39 "compact" exists and the picture clearly shows a greater difference in the front chainrings (Hell, with 53/39 the rings look closer together than in that pic.)

jdt101

Check out this link regarding correct size: http://www.cervelo.com/content.aspx?t=Company&i=WhitePapers#1

Cervelo only do 6 sizes, last year CSC used only 4 sizes to cover all their team (exclude 48 & 61). All bikes should be sized this way, reach is the most important measurment. My pennys worth.

TheTubes

I'm not too sure what the deal with the size stuff going on here is but the gt site says its 50/39 aswell (which i take it would be a problem?)
It was suggested I ring GT about the size, I emailed them and got a reply already :eek: the guy suggested that the M would be ok.
Should I reply and ask about the issue with the crankset size? i'd prob link to here instead of trying to explain

psycholist

TheTubes wrote: »

I'm looking to buy my first road bike.
From all the reading I've done I think im looking for a bike that is 54/55cm (I'm 5'9").
I'm looking at a GT GTR Series Four on CRC.

The bike is available in 50/54CM (M/L).
I assumed the 54Cm would be the one I'm looking for but then I looked at the sizing chart.
The frame size is 54 (L) but the top tube is 57.6cm, the top tube on the 50CM (M) is 55.5cm.

I'm just wondering if its the frame size or top tube I should be looking at given that its the top of the inside leg that I was told to use to work out the bike size?


Also, is that bike ok? I read here that Shimano Tiagra drivetrain is the minimum to go for so I'm guessing that the rest of the spec should be of the same level...

it all depends ,

a good bike shop's the best way to go to get it sorted theyll be able to tell you what quality of parts & sizes you need.
tiagra's grand btw

Lumen

blorg wrote: »

It's a typo CRC just copied then I reckon. I do not believe that a 50/39 "compact" exists and the picture clearly shows a greater difference in the front chainrings (Hell, with 53/39 the rings look closer together than in that pic.)

50/39 is two-thirds of an FSA Vero 50/39/30 (Triple).

Surely they haven't just dropped the granny cog?

TheTubes

so, what do ye think? any consensus?
I was going to order it in the morning if I got the go ahead from you guys.
Should I just let it or should I email crc/gt to ask about the stuff ye noticed?

Thanks for the help.

TheTubes

Just an update on this,
I emailed GT about the size of the chainset, I got a reply in under 2 minutes
Very impressed with the customer service.

He didn't have a bike in front of him but he is pretty sure its 34/50.

I'll be ordering tomorrow

Last question, will these 35mm mudguards fit the bike? I saw them recommended in another thread.

Lumen

TheTubes wrote: »

Last question, will these 35mm mudguards fit the bike? I saw them recommended in another thread.

Don't think so. Look at the gap (or lack of) between the seat tube and rear wheel - you won't fit normal mudguards in there, even if you have eyelets for them (which I can't see either).

Maybe clip-on mudguards like SKS Race Blades.