Top Tube – Longer or Shorter?

[friedmikey]

When choosing a frame, is it better to err on the short side or long side when it comes to top tube length?

I’m shopping for a new frame. My top choice is the Look 555. However, I can’t decide if I’d be better off with the 59 or the 61. The biggest deciding factor between these two for me is the top tube length and to a lesser extent, the head tube length.

My current setup: 58.5 cm top tube, 20.95 cm head tube
Look 555 59: 58 cm top tube, 19.3 cm head tube
Look 555 61: 59 cm top tube, 21.0 cm head tube

Depending on who measured me, I’ve been told I need an overall reach of 69.25 – 70.5 cm. I had been planning to drop my bars a tiny bit, so I can deal with a slightly shorter head tube, though I'd still like to keep it comfortable. Also – this is going to sound a bit silly – I would like to reuse my current 120mm stem, if at all possible.

FYI, I'm a recreational cyclist, doing 25-100 mile rides four to five days per week.

 

[artmichalek]

69.25? Anyone who tries to give you bike dimensions down to the half mm probably doesn't know what they're talking about. Reach is best determined by feel rather than measurement anyway. Since you're looking at two different sizes of the same bike, it's best not to worry about the top tube lenght at all. It's only +/- 5mm, and other factors such as the seat tube lenght and saddle to bar drop are going to have a much bigger effect on how the bike fits.

 

[boudreaux]

When choosing a frame, is it better to err on the short side or long side when it comes to top tube length?

I’m shopping for a new frame. My top choice is the Look 555. However, I can’t decide if I’d be better off with the 59 or the 61. The biggest deciding factor between these two for me is the top tube length and to a lesser extent, the head tube length.

My current setup: 58.5 cm top tube, 20.95 cm head tube
Look 555 59: 58 cm top tube, 19.3 cm head tube
Look 555 61: 59 cm top tube, 21.0 cm head tube

Depending on who measured me, I’ve been told I need an overall reach of 69.25 – 70.5 cm. I had been planning to drop my bars a tiny bit, so I can deal with a slightly shorter head tube, though I'd still like to keep it comfortable. Also – this is going to sound a bit silly – I would like to reuse my current 120mm stem, if at all possible.

FYI, I'm a recreational cyclist, doing 25-100 mile rides four to five days per week.

Even bar affects the overall reach. If you want to use your 120 stem then you have to consider you old seattube angle and TT length relative to the specs o the look and consider how much difference you are really dealing with between the 3...If you are on either end ot the 58/59 range as to preference,then the other may not work. Some worry about TT length to .4 significant figures,and others can deal with about a 1cm difference.

 

[friedmikey]

My Marin is 73/73. The Look is 72.5/72 (SA/HA) in both sizes. Given that the seat angle is steeper than the head angle, does that, in effect, shorten the reach? I would think that the slight difference in SA would be mostly irrelevant, given fore-aft adjustment of the seat (not to mention a setback post) necessary to line things up for my legs. As far as bars go, I’ll be using the same bars that are on my Marin (Easton EC90 Equipe).

I know that getting on the bikes and going by feel is the best measure. I’ve tried the 59. I haven’t found anyone with a 61 that is built. The 59 felt good, but this was only on a 15 minute test ride. How that compares to a 100 mile ride is hard to say. Obviously the bars were lower than what I’m used to now, but I also know that my fitness level and comfort in a road bike position have made huge improvements since I stepped up my training in February, which is why I was planning on lowering the bars a bit. I did love the general “road feel” of the 555, which is why I’m so interested in the frame. I think it’s becoming apparent (at least to me!) that my real concern is saddle to handlebar drop.


The 69.25cm measurement is the number that somebody at Wrench Science generated from their program after measuring me. The 70.5 is what Competitive Cyclist’s online fit calculator generated from the measurements I took with the help of a friend. Ignoring these calculated numbers for a moment, would a useful approach be to measure the reach from the tip of my saddle to the inside of my bars on the Marin, then see where that would put the saddle on the 59 cm Look?

Thanks for the comments so far.

 

[artmichalek]

Ignoring these calculated numbers for a moment, would a useful approach be to measure the reach from the tip of my saddle to the inside of my bars on the Marin, then see where that would put the saddle on the 59 cm Look?

You want to measure from the seat tip straight ahead to the point in space over the center of the bars.

 

[litespeedguy]

In my opinion you start with correct frame size ( I used Huggi's formula of .65 of inseam length which I found in LeMond's book) and maybe seat tube angle (72-73 degrees) and then solve the reach by adjusting seat and/or stem.

I also used Guimand's formula for BB to seat top distance of .883 of inseam.

I originally had a 100mm stem and replaced it with 110mm as a final tweaking.

I'm also recreational and just did a little research before buying what may be my last bike - a Litespeed Ti roady.

Good Luck .

 

[litespeedguy]

Essentially what I'm saying is get the frame size and seat tube angle right and let top tube length be whatever it is.

 

[53-11]

Top tube length is inflenced by the seat tube angle also . For example in my case switching from a 72.5 seat tube angle to a frame with a 73.5 seat tube angle effectively adds 1.5 cm to my top tube because I have to use 1.5cm more setback on my seat position.

 

[boudreaux]

You want to measure from the seat tip straight ahead to the point in space over the center of the bars.

That is nonsense and BS.

 

[boudreaux]

Essentially what I'm saying is get the frame size and seat tube angle right and let top tube length be whatever it is.

That's BS too.

 

[boudreaux]

When choosing a frame, is it better to err on the short side or long side when it comes to top tube length?

Well, if you are dropping that kind of money, I suggest that if you can 't figure out what you need, you may as well just flip a coin as to rely on the internet 'expert fitters and BS'ers'. Quicker and easier and alot less pucky to wade thru.

 

[litespeedguy]

53-11 has a good point !!!!!!

 

[andrello]

Well, if you are dropping that kind of money, I suggest that if you can 't figure out what you need, you may as well just flip a coin as to rely on the internet 'expert fitters and BS'ers'. Quicker and easier and alot less pucky to wade thru.

I think that if he cannot tell the difference it would be better to go shorter than flip a coin because the shorter tube will flex less and weigh less (although almost negligibly so).

 

[supergrill]

Essentially what I'm saying is get the frame size and seat tube angle right and let top tube length be whatever it is.

That's ridiculous; just about exactly backassward!

 

[boudreaux]

That's ridiculous; just about exactly backassward!

That's the same as BS and nonsense...right?

 

[litespeedguy]

I still contend ,that unless your knuckles drag ,if you measured the reach on a custom frame you would be within millimeters of the reach achieved with a correctly puchased stock frame that has been "customized" by adjusting the seat fore-aft and by selecting the right stem.