Top Tube Length

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lockersgm
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Top Tube Length

Postby lockersgm » Fri Oct 11, 2013 16:57 pm

Hi,
Could someone please settle an argument for me?
If a frame has a 56cm horizontal top tube,would a frame that had an effective top tube of 56.5cm be a fundamentally larger frame,assuming that head/seat tube angles and head tube lengths were the same on both frames?
Thanks.

Wirral_Paul
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Re: Top Tube Length

Postby Wirral_Paul » Fri Oct 11, 2013 17:21 pm

I'd say yes - as ETT and TT length is the same on a horizontal top tube frame. ETT is more important when comparing sloping top tubes - as it eliminates differences in angles.

neeb
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Re: Top Tube Length

Postby neeb » Fri Oct 11, 2013 18:46 pm

It'll be a frame with a longer reach, IF as you say, the angles, head tube length etc are exactly the same. But beware that small changes in things such as seat tube angle or head tube length can also affect reach given the same ETT length, e.g. if the frame with the 56.5cm top tube had a 73 degree seat tube angle instead of 73.5, that would more or less cancel out the difference in ETT length.

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mfin
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Re: Top Tube Length

Postby mfin » Fri Oct 11, 2013 18:59 pm

Imagine it in a different way, make the 56cm bike and all it's other measurements the base... then make another bike where the only increase is the ETT going from 56cm vs 62cm... it's easier to visualise I think, then the 62cm would suit a larger person, but, probably a larger person that it would only suit if they ride in a low position or like a big bunch of spacers, and the larger person would then be riding with loads more seatpost showing.
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thecycleclinic
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Re: Top Tube Length

Postby thecycleclinic » Fri Oct 11, 2013 19:52 pm

56cm is more medium sized. if you had a 52cm c-t frame with a 4cm slope then you have a 56cm c-t or thereabouts. the 58-60cm is in the large end of the spectrum while the 62 and above is for giants.
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t4tomo
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Re: Top Tube Length

Postby t4tomo » Fri Oct 11, 2013 19:59 pm

^^^^^^^?????????

I think what you are asking is 56.5cm ETT fundamentally bigger than 56cm ETT. The answer is no, 5mm is not a big difference
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diamonddog
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Re: Top Tube Length

Postby diamonddog » Fri Oct 11, 2013 20:00 pm

t4tomo wrote:^^^^^^^?????????

I think what you are asking is 56.5cm ETT fundamentally bigger than 56cm ETT. The answer is no, 5mm is not a big difference

^^This

neeb
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Re: Top Tube Length

Postby neeb » Fri Oct 11, 2013 21:23 pm

Well, it'll be 0.5 cm longer obviously, whether that's "fundamentally" longer (or bigger) is completely subjective.

It could make the difference between whether you fit a 100mm stem or a 110mm one.

Wirral_Paul
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Re: Top Tube Length

Postby Wirral_Paul » Fri Oct 11, 2013 22:27 pm

t4tomo wrote:^^^^^^^?????????

I think what you are asking is 56.5cm ETT fundamentally bigger than 56cm ETT. The answer is no, 5mm is not a big difference


Genius - he'd never have worked out how much bigger 5mm is on his own!! He only asked "is it bigger" - and the answer is obviously yes........ by 5mm

t4tomo
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Re: Top Tube Length

Postby t4tomo » Fri Oct 11, 2013 22:32 pm

Wirral_Paul wrote:
t4tomo wrote:^^^^^^^?????????

I think what you are asking is 56.5cm ETT fundamentally bigger than 56cm ETT. The answer is no, 5mm is not a big difference


Genius - he'd never have worked out how much bigger 5mm is on his own!! He only asked "is it bigger" - and the answer is obviously yes........ by 5mm

Actually he asked if it would be a fundamentally larger frame, which attracted a load of random posts that didn't answer the question.

Hey but don't let reading the thread get in they way of flaming someone :D
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Wirral_Paul
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Re: Top Tube Length

Postby Wirral_Paul » Fri Oct 11, 2013 22:39 pm

Clearly the question was answered with a "yes" in my first post!

You clearly think 5mm bigger isnt "fundamentally bigger" though!!! He didnt ask by how much - he asked to "settle an argument" - and 1mm bigger is "bigger" - unless you know better??

neeb
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Re: Top Tube Length

Postby neeb » Fri Oct 11, 2013 22:58 pm

I think the confusion here could be due to the two different meanings of "fundamentally". The word can mean either "in essesnce" or "in a major way". I, and the other initial resonnders, were clearly assuming the first meaning, while the later responders were assuming the second meaning.

lockersgm
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Re: Top Tube Length

Postby lockersgm » Sat Oct 12, 2013 13:58 pm

Calm down guys! :D
I posted the question with the aim of establishing whether there is a difference between actual top tube length (56cm horizontal top tube) and effective top tube length (56.5cm).
As I understand it we have established that the effective top tube of 56.5cm would give a longer reach than a 56cm horizontal top tube based on the seat/head tube angles and head tube length being the same on the respective frames.
Thanks to all for their input.
Regards,
Gary

neeb
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Re: Top Tube Length

Postby neeb » Sat Oct 12, 2013 16:30 pm

lockersgm wrote:Calm down guys! :D
I posted the question with the aim of establishing whether there is a difference between actual top tube length (56cm horizontal top tube) and effective top tube length (56.5cm).
As I understand it we have established that the effective top tube of 56.5cm would give a longer reach than a 56cm horizontal top tube based on the seat/head tube angles and head tube length being the same on the respective frames.
Thanks to all for their input.
Regards,
Gary

Yup - effective top tube length is designed to indicate exactly what the top tube length would be if the frame had a horizontal top tube. So if the rest of the geometry is the same, an ETT of 56.5cm will be 5mm longer than a horizontal top tube of 56. On a bike with a horizontal top tube, effective top tube length and actual top tube length are the same.

ilovegrace
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Re: Top Tube Length

Postby ilovegrace » Sat Oct 12, 2013 18:04 pm

never understood one word of this.
All i know is the top tube on my lappierre Xelius is 570mm and with a 110mm stem for me @ 5ft 11 was more than long enough, ended up putting a 90mm stem on . better but still stretched.
Numbers are numbers,feel is the thing .

neeb
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Re: Top Tube Length

Postby neeb » Sat Oct 12, 2013 20:01 pm

ilovegrace wrote:never understood one word of this.
All i know is the top tube on my lappierre Xelius is 570mm and with a 110mm stem for me @ 5ft 11 was more than long enough, ended up putting a 90mm stem on . better but still stretched.
Numbers are numbers,feel is the thing .

But once you know what feels right and you know what the numbers are for that, you'll be able to tell exactly whether any bike will feel right just by looking at the numbers.

ilovegrace
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Re: Top Tube Length

Postby ilovegrace » Sat Oct 12, 2013 21:01 pm

neeb wrote:
ilovegrace wrote:never understood one word of this.
All i know is the top tube on my lappierre Xelius is 570mm and with a 110mm stem for me @ 5ft 11 was more than long enough, ended up putting a 90mm stem on . better but still stretched.
Numbers are numbers,feel is the thing .

But once you know what feels right and you know what the numbers are for that, you'll be able to tell exactly whether any bike will feel right just by looking at the numbers.

I have to disagree, I used to play a decent standard of cricket before I started cycling , two bats of the same weight were not always the same feel , I have heard Magnus Backstead (sorry for the spelling) say about the wgt of bikes been the same but the balance different and I cold not agree more .
regards
ILG

neeb
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Re: Top Tube Length

Postby neeb » Sat Oct 12, 2013 21:24 pm

Well, there are different aspects of "feeling right". One of these is simply the contact points, and that's mainly what we're talking about here in the context of top tube lengths etc. Your contact points with the bike are the saddle, pedals and bars - get these things in the same place relative to each other on two bikes and the bikes will feel the same in the way you interface with them. Of course there are other things that alter the feel of a bike (other aspects of geometry such as head tube angle, chain stay length, wheelbase etc, stiffness, weight), but the best way to feel the effects of these is to set the bike up exactly the same in terms of contact points so you are comparing like with like. To do that, you need to know the numbers or else measure very precisely (or usually a combination of both). I suppose it's possible that there could be interactions between ideal contact points and other frame properties such that you would set up the contact points on two bikes differently to get the same feel, but it's very hard to imagine what these could be. You are not very likely to want to have the saddle at a different height on a stiffer bike, or the reach slightly different on a bike with a different head tube angle / trail, although I'll concede it's not beyond the realms of distant possibility..

At the end of the day, once you have found the setup (relation of contact points) that feels right for you, you are going to want to duplicate that on any new bike you get, and to do that you need to know the numbers...

on-yer-bike
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Re: Top Tube Length

Postby on-yer-bike » Sun Oct 13, 2013 19:25 pm

The OP is asking for a comparison between effective tt and actual tt. So does 5mm longer on a 565 ETT give effectively the same length as actual top tube of 560?
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