Frame Mesurement Importance ?

[ASTANA]

So I got a really great setup, and according to my setup done by Jeroen Swart, my top tube length should be 54cm, on my current bike its a bit shorter. I'm looking at new bikes now,

 

 Does the top tube length play any other role other than reach to the handle bars ?

 

Surely one can fix this with a longer/shorter stem ?

 

What other important things come to play with frame size. Everyone knows that frames come in XS S M L XL

 

But lets say in Medium there is frame size 50 52 54 56 just for example - not sure witch fall into what catogory. So does a 51 cm frame differ that much from a 54 cm frame ? Most of the mesurements are the same on the website for a spesific brand, but somthimes the only mesurement that differ is the length of the TOP tube and sometimes the Head tube.

 

What is your opinion on this topic ?

 

[Canaris]

top tube measurements can be "manipulated" by moving the saddle back and forward and putting on a shorter/longer stem.

 

Bikes like the Eddy Merckx have "longer" top tubes, because of their slack seat post angle, which is normally 2deg less than most other bikes.

 

On your bike set up how far back is your saddle?  This is a hint about your prefered seat post angle. On small bikes that angle is 75deg, and as much as  72.5deg for a extra large bike.  If you have short crank (say 170mm instead of 175mm, or 172.5mm) you should be able to more your saddle back by a few mm giving you a longer "virtual" top tube length.

 

What is the length of your stem?  most guys set with the 100mm stem, but you can push to 110mm and 120mm without serious stearing issues.  THis also give a little more "length" on your bike.

 

Finally the trend seems to be for smaller frames (as against larger frams in the 70's and 80's)  so being a bit short on the TT may be seen by some as an advantage.

[Barend de Arend]

 

 

 Does the top tube length play any other role other than reach to the handle bars ?

 

 

The top tube is basically just for reach.  There are other questions that influence reach (like seat tube angle' date=' saddle setback), so a 54cm Trek isn't necessarily the same as a 54cm Cervelo, or a 54cm Pinarello.

 

Surely one can fix this with a longer/shorter stem ?

 

 

Yep, you can.  However, stem length affects steering, and hence stability, so a very short or very long stem is usually a bad idea.

 

What's "very short" and "very long?" depends on who you ask.  Usually 8cm and 14cm.

 

 

What other important things come to play with frame size. Everyone knows that frames come in XS S M L XL

 

 

 

No' date=' they don't.  Most "old-school" frames come in 48, 50, 52 ... 63.  Most Italians will make a custom frame size (De Rosa even do custom carbon).  It'll fit like a custom tailored suit, or custom shoes, but it will cost more.

 

You send them your measurements (inseem, knee, foot size, arm size, etc.) they send you a frame.  It gets more complicated when you calculate how flexible you are (how low do you want the bars?)

 

 

 

But lets say in Medium there is frame size 50 52 54 56 just for example - not sure witch fall into what catogory. So does a 51 cm frame differ that much from a 54 cm frame ? Most of the mesurements are the same on the website for a spesific brand, but somthimes the only mesurement that differ is the length of the TOP tube and sometimes the Head tube.

 

A *lot* of things change: seat angle, headtube angle, seat tube size, etc.  In the middle of the range, almost all angles are 73 degrees, but that's not necessarily true for smaller (<52) and larger (>58) bikes.

 

 

You only need to worry about four things: (four, I need to learn to count!)

* effective saddle height.

* effective saddle setback.

* effective reach.

* effective drop.

 

In other words: where are your feet, your butt, and your hands, in relation to each other.

 

 

 

What is your opinion on this topic ?

 

 

A bike that doesn't fit is like a shoe that doesn't fit.  OK for short walks, but it will really hurt on long(er) rides.

 

Barend de Arend2009-04-23 06:10:48

[splat]

Dr Swart should be able to help with an answer this question seeing as he did your set-up...

[ASTANA]

Thanx a lot guys - looks like I ddn't miss the pot that much 

 

Here is my mesurements :

                                Road    

Crank length           172.5    

Seat height               71.3          From middle of BB

Layback                     7        from te BB

Drop                         5.5         high from seat to handlebar

Reach                      65.7          for seatpost to handlebar

TopTube                   54.5    

Stem                         110  

 

This is how it should be.. according to Jeroen's Setup

 

 

 

 

[Guest colonel]

Jeroen in is top of his game with regards to these matters, you should phone or mail him with your questions and get the correct answer considering he knows your dimensions and not ask anyone on the hub as they do not know you or your measurements.

[Dirtbreath]

Very ineterested that you guys mention moving your saddle backwards/forwards in the setapost to manipulate reach. Surely your forward/rear positioning is there to position your knees correctly over the pedals and so is fixed and cant be used to correct reach?

[DaLoCo]

If the changes are too drastic, I would suggest you slowly move toward the correct setup. It is afteall the setup designed for you to get the most efficient ride Colonel is right, if the man is the best there is, listen to him.......

[Guest colonel]

Jeroen does frequent the Hub so maybe he will pick this topic up. What amazes me is why Astana doesnt mail or phone Dr Swart and ask him instead of asking people on the hub???

Its like phoning Mercedes and asking for specs on the latest Sanyo DVD player.

[ASTANA]

 

Jeroen in is top of his game with regards to these matters' date=' you should phone or mail him with your questions and get the correct answer considering he knows your dimensions and not ask anyone on the hub as they do not know you or your measurements.[/quote']

 

Yeah - did contact him, he quite a busy guy so just hear you guys out.

Movie the saddle back and fort will not work - its there for a reason.

 

That is the top tube length of a Cervelo Soloist carbon 51 cm bike ? Cant get the older models on cervelo's website to see the measurements

 

[splat]

Astana, you would possibly get some better insight if you compared your current frame to your new one's geometry.

You have had a set-up done already, so you know the range you should be in.

[ASTANA]

 

Jeroen does frequent the Hub so maybe he will pick this topic up. What amazes me is why Astana doesnt mail or phone Dr Swart and ask him instead of asking people on the hub???

Its like phoning Mercedes and asking for specs on the latest Sanyo DVD player.

 

AMAZING isn't it. Don't be rude.

 

[splat]

I think he means that you gotta ask the right people the right questions and not fire vague questions out into the open.

[DaLoCo]

Astana' date=' you would possibly get some better insight if you compared your current frame to your new one's geometry.

You have had a set-up done already, so you know the range you should be in.

[/quote']

 

I think the problem is that we are all misunderstanding the man......there is no new frame yet!! Just an interest in one. So the original question is, how does the top tube influence the sizing of the bike, am I correct?

[The Doctor]

Hi Guys

Simply changing the stem length or the saddle setback to alter reach are both going to lead to compromises.

Firstly, the stem length not only affects the directness of the steering but also alters the forces acting on the front tyre. Top tube length and stem length in combination with setup together determine the front contact patch loading. On a mountainbike this has a fairly dramatic effect on handling. The same applies to road bikes but requires that you ride at some speed into a corner to notice the difference.

The front tyre contact patch is the area of the tyre which is in contact with the road surface after deformation of the tyre. In addition to friction co-efficients, the angle of forces acting on the contact patch determine when the tyre will break free. In addition, the fork offset and head tube angle affect the lateral loading of the tyre sidewall during cornering. At low tyre pressures and high tyre volumes (such as on a mountainbike), this can be a signifcant factor affecting the grip levels and handling. On a road bike, off camber corners and wet and dirty roads can result in either understeer or oversteer depending on the position of the centre of gravity over the front axle. Think Joseba Beloki and broken hips as an example.

Messing around with the saddle setback is also not such a good idea.

Saddle setback is a key determinant of which muscle group the cyclist uses to recruit force. A very large setback will result in having to push the cranks forward during the knee extension phase and as a result will recruit more muscle from the hip extensors (gluteal muscles). A short setback results in the quadriceps becoming more active. Which of these two is better?

Using the gluteal muscles (the single largest muscle in the body) can result in greater force being applied to the pedals or otherwise greater endurance when lower forces need to be applied for prolonged periods of time. In addition, the body?s ability to recruit the gluteal muscles improves with time spent on the bike. This is why a number of elite cyclists and older cyclists use such excessive setbacks.

However, there are a number of negative consequences to having large amounts of setback. The first is that the knee extensors (quadriceps) utilise the lowest oxygen consumption to generate a particular force. This means that for shorter duration exercise or very intense efforts, the quadriceps act more efficiently in generating power. Secondly, the knee extension cycle (produced by the quadriceps) produces forces which are more perpendicular to the crank arm, making the force production more efficient. Thirdly, the transition into and out of the saddle is easier with less saddle setback. Finally, a more rearward position created by excessive saddle setback will effectively increase the reach of the cyclist, possibly over extending the position, with all of the negative consequences associated with this as well as placing the hip joint in an overflexed position, reducing the ability to produce power.

 

So in short, when I recommend that you buy a bike with a 54cm or 54.5cm top tube, it is for a valid reason. I don't profit from the bike industry.

[The Doctor]

For more on bike setup please read my article in the Feb issue of Bicycling