Frame Size Calculation

[cyclingfan]

Hello everyone. I am a new member to this forum and like all newbies, I am looking for some advice. Hope some of you can help me out. I am in the process of buying my first road bike (I ride a mountain bike for now). I have chosen as my entry bike a TREK 1500 (the 2005) model. My question is on how to determine the frame size. I measured my inseam and (after several measurements) it is between 84.2cm and 84.5cm. I then multiplied this value by 0.67 (to calculate C-T size). This calculation gives me a Frame size between 56.4cm and 56.6cm. The first question I have is if this calculation is a good approximation?? The second question is, if it is a good approximation, should I look for a Frame size of 56cm or 58cm (since the TREK 1500 doe not have a 57cm C-T frame size)?? I checked the geometry information on the TREK web site, but I am still not sure. I woul appreciate any help. Thank you in advance.

Regards,

cyclingfan

 

[dmac]

Head to your LBS on have them "fit" you. Most fit formulas are a good rough approximation, but they assume idealized body symmetry and proportions. There is no substitue for having a good LBS fit you.

 

[cyclingfan]

Thank you for your response. I went to two different LBS' and they both came with different answers. That is why I started looking into it myself. Besides, there is a chance I will be able to buy the TREK I want at a very good price (from a friend) and I will have to provide the Frame Size myself. I visited the CompetitiveCyclist.com web site and followed they "Fit" procedure. The results are pasted below.


Measurements
-------------------------------------------
Inseam: 33.25
Trunk: 27
Forearm: 14.5
Arm: 28
Thigh: 24.5
Lower Leg: 22
Sternal Notch: 58.5


The Competitive Fit (cm)
-------------------------------------------
Seat tube range c-c: 54.7 - 55.2
Seat tube range c-t: 56.4 - 56.9
Top tube length: 57.0 - 57.4
Stem Length: 12.2 - 12.8
BB-Saddle Position: 72.3 - 74.3
Saddle-Handlebar: 57.1 - 57.7
Saddle Setback: 5.7 - 6.1
Seatpost Type: NON-SETBACK


The Eddy Fit (cm)
-------------------------------------------
Seat tube range c-c: 55.9 - 56.4
Seat tube range c-t: 57.6 - 58.1
Top tube length: 57.0 - 57.4
Stem Length: 11.1 - 11.7
BB-Saddle Position: 71.5 - 73.5
Saddle-Handlebar: 57.9 - 58.5
Saddle Setback: 6.9 - 7.3
Seatpost Type: SETBACK


The French Fit (cm)
-------------------------------------------
Seat tube range c-c: 57.6 - 58.1
Seat tube range c-t: 59.3 - 59.8
Top tube length: 58.2 - 58.6
Stem Length: 11.3 - 11.9
BB-Saddle Position: 69.8 - 71.8
Saddle-Handlebar: 59.6 - 60.2
Saddle Setback: 6.4 - 6.8
Seatpost Type: SETBACK


Hope you or someone else can help me. Thank you in advance for any input you guys can provide.

Regards,


cyclingfan

 

[hashde]

Thank you for your response. I went to two different LBS' and they both came with different answers. That is why I started looking into it myself. Besides, there is a chance I will be able to buy the TREK I want at a very good price (from a friend) and I will have to provide the Frame Size myself. I visited the CompetitiveCyclist.com web site and followed they "Fit" procedure. The results are pasted below.


Measurements
-------------------------------------------
Inseam: 33.25
Trunk: 27
Forearm: 14.5
Arm: 28
Thigh: 24.5
Lower Leg: 22
Sternal Notch: 58.5


The Competitive Fit (cm)
-------------------------------------------
Seat tube range c-c: 54.7 - 55.2
Seat tube range c-t: 56.4 - 56.9
Top tube length: 57.0 - 57.4
Stem Length: 12.2 - 12.8
BB-Saddle Position: 72.3 - 74.3
Saddle-Handlebar: 57.1 - 57.7
Saddle Setback: 5.7 - 6.1
Seatpost Type: NON-SETBACK


The Eddy Fit (cm)
-------------------------------------------
Seat tube range c-c: 55.9 - 56.4
Seat tube range c-t: 57.6 - 58.1
Top tube length: 57.0 - 57.4
Stem Length: 11.1 - 11.7
BB-Saddle Position: 71.5 - 73.5
Saddle-Handlebar: 57.9 - 58.5
Saddle Setback: 6.9 - 7.3
Seatpost Type: SETBACK


The French Fit (cm)
-------------------------------------------
Seat tube range c-c: 57.6 - 58.1
Seat tube range c-t: 59.3 - 59.8
Top tube length: 58.2 - 58.6
Stem Length: 11.3 - 11.9
BB-Saddle Position: 69.8 - 71.8
Saddle-Handlebar: 59.6 - 60.2
Saddle Setback: 6.4 - 6.8
Seatpost Type: SETBACK


Hope you or someone else can help me. Thank you in advance for any input you guys can provide.

Regards,


cyclingfan

Based on that, I'd get a 58cm frame, and adjust stem, seat height as needed.

 

[boudreaux]

Based on that, I'd get a 58cm frame, and adjust stem, seat height as needed.

BS................

 

[hashde]

BS................

If you are going to call me a liar, at least explain youself.

 

[boudreaux]

Can't you see the issue with all the different answers you are getting?? Find a shop that has a Serotta fit type cycle and someone that knows how to use it,and pay a few bucks for a proper fitting.There are even a few that can do a proer fitting with you on a trainer.Keep in mind too that since makers size bikes differently,nominal frame size can be confusing to meaningless. Assuming adequate standover,TT length is more important.

 

[boudreaux]

If you are going to call me a liar, at least explain youself.

Has nothing to do with being a 'liar'. But likely not being anything even close to a professional fitter,don't really have a clue.You are just tossing lame advice that could cost to poster alot of money.Given his inseam and knowing mine and what I ride,most if not all 58s could be too big.Internet Bike fitters should just 'give it a east'.

 

[hashde]

Has nothing to do with being a 'liar'. But likely not being anything even close to a professional fitter,don't really have a clue.You are just tossing lame advice that could cost to poster alot of money.Given his inseam and knowing mine and what I ride,most if not all 58s could be too big.Internet Bike fitters should just 'give it a east'.

Please read my post.
I said "Based on that" By this statement I clearly meant, based on what I see here. I aslo said "I'd get a 58cm frame, and adjust stem, seat height as needed." By this statement, I meant I would, I did not tell him to do so. Fit is largely trail and error, which he'll find out soon if he does not already know.

But likely not being anything even close to a professional fitter,don't really have a clue.

And you are a fitter with a clue? Can you demonstrate in some way that your advice is any more valid?

Given his inseam and knowing mine and what I ride,most if not all 58s could be too big.Internet Bike fitters should just 'give it a east'.

Given his inseam and knowing mine, I stand by my original statement.

Internet Bike fitters should just 'give it a east'

Any chance you will take your own advice?

 

[boudreaux]

Please read my post.
I said "Based on that" By this statement I clearly meant, based on what I see here. I aslo said "I'd get a 58cm frame, and adjust stem, seat height as needed." By this statement, I meant I would, I did not tell him to do so. Fit is largely trail and error, which he'll find out soon if he does not already know.



Any chance you will take your own advice?

That is even lamer BS...I didn't mention size at all.

 

[hashde]

That is even lamer BS...I didn't mention size at all.

You implied that 58 was too big, so he should get a smaller size.

 

[boudreaux]

You implied that 58 was too big, so he should get a smaller size.

That was in response to you,and that a 58 could be too big.Sorry for the apparent confusion.

 

[cyclingfan]

Thank you guys for your advice. I see that there are a lot a passionate people in this board!!! I have not yet made the decision regarding the Frame Size. I went to three LBS' and I had three different answers (54cm which I think is to small, 56cm and 58cm). The impression I had is that the fitting was done so they could sell the bike they had available at the moment in the store. I don't trust that I am getting the right information regarding the Frame Size. That is why I came to this board. Another piece of information that may help is my height. I am 5'11". Does this information, together with the rest I posted before, help in deciding the Frame Size?? Once again, I really appreciate the help.



Regards,


cyclingfan

 

[Deafcon]

I purchased a Trek road bike (a Madone 5.2) in early September, and my measurements are close to yours. My inseam is 85 cm. I went with a 58 cm, but I had to put a 100mm stem on it instead of the 120mm stem that particular model came with. 600 miles later and it feels great...

 

[boudreaux]

I went to three LBS' and I had three different answers (54cm which I think is to small, 56cm and 58cm). The impression I had is that the fitting was done so they could sell the bike they had available at the moment in the store.

That happens,but a least you weren't suckered.Anything you would get here is just a guess,without seeing you on a bike.And remember,frames are measured c-c,c-top and center -t top of an extended seattube. All 56 or 58s aen't the same,and even TTs vary alot with the same nominal size.Compact geometry throws another wrinkle into it,and are often more suited to people with shorter legs and longer torsos.

 

[cyclingfan]

Thank you boudreaux for the information. I am looking to a get TREK 1500 (no compact geometry). TREK measures the Frame Size by C-T (where T = top of the seat tube), according to the chart I found on their website. Looks like I will have to approximate it. I stood by a 56cm Frame and it seemed a bit short. My guess is that the 57cm C-T would be the right size, but since TREK does not have a 57cm, I will probably follow hashde and Deafcon suggestion and get a 58cm and replace the stem in case it doesn't feel right. I rather have the frame on the big side then on the small side of it. If you guys have any other suggestions, I am open to them. I will be making my decision by the end of the week, so I still have some time. I really appreciated all the information and suggestions you guys provided up to know. Once again, thank you for the help.


Best regards,

 

[boudreaux]

Thank you boudreaux for the information. I am looking to a get TREK 1500 (no compact geometry). TREK measures the Frame Size by C-T (where T = top of the seat tube), according to the chart I found on their website. Looks like I will have to approximate it. I stood by a 56cm Frame and it seemed a bit short. My guess is that the 57cm C-T would be the right size, but since TREK does not have a 57cm, I will probably follow hashde and Deafcon suggestion and get a 58cm and replace the stem in case it doesn't feel right. I rather have the frame on the big side then on the small side of it. If you guys have any other suggestions, I am open to them. I will be making my decision by the end of the week, so I still have some time. I really appreciated all the information and suggestions you guys provided up to know. Once again, thank you for the help.


Best regards,

Have you actually tried riding any of them? The dealer can easily switch out the stem to confirm proper fit before handing over cash.Make sure you can get the bars high enough too.

 

[cyclingfan]

I will try to test the bikes (56cm and 58cm) and see how it feels. Depending on how it goes, I will ask them to replace the stem. Are you refering to the handle bars?? If I may ask, what you mean but getting the bars high enough??

Regards,


cyclingfan

 

[MattAussie66]

I've just been through the whole bikefit palava - I found the best bike for
me but I had to put in a heap of excel and ringing around.

I now think that people think about setting up bikes all wrong.

Firstly position your **** relative to your foot, so take your inseam
and your setback to work out the seat tube angle. The inseam is usually
109% less cleats/shoes less cranks to get BB c/l to middle of the seat.
BUT the setback is more related to your lower body build (muscle bulk),
flexibility and what you want to do, hillclimbing a little further back, I have shortish legs (like treetrunks) and want to climb hills so my setback
is 85mm.
If your inseam is 845mm with 172.5mm cranks and look pedals you get
a BB c/l to seat of 750mm, I would guess that you need a setback of around 80mm, If you want the seat in the middle of its adjustment, gives
a seat tube angle of 73.5 degrees. Or a you need a setback seat post.
If you have 180mm of seat+seatpost, this gives a frame size of
57cm (C-T) .
Most frames (and virtual frames) are square these days giving a
toptube c-c of 57cm.
Once your **** is in place then you need to get your hands in a comfortable position, I would guess from your height you would need
a seat nose to bar c/l of around 56cm, with a 57cm toptube this is
probably around a 120mm stem.
As long as the seat tube angle is ok, if you can't get a 57, I would
personally go for the 56 with a slightly longer stem 130mm stem.

BUT - I did a bikefit at a very good LBS (probably the best
in Sydney) and then used this data and a heap of excel spreadsheets
to prove to myself that I was an odd shape and that only a Look frame
with a lazy seatpost angle and an over square toptube would fit me.
From your measurements I would guess that you are fairly normal - so
there should be no problem.

Regards,
Matthew

 

[cyclingfan]

Thank you Matt for your answer/explanation. I ended up buying a Trek 1500 58cm C-T. According to the LBSs I re-visited, and some bike mechanics I spoke, they agreed on the fact that the Trek seems to be a little "shorter" on the frame size issue. I then did a test ride of a 56cm C-T and a 58cm C-T and decided on the 58cm C-T. It is on the upper side of the range size wise but it felt right. Once again thank you guys for the input. Best regards,



cyclingfan