Going from 54 to 48?

yamagold said:

i am using a size 54 C-T bike with the following specs:
frame: 540mm, seat tube: 490mm, toptube (virtual): 550mm, headtube:152mm, chainstay: 408mm, seat angle: 73.2 deg
head angle: 72.6 deg

the size 54 fits me right and this are my personal datas i based my frame size.
height 67.5 inches, sternum notch 54.2 inches, inseam 31.5, arm length 24 inches

which resulted on a size 54 c-t and fits me right and this are the datas that resulted from my above measurements.

over-all reach 63.31 center to center
saddle height 70.65 (ACTUAL HEIGHT IS 73.5INCHES)
stem length used 100mm

will i be able to use a size 48 frame and feel as comfortable as size 54 if the 48 frame has the following specs:

frame: 480mm, seat tube: 430mm, toptube: (virtual): 510mm, headtube: 102mm, chainstay: 405mm, seat angle: 73.7 deg, head angle: 69.3 deg

I WILL USE A 140MM STEM - SO MY OVER-ALL REACH IS STILL 63.31 INCHES C-C
RAISE THE SEATTUBE 60 MM TO HAVE THE SAME SADDLE HEIGHT OF 70.65 INCHES.
I WILL BE MORE AERO IN THE 48, BUT WHAT ABOUT COMFORT?

3cm difference in the virtual top tube is about as much as you can compensate for with a different stem and raising the seatpost isn't that big of a deal, but although you may be able to position yourself similarly in relation to the seat, pedals, and bars, the ride may not feel as good as the larger frame. Steering might feel a bit twitchy with the longer stem, but this may be mitigated somewhat by the slack head angle. Also the bars are going to be quite a bit lower, although it sounds as if that is one of your goals.

I would want to test ride a set-up that was this different from my current before I purchased.

yamagold said:

i am using a size 54 C-T bike with the following specs:
frame: 540mm, seat tube: 490mm, toptube (virtual): 550mm, headtube:152mm, chainstay: 408mm, seat angle: 73.2 deg
head angle: 72.6 deg

the size 54 fits me right and this are my personal datas i based my frame size.
height 67.5 inches, sternum notch 54.2 inches, inseam 31.5, arm length 24 inches

which resulted on a size 54 c-t and fits me right and this are the datas that resulted from my above measurements.

over-all reach 63.31 center to center
saddle height 70.65 (ACTUAL HEIGHT IS 73.5INCHES)
stem length used 100mm

will i be able to use a size 48 frame and feel as comfortable as size 54 if the 48 frame has the following specs:

frame: 480mm, seat tube: 430mm, toptube: (virtual): 510mm, headtube: 102mm, chainstay: 405mm, seat angle: 73.7 deg, head angle: 69.3 deg

I WILL USE A 140MM STEM - SO MY OVER-ALL REACH IS STILL 63.31 INCHES C-C
RAISE THE SEATTUBE 60 MM TO HAVE THE SAME SADDLE HEIGHT OF 70.65 INCHES.
I WILL BE MORE AERO IN THE 48, BUT WHAT ABOUT COMFORT?

All other things being equal, a longer stem will make the steering seem slower/less twitchy. The 40mm extra stem length combined with the much slacker head angle will result in very different handling than the bike you have now. I strongly recommend you ride this combo before you pony up for one.

BTW, what is the frame? A 69 head angle is very slack. Any idea what the fork offset ("rake"😉 is?

John M said:

3cm difference in the virtual top tube is about as much as you can compensate for with a different stem and raising the seatpost isn't that big of a deal, but although you may be able to position yourself similarly in relation to the seat, pedals, and bars, the ride may not feel as good as the larger frame. Steering might feel a bit twitchy with the longer stem, but this may be mitigated somewhat by the slack head angle. Also the bars are going to be quite a bit lower, although it sounds as if that is one of your goals.

I would want to test ride a set-up that was this different from my current before I purchased.

Good day John M and thanks for your input.
The main reason for the going down to size 48 is the availability of the frame. as it is the only available size locally, i thought it might work out. You see i just broke my CF frame (ouch!?) and wants to replace it soonest. But i can see that it is too much of a difference and im also pretty sure i wont enjoy the ride. Finally i will available for the manufacturer's crash replacement.

Now im considering going down just one size smaller from 54 to 51.
here's the difference.

Frame size 54 540 C-T, seat tube 490, virtual TT 550, headtube 152, chainstay 408, seattube 73.2, head angle 72.6
Frame size 51 510 C-T, seat tube 460, virtual TT 535, headtube 122, chainstay 405, seattube 73.5, head angle 72.3

Probably will be using a 115 stem? and just maintaining my actual saddle height 73.5 (70.65 per computer). as the frame will have to cross oceans, got no way to test the size 51. There is a gamble to this though as even a 1 cm change in the distances can mean a lot between com and discomfort.
OTOH i have come across some information that the pros uses a size smaller their normal. What is their main purpose, i wonder?

What's your opinion?

Other posters opinion are highly solicited most especially those who have the experience of not depending on the computer fitting programs.

Tks

Ozark Bicycle said:

All other things being equal, a longer stem will make the steering seem slower/less twitchy. The 40mm extra stem length combined with the much slacker head angle will result in very different handling than the bike you have now. I strongly recommend you ride this combo before you pony up for one.

BTW, what is the frame? A 69 head angle is very slack. Any idea what the fork offset ("rake"😉 is?

Hi Richard and thanks.
The frame is an Orbea columbus starship. Regret i couldnt find the rake data.
i finally junked the 48 idea as its too much of a gamble. I do gamble during my early days and more often than not, i lose 😉. The last gamble i had 2 days ago resulted in a broken CF seatstay, broken helmet (head hit pavement), road rashes, neck and arm pains. thank GOD for the intact bones and head. NOW I WOULD HIGHLY RECOMMEND THAT HELMETS BE WORN CORRECTLY AND SHOULD BE YOUR PROPER FIT.

Im considering a crash replacement and going down 1 size smaller from 54 to 51.

Would be glad to hear your opinions.

yamagold said:

Hi Richard and thanks.
The frame is an Orbea columbus starship. Regret i couldnt find the rake data.
i finally junked the 48 idea as its too much of a gamble. I do gamble during my early days and more often than not, i lose 😉. The last gamble i had 2 days ago resulted in a broken CF seatstay, broken helmet (head hit pavement), road rashes, neck and arm pains. thank GOD for the intact bones and head. NOW I WOULD HIGHLY RECOMMEND THAT HELMETS BE WORN CORRECTLY AND SHOULD BE YOUR PROPER FIT.

Im considering a crash replacement and going down 1 size smaller from 54 to 51.

Would be glad to hear your opinions.

If you were well fitted on the 54cm frame, why would you want to go to a 51cm? This is less radical than going to the 48cm frame with it's very short TT and slack head angle, but you are still taking a gamble (as you say). If the 54cm felt right, stay with it, IMO. If you want to get lower in front, try a stem with a different "rise" and turn it "upside down".

We agree about helmets; I cracked one in a big way back in '99. It could have been my head. 🙁

Ozark Bicycle said:

If you were well fitted on the 54cm frame, why would you want to go to a 51cm? This is less radical than going to the 48cm frame with it's very short TT and slack head angle, but you are still taking a gamble (as you say). If the 54cm felt right, stay with it, IMO. If you want to get lower in front, try a stem with a different "rise" and turn it "upside down".

We agree about helmets; I cracked one in a big way back in '99. It could have been my head. 🙁

Yes i may have to agree with your opinion. Why gamble when you are sure with the former size. In the end there will be no regrets. 🙂

The Orbea CF bike that broke was actually i could say what the fitting calculator say my size is. It was almost i would say a custom bike for me based on the calculated results taken from my measurements except the saddle height which i feel more comfortable when raised 3 inches higher than what the calculator says. Yes i would have loved to lower the front a bit but the itm stem currently installed is already on zero rise.

still and all im just wondering why the pros choice is a smaller size than their normal.

happy safe riding.

yamagold said:

Yes i may have to agree with your opinion. Why gamble when you are sure with the former size. In the end there will be no regrets. 🙂

The Orbea CF bike that broke was actually i could say what the fitting calculator say my size is. It was almost i would say a custom bike for me based on the calculated results taken from my measurements except the saddle height which i feel more comfortable when raised 3 inches higher than what the calculator says. Yes i would have loved to lower the front a bit but the itm stem currently installed is already on zero rise.

still and all im just wondering why the pros choice is a smaller size than their normal.

happy safe riding.

This was recently discussed here a couple of weeks ago in the following thread:

http://www.cyclingforums.com/t300953-frame-sizing-among-the-pros.html

John M said:

This was recently discussed here a couple of weeks ago in the following thread:

cyclingforums.comt300953 frame sizing among the pros.htmlOpen ↗

Thanks for the link John M.
I think ill just stick to my original size.

Good day and Happy safe riding!!!