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What size to choose for a De Rosa bike?

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What size to choose for a De Rosa bike?

Old 09-09-23, 10:25 PM
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What size to choose for a De Rosa bike?

Hi, I need advice on which size to choose for a Rosa 70 model bike (you can find the geometries in the attached photos)


These are my measurements
  • 175.5cm height
  • 82.4cm inseam
  • 45eu foot size
  • I pedal with a saddle height of 72.7/73 cm
  • Some problems maintaining a very relaxed position.


Which size would you choose? a 50.5 or a 48?

De rosa indicates the sizes with the length of the seat tube... would size 48 correspond to an M 54 frame? and the size 50.5 to an L size 55 frame?

https://derosa.it/model/70/



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Old 09-10-23, 08:31 AM
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(Nice looking De Rosa!)
What changes do you want to make from your current bike? Are the bars too far, so you are stretched out and you always seem to pull your hands back from the hoods? or what? with a range of bar position changes, you can see if the new bike is marginal or if it has room for adjustment after you ride it.

I'm still riding that 2014 bike mentioned in my posts below! It's still exactly what I want. I have the top surface of the bars set about 1 1/4 inches / 30mm below the saddle top. It's great: the drops are very comfortable and usable. I probably ride 50% hoods, 40% drops, 10% tops. So many riders rarely use their drops -- the bars are really too low for them. Drops advantages: A little more aero. Much better control on bad roads, and more comfort on bumpy roads with the shocks spread out across my palms. My back is stretched out a little in the drops--nice.

How to compare bike geometries

From another thread, I posted:

I found it hard to compare bikes, since they don't always measure the same way.

Stack and reach worked great when I bought my new road bike in 2014. Some bikes were 53cm, others 55cm with very similar stack and reach numbers. The old bike fit was pretty good, so I used it to find similar fitting bikes. The goal was to have maybe 20mm of spacers under the stem, to allow later adjustments either up or down. After 30,000 miles, it still is set at 20mm!
Here's an easy way to measure stack and reach for your current bike.

And the first link mentions a nice stem angle comparison tool--very useful. This makes it easy to see the net effect of angles along with stem lengths. Helpful to adjust from an ill-fitting frame with a very short or very long stem to a better frame with a normal 90 mm to 110mm stem.

I ignored seat tube angle. I'm guessing that most road bikes seat tube angle differences won't really affect the saddle clamp placement very much.

~~~~~~~~~~~~~~~~~~~~

The "measure stack and reach" linked post uses this measuring method:
Lynskey..how to decide on model?

Measuring Stack and Reach
Bike rear tire against a wall.
Stack is the difference between the two vertical measurements.
Reach is the difference between the two horizontal measurements.
(convert inches to mm with google search, like this: 21 5/8 inch in mm)



~~~~~~~~~~~

One more thread, mentioning how the bike stem calculator works:
How to use Stack and Reach in selecting a bike

~~~

Last edited by rm -rf; 10-29-23 at 02:31 PM.
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Old 09-10-23, 10:25 PM
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ok very interesting but based on my anthropometric measurements (height and inseam) which of the two sizes should I choose? 48 or 50.5? Would the 48 be an size M and the 50.5 an size L? Or 48 size s and 50.5 size M?
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Old 09-11-23, 06:16 AM
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50.5. 48 is too small.

You could ride the next size up, 52.5, easily.
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Old 09-11-23, 08:35 AM
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If you scroll down the linked page, they have a "Book A Meeting" button. Why don't you do that and see if you can get their opinion of what size will fit you best.


Are you sure you are going to like that very aero position it gives you?

I'm not sure what this means...

Some problems maintaining a very relaxed position.
If it means you like to stay aero, then maybe it is the right bike for you. However, if it means you don't feel relaxed on a bike, then that might mean you are hard to please in any position.

If you don't want to be in a aggressive race position, then don't buy a bike that is made for a aggressive race position.

Last edited by Iride01; 09-11-23 at 08:43 AM.
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Old 11-15-23, 01:17 PM
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I would do the actual seat tube height measurements of your road bike that you ride, and make the same measurements on those two bikes, measuring the same way. If you can do the same measurement for the three effective top tubes, that would also help. Better would be to have stack, reach, and seat post setback for all three bikes.
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Old 11-15-23, 01:26 PM
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I would try not to ignore seat tube setback. If you have to set your saddle back farther than you like and are not able to reduce stem extension, you could be uncomfortabl ereaching out too far.

One way to approximate it, so you don't have to measure with a plumb line, is to measure length from the tail of the saddle to the midpoint between yur two brake handles, at the front of the brake lever. That gives you a decent picture of the total cockpit length of the bike that fits best, your older one.
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Old 11-15-23, 01:41 PM
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Originally Posted by Road Fan
I would try not to ignore seat tube setback. If you have to set your saddle back farther than you like and are not able to reduce stem extension, you could be uncomfortabl ereaching out too far.

One way to approximate it, so you don't have to measure with a plumb line, is to measure length from the tail of the saddle to the midpoint between yur two brake handles, at the front of the brake lever. That gives you a decent picture of the total cockpit length of the bike that fits best, your older one.
I don't see what that accomplishes. Measuring the saddle to bars without reference to stem or setback can't tell you anything about the frame.
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Old 11-15-23, 07:53 PM
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In the case where one cannot measure actual seat setback, which I find useful in saddle placement, one can do better than just ignoring setback completely. That was my point.

I found I can match my reach between two bikes, not just the frames, by measuring total length from hand contact to butt contact and making adjustments to one of the other, so hthe lengths match. My interpretation of the goal was that he could best choose his new frame by making that comparison, in addition to other measures, such as riding carefully and with awareness. YMMV.

You can also line up a pair of frames so their BB axes line up, and then measure seatpost setback directly, if you are handy with a plumb line.
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Old 11-15-23, 08:40 PM
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Originally Posted by Road Fan
In the case where one cannot measure actual seat setback, which I find useful in saddle placement, one can do better than just ignoring setback completely. That was my point.

I found I can match my reach between two bikes, not just the frames, by measuring total length from hand contact to butt contact and making adjustments to one of the other, so hthe lengths match. My interpretation of the goal was that he could best choose his new frame by making that comparison, in addition to other measures, such as riding carefully and with awareness. YMMV.

You can also line up a pair of frames so their BB axes line up, and then measure seatpost setback directly, if you are handy with a plumb line.
You can get the same saddle-to-bar length on the same bike with the saddle slammed forward and a 140mm stem as with a 90mm stem and the saddle all the way back. Those two aren't vaguely the same position.
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Old 11-16-23, 05:15 PM
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Originally Posted by Kontact
You can get the same saddle-to-bar length on the same bike with the saddle slammed forward and a 140mm stem as with a 90mm stem and the saddle all the way back. Those two aren't vaguely the same position.
True - ya caught me, congratulations!. I'm just sharing what I do in my own context I'm assuming others will take what is useful from my words, and not use what is not useful. You are correct, it is not universally useful, but I'll still use it where I think it could get me some insights I think I need.
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Old 11-17-23, 05:33 PM
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Originally Posted by Kontact
50.5. 48 is too small.

You could ride the next size up, 52.5, easily.
The 52.5 is longer in the top tube than some 56s 48 is really tiny and you're about medium height, with large feet and slightly short legs. I concur with 50.5. These bikes seem to run about 2-3 cm larger than their nominal size would indicate, and they're rather long in the top tube.
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Old 11-25-23, 05:29 AM
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I'd pick the size that gives you the most flexibility for setup. However, to know which size will give you the most flexibility for your final fit, you need to know where your saddle and your handlebars will sit in space in relation to the published reach and stack numbers in the geometry chart. The geometry chart only provides so much info.

For example, if the "reach" on the larger size is already at the long end of what you can tolerate, your stem length will be limited along with your ability to utilize saddle setback. Keep in mind that the reach figures in those geometry charts are from the center of BB forward to the center of the headtube. "Reach" in no way accounts for your saddle position (i.e. fore / aft), so make sure to factor that into your calculations.

You also need to account for saddle height (which is specific to you and is not accounted for in the geometry chart). As you raise your saddle height you are effectively lengthening your reach due to the rearward angle of the seatpost.

Similarly, "stack" is also measured to the top center of the head tube and does not account for any spacers under your stem. As you raise your stack height (via spacers under the stem) you are effectively shortening your reach. The angle of the steerer tube will inform you as to how much the reach will be shortened for a given height above the top center of the steerer tube.

It would also be helpful to compare the geometry chart for the bike you currently ride against the DeRosa chart. I don't think you told us in your original post which bike you currently ride (which is relevant). If you already ride a bike with aggressive geometry, the selection of a new frame might be pretty simple. If you are transitioning from a bike with a significantly different geometry as compared to the DeRosa, then the selection process can be much harder.

Lastly, if you are dropping a lot of coin on a new bike and are not certain which size will fit you best, then I strongly suggest you see a good bike fitter before you make the purchase. One of the biggest mistakes people make when buying a bike is going for the fit after the bike has been purchased.

Last edited by Turnin_Wrenches; 11-25-23 at 05:32 AM.
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Old 11-25-23, 05:44 AM
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Size, schmize.
What color are you going to get?
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Old 01-22-24, 03:45 AM
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Hi
I am planning to get a de Roas 70 as well. Did you finally order one - and how ist your ride impression? What size did you end up buying?
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