My rust bucket is a Specialialized and is called a 56 CM

GEOMETRY IS:

Top-tube C to C is 56 CM

Head Tube is 152 MM

Seat Tube Angle is 74 Degrees

Chain Stay is 408 MM

Seat Tube C to C is 56 CM

FOUND WHAT I THINK IS A DEAL ON A NEW FRAME, THE BUT IS TOP TUBE LENGTH

Effect Top Tube is 56.5 CM C to C

Seat Tube is 55 C to C

Seat Tube Angle is 73 Degrees

Head Tube is 144 MM

So my question is are these measurement close enught to to do a part/componants switch?

As there is a One Degree Difference in Seat Tube Angle how will that effect ride, and the Head Tube is shorter 8 mm's on NEW FRAME will that effect much ??

Hate to make a big boo boo.

Im Happy with the RB1 frameset I got in the 90's it, a 56, has a 565 top tube .

73 seat tube angles are very common these days .. you are asking mostly about an Opinion ..

handling is mostly Trail dimension ..


roll the dice , you can re sell it if not ideal.

I don't memorize the sizes that fit me but do take out the tape measure and check the following before ordering a frame that is the same style as the measured one.

I measure the effective top tube which is the horizontal dimension between the center of the head tube at its top to the center of the seatpost/seattube (depending on tube slope). That tells me if I'll be able to find my fit within the commonly adjustable components (stem, stack, and seatpost). Straying too far from the effective seat tube might result in a bike frame too small to be adjusted properly with a 400mm seatpost or a 120mm stem.

The second measurement I make is from the center of the bottom bracket to the rails of the saddle using the seattube as a guide for alignment. This tells me the fit measurement that works for my legs. Published frame sizes differ on the best way to measure the length of the seattube but it should be fairly obvious that you can't make up for a too small frame if you can't get a seatpost which offers the extension you need AND meets maximum height limitations.

Thanks for the input like I siad the tops frame is what I ride now, the bottom is what I am looking at.

Yeah, you should be able to dial in that new frame no-problem. May need a little more pushback on the seat rails than current, or maybe more layback at the post. Other than that, I bet a component swap would be just comfy (in terms of reach).

The new frame has a half a centimetre longer top tube AND a 1 degree more relaxed seat tube angle. This adds up and is what I would expect to see between two frames which were pretty much the same but with a different seat tube angle. Personally I think the new frame will be better. The more relaxed seat tube angle will take some weight off your hands and shoulders.

If you really want to you could push the seat forwards slightly on the new frame so that the seat would be in the same position as on your existing frame but honestly I would try first with the seat set back first.

Anthony

I think I'm missing something about the assumptions posters above are making. Can't I take the measurements for the new frame given above and end up with the head tube positioned just about anywhere? I mean, I was thinking it could be a bit towards the gran fondo style frame, or a very aggressive geometry, depending on angles that are not given. I thought the only way to truly know would be comparing frame reach and frame stack. As I said, though, I'm likely missing some assumption that makes this all work out.

As for saddle relative to bottom bracket, I can see that being similar on the new bike with the adjustment of moving the saddle forward relative to seat post.

Reach and stack are VERY good measurements for comparing frames. However they are only measuring the frame from the Bottom Bracket forwards. They don't describe behind the BB and saddle position.

I'm comparing seat tube angle and top tube length. Your right that I'm making assumptions yet the data matches what you would assume the results would be given similar reach with different seat tube angles. It's already been noted that the head tube length is different.

Yes, its not exact.

Anthony

Ok, thanks.

The seat tube length difference is not an issue, you just set the new saddle height measuring to the saddle top at the same number. A fine-tuning of a mm or so may be needed later.

The seat tube angle can be significant. The new bike is 73 deg and the current one is 74. If you just take the saddle/seatpost off the old bike and put it on the new, it will be located about 1 cm farther behind the BB (really a plumb line down to the BB center). Your body support will be 1 cm farther back. You might want to move the saddle 1 cm farther forward when you install it. You also might have to adjust the saddle angle - I would have to.

So with the end of the top tube is 1 cm farther back from the BB and the TT length is 56.5 versus 56. The handlebars will be up to 2.5 cm closer to your body if you use your current stem. You might want to experiment with longer stem lengths.

Another result should be that the front-center will be shorter on the new frame, if the fork offset is the same between the two bikes. You can measure that, its the distance from the BB axis to the front wheel bearing axis. It directly reflects whether your toes will clear the front wheel if you turn the fork while your foot is forward. If this toe overlap is a problem for you, there's no fix; you either tolerate it or get another frame. Some folks can tolerate it just fine.

The shorter head tube could mean it is difficult to place the saddle to handlebar drop at the same place as the old bike. Not a handling problem but it could make you bend farther down to reach the bars. OTOH, you might find it more comfortable since the bar is closer to you. Gotta see how that will work out.

Most of it can be worked out, but if there is toe overlap you will be stuck with it. If your toe clearance is generous on your old bike, the new one could be ok. But if now, you might have overlap on the new one. Measure the Front-Center for both bikes and let me know.

Good measurements!

One degree in seat tube angle is probably not going to make a difference, since seat posts allow some fore-aft adjustment. Assuming you set your bike up with about 10 cm of seat post exposed, the 73 deg seat tube will place your seat about 1 cm behind where a 74 deg seat tube would put it. So all you have to do is adjust your saddle 1 cm farther forward, and the difference disappears.

On paper the new frame will offer a more aggressive fit. In practice you can get the two frames to fit pretty close to identical with different stems, and depending on how much room you have to play with on the fork's steer tube.

It all depends on the details - what setback does he need, what is the adjustment range of the saddle/seatpost combination, et cetera.

That 1 cm of extra adjustment might or might not be possible, without a change of seatpost or saddle.