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I am looking to buy a new bicycle but don't know whether to go with compact or traditional geometry, please discuss this and tell me the applications and reasons for both types of frames as I'm confused

Thanks :)
 

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trivial difference..

You should buy a frame that fits. Riders with short legs and long torso can sometimes benefit from the increased standover clearance the a compact provides.

Many brands have a reduced size range on their compact frames. Instead of the common 2cm increment, some brands have increased the gap to 3cm between sizes. That can result in a goofy looking setup for some.
 

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Sloped top tube

TI_roadracer said:
My recommended top tube is 570. What would you go for, a 560 scott, 575 scott or a 570 giant?
So-called "compact geometry" consists of a sloped top tube. It has minimal effect on anything, except offering more standover height for a given top tube length. Given the variables in fitting a frame, the three you mention are functionally equivalent regards the TT length affecting total fit.
 

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meaningless...

A TT length without a seat tube angle to go with it means nothing. Every degree steeper STA lengthens the effective TT by about 1cm. Also, buying just by TT length is a mistake. You should always look carefully at the total head tube length, with the headset, to avoid a goofy looking stem and spacer setup.

Among the frrames you've mentioned, the Giant's head tube is 160mm, while the Scott's are 170 and 190mm. The Giant's slack 72.5 STA makes the reach about the same as the smaller Scott. The XL Scott is both longer and much taller than either of the other frames.

You didn't mention a stem length to go with that 57cm TT either. That could make a difference in the selection.
 

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titanium junkie
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???

C-40 said:
A TT length without a seat tube angle to go with it means nothing. Every degree steeper STA lengthens the effective TT by about 1cm.
Did you have this backward? A steeper seat tube angle means 75 degree vs. 73 degree? Steeper means more angle while slacker means less angle, right? If you hold the front triangle constant but rotating the seat tube relative to the BB from 73 degree to 75 degree, then you will end up with a shorter top tube, not longer. Correct me if my logic is incorrect. :confused:
 

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wrong...

The fit of a bike frame is compared with the rider (and his saddle) in a given position relative to the BB. With a slack (numerically smaller) STA, the saddle must be moved forward to achive the same position as it would on a frame with a steeper STA. This saddle movement makes the reach shorter.

This is one of the most common mistakes that can lead to some real surprises if you expect a frame to be 1cm longer and it turns out 1cm shorter than anticipated.

As an example, I've got one frame with a 72.5 STA and 54cm TT. It's actually about 2mm shorter in reach than my other frame with a 74.5 STA and 52.5cm TT.
 

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absolutely....

These two frames have the same head tube angle, the same head tube length, stem length/angle and spacer setup. The only difference is the frame with the 72.5 STA requires a no-setbacl post (Thomson).
 

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C-40 said:
These two frames have the same head tube angle, the same head tube length, stem length/angle and spacer setup. The only difference is the frame with the 72.5 STA requires a no-setback post (Thomson).
Perhaps these two drawings will help everyone understand what C-40 is talking about. (all dimensions in cm).
 

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So the only benefit of a compact frame geometry is to have more standover space? Why is this so important that most if not all modern road bikes are compact? I personally do not like the look of a compact frame, it looks too much like a mountain/hybrid bike. I still very much appreciate the beauty of a tradtional road bike, especially with good O' steel tubing.
 

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titanium junkie
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C-40 said:
The fit of a bike frame is compared with the rider (and his saddle) in a given position relative to the BB. With a slack (numerically smaller) STA, the saddle must be moved forward to achive the same position as it would on a frame with a steeper STA. This saddle movement makes the reach shorter.

This is one of the most common mistakes that can lead to some real surprises if you expect a frame to be 1cm longer and it turns out 1cm shorter than anticipated.

As an example, I've got one frame with a 72.5 STA and 54cm TT. It's actually about 2mm shorter in reach than my other frame with a 74.5 STA and 52.5cm TT.
Thanks for the insight! I still don't buy into this theory yet but what do I know!
 

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kdub said:
So the only benefit of a compact frame geometry is to have more standover space? Why is this so important that most if not all modern road bikes are compact? I personally do not like the look of a compact frame, it looks too much like a mountain/hybrid bike. I still very much appreciate the beauty of a tradtional road bike, especially with good O' steel tubing.
I'm sure this will be corrected but....

I think one idea behind compacts was to allow more "sizes" to be available with fewer available incremental sized frames. Meaning one size in a compact could fit a greater range of people than a traditional frame. Since they are also using less material they can be made cheaper (and some of this cost savings gets passed on to the consumer??).

The other thing I believe to be true is that the frames, in some ways, can be made stiffer (tortionally & laterally) with the smaller front triangle.

I'm no expert but these are my thoughts perceptions. Someone else may have some real data to back up or disprove the above.
 

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titanium junkie
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kdub said:
So the only benefit of a compact frame geometry is to have more standover space? Why is this so important that most if not all modern road bikes are compact? I personally do not like the look of a compact frame, it looks too much like a mountain/hybrid bike. I still very much appreciate the beauty of a tradtional road bike, especially with good O' steel tubing.
Beside all the benefits mentioned, a compact geometry also has a lower center of gravity, which makes the bike more stable and accelerate more confidently. Also pointed out, a road bike with a compact geometry resembles a mountain bike, which gives it a rugged look, but that is strickly for looks. With everything said, the biggest benefit with a compact geometry would probably be stand over height, which can be made to accomodate more variety of riders.

Cheers!
 

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merckxman
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Compact Lugged Steel Bike

I picked up this made in Verona, Italy, CHESINI bike as I found it to be interesting. It's a compact design made in 1994. Nice EL-OS steel with an interesting top tube-seat tube lug. A future project....
 

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soy un perdedor
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tigoat said:
Thanks for the insight! I still don't buy into this theory yet but what do I know!
C-40 is correct, and I would not describe this as a "theory". Understanding how STA and TT length are related is essential to bike fitting.

My rule of thumb:

use 73.5 STA (or whatever your current bike has) as a baseline
Subtract 1 cm for every degree slacker (ie 72.5) or add 1cm for every degree steeper to the listed toptube length. It works out pretty close. I believe for a 56cm bike it's really about 9mm.
 

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A lot of the compact frames available today, such as those from Specialized and LeMond, have not only a sloping top tube but an elongated head tube (compared with a traditional frame) as well, and that's where the dorky look comes from. Compact frames with a normal-sized head tube and slightly-sloping top tube look cool. I think the rise in popularity on compact frames comes from the fact that: 1). they cam be made in fewer sizes, 2). they cost less to make (but don't expect the savings to be passed on), 3). they look sort of like mountain bikes, 4). they can be made lighter and stiffer, and 5). a response to lawsuits claiming that the high top tubes of conventional frames were dangerous (easy to crush your manly bits if you slip off the saddle).
 

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You're Not the Boss of Me
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tigoat said:
Beside all the benefits mentioned, a compact geometry also has a lower center of gravity, which makes the bike more stable and accelerate more confidently. Also pointed out, a road bike with a compact geometry resembles a mountain bike, which gives it a rugged look, but that is strickly for looks. With everything said, the biggest benefit with a compact geometry would probably be stand over height, which can be made to accomodate more variety of riders.

Cheers!

Lower center of gravity? I just don't see how that can be true. The BB height will be the same, as will the seat height. The "center of gravity" involved with bike and rider will be the same whether the TT slopes or not.

And as for being more stable and accelerating better, that's just marketing hype. Compact geometry helps some folks (the short legged folks) with fit but is otherwise generally merely an aesthetic issue. There's a debate as to whether it can create a modest weight savings (shorter seat tube, but longer seat post) but that's about it.
 
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