[Foye]

what are peoples thoughts on this. does it really make a difference? seems like the sloping frames are better for people with shorter legs. if they fitter a wider range of people, why are traditional sized frames still made?

 

[ultimobici]

what are peoples thoughts on this. does it really make a difference? seems like the sloping frames are better for people with shorter legs. if they fitter a wider range of people, why are traditional sized frames still made?

They do give a smaller standover height, but generally they are no better or worse than traditional level top tube designs. There are claims that the rear triangle is stiffer and that the frame is lighter, but generally it's marketing hype. The weight loss is offset by the longer seat post. The stiffness is offset by more flex in the post. Compact geometry was originally conceived to reduce the number of frame sizes needed. That was the original TCR designed by Mick Burrows for Giant. S M & L have given way to XS S M L & XL as they found that their theory was flawed. Most other manufacturers have merely sloped the top tube of conventional frames.

 

[C-40]

do a search...

This topic has been beat to death. Manufacturers offer what they think they can sell. Some buyers don't like the look of compact frames. Some "compacts" have a barely noticeable 2cm slope, while others have as much as 6cm.

Compact geometry really doesn't improve the fitting situation very much. People with short legs/long torso who want the bars up high can select a larger frame than they might be able to straddle in a conventional design. Other than that, there is no fit advantage.

If the jumps between sizes are greater than 2cm, there will always be folks who can't be fit without an odd stem length and/or angle, so compact geoemtry can create as many problems as it solves.

Personally, I like the two compacts frames I've owned and I suspect that my future purchases will be compact. Some brands however, miss the mark when neither of the two sizes I might consider have the right combination of reach and head tube length.

 

[Foye]

If the jumps between sizes are greater than 2cm, there will always be folks who can't be fit without an odd stem length and/or angle, so compact geoemtry can create as many problems as it solves.

i am guessing that you are refering to the top tube length when talking about 2cm jumps?

 

[terry b]

what are peoples thoughts on this. does it really make a difference? seems like the sloping frames are better for people with shorter legs. if they fitter a wider range of people, why are traditional sized frames still made?

My #1 reason for prefering a sloping top tube is that I never have to adjust the seatpost height when I clamp my bike in the stand for maintenance. My #2 reason is I think a little slope provides a nice looking bike. Aside from that, no difference whatsoever.

They can certainly help long torsoed/short legged people achieve a more ideal fit. But as said above, for the person with an average conformation they might create situations where oddball combinations of stems and spacers are needed to mimic the fit one would get from a traditional frame. That though applies only to MFGRs who have gone to the XS, S, M, L, XL sizing solution. Which is the reason you'll never see me on a Giant. And that also is the reason that traditional designs still rule. You're far better off with frames offered in 1cm increments.

 

[C-40]

No...

i am guessing that you are refering to the top tube length when talking about 2cm jumps?

When I say "jumps between sizes", it means frame sizes. Frame size is a measurement along the seat tube. The most traditional is center to center, others may use center to top and the real oddballs like Trek and Fuji use the entire seat tube length, which is the least meaningful. The chart linked below is one of the best, where Pcc is the c-c frame size. For a sloping TT frame, there is still a c-c frame size to a "virtual" (horizontal) TT.

Although many folks compare only the TT length for horizontal fit, the proper thing to compare is frame reach (TT length minus setback). In the linked chart, that's Pcc minus Sc. This comparison eliminates errors due to any difference in the seat tube angle, but it's only a valid comparison between frames of the same size. With frames of differing sizes, some additional compensation is usually required.

 

[jimcav]

having both i can only say

i think if you had 2 steel frames the same except for traditional vs compact the compact is actually lighter when built because higher end seatposts are probably lighter than the seat tube--but that is not going to be a huge weight savings--if your frame was carbon or aluminum i am not sure the tubes weigh more or less than a post.

i will say if you like to clamp the top tube on descents--and i do as i get near 40mph then you can't on some sloping designs--for instance my kelly i simply can't sandwich the bar with my legs

other than that i get the same position on all my bikes and i think it will mostly be aesthetics that make you choose one over the other

agree a short leg long torso person may find a larger compact a good fit, not sure else who would really benefit

jim

 

[critchie]

what are peoples thoughts on this. does it really make a difference? seems like the sloping frames are better for people with shorter legs. if they fitter a wider range of people, why are traditional sized frames still made?

Hi Foye,

You've already had a bunch of feedback, but let me address it as well and what some others have said.

First, compact frames can be an aid in fitting short-legged persons to the correct frame size. The claims about stiffer rear triangles (and front ones) are mostly true and are not just marketing hype. True the weight may be offset by a longer seat post, however, it is not true that the stiffness is offset by more seat post flex. The seat post does flex more and that is one of the advantages -- that flex provides additional compliance and therefore additional comfort. It does not change the BB stiffness which is the important factor. More BB stiffness means the bike accelerates quicker. Let us also not forget torsional rigidity in this equation. The shorter tubes lengths of compact frames all help increase torsional rigidity.

Wanting bars up high is really not the issue for short-legged persons. It is that they often require a longer TT than they can properly standover on traditional frames. Do you all remember the fit by which you stood over the bike and lifted it up to your tender bits -- this is/was stupid. Proper fit must first be achieved in the TT length, and just changing the stem and moving the saddle fore/aft is not the correct way. Small adjustments can be acheived this way, but they need to be small -- especially with seat fore/aft adjustments. There is more at play there then just overall reach. Two cm jumps in frame sizes were the rule before compact frames and they mostly are now (thru the middle sizes) -- Giant & Orbea are two examples of those that aren't and this can create problems for some. However, if the sizes they have fit, the fact that they don't have 2cm jumps is not a reason not to buy one.

Things like setback, standover, head tube length, etc. are factors in all fit situations, not just with compact. There are five items that may/may not make compact better.

• increased standover for short-legged riders
• increased frame stiffness
• lighter weight
• increased comfort - that all important seat post flex
• increased power transfer

Some or all of these could be at play with compact frames. I personally find the increased seat post extension the most important aspect -- this definitely increases comfort, especially when using a carbon seat post.

Lastly, we can not forget asthetics -- I personally prefer the look of compact frames.

 

[Foye]

cool. i really appreciate all the feedback that everyone has given. it is definitely helpful to hear from those that are as passionate about bikes as i am.
-foye

 

[alienator]

The claims about stiffer rear triangles (and front ones) are mostly true and are not just marketing hype. True the weight may be offset by a longer seat post, however, it is not true that the stiffness is offset by more seat post flex. The seat post does flex more and that is one of the advantages -- that flex provides additional compliance and therefore additional comfort. It does not change the BB stiffness which is the important factor. More BB stiffness means the bike accelerates quicker. Let us also not forget torsional rigidity in this equation. The shorter tubes lengths of compact frames all help increase torsional rigidity.

You can't just dispose of the geometry of a frame by saying that since the tubes are shorter, rigidity is better. That is simply not the case w.r.t. compacts. The tubes might be shorter, but they also form different angles in the frame. This directly impacts how the frame behaves.

 

[alienator]

The claims about stiffer rear triangles (and front ones) are mostly true and are not just marketing hype. True the weight may be offset by a longer seat post, however, it is not true that the stiffness is offset by more seat post flex. The seat post does flex more and that is one of the advantages -- that flex provides additional compliance and therefore additional comfort. It does not change the BB stiffness which is the important factor. More BB stiffness means the bike accelerates quicker. Let us also not forget torsional rigidity in this equation. The shorter tubes lengths of compact frames all help increase torsional rigidity.

You can't just dispose of the geometry of a frame by saying that since the tubes are shorter, rigidity is better. That is simply not the case w.r.t. compacts. The tubes might be shorter, but they also form different angles in the frame. This directly impacts how the frame behaves.

 

[critchie]

You can't just dispose of the geometry of a frame by saying that since the tubes are shorter, rigidity is better. That is simply not the case w.r.t. compacts. The tubes might be shorter, but they also form different angles in the frame. This directly impacts how the frame behaves.

No one just disposed with the geometry!!!!! See my quote:

Originally Posted by critchie
The claims about stiffer rear triangles (and front ones) are mostly true and are not just marketing hype. True the weight may be offset by a longer seat post, however, it is not true that the stiffness is offset by more seat post flex. The seat post does flex more and that is one of the advantages -- that flex provides additional compliance and therefore additional comfort. It does not change the BB stiffness which is the important factor. More BB stiffness means the bike accelerates quicker. Let us also not forget torsional rigidity in this equation. The shorter tubes lengths of compact frames all help increase torsional rigidity.

I said mostly true. In addition, having a compact frame does not change the geometry. Geometries may be completely unchanged by having a compact frame -- the TT and seat tube may simply be shorter in length. Does this angle of the TT toward the seat tube and its inherently shorter length change the frames behavior -- not likely, but I am certain you will differ, and without any specific testing on a specific bike model using test equipment that is common to the bike manufacturers

 

[alienator]

No one just disposed with the geometry!!!!! See my quote:

I said mostly true. In addition, having a compact frame does not change the geometry. Geometries may be completely unchanged by having a compact frame -- the TT and seat tube may simply be shorter in length. Does this angle of the TT toward the seat tube and its inherently shorter length change the frames behavior -- not likely, but I am certain you will differ, and without any specific testing on a specific bike model using test equipment that is common to the bike manufacturers

By geometry, I mean the angles between the TT & HT & ST; DT & HT & ST; ST & seatstay& chainstays. Those dimensions WILL change. They have to. If the seatstays and chainstays are exactly the same dimensions as they are on a standard frame, then the ST will have to have a different angle to close that triangle. By geometry, I don't necessarily mean HT and ST angles. To completely constrain a triangle you need three angles, three sides, or two angles and an included side.

 

[critchie]

By geometry, I mean the angles between the TT & HT & ST; DT & HT & ST; ST & seatstay& chainstays. Those dimensions WILL change. They have to. If the seatstays and chainstays are exactly the same dimensions as they are on a standard frame, then the ST will have to have a different angle to close that triangle. By geometry, I don't necessarily mean HT and ST angles. To completely constrain a triangle you need three angles, three sides, or two angles and an included side.

Only two angles have to change in the main triangle of a compact frame -- the angle between the HT and TT, and the angle between the TT and ST. There will also be a different angle at the seat stay/ST junction and the angle at which the seat and chain stay converge. I doubt however that these changes have much/any effect on the finished product. Manufacturers must certainly change tubing (carbon, steel, Al, Ti, etc) slightly to account for any torsional changes that occur because of these minor convergence changes.

 

[alienator]

Manufacturers must certainly change tubing (carbon, steel, Al, Ti, etc) slightly to account for any torsional changes that occur because of these minor convergence changes.

So apparently compacts aren't necessarily stiffer, if manufacturers alter tubing. Hmmmmm. Back to the marketing thing.......

 

[critchie]

So apparently compacts aren't necessarily stiffer, if manufacturers alter tubing. Hmmmmm. Back to the marketing thing.......

What? Do you use, because surely you could not have gotten there from what I said. Maybe they make adjustments to decrease stiffness. This is not marketing!!!!!!!!!!! But think what you want.

 

[alienator]

What? Do you use, because surely you could not have gotten there from what I said. Maybe they make adjustments to decrease stiffness. This is not marketing!!!!!!!!!!! But think what you want.

It's not a matter of thinking what I want to think. It's a matter of engineering and science. Using the exact same tubing in a compact and a standard frame, there's NOTHING that implicitly says that the compact will have a stiffer front or rear triangle. What determines that are the starting and ending tube lengths and angles. That's it. Compacts do NOT necessarily have optimal triangles. Saying that they are "mostly stiffer" is stupid at best, because it completely negates the effect of geometry. Changing tube types between a compact and a standard model completely negates any comparison w.r.t. compact vs. standard. It's that simple.

 

[critchie]

It's not a matter of thinking what I want to think. It's a matter of engineering and science. Using the exact same tubing in a compact and a standard frame, there's NOTHING that implicitly says that the compact will have a stiffer front or rear triangle. What determines that are the starting and ending tube lengths and angles. That's it. Compacts do NOT necessarily have optimal triangles. Saying that they are "mostly stiffer" is stupid at best, because it completely negates the effect of geometry. Changing tube types between a compact and a standard model completely negates any comparison w.r.t. compact vs. standard. It's that simple.

It is a matter of what you think! You have done NO engineering studies to indicate that a compact is not inherently stiffer, but you are telling me that it is a matter of engineering and science. Compacts may well have optimal triangles but I did not say they do, and you cannot say they don't.

All the manufacturers claim compacts are stiffer, and it is obvious to even the retarded that a long tube is easier to bend then an equally made short one, so it stands to reason that a compact would be marginally stiffer. We can call it marketing, but unless you have your vaunted engineering and science studies to disprove the manufacturers claims, I am going to believe they are valid.

Lastly, my biggest reasons for liking the compact design were, the improved comfort gained from having the seat post extended and the flex that provides, and I like the asthetics better. Nothing more.

 

[Eric_H]

Slight slope for me

My #1 reason for prefering a sloping top tube is that I never have to adjust the seatpost height when I clamp my bike in the stand for maintenance. My #2 reason is I think a little slope provides a nice looking bike. Aside from that, no difference whatsoever.

Agree with Terry on #1. I generally ride a bike with a 57 top tube and 73 degree seat angle, but my saddle height is not that high. On a traditional frame that means I might only have 10 cm from the bottom of the saddle rails to the top of the seat tube clamp. That is why I prefer a frame with a gentle slope, usually about 5 cm off of what would be a square frame.

Also, having a sloping top tube can provide a little extra clearance if one pedals knees in. I have two bikes with a 5 cm slope, and my winter bike is non-sloping. Every now and then I catch my inner thigh on the rear brake cable guide on this bike, but on the other two it is not a problem.

But in the end, if two frames have the same geometry but one is sloping there will not be any difference in how the rider fits them. A lot of the misconceptions about compact fit came about from the Giants, and their stupid fit system with 3 or 4 frame sizes and then a bunch of stems and seatposts.

 

[alienator]

It is a matter of what you think! You have done NO engineering studies to indicate that a compact is not inherently stiffer, but you are telling me that it is a matter of engineering and science. Compacts may well have optimal triangles but I did not say they do, and you cannot say they don't.

All the manufacturers claim compacts are stiffer, and it is obvious to even the retarded that a long tube is easier to bend then an equally made short one, so it stands to reason that a compact would be marginally stiffer. We can call it marketing, but unless you have your vaunted engineering and science studies to disprove the manufacturers claims, I am going to believe they are valid.

Lastly, my biggest reasons for liking the compact design were, the improved comfort gained from having the seat post extended and the flex that provides, and I like the asthetics better. Nothing more.

Well, I don't have to do any studies because I'm not the idget parroting the marketing-speak. I didn't say that a compact was necessarily this or that. You did. And while it is true that a long tube will flex more than a shorter tube of the same material and diameter under the same LOAD, it is the geometry (i.e. "angles" for the Newtonian mechanics impaired) that determine how the tubes are loaded. THEREFORE, given the same forces and two frames that are exactly the same except for angles and tube lengths, NOTHING can be implicitly known without figuring how the loads are DISTRIBUTED due to the geometry.

I like how you pull your reasoning out of thin air with no knowledge to back up what your saying other than what the sales reps visiting your bike shop have told you.