Sorry, you lost me. Can you exapnd on that a bit?

Yeah, you REALLY don't want that. I had a Suzuki GS1100E back in the day that developed an occilation at high speed and caused me to crash in at 110-mph. It was not a pleasant experience.

RE:>>>Caterham: ..."with "standard" tube diameters, lateral stability in locating the headtube/steerer was too compromised. oversized top & downtubes created a much more stable steering geometry which could be exploited without serious compromise."<<<

i earlier pointed out one of the compact design's major effects as being to significantly stiffen the rear triangle by the shortening of the seatstays & thus creating a very rigid pyramidal structure with the seatpost as its leading "leg" and the main triangle extended forward from the seatube.
using the earlier 25mmTT/28mm DT tubing "standard" in a compact design, the main triangle would be much less resistant to sideloading & twisting than the heavy braced rear triangle,calling into play my premise that the ideal frame should exhibit a smooth, even deflection over it's entire length to minimize the "hinging effect" with detrimental effects to steering geometry,stability and cornering. modern oversized and shaped tubesets increase the TT & DT's resistance to lateral and torsional loads and will reduce the disparity of deflection between the compact's main triangle and that of the rear.

Smaller triangles.

Even Zinn, which specializes in bikes for very large cyclists (over 6'5" which can't be served by an off the shelf bike) uses compact geometry bikes.

Even Rivendell, which specializes in bikes that aren't trendy or fashionable, but appeal to the classic style uses sloping top tube geometry.

However, there are plenty of classic horizontal tube geometry bikes that are both stiffer and lighter than modern compact geometry bikes. Most modern bikes are made in Taiwan/China. The margins on bicycles are razor thin. The quality and materials aren't there compared to what they have been historically (obviously not true at the high end).

Believe it or not you can get a better bike by looking backwards rather than to the current product line.

I have a couple of 'road' bikes. You can't even begin to compare my '89 Cannondale 3.0 to my '04 Giant OCR1 frame. The Cannondale is a 63cm classic horizontal top tube bike. It came spec'd with Suntour Blaze back in the day. A horrible group. However, Cannondale didn't make different frames back then. Their top of the line road bike got the same frame as their bottom of the line road bike.

And its an epic frame. The Cannondale 3.0 was the lightest frame on the planet when it made its debut. It also set the benchmark for being the stiffest frame ever measured on the Bicycling Magazine 'tarantula' jig (back when Bicycling wasn't just a big advertisement or when editorial wasn't dominated by advertising dollars).

My '04 Giant Aluxx OCR1 frame is aluminum. It came on an Ultegra spec'd bike. You'd think the Giant, which was made fifteen years later than the Cannondale would be a 'better' frame. More optimized, stiffer, lighter, etc. Dream on. The Giant has a mass produced Taiwanese compact geometry aluminum frame and is a price point bike based on the components. The frame is nothing special. Its completely forgettable in every way. The only reason I bought the Giant is because they were marketing the XL as fitting up to being a virtual 67cm. Giant no longer makes that claim, and rightly so, the bike fits no bigger than as a virtual 63~64cm. No bigger than the Cannondale (which is 63cm c-c and 66cm c-t, and yes I need that extra 1cm I was hoping to get, more even).

Is the compact geometry Giant stiffer? Lighter? Better?

Nope.

The truth is that the Taiwanese and Chinese bikes being sold for between $1200 and $2500 today take a back seat to frames that were made fifteen years ago, and that's with compact geometry.

Now if you could find me a compact Geometry XXL Cannondale 3.0 frame, well, sign me up...but the Giant OCR1 ain't it, and the carbon bikes aren't nearly as stiff either.

So that's my rant. I've got a modern aluminum compact geometry bike, and a classic high quality American aluminum traditional horizontal geometry bike. The truth is that smaller triangles only make for a stiffer and lighter frame everything else being equal. However, it isn't. You just can't compare a Taiwanese compact geometry aluminum frame with the quality of the classic Cannondale. Its like comparing Wal-Mart Schwinn with bike store Schwinn, only dressing the Wal-Mart Schwinn up with high end components (okay, its not that bad, but its not that far removed as you might think either).

There are epically good bikes that are worth only hundreds of the thousands they used to cost that will embarrass modern production bikes (Klein, Cannondale, etc.).

thanks for the rant,sport!

ps- leonard zinn and grant p use a sloping tt for a reason -an ergonomic one-to raise the headtube,minimizing stack height using threadless steerers

I really didn't want to get into the which is better argument. I mainly was looking for a pseudo-scientifc explaination of why a bike made with a compact frame would be stiffer, not whether stiffer is better. I suppose I could have asked whether riders of compact frames have noticed the increased stiffness but there is a BIG problem with that - most compact bike are modern bikes and are likely to be stiffer because of the larger diameter tubing, oversized bottom brackets, etc and thus the effect of the compact frame design will be masked by the other factors. Somebody might say, "yeah, my compact frame is much stiffer and handles great" but is that because of the compact design or the other factors?

Support a 5ft long 2x4 with two cinder blocks placed under the ends. Stand on it mid span. Measure distance to ground. Do the same with an 8 ft long 2x4.

Assume we'll make two frames out of straight-gauge tubing one with horizontal TT and one sloping. Now consider that you'll have 4 tubes shortened by using a sloping top tube design, assuming all tubes on both frames meet in a fairly typical seatcluster.

Which one would be stiffer?

Sure, the front triangle would be moving away from the "ideal" equilateral triangle, and on smaller frame sizes, the rear triangle would be, but for larger frame sizes, the rear triangles would be moving towards that ideal.

Ok, but the 5ft 2x4 is going to fall on the ground because the cinder blocks can't move. In other words, take a bare seat tube of say 56cm and stick a seat post in it extended out about 10cm and rest the ends on the cinder blocks. Now take shorter seat tube of maybe 48cm or so and a longer seat post so that they both extend to 66cm. AND, make sure they weight the same - that is, use a lighter seat tube for the 48cm one such that the combination of the seat tube and heavier seat post weigh the same and then push on them and see what the deflection is. At any rate I think, as caterham has been pointing out, the interaction of all the various parts is probably more important than any one tube being shorter.

Short of a bicycle engineer coming along to add his 2 cents I think we've beat this topic to death.

Well, actually, all other things being equal, the sloping top tube would be less stiff than its shorter cousin (the level top tube). This is due to the extra length which, as you may know, is a major driver in stiffness.

For the sake of simplicity, let's assume we're making a bike for 200 ft. standing sprints. Rules for this hypothetical new event don't require saddle, yet require a diamond frame bike.

Now build your two hypothetical frames, do your 200 ft sprint and measure BB deflection.



oh, BTW, you can move one of the cinderblocks in the 2x4 test, just as we'll be moving the seatcluster while we build our compact frame.

This is dependent on ST angle, if I'm not mistaken. If we're making a frame with a 90 degree ST, then the sloping tube would be longer, for sure. On my Mongoose, a hypothetical horiz. TT would be approx a 1/4" longer than the sloping one it was born with.

Sounds backwards -- why would a sloped TT be longer than a horizontal TT on two bikes of the same size and geometry?

I'm sure you're correct.

I was thinking of a sloped top tube that goes very far down, near the bottom bracket (a ladies frame).

A Rivendell isn't a compact geometry bike at all. A compact geometry bike has the head tube in the traditional position and the top tube slopes downward creating smaller frame triangles. A Rivendell is sized at the absolute largest frame one can possibly stand over, including with some 'discomfort'. The top tube does not run down from the head tube, so much as the top tube runs up from the seat collar to an elevated head tube. Much like what a bike with an add on Serotta Heads-Up looks like. However, almost all Rivendell bikes go out the door with beautiful lugged quill stems, or Nitto Technomic quill stems. The founder of Rivendell definitely is NOT a fan of threadless.

Zinn definitely incorporates compact geometry principles into his Project Big bikes. He also uses elevated head tubes. Zinn stocks carbon forks with 450mm steerer tubes. However, the reason Zinn utilizes compact geometry has nothing to do with the extended head tubes. The compact geometry allows the fabrication of very large frames without having to use as much frame material, granting all the benefits of a smaller compact geometry frame, only with increasing returns of stiffness and lighter weight. The elevated head tube has nothing to do with the use of compact geometry. You can use an elevated head tube on a classic geometry bike (Riv does, Zinn did, and does).

You can extend the head tube of either a compact geometry bike or a classic geometry bike with a head tube extension (either a Serotta Heads-UP or a similar product).

At the end of the day an extended head tube (or not) has nothing to do with compact geometry.

Ever heard of the Pythagorean Theorem?

When talking about the advantages of compact geometry versus vintage classic geometry bikes its easy to say that modern aluminum frames with compact geometry are obviously 'stiffer' and thus the design (the compact geometry) is the reason.

This clearly isn't the case. Vintage lightweight steel bikes with classic geometry, when ridden today, can not be reasonably be compared to modern aluminum bikes, with shaped and ovalized down tubes, oversized tubing, larger head tubes, and superior engineering. The truth is, for all the ranting from the 'steel is real' crowd, a vintage steel frame just can't begin to compare to a modern frame. Its completely inefficient in terms of transferring wattage to the ground, the amount of bottom bracket flex and chainstay flex is unreal.

However, you don't have to compare vintage steel lightweights to learn that. When Cannondale and Klein changed the paradigm with oversized aluminum bikes it completely rewrote the standards for frame weight, stiffness, strength, and efficiency. Bicycling Magazine used to have a 'tarantula' test jig for measuring frame stiffness. The Cannondale 3.0 frame was the stiffest frame ever measured.

People enjoy riding steel bikes. People certainly enjoy riding vintage steel bikes with period correct kit and components. Another great way to enjoy cycling. However, no one rides steel bikes because of the 'performance' they offer. Quite simply steel bikes were cheap to produce, required almost no specialized labor to craft (unlike Aluminum and Carbon fabrication), and resulted in a very compromised ride.

Comparing a vintage steel classic geometry bike to a vintage aluminum classic geometry bike (Klein or Cannondale) will reveal the inherent disadvantegeous of the steel bikes, and reveal why any discussion of compact geometry versus classic geometry absolutely should not involve any consideration of steel bikes, vintage or otherwise.

However, all that being said, compact geometry bikes are stiffer than classic geometry bikes. All other things being equal (shaped and ovalized downtubes, identical frame tubing, identical chain stays, etc.) a compact geometry bike is going to be lighter, stiffer, and stronger than its larger classic counterpart.

Its simple engineering really.

Years ago GT came up with their triple triangle concept. It was mostly marketing, but not entirely.

The larger the frame size the more significant the benefits of compact geometry (as compared with classic geometry). Very small frame sizes have such small triangles to begin with that the benefits are minimal in comparison with larger frames.

This is kind of funny.

With tandems some 'racing' tandems get rid of the additional tubes (lateral tubes) to save weight. Removing lateral tubes on a tandem saves about 400g on the bike. The average racing tandem weighs between 12000 and 18000 grams. The really funny thing is that the couples and tandem teams that own these 'open' design tandem frames swear (from their seat o' the pants meter) that the bikes are just as stiff (if not stiffer) than equivalent tandems with lateral tubes. Apparently when you spend between $6k and $12k on a tandem, its not easy to acknowledge that you bought something that doesn't make sense on paper. However, there isn't really a competitive advantage in having a stiffer more efficient tandem in racing, because the tandem racing cult all seem to buy 'open' design bikes.

Bill McCready of Santana Bicycles has spent serious time and money researching frame designs, and testing comparable designs (overbuilt frames sans lateral tube, standard tandem design, etc.) and determined using benchmark testing and real metrics that the loss of the tubes results in removing "a tandem's lateral tubes to make it lighter, because the resulting bike will have a lower level of pedaling efficiency, it will also be slower. While lighter or weaker teams might not be able to detect the loss of performance---repeated scientific testing shows that no competitive tandem team is so light or weak that they should prefer a frame without laterals." (Source)

The irony being that no one has done more tandem frame testing than Santana, and they still produce frames that are significantly less efficient and noticeably flexier than other tandem makers.

Triangle size is very important on tandems, where the frames are subject to twice the drivetrain forces of a single bike. You can actually see a steel tandem torque itself laterally from the wattage the team produces.

However, there are unusual bikes that have open designs, that are effective. Bikes like Co-Motion's Periscope, and Bike Friday's Twosday. McCready acknowledges why these 'open' designs work: "Other tandems lacking laterals...are frames of exceedingly small stature. In this group I include Bike Friday's "Two'sday" and Co- Motion's Periscope. What these smaller "open" frames have in common is that there isn't much room between their top and bottom tubes." (Source)

So what is all this talk about tandems in a thread about compact geometry? Its relevant empirical proof that compact geometry makes sense, and allows builders to make lighter, stiffer, and stronger bikes with compact geometry than they could with otherwise classic geometry.

Tandems are the ultimate torture test of bicycle frame design. Every production tandem made utilizes 'compact' geometry, or some variant geometry to a great extent. Tandem frames utilize significantly longer seatposts, and typically higher stems than do normal single bikes.

There is a reason for this. Smaller triangles.

The frames of UCI pro roadies are some of the stiffest bicycle frames made. They are about pure efficiency, getting the produced wattage onto the road, with minimal compromises. Racers absolutely do not want to introduce 'flex' into their frames.

What they do want is bikes that don't compromise efficiency for the sake of comfort.

A steel bike, aside from the nonsense you'll hear from the 'steel is real' cult, is just generally inefficient, and just generally flexy. The benefits of comfort come at the cost of pedaling efficiency and stiffness. If you don't believe this to be true go test ride a Santana steel tandem some day then go hop on a Cannondale tandem and the difference will be beyond evident.

A modern race bike can utilize a carbon front fork, a carbon seatpost, a carbon stem, and carbon handlebars to contribute to racer comfort. The frame itself is all about performance, not comfort.

However, carbon frames can be laid so that there is vertical compliance without any compromise of lateral compliance or drivetrain efficiency. Essentially building into the bike 'micro' suspension for the cyclist isolated from the drivetrain. This is possible, to a lesser degree, with titanium frames as well (ti can be made stiffer than carbon or aluminum, or made merely to be 'better' steel).

As for Mountain bike suspension frames. These are the stiffest and strongest frames of any bicycles. The frames are designed oversized and overbuilt, and are specifically engineered to not flex, but rather, to let the suspension absorb the riding surface irregularities and impacts. The frames on these bikes are off the scale in terms of how small the rear triangles are, how stiff the frames are, and how strong they are.

You can use inferior frame materials like steel, and make them less inferior with compact geometry. You can also take epic frame designs made from Titanium, aluminum, and carbon and make them even more legendary.

He was right and I was wrong. I was shooting from the hip but had a conceptual error, probably the same one you are making. The head and seat tubes are canted relative to the horizon. The top tube is shortest when it intercepts those two tubes at a 90 degree angle, not the 72 degrees typical of many frames.

Yes, actually, I have; have you ever used it in a real world example?

correct. i offered my elaboration because your disjointed & confused name dropping of Zinn & Peterson for the sake of feining authority made no sense in the context of this discussion.
It's also noted from your most recent posts that you haven't sobered up in the interim.