the5h4rk

as a newbie to this forum, a budding young cyclist, and an engineering student, i am rather intrigued by the varying frame geometries going around and their 'claimed' structural advantages.

i donk know who pioneered it, but it appears giant along with a few others have taken the compact design under their wing and use it almost exclusively in all their bikes. if compact frames are as soo good, then why arent all bike manufacturers making their top of the line bikes in compact frames? and why didnt everyone figure this out decades ago?!

what do people mean when they talk about 'aggressive geometry' and 'relaxed geometry'?

and what geometry is best for handling, speed, acceleration, comfort, stiffness, strength/weight?

...and what do you prefer

cheers

AndrewP

The compact geometry, or small frame size, makes the rear triangle, stiffer laterally, which gives more precise handling on corners. This results in longer seat post extension which gives more flex in that area, so any benefit one way or the other is marginal. 'aggressive geometry' and 'relaxed geometry' usually refer to the angle of the steerer tube and resulting steering trail. The steeper the angle the shorter the trail and the twitchier the steering - good for rapid manoeuvres. Relaxed geometry is what you want on a tourer or if you want to use your hands for carrying your groceries rather than steering. Relaxed geometry bikes will also have a longer wheelbase.

humble_biker

Andrew is right but what you have to remember is Giant is one of the largest bicycle manufacturers in the world and created the compact geometry to limit the number of frames thay have to manufacture. There decreasing their over head expenses.

SeattleTom

IMHO, the compact frame is primarily a style thing, a way to sell a bike that looks distinctively different from what's come before. There's a much bigger difference in the materials and workmanship than in the inherent difference between a 'compact' and 'regular.'

WRT relaxed vs. aggressive geometry, AndrewP summarized it well. Again, the difference is moderate, and the geometries change over time. I'd say that an 'agressive' geometry is what you want if you plan on racing in criteriums, 'relaxed' is what you want if you're going to by riding centuries. But without going around with a protractor, you're going to have a hard time telling the difference. And, different tires, wheels, handlebars, and plenty of other variables will make as much or more difference than the geometry.

sch

Although Andrew is certainly correct, I suspect the real reason is humble bikers. You have to know that the compact geometry originated in the ATB bike in the '70s and '80s as a way to allow the front fork to rise up without lifting the rear so high. By compressing the seat tube the frame could be kept in the usual range of bike rider heights for stand over correlating with roughly 58-72" rider height. The other advantage of the frame is that it greatly simplifies the number of jigs the manufacturer needs to make the frames as 3 frame sizes will cover the rider height range listed, and adding a size under and over allows coverage down to the 52-54" tall at the bottom and 77+" at the top. The resulting 4-5 frame sizes compared with classic road frames where covering the 48 to 64cm size range in the frame with increments of 2 cm requires 8-9 frame sets and jigs. LBS really appreciate not having to stock 5-6 frame sizes also instead of the 3 needed for compact. The occasionally shorty (sub 60") or giant (above 76") quickly find they will have to special order a bike, at least until the WSD bikes came along. So the compact evolved from the ATB in an era when ATB bikes were outselling road bikes by 5-8x and makes life a lot easier for the manufacturer, the LBS and the customer. Nowadays, the proliferation of odd tubing by the metal frame builders and CF designs using foam and mandrel techniques means that jig numbers are no longer a limiting consideration at least for bikes above the 2500 to $3000 range. Bikes sold in this range are a very small part numerically of the market, but a big profit center for everyone.

bloodhound

Can you (anyone) give example(s) of a road bike ($1k - $2k range) that would be considered a 'relaxed geometry' bike in the XL (60-64cm) frame size?

This is exactly the thread I was looking for.

moxfyre

I, for one, think that compact frames are ugly. "Give me a horizontal top tube, or give me death." I think the main reason for compact frames is to save money by producing fewer sizes. I think that, mechanically, there is nothing wrong with compact geometry on racing bikes... and if it saves the customer some money, it's a good idea.

But for a *practical* bike, a commuter bike or a touring bike, compact geometry offers other problems: (a) less space in the main triangle for mounting water bottles, (b) seat stays are often too low to mount a rack easily and sturdily. If you look at touring bikes, such as the Trek 520 or Surly 520, they all still use the classic horizontal top tube geometry.

Agressive geometry would mean twitchier steering (steeper head tube => less fork trail), shorter chainstays, and a shorter wheelbase for tighter turns. Relaxed geometry is more or less the opposite.

One of the nice things about long chainstays is that it makes for a smoother ride, since the rear wheel effectively has less leverage on the saddle, thus reducing the magnitude of bumps reaching your butt! Also, many racing bikes have such short chainstays that it's not possible to use tires wider than 25 mm, or to mount fenders

If I had just one road bike, I'd *definitely* make sure it had touring bike or cyclocross geometry. That makes for a more comfortable, stable, and practical bike (since it will have mounts for rack and fenders, and can take wider tires). As it is, I have two geared road bikes, one is a touring bike and the other a racing bike. The touring bike is NEARLY as fun and NEARLY as fast and NEARLY as maneuverable as the racing bike... while the racing bikes is NOT nearly as comfortable or as practical as the touring bike.

I consider the touring bike geometry to be the best for all around use! I'd have no qualms about taking my touring bike out on a 30 mile club ride, but I am definitely glad I don't commute on the racing bike.

bloodhound

So is the Specialized Roubouix(sp?) an example of a 'relaxed geometry' bike?

grolby

Actually, the Surly "520" (I think you mean the LHT) doesn't have a level top tube. It slopes downwards a bit from the front, though not enough to qualify as compact or semi-compact geometry. This is a feature it shares with many Rivendells, presumably to make it easier to get the bars up higher.

Touring bikes and many cyclocross bikes not designed for competitive racing have slacker angles and more relaxed handling than road racing bikes. Older road bikes and road bikes intended for more practical or less aggressive use will also have gentler handling characteristics. Compact or traditional geometry has little to do with this. A stiffer rear end, even if it is of some benefit to the rider, doesn't contribute to more aggressive handling tendencies. One of the major benefits of compact geometry is to the manufacturer, who only needs to make the frame in a few sizes in order to cover the full market. Racers might get some benefit from the reduced weight and increased stiffness. Maybe. Other than that, it really doesn't mean much. I happen to like the look of traditional geometry, which might be one reason that I end up with so many old bikes!

Ray Dockrey

Yes, and so is the Trek Pilot series.

Al1943

+1

TallRider

I think Rivendell is partially responsible for getting the current "road sport" trend rolling. They produce beautiful and expensive bikes, but have more relaxed angles (and handling), better for a somewhat more upright rider posture, and have more space under the brakes for larger tires and/or fenders. Trek and Specialized etc. started producing their road-sport lines (Pilot and Roubouix, respectively) after Rivendell's philosophy had gotten "out there" a bit.

Another recommendation is the Soma Smoothie ES. Comes in sizes up to 66cm. I've not heard much feedback about it, but the few things I've heard sound like a very good bike, and it looks great on "paper" (or online).

moxfyre

Wow... you're right. Those @#($@#$ Surly people... sellouts!!! Nah, just kidding, I think the LHT frame still looks good!

bigbossman 

Giant OCR series
Trek Piliot Series
Specialized Roubaix (I think)

gpelpel

I agree with others that the head tube and seat angles are what defines a bike handling and comfort characteristics. A slopping vs a traditional top tube doesn't change much except for helping the manufacturer reducing the number of frame sizes and thus production costs.
In the Specialized line there's a difference of 1 degree on the headtube angle between the race frame Tarmac (73.5) and the more relaxed Roubaix frame (72.5). Their seat tubes angles are the same.
In general the lower the headtube angle the more stable the frontend/direction is. A pure racer bike will tend to have an higher angle thus a twitchier frontend. The fork rake (distance between fork end and straight line coming down the headtube) has also to be considered though as a fork with more rake will compensate for a steepier headtube.
On the seat tube side, the lower the angle the more comfortable the bike.
Even within frames in the same category, such as racing, you will find different angles depending of the designer philosophy and preferences.
That's mainly why it's recommended to test ride different bikes before buying.

Moose

Raleigh Cadent
Giant OCR
Bianchi Coast 2 Coast
Trek Pilot
Specialized Roubaix
Felt Z-Series

operator

Why did they switch to compact?

Because it's cheaper.

End of story.

The rest are just ancilary benefits that came after the switch.

Moose

This attitude, that "Big Bicycle" just makes sweeping changes for their own benfit, then forces it down the consumer's throats, really annoys me.

I love classic bikes but the bicycle industry could not thrive if it were pumping out the same old thing year in and year out instead of coming out with new designs each year.

The fact is there have been plenty of changes, driven by many factors, that have made modern bikes more enjoyable and accessible.

kranz

Is a compact frame any less prone to high speed wobble than a traditional geometry?

operator

That's impossible to say because the wobble depends on a million things as well as frame geometry.

TallRider

No, In principle it's actually entirely testable, and I'm guessing that bike companies have done such tests. Produce identical frames aside from sloping vs. horizontal top tube, outfit them with the same components, etc. To my knowledge, the factors for high-speed wobble are well-enough understood (by engineers, not by me) and so this is a question they should have some purchase on it.
But I'd say that high-speed wobble shouldn't afflice well/carefully-designed frames, compact or traditional.

wahoonc

It is at least partially true.

Why not? It's not their fault that the advertising types and the American public (in general) has been brainwashed into thinking newer is better. FWIW I very seldom buy something the first year it comes out, I wait for it to be proven...and go on sale. Plus the fact the "average" bicycle purchase in an LBS is by a WM between 34-46 with a high5 to 6 figure income.

I agree that there have been advances, and some of them have been great. LED lighting, better generation systems, better brakes, better tires. But some really don't help the average rider; gears in excess of about 5 are overkill for all but the experienced touring or racing rider. I bought into this theory 30 years ago and just now am coming to my senses. Index shifting is another mixed bag it is good but also can be the source of many problems.

Aaron

operator

Sorry don't buy it. Theoretically you can predict such things but in real life you can't, rider positioning, wind, speed, current state of parts. You can't predict this stuff even with a super computer.

Anyways here's jobsts take on this; https://yarchive.net/bike/shimmy.html