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Old 09-22-11, 11:35 AM   #1
cpsqlrwn
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Relaxed Fit or Geometry - What does that mean exactly

I am often perplexed by the phrase "that bike has a relaxed fit or geometry". When I hear this the first thing that comes to mind is a lower (slacker) seat tube angle which results in a less upright seat tube which results in a longer top tube length and is usually accompanied by a longer wheel base. This is supposed to result in a more confortable ride ("an all day ride").

Is this more comfortable ride due to the longer wheel base which surely results in more stability or is it also linked to where you end up sitting in relation to the entire length of the bike?

What perplexes me is this. In terms of your riding position, I have always been taught and told that your position in relation to the pedals (or bottom bracket) should be more or less the same across different bicycles because that position is directly related to your pedalling efficiency and strength. Once you find that sweet spot for strength and efficiency, you should always try to achieve that same position in relation to the bottom bracket (assuming consistent crank arm lengths). If that is the case, then with a relaxed geometry bicycle (slacker seat tube angle), it would seem to me that one would need to move the saddle forward to achieve that same relationship to the bottom bracket position. That would end up more or less putting you in the same position in relation to the handlebars (you would effectively be shortening the top tube length on the relaxed fit geometry bike) and your reach to the bars would be similar to the reach you would have if you were riding on a racing geometry bike (shorter top tube, steeper seat tube angle, saddle a bit further back). So how is the ride more "all day" comfortable when the cockpit is essentially the same? Is it the longer wheelbase that everyone is referring to when they talk about a relaxed fit or geometry? I know when I think of relaxed fit or comfortable riding, I think of a bike that pushes the upper limits of my size threshhold which allows me to ride with a somewhat lowered saddle (in terms of seatpost showing) and thus causes the handlebars to be a little higher in relation to the saddle. This does two things... It allows me to ride a little more upright (more RELAXED) and it shortens the reach to the handlebars (if I leave the stem height constant) without altering my saddle position in relation to the bottom bracket. As the saddle is lowered a little more in the seat tube it comes forward toward the handlebars but still achieves the same position in relation to the bottom bracket because the frame is just a little taller. The distance from the bottom bracket to the saddle is the same, it's just made up of more seat tube and less seat post. As the saddle is lowered further into the seat tube it is brought closer to the handlebars due to the seat tube angle, but ultimately, when the saddle is at the proper riding height with less seat post showing, it is in the same position as it is on a smaller frame in relation to the bottom bracket and pedals.

Looking for comments on this "relaxed" geometry, what it really means, and whether what I am talking about here is just all gibberish or makes any sense.

I guess another question that might pertain to the relaxed fit issue is whether bottom bracket height is a factor in relaxed geometry or relaxed fit. That would affect this whole discussion as varying bottom bracket heights would directly impact saddle height. I've never really looked into that.

Last edited by cpsqlrwn; 09-22-11 at 11:44 AM.
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Old 09-22-11, 11:56 AM   #2
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I'd think typically "relaxed" would mean less steep head and seat tube angles, longer chainstays and greater fork rake, which would result in a longer wheelbase, but not necessarily a longer top tube. I believe all this results in a more comfortable, less jarring ride than a shorter, more upright bike.

Proper fit (and weight distribution) are affected by the angles and seat tube/ top tube lengths but can also be adjusted by stem length, seat fore and aft and seat height (probably the only consistent position I shoot for).

The concept of knee over pedal spindle is a fine concept, but I've always used it only as a starting point. Imagine the rider on the bike pivoting in a circle from the bottom bracket as the bike goes up and down the terrain and you'll see knee over pedal only applies to the totally flat. I believe what's more important is proper weight distribution front to back. Too much weight to the front and you'll be hard pressed to ride all day. That's where I resort to sliding the seat back and testing stem length. Typically, my seat is back of bit, but I'm big.

Your position is not constant anyway. You might be on the front of the seat climbing and to the back of the seat cranking.

Back when I started riding in the 70s, my racer friends usually preferred a frame 1/2" to 1" smaller than they normally would ride: smaller, lighter and tighter. Contemporary bikes seem to have returned to that concept. The very little seatpost showing was more of a touring concept.

But assuming the cockpit is the same, its going to be more comfortable because its more compliant: less rigid and upright, more stable but less responsive, which I've never really found to be a problem.

Last edited by dbakl; 09-22-11 at 11:59 AM.
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Old 09-22-11, 12:03 PM   #3
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I'd think typically "relaxed" would mean less steep head and seat tube angles, longer chainstays and greater fork rake
Fork rake is something I know next to nothing about and I have no knowledge as to what effect differing fork rakes have on handling and comfort.
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Old 09-22-11, 12:12 PM   #4
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Fork rake.

Think of a panel van in which your nose is inches from the windshield as you drive.
Then get behind the wheel of a Jag XKE where the front wheels are a first down away.

Tight rake means you slightly move your bars and you were there already.
Touring rake means you turn like a large boat.

Does that help?
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Old 09-22-11, 12:14 PM   #5
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Fork rake.

Think of a panel van in which your nose is inches from the windshield as you drive.
Then get behind the wheel of a Jag XKE where the front wheels are a first down away.

Tight rake means you slightly move your bars and you were there already.
Touring rake means you turn like a large boat.

Does that help?
Yes and there's a good article here (http://www.phred.org/~josh/bike/trail.html) about it. Seems more to do with handling and responsiveness than the concept of relaxed fit or geometry.
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Old 09-22-11, 12:31 PM   #6
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Seems more to do with handling and responsiveness than the concept of relaxed fit or geometry.
Other than rake is derived from head tube angle: they work hand in hand.
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Old 09-22-11, 02:28 PM   #7
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Well, in fairness, it begins with the head tube angle and is then completed by the bend in/of the fork blades.

In any event, geometry IS about fit, handling and responsiveness. Using "relaxed" has become more of a sloppy slang, but we generally know and accept that to what it refers as understood.
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Old 09-22-11, 02:43 PM   #8
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I don't think shortening the reach to the bars will make the bike more comfortable. Until recently I've been riding with stems that were too short (~90mm) and went to 120mm stems, the difference in comfort is huge. I think reach is one of those things that should be close to the same. Handlebar height relative to the saddle on the other hand is something that I've found to be very important as far as comfort, since if the bike fits you right, you are using your back/core muscles to hold up your torso (your elbows should be bent some, and there shouldn't be an uncomfortable amount of weight on your hands).

I think you are right that a taller frame can be more comfortable because of the handlebar height. I'm not sure if the reach is actually decreased because the seat is lower, since you will need to compensate for the saddle fore/aft position either way.

Anyhow, to get to the point, I don't think the frames geometry itself makes the bike more comfortable, I think it's really just a matter of fit. A touring bike might be more stable feeling or compliant than a racing bike though.
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Old 09-23-11, 08:52 AM   #9
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Looking for comments on this "relaxed" geometry
Doesn't really exist on classic racing bikes. Thats why they are so beautiful.
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Old 09-23-11, 08:56 AM   #10
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relaxed fit or geometry = less butt up, nose down riding position.
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Old 09-23-11, 06:39 PM   #11
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I'm just guessing here but I see two things happening.
First is that a bike with more rake and trail will be more docile in steering and less twitchy. Easier on the attention span.
The longer fork blades, seatstays and chainstays will flex more absorbing some of the vibration.
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Old 09-23-11, 08:49 PM   #12
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I'm just guessing here but I see two things happening.
First is that a bike with more rake and trail will be more docile in steering and less twitchy. Easier on the attention span.
The longer fork blades, seatstays and chainstays will flex more absorbing some of the vibration.
No, More fork rake = less trail. Trail outside of the normal range produces odd and undesirable handling characteristics, not simply relaxed or quick steering.

One of the best explanations I have seen on effect of trail is;
http://www.spectrum-cycles.com/geometry.php#trail

Steep or shallow head tube angles can be used to produce a more relaxed or quick steering feel, but headtube angles outside the normal 73+/- 1 range should really have a fork with rake customized to produce normal trail for neutral steering. All to often these days, a bikes are speced by manufacture with a standard fork without any real regard to the rake of the fork. Typically same rake fork will be slapped on a 49cm bike as their 62cm bike even though head tube angle is drastically different.
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Old 09-23-11, 08:55 PM   #13
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bikes with longer wheelbases are more "stable" and tend to go straight more easily

more slack angles mean less road force is delivered directly to your body
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Old 09-23-11, 10:26 PM   #14
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Relaxed:

Not relaxed:

Very relaxed:
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Old 09-24-11, 04:30 AM   #15
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did someone say fork rake?

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Old 09-24-11, 04:51 AM   #16
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So maybe some generalizations can be made (with due trepidation):

"relaxed" = seat tube angle 71 to 73 degrees with trail in the 45 to 55 mm range. Realize trail will be influenced by fork offset (aka rake), head tube angle, and front wheel diameter. One common consequence of a laid-back (numerically low seat tube angle) seat tube is longer chainstays (41 to 45 cm) to provide adequate wheel and fender clearance at the seat tube. A result of that is to extend front-center (long TT, numerically low head tube angle, higher rake) to ensure proper front/back weight distribution. Hence relaxed bikes often have a long wheelbase. For long-distance tourers, light or heavy, the BB drop is often close to 8 cm, which also tends to make a longer chainstay.

What's an example of a bike with nearly all of these characteristics? A Peugeot UO-8, early '70s.

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Old 09-24-11, 05:01 AM   #17
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^ an early 80s UO-9 was one of the most comfortable rides i've experienced on a 700c/27" wheeled bike
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Old 09-24-11, 06:24 AM   #18
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bikes with longer wheelbases are more "stable" and tend to go straight more easily

more slack angles mean less road force is delivered directly to your body
Not necessarily true. Some short wheelbase racing bikes have strong understeer and ride no-hands readily. Maneuverability and twitchiness do not always go together.
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Old 09-24-11, 11:03 AM   #19
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Old 09-24-11, 11:22 AM   #20
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But assuming the cockpit is the same, its going to be more comfortable because its more compliant: less rigid and upright, more stable but less responsive, which I've never really found to be a problem.
Of course there are always exceptions to the rule, but I agree with dbakl. The position of the seat in relation to the bars is quite constant with my bikes as is the overall length from the seat to the BB. The only diference between the 3 is the relative forward and back distance between the seat and BB. I really notice that forward and back difference when I am out of the saddle, not so much when in the saddle. So on the flats, the longer wheelbase and more relaxed geometry is great to ride but on climbs, I prefer the steep bike.



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Old 09-24-11, 12:03 PM   #21
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I consider my ca. 1960 Capos (72 degrees parallel w/ long, skinny stays) relaxed and my ca. 1980 Bianchi (73 degrees parallel w/ shorter, beefier stays) moderate. I do not have anything super stiff or super tight. I would also put my ca. 1970 Peugeot UO-8 under the relaxed rubric.

I have a few observations:
1) The Capos are, as expected, very forgiving on bumps and over long distances.
2) They are also notably mushy if I do not climb or sprint w/ utmost care and smoothness.
3) The Bianchi is noticeably less forgiving/stable in a crosswind than the Capos or the Peugeot UO-8.
4) The Bianchi feels like the fastest of the bunch, and it is arguably the most fun to ride in good weather.
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Old 09-24-11, 01:20 PM   #22
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did someone say fork rake?

that guy could at least have inflated the tires for the photo....
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