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Old 08-27-08, 09:05 PM   #1
mr_b
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Touring Frame Differences

Four touring bike frames made by various bike manufacturers for heavy loaded touring are under consideration. All frames are the same in almost every way. Same top tube length, same stand over height, same seat tube height, chain stay etc. The only major differences between them are the head and seat tube angles. Bike 1 has a head tube angle of 71 deg. and a seat tube angle of 73.5 deg. Bike 2 has head/seat tube angles of 72/72.5 degrees respectively. Bike 3 has head/seat tube angles of 72.5/74 degrees respectively. Finally Bike 4 has head/seat tube angles of 70/73 degrees respectively. How do these angle differences affect the overall behavior and comfort of these potential bikes? Thank you.
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Old 08-27-08, 09:39 PM   #2
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Not sure which bikes you are comparing, but I don't think all the TT, SO, ST and CS dimensions are the same on popular touring bikes. I just looked at the LHT and 520 and they aren't the same for example.
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Old 08-27-08, 09:56 PM   #3
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In general, steeper HT and ST angles allow for a shorter wheelbase, more responsive steering (although fork rake and HT angle together account for the amount of trail, which is more the determining factor in steering), and a more powerful -- but less comfortable -- riding position. Pretty much the opposite of what you want for heavily loaded touring. Chances are, however, that you wouldn't notice a 1 degree difference either way. Furthermore, you can compensate for ST angle by adjusting the saddle fore and aft (further adjustment can be had with an offset seatpost), and you could, if you wanted to, compensate for HT angle by getting a fork with a different rake.

For me, the saddle position relative to the bottom bracket is a very significant factor in riding comfort. Further back is more comfortable (but less powerful), so all else being equal, I'd choose the bike with the shallowest ST angle.

Do all of these frames come with forks as well? If so, then I would be concerned more with wheelbase (longer is more stable) and trail if you can get those specs. More trail means the bike will track straighter and feel more stable, but the steering will be more sluggish -- not an issue for touring. If two bikes have the same fork rake, then the one with the shallower HT angle will have more trail (more fork rake decreases trail).

Here's more on bike geometry:
http://davesbikeblog.squarespace.com...-steering.html
http://davesbikeblog.squarespace.com...f-history.html

Bike 2 makes the most sense to me. The 70 degree HT of bike 4 is unsually shallow and would require an unusual fork to achieve the right amount of trail.
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Old 08-27-08, 10:01 PM   #4
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Partial answer: The head tube angle could be decreased or increased by several degrees but it would matter very little if the forward curve of the front forks what increased or decreased correspondingly to give the same trail in all the bikes. To a point more trail can give more stability. The other angles might have something to do with giving the same wheelbase for different sized riders. What says Sheldon Brown?
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Old 08-28-08, 06:55 AM   #5
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I like the look of my 520's traditional frame however I enjoy far more the sloping top tube on my Sherpa 30.
Standover and reaching to a pannier are never a problem.
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Old 08-28-08, 08:40 AM   #6
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Quote:
Originally Posted by ken cummings View Post
What says Sheldon Brown?
From Sheldon Browns website:
<http://www.sheldonbrown.com/gloss_an-z.html>
Angles
The usual angles that are referred to in frame design are the head-tube (or fork) angle and the seat-tube angle. These angles are usually measured with reference to the horizontal. The typical range is from 68 to 75 degrees.

In general, bicycles with shallower, "slack", "relaxed" angles (lower numbers) tend to be more stable and comfortable. Bicycles with steeper, more upright angles (higher numbers) tend to be manuverable, but less comfortable on rough surfaces. Shallower frames tend to have longer wheel bases than more upright frames; bicycles with shallower head angles normally have more fork rake. All of these factors contribute to the riding characteristics cited.
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Old 08-28-08, 10:36 AM   #7
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Hi mr b, don't get to bogged down in spec's. Test ride the various bikes adjusting them to get a good fit even on the test ride, if you feel comforable on the bike and your heels don't hit the rear pannier then thats the frame you want. For me the best frame/component combination was the Cannondale T2000 and I don't even know the spec's. I'm not saying that other bikes wouldn't of worked but I liked the black paint job. There are so many touring bikes on the market now and the frame spec's are very simular.
Enjoy the hunt!
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Old 08-28-08, 02:03 PM   #8
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Originally Posted by cyberpep View Post
Test ride the various bikes . . .
The likelihood of being able to test ride four different touring bikes is very low. I live in a large town with a huge cycling community and the number of dedicated touring bikes I've seen in stock at any local shop is zero. Unfortunately, at this time, a touring bike must almost always be special ordered.
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Old 08-28-08, 05:43 PM   #9
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guess I agree that the only real way to determine what those measurements mean to you would be for you to test ride each of the frames and decide for yourself. I agree that the odds of finding the bikes to test ride are slim.
I do think that you may be a bit anal about this. Even if someone came up here and listed what they felt were behavioral differences, you really won't understand what they mean until you ride the bike for yourself. Just find the green bike and buy that.
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Old 08-28-08, 07:37 PM   #10
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If you can't test ride them compare the specs to a bike you have. If for instance you wish could push your saddle back more on your current bike but have run out of saddle rail, consider choosing the frame with a slacker ST angle. Finding the right bike is so subjective that it seems silly to worry too much about the numbers unless you have a lot of riding experience and are opting to go custom.
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Old 08-28-08, 10:29 PM   #11
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Greetings and thank you all for your replies. I learned a lot and to sum up what I have read it seems that the variation of these angle do not matter much because the seat position can be adjusted to compensate for seat tube angle, the handle bar position and height can be adjusted by stem selection and the trail is more of a determining factor with respect to stability than head tube angle. Thanks again.
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