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Thread: Head Angle Help

  1. #1
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    Head Angle Help

    I'm in need of some guidance on headtube angle, and hope that everyone's collective wisdom can help me out. I have a compact steel frame that is too tall at the front end. I have a negative 10 degree stem jammed down right on top of the headset, yet I still feel like I'm too high. The headtube length is 225mm, which may sound long, but is consistent with the HT lengths that typically come on the 62-63 cm frames that I've ridden over the years.

    The problem is not so much that I can't get low enough on top of the bike, but rather that the headtube can't get low enough on the fork. Or, put another way, the bike seems slanted to far toward the rear wheel.

    Therefore, I'm interested in changing the head angle. I think this would mean increasing the head angle. Other than getting a fork with a shorter crown to axle length then I already have, what else can I do to increase the head angle?

  2. #2
    headtube. zzyzx_xyzzy's Avatar
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    Other than a shorter fork or 650b wheel in front I can't think of anything.

    Note that in theory lowering the front end will also reduce pedal clearance, move the saddle forward, effectively lengthen the top tube, and change the handling to be lighter/less self-stable. It's not clear to me that you want ALL those effects.

  3. #3
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    Unless you have a fork with a ton of wheel clearance, you cannot lower the crown meaningfully without going to a smaller front wheel. To give you some perspective, a 15-20mm drop at the head would translate to a one degree change in head angle. Also be aware that this would also change the seat tube angle by the same amount as the entire frame is rotated down around the rear axle.

    IMO there's no practical way to address your issue by changing the fork, and reworking the frame would be prohibitive. I don't think your frame is wrong in any way, except that maybe it's a poor fit for you. Years ago horizontal top tubes were almost religious icons, but that's out the window these days. Once the mountain bike community proved that long seat posts were practical, seat lugs were dropped, and manufacturers felt free to use sloping top tubes to set head and seat tube height independently. You're frame thus represents the makers idea of a best fit.

    Based on my 40 years in the industry, I can say with authority, that most people unhappy with frame fit issues wanted higher heads, not lower, and the sloping top tubes and long seatposts in common use today reflect a desire to respond to that need.

    I see only two practical choices for you.

    1- find a high angle stem and mount it angled down. A 17° stem would have zero rise, and a higher angle would drop the bars a bit. Note that impact of stem angle on bar height is proportional to stem length, so this remedy may not help if you have a fairly short stem.

    2- replace the frame with one better suited to your fit.
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    coprolite fietsbob's Avatar
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    new frame, new bike, maybe something in a real time trial bike design?
    you learned something with the one you have , to take to the marketplace ..

    might be time to talk to a custom framebuilder.


    Note: some designs mounted the handlebars to the fork crown.
    Last edited by fietsbob; 03-27-11 at 10:50 AM.

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  6. #6
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    Thanks for the meaningful insight. As suggested, I am not really interested in radical changes in the handling of the frame. So, a 650 wheel is out. Regarding fit, the bike was custom built for me by a very well respected American builder. I went the custom route because I have a non-typical combination of long legs, short torso, and long arms. As a result, I'm used to riding bikes with seat tubes that fit me well, top tubes that are up to 4 cm longer than the frame I had built, and plenty of headset spacers.

    I ride 61 & 62 cm frames. They fit me well in the legs, but typically come with top tubes between 58.5cm and 60cm. The head tubes are typically 19.5 to 21.5 centimeters depending on the brand (I still always seem to need at least 20mm of spacers). The frame I'm trying to make work has a 61cm seat tube, a 55.5cm top tube, and a 22.5cm head tube.

    I'll try a negative 17 degree stem with some extra length and see what happens. From the advice that was given. It seems that maybe I'll just have to get used to riding something that actually fits me. It just seems that I'm tilted to far back. Kond of like riding seated on a 4 percent hill. Yet, I feel low enough on the frame. The drop seems right, and the overall bar height is consistent with my other bikes.

    We'll see. Thanks!

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    Since the frame was custom built, consider letting the builder, or the person who did the measurements finish the fit. They should have an idea of what they were working toward in the first place.
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  8. #8
    bike whisperer Kimmo's Avatar
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    As mentioned, you can't do much about the head angle; but maybe you can tighten it by up to half a degree.

    If there's enough spare metal, you could take a few mm off the bottom of the head tube. Check inside the tube for a machined recess for bearing cups... doubt it'd be feasible for a hiddenset frameset, though.

    You can put a size smaller tyre on the front, which should also provide some minimal rolling resistance, aero and acceleration advantage. It makes a lot of sense, given you only have like 40% of your weight on the front.

    And purely to get the stem lower, you may also be able to shave a few mm off the top of the head tube. If you have an external cup headset, you may be able to find one with a lower stack height too.

  9. #9
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    as per FBinNY, if this was a custom frame, should't you have worked all this out at the time of ordering! as that's the whole point of getting a custom frame, that it should fit perfectly.

  10. #10
    SmallieBiggs
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    Quote Originally Posted by Kimmo View Post
    You can put a size smaller tyre on the front, which should also provide some minimal rolling resistance, aero and acceleration advantage. It makes a lot of sense, given you only have like 40% of your weight on the front.
    A narrower front/wider rear tire is what I was thinking, too. Although if it is a modern tight road bike then you are very limited in what you can do... if it is a mountain bike you can run a 2" wide tire on the rear and a 1" wide tire on the front, but with a road bike you likely can fit a maximum of 25mm wide in the rear and minimum of 18mm wide in the front... won't make much difference.

    Also, narrower tires will likely increase rolling resistance, not decrease. Although there will be weight and aero advantages.

  11. #11
    headtube. zzyzx_xyzzy's Avatar
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    Head tube angle is not really a fit parameter, and you're describing a fit problem. Maybe you are feeling a difference in SEAT tube angle. Is the seat tube much slacker angled than your other bikes?

    I also fit the long-limbs, shorter torso description, and I find what works for me is a longer top tube and a steeper seat tube than most large bikes are built with. Which is interesting because if you follow bicycle fitting myth and lore like "knee over pedal spindle" (KOPS) you'd guess just the opposite and design a frame that feels the way you say yours feels.

    But KOPS is something that only works approximately for people of average proportions and weight distribution. It should NOT be used to fit a custom frame. I don't know whether that's what your builder did, but putting it out there as an idea.

    It sounds like you had a bike built with too slack a seat tube angle and too short a top tube and now you can't get your hands out far enough or your butt forward enough.

  12. #12
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    "Head tube angle is not really a fit parameter, and you're describing a fit problem. Maybe you are feeling a difference in SEAT tube angle. Is the seat tube much slacker angled than your other bikes?

    It sounds like you had a bike built with too slack a seat tube angle and too short a top tube and now you can't get your hands out far enough or your butt forward enough"

    __________________________________________________________________________
    The more feedback that I get and the more I think about it, I'm starting to feel that I will just have to give the fit some time. The head and seat angle are both 73 degrees, which is about average for what I ride. I have one bike with a 72.5 seat tube angle and a 60 cm top tube that is at one end of the spectrum (Merckx century Geometry), and another that has a 73.5 seat tube angle and a 58.5 top tube. The 73.5 seat tube angle bike seems to be a better fit, but I have always felt that the shorter top tube is the reason, not the seat tube angle.

    I only have about 200 miles on the frame that I'm concerned about, and over those two hundred miles I have been swapping stems, playing with fore aft and seat height trying to dial it in. However, It just did not work, and I stopped riding it. It is hard to see a bike that you had such high hopes for, and paid good money for, sitting around collecting dust.

    Maybe it is just so different than what I'm used to, even if it is the appropriate fit, that it just feels weird.

  13. #13
    Senior Member BCRider's Avatar
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    Quote Originally Posted by Vitix2 View Post
    .....Maybe it is just so different than what I'm used to, even if it is the appropriate fit, that it just feels weird.
    Could you post up some pictures taken from the side of you on the bike and in your various riding positions while either passing by or while leaning against a supportive tree or wall? That may help some of the better fitting gurus here to aid in second guessing your frame builder. But it may well be that you're right and it just isn't the poor fit that you're used to so it feels weird. Especially since the cockpit is obviously shorter.

    I must say that I'm a little surprised that your frame builder didn't use a slightly shorter head tube and figure on building up to the final height with spacers to give you some fudge room.

    Assuming your frame uses the threadless headset setup you could always look at some MTB higher angle stems used upside down to drop the bars moreso than your present 10 degree stem. Higher angles than 10 are common in MTB's. It's not as "clean" a solution as removing spacers and eventually trimming the steer tube but it would allow you to play around with how the bike fits you a little. Also drop bars come in a variety of drop depths. Some playing with those as well may offer some adjustment.

    In the end he was fitting what is apparently an odd body type to the frame. It may be that he didn't quite allow enough or went too far in trying to accomadate your body shape which was a little outside of the usual proportions. Did he build up the frame and let you come in and try it before painting? I would have thought for a custom fit bike for a body outside of the normal dimensions such a trial would be almost a requirement. That way any alterations could be made before painting. Hell, as the customer I would have INSISTED on such a pre-paint trial even if I had to come by, pick up the raw frame and build it up myself and then strip it and return it for final finishing. Especially if I knew that I was built a little differently than normal in proportions such as you state. I hate to say it but if you didn't get such a test ride then I'd say you share a bit of the blame for NOT INSISTING that you get to try it at such a stage in the process.
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  14. #14
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    I'm struggling with why you can't get the new frame to fit, but going through this w/ a custom frame builder, I gotta think both you and he know more than me about this stuff, but...

    The seat tube length shouldn't affect fit, just the amount of seat post exposed.

    The head tube is a 1-3 cm longer than the other two, but you said you used 2 cm of spacers anyway, so that shouldn't be a factor that you can't adjust for by using less spacers and a lower angled stem like you did.

    Maybe you aren't using a new stem that will make up for the ~3cm shortening of your TT? It's measured 3.5 cm longer, but because the STA is 12 degree slacker, should only result in a 3 cm longer reach because your seat won't be as far back on the rails. Is your new stem 3 cm longer than the old one? I think handlebars that are too close would also be or at least feel too high?

    Did you put your saddle at the same height and fore-aft position relative to the BB as the one you liked before (have you verified this by measuring the old saddle position and duplicating it with the new bike) before you started twiddling w/ stem length and height?

    I just can't figure out why, by using a longer stem w/ less spacers, this new frame can't get you in the ballpark of the old frame pretty easily, but like I said, both you and the builder probably know more about this than me.

    What am I missing?
    Last edited by Camilo; 03-31-11 at 07:47 PM.

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