I have a question reguarding the HD3, specifically the seat tube angle and top tube length. It seems the top tube is measured normaly from the centre of the seat tube to the centre of the head tube, parallel to the ground. The seat tube angle is measured normally from the horizontal to the actual seat tube. The difference is that the seat tube connects to the down tube well ahead of the bottom bracket. It looks to me that the seat tube angle and top tube length are based on the real position of the seat tube and not some theoretical seat tube position like other similar frames are. I think that this puts the seat post much more foreward than the numbers at first indicate. Thoughts or comments?
HD3 Geometry?
Legbacon
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I have a question reguarding the HD3, specifically the seat tube angle and top tube length. It seems the top tube is measured normaly from the centre of the seat tube to the centre of the head tube, parallel to the ground. The seat tube angle is measured normally from the horizontal to the actual seat tube. The difference is that the seat tube connects to the down tube well ahead of the bottom bracket. It looks to me that the seat tube angle and top tube length are based on the real position of the seat tube and not some theoretical seat tube position like other similar frames are. I think that this puts the seat post much more foreward than the numbers at first indicate. Thoughts or comments?
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hans mentioned on PB that the seat angle is with a given seat height. as i am waiting for an XL frame i asked him what that seat height is and he replied to me: "The XL seat angle was determined using 807 mm from the center of the BB to the top of the saddle."
maybe they should add these numers to their website.
along with the BB drop which is also missing.
maybe they should add these numers to their website.
along with the BB drop which is also missing.
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This is a good question, and one I posed over on the HD3 thread. I'm tall, and run a saddle height of ~33" from BB. So it's important for me to know actual ST angle (i.e. angle of the tube itself relative to horizontal) not just effective (i.e. angle from BB to an arbitrary extension of the actual ST.)
One of my worries with this bike, given its very short chainstays and relatively slack published STA, was that it would yield a saddle position that's too far back for tall guys. This makes steep climbing really hard, as you can't keep the front end down. This is the main thing that made the Mach 6 not work out for me.
I think this worry might be unfounded though. I messed around with a protractor app using the XL frame rendering posted by Hans (http://forums.mtbr.com/ibis/ibis-mojo-hd3-650b-2015-a-939035-4.html) and it looks like the HD3's actual STA is right around 70. For comparison, the Nomad's looks to be in the 70-71 range and the Mach 6 about 67, though that's with a medium; I didn't find a good image of an XL M6 in profile. Spesh has published the 650B Enduro's actual STA, which is 69.5 in a L.
That's a lot of numbers, but the bottom line is: I think you're right, the HD3 is actually a bit steeper in the ST than the numbers indicate, which is a very good thing for us tall guys. And, it'd be really nice if everyone would publish actual STA, and how effective STA is measured!
One of my worries with this bike, given its very short chainstays and relatively slack published STA, was that it would yield a saddle position that's too far back for tall guys. This makes steep climbing really hard, as you can't keep the front end down. This is the main thing that made the Mach 6 not work out for me.
I think this worry might be unfounded though. I messed around with a protractor app using the XL frame rendering posted by Hans (http://forums.mtbr.com/ibis/ibis-mojo-hd3-650b-2015-a-939035-4.html) and it looks like the HD3's actual STA is right around 70. For comparison, the Nomad's looks to be in the 70-71 range and the Mach 6 about 67, though that's with a medium; I didn't find a good image of an XL M6 in profile. Spesh has published the 650B Enduro's actual STA, which is 69.5 in a L.
That's a lot of numbers, but the bottom line is: I think you're right, the HD3 is actually a bit steeper in the ST than the numbers indicate, which is a very good thing for us tall guys. And, it'd be really nice if everyone would publish actual STA, and how effective STA is measured!
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Large HD3 with 2015 Fox 36 Float and Minion DHR2 2.3 front, Ardent Race 2.2 rear both mounted on Derby rims. HTA: 66.7 degrees (measured on the stanchions), STA (actual): 70.1 degrees (measured on the seat post)
Angles measured with a digital angle finder calibrated on the ground under the bottom bracket. Bike was turned around, angles measured with the bike in both directions, and the two measurements averaged.
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so the seat angle is actually 2.5 degrees slacker than claimed?
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No. What I measured is the actual seat tube angle; the number reported in the geometry chart is the effective seat tube angle, which assumes a certain seat to bottom bracket distance (probably in the middle of the suggested height range).
As discussed above, effective seat tube angle is what matters. However, at the extremes of the recommended height range per size, the actual seat tube angle allows you to estimate how different the effective seat tube angle is from the posted average value. A taller seat will result in a slacker effective STA, while a lower seat will result in a steeper effective STA.
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Normally the theoretical STA is measured horizontal with the head tube along the theoretical top tube. If you know you saddle height you can calculate the horizontal difference from the two. Take into account that the actual seat tube is quite forward of the BB. I looked at all this bike nerd stuff and estimate that I can easily get my saddle in my ideal position.
Good observations...
We didn't post the fore-aft change caused by raising and lowering the saddle because it's a small difference. I think we calculated something under 2mm fore-aft change for a 50mm change in saddle height. We didn't think it would be limiting in terms of getting the fit you want.
For those that are confused about actual vs effective seat tube angle, the effective seat angle is what determines the seat to BB relationship. That's the number to use.
We move the seat tube forward to clear the tire, so if you put an angle finder on the seat tube it will be different and not actually pointed at the BB.
Take care,
Hans
We didn't post the fore-aft change caused by raising and lowering the saddle because it's a small difference. I think we calculated something under 2mm fore-aft change for a 50mm change in saddle height. We didn't think it would be limiting in terms of getting the fit you want.
For those that are confused about actual vs effective seat tube angle, the effective seat angle is what determines the seat to BB relationship. That's the number to use.
We move the seat tube forward to clear the tire, so if you put an angle finder on the seat tube it will be different and not actually pointed at the BB.
Take care,
Hans
Hopefully Hans can answer this...
I noticed on the Ibis website today, the HD3 "standard fork" is now a 160mm Pike. Was that a change because of fork availability, or did Ibis decide to go away from 150mm for a reason? I was thinking 150mm would be "just fine" for my riding.
I noticed on the Ibis website today, the HD3 "standard fork" is now a 160mm Pike. Was that a change because of fork availability, or did Ibis decide to go away from 150mm for a reason? I was thinking 150mm would be "just fine" for my riding.
Requests for the 160 travel Pike persuaded us to switch.
H
Pike 160 is about 3mm longer than the 36 but also sags in easier in my experience. I doubt it would be very noticeable.
H
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Also worth noting that it's relatively simple to drop the 160 Pike to 150. Any RS dealer should be able to help you.
So if your HD3 has the 160 and you *absolutely hate* that extra 10mm of travel, well you've got options... :thumbsup:
I'm confused and desperate to find the answer as the slack seat tube angle is the in,y thing stopping me from buying a mojo. The way it's measured by mojo is the actual seat tube angle which by looking at the design is slacker than what the effective seat tube angle should be. What would the effective seat tube angle be on a medium with 125mm of seat post exposed?
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the seat tube ange would be, at a given seat height, the angle listed in the geo chart.
what seat height that is, you have to ask ibis as i did for size xl. but i think you can do the math and using the number from the above qouted xl frame minus difference in seat tube length.
what seat height that is, you have to ask ibis as i did for size xl. but i think you can do the math and using the number from the above qouted xl frame minus difference in seat tube length.
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