Nonsense geometry

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531colin
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Nonsense geometry

Post by 531colin »

Before I'm accused of using this forum for commercial sniping, I would like to point out a couple of things.
1) I didn't start a thread entitled "nonsense geometry"....I didn't title this post "nonsense geometry"
2) This post was made under the heading "how big a stack with carbon forks" on the thread of that title and in response to a question in that thread from David Cox dated Dec 31st. ...it is NOT a random attack on the Tricross, or on Specialised.
3) Tricross geometry is available here http://www.specialized.com/gb/gb/bikes/road/tricross/tricrosstriple#geometry


Can anybody make sense of this "geometry table"??
http://www.specializedconceptstore.co.uk/detail/12tricross/tricross/tricross%20sport/
Last edited by 531colin on 2 Jan 2013, 4:48pm, edited 2 times in total.
reohn2
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Re: How big a stack with carbon forks

Post by reohn2 »

531colin wrote:Can anybody make sense of this "geometry table"??
http://www.specializedconceptstore.co.uk/detail/12tricross/tricross/tricross%20sport/

No :?
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David Cox
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Re: How big a stack with carbon forks

Post by David Cox »

Hi Colin, me neither but my Tricross is an earlier model with different looking forks! We had a chat about threepenny bit steering at the York Show. I've checked and its not the headset. Bianchi just oversteered mostly made it unwise to be on the inside of a two abreast peleton on a left turn or outside on a right. Tri with short stem was reluctant to turn at first and then ok. Other bikes of various types and configurations seem to just go where you point them without thinking about it.
PH
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Re: How big a stack with carbon forks

Post by PH »

531colin wrote:Can anybody make sense of this "geometry table"??
http://www.specializedconceptstore.co.uk/detail/12tricross/tricross/tricross%20sport/


No, what a mess. There is a geometry chart here;
http://www.specializedconceptstore.co.u ... s/Tricross
Though I've no idea if it's changed, or which is the current version.
Malaconotus
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Re: How big a stack with carbon forks

Post by Malaconotus »

531colin wrote:Can anybody make sense of this "geometry table"??
http://www.specializedconceptstore.co.uk/detail/12tricross/tricross/tricross%20sport/


Specialized tables were garbled like that for a while due to some web formatting glitch, and the concept store site still suffers although the main site seems to be fixed. Current Tricross geometry in legible format here... http://www.specialized.com/gb/gb/bikes/ ... e#geometry AFAIK, not significantly changed for the last couple of years at least and nothing very unusual about the measurements for a modern bike of this type. I can't see a reason that the steering would be odd if a more angled stem were used, but I'm a little suprised it was needed if the bike was the right size. Even in the large sizes, the Tricross has just about the tallest front end I've seen on a mass produced drop-barred bike, with a massive 637mm stack on the 61cm model, and the fork not cut short at all. I find only those with very long legs for their height have to have the saddle higher than the bars.

(I know you'll hate the 46cm and 49cm model numbers, Colin, and I completely agree, but I don't think we'll see 26" wheels on smaller sized mass prodiced bikes any time very soon)
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CREPELLO
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Re: How big a stack with carbon forks

Post by CREPELLO »

Malaconotus wrote:[ Even in the large sizes, the Tricross has just about the tallest front end I've seen on a mass produced drop-barred bike, with a massive 637mm stack on the 61cm model, and the fork not cut short at all.
What does this stack figure allude to with the Specialized? I always understood "stack" to refer to the number of spacers under the stem.
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531colin
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Re: How big a stack with carbon forks

Post by 531colin »

CREPELLO wrote:......................What does this stack figure allude to with the Specialized? I always understood "stack" to refer to the number of spacers under the stem.


"Stack" and "reach" are 2 **new** dimensions that are coming into frame sizing.-......would be helpful if they gave a picture......
"Stack" is the height of the headset above the ground (I think)
"Reach" is something like the horizontal distance between the BB axle and the headset top.
Instead of "stack" I think in terms of top tube slope in millimeters....this is helpful for those of us brought up on horizontal top tubes, and means you can ignore head tube length (.....eg. effect of head tube length on riding position depends on the height of the fork crown/tyre clearance....)
"Reach" would be quite useful if it was universally quoted....its a better indicator of the actual reach to the bars than (effective) top tube length, which can be "fudged" by comedy seat tube angles.
reohn2
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Re: How big a stack with carbon forks

Post by reohn2 »

I've always understood Stack height to mean the height of the centerline of the top of the headtube above the BB centerline and reach to be the distance between those two centres when measured horizontally.
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531colin
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Re: How big a stack with carbon forks

Post by 531colin »

reohn2 wrote:I've always understood Stack height to mean the height of the centerline of the top of the headtube above the BB centerline and reach to be the distance between those two centres when measured horizontally.


You're right, R2....should always Google first, post afterwards........

Image

(I still think top tube slope is easier!)
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531colin
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Re: How big a stack with carbon forks

Post by 531colin »

David Cox wrote:Hi Colin, me neither but my Tricross is an earlier model with different looking forks! We had a chat about threepenny bit steering at the York Show. I've checked and its not the headset. Bianchi just oversteered mostly made it unwise to be on the inside of a two abreast peleton on a left turn or outside on a right. Tri with short stem was reluctant to turn at first and then ok. Other bikes of various types and configurations seem to just go where you point them without thinking about it.


David, I'm afraid I don't remember talking to you at York...... :oops: .....busy couple of days!
All you will be doing by fitting a high-rise stem is taking some of your weight off the front wheel....taken to extremes this can have the effect of making the steering feel "light" or "too lively", but this generally needs a big change in handlebar position.....although I suppose its possible if for example, your Bianchi was right at your personal tolerance limit for lively steering then un-weighting the front wheel a bit could have pushed it into "too lively".
The Tri sounds different.....the general recipe for a stable bike is "lots of trail", again taken to the extreme it can result in "steering flop" where the front wheel "turns in" once you start on a turn....this can be pretty subtle, you might for example notice it only when you have been riding a different bike for a while.
Perhaps its more obvious with less weight on your hands?
Of course whatever you do with the handlebar position, the bike will steer the same "no hands"......because the steering geometry is unaffected by handlebar position. It just feels different .....mostly you can get used to a different feel.
Talking of "no hands", I'm guessing that at say 15mph no hands you can slalom the cats' eyes on the Bianchi, but the Tri takes a lot of convincing to depart from "straight ahead"...?........the actual geometries of the bikes would be useful!
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Re: How big a stack with carbon forks

Post by David Cox »

Thanks Colin, the bike is a seemingly simple machine but my education continues! It looks like the original question is answered you can have a high rise stem without affecting the steering!! I understand your point and although I'm not at all good riding with no hands I can feel the difference between a sports set up and a tourer. I used to have a racing bike and a Galaxy the trail and handling difference was obvious and pleasing depending on how you wanted to ride In both cases whether sensitive or stable the steering feels linear and that's what I feel I lost with the short high stems. But from your insights it looks like its to do with my weight on the bars - I'll have to find a corner and try it on the tops and the hoods etc. The Bianchi and original stem is now happily settled with a old work colleague (my old work - he is relatively young) the Tri is in the LBS for new bb bearings. Most of my bikes have just gone where I point them in a consistent way - these two disconcerted/irritated me. - the Tri has a curious shapely carbon fork and toe overlap so its not quite the stable cruiser you might expect. A Trek Pilot (also with that work colleague now) was too long despite a "fitting" at an LBS but satisfactory with a short tall stem so presumably had sufficient trail and stability built in to obviate any weight transfer effect.

Glad to know what stack height is at last!! Now off for a ride on a lively Mercian!!
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CJ
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Re: How big a stack with carbon forks

Post by CJ »

reohn2 wrote:I've always understood Stack height to mean the height of the centerline of the top of the headtube above the BB centerline and reach to be the distance between those two centres when measured horizontally.

Well: I have ALWAYS understood stack height to mean the total height of all the bits that go to make up a headset - and I still do - just like Sutherland's Handbook and the catalogues of all good headset manufacturers.

I do not like it when people start to use for some other purpose, a term that already has one perfectly understood meaning. As an engineer turned wordsmith, this feels like someone has taken one of my chisels to use as a screwdriver!
Chris Juden
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CJ
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Re: Nonsense geometry

Post by CJ »

Whilst we're on the subject, here's another nonsense geometry table: http://chargebikes.com/products/juicer-hi/.

See how the 'Large' size is apparently smaller than the 'Medium'. I noticed this because I'm currently reviewing that model and requested the medium size out of blind hope, being kinda medium sized myself. I'm actually quite relieved to find that very few of its dimensions bear any relationship to that table of random numbers!
Chris Juden
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reohn2
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Re: How big a stack with carbon forks

Post by reohn2 »

CJ wrote:
reohn2 wrote:I've always understood Stack height to mean the height of the centerline of the top of the headtube above the BB centerline and reach to be the distance between those two centres when measured horizontally.

Well: I have ALWAYS understood stack height to mean the total height of all the bits that go to make up a headset - and I still do - just like Sutherland's Handbook and the catalogues of all good headset manufacturers.

I do not like it when people start to use for some other purpose, a term that already has one perfectly understood meaning. As an engineer turned wordsmith, this feels like someone has taken one of my chisels to use as a screwdriver!

Perhaps i should have written "in this context".As for stack height where threaded headsets are concerned I'd agree.
BTW as a retired Joiner/cabinetmaker/woodturner and currently a massacrer of the English language,using a woodchisel as a screw driver is sacrilege :shock:
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PH
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Re: Nonsense geometry

Post by PH »

Putting aside the matter of language, what do people think of the frame stack as a measure for comparison? It looks to me that knowing this would give a good idea of the frame when compared to another.
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