Author Topic: Frame sizing bamboozlement  (Read 1379 times)

ravenbait

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Frame sizing bamboozlement
« on: 25 April, 2022, 05:05:20 pm »
I've read various geometry threads but am still struggling.

I want to get a Planet X Hurricane. The recommended size is a small (48cm). BUT.

I have a 50cm Pinarello Galileo (before they got wobbly seat stays) that feels a little small, a small Stealth that also feels a little small, a 50cm Orbit Harrier that fits perfectly, and a medium Pompino that is also very comfortable. Both the Pompino and the Harrier are nominally a sniff too big for me. I originally got a small Pompino on their recommendations (it's version 1, for those who care) and had to swap it for a medium.

Bike:PGStealthHarrierPompinoHurricane (small)Hurricane (medium)
Effective top tube528510550541535550
Seat tube C-T500480500510480500
Head angle72.372.571.373.57172
Seat angle74.37674.573.574.574

Is there any way to look at the geometry of my bikes and work out whether the small or the medium Hurricane would be a closer fit to the Harrier or Pompino?

Sam
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Re: Frame sizing bamboozlement
« Reply #1 on: 25 April, 2022, 05:16:16 pm »
In these days of sloping geometry, effective top tube is king.

ravenbait

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Re: Frame sizing bamboozlement
« Reply #2 on: 25 April, 2022, 05:18:50 pm »
Then as I want to be going long distances, possibly with a modicum of luggage, at a moderate pace, rather than shortish distances as fast as I can go with nothing but some water and minimal spares while leaving some legs left for running, I think the medium is likely to be the size for me. I just wasn't sure if the angles made any difference.

Sam
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BFC

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Re: Frame sizing bamboozlement
« Reply #3 on: 25 April, 2022, 05:33:02 pm »
Fine tuning of geometry is down to bar/brake design, stem length/angle and spacers, and seat rail adjustment (fore/aft).
You can make any frame not fit you by adding the wrong components (for you).

For basic set up I use dimensions for pedal (top surface, bottom of stroke) to sitting surface of saddle, and nose of saddle to centerline of handlebar with fine tuning depending on reach/drop of the actual bars.

Seat post height setting is assumed to be "fixed" at your setting but recheck measurement after any fore/aft saddle adjustments.

Raw data points to the medium Hurricane from the info in your post unless the bikes that are comfortable for you are at the limits of seat rail adjustment or use unusual seat post offset.

Re: Frame sizing bamboozlement
« Reply #4 on: 25 April, 2022, 06:09:33 pm »

You could try inputing the measurements into BikeCAD and then overlaying the resulting geometries over each other for a comparison.
https://www.bikecad.ca

Might be a steep learning curve with the software, but there is a free web version available (via the quick start menu tab), so you can give it a go. I've got the pro version here, so shout if this approach is something that seems useful but you're hitting hurdles.

ravenbait

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Re: Frame sizing bamboozlement
« Reply #5 on: 25 April, 2022, 06:11:08 pm »
Hmmm. The saddles may well be at the limits of seat post adjustment. I will have to check. But if I can get the Harrier to fit comfortably, presumably the Hurricane would as well, as they seem to be similar in the places that count the most.

Nikki, I had a look at the free version of Bike CAD but it wouldn't work, even though I left it for ages.

Sam
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"Created something? Hah! But that would be irresponsible! And unethical! I would never, ever make... more than one."

Re: Frame sizing bamboozlement
« Reply #6 on: 25 April, 2022, 06:19:56 pm »
Planet x give lots of dimensions so you should be able to measure your current bikes to compare.  Two measurements to take are the stack and the reach, these tell you how the handlebars are positioned relative to the pedals.  On your current bike run a string from the front to rear hub, then measure vertically from that line to the centre of the chainset and vertically from the line to the centre of the top headset. The first of these is the bb drop and the sum of the two is the stack. Drop a vertical line through the centre of the chainset and a vertical line through the centre of the top headset, the horizontal distance between these lines is the reach. Compare the stack and reach you measure with the planet x values and you can determine what stem and spacers will be needed to replicate your current handlebar position on the new bike.

Re: Frame sizing bamboozlement
« Reply #7 on: 26 April, 2022, 09:46:37 am »
^^^ As above, stack and reach is a far better comparison than any other measurement.
I wouldn't get too hung up on minor differences in ST angle, as long as you have a bit of saddle rail adjustment.  I can't remember how it's worked out, possibly Pythagoras from the BB, when I did it for my large sized bikes one degree ST angle moves the top of the seatpost about 8mm.  So the less steep ST on the medium will need the saddle moved forward 2/3mm to put you in the same position over the pedals, which takes away from the 15mm ETT difference.
 

ravenbait

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Re: Frame sizing bamboozlement
« Reply #8 on: 05 May, 2022, 07:07:46 pm »
OK, so the more I look at this the more bamboozled I get.

The Harrier is in bits, so not really in a position to measure the stack and reach.

The Pompino has a stack of 525 (I think, bearing in mind I'm using string and I'm by myself and have no depth perception) and a reach of 380ish, and is currently fitted with a 110mm stem and ultrawide bars (I only mention this as I can reach the hoods comfortably). The saddle is as far forward as it'll go, but needs to be shifted back maybe 20mm.

Geometry Geeks have the Stack and Reach of the Large and XL 2012 Pompino as (554, 391) and (585, 403). I should be able to work out what the stack and reach are for the medium, but I can't. My brain is tired. Naively assuming they drop in constantish values, my measurements don't look too far off. GG does not have the geometry of either the Harrier or the Galileo.

Hurricane stack and reach Small and Medium = (536, 386) and (558, 389).

I have compared the large sizes of the Pompino and the Hurricane. The Hurricane is 2mm longer in the reach and 21mm higher in the stack.

The Pinarello has a stack of about 517mm, with a reach of 370 and again, the stem is 110mm. This is too small.

If it weren't for the general shortage, I'd just order one, check it for size, then swap it if it was wrong. But that's not really possible in the current circumstances.

For reference, I'm a whisker under 5'6, which suggests I ought to go for the small.

Sam

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"Created something? Hah! But that would be irresponsible! And unethical! I would never, ever make... more than one."

Re: Frame sizing bamboozlement
« Reply #9 on: 06 May, 2022, 07:57:57 am »
Just to say that I feel your pain! It’s a bit of a minefield.

Also, small sizes don’t always progress in consistent or logical decrements of stack and reach. Steeper seat angles and shallower head angles on small sizes often throw things off and can lead to similar reach numbers (or occasionally even increasing reach) with smaller sizes. This isn’t really a good thing in general. Just a need to be a bit careful. Stem length can accommodate a fair bit of course, once the saddle’s in the right place.

By way of example, I’m between large and extra large usually. I’ve made both fit with -17 degree 90mm stems on XL frames and -7 degree 110mm on L. They still feel different of course.

ravenbait

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Re: Frame sizing bamboozlement
« Reply #10 on: 06 May, 2022, 10:47:37 am »
I have given up. I collected all my numbers plus a screenshot from Geometry Geeks and sent it to Planet X asking them to advise which size, or even which bike, would most closely match my desire.

What I probably needed to do was get a London Road while they were available in titanium. But that wasn't an option.

I basically want my Pompino. But in titanium.

Sam
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"Created something? Hah! But that would be irresponsible! And unethical! I would never, ever make... more than one."

Cudzoziemiec

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Re: Frame sizing bamboozlement
« Reply #11 on: 06 May, 2022, 11:35:40 am »
I basically want my Pompino. But in titanium.

Sam
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ravenbait

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Re: Frame sizing bamboozlement
« Reply #12 on: 06 May, 2022, 03:31:45 pm »

Not in bamboo for total bamboozlement?
I'd be too worried about being mugged by giant pandas.

Alex at Planet-X says I'm between sizes, so it's up to me. Small frame would be nippier and more aggressive, the medium would be more comfortable and stable. So medium it is.

Sam
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"Created something? Hah! But that would be irresponsible! And unethical! I would never, ever make... more than one."

ravenbait

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Re: Frame sizing bamboozlement
« Reply #13 on: 30 May, 2022, 01:31:42 pm »
Have ordered the medium. We'll see what it's like. It doesn't look massively dissimilar to my Orbit Harrier, comparing lengths and angles, so here's hoping it's as comfy as that.

Sam
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"Created something? Hah! But that would be irresponsible! And unethical! I would never, ever make... more than one."

ravenbait

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Re: Frame sizing bamboozlement
« Reply #14 on: 11 July, 2022, 05:16:14 pm »
Got the medium.

It's perfect. I have the N+1 grin.

No photos because he doesn't have a name yet, and I need to do things like change the saddle (the one supplied is fine to sit on, but weirdly sticky on my bike shorts, which makes it difficult to go from standing to sitting and vice versa) and the bar tape.

Sam
https://ravenbait.com
"Created something? Hah! But that would be irresponsible! And unethical! I would never, ever make... more than one."