Geometry Comparison

Discuss light weight issues concerning road bikes & parts.
CAAD8FRED
Posts: 209
Joined: Mon Jun 18, 2018 10:52 pm

by CAAD8FRED

When trying to look for a bike that has a similar geo to another bike, what geo numbers should be specifically compared?

by Weenie


mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Stack, Reach. That'll get the fit of the bike.

What were you actually looking to compare?

CAAD8FRED
Posts: 209
Joined: Mon Jun 18, 2018 10:52 pm

by CAAD8FRED

mattr wrote:
Sat Apr 20, 2019 6:34 pm
Stack, Reach. That'll get the fit of the bike.

What were you actually looking to compare?
I knew stack and reach mattered but I wasn’t sure how much angles or tube lengths mattered too in comparison to S/R

Karvalo
Posts: 736
Joined: Fri Aug 10, 2018 6:40 pm

by Karvalo

For fit, stack and reach specifically, and a reasonably similar STA (unless you already have an extreme saddle setback either way, then its more important to get right).

For handling, loads of stuff.

Karvalo
Posts: 736
Joined: Fri Aug 10, 2018 6:40 pm

by Karvalo

CAAD8FRED wrote:
Sat Apr 20, 2019 6:36 pm
I knew stack and reach mattered but I wasn’t sure how much angles or tube lengths mattered too in comparison to S/R
Tube lengths don't, S/R sorts all that out. Angles theoretically do - but except for on tiny bikes HTA rarely varies by any significant amount, and STA can usually be compensated for by saddle rail adjustment or seatpost setback.

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dj97223
Posts: 701
Joined: Sun Nov 06, 2005 7:27 pm

by dj97223

Have a look at this if you want to compare 2 bikes in detail:

www.bikegeocalc.com
“If you save your breath I feel a man like you can manage it. And if you don't manage it, you'll die. Only slowly, very slowly, old friend.”

spartan
Posts: 1285
Joined: Fri Sep 03, 2004 2:52 am

by spartan

the best site to compare geo . great database of all current road brands

https://app.velogicfit.com/frame-comparison
Current Rides:

2018 Madone SLR DISC DI2 9XXX
2017 Giant TCR Advanced SL 0 DI2 9150

citrusparty
Posts: 22
Joined: Fri Apr 14, 2017 12:44 pm

by citrusparty

This is my favourite site at the moment: https://www.bikegeocalc.com/#7Unnameda0 ... 2.5G30H30Z

robeambro
Posts: 611
Joined: Sat Jul 07, 2018 6:21 pm

by robeambro

CAAD8FRED wrote:
Sat Apr 20, 2019 6:36 pm
mattr wrote:
Sat Apr 20, 2019 6:34 pm
Stack, Reach. That'll get the fit of the bike.

What were you actually looking to compare?
I knew stack and reach mattered but I wasn’t sure how much angles or tube lengths mattered too in comparison to S/R
Seat Tube Angle matters for fit purposes only if it is so extreme that you can't roll your saddle forward/backward enough.

Provided that your saddle fore-aft vs the bottom bracket is dialled in, then stack and reach are quite comprehensive. The only other factors you need to take into account are stem length/angle and head tube angle -unless you have a spacer tower, the latter doesn't matter a lot, but still- for which I use http://yojimg.net/bike/web_tools/stem.php, and finally the handlebar reach. Whilst most bars have 80mm reach or so, there can be wild exceptions, with some Bontrager alloy bars or the 3T Aeronova going to around and above 100mm, which could potentially make an otherwise perfectly sized bike uncomfortable.

The websites above like bikegeocalc and velogicfit are also quite valid, especially for comparing bikes.

cyclenutnz
Posts: 800
Joined: Tue Jul 18, 2006 5:18 am
Location: Cambridge, New Zealand
Contact:

by cyclenutnz

Things that matter for matching bikes:
Hood XY - if you use the same bars and levers this can be simplified to Bar XY - this gets your hands in the same position
Seat tube angle and post offset options - as mentioned above - only matters if it stops you getting your posterior in the right place
Chainstay length and front centre - weight distribution, stability, handling behaviour
Head tube angle and fork rake - handling behaviour

Everything else is just part of filling in the dots between the important coordinates (rider contacts and road contacts)

The yojimg stem tool (and every other calc I've seen) has an an error in the formula for bar XY. Not having calcs match reality really bugged me so I spent the time to figure out why and the velogicfit tool uses the formula that resulted (note that I'm the founder of VF). It's not a lot but it does make a difference to the calculated bar Y
http://www.speedtheory.co.nz
http://www.velogicfit.com - 3D Motion Capture and Frame Finder Software

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wheelsONfire
Posts: 2949
Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

Well, perhaps trail/ rake should be of interest?
Possibly chainstay lenght...
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

wheelsONfire wrote:
Sun Apr 21, 2019 7:14 pm
Well, perhaps trail/ rake should be of interest?
Possibly chainstay lenght...
Not for bike fit, that's into handling, which is a whole new can o worms.........

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wheelsONfire
Posts: 2949
Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

mattr wrote:
Sun Apr 21, 2019 8:35 pm
wheelsONfire wrote:
Sun Apr 21, 2019 7:14 pm
Well, perhaps trail/ rake should be of interest?
Possibly chainstay lenght...
Not for bike fit, that's into handling, which is a whole new can o worms.........
Well, ofcourse it's about handling. I just missed that it was ONLY about fit.
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

Hexsense
Posts: 933
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

For trail/rake values, simple rule of thumb is that Most bike in size 52-56 are good.
Size 50 and smaller on some brands are poorly handle (generally have too much trail due to same fork but slacker head tube angle). So go up in size to 50+ and short stem make bike handle better in some certain bike model/brand.
Size 58+ sometime start to face opposite problem when manufacturer use very steep head tube angle.

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wheelsONfire
Posts: 2949
Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

Hexsense wrote:
Mon Apr 22, 2019 5:40 pm
For trail/rake values, simple rule of thumb is that Most bike in size 52-56 are good.
Size 50 and smaller on some brands are poorly handle (generally have too much trail due to same fork but slacker head tube angle). So go up in size to 50+ and short stem make bike handle better in some certain bike model/brand.
Size 58+ sometime start to face opposite problem when manufacturer use very steep head tube angle.
They can vary quite much actually. BMC for instance have slow steering. My Ax bike has very quick steering.
I changed model when i bought a new Ax, to use a longer stem. I have a 120mm on this bike, on the previous i had a 105mm stem.

Anyway, it's something i wouldn't leave blank if i bought a custom frameset.
I would probably oversee chainstay lenght to. Not to mention BB!!
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

by Weenie


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