are bike sizing charts reliable?
11-13-09, 08:53 AM
#1
Senior Member
Thread Starter
Join Date: Aug 2009
Posts: 474
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
are bike sizing charts reliable?
i found a sizing chart for my friend's bike and decided to compare the sizes to the bike i want to get online, and found out, the chart is off, my friend bought a 53 frame, supposidly the stand over should be 31.5'' but in reality its a few inches shorter, has anyone found this with any other sizing charts? or is it just this one?
11-13-09, 12:05 PM
#2
Senior Member
Join Date: Sep 2009
Posts: 219
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
it's a good starting point when you have no clue about your size. think of it as the snowboard size chart they use at resort rental store, it's there to get you started and that's all about it.
bike frame geometry + body geometry = way more complex than "54cm for 5'8" "
that's why test ride is very important, sorry about your friend's mishap, perhaps try to return it for a smaller frame?
the frame of my trek and canyon varies quite a lot despite they are similar in size 54 vs 56
bike frame geometry + body geometry = way more complex than "54cm for 5'8" "
that's why test ride is very important, sorry about your friend's mishap, perhaps try to return it for a smaller frame?
the frame of my trek and canyon varies quite a lot despite they are similar in size 54 vs 56
11-14-09, 08:05 AM
#4
Senior Member
I've never known a geometry chart to have any significant error. Several inches of error would have to be a typo or a failure to update a chart for a sloping TT. Even a 6cm slope to a TT would only change the standover by about 3cm.
Standover is a poor way to judge frame size anyway. It's the head tube length, with the headset that really defines the vertical frame size.
Standover is a poor way to judge frame size anyway. It's the head tube length, with the headset that really defines the vertical frame size.
11-14-09, 10:16 AM
#5
Senior Member
Join Date: Apr 2005
Location: Northern California
Posts: 10,879
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 104 Post(s)
Likes: 0
Liked 5 Times
in
5 Posts
Geometry charts from the big brands are very accurate. However, geometry can change from bike model to model and year to year, so make sure you have the right chart for your bike. Also make sure you have the right size bike. "53" means different things to different people. And some shady mail-order bike sellers have been know to ship what they have in stock, not what you really ordered.
11-14-09, 11:33 AM
#6
Over the hill
Join Date: Mar 2006
Location: Los Angeles, CA
Posts: 24,376
Bikes: Giant Defy, Giant Revolt
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 998 Post(s)
Liked 1,206 Times
in
692 Posts
Yeah, the geometry is usually very reliable and much more important than standover height, which is just an estimate thrown in for newbies who think they can size themselves based on their inseam alone. I'm guessing it's a couple inches off because the noob's rule is to have a couple inches of clearance, so the manufacturer adds that in... or it could be a sloping top tube as mentioned above.
__________________
It's like riding a bicycle
It's like riding a bicycle
11-14-09, 11:53 AM
#7
Senior Member
Join Date: Feb 2001
Location: England
Posts: 12,948
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 19 Post(s)
Likes: 0
Liked 7 Times
in
7 Posts
When I am replacing lost bikes and the rider wants the same size, I base the new size on the top-tube length of the old bike. Usually this is a like-for-like when using s/m/l but when it comes to numbers, the advertised seat-tube length may not be the same as the replacement, esp if using a different brand of bike.
11-14-09, 01:50 PM
#8
Senior Member
Comparing only the TT lengths will not always produce the desired result. It is the combination of TT length and seat tube angle that work together to create the frame reach. A bike with a 55cm TT and 73 degree STA wll fit about the same as one with a 54cm TT and 74 degree STA.
The head tube length (with the headset) should also be considered, since the HTL usually changes far more than the frame reach, with each size increment.
The seat tube length isn't of any consequence with regard to fit.
Whan I consider a new frame brand, I look at the head tube length first, to get the correct length I need to produce my desired bar height, without some goofy stem setup, then I see is the frame reach will fit my needs. The STA is also important since it defines the amount of setapost setback that will be needed.
The head tube length (with the headset) should also be considered, since the HTL usually changes far more than the frame reach, with each size increment.
The seat tube length isn't of any consequence with regard to fit.
Whan I consider a new frame brand, I look at the head tube length first, to get the correct length I need to produce my desired bar height, without some goofy stem setup, then I see is the frame reach will fit my needs. The STA is also important since it defines the amount of setapost setback that will be needed.
