Difference in frame sizes and bike geometry
03-31-16, 05:09 AM
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Difference in frame sizes and bike geometry
Again sorry about asking more silly questions, but I don't really know much about bicycle geometry, I do hear that it gets very technical though.
I am trying to pick a new frame, I had a look about Surly Disc trucker, 520, Fuji touring, AWOL, I decided I like the Kona Sutra the best(although I hear very good things about the disc trucker)
I owned a 53cm 2015 Kona Sutra, on this I had a 110mm 6 degree rise stem, and I had not that much of the seat post showing.
KONA BIKES | 2015 BIKES | FREERANGE | SUTRA
For the 2016 Kona Sutra, their website recommends 3 sizes for my height range 168-180cm (I'm 173cm)
The 3 sizes are 52, 54, and 56cm
KONA BIKES | 2016 BIKES | SUTRA | Sutra
Now to my question. How much difference will I notice in the frame sizes, I will want to be able to run a seat post bag that needs 5inches of exposed seat post, which I was pushing it with the old 53cm frame. my LBS doesn't stock Kona bikes, so I would have to order a bike online without testing out the frame size first. Or I may just wait until the 2017 bikes come out.
I am trying to pick a new frame, I had a look about Surly Disc trucker, 520, Fuji touring, AWOL, I decided I like the Kona Sutra the best(although I hear very good things about the disc trucker)
I owned a 53cm 2015 Kona Sutra, on this I had a 110mm 6 degree rise stem, and I had not that much of the seat post showing.
KONA BIKES | 2015 BIKES | FREERANGE | SUTRA
For the 2016 Kona Sutra, their website recommends 3 sizes for my height range 168-180cm (I'm 173cm)
The 3 sizes are 52, 54, and 56cm
KONA BIKES | 2016 BIKES | SUTRA | Sutra
Now to my question. How much difference will I notice in the frame sizes, I will want to be able to run a seat post bag that needs 5inches of exposed seat post, which I was pushing it with the old 53cm frame. my LBS doesn't stock Kona bikes, so I would have to order a bike online without testing out the frame size first. Or I may just wait until the 2017 bikes come out.
03-31-16, 06:57 AM
#2
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Again sorry about asking more silly questions, but I don't really know much about bicycle geometry, I do hear that it gets very technical though.
I am trying to pick a new frame, I had a look about Surly Disc trucker, 520, Fuji touring, AWOL, I decided I like the Kona Sutra the best(although I hear very good things about the disc trucker)
I owned a 53cm 2015 Kona Sutra, on this I had a 110mm 6 degree rise stem, and I had not that much of the seat post showing.
KONA BIKES | 2015 BIKES | FREERANGE | SUTRA
For the 2016 Kona Sutra, their website recommends 3 sizes for my height range 168-180cm (I'm 173cm)
The 3 sizes are 52, 54, and 56cm
KONA BIKES | 2016 BIKES | SUTRA | Sutra
Now to my question. How much difference will I notice in the frame sizes, I will want to be able to run a seat post bag that needs 5inches of exposed seat post, which I was pushing it with the old 53cm frame. my LBS doesn't stock Kona bikes, so I would have to order a bike online without testing out the frame size first. Or I may just wait until the 2017 bikes come out.
I am trying to pick a new frame, I had a look about Surly Disc trucker, 520, Fuji touring, AWOL, I decided I like the Kona Sutra the best(although I hear very good things about the disc trucker)
I owned a 53cm 2015 Kona Sutra, on this I had a 110mm 6 degree rise stem, and I had not that much of the seat post showing.
KONA BIKES | 2015 BIKES | FREERANGE | SUTRA
For the 2016 Kona Sutra, their website recommends 3 sizes for my height range 168-180cm (I'm 173cm)
The 3 sizes are 52, 54, and 56cm
KONA BIKES | 2016 BIKES | SUTRA | Sutra
Now to my question. How much difference will I notice in the frame sizes, I will want to be able to run a seat post bag that needs 5inches of exposed seat post, which I was pushing it with the old 53cm frame. my LBS doesn't stock Kona bikes, so I would have to order a bike online without testing out the frame size first. Or I may just wait until the 2017 bikes come out.
03-31-16, 07:16 AM
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I will most likely be buying 170mm cranks if that helps, since Shimano don't seem to make 167.5mm in the XT trekking groupset.
03-31-16, 07:34 AM
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The crank length is immaterial to what you're asking.
A rough guide is to measure your inseam accurately then subtract 25cm. So if your inseam is 77cm a 52cm frame would be a good place to start, and a 56cm would almost certainly be too big. If you are between sizes it is usually better to go for the smaller one.
How much seat post is exposed depends in part on whether the bike has a sloping top tube. A traditional horizontal top tube will mean less seat tube being exposed.
A rough guide is to measure your inseam accurately then subtract 25cm. So if your inseam is 77cm a 52cm frame would be a good place to start, and a 56cm would almost certainly be too big. If you are between sizes it is usually better to go for the smaller one.
How much seat post is exposed depends in part on whether the bike has a sloping top tube. A traditional horizontal top tube will mean less seat tube being exposed.
Last edited by chasm54; 03-31-16 at 07:40 AM.
03-31-16, 07:38 AM
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According to the geometry charts offered, your 2015 has a seat tube length of 53 cm and the nearest in the 2016 line up is the Med. with a 52 cm length seat tube so you would gain an extra 1 cm of exposed seat post theoretically. The next size larger, the M/L has a 54 cm seat tube so you would lose another 1 cm of exposed seat tube. The new medium frame is definitely closest to what you have now in terms of reach and stack and a 110 stem is a solid average length that is neither too short nor too long, soooo bottom line is, if you feel your present frame fits you well, go for the M.
04-01-16, 03:29 AM
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According to the geometry charts offered, your 2015 has a seat tube length of 53 cm and the nearest in the 2016 line up is the Med. with a 52 cm length seat tube so you would gain an extra 1 cm of exposed seat post theoretically. The next size larger, the M/L has a 54 cm seat tube so you would lose another 1 cm of exposed seat tube. The new medium frame is definitely closest to what you have now in terms of reach and stack and a 110 stem is a solid average length that is neither too short nor too long, soooo bottom line is, if you feel your present frame fits you well, go for the M.
04-01-16, 07:11 AM
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azza, you could do that but realize the effective top tube on that 54 will be a full 2 cm longer on the new bike and you may very well need a shorter stem, no big deal since you're sporting a 110 now, unless you're already pretty well stretched out. Look forward to seeing pics.
04-01-16, 07:23 AM
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Unfortunately your saddle height is pre-determined by your leg length. The amount of exposed seat post will be determined by your "saddle pedal start height" combined with the frame geometry. The only way to add more exposed seat post is to choose the smallest possible frame along with a more sloping top tube. Even with a steeper TT your saddle rear will be the same distance from the rear wheel.
Pictured are my 52cm Litespeed with level TT and 41cm BG Rock & Road with steeply sloping TT. Identical pedal start heights. Seat bag clearance to rear wheel is identical on each. Of course a bit closer clearance on the bike with rack and fenders but same distance to wheel.
As an example, a Revelate Viscacha requires 9.5" clearance between rails and tire. I only have 8.5" on either bike despite the difference in seat post extension. Short people just have to ride closer to the rear wheel. Aside from going to 26" wheels altering frame shape will never change that!
Pictured are my 52cm Litespeed with level TT and 41cm BG Rock & Road with steeply sloping TT. Identical pedal start heights. Seat bag clearance to rear wheel is identical on each. Of course a bit closer clearance on the bike with rack and fenders but same distance to wheel.
As an example, a Revelate Viscacha requires 9.5" clearance between rails and tire. I only have 8.5" on either bike despite the difference in seat post extension. Short people just have to ride closer to the rear wheel. Aside from going to 26" wheels altering frame shape will never change that!
Last edited by BobG; 04-01-16 at 08:25 AM.
