BikesDirect Bike Sizes



Saephan215

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Feb 11, 2012
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I am planning to buy a bike on bikes direct and I know my bike size is 50cm (I'm 5'6). However, the bike I'm planning to buy says the bike for people my height is 46cm. Does anyone know whether there are any inaccuracies with the bike measurements on bikes direct? Or should I just go with what the website says and buy the 46cm?

http://www.bikesdirect.com/products/mercier/galaxy_al_xi_sc1.htm
 
If you already own a bike that you are comfortable riding go to the manufactures website and print down a geometry chart. You can then use this chart as a comparison to bikedirects and find one that closely matches the size of your current bike.

The most important dimension will be C-2 the effective top tube length followed by J the stand over height going by the BD geometry chart.

Although at your height I think the 46 is on the small side.
 
FWIW. Due to many bicycle frames being made with sloping top tubes, it has become customary to use the TOP TUBE length as the gauge for sizing frames ...

  • THIS method of sizing has been confused in the past when magazine reviewers compare a Medium 29er ([COLOR= #808080]whose top tube is comparable to a Large MTB[/COLOR]) with a Medium MTB which has 26" wheels ([COLOR= #808080]26er, in some parlance[/COLOR]) and then ([COLOR= #808080]stupidly, IMO[/COLOR]) declare that the 29er was too large.

On a frame with a sloping top tube, the VIRTUAL TOP TUBE (or, "Effective Top Tube") becomes the measurement which you should be interested in.

Since a typical (?) 50cm frame would have a ~52cm top tube, I think that you would want the frame which has a 52cm Virtual Top Tube ...

Since the two options straddle the length of a typical 50cm frame, YOU have to decide if you want a slightly smaller or slightly larger frame ...

  • if necessary, you can eventually adjust the "fit" by changing the length of the stem
  • the XS frame has a shorter head tube which will result in a lower stem & handlebar
  • the S frame will, therefore, allow-or-force you to have a slightly more upright riding position which will be slightly less aerodynamic ([COLOR= #808080]if it matters[/COLOR])
  • how "fit" you are can be a factor
  • the 50cm frame will result in an even more upright riding position ([COLOR= #808080]not necessarily a bad thing[/COLOR])

BTW. I'm 5'9" and the top tube on my preferred frame size is 54.5cm with a 120mm stem ... a 54.5cm top tube with a 100mm stem could be feasible for you ... so, in addition to "comfort" ([COLOR= #808080]some people prefer a more upright riding position[/COLOR]) you may want to consider cosmetics ([COLOR= #808080]i.e., a the 53cm top tube +115mm stem is roughly the same "fit" as a 54.5cm top tube + 100mm stem ... the head tube length & actual handlebar height affects the rider's reach & the net reach may not be significantly different ... it just depends[/COLOR]) ...

That's a long way of saying that you may want to let your aesthetic sensibilities be the deciding factor between a S and a M frame.
 
Thanks for the reply guys.

According to the geometry chart, the 46cm has a effective top tube of 53cm and a standover height of ~29inches. And the 50cm has a effective top tube 54.5 cm and standover height of 30.4inches. The numbers doesn't seem right but I never dealt with sloping top tubes. I roughly measured my inseam and it is about 29.5 inches. Should I get the 46cm?
 
FWIW. If I were you ([COLOR= #808080]i.e., if I were 5'6"[/COLOR]) then I would probably get the bike with the 46cm frame rather than the 50cm frame... but, I don't know your fitness level ...

BTW. To some extent, as I vaguely alluded to earlier, frame size is often an aesthetic choice ...

AND, the so-called "stand over height" is an arbitrary measurement ...

  • the first bike a bike shop sold me as a 60cm GITANE ...
  • it was customary to lean the bike when stopped
  • the concept of stand over is influenced by the comparatively small frames which "professional" riders used + the further influence of MTB sizing
 
Originally Posted by alfeng .

FWIW. Due to many bicycle frames being made with sloping top tubes, it has become customary to use the TOP TUBE length as the gauge for sizing frames ...

  • THIS method of sizing has been confused in the past when magazine reviewers compare a Medium 29er ([COLOR= #808080]whose top tube is comparable to a Large MTB[/COLOR]) with a Medium MTB which has 26" wheels ([COLOR= #808080]26er, in some parlance[/COLOR]) and then ([COLOR= #808080]stupidly, IMO[/COLOR]) declare that the 29er was too large.

On a frame with a sloping top tube, the VIRTUAL TOP TUBE (or, "Effective Top Tube") becomes the measurement which you should be interested in.

Since a typical (?) 50cm frame would have a ~52cm top tube, I think that you would want the frame which has a 52cm Virtual Top Tube ...

Since the two options straddle the length of a typical 50cm frame, YOU have to decide if you want a slightly smaller or slightly larger frame ...

  • if necessary, you can eventually adjust the "fit" by changing the length of the stem
  • the XS frame has a shorter head tube which will result in a lower stem & handlebar
  • the S frame will, therefore, allow-or-force you to have a slightly more upright riding position which will be slightly less aerodynamic ([COLOR= #808080]if it matters[/COLOR])
  • how "fit" you are can be a factor
  • the 50cm frame will result in an even more upright riding position ([COLOR= #808080]not necessarily a bad thing[/COLOR])

BTW. I'm 5'9" and the top tube on my preferred frame size is 54.5cm with a 120mm stem ... a 54.5cm top tube with a 100mm stem could be feasible for you ... so, in addition to "comfort" ([COLOR= #808080]some people prefer a more upright riding position[/COLOR]) you may want to consider cosmetics ([COLOR= #808080]i.e., a the 53cm top tube +115mm stem is roughly the same "fit" as a 54.5cm top tube + 100mm stem ... the head tube length & actual handlebar height affects the rider's reach & the net reach may not be significantly different ... it just depends[/COLOR]) ...

That's a long way of saying that you may want to let your aesthetic sensibilities be the deciding factor between a S and a M frame.
This is good info Alfeng. Do you take your inseam into the equation? I saw you mentioned your height at 5'9" but no word about your inseam which could vary from person to person even if their both the same height. I believe the Bikes Direct site starts you at the inseam measurement or also known as stand over height (letter J on the BD site). Usually once the inseam is known and you fit your bike to the inseam, the rest of the bike is adjusted by altering stem height and length, and saddle height and fore and aft positioning. I know you can vary that a bit, but too small of a bike may hunch your body too much, and too big may stretch you out to much, again I know you can change that to a certain degree with stem length and saddle position. That's why in my experience the inseam was the most crucial. Obvious in custom fitted bicycle the builder will take a lot of measurements to make the bike fit you "perfectly" in all areas, but you can't do that for a factory production bike.

However, I don't own a sloping tube bicycle so not sure how the inseam measurement does compared with your method, but BD does offer the stand over measurement so I was assuming it was essentially the same thing. And if the top tube measurement is the most important factor in a sloping frame, how do you measure your body to get the right top tube length?

Perhaps you can explain why I'm wrong.
 
Originally Posted by Froze .


This is good info Alfeng. Do you take your inseam into the equation? I saw you mentioned your height at 5'9" but no word about your inseam which could vary from person to person even if their both the same height. I believe the Bikes Direct site starts you at the inseam measurement or also known as stand over height (letter J on the BD site). Usually once the inseam is known and you fit your bike to the inseam, the rest of the bike is adjusted by altering stem height and length, and saddle height and fore and aft positioning. I know you can vary that a bit, but too small of a bike may hunch your body too much, and too big may stretch you out to much, again I know you can change that to a certain degree with stem length and saddle position. That's why in my experience the inseam was the most crucial. Obvious [COLOR= #008000]in custom fitted bicycle the builder will take a lot of measurements to make the bike fit you "perfectly" in all areas[/COLOR], [COLOR= #008000]but you can't do that for a factory production bike.[/COLOR]

However, I don't own a sloping tube bicycle so not sure how the inseam measurement does compared with your method, but BD does offer the stand over measurement so I was assuming it was essentially the same thing. And if the top tube measurement is the most important factor in a sloping frame, [COLOR= #0000ff]how do you measure your body to get the right top tube length?[/COLOR]

[COLOR= #ff0000]Perhaps you can explain why I'm wrong[/COLOR].
[COLOR= #ff0000]What you say was probaby always valid for frames used by racers[/COLOR] ... but, in the pre-MTB era, Road frames were generally sized larger than they currently are BECAUSE the apparent expectation was that the stem would be at about the same height as the saddle for most riders, so I don't know how you were sizing your non-racing frames way-back-when ...

  • having said that, my brother, who is an inch taller than I am, did choose to ride 21" ([COLOR= #808080]53.4cm[/COLOR]) frames way-back-when even though he didn't race because it ([COLOR= #808080]competition sizing[/COLOR]) was apparently the norm amongst the people with whom he went to college ... so, I can believe that some people always preferred smaller frames than the accepted, recommended size way-back-when
  • even about 10 years ago, and I presume now, one shop in town sizes the frames on the bikes he sells 1-or-2cms larger than I would suggest that most riders choose.

In the here-and-now, WE can-and-should take advantage of the online sizing charts which can be used as a [COLOR= #0000ff]rough guide [/COLOR]... plus, [COLOR= #0000ff]some subsequent trial-and-error for tweaking[/COLOR],

  • FWIW. I reckon that there IS a way that anyone can approximate the size of the top tube + stem length [COLOR= #ff0000]from-the-comfort-of-their-living-room[/COLOR] while they are watching TV ... if if you sit on a forward edge of a kitchen chair-or-equivalent
  • hold onto an unattached handlebar
  • lean forward & look at the TV AND then hold that position for 10 minutes to 2+ hours ([COLOR= #808080]whatever works for you ... 10 minutes should do it[/COLOR]) to find the maximum forward position that you are comfortable holding ... I suppose you could rest the handlebars on something that is in front of where you are sitting
[*] gauge the distance ([COLOR= #808080]or, have someone measure it[/COLOR]) from where your sit bones are ([COLOR= #808080]hence "the forward edge" of the chair[/COLOR]) to the handlebars
  • I reckon THAT will approximate the [COLOR= #0000ff]comfortable[/COLOR] saddle + top tube + stem length for the individual ... subtract the distance from the back edge of the saddle-of-your-choice to wherever on the rails that you want to mount the saddle to the seatpost ... subtract the stem length you want to use ... and, [COLOR= #ff0000]voila[/COLOR] -- the remaining measurement is roughly the top tube length you want (+/-).

FWIW. By my recollection, which anyone can correct, in the days of lugged bikes ([COLOR= #808080]i.e., pre-TIG welding[/COLOR]), it seems that it was not uncommon for the TOP TUBE length to be closer to being the same ([COLOR= #808080]i.e., 57cm[/COLOR]) regardless of the frame size, than not! That is, it was undoubtedly expedient to mass produce frames if the top tube & down tube were the same & the head tube & seat + seat stays were the only variable in fabrication ...
  • That may have been more true for British frames than French & Italian frames ... or, maybe it was just with ANY of the less expensive frames.
It seems that tThe Japanese frames which began to trickle in during the late 70s which also used the English threaded BB may have changed the trend on less expensive frames by being proportional. So, [COLOR= #008000]by serendipity, my 60cm GITANE had a 57cm top tube & a 9cm stem[/COLOR] ... [COLOR= #008000]Lucky me because that's still approximately the top tube + stem length that I still prefer![/COLOR]
  • [COLOR= #008000]a perfect fit[/COLOR]
If I had been sold a GITANE with a smaller frame, it probably would have had the same 57cm top tube BUT a shorter stem. When I ordered my FUJI S12-S LTD frame ([COLOR= #808080]NOS overstock[/COLOR]) from Colorado Cyclist, I chose the frame whose top tube was 57cm; and, that meant a 57c frame. The notion of a longer stem ([COLOR= #808080]and, therefore a shorter top tube[/COLOR]) just didn't occur to me. Stand over? Inseam? I say "who cares?" IMO, stand over is still more of a cosmetic issue for most people ....
  1. Over 6'0" (?) and it probably becomes an issue, but the top tube length is probably more of an issue.
  2. Under 5'6" (?) and it could be a problem if the saddle can't be lowered enough to allow the rider's feet to reach the pedals.
  3. you can probably estimate my inseam by looking at the seatpost exposure & extrapolating

As I mentioned, currently, my "preferred" frame size has a 54.5cm top tube ... 55cm works for me ... 57cm works for me ... 53cm works for me ...
  • with the larger frames, as in the past, 'I' simply lean the bike when I am stopped OR if I am in an urban area with curbs, I rest my curbside foot on the curb
FYI. I adjusted the fit on ALL of the following bikes so that they are the same [COLOR= #008000]perfect fit[/COLOR] for me ([COLOR= #808080]the red Raleigh has 27" wheels & 170mm cranks, the rest have 700c wheels & 175mm cranks[/COLOR]):
For me, after setting the saddle to the pedals, getting the reach to the hoods as close to the same as possible + the DROP in roughly the same place is my goal regardless of the frame's actual size ...
  • the handlebar width affects how I measure the alluded to reach, BTW ...
  • whether it seems arbitrary, or not, you may have noted that the height of the DROPS on my handlebars are all in the vicinity of the lower headset cup because that differential from the top of the saddle to the Drops did-and-still works [COLOR= #0000ff]for me[/COLOR] ... some people have a greater differential to the Drops and/or hoods from the top of their saddle, and others have less.

  • the Track frame has a shorter top tube ([COLOR= #808080]53cm[/COLOR]) which I anticipated would need a 130mm stem, but using my gauge of the distance to the hood AFTER establishing the positon of the saddle relative to the pedals, I ended up with a 110mm stem because of the slightly greater differential between the saddle & the Drops due to the higher BB.
 
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Alfeng, thanks for the detail reply. How old are you? Reason I ask that is because I use to race in the late 70 till the mid 80's, and almost all of us bought bikes that were SMALLER not larger because back in those days the frames flexed too much and so by getting a smaller frame it decreased the amount of flexing. Then to make the bike fit we got the seat up higher then the handlebars not the same height. My first racing bike, a 76 Trek TX900 was a 21 inch bike which was about a 54cm frame, if I remember correctly, but the seat was about 4 inches higher then the bar with a long reach stem. Later when I got my 84 Trek 660 steel frames had become stiffer so I got a 56cm frame because it fit better and I felt more comfortable then I did on the 54. Even on the 56 the seat was higher then the bars by about 3 inches but the stem was shorter in length. When I became 52 on the 660 I put a Nitto Technomic stem with a very short length stem so I wouldn't have to reach out quite as far. But both of my touring bikes, and one was a custom built 07 Mercian Vincitore, one is an older 85 Schwinn Le Tour Luxe and is measured in inches at 23; and the custom Vincitore is a 58cm and the seat is level with the bars on both bikes.

My inseam length is 34. The calculation we used back then is essentially the same as they use today on road bikes; for a road frame size take your inseam (pants length in inches) x 2.54 (cm per inch) x 0.67; thus with my 34" inseam I would be "best" on a 57 to 58cm frame, but I've been able to fit on the 56 without any problems, and what's weird is that I have a Fuji Club 55cm frame and that fits fine also, but I'm back to a seat up to it's max height putting the stem about 2 inches lower then the seat close to what I use to be on the TX900.

On the flexing issue as a side note, the TX900 was very flexy in case you were wondering. The TX900 use Columbus SL and any bike that used Columbus SL regardless if Trek, Ciocc, Colnago, Italvega, or Cinelli all flexed with the Columbus SL tube set. But the French tube sets used in the Peugeot and Motobecane were the worst. When I say flex I mean if I hammered the bike especially up a grade, the chain would rub both sides of the front derailleur and the rear wheel would rub both sides of the rear brake blocks on the French frames, on the Columbus SL it would rub one side of the front derailleur and one brake block. I thought the fastback seat design found in a lot of Italian and on the TX900 was a failure because some of the Italian bikes I tested in 81 didn't flex as much if they didn't have the fastback design as the older Trek with the fastback design, yet the Italian jobs still used the same Columbus SL tube set they used in the late 70's. But by mid to late 80's time Japanese steel came out putting any Italian frame to shame in the flex department. My Trek 660 with Reynolds 531cs tube set will flex but I can't get it to rub anything, but I do notice that on both of my 87 Miyata Team and the 88 Miyata 712 the frame (which are both Miyata triple butted splined tubing) is noticeably stiffer then the 531cs on the 660. The only stiffer frame bike I had was a Schwinn scandium racing bike but it failed at the head tube which cracked for no known reason after about 13,000 miles. I'll never buy another aluminum bike.
 
Originally Posted by Froze .

How old are you?
I'll be eligible for Social Security in less than two years!

No Penny Farthings in my past, but I've probably seen ([COLOR= #808080]and, ¿maybe? used[/COLOR]) a lot more & different bike "stuff" of varying quality than most people who don't work in a shop ever will ... and, some of those people may never have occasion to see the lesser-or-older stuff ([COLOR= #808080]lucky for them![/COLOR]).

I do think that I am fortunate because my height is in the what I perceive to be the middle-range and so off-the-shelf stuff works for me & frame size is-or-can-be, for me & IMO, either an aesthetic choice or one of convenience-of-the-moment.
 
Originally Posted by alfeng .



I'll be eligible for Social Security in less than two years!

No Penny Farthings in my past, but I've probably seen ([COLOR= #808080]and, ¿maybe? used[/COLOR]) a lot more & different bike "stuff" of varying quality than most people who don't work in a shop ever will ... and, some of those people may never have occasion to see the lesser-or-older stuff ([COLOR= #808080]lucky for them![/COLOR]).

I do think that I am fortunate because my height is in the what I perceive to be the middle-range and so off-the-shelf stuff works for me & frame size is-or-can-be, for me & IMO, either an aesthetic choice or one of convenience-of-the-moment.
You and I are close, technically I have 6 years before retirement, but the 401K took some hits so I may have to wait 10 years. The day I retire...well ok, the month I retire I'm doing a self supported bicycle tour across the USA, then I'll come back and try racing again while I work part time doing something, maybe I'll be a Walmart greeter!

My height is really good for stock bikes and my body doesn't scream out for custom fitted or even pro fitted shelf bikes, I fit them myself, and all my bikes range from 55 to 60 cm, and I can ride any of them for hours without complaints from the body department. I do have a custom Mercian because I got a moment of insanity, but it's not anymore or less comfortable then my 5 other off the shelf road bikes. My body, well my hands, arms and shoulders don't like to ride the 2 mountain bikes I have though for long distances; I can ride either of the MTB's for about 30 miles then I'm done, but the road bikes I routinely ride over 100 miles and no pain or comfort problems.

Penny Farthings? I don't even know how those people rode those things! I use to see them in parades when I was kid, but I never saw how they got on one or dismounted it. I'm glad the cycling world didn't embrace those as the ultimate design for cycling, I probably would have taken up a different hobby!!
 
Originally Posted by davereo .

If you already own a bike that you are comfortable riding go to the manufactures website and print down a geometry chart. You can then use this chart as a comparison to bikedirects and find one that closely matches the size of your current bike.

The most important dimension will be C-2 the effective top tube length followed by J the stand over height going by the BD geometry chart.

Although at your height I think the 46 is on the small side.
Bump.

Another one of my scathing reviews of BD.
 
I don't know anything about BD and how they fit bikes.

But it seems to me that if they had you stand against a wall and mark the height to your crotch, height to the top of your shoulder, and height to the top of where your thumb comes out from your palm when stretching both arms straight above your head... they would be able to compute three key measurements to use as a starting point for bike fit.
 
Originally Posted by AlanG .

I don't know anything about BD and how they fit bikes.

But it seems to me that if they had you stand against a wall and mark the height to your crotch, height to the top of your shoulder, and height to the top of where your thumb comes out from your palm when stretching both arms straight above your head... they would be able to compute three key measurements to use as a starting point for bike fit.

Exactly. Initial bike fit is not rocket science, even once you get the bike and do some fine tuning it's still not rocket science unless your a pro racer then your coach may put you in a wind tunnel for purpose to fit you and get your body perfectly aligned on the bike...that's rocket science, but I don't think there is anyone on this forum that needs anything that extreme and costly. I've got bikes ranging in size from 55cm to 60cm and they all fit just fine, and I got them to fit just fine by myself not some LBS BS costly fitting program. I've only heard on the 5 different cycling forums I frequent of one person getting a bike from BD that didn't fit, he had to send it back on his nickle and BD sent him a new bike, but he even admitted getting a smaller frame then he should have because most people on that forum were advising him to get the size smaller then BD said to get! There were a few, including me that told him to get the size BD recommends. Size recommendations from any online bicycle place are there for a reason, if you don't follow those recommendations then you have to deal with the fit issues...if any.
 
Froze said:
Exactly. Initial bike fit is not rocket science, even once you get the bike and do some fine tuning it's still not rocket science unless your a pro racer then your coach may put you in a wind tunnel for purpose to fit you and get your body perfectly aligned on the bike...that's rocket science, but I don't think there is anyone on this forum that needs anything that extreme and costly. I've got bikes ranging in size from 55cm to 60cm and they all fit just fine, and I got them to fit just fine by myself not some LBS BS costly fitting program. I've only heard on the 5 different cycling forums I frequent of one person getting a bike from BD that didn't fit, he had to send it back on his nickle and BD sent him a new bike, but he even admitted getting a smaller frame then he should have because most people on that forum were advising him to get the size smaller then BD said to get! There were a few, including me that told him to get the size BD recommends. Size recommendations from any online bicycle place are there for a reason, if you don't follow those recommendations then you have to deal with the fit issues...if any.
Wow. You assume a lot. It might be true that a lot or even the majority of folks can get by without a formal "fitting", but it is absolutely not true that everyone can. There are many riders out there with asymmetries that don't cause any issues until they're on a bike, and many of those riders need or have needed formal fittings to find solutions. A formal fitting in many cases is much more than just finding the right sized frame and stem for someone on a bike. Claiming anything that doesn't acknowledge that is disservice to any poor sap that would believe those claims.
 
Originally Posted by alienator .


Wow. You assume a lot. It might be true that a lot or even the majority of folks can get by without a formal "fitting", but it is absolutely not true that everyone can. There are many riders out there with asymmetries that don't cause any issues until they're on a bike, and many of those riders need or have needed formal fittings to find solutions. A formal fitting in many cases is much more than just finding the right sized frame and stem for someone on a bike. Claiming anything that doesn't acknowledge that is disservice to any poor sap that would believe those claims.

Please reread my post, I was talking about wind tunnel testing and fitting, so in that light, the majority of people here, if any, need that. Or do have a place you go to that does wind tunnel testing for your "pro" fittings? Even if by some odd chance you do, I would still be right because the majority here don't, and one person doesn't represent the majority unless this forum only has one or two members. And the majority of the bikes sold in America and LBS's are not custom built so they can only estimate which frame size is best for you...something you can do on your own.

Your statement is odd because in light of the fact you agree with me that the majority don't need a fitting, you turn around and attack me for something I didn't say.

I'm chalking this up to misinterpretation of what I said by you, because I don't want to think I'm beginning to see a trend here concerning you and I.
 
Originally Posted by davereo .


Although at your height I think the 46 is on the small side.
In the universe inhabited by mainstream brands, 46 would be too small, but the geometry chart for the Mercier Galaxy (I thought only Dawes and Ford made Galaxies) says the virtual (horizontal) top tube is 53 cm. That makes it equivalent to 51-53 cm. This is right where you should be.

The way bikes are designed these days, seat tube length is so random and irrelevant. I wish they'd just list the top and head tubes.
 
Originally Posted by oldbobcat .

In the universe inhabited by mainstream brands, 46 would be too small, but the geometry chart for the Mercier Galaxy (I thought only Dawes and Ford made Galaxies) says the virtual (horizontal) top tube is 53 cm. That makes it equivalent to 51-53 cm. This is right where you should be.

The way bikes are designed these days, seat tube length is so random and irrelevant. I wish they'd just list the top and head tubes.

In my original post I did state that the effective top tube length was the important dimension.
 
davereo said:
In my original post I did state that the effective top tube length was the important dimension.
You just don't quit, do you, you slanderous bastage! You continue to ooze slanderous filth from your pores, like some slanderous filth oozing beast from Hell.
 
Originally Posted by alienator .


You just don't quit, do you, you slanderous bastage! You continue to ooze slanderous filth from your pores, like some slanderous filth oozing beast from Hell.

HAHAHAHAHAHAHAHAHAHHHHHHHHHHAAAAAAAAAAAA!!!! That was great word selection.
 
Originally Posted by alienator .


You just don't quit, do you, you slanderous bastage! You continue to ooze slanderous filth from your pores, like some slanderous filth oozing beast from Hell.

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