Mountain Bike Sizing Confusion- Mtbr.com
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  1. #1
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    Mountain Bike Sizing Confusion

    Hi,
    I've been reading a lot up on mountain bikes and sizing myself up to make sure the bike fits me comfortably and correctly. Today, I went into my LBS and try sitting on a Trek Fuel EX 7 17.5 and Fuel EX 6 18.5.

    From my own measurement, without wearing any shoes, from the floor to my (nice way to put it) testicals measure approx 27 to 28". I'm 5'7.5" tall w/out shoes.

    One of the employee that help me out explain it saying something about the fork 120mm height and how it was higher in the front that is causing this. I didn't really understand it too much and didn't want to bother the guy too much. My understanding was that on a mountain bike, you should have at least 2 to 3 inches of clearance. With both of these bikes, I had at most, 1" clearance. My back was about a inch away from the tip of the seat.

    Could someone explain if this is right?

    He was also saying that what I should also worry about was to make sure I have about a 90 degree formation at my elbow; too much or too little will make turning hard. This part understood, but this lead me to my other questions. Should I have a 90 degree angle at my elbow when the wheel is straight in front or the front wheel is at a 45 degree angle whiling sitting down and holding onto the handle bar?

    My first bike and I just want to make sure I buy something that I don't regret and looking at a full suspension bike over a hardtail.

    Thank You!

  2. #2
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    There's no way you should be riding with your arms at 90 degrees at the elbow. If that's what he meant, then I'd forget about anything else he had to say. I'm nearly identical in measurements as you and on most frames, 17-17.5 is about right. With longer travel forks, you're not always going to have the extra space with stand over. What's more important is fit while ON the bike.

  3. #3
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    This is correct...sort of. Standover should be 2-3". Although this was adopted more back in the day when TT weren't so sloping...so to speak.
    If your 5'7", I can almost guarantee that a medium in Trek or Specialized would be the right bike. My wife is 5'5" and rides a medium stumpy fsr..fwiw.

    If you feel too stretched out you can change stems from a 90mm to a 75mm...for example.
    Unless you have extremely short legs...I can't see how you only had a inch. Did you stand over like you were and pull up on bike. That is how you measure. My wife has 3" easy and she has normal inseam. You should have close to the same.
    Get on a medium and ride around lot or better yet...rent one and get on trail. It is not uncommon to make changes and a good lbs will do this as part of the fitting process. Some employees do not know what they should and are just salesman. Bike shop jobs aren't what they used to be.
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  4. #4
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    Like dunrinaz said the most important thing is how the bike fits while riding it. It's easy enough just to lean the bike over a little when you dismount.

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    Thanks everyone! I'm waiting for a dryer weekend so I can take the bike out for a ride to test out the feel and comfort level.

  6. #6
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    Standover is important....its more than just being able to dismount leaning the bike over
    Go Solar...

  7. #7
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    If your inseam measurement is correct you'll have a hard time finding a full suspension bike that gives you 2-3" clearance. The Fuel posts a 29.8" standover height. I've checked a few other brands, too. Most medium and even small FS bikes seem to be in that range.

    Check out the geometry pages of the bike brands. Most publish standover height data for their bikes.

    You might be a bit long in the torso (compared to the average Joe). So you might have to compromise on standover height and/or have stem and bar adjusted for you.

    I'd focus more on the top tube length and consequently the bike handling. Standover height is most important for getting off of the bike. The mentioned 'leaning' happens mostly when you stand on the pedals. You'll have plenty of clearance for that. Easy to check in the parking lot. And yes, test riding is a good idea.
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  8. #8
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    Quote Originally Posted by larlev
    Standover is important....its more than just being able to dismount leaning the bike over
    standover is probably the LEAST important thing when sizing a bike
    Honestly... ahh I give up

  9. #9
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    Haha....you must be kidding.

    Jimmy, here is a good rule of thumb. Inseam x .67 - 4" = frame size
    Last edited by larlev; 01-03-2011 at 08:31 AM.
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  10. #10
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    Quote Originally Posted by larlev
    Haha....you must be kidding.
    Absolutely not.
    How I dunno know 'bout you, but I go out for bike RIDES - not bike 'stand-overs'

    That formula is whack - what if they have really short legs and a long torso? or how about vice-versa?

    To add, frame "sizes" are hardly reliable anymore with the different shapes of frames, geo and the way an individual MFR actually 'measures' the frame "size" vs. another one..
    Honestly... ahh I give up

  11. #11
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    If you can't standover the bike with feet flat on ground your asking for problems. Period, no need to even go any further.

    The formula works for 99%....good grief, there is always exceptions.
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  12. #12
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    Quote Originally Posted by JimmyNeutron10101
    ...From my own measurement, without wearing any shoes, from the floor to my (nice way to put it) testicals measure approx 27 to 28". I'm 5'7.5" tall w/out shoes....
    FWIW...I'm guessing you aren't measuring your biking inseam correctly.

    Taken from Colorado Cyclist..".To determine your proper frame size, you'll first need to get an accurate inseam measurement . Stand with your back against a wall, your bare feet 6" apart on a hard floor, looking straight ahead. Place a book or carpenter's square between your legs with one edge against the wall, and pull it up firmly into your crotch, simulating the pressure of your saddle while riding. Have a helper measure from the top edge of the book to the floor, in centimeters. (You can convert inches to centimeters by multiplying inches by 2.54.) Repeat two or three times, for consistency, and average the results to get your inseam length."

  13. #13
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    Quote Originally Posted by larlev
    Haha....you must be kidding.

    Jimmy, here is a good rule of thumb. Inseam x .67 - 4" = frame size
    No, he is not kidding, he is absolutely correct.

    And that is a terrible rule of thumb for buying a bike. It might be OK for guessing what size beach cruiser to rent, but a lousy way to look for a mtb. Any rule of thumb that goes by seat tube length for a mountain bike is fairly worthless these days. I have fit mountain frames ranging from 16"-19" seat tubes (which is what my two current frames are).

    I've had one 16", one 17", one 18", and two 19" mountain frames that fit just right.
    I've had one 17" frame that was to small, and one 18" frame way to big (I now ride the 16" version of that frame).

    I have also owned bikes that had basically zero stand-over, and it is a non-issue. Yes, it is more convenient in some cases to have more, but the correct reach (related to top tube length) is 20 times more important. In other words, go by top tube and reach, NOT by stand-over, and certainly not by seat tube length.
    15mm is a second-best solution to a problem that was already solved.

  14. #14
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    For a NEW rider..its a damn good starting point. Thats all it is....
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    Test them out if you can, but I would guess that you'd be happier on a 17.5. The 17.5 has an effective top tube length of 23.3" and the large is 24.1". If you don't feel comfortable with the standover, try a different brand of bike.

    I am 5'8" and my boyfriend is 5'9". We both like bikes with effective top tube lengths between 23" and 23.5". I recently agonized over sizing and ended up choosing a medium Ibis Mojo (22.8" effective tt) vs. large (23.6" effective tt) and I'm soooo happy. I feel like I can whip around the smaller bike and control it easier in technical terrain and tight terrain. If I was into riding fast down straigher, less technical trails, the larger bike may have been a better choice.

    I have heard a lot of people complain that their bike is too large for them, and not too many complain of their bike being too small (unless it was a hand-me-down and clearly the wrong size). Especially for a beginner, a bike that is a little too big is harder to handle than a bike that is a little too small.

  16. #16
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    Quote Originally Posted by JimmyNeutron10101
    Hi,
    I've been reading a lot up on mountain bikes and sizing myself up to make sure the bike fits me comfortably and correctly. Today, I went into my LBS and try sitting on a Trek Fuel EX 7 17.5 and Fuel EX 6 18.5.

    From my own measurement, without wearing any shoes, from the floor to my (nice way to put it) testicals measure approx 27 to 28". I'm 5'7.5" tall w/out shoes.

    One of the employee that help me out explain it saying something about the fork 120mm height and how it was higher in the front that is causing this. I didn't really understand it too much and didn't want to bother the guy too much. My understanding was that on a mountain bike, you should have at least 2 to 3 inches of clearance. With both of these bikes, I had at most, 1" clearance. My back was about a inch away from the tip of the seat.

    Could someone explain if this is right?

    He was also saying that what I should also worry about was to make sure I have about a 90 degree formation at my elbow; too much or too little will make turning hard. This part understood, but this lead me to my other questions. Should I have a 90 degree angle at my elbow when the wheel is straight in front or the front wheel is at a 45 degree angle whiling sitting down and holding onto the handle bar?

    My first bike and I just want to make sure I buy something that I don't regret and looking at a full suspension bike over a hardtail.

    Thank You!
    Judging from the top tube lengths listed on the trek site, I have a hard time seeing a 5'7" person on the 18.5 size.

    I would go to the trek board and ask what size Fuel people close to your measurements (height and inseam) are riding.

    And that is good advice above about how to measure your inseam.
    15mm is a second-best solution to a problem that was already solved.

  17. #17
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    Quote Originally Posted by gmcttr
    FWIW...I'm guessing you aren't measuring your biking inseam correctly.

    Taken from Colorado Cyclist..".To determine your proper frame size, you'll first need to get an accurate inseam measurement . Stand with your back against a wall, your bare feet 6" apart on a hard floor, looking straight ahead. Place a book or carpenter's square between your legs with one edge against the wall, and pull it up firmly into your crotch, simulating the pressure of your saddle while riding. Have a helper measure from the top edge of the book to the floor, in centimeters. (You can convert inches to centimeters by multiplying inches by 2.54.) Repeat two or three times, for consistency, and average the results to get your inseam length."
    Thanks! I'll have to re-measure myself later tonight. I was standing with my feet together and not 6" apart.

  18. #18
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    The only parts of the bike that effect how it fits when you're riding are the saddle, pedals and handle bars. If those are in the right places, the bike fits.

    If you have to use a really long or really short stem to make it fit, the handling will be screwy. So, to me, the right size bike is one that fits with a stem size that's good for good handling. That's subject to a lot of debate too, but I think a range of 70mm to 100mm is pretty good for most trail riding that involves climbs. For me, an 80mm or 90mm stem is preferable. I'm a little over 5'8", and I've noticed that much taller people are often happier on longer stems. I don't know if that's something about proportions or something about how frame lengths change as the size increases, though.

    My point with all this is that when you test-ride some bikes, they'll almost all have stems in a pretty "normal" size range. So you can fairly confidently buy the one that feels best, and maybe get a stem a centimeter longer or shorter when you've got some saddle time in.

    I think a 90 degree bend in the elbows is pretty excessive for someone riding at cruising pace. Your effort level will have some effect on your riding position, so someone riding very hard might get that low. If you have no bend in your elbows, or your back is completely straight, when you're riding, your bike will beat you up. The straight back thing tends to happen on too small a bike, the straight elbow thing tends to happen on too big a bike. So look for the size that you tend to sit on with a curved back and bent elbows. My guess would be that the 17.5" is better for you, but if you have a longer torso than me, you might prefer the 18.5", and if you're only going to be riding for short periods, in very technical areas, you might like the 15.5". I suspect that when you have time to ride the bikes a little bit, you'll develop a pretty strong idea of which one you prefer. Don't be afraid to ask the shop guy to move the handlebars up or down, or even swap for a longer or shorter stem. This is a very expensive bike, so it's worth taking the time to get the size right, and it ought to make a decent amount of money for the shop, so if they won't work with you on getting the right one, look for another shop.

    I've been riding, and crashing mountain bikes for a long time. I have to say that I've never had a crash in which standover height was an issue. I've gone over the bars, in which case it doesn't matter... slid out, in which case it doesn't matter... high-sided, in which case it doesn't matter. Really, the only thing for which I find some standover clearance useful is standing at a longish traffic signal.
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  19. #19
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    Quote Originally Posted by larlev
    If you can't standover the bike with feet flat on ground your asking for problems. Period, no need to even go any further.

    The formula works for 99%....good grief, there is always exceptions.
    Explain how this formula incorporates ETT length (the single post important starting point in bike fitment)?
    Honestly... ahh I give up

  20. #20
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    Quote Originally Posted by larlev
    For a NEW rider..its a damn good starting point. Thats all it is....
    No it's not and another good example of poor information on these forums.

    OP, try another bike shop you feel more comfortable with if that salesman didn't seem competent. It's a good idea to get a bike fit for your first bike. Write down the measurements and keep them from bike to bike. Also try test riding different manufactures as they all are just a little different and one might fit better than another.
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  21. #21
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    Quote Originally Posted by Mount Dora Cycles
    No it's not and another good example of poor information on these forums.
    ANOTHER? You mean this has happened before on MTBR?
    15mm is a second-best solution to a problem that was already solved.

  22. #22
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    Blah, Blah....it works.
    Did I ever say it was the be all end all of bike fitting. It's funny how that formula came from the MTB training facility in San Diego. They must be clueless.....

    Wow...Mount Dora...you really added something beneficial there with that post. Pussa, Highdoll what have you offered? Not a damn thing...not unusual though
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  23. #23
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    i was gonna say that if your boys still clear the top tube you're good. you need the clearance up to the pubic bone, not just the lowest dangling bits. in most brands a medium or ~17 inch frame should be the right one. test ride and see if it's comfortable.
    mtbr says you should know: i work in a bike shop.
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  24. #24
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    Quote Originally Posted by larlev
    ..., Highdoll what have you offered? Not a damn thing...not unusual though
    I only offered the truth...if that's 'not a damn thing' to you, that must mean it's a DAAAMN TAHNG!
    Honestly... ahh I give up

  25. #25
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    how is this stand-over for rideability?


    Good leg-extensoin, they don't look , sorry LUK, too stretched nor cramped - I say it fit's nicely
    Honestly... ahh I give up

  26. #26
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    I just measured my inseam with shoes on and my feet six inches apart.

    If I use the MTB training center (in San Diego) formula, apparently I should be riding a 20" frame (36" x .67= 24.12. . . . . . 24.12 - 4" = 20.12").

    I'm not built like Steve Erkel, but I'm not built like Cotton Hill either. I'm 6'5" with a 36" inseam (very average proportionally) with shoes on and currently ride a 23" frame with 33" standover.

    I can alter the saddle height with minimal effect on geometry and I can adjust for that as well with little to no effect on handling. I can't adjust for top tube length (using stem length or saddle position) without having considerably more effect on handling and/or pedaling position.

    It just doesn't make good sense to go at it that way IMHO (no concern for top tube length?) and it didn't (magically) come close to hitting my size.

    However, 36" x .75 - 4" does happen to (magically) = 23"

  27. #27
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    Quote Originally Posted by jeffj
    ...
    However, 36" x .75 - 4" does happen to (magically) = 23"
    SWEET - now a real formula...

    ..


    ..

    ..haaay, how come it doesn't werk for me?
    Honestly... ahh I give up

  28. #28
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    Quote Originally Posted by highdelll
    SWEET - now a real formula...

    ..


    ..

    ..haaay, how come it doesn't werk for me?

    Hint: .alumrof cigam nwo ruoy rof sdrawkcab kroW

    Current preferred frame size + 4" divided by your cycling inseam in inches

  29. #29
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    Quote Originally Posted by jeffj
    Hint: .alumrof cigam nwo ruoy rof sdrawkcab kroW

    ...
    AH...werks perfectly!
    thanks Jeff!

    the cigam was a bit tho...I have to admit
    Honestly... ahh I give up

  30. #30
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    Quote Originally Posted by larlev
    Wow...Mount Dora...you really added something beneficial there with that post. Pussa, Highdoll what have you offered? Not a damn thing...not unusual though
    I could have put "i like girls" as my post and it have been more useful to the OP than what you posted incorrectly. However, I did not and gave the OP the information he needs to get the correct size bike. Now please just ride and stop posting just to post.
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    "It's amazing how people can make bicycle riding seem so complicated on the internet."

  31. #31
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    Quote Originally Posted by larlev
    Blah, Blah....it works.
    Sometimes. And a broken clock is accurate twice a day.

    Did I ever say it was the be all end all of bike fitting. It's funny how that formula came from the MTB training facility in San Diego. They must be clueless.....
    In this matter, they apparently are.
    15mm is a second-best solution to a problem that was already solved.

  32. #32
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    I like the new formula. I have a 33" inseam 33x .67 -4 = 18.11 Guess what? No way I could ride a 18" frame on either of my bikes. Now a 21" for both is great 33 x .75 - 4 = 20.75. One of my rides has a much higher stand-over than the other (1.5") and that only gives me about 1" stand over, but the 19" felt cramped in the cockpit and I want to ride my bike as HighDell said not stand over or rest on it like a roadie.

  33. #33
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    the formula worked for me...

  34. #34
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    Quote Originally Posted by William_Cannon
    the formula worked for me...
    Details?

  35. #35
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    Quote Originally Posted by jeffj
    Details?
    his boobs are twice as big
    Honestly... ahh I give up

  36. #36
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    Quote Originally Posted by JimmyNeutron10101
    ...without wearing any shoes, from the floor to my (nice way to put it) testicals measure approx 27 to 28". I'm 5'7.5" tall w/out shoes...
    I'm also a newbie and here's a little tip: Just because you can ride a certain size of bike that it is the right size of bike for you. The wrong size bike may feel okay for a 5-minute ride around the LBS parking lot but you will hate it once you go out on your first extended ride. I can ride a medium (18in, and per sticker on the bike is good for 5'7"-5'11" riders) and even a large (20in) Giant Trance just fine but I know from past experience that they are not right size for me.

    I'm exactly the same height as you and my measured inseam is 30in. (With the help of my wife, stand against the wall, use a hardbound book and push really hard up against my, you know... <cough>) I like to ride a little bit upright so my prefered effective toptube is 21-23in. I found that Giant's small size (16in seattube) is the perfect size for me.

    And oh, most full suspension bikes with 120mm fork seem to have a standover of around 30" so you probably won't find any that will satisfy the 2"-3" over standover rule.

  37. #37
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    There seems to be no really way to determine the correct size unless you owned the bike for a week or so while riding it like you bought it for. then you will know..

    Seems to me that the formula given is the closet estimate you are going to be able to get next to actually riding the bike on a full day trip.

  38. #38
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    It's not as hard as all that. It's really just trying to take something that's basically qualitative - how does a bike feel - and make it quantitative that's the problem. Mountain bike sizes are different enough from each other that on riding two different sizes back to back, one of them should feel better. It's not necessarily that easy either. I think it takes some saddle time to develop a sense of whether or not a bike fits. The difference in top tube length between the two bikes the OP was looking at is 2cm - actually quite a lot, especially if the larger bike comes with the next size longer stem. Hopefully if he's planning to buy a bike as expensive as one of the Fuel EX, he's been riding long enough to have his current bike either fitting well, or an idea of how he'd like it to be different.

    Although it's not unusual for some fine tuning of fit to take a week, or a season, of riding to work out.
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  39. #39
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    I don't understand. This is exactly what bike shops are there for. Find a bike you like, have them put it on a trainer and get a bike fit. If they look at you funny, walk out and find a new shop.
    Quote Originally Posted by rkj__
    "It's amazing how people can make bicycle riding seem so complicated on the internet."

  40. #40
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    I have a Fuel EX. I ride a 15.5 frame. My inseam is 30 inches and I am 5'6". I had a choice between that and the next size up which is the 17.5".

    I find that the smaller frame responds to pedal input better. I also like the upright riding position. Working the cockpit comes easier too.

    The thing i dont like about the small frame is that i use such a long seat post, that it does not go into the seat tube as much as i would like.

    Standover height is not an issue for me. Top tube is where its at. I find that top tubes in the high 22s give me upper back problems.

  41. #41
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    Quote Originally Posted by bing!
    snip...
    The thing i dont like about the small frame is that i use such a long seat post, that it does not go into the seat tube as much as i would like.
    I use a 400mm post with about 5 inches of post in the frame. Any less than 4 inches of seat post in the frame and a 400mm post and I think I would need the next sized frame. Really a 350mm post should be long enough for most people to get a suitable seat height.
    I went with a smaller frame and longer post rather than the next sized frame because the ETT was too long on the bigger frame.

    Not enough post in the frame can result it the seat tube cracking.
    Last edited by mitzikatzi; 01-06-2011 at 05:04 PM.
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  42. #42
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    This thread is out of control. Seatpost size has nothing to do with frame sizing.

    Bing!: As long as the seatpost is below where the top tube attaches to the seattube, it is fine. If your seatpost doesn't go down that far, get a new, longer seatpost.
    Quote Originally Posted by rkj__
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  43. #43
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    Quote Originally Posted by Mount Dora Cycles
    This thread is out of control. Seatpost size has nothing to do with frame sizing.

    Bing!: As long as the seatpost is below where the top tube attaches to the seattube, it is fine. If your seatpost doesn't go down that far, get a new, longer seatpost.
    Which more often or not is a minimum 4 inches
    If you need more than a 400mm post to get 4 inches of post in the frame and the correct seat height. I think you need a bigger frame.
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  44. #44
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    go here

    http://www.competitivecyclist.com/za...LCULATOR_INTRO

    take the measurements.
    look at the results
    go to the bike manufacturers website and look up the geometry of the bike you are interested in.
    pick out the frame size(s) that best fit.
    Head to LBS and test ride those frame sizes.
    yes adjustments can be made (move saddle forward/back, shorter/longer stem)
    buy the bike that best fits YOU

    just because someone is the same height/inseam does not mean the bike size they ride will work for you.

  45. #45
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    Quote Originally Posted by Simplejack
    There seems to be no really way to determine the correct size unless you owned the bike for a week or so while riding it like you bought it for. then you will know..

    Seems to me that the formula given is the closet estimate you are going to be able to get next to actually riding the bike on a full day trip.
    NO, as pointed out earlier,
    ETT or effective top-tube length is a great way to determine sizing.

    Yeah, this will not help a newb when buying a frame or bike. But hopefully said 'newb' has a decent bike shop that knows what they're talkin about and can hook them up with a good fitment
    Honestly... ahh I give up

  46. #46
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    Quote Originally Posted by Mount Dora Cycles
    This thread is out of control. Seatpost size has nothing to do with frame sizing.

    Bing!: As long as the seatpost is below where the top tube attaches to the seattube, it is fine. If your seatpost doesn't go down that far, get a new, longer seatpost.
    seriously...
    Honestly... ahh I give up

  47. #47
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    Quote Originally Posted by mitzikatzi
    Which more often or not is a minimum 4 inches
    If you need more than a 400mm post to get 4 inches of post in the frame and the correct seat height. I think you need a bigger frame.
    where do you get "4"" from?
    the insertion length is dependent (foremost) on how far the collar of the seattube is to the bottom of the top-tube.

    The 'min insertion line' is a CYA for post makers .

    I'll tell you this tho...I'd rather a broken post than a broken frame..
    Honestly... ahh I give up

  48. #48
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    Quote Originally Posted by Simplejack
    There seems to be no really way to determine the correct size unless you owned the bike for a week or so while riding it like you bought it for. then you will know..
    This is very true. Particularly with mountain bikes, it is a fairly inexact science, and experience often changes what you want from your fit.

    Seems to me that the formula given is the closet estimate you are going to be able to get next to actually riding the bike on a full day trip.
    No, it is not, because it relies on seat tube length. Any system that uses seat tube length to determine size is deeply flawed. A MUCH better way to get a starting point for someone without previous experience as to what fits is the calculator from competitive cyclist (linked to in a post further down), because it takes into account the rest of your measurements, and it will let you know what top tube length to look for. It is still not as good as time on a bike, but it is a heck of a lot better then the formula thrown out here.
    15mm is a second-best solution to a problem that was already solved.

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    Quote Originally Posted by bing!
    I have a Fuel EX. I ride a 15.5 frame. My inseam is 30 inches and I am 5'6". I had a choice between that and the next size up which is the 17.5".
    Quote Originally Posted by JimmyNeutron10101
    Hi
    I think you should try 15.5 frame size like bing! has. You might discover it to be the right size for you. If you're looking at other brands, try ones with a effective top tube of around 22 inches and frame size (seat tube) of 15.5 to 16.5 inches. On a mountain bike, and being a beginner, I don't think you will want to be stretched out on the cockpit like on a road bike.

    Don't worry too much about the 2-3" gap-over-the-toptube rule. You'll be hard up finding a full suspension bike that will satisfy that rule and still be the right size, has the right price, color, components, etc. Your 'precious' may be touching the top tube but as long as you can straddle the bike while standing straight, it should be ok. The effective top tube is more important.

    Sorry if I'm talking here like an expert (which I'm not) but I'm just hoping you don't end up like me. I bought 3 bikes before discovering the right fit :-)

  50. #50
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    Reading comprehension fail. I didn't realize this is the OP's first mountain bike.

    OP, borrow a bike or buy an inexpensive one if you have to and get some saddle time. You don't necessarily need to spend all season, or even the rest of the month on it. Just go riding a few times, figure out your saddle height, and get the cockpit as good as you can without spending more money. Then go try the Treks again. Do you have a sense of what kind of riding you want to do? (Like long rides in beautiful places vs. challenging yourself to get through demanding terrain - don't worry about what the discipline is called, that's a whole other long, acrimonious thread.)

    I'm sure you can see from this thread that there are a lot of different opinions about how to size a bike. I think you're best off if you can develop your own.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  51. #51
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    Quote Originally Posted by highdelll
    where do you get "4"" from?
    the insertion length is dependent (foremost) on how far the collar of the seattube is to the bottom of the top-tube.

    The 'min insertion line' is a CYA for post makers .

    I'll tell you this tho...I'd rather a broken post than a broken frame..
    The first thing I do when deciding if a frame will fit me is set the seat height. If I can't get the seat to the correct height I won't be able to ride the bike because I get sore legs. Then I look at the relationship between where the seat and the bottom bracket are. When I sit on the seat is my knee over the pedal spindle (at the 9 o clock position) or a bit behind it. Can I adjust this by changing the post length and set back.If good then I look at the seat to handle bar height difference. Then I get a tape out and measure the distance from seat tip to handle bars. etc etc You get the picture there are a lot of things to consider.

    A bike might have a perfect for me ETT length of 25.234 inches but if I can't set the seat height to my required level then I won't be able to ride the bike. So seat height is one factor you need to look at.

    I have 6 bikes in my spare room. To ensure the seat post extends below the top tube of the frame when inserted 5 of them need 3.5 to 4 inches of post in the frame. One requires about 3.5 inches. I don't care if the minimum insertion line on a seat post is two inches. I think the post should be inserted so it is below the top tube. So as a rule of thumb a minimum of 4 inches is a pretty save rule IMHO. I have a lot of seat post exposed on my bike and you can feel it flex (a Thomson elite btw) I like to have more than 4 inches of seat post in my frame.

    @highdelll I don't want frame to break thats why I try to have the bottom of the seat post well below the top tube. I really hope I never break a seat post I think it would end up being a painful crash. The less seat post in the frame the more likely the frame is too crack. There has been threads on frames with cracks in this area and the consensus seems to be too little post in the frame.

    "The 'min insertion line' is a CYA for post makers ." each frame is different. Just because a post is strong enough a min insert line of 2 inches doesn't me a frame can take that stress.

    Go measure a number of frame from the very top of the seat tube to .5 to 1 inch below the top tube. I reckon 4 inches will be a save bet. I guess some are more. I am yet to see a seat post with a manufactures minimum insertion line that is more than 4 inches. Most of mine are between 2 and 4 inches.

    AND provided you are a "normal" shape (within the range bike designers have in mind when designing frames). If you need a 500mm seat post to get your saddle height correct I think for the size of that person the ETT on that bike in question would probably be to small.

    Ultimately you can get some really crap advice on this forum that is just plain wrong from people who think they are experts. My advice is just as crap as the next person BTW. I too think stand over height is important and that a frame should not be picked on ETT length on it's own. Which to me seems to be what the advice given on here is ETT is all that matters. I disagree. Picking the correct size bike is a compromise between a number of factors on a standard frame ETT is one of them so is stand over .
    Last edited by mitzikatzi; 01-06-2011 at 04:45 PM.
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  52. #52
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    Like others have said. Most likely the first bike you buy will be the wrong size. If you get good help from a LBS then it should be close and reasonably comfortable to ride. It might even be spot on. After you have been riding for a while you find what handle bar width and stem length is comfortable for you. Same with saddle to bar height difference. As you ride more you become more flexible and hopefully a stronger rider. So after a while you might decide you want a more bent over racer position. So the frame you brought with the upright position doesn't really suit you or vis versa. You might decide you need shorter or longer cranks. So buying your first bike is a learning experience.

    I still have my first MTB brought on advice from a shop. I have come to realize that I prefer a frame one size bigger. Same with my road bike (again picked with advice from shop) Maybe I should have looked at different brands and tried to find a frame half a frame size bigger.

    Buying the wrong size bike is a good thing. It gives you a genuine reason to buy another bike in 12 months time thats how I look at it.

    Just like on here different shops will have different bike fitting philosophy.

    The possible effects of too little seat post in the frame here note I said possible
    Last edited by mitzikatzi; 01-06-2011 at 06:26 PM.
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  53. #53
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    Quote Originally Posted by mitzikatzi
    ...
    @highdelll ....
    Hey, I can't tell if you are trying to disagree w/ me?
    I'm pretty sure were on the same page.

    If I'm wrong, please point it out easier for a dum fcuk suck as myself
    Honestly... ahh I give up

  54. #54
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    ETT for me

    I got a Dunlop special with 50 cm Top tube that I found being thrown away outside the local club. Besides it weighs a ton its the best bike for me and cost me zilch.

    Before I found this forum I started building a super bike from ebay bits.
    The Mongoose frame ETT was 55 cm long and it is light as feather and goes like the wind but I hate it.
    It gives me bad back pain cause I am too stretched out even with the shortest stem I can find and seat pushed as far forward as I can.
    My next bike is in planning and I will be paying close attention to ETT before i worry about standover height.

    On both bikes I can stand flat footed over top tube without squashing the jewels.

    my 2c
    If I can't ride to work then it 's not going to be a good day

  55. #55
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    Quote Originally Posted by JimmyNeutron10101
    Hi,
    I've been reading a lot up on mountain bikes and sizing myself up to make sure the bike fits me comfortably and correctly. Today, I went into my LBS and try sitting on a Trek Fuel EX 7 17.5 and Fuel EX 6 18.5.

    From my own measurement, without wearing any shoes, from the floor to my (nice way to put it) testicals measure approx 27 to 28". I'm 5'7.5" tall w/out shoes.

    One of the employee that help me out explain it saying something about the fork 120mm height and how it was higher in the front that is causing this. I didn't really understand it too much and didn't want to bother the guy too much. My understanding was that on a mountain bike, you should have at least 2 to 3 inches of clearance. With both of these bikes, I had at most, 1" clearance. My back was about a inch away from the tip of the seat.

    Could someone explain if this is right?

    He was also saying that what I should also worry about was to make sure I have about a 90 degree formation at my elbow; too much or too little will make turning hard. This part understood, but this lead me to my other questions. Should I have a 90 degree angle at my elbow when the wheel is straight in front or the front wheel is at a 45 degree angle whiling sitting down and holding onto the handle bar?

    My first bike and I just want to make sure I buy something that I don't regret and looking at a full suspension bike over a hardtail.

    Thank You!
    Wow dude, sorry your perfectly normal question got turned into a p!$$!ng contest... Hope you found another shop, or maybe tried talking to someone else at the shop you went to? I'm not sure where the guy is going with the 90 degree elbow thing? (that's a good steep climbing position cause you normally have to be leaning forward and low to get that kind of arm bend?)

    Keep in mind that there is allot of "opinion" in bike fit, and that a good number of pro cyclists get custom frames!

    As far as the elbow bend you kinda need to start by getting your seat at a good height. Ballpark it by sitting on the bike with heel of your foot on the pedal spindle, then adjust the seat height till your leg is straight. Then when you move your foot the way you normally ride, (with the spindle inline with the ball of the foot), you should have a good knee bend. Having your seat height set lets you better determine how the top tube will feel to you. You usually want a comfortable arm bend when sitting on your bike with some arch in your back. Too stretched and you'll have too much weight on your hands (just waiting to endo!), too much bend/upright position and you could have steering, climbing and washout issues cause the front end doesn't have enough weight. And if your spine is too straight up you can hurt your back!!! (Certainly ask if the shop will swap out stems if needed at this point when you get close to buying!) Really this is just a starting point, it usually takes some time on the bike and experimentation to get good bike fit. Besides stem length and rise you have to adjust your seat for and aft and fine tune seat height/tilt after you get your suspension set up!

    As far as the standover an inch is cutting it close IMO, it's not the end of the world but certainly not ideal. Unfortunately I don't really see many bikes that improve on that standover. (A notable exception would be If you rode a large Specialized Safire, (yes a chick bike, but unless it has weight limits it's just a mountain bike with shorter/tighter geometry), you would get a 23.6" TT with 27.3" standover! ) A large GT Distortion or Force would get you a 28.8 Standover and 23.6 TT, Medium Force might be good with a 28.2x23TT. The 2011 Mongoose Teocali's are gonna have good standover, but they haven't updated their website with geo numbers for 11" yet? A Santa Cruz Nickel will also give you a 28.2x23TT. I just noticed the Fuel EX's have slightly longer TT's than the Top Fuel XC race bikes? That doesn't make sense to me...?

    A couple of these give you about another inch off the Trek's TT (oops I meant off the Treks standover), but if your sold on the Trek you'd probably be OK. (get good bike shorts! baggies! good chamois padding and the two layers of baggie shorts will help with incidental top tube contact! ) It's also a matter of how aggressive you ride, or end up riding since it's a new bike. Small get offs shouldn't be an issue, but when you have to bail on steep rocky rooty terrain and you don't have even or level footing you may wish you have more than an inch!

    Good luck! Try and test several models before you buy, don't get rushed into a purchase if your not sure! Also lots of good shops have demo/rental bikes/fee's that will be good towards the cost of the bike if you buy. Nothing beats riding a mountain bike in the mountains to find out if you really like it...
    Last edited by stiingya; 01-10-2011 at 08:59 PM.

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