1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
mtn. biking 101
2. If possible, try to find a shop that will let you demo the bike on real dirt. Five minutes in a parking lot won't cut it. You wouldn't buy a car without a real world test drive, and a bike should be no different.
3. Don't belive the hype. Just because your favorite rider or best friend rides a certain bike, that doesn't mean that's the best one for you. Have an open mind and be realistic about your needs and ability.
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  1. #1
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    New question here. difference in feel between an 18.5 and 19.5?

    Hi all,

    I've been doing lots of research and have waffled over a number of trail/AM bikes, finally deciding on a Trek Fuel EX 7. I'll mostly be riding a mix of singletrack, fire road and very light DH.

    I hope to pull the trigger on this rig between now and early spring, but had a question about sizing.

    Am I going to feel a huge difference between an 18.5 and 19.5? I'm 5'10', 175 w/ a 33 in. inseam. I've been riding a Trek 3500 hardtail 19.5, 26er so I'm not sure how/if the 29 inch wheels and a shorter frame will affect me if I switch over to a 18.5. I like the idea of being able to flick the bike around more easily if I went with the 18.5, but then again I'm not too sure if I know what I'm talking about....ha...still kinda new to the sport.

    I did go into a shop last weekend and the rep told me I could go with either one. There was no precise "measuring" happening, which I was a little perplexed about.

    Any advice? Thanks.

  2. #2
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    Is that 33" inseam your pants measurement or measured for a bike fitting? I have a 32" inseam but measure at 34, 6'1" tall.
    I ride a 19.5 and on a 18" I use most of a 410mm seat post.
    Sounds like you are long legs, shorter torso.
    You should compare the reach measurements from your current ride to the bikes you are looking at.
    I'd guess you should be leaning towards the 18.5 - shorter wheelbase, be slightly lighter. The stack height of both sizes is the same, reach is 1.5 cm longer.
    Bike shop is right, I'd say you could ride either one fine.

  3. #3
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    There are two parts to sizing. First, can you make the bike fit? Second, how will it handle? Most of us could make a pretty wide range of sizes fit. Stems range from about 40 mm to about 140 mm, and head tubes are usually low enough not to present a problem, even on bigger bikes.

    At the extremes of bikes that can be made to fit, handling will be pretty ass. Closer to the middle, the differences are more subtle. I think it becomes a matter of weight distribution.

    Between a couple sizes that are close to right for you, the larger bike is going to have less weight over the front wheel. For me, that's the biggest difference I notice. On a climb, it'll be a little harder to hold a line. The smaller bike will hold a line better, but you'll need to pay a little more attention to your weight distribution not to nose dive under braking or when you roll through a compression.

    Does "light DH" mean your trails sometimes go down hills, or are you actually shuttling dedicated DH trails sometimes?

    Be aware that the sizing on the Trek 3500 is weird. It doesn't fit like other 19" or 20" bikes. It's likely to have a more similar fit to the 18.5" Fuel.

    For flickability, as long as you don't have to compromise your reach, I actually don't think it makes much of a difference. The change in wheelbase is not that big, there's very little change in weight, and probably no change in bottom bracket height.

    How much demo/test riding are you able to do?
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  4. #4
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    Minimal testing. I rode the Fuel around the parking lot - and I liked what I felt - but then again, its a parking lot. I've ridden my friend's Specialized Camber Comp 29er, which from my research is pretty similar to the fuel. That's the only "testing" I've done though.

    By "light DH" I mean lots of pedaling uphill, followed by charging downhill. Overall I'm riding XC, period. I don't plan on using the Fuel for shuttled/lift-access DH.

    The inseam (33 in) I mentioned is my proper bike-fitting inseam.

    What do you mean by "compromise my reach"? Taking your word for it, I think the 18.5 is more of what I want. My buddies Specialized Camber is a 19 or 20 in, and to me it felt "long."

  5. #5
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    Keep in mind that in most cases an inch taller also means a longer top tube and if you are long legs/short torso that could be a problem in terms of reach and off course that can be dealt with with a shorter stem.

  6. #6
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    Re: difference in feel between an 18.5 and 19.5?

    Quote Originally Posted by bear99 View Post
    Minimal testing. I rode the Fuel around the parking lot - and I liked what I felt - but then again, its a parking lot. I've ridden my friend's Specialized Camber Comp 29er, which from my research is pretty similar to the fuel. That's the only "testing" I've done though.

    By "light DH" I mean lots of pedaling uphill, followed by charging downhill. Overall I'm riding XC, period. I don't plan on using the Fuel for shuttled/lift-access DH.

    The inseam (33 in) I mentioned is my proper bike-fitting inseam.

    What do you mean by "compromise my reach"? Taking your word for it, I think the 18.5 is more of what I want. My buddies Specialized Camber is a 19 or 20 in, and to me it felt "long."
    Ride them both. Try riding up and down some stairs and steep banks. You should be able to feel it if the wheelbase is a problem, even if you don't have a real trail available. You just need to find some grades, compressions, curbs, etc.

    If you're not a shuttle bunny, don't say "DH." Hold your head up and say "XC." That people are forgetting that XC trails do both climbing and descending is their problem. The kind of DH that needs a different bike is a really different animal. Also, people who do "Trail:" you're doing XC too. The industry just cooked up a new name to help it sell you a gentler-riding bike. (And the final part of my rant: if you're riding a greenway, don't call it mountain biking. It's okay. I do riding that's not mountain biking too. I'm going to ride my road bike over a hill and to the gym in about an hour.)

    When you set up a bike for yourself, you (hopefully) set the saddle position and then put the handlebars in a good place with respect to the saddle and pedals. These three points are the only place your body contacts the bike. So you can imagine a lot of different bike shapes that have no effect on where your contact points are. They all fit you okay in terms of your personal biomechanics. But if you get to a big enough or small enough bike, you stop being able to buy parts that get you to your natural riding position. So the goal here, assuming both sizes allow you to ride in your natural position, is to choose the one that handles better once you've got it set up for yourself.

    Have you dialed in the fit on your old bike?
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  7. #7
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    If you're looking to keep 'flickability', you might also want to do some test rides on bikes with smaller wheels. 3" of extra wheel diameter affect things far, far more than 1" of frame size will.

    FWIW, I'm 5-10ish, 175, 32" inseam and usually ride 18" frames and 26" wheels.

  8. #8
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    One thing to consider: both bikes will feel "bigger" when you get them on dirt, so if the larger frame size feels a bit too big on pavement, it will feel even bigger on dirt, well, depending on the type of terrain you ride. If the smaller bike feels just a "tad" small on pavement, that might translate to feeling right on when you get it on dirt, plus you have the flickability factor with the smaller bike.

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