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I am about to purchase a 2018 Kona Sutra touring bicycle but I need some advice on how to know which is the right size for me.

My measurements are 174cm tall with a 79cm inseam. I was advised that a 52cm size frame was the right size but I am 18 years old and I still have the potential to grow.

On a 54cm frame the top tube almost touches my crotch but I was told that if I were to grow anymore that a 54cm frame would be perfect and now I am left with the decision on which size to buy.

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    Most guys stop growing by any significant amount by about age 16. If you're already 18, you probably aren't going to grow any taller. – David Richerby Nov 15 '17 at 14:04
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    @DavidRicherby agreed - people start bulking out around that age, solidifying instead of stretching. – Criggie Nov 15 '17 at 19:27
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I would go for the bike that fits well today. You can allways increase the saddle height a bit should you grow a bit more. A good fit is very important when it comes to your enjoyment of the bike.

If you do grow, you can get a new bike in a couple of years, if you don't grow you're not stuck with a too large bike.

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    I think the OP is trying to avoid getting a new bike if she/he does get taller, but at 18 going with the right size now is the correct choice. – Argenti Apparatus Nov 15 '17 at 14:54
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    Yes, but eventually that bike will be old and he older with a better economy. It’s a high probability this won’t be he last ever bike. Besides, there’s always n+1 … – Kristian Kalvå Nov 15 '17 at 23:02
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The 2-20 years growth charts here includes predictions of adult height. The boys chart shows that growth between 18 and 20 is less than 1cm (obviously this is averaged over a arge population, and delayed puberty would have a bigger effect, but that would be a different issue). There are two ways given to predict final adult height. One is percentile based (i.e. based on which line you;re on now) and the other is based on parental height (via the percentile you're likely to end up on). Unless there's a big mismatch between the two, you don't need to worry about it.

Unless you're very unlucky or your growth has been delayed for some reason you should be within minor adjustments of your current height for the foreseeable future. Just don't get a bike that's on the small side.

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As @Kristian said, best option is to choose bike size that fits you at the moment.

If you're afraid that your bike will become too small too fast and you don't want to spend money on second new bike, consider buying pre-owned bike now.

If you really want to buy oversized bicycle, make assumptions about your future height by taking into account your (especially male) kin's height. It could be burdened with non-negligible error.

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I would go with the 54 on a touring bike. I grew an inch between 18 and 22, and the clearances for Paineers are greater for the larger frame. You might want your handlebars closer to your center if you get the bigger bike by asking for a shorter stem.

When you say “I was told” listen to the certified bike fitter. If you’re buying the bike from a shop, they should give you a free fit. You should have your seat fit for you as well.

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