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Hello all. I'm a long time recreational mountain biker, but I'm new to this new geometry and was hoping I could get some help on better understanding what I might need. I grew up on the older geometry and even my newest bike is more in line with the "old school" geometry.

A little about me first. I am between 5'9" and 5'10" and somewhere around a 29 to 30" inseam (sorry, I'll have to get back to you if you need more specific answers than that, I didn't come prepared). I grew up riding bikes and practically lived on one for a good portion of my life. Fast forward quite a few years and I found myself riding less and less.

It's probably been 5 years ago now but I decided to get back into riding for a handful of different reasons and bought a newer bike at that time rather than fix up the bike I left off on. Even at that time, it was a lower end, basic, old geometry bike and now as years have passed it's become even more outdated. I just wanted something to get me back out riding again and I figured riding something that was cheaper and more basic was better than sitting at home dreaming about saving up for a better, more expensive bike. I absolutely loved getting back out and riding on my bike and it has served me well, but I've enjoyed it so much that I think I'm ready to upgrade to something newer now. But as someone who has never riden the newer geometry I find myself being a little overwhelmed trying to decipher it all. Unfortunately this hasn't really been the best time to just run out and try on some bikes with all of the ongoing shortages and supply issues, as that would answer many of my questions. I have a couple of bikes that are my main contenders at this point, but I'm trying to narrow down my sizing options so I can know which avenue I need to pursue.

In the most basic form, I have heard someone say "medium is the new large" when speaking about new geometry vs the old. Does it really boil down that easily or is there more to it than that? My current bike is a large (old geo) and I haven't really had any complaints with it. Again, I'm about 5'9" to 5'10" with about a 29 to 30" inseam, which on most geo charts seems to put me between a medium and large. I'd love any input or help on how to narrow down which side of the fence I should fall on.

Thank you, and sorry for the long read.
 

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Welcome back to the sport. First things first, bikes these days are a huge improvement from bikes from the past. The quality of parts, the ride quality, and the number of options these days is great. With so many good bikes it is easy to get decisions paralysis or get overwhelmed with details.

Bikes have gotten longer(reach and wheel base), lower (lower stand over, lower bb) and slacker (head angle). Given these changes a size large from yesteryear is probably smaller than a modern size small. Given you have short legs and a longer torso, you can size up easier and not worry since most frames have lower stand over. You could be a good candidate for brands that have a medium/large size (I know trek does).

Bikes have definitely gone from riding “on” top of them to riding more “in” them. It is something that will feel off for a bit, but overall much safer and confidence inspiring.

Do you know what type of bike you want? A good short travel 29er is a great choice if you want to do general trail riding.


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I was in the same boat when looking this summer at new MTB's as I'm 5'10.5" which places me right in between a "M" and "L" for most offerings.
I luckily went with a Specialized which uses a closer ratio sizing (S1 - S5) and ended up with an S4. If I went with another make I most likely would have chosen a "L" as I value the
stability vs playfulness (which a "M" would be better for).
 

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Again, I'm about 5'9" to 5'10" with about a 29 to 30" inseam, which on most geo charts seems to put me between a medium and large. I'd love any input or help on how to narrow down which side of the fence I should fall on.
Manufacturers constantly push what defines a size, so you'll just have to make some friends and ride their bikes to figure out what you like.
 

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I am also 5' 9.5" and have a inseam of 29-30 inseam. I have found when between a Medium and Large that Medium is the way to go. Most bike makers see people our height with inseams closer to a 31-32".
 

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If you are between sizes like me, then one measurement to pay attention to is the 'effective top tube (ETT)'. Even if the reach numbers and/or the wheelbase seem much longer than you're used to, and almost too big to make sense, don't read into those to the point you get a bike with a shorter ETT than a bike you have now.

If you get one that's shorter, it may feel fine in the 'parking lot test', since the long wheelbase and slacker angles make the bike feel so planted...but once you get into the trails your knees will be hitting the end of the bars in tight turns, and it'll feel more cramped than what you ride now. Just make sure the ETT is the same as a bike you feel comfortable on now.

The new geometry basically pushes your body forwards, which means you'll sit a bit more upright and have a bit more weight on your hands on the flats, but you'll feel much more centered on the climbs, and you'll have much more room to move around when you drop the saddle and stand on your pedals on the downhills.
 
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I will add in that toptubes have gotten much longer, but stems shorter, so the seated cockpit length has changed little while reach (standing cockpit length) has grown by several inches due to steeper seat angles. New geometry requires a different riding style, but works great when you adapt. At 5’10” you are on the cust of medium and large for most manufacturers. Some more info:


 

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A year ago I went from an xc bike from 2002 to a “down country” bike from 2021 (which is really still an xc bike). The change was vast. First it felt like a beach cruiser. The new bike (epic evo) was 4.5 degrees slacker in the head angle and the wheels are 3” bigger. Both are a size medium but the reach is way longer on the new bike. Basically the new xc bike is not far from the geo of a trail bike just a few years ago. As I got used to the new bike the old one started to feel more and more archaic. The new one out climbs, out distances, is more comfortable and goes downhill better than the old one. Understanding how to ride the new bike took a little time but the new geo these days is there for a reason. I was more stretched out and very on top of the old bike and felt twitchy on anything that wasn’t smooth. The new bike is very stable and forgiving and so fast. The only place where the old one shines is going up very tight switch backs. I’m 5’8.5” and a medium is a good fit for me in most brands. If I was an inch or two taller I would go with a large. The new geo puts the rider in the center of the bike and you can stay there until you get on the very steep hills then you can shift back over the rear more but the days of hanging your ass way off the back are mostly gone. The longer the bike’s reach the more you can stay centered (to a point then it’s just too big) so having a longer reach is usually better. The seated position will still be rideable since the stem will be short and the seat tube angle is steeper making the effective top tube no longer than it was many years ago. The short stem with wide bars is also great for control compared to the old bikes. With your long torso it sounds like a large is definitely the way to go. Something with about 475 reach and 780 bars probably.
 

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I'm at least an inch shorter than you, and my inseam is at least an inch longer. It does sound like you have a long torso. You should be a swimmer instead of a cyclist 😉. You'll probably want to try a couple bikes. The good news is that I think basically all modern bikes try to get the lowest stand over possible, so if you find a bike with the right reach and effective TT, you should still have plenty of clearance to stand over the thing.

In the old days, a bike long enough for your torso might have meant the TT would be quite intrusive into the nether regions when you're standing over it.

The new bikes are pretty great. They're heavy and long, but it's really pretty amazing how they can climb and maneuver so well and still be so capable on descents.
 

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I have the same height and inseam as the OP, and sizing can be bothersome. I've asked here in the past about what size to go to, and some people have been very informative and helpful, while others have been outright rude. Hopefully the OP can avoid trolls.

Ideally bike shops would have demo fleets where you can ride a bike for a rental fee and every time you do, your rental fees can be applied to the purchase of a new bike, or maybe one of the demo bikes for a discount. It seems even without the pandemic shortages and recent demand that shops only buy entry level bikes for the showroom and expect people to shell out thousands for a bike they order without ever sitting on it. In the end you just have to pick a size and hope it works out. I (mostly) avoid paying retail for a new bike because of this.

Most people told me I should be on a large when making the move from my 2009 medium bike, and lots of people told me I was an idiot for riding a medium of that vintage, but 400 miles later riding the large from 2018, I still don't like it as much as my older bike.

As others have mentioned, there is a learning curve. At first I was a full 8 minutes slower over 6.5 miles at the same effort on the modern full suspension than I was on my old hardtail, but I've since closed that gap and set 4 PRs after I adapted to the new bike. I feel differently getting on the older one than most do after making a move... The older one is crisp, responsive, nimble and fast while the newer one still feels big, cumbersome and sluggish.

I'm seriously toying with selling it and getting a modern medium.

Take from that what you may, but I'm no one special and would never claim to be an authority.
 

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i demoed a medium Santa Cruz Heckler one time. felt good sitting down, but when i stood up and started throwing it around, i hit my knee on the fork crown. HOLY **** that hurt!

im 5'11". SC recommends i ride a large, theyre right!
 

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I have the same height and inseam as the OP, and sizing can be bothersome. I've asked here in the past about what size to go to, and some people have been very informative and helpful, while others have been outright rude. Hopefully the OP can avoid trolls.

Ideally bike shops would have demo fleets where you can ride a bike for a rental fee and every time you do, your rental fees can be applied to the purchase of a new bike, or maybe one of the demo bikes for a discount. It seems even without the pandemic shortages and recent demand that shops only buy entry level bikes for the showroom and expect people to shell out thousands for a bike they order without ever sitting on it. In the end you just have to pick a size and hope it works out. I (mostly) avoid paying retail for a new bike because of this.

Most people told me I should be on a large when making the move from my 2009 medium bike, and lots of people told me I was an idiot for riding a medium of that vintage, but 400 miles later riding the large from 2018, I still don't like it as much as my older bike.

As others have mentioned, there is a learning curve. At first I was a full 8 minutes slower over 6.5 miles at the same effort on the modern full suspension than I was on my old hardtail, but I've since closed that gap and set 4 PRs after I adapted to the new bike. I feel differently getting on the older one than most do after making a move... The older one is crisp, responsive, nimble and fast while the newer one still feels big, cumbersome and sluggish.

I'm seriously toying with selling it and getting a modern medium.

Take from that what you may, but I'm no one special and would never claim to be an authority.

new bikes need the seat to be dropper to turn well.

They carved better, but they "steer" like ****.

They also do not great on rolling terrain but you need to drop the seat to be as good as possible on rolling terrain.

With that said a size L can be way to big for people around 5'9 to 5'11 especially if the stock stem is not as short as possible.
 

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I have the same height and inseam as the OP, and sizing can be bothersome. I've asked here in the past about what size to go to, and some people have been very informative and helpful, while others have been outright rude. Hopefully the OP can avoid trolls.

Ideally bike shops would have demo fleets where you can ride a bike for a rental fee and every time you do, your rental fees can be applied to the purchase of a new bike, or maybe one of the demo bikes for a discount. It seems even without the pandemic shortages and recent demand that shops only buy entry level bikes for the showroom and expect people to shell out thousands for a bike they order without ever sitting on it. In the end you just have to pick a size and hope it works out. I (mostly) avoid paying retail for a new bike because of this.

Most people told me I should be on a large when making the move from my 2009 medium bike, and lots of people told me I was an idiot for riding a medium of that vintage, but 400 miles later riding the large from 2018, I still don't like it as much as my older bike.

As others have mentioned, there is a learning curve. At first I was a full 8 minutes slower over 6.5 miles at the same effort on the modern full suspension than I was on my old hardtail, but I've since closed that gap and set 4 PRs after I adapted to the new bike. I feel differently getting on the older one than most do after making a move... The older one is crisp, responsive, nimble and fast while the newer one still feels big, cumbersome and sluggish.

I'm seriously toying with selling it and getting a modern medium.

Take from that what you may, but I'm no one special and would never claim to be an authority.
I wouldn’t tell someone coming from an older medium to ride a modern large. If anything the modern medium is going to be bigger in many ways on its own, when compared to an older medium.
 

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I wouldn’t tell someone coming from an older medium to ride a modern large. If anything the modern medium is going to be bigger in many ways on its own, when compared to an older medium.
Yeah. People haven’t really changed sizes (maybe rounder on average). The way a mountain bike fits you may have changed, but they’re still intending size brackets to land more or less the same as before.
 

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I have the same height and inseam as the OP, and sizing can be bothersome. I've asked here in the past about what size to go to, and some people have been very informative and helpful, while others have been outright rude. Hopefully the OP can avoid trolls.

Ideally bike shops would have demo fleets where you can ride a bike for a rental fee and every time you do, your rental fees can be applied to the purchase of a new bike, or maybe one of the demo bikes for a discount. It seems even without the pandemic shortages and recent demand that shops only buy entry level bikes for the showroom and expect people to shell out thousands for a bike they order without ever sitting on it. In the end you just have to pick a size and hope it works out. I (mostly) avoid paying retail for a new bike because of this.

Most people told me I should be on a large when making the move from my 2009 medium bike, and lots of people told me I was an idiot for riding a medium of that vintage, but 400 miles later riding the large from 2018, I still don't like it as much as my older bike.

As others have mentioned, there is a learning curve. At first I was a full 8 minutes slower over 6.5 miles at the same effort on the modern full suspension than I was on my old hardtail, but I've since closed that gap and set 4 PRs after I adapted to the new bike. I feel differently getting on the older one than most do after making a move... The older one is crisp, responsive, nimble and fast while the newer one still feels big, cumbersome and sluggish.

I'm seriously toying with selling it and getting a modern medium.

Take from that what you may, but I'm no one special and would never claim to be an authority.
The new Geo is sized much different. I'm finding this out myself. Most people are probably riding around with the modern geo bikes that are too large for them. I found the videos from these guys to be very helpful. My previous bike fit me perfectly and no wonder, after calculating my RAD it was spot on with the reach of the bike.

 

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Original mountain bike geometry was copied from road bikes, with traits that may be useful on a road bike, but hinder performance on a mountain bike, and do not fit ergonomically an average human riding an off road bicycle. A few years ago some small companies went back to the drawing board and drew a bike around a human body with off road requirements (like shorter stems). The results are what you see today, bike are much longer for the same rider with lower top tubes, and some other geo changes which make the bike more stable.

In terms of fitting, some companies scratched the small medium large system and replaced it with arbitrary numbers. In the specialized system someone your height is about S3. An exception to the rule is Trek, which keeps an arcane and irrelevant sizing system based on seat post length. In the medium/large world, you can go with either one, more of a question of taste, which you can only tell after test riding. Both mediums and larges are going to be longer than an older bike which I assume you have, so don't make judgement because it feels different. Let it sink in. People tend to go with what they are used to, not what is actually better. So take that mind set when you go testing. Its going to feel a lot different, and after owning such bike for a month or two riding an older mountain bike will feel like a sketchy BMX bike.
 

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I'll add that my old Geo MTB was an early 2000 17" 26'er and my new 29'er is a 2021 S4 (29'er). At first the newer bike seemed big, but it tool all of a few min to get used to it.
After 3 months on the newer Geo, I took the old 26'er out for a spin. Wow, it seemed so small. Again, took a few min before it seemed normal.
I don't see an issue with either however how one rides (climbs, descends, rails/turns, Etc) is very different from one another.
 

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Interesting; and sorry I am not intending to troll this discussion. But drag13honda ask if it boils down to sizing when discussing new vs old geometry. How many out there feel that the new MTB works best with a dropper seat. How many feel it ONLY works with a dropper seat?? Stability, climbing ability and comfort are more important to me downhill speed.

I am just starting to look at the new geometry and hope to keep the new bike as simple as possible. I am retiring in a few years and need new bikes while I can afford to pay for them.
My ride is a 2000 Seven Sola that, if not for the larger tubes and somewhat sloping top tube, could pass for a road bike frame. Its past time for an upgrade, but there are so many issues to address this may take a lot of work.
 

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IMO it only works with one.

In fact you could say that the dropper seat post allowed the bike to get longer and the seat tube angle to become much more upright. Id go so far to say that for me there is timed difference between even a 180 to a 200mm dropper. There were a couple trails that I went 5-10 percent faster down when I switched to a 200 after riding a 180 for 3 years.

The biggest issue with modern geometery is with the seat at pedaling height, due to a long reach and steeper seat tube angle you hands are really heavy and its basically impossible to get weight on to your feet with out the dropper.

The makes modern bike FAR better climbers than anything old especially while in the saddle, and make them more stable an comfortable going down again if you drop the seat. I would not look at dropping the seat about DH speed but more about the control you have. but have you thought that maybe you do not like going downhill because old bikes with out droppers basically suck at going downhill?

The thing new bikes suck at is seated pedaling in rolling terrain, with that said most XC race bike are not in the 76-79 degree seat tube angle club but more like in the 74-76 sta club so XC race bike can still pedal on rolling terrain ok, but still having some ability to pedal in the saddle.

Basically on my bike I end up dropping the post literally for couple turns and I only sit while I am pedaling on flat or up, and will even use the dropper for parts of climb for split seconds because well ist quick enough to go up and down and if my body can move in better with out the seat there. Again not sure what the obsession is with not using a dropper.....
 

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One thing I disagree with on this second video is that the "arms locked hanging back" position isn't suited for old school geometry. That's the first thing you learn in "how to go OTB 101". It's just really poor technique born form ignorance and fear in the early days of mountain biking. I get on my old 26" bike from the mid 90's or my more modern trail bike I'm attacking a rolling drop in the same position, chest down arms bent pushing the front wheel down the drop. Because of the more forward bias weight distribution and much shorter wheelbase I do need to be further back on the 90's bike than the 2020's bike but the technique is the same. He says and I'm paraphrasing "if you ride with your arms locked like this you might like older geometry". In reality he should be saying "don't ride like this it's a terrible way to ride".
 
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