"Modern" MTB Geometry - Is Large the new Medium?

[laviedeboheme]

Hi,

I have researched (googled) this topic in other places but am just looking for some local (Aus) opinions.

I'm looking to get a new full-suspension bike for XC and moderate Trail duties. Considering from these options, all with 29" wheels:
Polygon Siskiu D7 (2021) - in stock (at bicycles online)
Marin Rift Zone 2 (2021) - not in stock anywhere
Merida One-Twenty 600 (2021) - not in stock anywhere
Norco Fluid FS2 (2021) - not in stock anywhere

I am 177cm tall (or about 5'10) in the old money. Which means I am one of those that usualIy comes in at the high end of Medium on most bike sizing charts (except for the current Norco chart, where I am showing as a Large).

I have pretty much always used Medium sizing, whether it be for a road bike, touring bike or mountain bike. I was brought up with the idea that sizing down was better when you are an in-betweener...

All of the above bikes have quite similar geometries, so why do Norco firmly suggest a Large, when the others still recommend a Medium?

I know of course that trying one out is the best idea, but it isn't always possible, especially in these days of bike shortages. I believe I need to pre-order to even get hold of the Merida or Norco. So I need to be somewhat sure on the sizing!

Also bear in mind that I'm approaching 60 years old, so not as flexible these days and not intending to be flying through the air and hopping over things very much. This will actually be my first full-suspension bike.

Any thoughts on Medium vs Large for the above bikes with my sizing characteristics?

[mikgit]

Dunno, I have an Intense sniper (so not the latest geo, but pretty new) and I got a Medium. I normally run a medium and would not want bigger.

[baabaa]

Been stuck at home with a thick head cold after getting wet a little too often last week. Swapped most of my bikes over to the winter tyres that suit each bike and got bored.
This popped up on my youtube "suggestions" and actually think it was quite good - have had pretty good luck buying frames based on swapping geo charts from a size that works to new bikes mainly using ETT. My "modern" mountain bike has been with me for 13 years and a non suspension large (or 20 inch) when most of my other bikes are xl - I really wanted a lower stand over height.
I think this vid is worth look on the "sizing up" which is something I always recommend to people who dont wish to ride fast and aggressive. Think that the owner of Rivendell Bicycle Works recommend the same? They may have some info on sizing for you as they go lots of off road but not mountain bike type bikes (quote - Don't get hung up on the numbers though. Go ride your bike!)

Hard to get the right size with such limited sizes in stock but the this vid moves around the bike fit vs adding on set back seatposts and long or short stems quite well even if it is more fast rider targeted...

[Mububban]

I've heard size up for stability, size down for more nimble handling? If you're not looking to jump and smash drops and corner hard etc, maybe the slightly longer bike will be more stable and forgiving.

But geez my XL dual sus is loooong! Makes some tight corners interesting

[Nobody]

My limited understanding of modern MTB geo is that the seatpost tends more to vertical and the frame reach gets longer to compensate for this. This is supposed to be to get you more to the centre of the bike with a slacker head angle. It is also supposed to help you to be seated on steep climbs without having to scoot forward on the saddle. Enduro bikes have pushed this geo for those that climb and descend on long steep slopes.

The down side being that on anything less than steep, your knee can end up being more forward compared to the pedal spindle. Which may affect the stability of the knee joint and is therefore more likely to cause injury for some. Those proponents of the geo say that unlike road bikes, MTBers don't spend a lot of time on the saddle, so it doesn't matter as much.

So it really comes down to the terrain one rides and if one climbs long steep hills seated. I would argue that if it really is that steep then traction is going to be marginal and therefore one might be out of the saddle anyway and pulling back on the bars to keep the rear tyre from slipping. Australia probably has shorter climbs than the US and Europe on average and so one might be able to spend a greater percentage of a climb out of the saddle than the higher peak altitude countries. Or to be able to tolerate scooting forward on the saddle more.

[bychosis]

Take ‘large’ and ‘medium’ with a grain of salt, they are marketing terms and also subject to the designers thoughts on handling. A small ‘large’ might make a rider think the bike handles nimbly while a big ‘large’ feels more stable. Designer marketer get together and decide wether their bikes need to feel nimble or stable and throw a name on it. Its a bit like pizza that comes in small, large and x-large. Large pizza is middle sized so should be ‘medium’

Unless you can physically try them out how do the true measurements stack up to what you normally ride or against one that you can test ride?

FWIW I tend to ride XL on road and L off road.

[laviedeboheme]

Unless you can physically try them out how do the true measurements stack up to what you normally ride or against one that you can test ride?

Thanks, I understand what you are saying. I can't physically try them because they are scarce as hen's teeth (except for the Polygon, which I would have to buy before I try). And I don't have a current MTB, previously had a 2014 KHS XC (100mm fork) hardtail.
Yesterday I spoke to a guy who owns a Norco Fluid FS and he did actually confirm their sizing chart. He is 6ft and rides an XL in that model, he thought that L would be right for me. Last night I managed to find one in stock in Toowoomba (whereas other dealers aren't getting any more until August or later). So I'm buying that one

[Cider]

I'm no expert, but I think there's something to be said for sizing down, especially as you get older, as it shortens the top tube and brings the handlebar closer putting more of your weight on the saddle and less on the hands.

This does seem to contradict some of the earlier posts though, so it may be that modern geometry doesn't follow those rules?

[laviedeboheme]

As the OP, I'm just updating this topic to let any interested people know what happened.

I bit the bullet and bought a Norco Fluid FS1 (sight unseen) in the Large size. Drove to Toowoomba (from Redlands) to pick it up.
Took one look at it and could tell straight away it wasn't going to be too "big" for me.

So as far as I'm concerned, yes, Large is the new Medium! (at least for Norco bikes)

[march83]

I'm 6'0". 57-58cm roadie. I've been buying large MTBs off the shelf since forever.

6mo on a Siskiu T8 large and it fits like a glove, couldn't go smaller, wouldn't want to go larger. Bought it sight unseen based on the sizing tool on the BO site which put me right on the L / XL border.

It's a hell of a lot shorter than my XC hardtails though. Very different bike to ride. Based on that, I wouldn't want to be on one that was too small.