Modern geometry is perfect. Until bike companies want to sell more bikes and invent a new geometry.

“ That doesn’t make much sense, surely?”

It does in terms of how you generate power when doing a clean or deadlift.

I read those two PVD articles and I think they, like also the LLB RAD thing, both fail to take into account body proportions. You can’t work out sizing precisely without knowing where a person’s body hinges. If you look at the world of powerlifting or Olympic weightlifting the experts there know how much your joint segment proportions change your movement patterns and your leverages.

I’ve liked going to bigger bikes but I like where I’m at now – which is short in reach for my height compared to the most current trends but makes sense if you analyse my proportions (and consider that I prefer the steering feel of a 50mm stem vs anything shorter).

I’m also running a lot of stack height with fairly tall headtubes and 40mm riser bars – which correlates with my high hip position due to my long legs for my height. And if you look at the RAAD (angle of the RAD) thing that Lee McCormack talks about, that is overlooked – it’s not just about what you’re riding down, it’s about where your body hinges.

“when you look at entry level mountain bikes etc it still feels like basically all of them could have an extra inch in the front centre and be just overall better for it”

I think it’s important to remember that you can increase front centre without increasing reach.

I think there’s been a lot of timidity in increasing front centre through slacker head angles and taller headtubes, it’s been a slow process for years. That’s improved a lot now we see enduro bike with DH bike head angles and trail bikes not far behind. With longer reach we need higher bars, so taller stack helps.

It will be interesting to see what else changes in geometry. I’m expecting actual seat tube angles to steepen to give more consistent seat angles at higher saddles, maybe size specific seat tube angles (steeper on bigger sizes). More short straight seat tubes for huge droppers. Size specific chainstays or adjustable chainstay lengths.

In answer to the OP: Maybe, it depends.

“ You could pick the angles you want and then choose from at least two frame sizes, couldn’t you?”

No, not if you’re a slightly shorter than average man or about 80% of women – a whole load of brands are now making their smallest size too long in reach for them.

I’ve been wondering about this too: Cotic FlareMax small, is, according to his method, still a bit reachy for me (I ride a medium, as per their sizing table). Might be time to think about culling a few mm with some SQlabs bars, maybe… Or a frame swap.

Are they too long? No, I don’t think so, you can still buy small bikes if you are small, or that’s your thing, but you can also buy big bikes now if you are tall, or that’s your thing.

I know what I like & I’m probably in the realms of ‘normal’ these days.

My thoughts on this are more specific being 6’6″
A longer bike is more stable but i find more stable a bit boring.
I currently ride an xl older stumpjumper evo with a decent sized stem (80mm i think). It’s more playfull than the previous bike that had a much longer wheel base.
I find at the min bikes are too short/ small (seat tube), yes i can fit a longer dropper but that leaves loads of seat post above the frame and bing taller means not light so subjecting the seat post and tube to a load of unnessesary force.

It’s similar in some ways to the more travel option, i found a more capable bike boring cause i could ride really rough peak trails sat down where previously i’d be up and picking lines.

Reach is not a great way to size a bike; it’s one of the few measurements on a bike where the same person could ride a massive range of lengths and still be perfectly comfortable. It is however good for helping decide what a bike will ride like.

As people spend more and more time at man made trails (both formal and informal) reach has got bigger to allow more stability at speed and of course as seat angles get steeper. This is compromising the slower speed / flat handling of course, but that’s the trade off.

Reach is an arbitrary measurement from the BB. It makes a difference it you stand up on you pedals all the time. Obviously GNAR gods do – but most of the rest of us use the seat a lot. So if you have a long reach with a 74 degree seat tube, it will be very long. A steep seat tube and it may well feel short when seated …
I like long shot geo as it fits my body – tall, long body, short legs – and have always found it difficult to get comfortable on a normal geometry frame.
But, like with most marketing, it will go to extremes, and then come back to a moderate position once the fashion is over.
In a few years time we will look at all the Marinos with 62 HA and laugh ….

Oi Bigdean, any chance you could donate me a couple of inches of your legs ?

5ft 5, 27inseam, try that on the Canyon sizing chart,

M levo, reach 435, the reach feels about right (*doddering xc ramble rider), but I do wish the bike was shorter (and lower tt)

Prior to that a Scott espark, m, also reach 435,

Come on ye smaller wheels !!!!

I found those videos interesting but this RAD approach is seriously flawed. Lee seems so focussed on this maximum power lift thing… maybe that would have some validity if you spent every ride trying to impress bystanders with your walking pace, waist-high bunny hops.

I decided to give the RAD measurement a try (I’m about 5’10” with very long arms and legs and a fairly short torso). This means I get a really short RAD measurement for my height… This makes my large Tallboy about 80mm too long for me! If my arms were shorter than “normal” then the RAD method would say the bike is ok! Clearly it would then be too long!

Reach is not a great way to size a bike; it’s one of the few measurements on a bike where the same person could ride a massive range of lengths and still be perfectly comfortable. It is however good for helping decide what a bike will ride like.

If you understand how the other measurements work alongside it, then it’s still the primary metric for me.

Alongside chainstay length actually.

Head and seat angle are also important, but can be fudged a bit easier.

Top tube length and front centre are irrelevant to me, as is wheelbase. They are just outputs from getting the other figures right.

Oh, and seat tube length is critical, bit just has to be low enough. Once it’s below a certain point it doesn’t matter.

Are sizing a bike and telling how it’ll ride not kind-of the same thing though?

Yes, at 5ft5 a trail bike is too long for me making it too difficult to left the front wheel off the ground. Can’t get my weight in the right place. My trail bike from 2015 is perfect for me. But current geometry is too long.

Lee seems so focussed on this maximum power lift thing… maybe that would have some validity if you spent every ride trying to impress bystanders with your walking pace, waist-high bunny hops.

Yeah that’s true. He seems obsessed about riders generating power without being interested in whether the bike will be fast or not. A longer wheelbase makes a bike more stable and faster through chunder. Even if that is a compromise when doing bunny hops that’s going to be a good compromise for most riders.

I don’t even think it is a compromise though. I’ve thought a lot about the mechanics of hopping (used to ride trials) and I’m pretty convinced that a longer reach is a good thing. If you do ‘American’ style hops, you pull the front wheel up first. You then launch your body weight upwards from a crouched position to the maximum extent you can – usually limited by the length of your arms at full extension. Obviously if you can jump upwards more forcefully in the space available, you can go higher. But another way to get more height is to increase the space available.

Something like this:

(Still taken from this video: https://www.youtube.com/watch?v=q5zBbLWIhHY)

Extra length is even more useful when doing ‘static’ moves I.e. you’re already on the back wheel, balanced. You’re generating all your upwards momentum in the reach-space* available.
Which is why trials bikes have been pretty long for years. NB the trials shop Tarty Bikes has used ‘reach’ meaning BB to bars (AKA ‘R.A.D’) for probably 15 years. It’s not a new concept, although they’ve updated their website and are now using the industry-standard reach to mean the horizontal distance (a concept that’s a bit irrelevant if your bike spends most of its working life with its front wheel in the air).

* Reach-space is my made-up name for this.

TLDR: More reach is a good thing for stability. It’s also potentially a good thing for getting a lot of power into your moves.

On paper my bike is undoubtedly too long for me and yet it feels good nearly all the time riding it.I’m 5’7″ and my bike has a 490mm reach – far far longer than any of my previous bikes.The same as Chiefgrooveguru-I seem to have relatively long legs so I find I need to stand tall and keep my hips high on the bike to keep my weight centered,rather than lowering/squatting down more and moving my weight backwards-this is very noticeable difference when cornering. The longer reach and higher stack that my bike has helps me maintain what feels like a more centered and balanced position.

People can be built very differently.

A bike sizing system that purported to be truly accurate would need to offer alternatives for different types of riding, and also suggest more fine-grained aspects of geometry, eg ideal chainstay length, head angle/reach options, seat tube angle, crank length(eeeek!) and so on. You can’t represent a bike with just one number any more than you can represent a human.

I’m 5’10” if I stand up straight. My bike has a 480mm reach. I’m by no means a dirt jumper or enduro racer, more of a trail trundler. Strava tells me I climb and descend way faster on this bike than any other I owned before (the last bike had a 435mm reach). And it makes me laugh like a kid when I ride it, too. So I reckon fairly long reach (with a steep seat angle) suits me pretty well. Sweeping statements about geometry “bikes are too long” “head angles are too slack” or whatever probably aren’t that helpful except for click bait and forum rage. 😆

Funny isn’t it. I’ve been looking at my old 26 inch blizzard from 15 years ago… i’ve no idea how i rode the bloody thing for so long. I raced it, went touring on it, rode it 3-4 times a week for years and years… and it just looks like a kid’s bike.

I have been looking at this recently too, as I’m looking at a new bike. I will moving from 10yo 26″ bikes, so everything is going to feel strange and almost no test bikes seem to be available. At 5′ 7″ with short legs and a +5″ ape index I’m certainly an average build. If I were to use the RAD calculation I would end up on an extra small frame but would then end up ridiculously cramped when riding seated.

Chainstays on the whole are still far too short and should vary with frame size, small bikes shorter, xl longer and everything else in between. Bikes simply aren’t balanced front to back, huge front ends and short rear ends make for some odd handling.

But how long is too short for chainstays? I ride XL size bikes and don’t want long chainstays that make it handle like a barge. We spent the first half of the last decade asking for shorter chainstays on 29ers, and I stand by that. No need to ‘balance’ the front and rear just because the front has gotten longer.

I’ve got one bike now with adjustable chainstays. Tried the long setting and all it did was take the fun out of the handling, make it more difficult/slower to turn, and harder to manual. Don’t really see much need to vary the length by size but have another bike where it does, longest being a rather short 430, perfect, no odd handling. Both bikes 510-520 reach.

Decently steep seat tube angles are important so short stays don’t feel like you’re too far back over the axle or cause the front to lift climbing.

Bikerumor have something on this…

https://bikerumor.com/2021/03/19/aasq-110-six-mountain-bike-frame-mfgs-discuss-proportional-length-chainstays/

430 on the XL Smuggler I use for XC, 455 on the large G1 for gnar.

G1 feels more balanced and can climb steeper gradients, horizontal seat offset from the BB is the same on both bikes (virtual seat tube angle). Going down, G1 is faster through the turns, all the time. G1 has a 82mm longer wheelbase (1242 vs 1324).

But how long is too short for chainstays?

430mm

😉

It’s clearly personal innit – and comes down to handling priorities.

I ride bikes with 460mm and 475mm reach – and chainstays of 435mm, 445mm and 450mm.

The 460 reach/450mm CS bike is the best-balanced and most-intuitive handling for me.

Yes, a steeper seat angle would stop the 435mm rear one lifting at the front on climbs, but it would still lack have the same planted feel and stability on rough or steep trails. I buzz my bum most on that one too as I need to get my weight back more.

I used to have Konas with long fronts and short rears, and they were more playful, nippy and easier to manual – but felt like they got out of their depth a bit easier.

Adjustable chainstays do seem to be the answer here.

I always wanted the shortest chain stays possible but bought a used frame with sliding dropouts and the shortest I can get them is 450mm.
Turns out it climbs better than shorter chain stay bikes I have had and the handling is great but they seem to be very much against the latest trend in chain stay length but then my head angle is only 68 degrees so the whole bike is clearly a death trap.

Watched both videos, they speak with confidence about what “suits them”, also read the link and this bit caught my attention about RAD and its founder/author:

He also works with a ton of novice riders that are looking for easy confidence.

RAD or Reach or any other new way of measuring bikes doesn’t account that these are personal preferences. As with a few other posters on this thread, I’ve just gone from a bike which was “short” to a new “LLS” and am loving it, got an extra 49mm in reach, 10mm in the chainstay with a wheelbase increase of 84mm and could not be happier, the bike does exactly what I purchased it for which is enable me to go fast downhill, I know it wont be good doing XC and I dont care, it also hasnt impacted my other abilities as I can hop fine on it and actually manual better!

As a footnote on chainstays.

It’s nice that proportional CS lengths have become a hot topic – but I find most brands who do it seem to start at “too short” and go up to “getting there” by the time they hit the XL and XXL.

Instead of 430-445mm across the range, I’d probably suggest 445-460mm.

But even better to do that and allow some adjustment.

Frames need to be shorter/longer to suit the riders height. You can’t just have one length for all heights. I’ve noticed recently that some bikes start at a medium for 5ft 6 and above. Why no small? Or maybe its just down to stock being low.

https://enduro-mtb.com/en/enduro-race-bike-mtb-review/

This is worth a read. It is a timmed group test with team bikes that lead to some interesting observations about reach, chain stay length, the proportion of the two and also handle bar width.

“I ride bikes with 460mm and 475mm reach – and chainstays of 435mm, 445mm and 450mm.”

Do you know what the chainstay lengths are at sag or how they change through the travel? Only the high pivot idler bikes get noticeably longer at sag but some bikes get a bit longer to sag whilst others get a bit shorter. And towards full travel the differences can get really big.

2019 bikes:
Orange Stage 6 = 450mm static / 453mm @ sag / 444mm @ full travel
Stumpy Evo 29 = 443mm static / 441mm @ sag / 422mm @ full travel

@mwleeds I’d forgotten about that group test. Interesting reading, especially “In size L, the COMMENCAL is the loser of this test and proof that the trend towards increasingly longer bikes has definitely reached its limit.” Although it sounds like it was as much the disproportionately short chainstays that were the problem.

This is worth a read.

A “team bike” should be optimised for the team rider… who cares how fast someone else is on that bike, especially when compared to another bike optimised for another different team rider?

This combination means that you have to ride the bike very actively to generate enough grip on the front wheel when cornering.

Sounds reasonable. But perhaps some pros want to ride a bike in that way, and know how to turn it into pure speed in a way the test riders do not?

The whole test was an interesting read on the trends in setups favoured by team riders, but the timings (and labelling one bike the “loser”) is all a bit silly.

Do you know what the chainstay lengths are at sag or how they change through the travel?

Good lord no.

That is interesting, but I wouldn’t have the bandwidth to factor that into my bike buying along with everything else.

it sounds like it was as much the disproportionately short chainstays that were the problem.

That website has form for jumping to conclusions on the basis of partial evidence, or results which could have been influenced by a multitude of factors.

Longer and slacker certainly isn’t always better, but when it is – it really is.

Was At Nant yr Arian yesterday on the Scandel. It’s just under 1200 whereas my Dog is just over. TBH I couldn’t tell much difference in any thing except the Scandel has a longer cocpit, even though the reach is shorter. There’s no fast stuff there and the difficult definately isn’t, or I wouldn’t be able to do it…
The Scandel effectively has a slacker seat angle. I have the seat right forward and it’s still further back than the Dogs’s most rearward one. The Dog is more sit up and beg.
The seat being further back on the Scandel means it doesn’t need a Dropper so much. On the Dog the seat tends to pitch you forward downhill, putting me over the front wheel which I don’t like, so need the Dropper to lean back.
I scraped the 175 cranks once too so I wouldn’t want a Squatch or Morph and most of my riding is cross country so I don’t want a ultra steep seat angle, dropper or no.
So yes I think for many the trend is beyond optimal right now but 1200 and 65/66 doesn’t seem too much for a medium. A lot of the new stuff is winch and plunge for man made trails.

I was pondering this at the weekend. My (longshot) FlareMax is great for riding down mountains on natural trails. Ideal for the sort of fairly open rocky landrover tracks that I often find myself on where it can really fly. But once I get down to the woods and the more man made trails with tight berms and various other obstacles I find it a bit of a handful with my very limited skills. Suits me as I tend to avoid anything marked as a mountain bike trail and prefer the open hilltops. But, given that most normal people prefer “proper” mountain bike trails it does surprise me a bit that bikes have become so long. Probably just a skill thing though.

More leaning of the bike required?

Yes, that and more commitment. Mincing into a “berm” and then finding you don’t have enough speed to get round and it is too deep for a pedal stroke can be very embarrassing 🙂

“That website has form for jumping to conclusions on the basis of partial evidence, or results which could have been influenced by a multitude of factors.”

They did a similar thing on bar width if I recall correctly. One doesn’t like to stereotype the Germans too much but they do have a talent for thinking that everything can be measured – and although many things can be measured, it’s not often possible to measure something in a way that can translate into journalism and be understood by laypeople. And if it’s a journalist doing this so-called scientific analysis, well, it’s not going to be very scientific…

Going back to chainstay length, I now swap between a 29″ ebike with 455mm chainstays and a 27.5″ hardtail with 420mm chainstays. Everything else about the geometry and build is similar but you’d think those four big differences (massive frame weight, bigger wheels, longer chainstays, and absence of rear suspension) would make a huge difference but I can swap between them really easily. I guess the Levo just needs earlier timing and more leverage to do anything but otherwise they behave quite alike and when I find myself dealing with anything gnarly my feet and hands are in a similar place vs the front wheel.

Watched both videos, they speak with confidence about what “suits them”, also read the link and this bit caught my attention about RAD and its founder/author:

Both riders clearly been riding a long time, grew up on BMX, spent decades riding bikes that are too small for them and have got used to riding around the inherent characteristics of smaller bikes quite clearly… If you want a Dirt Jump bike, or are only concerned with how easy a bike is to manual, then knock yourself out, go for RAD-… Doesn’t work for me any more though!

Are they too long? No, I don’t think so, you can still buy small bikes if you are small, or that’s your thing, but you can also buy big bikes now if you are tall, or that’s your thing.

I know what I like & I’m probably in the realms of ‘normal’ these days.

Echos my sentiments mostly… At 5ft10 the biggest realisation I’ve had in the last few years is that in *most* manufacturers geometries I should be riding a Large rather than persisting with medium sized frames in general. This only tends to buy you about 20mm of reach, but generally I feel more “in” a large sized frame (sweeping generalisation I know) than perched on a medium (most notable exception being my Geometron G15 which is a Medium, I tried a friends Large and it just felt too long).

My Large XC bike has a reach of 445mm, Large eBike has a reach of 478mm, Medium Trail Bike has a reach of 490mm. Chainstay lengths are 438, 442 and 445mm respectively, and Seat angles are 74.8, 77.5 and 77 effective respectively too.

Crucially, and so much for the concept of sizing by horizontal top tube length being irrelevant these days, my saddle nose to handlebar length (so cockpit length I guess) is between 495 and 500mm on all 3 bikes…

It’s nice that proportional CS lengths have become a hot topic – but I find most brands who do it seem to start at “too short” and go up to “getting there” by the time they hit the XL and XXL.

Instead of 430-445mm across the range, I’d probably suggest 445-460mm.

I’m certainly not tall enough to decide what’s long enough at the upper end, nor am I short enough to dictate what suits at the lower end… I do know that I’m happier now with a slightly longer Chainstay length than I was a few years ago. All 3 of my full sus MTBs feel very well balanced with their respective reach and chainstay lengths listed above. Previous bikes have tended to have shorter chainstays, which arguably felt snappier, but less composed in high speed corners. There’s also the climbing benefits that a longer stay length brings too… To a point.

By biggest gripe is with seat angles for many/most brands… They still tend to follow the traditional roadie method of slackening the seat angle slightly as frames get larger (though head angles thankfully don’t tend to get steeper still, that stopped a long while ago on MTBs). This is totally counterintuitive, and is a pure old school roadie hangup for trying to minimise the wheelbase growth of a road bike as the sizes get larger. There’s VERY few companies that have bucked this trend… Geometron being an obvious one, Vitus have started steepening their seat angles as the size gets larger too, I am sure there are a few others but they are the exception not the norm still.

The focus still is in many cases, and always was, on keeping the wheelbase down to a practical minimum, where actually the wheelbase length should just purely be a byproduct of putting all of the contact points in the correct place, combined with desired angles etc… Anyway…

It’s becoming increasingly clear for the more educated of customers that “balance” is key… My XC bike has a wheelbase of approximately 120mm shorter than that of either my eBike or my trail bike, but it feels superbly balanced still, and I’m fast on it even where you wouldn’t necessarily expect an XC bike to be quick as a result. I’ve seen many modern Enduro bike reviews where the testers have commented about the bike having a much longer reach than previous iterations, but no extra length in the rear end and as a result, feeling less balanced and therefore being slower against the clock despite increased reach figures. Clearly MTBing isn’t the “point and squirt” sport that some of the manufacturers would have us believe with their geometry and marketing!

The fastest bike I’ve owned was a Trek Session 88. I think it was a 2010. It was a medium and had a reach of 390mm I think. It’s a long time ago now but it felt perfect and was very fast, fun and confidence inspiring for me when riding down hill tracks in the Alps, Spain and in the UK. I’ve just checked and the current session has a reach that is 18mm longer. I’ve no idea if Trek are an anomaly here and if most downhill bikes have grown in length with trail and enduro bikes, or if downhill bike geometry hasn’t really changed generally in the last 10 years. Possibly a bit of both as I think Trek do stick to the conservative side of geometry changes/trends.

I also owned a Strange Alpine five. I can’t remember the geometry numbers but it was a prototype orange frame that singletrack once reviewed. It was probably built around 2008. It also had a reach of 390mm but was also very slack with a longer wheel base than some of my mates DH bikes at the time. It was also an amazing bike to ride in the alps down very steep, very rough trails. Both bikes were very capable descenders that I struggle to imagine would be quicker or ‘better’ bikes with longer reach. It’s tempting to say that they were amazing because they both had slack head angles but that’s probably not true – it was probably also that everything else was just right (for a very specific use!) eg. CS length, BB height etc.

I’m not sure what my point is. Probably that slack and short (by modern standards) bikes were and are still very quick and that (some) downhill bikes don’t appear to have been effected by the slacker and longer trend.

But perhaps modern slack AND long bikes take what was great about my previous bikes and makes them better everywhere else…I’ve no idea as I’ve yet to ride one 🙂 It’s good to keep a open mind though and it’s interesting to read about RAD as an alternative to the longer and slacker trend. In the past I’ve very rarely test ridden bikes but I think that now with the rapid changes in geometry it’s getting a bit riskier to buy new without a proper test ride – not helped of course by the fact that bikes are more expensive than they used to be.