Geometry & Numbers

[caad9]

I was just reading the Stumpjumper thread and it prompted me to try and create some discussion on something that has always confused me in regards to the all important numbers on new bikes.
From a sizing point of view, I understand why stack & reach are important.

What I don't understand is how people can completely dismiss a bike based on HA or STA or any other seemingly conclusive measurement?

At present I'm riding a bike that's considered fairly odd to most people, the all new Kona Satori DL.
It pedals well, handles well and is a lot of fun as a do it all trail bike. It won't win XC or DH medals anywhere, but nor will 99% of bikes or riders.

So to the people that focus purely on the numbers, tell me why a head angle or seat tube angle means so much to you?

 

[Zaf]

Have a read of the Chris Porter thoughts on Geometry, they outline a lot of why the new Geo is being adopted, even if it's taken several years for everyone to catch up with the idea.

Steep seat tube angles will place you more centrally on the bike in climbing, which allows you to control the front end. They also overcome a lot of the sizing issues that come from different saddle extensions and slacker STA's.
A slacker front end will usually have a larger trail and more stable steering because of it. As bikes have become more capable, they have naturally slackened in response to gaining stability in your steering axis at higher speeds. A good analogy of this has always been look at what a wheel with zero trail (shopping trolley) does the moment you go quickly.

In any case, the numbers should always be looked at together. The one I always see is people saying that longer chainstays ruin flickability, and longer is 445mm vs 430mm. If you can't flick because of 15mm, your problems aren't the frame.

 

[beeb]

Steep seat tube angles will place you more centrally on the bike in climbing, which allows you to control the front end...

Also get you in a more efficient position over the pedals too. Not "pushing forward" as much if the seat-tube is steeper.

 

[caad9]

I understand the effects of the changes, just more interested in why someone chooses 'X' bike over 'Y' bike, purely based on half a degree in either angle.
A whole generation of keyboard enthusiasts think they have more knowledge than the top engineers and designers of absolutely enormous bike companies?

 

[Zaf]

I understand the effects of the changes, just more interested in why someone chooses 'X' bike over 'Y' bike, purely based on half a degree in either angle.
A whole generation of keyboard enthusiasts think they have more knowledge than the top engineers and designers of absolutely enormous bike companies?

If it's not what that rider is looking for, it's not going to appeal. Some people like a steeper head angle and the twitchier steering, some people prefer the slack angles and using the stability to muscle the bike through a corner, and depending on how riders use those characteristics of their riding style will influence their decision.

We can't even get @moorey off 26" wheels, some people just have their preferences, and that's fine too.

 

[ianganderton]

What I don't understand is how people can completely dismiss a bike based on HA or STA or any other seemingly conclusive measurement?
So to the people that focus purely on the numbers, tell me why a head angle or seat tube angle means so much to you?

Because when choosing a bike you have to narrow it down somehow otherwise there is just too much to choose from. Some folks pick brands, some travel, some colour, some VTT, some head angle.

When I get the chance I like to demo bikes, then afterwards I look at the bikes I like and the bikes I didnt to see what the differences were (results in killer nerdy spreadsheets!!). This gives me a list of things I really like and what I really dont like. I can then look around at other options that fit the bill.

For me this might seem like I'm writing off some bikes very quickly based on one particular thing. Yes I am but there is logic behind it

 

[moorey]

We can't even get @moorey off 26" wheels, some people just have their preferences, and that's fine too.

Chopped liver?
Admittedly it’s stripped now, and will return soon as 26...

 

[Zaf]

View attachment 344535
Chopped liver?
Admittedly it’s stripped now, and will return soon as 26...

You stripped it down to remove the superfluous pivot point, didn't you?

 

[Dozer]

The geometry thing is very important and does dictate choice to a lot of riders. I'll admit though, I reckon most of the people who talk about degree's and millimeters in the car park before a ride are wankers who don't know what the reference to the measurement actually does to improve your ride, it's just people acting like they know what they are talking about.
Me personally, I ride XL or sometimes large frames and I pay close attention to seat angles and cockpit measurements as that dictates my comfort on a bike that I'll be spending hours at a time on. I don't like to be stretched out too much and a tighter cockpit measurement suits me; hence the seat angle importance. When it comes to shopping for downhill bikes, I have never looked at a seat angle or fork rake or anything of the sort, it's only relevant to me on bikes that I sit down on.

 

[Nambra]

Right on Dozer - geometry just gives you a point of reference for bike to bike comparisons and sizing. Just sitting on a bike changes all the static numbers anyway.

"Looky my new SpeshIntenSheeCruz Fandangalo, with an optimum 73.39 degree STA"
"But you're sitting on it, so now it's like 68 degrees..."
"Yes, but it's what it started out at that's important!"
"Wanker."

 

[Mywifesirrational]

I understand the effects of the changes, just more interested in why someone chooses 'X' bike over 'Y' bike, purely based on half a degree in either angle.
A whole generation of keyboard enthusiasts think they have more knowledge than the top engineers and designers of absolutely enormous bike companies?

I wager the top engineers mostly don't have a clue, how many actually ride the same trails we do? I have been 'sticky becking' a little at a new prototype frame that's being built / designed over the last few years and was asked to ride it and write a report, I can assure you some of the top freelance deisgners don't seem to have a clue about geo, probably great at maths however.

I'm 6.3 and mostly legs, after riding an owning many bikes, my favourite reach measurement is 475mm, not 480 and not 470, precisely 475. Anything longer is a compromise, real steep stuff with drops mid descent I am way too far forward - hanging on but not actually controlling the bike, or too short out of the saddle technical climbs are too crowded. 475 for me is the perfect medium and is the first time a bike has fit quite well.

I don't care about HTA, that can be modified +/- 2 degrees, STA is very important, steeper is better in every regard, help keep the front weighted for climbing, efficient pedaling position and all that.

Unlike Zaf, 430-445mm is an incredible difference in the way a bike handles, it takes heaps more effort to throw a barge around. Shorter stays are better in every regard except super steep climbs and doing 70+km don't a fire road. Geo is a compromise, depends what you want from a bike, my gravel bike has the longest chain stays I could find for a boring straight ling stability - but for the purpose I want its perfect.

Also, the current craze of longer and slacker is completely retarded, driven by marketing and aimed at the enduro sheeple. Unless you only ride 'flow' trails, you 510-530mm reach with 455mm stays are great, on anything with some tight corners, steep shoots and anything where a playful bike would be fun, the barge of a bike is shithouse. Market will swing back sooner rather than later in regards to geo and sizing, and the market will be flooded with ginormus bikes in the coming 18 months when people realise 1300mm wheel bases are shithouse for anything other than the dumbed down straight line WC circuit.

Quality Saturday night rant over.

Actually... no its not, why do I need such a shitty low BB, do bike designers actually ride the pieces of shit they designed, I wager not a single one has ridden up a loose rocky climb, where its impossible to avoid pedal strikes, then you come to a halt. Dave Turner has higher than normal BB's on his bikes (normal being retardedly low) for this very reason, Banshee and Rocky mountain offer adjustable geo (top brands) which helps alleviate this, and Transition increased the BB height on the Scout in 2017 - I bought that bike as it had the perfect geo for all round riding.

Rant is now over, going to watch clint eastwood killing people, or cry when he gets himself killed to save the zipperheads.

 

[Flow-Rider]

Low BBs with long rear ends are just a pain to climb anything technical.

 

[ianganderton]

I wager the top engineers mostly don't have a clue, how many actually ride the same trails we do?............do bike designers actually ride the pieces of shit they designed, I wager not a single one has ridden up a loose rocky climb.

I’ve met quite a few engineers for major brands

I’m in for $100




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[LPG]

Effective geometry is where you contact the bike at the seat, grips and pedals/bb centre and how these relate to the wheels.
Sliding your seat forwards and back in the rails changes your effective seat tube angle and your cockpit length. Changing your stem length changes your cockpit length and moves your weight distribution forwards/back relative to the centre of the bike. There is a fair amount of flexibility to move these around. Most bikes have dimensions here that are close enough for most people to be able to adjust to suit them.

Rear centres (chainstay length) are fixed and cant be adjusted (unless you have sliding dropouts) you want to get this right. Shorter is more playful particularly by making it easier to lift the front wheel. It's also easier to place your rear wheel where you want it. Longer makes it more stable and transmits less shock to the rider from impacts to the rear wheel.

Front centre (related to quite a few geo measurements) effects how easily you can shift your weight forward and how easily the bike can spit you over the bars.

Headtube angle effects how quickly/easily you can turn and how easily a rock you hit can make you turn involuntarily. Slacker ht angles tend to make you lean the bike more to turn. This is related to other geo measurements like cockpit lengths.

Personally I love a short chainstay and put a fair bit of emphasis on getting this measurement short. Other measurements I worry less about and are too interrelated to look at in isolation.

I spent years riding a bmx bike and love to thow the bike over obstacles which is why the short cs suits me. A bike that is too stable at speed is going to be boring on all but the most hard core tracks. Having something a bit more nimble can make more sedate tracks more fun. Hop that root and land on the downside of that rock to boost forward is a lot more fun and involved than just plowing through on a long, low and slack bike. Of course you don't want it too squirrely and the geometry should suit what you ride most and how you ride.

A test ride on similar tracks to what you ride can mean you don't have to think about all this, but this is the internet...

 

[caad9]

I think we have covered all the varying sides of the fence here. Just what I wanted to see.
Some people take the numbers very seriously, others merely use them to narrow options down.

 

[Dales Cannon]

Over the years I have test ridden quite a few bikes and I know what range of measurements suit me. Reach though is the key to not getting sore wrists or lower back problems and that means ETT length is something I watch. At 181cm depending on brand I am on the cusp of M to L or L to XL. Having that covered HA is what I next look at. I cannot stand the front end washing out and that is 100% the reason I went Bronson over Solo. The Bronson is more bike than I need or can usually use but it just sits where I want it. It was the first bike where I went shorter stem and wider bars and that was a revelation to the extent I did the same on the Muru. The Bronson is probably 25/75 out of the seat while the Muru is 99% in the saddle. Both have to be comfortable.

I have heard the discussions in the carpark about different setups, angles and penile lengths but mostly the guys who test ride, pick something that suits and then ride the wheels off it are the ones who got it right.

 

[Paulie_AU]

I just bought my current bike barely looked at anything apart from noting I was supposidly in the right size range for the size. At the time I was still racing bmx so it being what I now find a little small suited me. Next frame will have slightly longer reach (20mm) which I will reduce with a slightly shorter (10mm) stem.

 

[The Duckmeister]

I wager the top engineers mostly don't have a clue, how many actually ride the same trails we do? I have been 'sticky becking' a little at a new prototype frame that's being built / designed over the last few years and was asked to ride it and write a report, I can assure you some of the top freelance deisgners don't seem to have a clue about geo, probably great at maths however.

I'm 6.3 and mostly legs, after riding an owning many bikes, my favourite reach measurement is 475mm, not 480 and not 470, precisely 475. Anything longer is a compromise, real steep stuff with drops mid descent I am way too far forward - hanging on but not actually controlling the bike, or too short out of the saddle technical climbs are too crowded. 475 for me is the perfect medium and is the first time a bike has fit quite well.

I don't care about HTA, that can be modified +/- 2 degrees, STA is very important, steeper is better in every regard, help keep the front weighted for climbing, efficient pedaling position and all that.

Unlike Zaf, 430-445mm is an incredible difference in the way a bike handles, it takes heaps more effort to throw a barge around. Shorter stays are better in every regard except super steep climbs and doing 70+km don't a fire road. Geo is a compromise, depends what you want from a bike, my gravel bike has the longest chain stays I could find for a boring straight ling stability - but for the purpose I want its perfect.

Also, the current craze of longer and slacker is completely retarded, driven by marketing and aimed at the enduro sheeple. Unless you only ride 'flow' trails, you 510-530mm reach with 455mm stays are great, on anything with some tight corners, steep shoots and anything where a playful bike would be fun, the barge of a bike is shithouse. Market will swing back sooner rather than later in regards to geo and sizing, and the market will be flooded with ginormus bikes in the coming 18 months when people realise 1300mm wheel bases are shithouse for anything other than the dumbed down straight line WC circuit.

Quality Saturday night rant over.

Actually... no its not, why do I need such a shitty low BB, do bike designers actually ride the pieces of shit they designed, I wager not a single one has ridden up a loose rocky climb, where its impossible to avoid pedal strikes, then you come to a halt. Dave Turner has higher than normal BB's on his bikes (normal being retardedly low) for this very reason, Banshee and Rocky mountain offer adjustable geo (top brands) which helps alleviate this, and Transition increased the BB height on the Scout in 2017 - I bought that bike as it had the perfect geo for all round riding.

Rant is now over, going to watch clint eastwood killing people, or cry when he gets himself killed to save the zipperheads.

Designed squarely for the "Now!" generation who want to bomb down shit straight out of the shop door without having to waste time on irrelevant stuff like actually learning how to ride.....

 

[Zaf]

Unlike Zaf, 430-445mm is an incredible difference in the way a bike handles, it takes heaps more effort to throw a barge around. Shorter stays are better in every regard except super steep climbs and doing 70+km don't a fire road. Geo is a compromise, depends what you want from a bike, my gravel bike has the longest chain stays I could find for a boring straight ling stability - but for the purpose I want its perfect.
...
Actually... no its not, why do I need such a shitty low BB, do bike designers actually ride the pieces of shit they designed, I wager not a single one has ridden up a loose rocky climb, where its impossible to avoid pedal strikes, then you come to a halt.

Are you really that precious that 15mm is the difference between a "barge" and a zippy and agile bike?

As for the BB, it's not terribly difficult equation; your pedals go around in a predictable circle, and depending on the gear you're in, the bike will move forward at a predictable rate. If you're smacking your pedals on rocks, it's rider error.

And even if it does affect clearance, the pay off in the corners when you have a ice stable wheelbase and low centre of gravity is totally worth it.

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[born-again-biker]

I didn't worry too much about numbers when I bought my first dualie (and current bike).
I reckon that's prolly the case for many people.
At the time the biggest factor for me was value for money (and still is). I hate paying extra for intangible brand cred/wank.
I do remember checking/comparing HTA & the Trance was best v.f.m. AND close-to slackest HTA in that category, at that time.
The bike has been great for the last few years - done everything well. Easy to upgrade as I improved too.

And then I went to Maydena.

Nothing brings the geometry numbers into focus more than a full day of death-grip, holy-shit, arse-off-the-back flat-out descending.
Nothing shows up a bikes' (and riders) weaknesses more than "expanding the envelope".

Would the OP take the Satori to Maydena if he/she had a burlier bike in the shed? I'd argue, no. That's because the numbers matter.
Would the OP enter a local XC race on a 160+mm, slack Enduro sled, if they had a stiff, short, upright 100mm travel bike? Prolly not. Wrong numbers, yeah?

When you can only own one bike, shit yeah the numbers matter. I've been studying them like a nutter lately. If that makes me a car park wanker, so be it.
F@ckin' oath I'll dismiss a bike because of a particular number. No apologies. Have I ridden it? No I haven't.
But you try getting a demo ride on an XL frame from a boutique manufacturer....in Tasmania.
You'd have more luck finding Tasmanian Tiger shit on the footpath. When you can't demo bikes (because the distributors don't give a shit about demos) you have no choice but to study the numbers & try to narrow it down. The numbers are your only clues. I don't have the luxury of riding lots of different bikes & just going by the "feel".

My next bike will be my best attempt at choosing the ultimate all-rounder. I'm unapologetically looking for The Unicorn. I will be ruthless about numbers. I can't afford to own it for 3 or 4 years and hate the seat tube angle or fight with the stand-over height etc etc

These bikes that we love so much are some of the most over-priced things on the planet (when you try to look at them in isolation vs other things in life).
When you're handing over thousands & thousands of dollars, why wouldn't you be ruthless about a degree here or there....or a less-than-competitive spec...?

If the numbers didn't matter, and TrekSpeshGiantScott knew everything about bike design, then old mate Leo wouldn't have sold a single Pole & no one would care about his bikes & influence. He would have made no impression & been laughed outta town.
But he's doing well. He's selling bikes & ruffling feathers. People are really interested in his numbers.