Now that's what I call a new take on geometry....

[2manyoranges]

I suppose the thing which surprises me most is the extremely slow way in which geometry changes - and the inherent conservatism of the industry and consumers. The Grim Donut is one notable experiment, as was the less publicised UK BikeRadar version:

And

There are some personal moments which stick in my mind...in the early 90s remember flogging myself up a medium climb just outside Lewes and wondering why the Klein I had just built was such a s+it climber. Reason...the frame was too small...I has opted for the 18 inch and I am 5ft7in, outside the range quoted for the frame, but was encouraged by the retailer...grrr....and the only way I could get it to fit was to run the saddle way aft. The already-slack 72.5 STA thus became an even sillier number, and frankly it was like pedalling a recumbent up the hill. Scrub bike and start again...or rather, my much smaller wife suddenly got a new Klein. Mental note...start thinking about TT length and STA. And don’t again forget the fact that 1950’s hillclimbing frames had super-steep seat angles.

Moment two. Hurtling down the long, straight and smooth downhill on Balmer Down I knew I’d built something Right. Having tried to get much longer bikes with low standover - almost impossible - I had put together a 15.5inch Team Marin (nickel) - whilst having low standover (for the time) this had (for the time) a very long top tube (57cms) and this meant I could run an inline post with the saddle forward on the rails - giving me an actual seat angle which was pretty steep - and a shorter stem (for the time), at 120mm. This thing was utterly solid downhill, and had a fluid and grippy pace up steeps. Better.

Now it was about this time that Gary Fisher did the same thing with his first incarnation of Genesis geometry - not to be confused with Genesis 2.0, which focussed on head angle and fork offset. Genesis 1 extended the top tube and shortened the stem, and in reality steepened the STA since you could run an inline post with the saddle forward on the rails. But whilst the big industries kept an eye on Fisher and started to lengthen top tubes a wee bit, it had little effect on consumers. No social media at the time, but this comment on Genesis 2.0 is typical of what was said amongst riders:

‘...longer top tube than some designs. It might fit your needs, but to say that geometry improves climbing descending and steering (right from the GF glossary) for everyone is a bit much. Unless of course you believe advertising hype...BTW GF certainly didn't invent this type of geometry, he just "branded" it (probably more a carry over from his road biking days)...’

This is wrong in quite a few ways. It says ‘it’s all hype’ (proposition = it doesn’t work) and ‘he copied it anyway’ (‘it works but he just copied it’) - which is nonsensical. I think this highlights a problem. Manufacturers need to sell bikes. Bikes last ages (don’t we know it on here) and manufacturers genuinely don’t want to p+ss off people they sold a bike to four years ago. A lot of very vocal people slag off attempts at innovation, and so a cycle of conservatism is set up. Mondraker decided to step out with Forward Geometry, and Genesis 2.0 got people thinking about fork offset.

Personal moment three...2017...Ant is on his Kinesis with very old geometry, and I am on a then-radical 26er steel British hardtail which is so solid downhill. The thing is this, though. He gets up the steep climb into the woods at the A27, while I fail. I’ve not ridden here for 15 years, and it’s a reference climb which you can do, but it’s right on the limit. OK, maybe I was just being c+ap. I have another go...this was fine on my Marins and Oranges. But there’s no way I will get up it with all this front end lift and wandering. I walk up in a fug and think that we just are not there yet with geometry....time to start researching again, and get building.

Since then, the work by Transition on Speed Balanced Geometry has by stealth trickled through the industry. In the UK, Dan Stanton and Cy Turner have pushed HTA and STA further and further, and it has helped sales not hindered them. When Transition launched the big jump represented by SBG the industry tutted, shook their heads in public, but went back and tweaked their geometry without labelling it or shouting about it...

Moment four...2021...somewhere deep in Welsh woods, my son and I are hacking up a steep, loose, stony chute on our FS Transitions, with SBG geometry - slack HTA, 40ish fork offset, 76 STA. We just sit there and grind, carefully picking the next micro route, lifting the wheel over rock steps knowing the rear will dig in and follow us. There’s no way a bike from the 90s would get up this stuff. We stop at the gate at the top, puffing and wheezing...but smiling...a lot


Meanwhile, The 410 from Ra does something very interesting with BB height, but appears to me from the geometry charts has an actual STA which is a lot slacker that the 75 quoted - since seat tube configuration means that the actual STA will increase significantly as the seat is raised. The problem here is dropper insertion. The hill climbing frames of the 50s played with split seat tubes, so you could have really tight rear triangles and really steep STAs. But you can’t get a dropper into a split seat tube. Perhaps now go with shorter droppers (at 210mm it’s all got a bit mental...’Pah; you only have a 150 dropper??? Pathetic...’) to get less insertion and more to play with around STA....yet another example of one factor determining too much in overall design..

I was very disappointed with the recent reviews of the Cotic BfEMax with Cy Turner’s Longshot geometry - extended toptube used with short offset forks. The bike was marked down significantly for wheelbase. Reviewers seem very hard on long wheelbase bikes, and I think irrationally so. I built a BfEMax this year and have compared it back-to-back with a load of new geometry bikes. The bike is long, no two ways about it, but the reviewers seem to have forgotten that this bike has gobs of rear end traction due to the overall set of geometry decisions in the frame, and has no flop or wandering at the front when pointed up steeps. This thing went up reference climbs like a bike in the 90s, bu at the same time is hugely capable on downhills. Massively so. In stupidly tight singletrack you can occasionally feel the length, but it’s not life-threatening, it just demands a slight change of style. I think they were wrong in the reviews, and yet again we saw focus on one thing dominating, rather than an holistic look at this complex optimisation we need in bike geometry.

What’s clear is that there’s still a lot of optimisation to do...and I for one am waiting to see what the Grim Donut 2.0 delivers....

 

[2manyoranges]

A ‘dynamic geometry’ footnote: natch the sta changes with fork sag and the bb height descends slightly as the whole bike rotates around the contact patch of the rear tyre. In the case of the RA with an apparently slack sta this would increase sta a bit, and more if you run the 40 pc Rafi is advocating. This would also lower that bb further by a little bit….

Real world performance is not magic - it can quantified and understood, and then applied. Obviously riding something is a good idea, but understanding why something is the way it is, is not voodoo.

 

[Mikey08]

I just think most modern bikes except xc race rigs looks freaking bizzare. The one at the top of this pot is one of craziest things ive ever seen bar the grim doughnut. How low is that bb gonna be when the fork is fully compressed....daft.

 

[catf]

regards geometry evolution, poss to do with how most riding is done on managed trails these days, especially trail centres, so that the trails get more extreme as the bikes get more capable, so ppl wasnt more extreme bikes to ride those trails. and so it goes on in a merry waltz. maybe. idk cos i dont ride trails, just offroad xc instead of roads.

i can never understand why dh didnt just move to cut down motorbikes with cranks welded on, instead of beefed up xc bikes. the way all the dh stuff has filtered down through fr and enduro style bikes, that couldve been done 30 years ago. why nobody thought of that?

i mean same with 29er, why was there ever 26er? tom ritchey even deliberately cut down 622 touring rims to make the original 559 size. just the rubber issue? cos he wanted to use cruiser bmx tyres? no idea. bikes eh.

 

[Woz]

Interesting. Only thing I can add is old school road and retro MTB stuff:
- seat angle is more related to custom fit biodynamics and saddle of choice, but it assumes you are seated and pedaling;
on a modern MTB gravity assisted not so important. I can't see a decent argument to sub-optimise on mud clearance. though.
- the front end is always going to be contested between responsive and stable. It's ironic that early road bikes had piddly shitty
small stems where you couldn't control the bike at speed around corners on descents - akin to getting a Raliegh 3 speed roadster
to go down a 45 hairpin Alpine descent safe and fast wasn't on the design spec.. Brown chamios was the norm.
. The Italians got it all right with a slightly lower BB, fork-offset, head-angle and longer stem for better leverage. We all know where
Ritchey got is influences, from being a roady and no surprise that was integrated into early MTB geometry; with cut-down handle bars
of course.

Carry-on. I know very little about geometry and suspension so hoping to learn something about modern tech.

 

[2manyoranges]

Catf - interestingly, DH rigs went very heavy and very brutal from around 2012. The Commencal Supreme went heavier and heavier year on year until 20kg was just a normal weight - and the Athertons were smashing every time and pinning every course. The idea was ‘point it straight and carry on....’ - and at the time, that worked. Those bikes just soaked it up. They were, as you say, almost MX bikes without the tank and engine. But something started happening from about 2018. A lot of effort and thought went into understanding suspension curves. Nicolai really started it some years earlier and Santa Cruz, with its virtual pivot point (VPP) designs enabled an understanding of axle path, compression and ramp up, and anti-squat that meant frames could begin to get lighter again, but still have seemingly bottomless rear suspension. Combine that with two forks: the Fox40 and the RC Boxxer WC and you could begin to get stunning suspension performance without massive sprung weight. The unsprung weight went down and down (carbon rims, feather weight 220 discs, light four-pot calipers, and much more rigid, lighter forks and rear triangle) and that meant the sprung weight could go down too. Last year’s DH rigs were much much lighter...and yet the times are going down just as the courses are getting gnarlier and more demanding.

And you are right...a lot of this is not to do with new materials or new forms of machining....it’s just knowledge. The materials and tools existed in 1990 to do exactly the same things (not all bikes are carbon fibre) - but the experience and knowledge were not sufficiently refined and developed....