[Closed] Have we done this yet? - latest Chris Porter Geometry article

In practice, does a few mm of BB drop make the slightest difference

It did on my Patriot. The reason for moving the shock mount was to lower the CoG. Worked, made the bike much better.

If the bb solely is dropped and all other measurment are kept the same yes to a certain extent.
However in Molgrips case shifting the shuttle will have an affect on headangle, wheel base, bb which as an overall effect it's not just one thing but a number of things giving the result.
2005 my 20" Patriot 66, in slackest positon with 40s was rather good down stuff...

molgrips - Member

It did on my Patriot. The reason for moving the shock mount was to lower the CoG. Worked, made the bike much better.

In the front braking terms Chris was talking in, I meant, not in total. And as Loco says you've changed a whole bunch of stuff, not just BB height

Having spent 3 hours with the man this morning, I'd trust most of what he says regarding suspension & bike set ups for certain types of riding.
I'm hardly the greatest rider in the world, but even for me sitting on his bike that looks so wrong, but feels so right is really bizarre!

I like his bike, or I like the fact that it exists. But there's no way I would want to own it.

The feel of the bike is secondary to how fast it is for him as a racer/team manager.

For racing! This!

but for the rest of us this is not relevant. There's a really interesting course at california polytechnic uni about designing bicycles to optimise handling and one of the things they emphasize is that bikes which handle well all have control spring (handlebar forces at the grip area required to disturb the steering) which fall within a very small range despite their very different geometries - (mechanical) trail, bar widths and stem/tiller - be they road, bmx or mtb.

because how a bike feels DOES matter for being able to control it well at high speed.

He flies in the face of all that

Reading that article made me like bikes a little less...which is a bad thing.....

He seems to be looking for the perfect bike, and of course we all know that the perfect bike is the bike you're riding on RIGHT NOW....

DrP

The feel of the bike is secondary to how fast it is for him as a racer/team manager.

Retrodirect

For racing! This!

One problem though is that 90% of bikes claim to be the best and the fastest, and that seems to be what sells them, irrespective of whether that's what people actually want. Or think they want.

If there was a bit more openeness or clarity, ie a company said "this bike won't win races but it's fun and comfortable" or indeed "this bike will win races but it's a pig otherwise" then there might be a chance for more daring design.

Perhaps it's a symptom of a young sport/industry where we haven't yet got much maturity in terms of branding. Every manufacturer seems to be trying to sell every customer a super car, when perhaps a lot of people need a cruiser.

[i]In practice, does a few mm of BB drop make the slightest difference, considering the COG of the bike is always going to be above the hubs, and the rider makes up 70% or more of the weight of the bike and is almost entirely above the hub, and totally mobile... I think it's probably totally meaningless tbh. Or if it makes a difference, it's one that's tiny compared to the effect of body movement. Just because your weight connects to the bike via the pedals, doesn't mean it acts on the bike as if it's all at the crank axle[/i]

You are wrong, unless your BB is above the hubs.

[i]I feel that his argument falls apart here. Not every rider will have the same technique, indeed they need to be user-friendly enough to avoid intimidating relatively new and inexperienced riders.[/i]

Not all bikes need to be 'user-friendly' for beginners.

You are wrong, unless your BB is above the hubs.

It's that point about riding uber slack bikes uphill where he loses me:

"Yeah they're a bitch to ride uphill, you have to totally change your technique. People don't want to, so they blame the bike..." Well yeah... Because it's the bike that's a handful to ride! 😕

b r - Member

You are wrong, unless your BB is above the hubs.

In what way? There's about 5 points in there, narrow it down a bit?

In practice, does a few mm of BB drop make the slightest difference, considering the COG of the bike is always going to be above the hubs, and the rider makes up 70% or more of the weight of the bike and is almost entirely above the hub, and totally mobile... I think it's probably totally meaningless tbh. Or if it makes a difference, it's one that's tiny compared to the effect of body movement. Just because your weight connects to the bike via the pedals, doesn't mean it acts on the bike as if it's all at the crank axle.

If wheelbase/rear centre and BB drop are optimised you don't need to move your body around anywhere near as much. Front/rear grip is balanced, you don't need to hang off the back descending or sit on the nose of the saddle climbing.

Porter is correct in that almost all bikes (apart from Mondraker-Zero) are too short in wheelbase. The quest for short rear centres is idiotic. As is running longer than a say 40mm stem. The only thing I would disagree with him is the efficiency of 29". The acceleration/deceleration factor is a barely a consideration compared to the reduced rolling resistance IMO.

agree with a lot of what he says

long reach, teeny stem, wide bars, slack(ish- by porter standards) head angle, long wheelbase, short chainstay bikes are brilliant

getting back on a cramped, steep old skool bike makes you realise how much things have improved, these are golden days my friends 🙂

Like the fashion industry, everyone wants to copy whatever’s popular, and we end up with the bicycle equivalent of X-Factor; just because something’s popular doesn’t mean it’s good. If you followed this train of thought to its logical conclusion you’d end up with every single manufacturer making heavy, rigid bicycles with 4-inch wide tyres. In all seriousness, that would be stupid wouldn’t it?

For racing, a bike should be the fastest it can be, even if that means it's sketchy as hell, cos all that matters is the stopwatch.

For normal riding, ride whatever the hell you enjoy.

It's not rocket surgery.

long reach, teeny stem, wide bars, slack(ish- by porter standards) head angle, long wheelbase, short chainstay bikes are brilliant

He's not advocating "short chainstays". That's the worst idea he bike industry ever had.

Short chainstays are fun, they are moroninc on downhill bikes.

Short chainstays are rubbish for climbing. Draw a diagram and see.

Short chainstays are fun, they are moroninc on downhill bikes.

They make slightly more sense on a DH bike than a trail bike.

Meh, they give more stability in the rough and keep you more centered in the bike.

For climbing short chainstays suck but I quite like my shorter travel bikes to be playful.

I think this article mostly confirms how utterly baffled by geometry I am. I am quite tempted to try a longer bike though as i'm slowly coming to the realisation that my instincts to always buy bikes slightly too small actually doesn't suit my riding style at all 🙁

I definatly agree with the low bb though, though in my head this possibly makes more sense on a hardtail where you are less inclined to pedal through the rough.

What baffles me is knowing that the bike which i probably felt most confident on, especially descending was 100% too small for me (old shape giant reign with 36s on the front in a small), whereas my current bike a fuel ex (virtual 17.5) feels too small and a bit sketchy sometimes. God knows

Meh, they give more stability in the rough and keep you more centered in the bike.

The physics isn't on your side there man.

What baffles me is knowing that the bike which i probably felt most confident on, especially descending was 100% too small for me (old shape giant reign with 36s on the front in a small), whereas my current bike a fuel ex (virtual 17.5) feels too small and a bit sketchy sometimes. God knows

Is the Fuel 26"?

If so, 12mm longer rear centre on the Reign and only 4mm shorter wheelbase, but already half a degree slacker and with a longer A-C 36 it would be at least another degree slacker and 20mm longer front centre.

The Trek probably fits you better in the saddle but the Reign, even though small, was the longer bike and far closer to what Porter is advocating. It's all in the numbers.

I think CP talks a lot of sense in terms of designing the bike to work for him in the way he wants it to work. Re. the chainstays, I'm a back wheel hopper apparently (I was in 1991....) and just prefer the feel of bikes with tight asses. That doesn't mean that I buy into the myth that short stays = a good climber. I always remember a steep rooty climb circa 1988 that you just had to hit as fast as possible and just keep going. I could do it on my Peugeot Ranger with 18.5" chainstays because the bike would stay planted on the climbs (as long as you didn't stand up). I never did manage it on any of my decent mountain bikes, which always ended up with 5ft long stems to keep the front end down on climbs and royally ****ed up the handling everywhere else.

My current 'XC' hardtail that I designed myself has 650b wheels, a top tube a couple of inches longer than my earlier bikes and a head angle around 6 degrees slacker (65dg. I guess it'd equal around 64dg if the wheels were smaller). I've only been out on it a few times but I've not felt the need for a steeper HA. After ditching the 29er, it's been awesome having a slack front end and longer suspension on steep techy stuff, rather than relying on bigger wheels.
I might play around with chainstay length (set to 16.5" at the mo, but sliding dropouts), but every bike that I've owned with long stays (such as the 29er and Nomad) have ultimately felt boring. That's just me though. I get that longer rear ends tend to be more stable both up and down.

JCL
Yeah its a 2011 Fuel EX so 26" And your right, the Reign definately felt a bit cramped sitting down whilst my Trek feels ok. Is it the front centre that makes the difference then?
Mostly i'm asking because im considering a new hardtail, and probably a stanton slackline or a bfe. I think a medium Bfe would be the right fit but less sure on the slackline. From what your saying the 18" would most likeley work better with a nice short stem.

Cheers

He's describing the type of geometry I dislike. I like modern ish geometry but if its too slack, low and long it feels cumbersome, slow and not as fun to me. Part of the fun comes from feeling a bit on edge and sketchy I think ! This is why I went back to my Trailstar from a BFe - the latter felt good and like it wasn't the bike that was holding me back, it was just plain dull to ride.

Load of old bollocks

short chainstays, short bike = a lot of fun for my type of local tight stuff in the surrey hills.

I have both a mega TR and AM, the AM is a dog around here in the tight stuff due to longer stays and slacker angles
likewise the TR gets out of its depth in the rough rocky steep stuff out in the alps etc.

Cant help but hink there is some connection between mondraker and mojo. Its like a marketing article. Fabien used to visit mojo when he rode for monds.

Yeah I realized he wasnt about the short chainstays, but I love the way a low bb, short cs bike feels in corners, maybe negates the problems with getting a slack, long front centre through the twisty stuff or something, but I find you can (in fact have to) lean into turns and pop out the other side better

[i]or unless your hands are on the bars ? [/i]

Eh?

Think about where your weight is, and it is pushing downwards on the pedals - there is very little on the bars.

And if your BB is below your axles then the weight is 'acting' the opposite to if the BB was above.

Cant help but hink there is some connection between mondraker and mojo

I agree - he completely failed to mention the fact that they fall apart and are designed by children with a pack of crayons without the the use of a ruler.

Who cares about angles when the rear wheel wanders off on its own, the bolts fall out, the rocker link smacks the seat tube on a big drop and the whole thing creaks more than my dads replacement hip.

I actually agree with quite a bit of what he says about geometry, although obviously the bias is more towards DH performance than accommodating the "generalists". I have to say though two key things strike me...

So the development process is more novelty led than performance led. Emperor’s new clothes, anyone?

1- So We're all morons? Meekly buying whatever toss the Bicycle Industry tells us we should... This of course from a fella who imports, flogs and services Fox shox, forks (with there excellent service life) and a [url= http://www.powa-productsstore.com/acatalog/Fox-Fork-Dfender-Mudguards.html ]£50 mud guard![/url]...

2- Why hasn't he put all this breath-taking, deep knowledge and understanding of what's wrong with the modern MTB into producing the greatest ever bicycle known to man? Rather than periodically berating everyone else...

Whenever I read something that he has written I end up thinking that he is a knob.

I don't think He's a Knob, he has ideas, and passion, this is good.
But he is in danger of becoming the UK bike industry's [i]opinionated fella in the corner of the pub[/i], pointing out all the problems with the world and fixing none of them...

Everyone just smile and nod...

The difficulty I have with articles and views like this is that they seem to focus too much on trying to say that this is 'the' answer rather than 'an' answer. It also is very much focused at the racers, and going measurably faster, which although important to some is not important to everyone.

I tend to agree with CP on most of his points for DH/Enduro and to some degree 'trail' riding (whatever that is to you!), but you need to not lose sight of the fact that people ride bikes in very different ways in very different places. Some people ride exclusively in one discipline, some are more varied, some race, some don't. The bike I ride when racing short-course XC is massively different to the bike I ride when I race Enduro, and same again for 24hr events and when I used to race 4X, but that is how it should be, promoting one particular geometry (long,slack,low) is all well and good but needs to be taken in context of the riding.

I think an uncomfortable truth that many riders wont admit to is that they are at least 50% more Gnar in their head than in real life, there are lot of people riding trails where their bike is massively over-capable, I won't fall on the cliche of calling it overbiked, because you need to ride whatever makes you happy, but if we are advocating the 'by the clock' approach then a lot of people would be quicker on lighter, shorter travel snappier handling bikes, that's not because the long low and slack approach is bad, it's just that your average weekend ride (and rider) in the hills or on a red route doesn't present the kind of terrain and crucially speed, where they come into their own.

If your average ride is hitting the jumps, lift-assisted or general tech-fest buffoonery then it's a different matter, and if I'm off out on a ride or race like that I pick my long low slack bike, if I'm heading into the hills for 40 odd miles of moorland for example, I wouldn't, I have bikes that are better suited to that.

I also think CP has a point about people (personally and commercially) being afraid to change and try new things. I don't think enough people (personally) play around with their bikes, to try new things, sometimes good, sometimes bad, to get a real feel for how things work and experiment.

Commercially it's difficult, the big guys aren't often willing to go out on a limb with something outrageous as they think it'll be a hard sell or they'll make a loss, so it's often left to the little guys to experiment, you have the same problems in racing though, it's unusual to find a top-5/top-10 racer willing to go out on a limb and try something radical for fear of ruining their season, and so it falls to out-of-season testing and incremental changes.

In summary, I agree with a lot of CP's points (if not his style) but I think it's easy to get blinkered by the riding *you* do, and either forget or dismiss others. For certain aspects of MTB I think he is bang on, but MTB is a very wide sport.

He's a contrary bugger eh?

Someone should tell him to sign up to this forum, I feel he'd enjoy himself.

I kind of lost interest in him when he suggested that MTBers throw our lot in with the MX crowd regarding access. Utterly stupid idea.

I've had the misfortune to deal with porter over the phone a few times back in the day when I foolish enough to believe fox was the best suspension out there.

The man is passionate and opinionated to the point where he can't absorb other people's views.

The fact that he clearly lives in his own little mojo world of Dh/enduro racing further denigrates his validity to the ranks of the trail riding commoners.

Like many have said already, it's clear that for his own narrow paradigm of riding, he has lots of ideas that are relevant.

For the rest of us who don't conform to his idea of riding, I think his ideas don't work as well. This is made worse by his inability to write anything coherent (anyone remember his RoW rant)

I'd be very cautious taking anything from those articles too seriously. It's clearly a badly written marketing piece.

my tuppence:

his ideas are not really unique - a lot of people already agree with him. He's just taken it a step further.

it's clear he reeally reeally likes a reeally slack head angle - good for him. But the only way he can get it to work is to balance it with reeally long chainstays.

his bike works because it's balanced (can i join the queue to have a go?)

i suspect he already knows that he could achieve roughly the same thing with a 'normal' slack head angle balanced with merely 'normal' chainstays - resulting in a bike that's much more versatile. but not so radical or provocative, and he wouldn't get so much attention. it would be a bit like a blue-pig, and we already know they're ace (they're not even weird anymore)

summary: mostly i agree with him, and he's taken it even further, probably to prove a point, good for him.

zero reach stems though? - a sure sign he's gone too far.

b r - Member

And if your BB is below your axles then the weight is 'acting' the opposite to if the BB was above.

Not in the way he's talking, regarding braking forces. The hammock/pendulum effect is different.

Taking it back to basics- within the same article he tells us lower is better on 26 inch and 650b bikes, but terrible on 29ers, does that make any sense to anyone but him?

Personally I think he's absolutely spot on! Trouble is 90% of mountain bikers don't ride steep techie stuff so won't appreciate needing slack low geo. Others spouting off saying he doesn't know what he'stalking about are clearly what I would call trail centre riders/ beginners.. pedal strike only happens to novices, so in that respect then yeah slack low and long is not for everyone

he's taken it even further, probably to prove a point

One of Chris’ main things with 29ers is wheel flex, hence him saying about £1800 carbon wheels to achieve the same stiffness as a smaller wheel. And he’s clearly not so off the mark given the new 142+ format to create a better spoke angle and so stiffer wheel. Even at 72kg, I found the flex on the wheels on my 29er HT very offputting when ridden hard.

There’s another article where Chris talks about having found the tipping point for the principle where it stops working in his favour:

http://www.mbr.co.uk/news/bike_news/size-matters-part-2-finding-limits-geometry-sizing/

It’s a good thing to have passionate people pushing the limits and finding the cutoff at which things stop – gives us the benchmark to do our own mods toward.

I’m now running lower, longer and slacker than ever and will happily compromise XC style climbing and “fun factor” for speed and stability at speed – but then that’s down to a preference thing. I’ve never been interested in technical climbing (climbing is just the way to get to the top) or that nadgery low speed tech on the flat either – for me it’s all about DH speed, so anything that improves this is good.

What CP has done is illustrate some things that anyone can do to their bike relatively cheaply (offset bushes, anglesets, short stem/wide bars) to make improvements for this kind of riding.

Some people don’t rate going fast downhill as the key thing, some don’t – but it’s good to look at and listen to someone who is at the forefront of development ideas.

A great bike designer said that you always need to go further than you think with an idea, or go 'too far', otherwise you never know where the ideas limits are.

^^This

[i]Taking it back to basics- within the same article he tells us lower is better on 26 inch and 650b bikes, but terrible on 29ers, does that make any sense to anyone but him? [/i]

I guess back to the braking issue, and with a 29er you can get the BB too low vs the axles.

He dismisses 29ers and says road bikes are rubbish.
10 out of 10!!

what are his metaphysical views on the totality of lateral stiffness and vertical compliance?

Someone should tell him to sign up to this forum, I feel he'd enjoy himself.

This 😉

I enjoyed the read, even if I didn't completely grasp a lot of the more technical aspects.

That Nicolai might be great on fast, wide open or really steep stuff but if you can't get it around corners, like he proved at TP then it's still a bad race bike. An enduro race bike needs to be fast everywhere (like awkwardly tight tracks), not just when it's flat out.

I'm a fan of long wheelbases and front centres with short stems, short chainstays make bikes more fun to ride on less extreme stuff and easier to handle when it gets really tight. CP might actually have been able to get the beast round tight corners if the chainstays were shorter...