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

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...

I think it's a mistake to think any one single 'way' is universally correct. A lot of what CP says makes sense but it is counter to more conventional thinking.
Fabien Barel's recent revelations about his stem/bar set up, which goes against the "slam them as low as they can go" herd mentality are also interesting in a similar way.

What works for some will not necessarily work for others. The stopwatch can't lie, but it also can't measure the feedback, fun and confidence a rider feels. It's all very subjective, but overall it's a good thing that there are people nudging the edges of the set-up envelope.

He's obviously very passionate about his ideas, and as someone further up said, if people don't try & find the limits, then nothing ever advances.

I do agree with some of what he says, although maybe not in the way he says it.

The big thing i'm not convinced on is his whole mantra of super long front ends & 10mm stems. I spent a lot of time last year riding a load of the Forward Geometry Mondrakers, and (which is the key bit - why we're all different) for me, they ride like sh*t.

They force you to ride in such a way over the front of the bike otherwise you have a lot less front end grip. I've never suffered so many front end washouts and feeling of looseness when riding anything else. I can ride noticeably better & faster on a more normal setup with a 55mm stem, which puts me in the same place on a current Mondraker Dune with their 10mm stem. That's not to say that what I like is in any way better for the next person either.

Let him crack on I say, its good we live in a world where he can put some of his ideas into reality. Even if they turn out to be hideous abominations like that Nicolai 🙂

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

I don't understand this comment, once you get used to the twitchyness they are great on the correct bike.

I don't get zero reach stems either. Putting the hands in line with the steerer, I can see, but behind!?

b r - Member

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

The braking issue that I've never heard anyone else mention or notice, and that isn't really backed up by logic or physics? 29er BB drop moves a small amount of grams a small distance, the overwhelming factor will always be the huge amount of grams still much further above the axles that you move around all the time. It's like obsessing about pedal drag because mathematically you know it slows you down. Or, you know, declaring that you HAVE to spend £2500 on wheels to sort out a 29er.

I'd be totally happy if he just said "I don't personally like 29ers because X", opinions are good and his are to pay attention to. But he doesn't want to do that, so he uses pseudoscience and dubious "facts" like "29ers have no pump" to try and turn his opinion into fact. TBH it seems like a pretty common thing in mountain biking, people aren't happy to say they prefer this to that- it has to be what they like is [i]best[/i], what you like sucks and you're wrong.

There's a bunch of stuff I agree with him but the other stuff undermines him and the article. Especially when he changes his mind on something and suddenly his new gospel is as right as the old one was right up til he decided it was wrong. (see- 26 vs 650b).

A rant about novelty-led product development and pandering to the lowest common denominator.

From the guy who imports Fox CTD technology into the UK.

I don't get zero reach stems either. Putting the hands in line with the steerer, I can see, but behind!?

Yeah, maybe it works but I just have images of pushing a shopping cart.

People seem to forget about bar sweep when it comes to stem length. My grips are in line with my steerer.

JCL, long chainstays push you over the front more and in turns keep the rear end more stable and less likely to break away. At the same time they are more comfortable through rock gardens.

Long chainstays are the way to go in downhill.

I don't get zero reach stems either.

MX stem.

[img] [/img]

Brake-neck - Member

I don't understand this comment, once you get used to the twitchyness they are great on the correct bike.

mostly, i was just talking shite.

if they work, go for it, i just think they look a bit weird.

Others spouting off saying he doesn't know what he'stalking about are clearly what I would call trail centre riders/ beginners.

mikewsmith - Member 
Others spouting off saying he doesn't know what he'stalking about are clearly what I would call trail centre riders/ beginners.

aw bless, nice of you to still talk to those folks you seem to look down on
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My comment does sound a bit arrogant and bless you I'm sorry if I offended you but you clearly do not understand his theory maybe due to lack of experience, but what cp is saying makes so much sense and I applaud him for having the balls and expressing his own opinion rather than being a typical sheep in the mtb industry...although I've never been a lover of Fox forks! 😆

I'm happy on the steep stuff, I'm happy going fast I enjoy my bikes but really can't be arsed with a lot of the stuff spouted about the "Perfect" bike which in reality is a bike for only one part of the experience. As you spotted it's also really easy to come across as condescending 🙂 I hope you don't get held up by anyone inferior today.

It all reminds me of a trip to Rotorua in June where the guide we had for the day took us of pisteing on some seriously steep and loose trails one one of these
[img] [/img]

For most people the bike is not the issue

It all reminds me of a trip to Rotorua in June where the guide we had for the day took us of pisteing on some seriously steep and loose trails one one of these

For most people the bike is not the issue

That's awesome! 😆 😉

pedal strike only happens to novices, so in that respect then yeah slack low and long is not for everyone

Come and ride our natural trails as fast as you can and you'll learn all about the challenges of pedal strike! When the gradient is steep enough and corners large enough that you don't need to get some pedal strokes in as soon as possible after the exit then super low BBs are great. But it isn't always like that in the real world outside trail centres.

Jared Graves pedal-struck a root at tweedlove and fired himself over the handlebars. But hey, he's only a world champion so probably still learning the basics.

Shorter cranks?

I've been advocating for 150mm cranks for years. Funny that Porter doesn't mention that.

Northwind - Member 
Jared Graves pedal-struck a root at tweedlove and fired himself over the handlebars. But hey, he's only a world champion so probably still learning the basics.

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Oh jeeez...of course its gonna happen every now and then even to the pro's
But in general it's a skill you learn to master even on the rockiest of tracks chief guru! 😉 where do you ride by the way? Sounds amazing! Surely you'd have picked up the skill of pedal positioning by now!

My Jones has a super low BB - initially I had the odd pedal strike, but you adapt and I hardly ever have them now. I ride the same areas as Chief. Actually the low BB, slack, big offset, and long wheelbase of the Jones Plus has elements of what Chris is proposing....... Just a thought, And H bars will put your hands pretty much inline with the headtube.

It isn't rocks that are the problem, it's roots and stumps. Such is life when your local trails are through very twisty deciduous woodland. On the steeper trails it's fine but on the flatter ones, or coming out of really slow corners on the steep ones, it's all too easy to catch a pedal when you put down the power out of the exit whilst the bike is still leant over. Doesn't help that I'm often riding them in the dark too!

FRC, I can't easily find the BB height of your Jones but I'm guessing it's around 300mm. And it doesn't vary because you have no suspension. The BB height of my Spitfire is 346mm in the middle setting, so about 306mm sagged. Fully bottomed out it'll be down at 200mm. Pumping out of a corner and then pushing the pedals it's going to be well below the lowest rigid bike's BB height.

chris85, you're a bit stalkery, you know that?

So pedal strikes only happen to novices, except when they're happening to pros. And that's got something to do with where I ride?

Northwind, please do not take it to heart. This is my opinion that I agree with cp..he clearly knows more about mountain biking than you...again that is my opinion.
To say that pros should never have pedal strikes is like saying they should never have a puncture or an otb...it happens, Just obviously the more riding experience you get you learn to manouver the crank arms about to avoid obstacles roots and rocks. I think you know exactly what I'm saying but your being slightly awkward mate 😉

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

ahh, purest stw gold

[img] [/img]

Very good that Jim 😉

Interesting article. Some of it makes sense, some not so much, and some just smacks of I want to be different to cause friction.

Comparing Moto gp handling to an mtb is frankly ridiculous

The only thing I took out of that is lose the clutch mech:

And I only just bought one.

FRC, I can't easily find the BB height of your Jones but I'm guessing it's around 300mm. And it doesn't vary because you have no suspension. The BB height of my Spitfire is 346mm in the middle setting, so about 306mm sagged. Fully bottomed out it'll be down at 200mm. Pumping out of a corner and then pushing the pedals it's going to be well below the lowest rigid bike's BB height.

Actually, maybe someone could measure to be sure, but I believe the Jones BB height is somewhere in the region of 280. That's REALLY low. You should be comparing sagged on an fs to the static rigid height, you're not riding around with no air in the shock and the bike bottomed out all the time are you?

The only thing I took out of that is lose the clutch mech:

And I only just bought one.

If you want to see what actual difference it makes, disconnect your shock and move the bike through its travel. Completely insignificant compared to the friction in a shock mount bush and of no concern wth your body weight flouncing around on top of it

I confirm that my Jones BB height is 280mm, mine doesn't have an EBB, but most do, so I presume it could be even lower if you desired.

Interesting article but all the guy has done is tried to build a bike that suits his own personal skills and riding style. Thing is Chris Porter is a not actually all that good an all round bike rider. He did Ok for an old man racing gravity events on the latest equipment but any properly good competitor could have beaten him on a short travel steep angled hardtail. Put Chris on the same hardtail and his results would have been laughable.

JCL. I'm not sure what you mean by advocating 150mm cranks, but why don't you just fit a set? unless you're around 5ft or smaller or only ride uplifted you probably won't find them very nice. Profile do everything you'd need.

Very good that Jim 😉

Are you having a stroke? You keep putting winking things after everything.

The article was quite interesting. I don't really like the writing style and the irony of the importer of Fox railing against herd mentality was a good one though.

JCL. I'm not sure what you mean by advocating 150mm cranks, but why don't you just fit a set? unless you're around 5ft or smaller or only ride uplifted you probably won't find them very nice. Profile do everything you'd need.

Yeah but they weigh a ton and they aren't PF30. Sram/Shimano should drop 175mm and do 150/160/170mm.

tomd - Member 
Very good that Jim
Are you having a stroke? You keep putting winking things after everything.

The article was quite interesting. I don't really like the writing style and the irony of the importer of Fox railing against herd mentality was a good one though.

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What a nasty comment! My girlfriend has suffered a stroke and its really not nice to ridicule..I hope you don't ever find yourself having to look after someone after a stroke... Tool

I'm sure it was a joke.
I've heard worse on daytime telly to be honest

[i]Interesting article but all the guy has done is tried to build a bike that suits his own personal skills and riding style. Thing is Chris Porter is a not actually all that good an all round bike rider. He did Ok for an old man racing gravity events on the latest equipment but any properly good competitor could have beaten him on a short travel steep angled hardtail. Put Chris on the same hardtail and his results would have been laughable. [/i]

Isn't that what he (and racer) should be doing, making the best bike that suits their skill and style?

It already is what he's doing. It's nothing new and it's nothing any of us couldn't attempt so long as you can justify the cost.

JCL. Yeah, as far as I know PF30 and profiles are not (yet?) compatible. I wouldn't rule them out on weight alone though. Profile racing cranks with their Ti axle and an aftermarket spider are very close in weight and arguably comparable to Saint in strength /stiffness and durability. I know those are the qualities I'd be looking for from a crank for a properly low BB long travel bike.

If you want a 150mm crank, would the easy way not just be to find a solid-armed crank and shorten it ?

I don't think I'd like it though- I can't really tell any difference between my 175s and 170s when riding but my 165s felt a bit odd, not when pedalling but when flat pedalled- gives you a shorter stance. Whether better or worse I don't know, but weird anyway.

When I ride a bike with 175's it feels like I'm surfing.

I wonder to what extent longer cranks just feel right for me, because I'm used to them...

It's actually not that you don't notice the difference between your bikes with 170s and others with 175s. It's simply down to muscle memory that they both feel "right" when you jump on each bike despite the change in crank length. Whether you are aware of the difference is another matter entirely.

It's amazing how 10mm difference in the length allows you to move around more. It's like going from a 100 to a 125mm dropper.

TBH, hitting stuff with your pedals is always going to be a risk, with any (serviceable) length of crank. If you get the impact just right (wrong?), with the crank about 15 degrees forward of bottom-dead-centre the results can be spectacular - like those airbag pranks all over the net ATM - and you feel like your being forcibly ejected from the bike.

mtbel - Member

It's actually not that you don't notice the difference between your bikes with 170s and others with 175s.

No, it really is- I once got the arms mixed up and put a 170 on one side and 175 on the other of each of my bikes, didn't notice that either.

Northwind - Member

If you want a 150mm crank, would the easy way not just be to find a solid-armed crank and shorten it ?

it's proving tricky to find any suitable cranks - all the nice ones are hollow, or scooped out (on the back - see deore)

my 165s felt a bit odd, not when pedalling but when flat pedalled- gives you a shorter stance. Whether better or worse I don't know, but weird anyway.

conversely, my poor wife* has to put up with 165's. if i wanted to experience just how weird/crap this must feel, i'd need to find 210mm cranks. No wonder her knees hurt.

(*she's not even 'that' short, it's just that for some reason the largest component manufacturers pretend that people under 5'8" don't exist)

Northwind, please refer to my last sentence. This could be down to you not riding all that much, only riding for short periods of time on each bike, length of time between riding each or just simple lack of perception. But I'd be surprised if you were to ride one of the bikes exclusively for a few hours each day for a few weeks then switch straight over to the other and not notice a slight difference in feel while pedalling .

mtbel - Member

Northwind, please refer to my last sentence. This could be down to you not riding all that much, only riding for short periods of time on each bike, length of time between riding each or just simple lack of perception.

I really don't know what you're getting at- you say "It's not that you don't notice" then come up with "lack of perception"- which is exactly what not noticing means- it's imperceptible to me, it makes no noticable difference.

I've got 170s on the winter road bike, 172.5s on the summer road bike and 175s on the MTB. I can't tell any difference between any of them, irrespective of how many hours I spend riding each one.

JCL, you do realise when switching to a shorter crank in order to maintain optimum pedalling efficiency you actually need to raise your saddle height by the same amount?
5mm shorter cranks (when stood pedal level) will only allow 1mm extra clearance at the pelvis and a tiny amount of extra extension /squat through the minute change in ankle, knee and hip angles.

I have a 155mm set of [url= http://www.canfieldbrothers.co.uk/products-to-buy/components/cranks-cranksets/ ]Canfield cranks[/url].

I am 175cm tall, with fairly average build. It's fair to say that you notice the loss of 20mm of crank length if you're pedalling. I [i]think[/i] I could detect reduced leverage and a much lighter feel - you spin nicely but it does feel a lot lighter and I wasn't convinced I could get the same power.

Ought to experiment some more. I tried 175mm back-to-back and ended up leaving them on rather longer than I intended!

Thing is Chris Porter is a not actually all that good an all round bike rider.

Sorry got to call you on that, Chris is pretty good on a bike and has podiumed at national events.

Confusing, I know. just part of what I typed probably isn't helping you either.
Muscle memory through repetition is what I meant by "notice"
what your body notices, your mind does not necessarily perceive. 😉

I'll explain to you in person if you come to the Golfie on Saturday.

I'll be racing up at kinlochleven. Noticing just means being aware of something, all you're doing is giving various reasons not to notice something, while saying "it's not that you didn't notice". But it is.

Sorry got to call you on that, Chris is pretty good on a bike and has podiumed at national events.

He said he's not a good "all round rider", he could be a very good DH racer...

I can assure you he is, not got any reason to 'big him up' either. 😉

If he's reading this he'll be pissing himself laughing

He knows fine he's not that great "all round" Loco. The guy rides 170mm travel at trail centres. Stick him on a traditional XC hardtail or a BMX and I'm sure he'll be laughing (but for entirely different reasons) 😉

I've used 165mm cranks - and I definitely notice the difference, much more of a 'spinny' feel to them.

futon - did you keep the same gearing, or did you adjust for the reduction in crank length?

I've used 165mm cranks - and I definitely notice the difference, much more of a 'spinny' feel to them.

^^This. I find I can turn them up to speed much faster than a longer crank.

Does any of this relate to someone (like me) who gets their 8 year old hardtail out of the shed and rides around the Surrey Hills once a week, being sure to avoid all the scary looking drops and jumps?

If you had a 20 foot long bike with a 45 degree head angle you could ride all that stuff. You might not be able to get round any of the corners though.

JCL, you do realise when switching to a shorter crank in order to maintain optimum pedalling efficiency you actually need to raise your saddle height by the same amount?

Yep. It'd probably mean I could just get away with a 150mm dropper without it bottoming on the seat tube.

Regardless it's better for cornering, reducing leg fatigue while descending, ground clearance.

So the shorter cranks, better feet level or up and down? For the up and down some fat pedals and soles would show it for the cranks flat moving cleats back should do it too.

HoratioHufnagel - Member
Does any of this relate to someone (like me) who gets their 8 year old hardtail out of the shed and rides around the Surrey Hills once a week, being sure to avoid all the scary looking drops and jumps?

No. The fun police have decreed that that is to be classified as tow path riding and therefore outside the acceptable limits of what is considered proper cycling.

Chris Porter is knowledgeable, no doubt but still comes across as a narrow-minded male chicken (but people who've met him seem to say he's a decent bloke...)

BigDummy - Member
futon - did you keep the same gearing, or did you adjust for the reduction in crank length?

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I can't remember !! Lol

I might try them again, obviously raises your CofG a bit, which I suppose works a bit against having the super low BB, but I liked that it also put a bit more weight over the bars, but that then put more pressure on my hands ( rigid bike) - so many swings, so many roundabouts!

I noticed the difference between 175mm and 170mm - I feel like I'm pedalling smoother circles with the shorter cranks. I swapped to a 32t from a 34t at the same time and that's working out well.