Have we done this yet? – latest Chris Porter Geometry article

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  • Have we done this yet? – latest Chris Porter Geometry article
  • Premier Icon amedias
    Subscriber

    I have many thoughts, I’m not sure how to corral them into sentences yet, in the mean time, discuss….

    linky linky clicky clicky

    Premier Icon mikewsmith
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    Low BB – pedal strikes and OTB pain
    Slack – Fall off the back climbing up hill
    Long Wheelbase – great at speed shit in the tight stuff

    It’s all a compromise really

    P-Jay
    Member

    I’ve met Chris Porter a handful of times, and he’s a nice bloke and it’s pretty obvious speaking to him he knows his stuff, he also posts some very, very quick Strava times around Cwmcarn so IMO anyway he’s very credible both on paper, and on the trail – not that he has to justify himself to me – but sometimes it seems he’s the one voice shouting “LEFT” when everyone of the thousands of people who work in the Mountain Bike industry are shouting “RIGHT”.

    Perhaps he’s right though, after all he’s being shouting for slacker head angles for years, and you only have look at the bikes about now they’ve been getting slacker and slacker year on year – perhaps he’s calling for a sea-change and the makers, fearful of being the odd one out are going for evolution – one thing I certainly remember reading years ago was an article by the bloke who designed the Atherton’s Commencal DH race bikes – he said something along the lines of “Gee’s bike as a X% head angle, really extreme – we’d never sell a customer bike like that, most riders couldn’t ride it” I’d bet my balls to a barn dance that extreme head angle is pretty normal nowadays – I just can’t find the article online.

    I once put my 2003 Spesh SX into ‘low and slack’ mode, which combined with it’s shorter air shock meant 62.5 HA and a very low bottom bracket … yeah it was great hammering down a hill, but like hell could you pedal it in even the slightest rut and it felt like a floppy whale at slow speed.

    I do agree clutch mechs are bad as a lot of frames have silly suspension designs in relation to chain growth. My DH frame is lovely, 2.5″ of chainstay growth but almost zero chain stretch makes it a beauty over fast bumpy stuff like roots and rocks (Canfield Jedi).

    Junkyard
    Member

    he is correct about compromises and big wheels
    The problem is he wants to ride downhill pretty fast and most of us want to do everything adequately without death

    PJM1974
    Member

    I’ve been following this, Chris Porter has always been quite opinionated and I don’t agree on everything he says, but some of it rings true.

    Seat angle (steep is actually good!)

    Agreed – a steeper seat angle noticeably improves a bike’s climbing ability by keeping the rider weight centered. There’s no place for a slack seat angle on anything other than a DH bike in my humble experience.

    I also agree that a longer reach is a good thing, so long as it’s combined with a steep seat angle. I’m willing to sacrifice some low speed agility for stability at faster speeds.

    However, it all begins to fall apart for me when he introduces the vague moto-x analogies.

    But this:

    A bigger wheel rolls over bumps better than a smaller wheel… zzzzzzzzzzz. Sorry, sent myself to sleep there with those fairy tales.

    I was very skeptical too, until I tried a 29er out. Now I’m converted, but I also understand that there are other factors at play here other than just the wheel size – geometry is paramount here but you can’t ignore the fact that a decent 29er rolls pretty darned well.

    And this went a little too far for me:

    A bad designer and a lazy bike tester will take these negatives and say it won’t climb. As they ride the slack(ish) bike with no thought to locking their core muscles and taking control of the bike, the bars flop from side to side and the bike gets the blame for the rider’s failings.

    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. We keep being told that we want ever slacker, ever racier bikes on which we must go faster and in doing so improve our technique. That’s all well and good if you’re riding bone-dry trails in Utah or wherever but such a bike will be unusable on the typical soggy, slippery UK trails that the majority of us have to endure for six months of the year when our average speed falls dramatically and we’re having to negotiate greasy Southern-British chalky hillclimbs.

    Premier Icon mikewsmith
    Subscriber

    A bad designer and a lazy bike tester will take these negatives and say it won’t climb.

    At this point I would also challenge anyone making claims like this to get off their arse (or back onto it) and design a bike, get a prototype made up and prove em wrong, you’d be sorted if you were right….

    happybiker
    Member

    Interesting read, he really doesn’t like 29ers though! I disagree with the heavier/wider tye comment. I thought wider rims allowed lighter tyres for the equivalent volume.

    Premier Icon brant
    Subscriber

    At this point I would also challenge anyone making claims like this to get off their arse (or back onto it) and design a bike, get a prototype made up and prove em wrong, you’d be sorted if you were right….

    http://www.bikeradar.com/mtb/gear/article/chris-porters-custom-nicolai-ion-16-super-bike-41048/

    Premier Icon mikewsmith
    Subscriber

    good on him, has anyone else ridden it?
    That was May wonder when it will hit the shops?

    Long Wheelbase – great at speed shit in the tight stuff

    It’s all a compromise really
    [/quote]
    I think CP’s argument is that you build the bike to be fast/safe on the most difficult bits of a trail where you actulay make up time. The feel of the bike is secondary to how fast it is for him as a racer/team manager. On a flatter, tight bit of trail there probably minimal time to be made up compared to being able to hit 40mph rather than 20mph on a rough open bit of track.

    The bars don’t ‘flop’ you just fail to hold them straight, thats a defficiency in the rider not the bike, and I can see his point.

    He’s been on the same oppinion for years though, he used to ride a 223 with Fox 40’s for XC/trail/enduro as he felt it had the best geometry for it, but could just about pedal as well (and it was down to the low 30’s lb weight).

    There’s always a comprimise, but why comprimise away from “this makes it faster, but……….”.

    I jumped back into sailing this year and there’s similar differences between boats (but there is a handycaping system to try and give a fair race rather than allow it to become a pure arms race).

    My boat (well not mine, but the same class), a Blaze huge sail, huge racks for leverage against it, probably what CP would sail as it’s fastest when things get really hairy, an bit less than nimble on a tight course in light winds.
    [quote]

    A boat I sailed last weekend, a D-zero, 25% sail area, 33% less beam, not as fast, posibly actualy harder work though (different muscles). It’ll be more popular for one reason or another than mine, mostly a mix of marketing and it looking less threatening, but it isn’t faster.

    mikewsmith – Member
    Low BB – pedal strikes and OTB pain
    Slack – Fall off the back climbing up hill
    Long Wheelbase – great at speed shit in the tight stuff

    Those are generalisations though – my current bike is longer, slacker (65°) and lower than the bike it replaced, and still climbs better, is more agile and I never notice pedal strikes.

    Good design trumps bad design, basically. Most of his principles are sound – if biased towards his own riding styles and preferences.

    Junkyard
    Member

    but you can’t ignore the fact that a decent 29er rolls pretty darned well.

    he did not he said it was great at getting over stuff but this came at a price

    wobbem
    Member

    To slack and you’ll bend stantions 😉

    Bazz
    Member

    Whenever I read something that he has written I end up thinking that he is a knob. I’m sure that everything that he writes is 100% accurate for his riding, but guess what, not everyone rides the same way or on the same terrain! each to there own and debate is good, but he always comes across as opinionated and up his own arse.

    Premier Icon Northwind
    Subscriber

    It is interesting but too often, he contradicts himself- he was banging on about the overwhelming and unmistakable superiority of 26 inch wheels right up til the second he decided 650b is better (but obviously 29ers still suck). And he never has a middle of the road opinion, it’s always thing A is amazing and thing B sucks.

    The thing about clutch mechs just strikes me as utter pish tbh- the difference in forces between a standard mech and a clutch mech is pretty trivial, and in any case works in parallel with the shock which is dealing with much greater forces- I’ll happily bet one scottish pound that he can’t actually tell the difference.

    I’d still love a go on that Nicolai though

    JonEdwards
    Member

    I’m intrigued by his ideas, but having met the guy at the TP this year, he can come across a bit off – misreading your map, then in retaliation trying to tear the timing monkey a new arsehole just made him look rather stupid. (he did say sorry a day or so later)

    While I suspect his geo ideas would be great on fast, long, steep, loose descents, they didn’t seem to work very well on the super tech trails around Sospel as the bike (a one-off Canyon at the time) was just too damn big to go round the corners. Horses for courses, and that Nicolai is a very specific horse for a very specific course.

    <<edit>> One could argue that my Rocket is a less extreme example of the Nicolai – pretty slack, pretty long, pretty low, fairly steep SA, but not extremely so in any department, and that does work as advertised. The “steel is real” side is irrelevant, it’s the geo that makes it special.

    plyphon
    Member

    but he always comes across as opinionated

    Well it is journalism. You can’t take opinions away from them – they’ll have nothing left!

    JCL
    Member

    He’s mostly bang on.

    neilforrow
    Member

    thisisnotaspoon – I think CP’s argument is that you build the bike to be fast/safe on the most difficult bits of a trail where you actuality make up time.

    This

    Northwind – I’d still love a go on that Nicolai though

    +1.

    There is a definite trend in the market to longer / lower / slacker, something I am all for, however, he needs to cover that all with ‘I lives in south wales, and rides technical trails all the time’ comment. He doesn’t plug round fields in Hertfordshire 95% of the year where a sharp handling 9’er would be way more fun.

    deviant
    Member

    JCL, I agree.

    Head angles could go slacker and seat tubes steeper to make the downhill sections of rides much easier while retaining climbing ability…. Don’t know why it hasn’t happened yet TBH…prob just the industry wanting to move in baby steps (and wanting us to replace our ‘redundant’ bikes each year in the meantime), after all why move straight to 63 degree head angles when you can make the consumer buy one at 64.5 degrees first…then another at 64 degrees the year after etc etc…

    Premier Icon brant
    Subscriber

    He’s great.

    I haven’t seen him mess about with fork rake/offset though. Which strikes me as odd.

    Premier Icon flange
    Subscriber

    Marketing genius, build a bike so horrific that it gets you loads of press coverage.

    I’ve never put much truck in what he says and after his treatment when I rang Mojo once, I certainly won’t be spending any money with him.

    He talks out his arse in my opinion. The fitting of a bike to someone has never been a one size fits all. I cannot for the life of me get on with Specialized bikes, regardless of wheel size. Many can and do. I happen to prefer a slack as possible head angle but hate long chainstays, maybe a bike feel slow to turn (IMO!). I like 29ers for covering distance but not for technical stuff. Others feel differently. To berate large proportions of the buying public seems pointless and somewhat childish. Build a bike that suits your needs by all means, I’m sure most would if they could. But don’t then claim its the future and rubbish everyone else.

    Incidently, he harps on about how awesome Mondraker forward geometry is. When Brook Macdonald was on MS_Mondraker he found he really didn’t get on with the bike until he changed the stem to something normal. He immediately when measurably faster.

    Different strokes for different folks..

    julians
    Member

    Been playing with the head angle on my Mojo HD, Stock is 67 deg, I now have it at 65 deg. I think I’ve gone a smidge too far, its great at speed/downhill, but on flat slower (but not slow) corners you really have to have decent technique to stop the front end washing out, its significantly less forgiving of poor body position.

    He’s probably technically correct with his thinking, but I dont reckon his thinking would suit your average weekend warrior.

    Premier Icon AlexSimon
    Subscriber

    The problem he’s highlighting is that many bike companies, just look at what they’ve just launched, tweak a couple of things according to market trends and release it a year later.
    His example of taking things way too far and riding it until your used to it, seems like a great way to try and evolve quicker.


    e.g.
    I was really nervous of going from my 680mm bars to 780mm that I test rode on two bikes last week. Previously I’ve just felt daft on wide bars. But after spending 2 full days on it, going back to my 680s seem very weird too – really eye-openingly weird. Made me think that going to a halfway house of 740mm was pointless.

    There are some good points amongst the combative writing – and quite a few typically journalistic bits of hyperbole to get people talking. 😉

    Something no-one ever talks about is how handlebar shape and rotation interacts with stem length. What actually matters is the forward offset of the centre of the grips (or possibly the back of the grips depending on which loading matters most?) from the steering axis. The big problem I see with so-called zero stems is they actually result in negative effective stem length with typical handlebar shapes.

    That forward offset of grips from steering axis gives you a stabilising tiller effect when you lean on the bars. Make that offset backwards and any imbalance in force between left and right grips and the bars want to flip left or right.

    As with all things in engineering the extremes, though exciting sounding, are rarely the best solution. Low, slack and long is good. Lowest, slackest and longest is good too – but in fewer situations. I do think there’s an issue with super-short chainstays and very long front-centres. Longer (not necessarily long) chainstays give a much better handling balance at decent speeds but might not seem as appealing when you’re messing around at low speed thinking how a bike ‘feels’.

    julians – Member
    Been playing with the head angle on my Mojo HD, Stock is 67 deg, I now have it at 65 deg. I think I’ve gone a smidge too far

    You’re riding something of a bodge, though – a bike that wasn’t designed to be 65 at the front and may not be suited to that.

    Premier Icon BillOddie
    Subscriber

    Porter does talk a lot of sense when it comes to riding bikes fast over technical terrain.

    My sadly departed Blue Pig had a daft slack HA (64deg static I think) and Steep SA and long-ish Chainstays.

    It was a f****** hoot on steep or fast downhills.

    Flat singletrack you had to muscle it around a bit but you just as CP states have use your core.

    Uphills we fine, either sit and spin and I winched myself up some truly daft steep stuff on that bike or stand up which makes the HA irrelevant.

    That being said on flatter less technical terrain the bike just felt bored.

    Premier Icon Rick Draper
    Subscriber

    I haven’t seen him mess about with fork rake/offset though. Which strikes me as odd.

    He mentions it in one of the articles, using a modified 26″ wheeled Fox 36 on a 650b wheeled bike. He mentions not even Honda knowing all about the effects of offset etc. That is unless I am terribly jet lagged and made all that up!

    deviant
    Member

    Chiefgrooveguru, motorcycles have been lengthening the swingarm for ages now, it is accepted that this provides better handling at speed, the swingarm axle on bikes has been moving more towards the middle of the machine year on year.

    Not sure bicycles can do this as it would put the chainstay pivot point way in front of the cranks/BB/rider’s feet.

    Premier Icon molgrips
    Subscriber

    I have a bike with an adjustable shock mount and I recently slackened it which was an interesting experiment because it was the same bike, same wheels, shock etc with different angles.

    It DID make climbing harder because my weight was now further back and the front wheel wandered. Then I shortened the stem because it felt wrong with the forks fully extended.. then I had to slam the stem and now it’s amazing – still worse on climbs than it used to be, but I’m prepared to accept it.

    Compromise, as has been said.

    robinlaidlaw
    Member

    Not sure bicycles can do this as it would put the chainstay pivot point way in front of the cranks/BB/rider’s feet.

    VPP and DW link type linkages can and do effectively put the point that the rear wheel pivots around way in front of the BB but that still doesn’t give you a long rear centre which is what confers the high speed handling benefits. That just needs the rear wheel moved backwards, simple as that.

    LoCo
    Member

    Having worked & argued 😉 with Chris he’s certainly passionate about his projects.
    worked on some interesting designs when I was there.

    Re. geometry etc John Robinson’s motorcycle chassis tuning books are quite interesting, especially the zero rake & reverse offset equipped bike, which is a great illestration of how there are quite a few ways of getting something to work.
    As said above everything is a comprimise with plus & minus points for each individual rider.

    andyrm
    Member

    I’ve met Chris a few times and also ridden on some of the trails where he does testing – he really does know his stuff when it comes to suspension and geometry for big bike riding. Maybe for XC riding round fields/bridleways, his methodologies don’t make the same difference, or perhaps are counterproductive – I don’t know, I don’t do that kind of riding.

    What I do know is that having slackened my bike out to 65 degree HA and dropping the BB a bit (offset bushings) have definitely improved it’s handling at speed. You have to adapt your technique in low speed twisty stuff and not be afraid to load the front wheel, and move lots on the bike to achieve this. Once you get used to being dynamic on the bike and “working” it, the negatives become much smaller.

    continuity
    Member

    What about clutch mechs adding an element of compression damping when chain growth occurs?

    LoCo
    Member

    Covered in the article, suspension works better without a chain/other outside influence, will be a pain for climbing though 😉

    ajantom
    Member

    Funnily enough I went for a ride with Geoff Apps today (to the uninformed he’s an early UK mtb pioneer).
    Anyway, his current bike contradicts everything in this article – it’s short, tall, has a steep head angle, and runs 2.5″ 29er tyres at a very low psi on narrow rims.
    Do you know what? I was amazed by how it rode. It is designed for UK conditions (wet, muddy bridleways, slow grindy uphills, and slop, lots of slop) I guess Geoff would call it a bike for ‘hacking’. I could clear stuff I would have no chance of on my full-sus, and it actually handles pretty well downhill, once you get used to the handling.
    Obviously, all this proves nothing, and this bike would probably do nothing for the average trail-centre warrior. But, CP is talking about bikes with a pretty narrow window of usage. There are other valid ideas out there.

    Premier Icon jameso
    Subscriber

    Brilliant read. May not agree with or relate to all of it but strong opinions like that result in out-there bikes. I like them, even if they aren’t your cuppa they’re worth a try, or make us think.

    Macavity
    Member

    People adapt to, and get used to using, what they are used to using.
    http://fcdn.mtbr.com/attachments/vintage-retro-classic/339252d1204397883-joe-breeze-otis-guy-head-angle-tests-pic-004.jpg

    Or in the opinion of Mike Burrows:
    “I think part of the problem is that the cycle industry doesn’t always attract the highest achievers”
    http://www.cyclingweekly.co.uk/news/latest-news/mike-burrows-cycling-innovator-27010

    For an idea of how much the wheelbase can change due to long travel forks on a full suspension bike:
    http://i.imgur.com/fOD42.gif

    Or an idea of what happens to head angles as forks compress
    http://www.btr-fabrications.com/category/geometry-design/

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