[Closed] 29er geometry geeks...

Head tube angle alone won't determine the handling. That's my thought...

Seat tube angle, top tube length, chainstay length - all these will affect it too by changing weight distribution, wheelbase, etc.

fair enough, though everything else is pretty unremarkable...

-- Seat tube angle = 73 degrees
-- Effective top tube length = approx 600mm
-- Seat tube = approx 450mm
-- Chainstays = approx 450mm
-- Head tube = approx 105mm
-- BB drop = 50 to 60mm

i don't know a lot about geometery but being STW i thought i'd get my tuppence out 😳

70.5 sounds slack. It's closer to a lenz behemoth (69.5) than a swift or on one (72)
however the singular gryphon (rigid only) has a 70.5 HA and this has been reveiwed as making it more capable than one would expect.
also although a niner air (small) with 100 mm fork is listed at 70.5. (there does seem to be a trend to have the smallest size 29ers with slacker HAs - which maybe to reduce toe overlap)

HA, fork offset and trail are all closely related and shouldn't really be chosen independently of one another.

add in to that the the top tube length will to some extent determine stem length which will also effect steering geo.

sorry for the draindump and lesson in geometery!!

Pedalhead:

what trail measurement does you headset, fork offset and length give you?

Clubber

changing weight distribution

Weight distribution is something that no one ever seems to talk about, despite slack angles, short stems etc etc dramatically affect f-r distribution

Seeing as your head tube's nice and short and BB drop is healthy, I'd steepen it a tad to 71° and go for the low-slung approach.

50mm bb drop would feel high would it not?

is that a personal preference?

EDIT:

In particular I don't want to feel like I'm going to be pitched over the bars on steep technical descents & small drops, but of course I still want it to go round corners.

i would have thought a little more BB drop 60-70mm would help achieve that.

please don't ruin your bike on what i say though 🙂

Work out what wheelbase your measurements give you. 1075mm or less should give good manoeverability. for the record an 18 inch Inbred 26er is 1100mm, my Dean Ti 26er is 1040mm and it flick-flacks in and out of the trees beautifully. If you want to keep your weight back on the bike you might want to consider a curved seat tube at a slacker angle to allow the bottom bracket to be as close as possible to the rear wheel to avoid toe overlap. Also see the Canfield Nimble 9 for another way of doing it with straight tubes.

Rather than just punch out a whole lot of numbers why don't you ride an existing frame, decide how you'd like to change the handling, and make the necessary modifications onto your custom frame.
I ride a 2010 Niner RIP9. In 2011 they have slackened most of the angles by 1 degree which is massive. Personally I don't think the 2010 geometry could be more dialled but clearly they think it needed changing.
I don't think you'll get a good answers to your question here or anywhere as its a matter of personal preference.
I would ride an On-one or something, decide what you don't like about it and adjust the geo to achieve your preference.

1075mm or less should give good manoeverability. for the record an 18 inch Inbred 26er is 1100mm, my Dean Ti 26er is 1040mm and it flick-flacks in and out of the trees beautifully

But this is the whole problem. Single measurements don't tell you anything - yes, check the wheelbase isn't silly long/short but don't base the whole thing on it. You could have a bike with short wheelbase that still handles like crap.

Thanks all, useful stuff. I currently get toe overlap on my 29er (I'm 5' 9" with mahoosive size 11 feet), but this design increases the top tube by approx 1cm and slackens the HA which may alleviate that.

I wish I knew how to work out the trail figure...I'll google it 🙂

Ok, I googled it, and according to [url= http://yojimg.net/bike/web_tools/trailcalc.php ]this[/url] site, with a 2.2 inch tyre, I'm looking at a trail of 83mm. I have no idea how to interpret that though!

The BB drop is something I'm still working out so I've estimated for now.

I've been riding a 29er exclusively for nearly a year now, and am currently on a 2nd (borrowed) 29er. It's the difference in the ride between the two that's got me thinking of designing my own ideal solution. I wish there were more opportunities to test 29ers...and sadly I can't make Charlie's beach party on the 25th!

Ignore wheelbase. It really doesn't tell you much. Knowing the front centre is useful. And knowing the chainstay length is useful.

cheers Ben. Front centre will indeed be useful from a toe overlap point of view as well.

just for comparison these are the swift dimensions:

http://www.singularcycles.com/swift.html

That's what I'd be basing it on but then I love my Swift. I'd probably keep it as is except shorten the head tube.

cheers guys, been riding a Pegasus for the past year or so 🙂

So what are the characteristics of that that you'd like to tweak?

as above really, slightly longer top tube, less twitchy steering...yes I know everyone else seems to love the Swift/Pegasus handling, but I don't find it very confidence-inspiring on steep techy downs in particular. It is possible that part of the issue is the Lefty I'm using...gonna look closely at that before making any final decision on figures.

It is possible that part of the issue is the Lefty I'm using...gonna look closely at that before making any final decision on figures

Slightly off topic, but on the lefty front the LBS here has started stocking Cannondales, and I'm seeing more lefty's about now. Saw a guy lent hard into a tight left hand turn in town - saw it front on and was really surprised to see how much his front wheel was out of line with the back one. Didn't look good.

Fork dive with the lefty when braking on steep stuff? As you say, I'd check that it isn't the fork. From my memory, when I had a headshok, it was quite noticeable that because it didn't bind when cornering in the way that a telescopic fork does, it actually dived more and made the bike feel quite squirrely (technical term!) in fast corners, particularly if bermed.

I don't think 70.5 sounds too slack, I had demo on a Scott Scale recently and that claims to have a 69.5 degree head angle and I thought it was fantastic, I found it very confidence inspiring!(not that I rode any steep techy downs) Might be worth seeing if you can find a demo one to have a play on...

Hi Ian, kind offer thanks, and one that I may well take you up on! Good excuse for a ride in some proper hills again too :-). Interesting on the Lefty thing...they're allegedly super stiff...I'm pretty sure mine was, though I haven't been riding with the best wheel builds and I know I've been getting some flex there so it's difficult to say for sure. Given the hassle & expense of the Lefty, I don't think it's worth it overall. The low weight is nice though of course. What I do know though is that I don't like the feeling I get where trail obstacles feel like they want to push the front wheel in & under the bike. Just doesn't feel right. I have a suspicion that bearing migration in my Lefty may have been causing an overly steep head angle...though I'm yet to confirm that.

clubber, yeah the Lefty is definitely prone to fork dive. Putting a spacer in the air chamber to correct for the reduced 29er travel helped enormously with that, as did a bit more pressure in the chamber. It's still more prevalent than on something like a F29 though.

sound like sensible numbers to me.. the front-centre and CS length should be nicely balanced and the tt / SA seem right with that, middling-ok.

that HA will give a relatively long trail but if you account for an 80mm stem and a less-than-xc narrow bar i expect it'd feel good. it won't be twitchy, but it shouldn't be floppy - i get 83mm trail there - a 50mm rake fork would give you 78mm.

a sagged 80mm fox will be less than 470mm though, so there may be a difference handling between the 2 forks. depends how you set them up. an 80mm 29er sus fork has an a-c of about 480-485mm so you're accounting for not-alot-of-sag.

i'd be tempted to go for a 460mm fork if you were getting the fork made and will only use 80mm sus forks. shorter rigid forks are better rigid forks.

thanks James, useful info, good point on the sag

shorter rigid forks are better rigid forks.

in what ways better? 🙂

Slightly off topic, but on the lefty front the LBS here has started stocking Cannondales, and I'm seeing more lefty's about now. Saw a guy lent hard into a tight left hand turn in town - saw it front on and was really surprised to see how much his front wheel was out of line with the back one. Didn't look good.

front wheel will always track different to the back when cornering - might just 'look' worse on a lefty as it looks odd to start with visually..

I rode one and thought it was very good.

almost every way, if designed well ) long rigid forks are not a mechanically sound idea.

leftys - one large tube will be stiffer than 2 slimmer ones for a fixed amount of material..

i've ridden a lefty and as odd as it looks, it's a pretty stiff fork. way beyond the other forks at the time (ie pre 20mm axles and taper steerers)

Singular Pegasus is a great bike. That is all.

a long rigid fork will give more flex though and take out vibrations better for a given tube. (maybe?)

i guess if the tube is as thin as possible it needs to be thicker when longer and my point is void.

I rode one and thought it was very good.

Good excuse for a ride in some proper hills again too

I can certainly take you up a few around here

have some pity for the chap from the flatlands though, ok? 😉

So what was the outcome of this?? what geo did you settle on pedalhead?

ah this is the thread 🙂 Have emailed you already but will send over the geometry details.

ta 😀

http://www.spanner.org.uk/2011/12/gallery-v2-adrians-second-radical-e-stay-titanium-29er-by-xacd/

Just had this made rides very well indeed similar geometry to yours I think

Pedalhead I see you are in Oxford , I am in Thame if you fancy a ride on my bike et me know

Very kind Ade cheers. I'm often riding on the road through that neck of the woods. Hopefully the Ti frame issue will soon be resolved, but frankly I'd be fascinated to try yours out anyway!

Surely one of the big advantages of 29ers is that it's a lot less likely that you will go over the bars compared to a 26in bike .
So many more factors affect the ride than just the angles . The big firms have had many years to get geometry sorted so you would be better off just buying off the shelf from one of them IMO .

Surely one of the big advantages of 29ers is that it's a lot less likely that you will go over the bars compared to a 26in bike .
So many more factors affect the ride than just the angles . The big firms have had many years to get geometry sorted so you would be better off just buying off the shelf from one of them IMO .

Depends what you want the bike for. Big firms make bikes for certain purposes and things that will fit most people. They don't cater for every end use. Many 'big firms' have also only just started making 29ers too.

Well Trek incorporate Gary Fisher who started the whole thing over 10 years ago so they , like most of the American firms , have been doing it for plenty enough time to get gometries really dialled , that's partly why the sudden explosion this year .
Also I'm sure they tried hundreds of designs that didn't work as well as they hoped they would . So the chances of the man in his shed knocking something up first time that's better is pretty remote .

So the chances of the man in his shed knocking something up first time that's better is pretty remote .

Just as good a chance as a design by comittee for the masses I reckon.

Probably correct but the comittee could afford to try and fail hundreds of times if necessary .

well having ridden a Gary Fisher 29er for a few weeks, amongst others, I still decided it wasn't what I was looking for, nor ideally suited to a specific task in mind. Great if an off the peg bike ticks your boxes, none do for me (that I have found / ridden), hence I have a custom frame coming along shortly.

Gary Fisher was an early adopter but he wasn't the first...

Back in '98 I happened to be passing through CB and stumbled into [url= http://www.willitsbikes.com/Willits.html ]this guys shop[/url]

He was expounding the joys of the 29er at that point.

There is some interesting stuff on his site IMHO inc a nice little video...

Edit: glad to see the price of his frames have come down since then 😀

I would ride as much as i could. Even if it meant hanging around for another year to do this.. it would be worth it. The costly mistake first time around might be fine if you can afford it but still a bit of a ball ache.

If you ride stuff and find a few that you cant really fault then why not copy it to a point but alter the finer details to make it perfect for you?

This is what i would do. I like the swift and having never thought about doing stuff to it i would like to try a slightly slacker headtube on it,maybe slap a pressfit bb in there and a tapered headtube. Sam would probably have a fit lol.. but thats just something random off the top of my head. I would also lower bottle cage bolts as far down the downtube as possible.Maybe fit an ugly (but functional) set of dropouts on it with a bit of adjustment.. not sure what else but i certainly wouldnt go playing around if i couldnt afford the mistakes.. and dont think that whatever you ask for is going to be built exactly like you asked for. Some frame company boffs will easily tell you the truth if you ask them nicely. Theres been some right old F-ups that have been very costly to some over the past year.A shame,but they would have put their trust in a name they thought were building great stuff.. only to find out the truth.

As for going to the local frame builder down the road.. theres someone on here (i wont say who) that got a frame built around 1995 out of a nice selection of tubes but once built.. the top caps of his judys caught the downtube. Not his fault but a pain in the ass all the same.

Theres so many other little details that you have to dodge before it turns into a great bike. To get something better than your fav bike first time around you will need a fair bit of luck (and a good builder) on your side.

Some frame company boffs will easily tell you the truth if you ask them nicely. Theres been some right old F-ups that have been very costly to some over the past year.A shame,but they would have put their trust in a name they thought were building great stuff.. only to find out the truth

My fave bike was a dbr the judy top caps also hit the down tube oh that was around 95-96 the handlebars also hit the toptube

Ramsey Neil - there are a number of geo tweaks that have only just started to come to market. In no way have the big manufacturers got things fully sorted.

e.g. The easy route to keeping the wheelbase sensible was steep head angle and long rear end. This conveniently suited the available short rake / offset suspension forks (made using existing 26er crowns). Long rear ends are also easy to build with no tyre clearance issues, front mech compatability problems etc. All great - yes? Errr - no, not for everyone. I hated the 29ers I tried with this format.

Slacker head angles and more fork rake can sometimes work better (e.g. I like 70 deg and 55mm) but there are no aftermarket or even general OEM suspension forks (only the Trek / Fisher specific forks have extra offset). So straight away that limits things (I went rigid only with my build).

And to counteract the slacker front, people have started to twig that a shorter rear end can be good. But that creates lots of problems (mud clearance, chainring clearance, front mech gets in the way, seat tube gets in the way etc). So straight away a frame might be single ring specific. Or it needs a forward offest and severely slackened seat tube to clear the wheel so limits the range of saddle adjustment. Therefore it is a brave mass market manufacturer that goes that route. You might note that current Treks have long rear ends and hence front and rear wheels that reside in different timezones 🙂 Hardly cutting edge........

Only now are we starting to see production frames that combine slack front / short rear (Kona Honzo, Canfield Nimble 9 / Yelli Screamy, Singular proto).

So going custom does still have a purpose - for my specific application, I think I got it right first time (and that was designed and built myself by hand from lumps of steel and brass). I can also get away with a design and tubing that suits my 64kg mass, as it does not have to pass EN fatigue tests based on a +100kg rider 🙂

And I could be wrong, but I seem to remember jameso has a bit of experience in the industry..........

I hope it all works out well and that we get to see the end product .

Here's the final result 🙂

[img] [/img]

[img] [/img]

Just built it up last night. Frustratingly, I won't get a chance to ride it today so I'll find out on Monday if the work & waiting was worth it.

(I know, the field is a mess)

Nice looking. Light too i'll bet. What seatpost please?

cheers yep it's about 20 lbs with alloy bars, M4 braided brakes and medium weight wheels. Post is an Eriksen"sweetpost" which has the best clamp around imho.

Thanks Pedalhead - will have alook at those as am keen to run a Ti post in my Pegasus - need a 430mm though.

have a chat with Kent, I'm sure he can sort something out. This post matched my previous Pegasus very nicely 8)