I’m ‘averaged’ size so im fortunate enough that bikes fit pretty well, but i’ve noticed people on small/large bikes are never sat in the same place. So why not just put the bike on the photocopier, hit enlarge 20%, then pick the wheel size/fork length etc that fits? Don’t the chainstays etc. need to be longer on a bigger bike to keep everything in proportion or is it more complicated??

Brant mentioned this the other day. Can’t remember exactly but something to do with maintaining the right weight distribution.

Hell, I’m drnuk so could be talking total bollax…

I suppose because wheels/forks only come in a very limited range of sizes.

I’d like to try a bike with dead long stays, as the back of my saddle is always above the rear axle. Don’t know how it would make the bike handle though

I guess frame designers know what they are doing…although it would be nice to know why

the vast majority of people see long chainstays as a “bad” thing. And infact, for STOOD climbing, they kind of are. It’s nice to keep short there.

If you look at hillclimbing motorcycles, they have dead long chainstays. But we have to go down as well as up.

Fast down, long stays are stable. Woodsy down and they’re not – you want something nippy and so you can get your front end up.

What I did on the new Ragley’s is to steepen the seat angle on the larger bikes, so that the rider is sat further forward on the front wheel.

I tend to recommend 29ers for very tall riders, as this gives the “scale up” you’re looking for – the bigger wheels have longer stays etc…

See Ton’s Chumba for a perfect example of an in-scale larger bike.

I dunno if I’d have noticed it was a 29er, it just looks like a normal bike.

Nice.

Interesting thoughts…

I’d always ignored 29ers as a freak show, but the Santa Cruz Tallboy caught my eye. At 6’3″ the whole scale up thing makes sense – I’ve always struggled to get the best saddle position and balance between weight to far back / forward etc.

don’t many hardtails have steeper seat angles and slacker head angles on larger sizes?

http://www.singletrackworld.com/forum/topic/chainstay-length

Thread on chainstay length for lanky people.

To be honest I think the main reason that manufacturers don’t scale swingarms is that they can get away with leaving them all the same size.

don’t many hardtails have steeper seat angles and slacker head angles on larger sizes?

It’s usually completely the opposite on road bikes.

I quick look around (trying to get kids to bed) didn’t show anything.

Perhaps I’ve got it all wrong, but it works for us.

Do bigger riders also get scaled up singletrack?

Do bigger riders also get scaled up singletrack?

Nope – same size as every other magazine piled next to the throne.

the desired effect is different on road bikes I guess.

I remember many mtb companies usin steeper seat angles and slacker head angles. On frames even in the 80s.

so should shorter riders say 5ft ish be on 24 inch wheels?

I remember many mtb companies usin steeper seat angles and slacker head angles. On frames even in the 80s.

I don’t, but maybe I took more drugs/drank more.

so should shorter riders say 5ft ish be on 24 inch wheels?

Why not?

Why not?

Economies of scale i’d imagine.

😆

I agree in essence. It was the reason I only do 29″ wheeled bikes down to a medium. The 26″ Hummingbirds were originally only intended to come in small and medium. It was only people pestering me that made me end up with a large as well – mostly to cater to people with big investments in tyres and the like.

I think a well designed frame will have subtle changes to things like chainstay length, bottom bracket drop, seat and head angle to accomodate the likely body shape of different size people. However in this age of mass production there are really only three relatively mainstream wheel sizes (29, 26, 24 – I won’t count 650B just yet) plus there are further restrictions in commonly available tubing lengths. And of course manufacturers can get more production efficiency (and thus cheaper bikes to a demanding public) the more standardised frame production is. Then you’ve also got the matter that components are designed to work within fairly narrow parameters. Ever tried to get a modern derailleur system working well on a tiny 650c wheeled bike? At the other end of the spectrum, you don’t need to be *that* tall to not want to chop any length of your suspension fork’s steerer at all.

What I did on the new Ragley’s is to steepen the seat angle on the larger bikes, so that the rider is sat further forward on the front wheel.

I guess it depends what you are try to achieve – I suppose the Ragley is more a ‘chuck it around’ kind of thing? For those of us who spend a bit more time with their wheels on the ground and arse in the saddle bigger frames usually get a bit slacker as they have relatively longer femurs. So you need to be a bit further back to maintain pedalling efficiency in having the COG over the pedals.

I guess in a perfect world we’d all have custom designed bikes for our own particular morphology, riding style and preferences. However while price is a factor (for most people) and standardised parts is a factor for everyone we will have to make do to work the best we can within what we have available to us.

Sam
Singular Cycles

With mountain bikes it depends where the handling/comfort compromise is. As Sam alluded to, slacker seat angles are good for taller guys because of their physiology, but I’d say that’s only really useful to road bikes in my opinion. I got CycleFit’d last year to try and cure a knee problem, and I learnt a lot, and at 6ft 3in with 36.5″ inseam they recommended some insanely slack seat angle like 71deg. It was comfy seated, no doubt, but when I laid it out on a Soul I’d have had to have lengthened the chainstays about 35mm to get the weight distribution even vaguely sensible. Everything else they did with cleats and saddle height and footbeds worked a treat, but on a mountain bike it’s a much more dynamic thing with you in and out of the saddle all the time, plus weight distribution has a really serious effect on handling and therefore has to be managed more carefully.

As a tall rider, my experience is that most frames having the same length chainstays across the sizes and typically the same or similar seat angle which results in me sitting with my weight too far to the back which in turn makes steep climbs a bit of a chore with the front getting very light. I find it noticeable that on full sussers (even locked out) which seem to typically have longer chainstays, I find climbing much easier and my experiences on sliding dropout hardtails with them adjusted long is similar.

If I was speccing a custom frame, I’d go for either adjustable or longer chainstays every time.

(29ers would probably be good in this respect but I just don’t really enjoy riding them as much as 26″ bikes – they always feel a bit ponderous to me)

For those of us who spend a bit more time with their wheels on the ground and arse in the saddle bigger frames usually get a bit slacker as they have relatively longer femurs. So you need to be a bit further back to maintain pedalling efficiency in having the COG over the pedals.

And indeed Sam, SINGLESPEEDS can (and should) have different geometry. Slacker seat angles for more low-rev power, and you don’t need to pay much attention to seated steep-climb problems as a singlespeeder will be out of the saddle.

My new SS frame has an effective 71deg seat angle.

drink and drugs? Wow. Kerrrazzzy!

Makes sense, but then most hardtails have the chainstays “slammed” to borrow and slightly adulterate the term from BMX.

i.e. With the absolute minimum length neccecary for clearance. So in fact its probably better to think the other way arround, a 18/19″ frame has the ideal chainsty length, but anything smaller should be shorter?

Dont commencal do something with the back end on larger sizes? Or is that just the leverage on the shock that gives it more travel?

clubber – at 6’4″ I saw the light when I finally went for a 29er.

Initially I chose a large size (21″) but have no settled for a mor emodest 19.5″ frame size. I cant say I consider 29er ponderous, and the benefits of having a frame more in proportion to my body size and layout really ads so much to the enjoyment of riding. Climbing in the saddle on a 20″ inbred became a real pain as my arse was pretty much directly above the rear axle.

I’m 6’5″ and have tried several 29ers and just don’t enjoy riding them (though I don’t dispute some of the benefits but since I don’t really race, ultimate pace isn’t the essential measure) as much as 26″ bikes – every single one has felt just that bit more cumbersome than I like and I constantly wished I was on a 26″ bike…

each to their own though…

I believe like others that the rear triangles are kept generic to decrease costs by leveraging mass production. Someone made an interesting comment on another forum about the size of the designer/testers playing a notable role: Some frame makers have large designers and others have small, and the frame will be ideally tuned for that tester’s size.

The CAD models have to be first made in one size, and then I imagine the sizeable parts are scaled, ie the front triangle. Anything else done after that probable varies, but I wasn’t aware that some manufactures tweak angles based on frame size as someone claimed. I bet lots don’t.

I’m not sure if my leg to torso lengths are non typical, but at 6’3″ I always seem to have my seat notably higher than my stem/stack, while many other people’s bike shots don’t. I do like full extension on my legs though, so it could be pedalling style as well.