Why doesn't chainstay length change with frame size.

As you go up in size for a particular bike, seat tubes and top tubes get longer, but chainstays always seem to stay the same. Why is that? Is it just a cost issue?

Standing up on a bike, your weight is going down through the bottom bracket and the inputs from the trail are coming through the wheels. So, surely, in order to keep the feel of the bike the same in the different sizes, you’d want the ratio of front centre to rear centre to stay the same.

I think it’s often cost related.

Liteville change their rear triangle size based on frame size, for example.

I think norco do it too

would also mean less mud clearance on smaller frames

Ragley do as well. Makes sense.

The current obsession with ubershort chainstays does not.

I wouldn’t think it’d be a big cost issue – you need different seatstay lengths, keeping the same CS lengths would be an odd economy.

The current obsession with ubershort chainstays does not.

Why not? It makes sense for those of us that can’t manual for toffee 🙂

It should but as usual people fixate on single variables as defining a bike without understanding the overall interaction – eg 29ers are selling based on their short chainstays and some reviews are marking down bikes with ‘long’ chainstays. Bigger frames should have longer stays than smaller versions if you’re looking for similar handling.

I ride big frames and some with short stays have been horrible on any remotely steep climbs as they put the weight too far over the rear axle. Add in a slack seat tube or layback post (depending on frame design) and it can get a bit silly.

Probably should change the wheel sizes too to match the size of the frame.

A rear triangle that’s as small as possible is always preferable (just need to be able to fit whatever wheel size in). Top tubes and seat tubes have to increase proportionally with arm and leg length to get the correct reach and to avoid huge seat posts…. but no real reason to increase the rear end – better to keep it as compact as possible.

Probably should change the wheel sizes too to match the size of the frame.

Again, Liteville do this.

[edit]

no real reason to increase the rear end – better to keep it as compact as possible.

a longer seat tube at the same angle as a shorter one will move your weight rearwards and nearer the rear axle if the chainstays are the same length?

A rear triangle that’s as small as possible is always preferable

Absolutely always? Really? Why? I don’t think so given that it affects your weight distribution on the bike.

Some frames do alter the lengths, but it’s usualy only a few mm (ragley were only about 3mm?), and the seat angle has an impact, what your trying to avoid is a really tall person sitting on the saddle and being right over the wheel.

If you look at the O-O inbred, the front center doesn’t actualy change that much betwen the 16, 18 and 20″ frames. I think Brant said something at the time that he wanted the bikes to handle the same betweent he sizes. And also he made up the geometry tables to fit what people though they would ride like, not what he’d actualy designed because it would have been unfashionable.

Tall people have longer torsos which is where your COG is, so actualy they’re naturaly putting the weight a similar disctance between the BB and handlebars anyway.

A rear triangle that’s as small as possible is always preferable (just need to be able to fit whatever wheel size in).

Rubbish. 16.5″ was pretty much the default 26″ chainstay length, that’s still about an 1/2″ clerance behind the BB with a 29″ wheel.

Completely slammed chaisntays feel great on a jump bike, but rubbish on any actual trail. Otherwise we’d all be riding bikes like the original Ellsworth Specialist, which was a hoot to ride, but completely unstable with the shortest chainstays they could make and a 13″ BB it would manual if you looked at it funny.

I was wondering about this too. I guess cost could be a factor, especially for the larger manufacturers. But as the trend is definitely toward shorter stays, a lot of frames have the shortest stays possible for the wheel size, especially 29ers. Maybe the manufacturers still see an advantage of shorter stays even in the larger frame sizes. But I guess it’s more about rationalising the number of parts, especially on a full susser where the same rear end can be used right across the size range. I can’t imagine the bean counters being up for size specific rear ends.

EDIT
A rear triangle that’s as small as possible is always preferable ….for me

For everyone else – unlucky

Norco, Ghost, Liteville and a few others I’ve forgotten do have size specific chainstay lengths in their range. Generally it’s the same rear triangle, just mounted differently. There are plenty of bikes out there with adjustable geometry or swappable dropouts which allow you to shorten the effective chainstay length.

Personally I really like bikes with short stays (assuming of course they have room up front). I’ve not ridden anything yet where I thought the chainstays were too short or had anything other than a positive effect on handling. I have noticed that shorter stays will have a detrimental effect on a bikes climbing, especially out of the saddle, but nothing so extreme that it couldn’t be managed by correct body position.

I’ve got a Norco Sight and the stays are different dependent on frame size.

Seems to make sense to me.

Craggyjim – Member
Probably should change the wheel sizes too to match the size of the frame.

Absolutely. 29er wheels on an XS or even a Small frame are ridiculous. Similarly I’m 6’4″ and my XL, 26″ frame has me perched precariously way up in the sky, high above the wheels. As far as I can see it would make sense for 26″ on XS and Small frames, 650 on Medium and Large and 29 on XL and XXL.

Personally I really like bikes with short stays (assuming of course they have room up front). I’ve not ridden anything yet where I thought the chainstays were too short or had anything other than a positive effect on handling. I have noticed that shorter stays will have a detrimental effect on a bikes climbing, especially out of the saddle, but nothing so extreme that it couldn’t be managed by correct body position.

^^^ this the benefits far outweight the negatives
(got 2 hardtails with sliding dropouts and a nu skool enduro bike with realtively short CS)

im just glad I need a medium sized bike 🙂

Absolutely. 29er wheels on an XS or even a Small frame are ridiculous

Some manufacturers do spec smaller wheels on their smallest frames. Not all small frames are ridiculous with 29″ wheels either. Just depends if they have been designed around bigger wheels or not.

I seem to remember that one of the Kona designers said they didn’t want to do it with their newer bikes as they wanted to keep them riding the same across the size range and didn’t want tall people to have long rear ends that were hard to Manual, etc and short people to have short rear ends that were less stable at speed.

I know Norco do it but I’ve never tried them out.

As you go up in size for a particular bike, seat tubes and top tubes get longer, but chainstays always seem to stay the same. Why is that? Is it just a cost issue?

No need to increase chainstay length unless the wheelsize gets bigger. You wouldn’t put longer forks on on a size large frame than you would on a medium frame would you.

Paceman

No need to increase chainstay length unless the wheelsize gets bigger. You wouldn’t put longer forks on on a size large frame than you would on a medium frame would you.

Think about that for a second. Are you suggesting that a rider of 5ft nothing and 6ft 8 will both have correct weight distribution relative to the bb and rear axle? As frame size increases and seat tubes get longer the rider will be placed further back. Assuming the same seat angle, the bigger rider is considerably further back than the smaller rider, changing their weigh distribution, but they still have the same cs.

It would mean on a big enough (albeit giant) frame the rider would be seated above the rear axle.

If you’re right Jimjam then some well-respected frame designers have been getting it wrong for years… 😉

Cotic Soul Geometry

Or doing what they know people will actually buy (or as above, just making up the figures 😉 )

As frame size increases and seat tubes get longer the rider will be placed further back.

But as the rider gets bigger the top tube gets longer, moving the centre-of-gravity forwards. It pretty much balances out.

There are other factors of course, but it’s not as simple as larger frames needing longer chainstays.

I guess once you’re stood up the seat tube length is pretty much irrelevant.

As has been mentioned; It’s all to do with cost. In order to keep costs down, manufacturers generally design around some middle-ground, best-selling size. Then just add or subtract some seat-tube and top-tube for the big and small versions. That way they keep the number of moulds to a minimum, and prototype and r&d costs are less (in many cases, they don’t prototype the ends of the scale at all).

As has been mentioned; It’s all to do with cost. In order to keep costs down, manufacturers generally design around some middle-ground, best-selling size. Then just add or subtract some seat-tube and top-tube for the big and small versions.

How can you keep the same seat stay, chain stay and angle between the 2…. and increase the seat tube length. That would look silly + create a weak point in the longer seat tube. Surely you need a completely new rear end, especially if you want to keep the same Rear-Center length.

…so I doubt its about cost saving

I didn’t mean that they just extend some tubes like that.

Most carbon [road/hardtail] frames are not single mould construction. They are either tube-to-tube construction with internal lugs or bonded with overwrap at the junctions.

For most large bike companies, parts of the construction will, however, be more than just a single tube. It’s common to have the head-top-down tubes as a segment. BB-chainstays are often moulded together. Seat tube and seat stays are usually separate. But this varies.

Manufacturers want to strike a balance between as few moulds as possible, as variables as possible, and as few pieces to assemble as possible.

It all goes in circles though. What was once just an expected part of getting a bike that works for you is now being used by some manufacturers as something new that differentiates them. (Jamis with their new Renegade, for instance)

There should be at least a 10mm difference between sizes with 430mm being the default small on trail/AM bikes.

Wheelsize as nothing to do with weight distribution.

But as the rider gets bigger the top tube gets longer, moving the centre-of-gravity forwards. It pretty much balances out.

Sat down I don’t see how that works

In my experience as a tall rider I have found the longer chain stays of a FS a big advantage when climbing

When I tested a bike with shorter chainstays it felt brilliant stood up when I needed to get the front end up. But climbing was too compromised for me

Maybe the reason I’m happy that chain stay lengths are constant is that most bikes are all too short to start with. To get a nice reach with a short (45mm) stem I went for a large (tracer 2). But there is no way I should be a large, I’m 5’8 on a good day. But the bike feels perfect, nice reach with a compact rear end. The seat tube is longer than I need but fortunately this doesn’t make any difference as there is plenty of standover due to the design of the frame.

Maybe if I was taller I would want the bike to be proportionally bigger in all dimensions…. including chain stay and wheels.

Sat down I don’t see how that works

It works even less standing on the pedals as 99% of mass goes through the BB.

Maybe the reason I’m happy that chain stay lengths are constant is that most bikes are all too short to start with.

Nail on head.

Sat down I don’t see how that works

Because you get bigger. Compare your CofG with the wheel position, that’s what matters.

Chainstay length is one of those things where there’s no “right” answer even for the same frame size – I remember the days when we were using elevated chainstays and the like to get ultra-short back ends, then they got longer, then they got shorter again, then wheels got bigger which meant they had to get longer again.

It works even less standing on the pedals as 99% of mass goes through the BB.

Where you’re connected to the bike is not the same as where the centre-of-gravity is.

Where you’re connected to the bike is not the same as where the centre-of-gravity is.

Wrong.

Front-rear weight distribution is defined by BB location.

It’s defined by lots of factors, BB position is just one of those. Look at recumbents.

It’s defined by lots of factors, BB position is just one of those. Look at recumbents.

I think he’s talking about mountain bikes when you’re standing up (which to be honest is when handling matters).

And whilst I’m here, with most full-sus designs the back half of a bike stays the same regardless of size, as not only are the chainstays the same length but the pivots are in the same place, hence the rest of the rear triangle matches. Adjusting chainstay length with size makes sense to me! But I’m not a member of the shorter is always better camp as is currently fashionable… Middling tends to be best even if it doesn’t make for good marketing blurb…

Ragleys got proportional seat angles, steeper on larger models, after I followed Ton up the Jack Bridge climb past mmmbop to the Nudie. I saw how much he was over the rear axle and doing wheelies on his Summer Season.

On One 456 Evos got proportional chainstay lengths. I think it was just the largest size was a bit longer. Due to ratios and stuff only 3mm at the dropout was the same as moving the saddle 12mm.

There is no cost difference for a manufacturer to do this in steel or alloy.

In carbon you often need different back end molds anyway due to different internal rear triangle angles so again it’s really a no cost option.

The “shorter is better” noise keeps things as short as possible much of the time. Recently two things have happened which might change that tide.

Chris Porters article IS being read by people in the industry.
Jeff Jones did his 29+ bike with 490mm rear stays.

Those things, and some other things that are going on will probably swing chainstay length trends a little.

I had a 400mm chainstay sample long travel alloy hardtail about 15yrs ago. I couldn’t ride it up steep hills.
This has stayed with me.

Andy Armstrong had it last time I heard. Pink Planet X thing with round main tubes and a back end off our trials frames.
BB was quite high though. Hmm 😉

The “shorter is better” noise keeps things as short as possible much of the time. Recently two things have happened which might change that tide.

Chris Porters article IS being read by people in the industry.

Chris Porter brags about riding DH bikes as trail bikes years ago. He’s done little more than build an enduro bike with DH bike angles (with a few exceptions). I rode a Mondraker Summum last year on one of my local trails, a looong, low, slack bike if ever there was one. It had 450mm cs if I recall and a 62 degree ha. The bb was insanely low. It was totally flawless on big, rough terrain and ponderous on tight twisty stuff, as you would expect a dh bike to be. I wouldn’t want my 160mm bike to feel like that.

Quite a few companies are doing it right already, or very close.

Ragleys got proportional seat angles, steeper on larger models, after I followed Ton up the Jack Bridge climb past mmmbop to the Nudie. I saw how much he was over the rear axle and doing wheelies on his Summer Season.

Exactly my experience and backs up my point about ‘shorter is always better’ being wrong.