[Closed] Why doesn't chainstay length change with frame size.

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.

[i]Probably should change the wheel sizes too to match the size of the frame. [/i]

Again, Liteville do this.

[edit]

[i]no real reason to increase the rear end - better to keep it as compact as possible. [/i]

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).

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... 😉

[url= https://www.cotic.co.uk/product/soul26#sizing ]Cotic Soul Geometry[/url]

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.

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

Or at least this year's version of "right" 😉

I went from a ti456 to a Stanton slackline, so going towards shorter chainstays, and find climbing easier. the ability to unweight the front with minimal effect means i can keep the bike moving up hill over obstacles much better than before. i do ride with a 70mm stem and 750mm bars. I'm 6,3.

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

You're talking about CoG.

Weight distribution is the location of mass (the rider) between the wheelbase.

I'm not sure I'm any clearer on the original question, but the debate on whether short chainstays are a good thing or just this year's fad is fascinating, with some strongly held views on both sides.

It seems to me that there is a trade-off between stability and playfulness (for want of a better word). For those of us who lack skill it is tempting to pick a playful bike for extra grins. However, with skill you should be able to move any bike around at will, but you'll never make an unstable bike more stable.

Weight distribution is the location of mass (the rider) between the wheelbase.

Well, yes, which is a function of where the CoG is in relation to the wheels.

The CoG is irrelevant regarding front/rear weight distribution. All the matters is the BB location relative to wheelbase.

The CoG is irrelevant regarding front/rear weight distribution. All the matters is the BB location relative to wheelbase.

Yep then the distribution changes (even more rearward). Who cares about climbing though? Only a problem with short rear centres...

You wouldn't put longer forks on on a size large frame than you would on a medium frame would you.

No, but i used to wonder (in the days of coils forks) why companies didn't spec forks with firmer springs in L or XL bikes. Stands to reason a taller chap will be heavier.

As for longer stays on bigger bikes? None of my bikes are (afaik) and although it might only be a minor increase, it makes sense. Next up is slightly wider diameter bars/grips for our bigger hands and longer pedals for our giant feet.

The CoG is irrelevant regarding front/rear weight distribution. All the matters is the BB location relative to wheelbase.

Take a bike. Hang your arse over the back. Now instead lean forwards over the front wheel. The BB is in the same place in both cases, but your CoG is very different and so the weight distribution is very different. Which is why you do those actions depending on the terrain.

Some companies do, some don't. We do change the length of the CS on our hardtails, but on the FS we dont as its long enough already, adding more length for the sake of it doesnt really get us much. We also spec wider bars, longer cranks, and bigger seatposts on the bigger bikes too. One thing I never did get though is the speccing longer stems on bigger bikes. How exactly does that help anyone?

The CoG is irrelevant regarding front/rear weight distribution. All the matters is the BB location relative to wheelbase.

What?

So leaning forwards or back does nothing to alter your weight distribution on the bike?

Do you want to re-think that statement?

How do you ride hanging off the back or with your head in front if the bars?

How does that help with front/rear cornering grip bias?

How do you ride hanging off the back or with your head in front if the bars?

How does that help with front/rear cornering grip bias?

Because if you lean forwards you push down on the bars and if you lean back you pull on them?

And that does next to nothing to increase front wheel grip. You think you're putting weight through the bars but in reality it's next to nothing as a percentage of total weight.

I've been riding hardtails with sub 400mm stays for well over 15 years. For sure it takes a little more input climbing super steep trails but it's never actually been a problem. Neither is keeping the front wheel on the ground.
But then, I rode a BMX and never looped out riding vert ramps either.

This stayed with me.

Brant and Chris aren't really qualified to comment on how to ride short stay bikes

And that does next to nothing to increase front wheel grip. You think you're putting weight through the bars but in reality it's next to nothing as a percentage of total weight.

Go out and try cornering on a loose surface with your weight right back, don't forget to film it!

Then try it normaly with your pelvis above the top tube.

JCL - Member
And that does next to nothing to increase front wheel grip. You think you're putting weight through the bars but in reality it's next to nothing as a percentage of total weight.
POSTED 10 HOURS AGO # REPORT-POST

It's not about "pushing on the bars", it's moving your COG forward by supporting more of your weight on your arms.

Some 'interesting' statements appearing on here today about body positioning.
Those DH riders moving themselves around on the bike eh, don't they know it doesn't do anything?!

STW does make me smile sometimes.

I thought anybody who had been riding for more than 5 mins knew that body position is a huge influence on what the bike is doing.

This thread confirms what I've long suspected, STW is full of clueless trail centre warriors that ride their long travel full sussers sat on them like a sack of spuds hoping the bike will do all the work for them.

(runs for cover)....

I was looking at a couple of recent tests of 29ers in magazines:

ST reviewed a Kona Process 111 alongside an Orange Segment and a Pyga 110

MBR reviewed a T129 SCR alongside the Segment and Camber Evo

So, both reviews included a bike with short (for a 29er) 430mm stays and others with "much" longer stays (450mm for the Segment and Camber). In neither review was the short chainstay bike a clear winner. ST didn't really declare a winner, but seemed to like the PYGA best and MBR went with the Camber (with its 450mm stays).

Obviously there is more to a good bike than any one measurement, but it doesn't look as though short chainstays are crucial.

I bet that if you had two identical bikes, absolutely the same apart from the CS length, you wouldn't be able to detect a 20mm difference in CS length when riding.

Obviously there is more to a good bike than any one measurement, but it doesn't look as though short chainstays are crucial.

Of course not, but they play a part just like every other variable. When I was looking at the Camber Evo I noted it had relatively long chainstays, which was obviously part of the overall geo for that particular bike. Spesh are certainly not stupid and have the experience and resources to test such variables. If you look at their range some of their bikes have fairly long chainstays and some very short. There isn't a right answer for all, just depends what trade-offs you make.

I bet that if you had two identical bikes, absolutely the same apart from the CS length, you wouldn't be able to detect a 20mm difference in CS length when riding.

Why do you say that? Have you tried it or just guessing it makes little difference? I wouldn't know personally, but bike manufacturers sometimes go to a lot of trouble to shorten stays on certain bikes by that sort of amount. Would they bother if it made little difference?

I bet that if you had two identical bikes, absolutely the same apart from the CS length, you wouldn't be able to detect a 20mm difference in CS length when riding.

I'd have to call you out on that, as having ridden one of my protos with sliding dropouts, I could probably call "differences" to 5mm at the chainstay.

It's a 3:1 ration of chainstay to seat position, meaning that moving wheel position 5mm is same as moving saddle position 15mm (seated climbing).

However - that's for the wheelietastic climbing stuff. Descending might be less sensitive.

bike manufacturers sometimes go to a lot of trouble to shorten stays on certain bikes

One criticism of the Whyte in the MBR review was that they were perhaps trying too hard to make the chainstays as short as possible and adding 5mm would make getting the wheel in and out easier and reduce build up of mud.

It's a 3:1 ration of chainstay to seat position, meaning that moving wheel position 5mm is same as moving saddle position 15mm (seated climbing).

However - that's for the wheelietastic climbing stuff. Descending might be less sensitive.

It would be interesting if that were the case. Generally shorter chainstays are sold as improving handling going down with the price being paid on the way up. If the negative effect increases more rapidly than the positive one then it doesn't sound so good.

ps. Why is it almost impossible to type ratio without instinctively adding an n on the end?

Generally shorter chainstays are sold as improving handling going down with the price being paid on the way up

I don't think that's how it's pitched at all.

I bet that if you had two identical bikes, absolutely the same apart from the CS length, you wouldn't be able to detect a 20mm difference in CS length when riding.

That would really surprise me. I can feel the chainstay length increasing as the suspension squats when I manual my full-sus and it certainly doesn't change by 20mm!

Generally shorter chainstays are sold as improving handling going down with the price being paid on the way up.

I thought they were sold as improving the manouevrability of a long front-centre bike at the expense of high speed stability (and ease of balancing two wheel drifts)?

Why do you say that? Have you tried it or just guessing it makes little difference? I wouldn't know personally, but bike manufacturers sometimes go to a lot of trouble to shorten stays on certain bikes by that sort of amount. Would they bother if it made little difference?

It makes a huge difference, to the marketing. How many people bashed the Segment when it was announced, depsite absolutley no one outside the Orange workforce having ridden it?

It's a 3:1 ration of chainstay to seat position, meaning that moving wheel position 5mm is same as moving saddle position 15mm (seated climbing).

Can you explain this? You've said it before but I still don't understand it, surely if the CS is 5mm shorter the saddle is 5mm further over the back wheel? Or is it related to the ~1:3 ratio between CS length and the front center measurement so you have to move the saddle 3x further to have the same effect on the two as a ratio compared to just shortening the back by the same ammount?

Generally shorter chainstays are sold as improving handling going down with the price being paid on the way up.

I always thought it was more about quicker handling v stability and ease of getting the front wheel off the ground. That could mean a price to pay on climbs, but then I've seen reviews and comments saying that tech climbing can actually be easier as you can get the front wheel over obstacles. My last bike had fairly short chainstays and was a good tech climber and plenty stable enough on the downhills. New bike has short stays too, but seems to climb well and is super stable on the downs.

So I guess chain stay length alone does not define a bike. But still a key variable I would say.

It makes a huge difference, to the marketing.

I don't think short chain stays are marketing led. Marketing may well pick up on it as a trendy feature, but I bet it wasn't their idea in the first place. I think a lot of the current talk about chain stay length is due to 29ers and the inherent difficulty in achieving a short enough chain stay to make them handle quicker. I don't remember chain stay length ever being an issue on 26" wheeled bikes.

I don't think short chain stays are marketing led. Marketing may well pick up on it as a trendy feature, but I bet it wasn't their idea in the first place. I think a lot of the current talk about chain stay length is due to 29ers and the inherent difficulty in achieving a short enough chain stay to make them handle quicker. I don't remember chain stay length ever being an issue on 26" wheeled bikes.

It was, but maybe not to the same extent. As you said, 29ers made it harder, but plenty of bikes seem to change for the sake of it, my El-Mariachi handles fine, with loads of clerance so they obviously settled on that gerometry, but they still lobbed 20mm of the stays this year. I can't help but thing that was a marketing thing.

A bit like 51mm forks, I've got some 46mm offset forks, which make the bike feel really stable, people who've ridden slacker (i.e. 68deg rather than 70deg) frames with 51mm offset forks (which results in a similarly slack 'feel' on a 29er) say they 'flop' much more when you try and turn tighter than the bike want's to go. To me that sounds like marketing said "we want 26er comparable head angles to sell the 29ers", and the designers comprimised with 51mm forks.

I may be wrong, I don't own enough frames and forks to do loads of meaningfull back to back testing, just anecdotaly my bike doesn't 'flop', thiers do, and both have similar ammounts of trail (steep angel, less offset, vs slack angle, more offset).

I bet that if you had two identical bikes, absolutely the same apart from the CS length, you wouldn't be able to detect a 20mm difference in CS length when riding.

Disagree!

I have done this test.

Can you explain this? You've said it before but I still don't understand it, surely if the CS is 5mm shorter the saddle is 5mm further over the back wheel? Or is it related to the ~1:3 ratio between CS length and the front center measurement so you have to move the saddle 3x further to have the same effect on the two as a ratio compared to just shortening the back by the same ammount?

I played with wheel position on a sliding (On-One Slot) dropout, and found that similar climbing traits could be got by either moving the rear wheel 4mm backward, or moving the saddle 12mm forward.

Or thereabouts.

The distance from the ground contact patch to the wheel centre was roughly 1/3rd of the distance from the ground to top of saddle, and seeing as I decided that climbing ability was dependant on weight distribution relative to the contact patch, I figured this might be important.

Hence the 3:1 comment.

It might be as inaccurate as stuff I've seen about inside leg compared to BB centre to bar tip measurements.

But seemed to make some degree of sense at the time. But I might have been drinking.

I'm not a fan of "super short stays" and generally tend not to artificially lie about stay length by quoting "horizontal effective stay" dimensions on bikes I design.

It's like measuring your cock from your bellybutton or something.

(Where should I measure it from?)

at the expense of high speed stability

There's a fairly big hill a few miles from my house and i've been down it on many a bike over the years. From BMX's to crap racers (with even crapper brakes) to early 90's mtbs (sometimes off my bonnet on shrooms with no lights 😈 ) and more modern bikes.

Earlier this year i used el stravos to record my speed on my 150mm, supertackied up FS bike and got to almost 55mph just by freewheeling over the top of the hill. I don't think i'd have been that much slower on the old Claud Butler or the bmx. As usual, my eyes watered like crazy but the bike still felt stable.

So, what speeds are we talking about here and has anyone ever complained that their bike actually felt unstable the faster they went?

I'm not a fan of "super short stays" and generally tend not to artificially lie about stay length by quoting "horizontal effective stay" dimensions on bikes I design.

I don't think "horizontal effective stay" is an artificial lie, I think it's a much more useful measurement for chainstay length then actual stay length. Just like top tube length is silly compared to effective top tube. The greater the BB drop, the shorter the chainstays will feel for an actual chainstay length.

So, what speeds are we talking about here and has anyone ever complained that their bike actually felt unstable the faster they went?

We're talking about off-road!

We're talking about off-road!

You mean like a hill?

The greater the BB drop, the shorter the chainstays will feel for an actual chainstay length.

Aye. But on 29er where the artificial lie is generally told, the drop is greater, so the difference between "proper" CS length and "made up" CS length is greater.

You mean like a hill?

If you can hit 55mph down a rough downhill trail on a BMX and it feel comfortable then I don't know why you're wasting time on here and not using your incredible talent to compete at the highest level of sport?!

If you can hit 55mph down a rough downhill trail

I never said it was a rough downhill trail. In fact i don't believe 'rough downhill trail' was mentioned in this thread, until you - just there. I'm not getting 'at' you in particular, you just happened to use the phrase i wanted to quote.

People talk about the length of chain stays and how they affect stability at speed. All I want to know how fast you have to go to notice this instability. Only cause i've not noticed it myself at various speeds on different terrain on v short/short/ medium length chainstays. I don't think how bumpy the ground is is relevant.

If you can hit 55mph down a rough downhill trail on a BMX and it feel comfortable then I don't know why you're wasting time on here and not using your incredible talent to compete at the highest level of sport?!

It doesn't take skill to do that, just stupidity. 😀 I like to think that if i'd started mtb when i retired the bmx i could have been pretty useful. Instead i spent 12 years riding motorbikes and getting old, lazy and afraid.