Forum menu
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.
Surely this isn't true when seated?
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.
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
Interesting - so bikes with sliding dropouts are making a difference you can notice? Do eccentrics make the same difference?
And, with all due respect, that wasn't a double blind trial - you could have been imagining it 😉
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.
And that is why you should never trust strava. Last time I got to 50mph on an MTB I was draughting a transit van about 6 inches from its back door... on a road, on a bloody big hill. Downhill world cup racer rarely breach 40mph. Hell even TDF riders seldom beat 60.
Interesting - so bikes with sliding dropouts are making a difference you can notice? Do eccentrics make the same difference?
My fatbike has rockers which go from 440mm down to 423mm actual CS length. I'm with Brant on this one, the difference between 435mm and 425mm is quite noticeable. I wouldn't consider myself particularly observant either.
In saying that though, I went custom because I was fixated on the CS effect when going downhill standing. Brant's fixation seems to be more about the CS length affecting seated climbing though.
One size really doesn't fit all. 🙂 427.5mm is the sweet spot BTW
Hmm, I wonder if the sweet spot is seat angle dependent. For instance, does altering an eccentric BB have the same effect?
Hmm, I wonder if the sweet spot is seat angle dependent. For instance, does altering an eccentric BB have the same effect?
I'll let you know in a few weeks 😉
brant - Member
After I followed Ton up the Jack Bridge climb past mmmbop to the Nudie
Ha ha! No personal reflection on ton - but Brant using him as a biking biomechanical model for bike design is very amusing indeed
And that is why you should never trust strava.
I don't think i do. I only ever used it the once, but i do know one thing, it's feels a lot steeper in real life than depicted by the wavy green line of lies in the diagram shown below. How's that for a bloody big hill? 😀
[img] 
[/img]
I reckon if you knew what you were doing you could top a real and bonafide 60 down that.
In saying that though, I went custom because I was fixated on the CS effect when going downhill standing. Brant's fixation seems to be more about the CS length affecting seated climbing though.
read this post with hope of being educated - i reckon understand the climbing contact/front end lift stuff ok especially as rarely stand to climb but don't get the downhill bit as would expect to be standing and can't really see how chainstay length impacts COG very much in this situation? or point me to answer above if its there somewhere
It's not about "pushing on the bars", it's moving your COG forward by supporting more of your weight on your arms.
There is no way you can effectively alter your mass location forward to compensate for a typical short rear centre/long front centre trail/AM bikes. Well, you possibly could but you would be in such a precarious riding position that you would eat shit often. If a bike requires you to move out a neutral position to give consistent front/rear cornering bias it's a dated, flawed, pile of crap.
What's more amazing to me is that people are advocating for bikes that ride just like that. The marketeers have done a great job. Most people have an idea what head angle or BB height they prefer for a certain bike but ask them about rear centre length and they usually say "duh as short as possible" Regardless of size! Personally I want bikes that allow me to drop the post, remain in a really similar neutral position, and predictably two wheel drift around a 30kph loose, flat corner. I'm no Sam Hill so I want all the predictable, stable, help I can get.
To whoever said you can't tell a 20mm rear centre difference? I reckon I could tell as easy as 20mm BB height. It's a massive, massive, difference.
And to the chap who said that DH riders move around the bike etc. No they don't, not these days.
I reckon 430mm at sag point is borderline too short for modern, long wheelbase bikes. Maybe okay for small trail bikes I guess but anything less and you start having to do weird things (whether you realise you are or not) with the suspension and the F/R grip bias starts to suffer.
but don't get the downhill bit as would expect to be standing and can't really see how chainstay length impacts COG very much in this situation?
It's much easier to manual. I ride a rigid bike and it's important to be able to loft the front over stuff easily when bombing downhill. My needs are different to a full sus where I appreciate that you might want a neutral position and let the suspension track the ground.
I just find a short bike you can pop off every rock, drop and unduation in the trail makes me smile more than one which does a great job of flattening it all out. Simple as that really. It's never going to win a world cup DH 🙂