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CS length - what do you prefer for cornering?

Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
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For those that have tried similar bikes with different CS lengths, or preferably the same bike in various settings, which numerical setting do you prefer and why? I'll leave a template as a guide if you need ideas:

CS length:
Wheelbase: (preferably self-measured)
Rear traction: (poor/good/excellent)
Ease of initiating drift: (poor/good/excellent)
Ease of controlling/predicting drift behaviour: (poor/good/excellent)
Riding style/position: (rear-heavy/centered/front-heavy)

Some caveats:

- The longer setting (on a multi-setting bike) will result in more wheel travel and more sag, thus better feeling suspension unless you correct spring/damper rate - obviously the travel change remains but bump performance will be similar. Chances are not many do this, so I prefer if bump absorption is factored out of comparisons, as well as the obvious change in wheelbase.

- High pivot bikes have a huge amount of dynamic variance in CS length (thus rear wheel weighting, thus rear traction) so I'm not largely interested in anything with more than 15-20mm of CS extension. Before someone gets offended, it's not that these designs have no merit, it's just that I can't learn anything from subjective data when you have a 16" CS that could be anywhere between 16" and 19" depending on corner type and corner/other loading. Even 20mm blurs the results a bit but that should cover a decent selection of bikes.

- I have my own take on this but am curious to hear what others have experienced, will chime in after some replies.
 
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BigHitComp04

BigHitComp04

Monkey
Jun 20, 2005
586
3
Morgantown, WV
I'm interested to see what people have to say on this as well. Im coming from a Demo 8 (crazy short CS) to an Intense M9 this year (not built yet). It does have some adjustment when it comes to CS length so I'll be interested to play with that as well. I suppose I'm going to just start it in the middle and lengthen/shorten it when I have a feel for the frame.
 
ianjenn

ianjenn

Turbo Monkey
Sep 12, 2006
3,001
704
SLO
Okay here is some idea. Athough I havn't hit a GYM in a decade I still have pretty strong legs/hips so can manipulate a bicycle pretty easily by twisting lower torso.

I suck A*( at cornering so traction is paramount for me......

Rear traction: (excellent)
Ease of initiating drift: (good)
Ease of controlling/predicting drift behaviour: (good)
Riding style/position: (centered)
 
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gemini2k

gemini2k

Turbo Monkey
Jul 31, 2005
3,526
117
San Francisco
I think long CS require you to be a bit more conscious of your body position and cornering technique. Like Ian said, I find that with longer CS I have to really depend on my hips and core to turn as opposed to arms are shoulders, which you should be doing anyways. I find that playing around with HA and BB height makes a far bigger difference in how a bike turns though. In general I find that a bike with longer CS makes up for the turning sacrifices with the stability enhancements.

The biggest challenge I find with CS though is hitting drops. It sounds weird but I definitely notice that extra 1/2-1/4 of an inch when pulling up on the bars off a jump or drop. Makes it feel just ever so slightly unnatural and awkward. That could just be because I originally learned to hit big jumps and drops on a small hardtail though. If frank comes through, I'm trying to get a custom swingarm made for my bike that will reduce the CS from 17.75 to somewhere between 17.5 and 17.25. I might then have 2 identical (frames at least) DH bikes, one with a 17.75 swingarm and one with a shorter one. That will be interesting to compare at resorts.
 
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Jm_

Jm_

sled dog's bollocks
Jan 14, 2002
18,998
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We need more batsh*t crazy-long stays I say. Remember 18.5" of 2000? Hell yeah I say. And then there's 29ers, which area already more stable due to the gyroscopic motion of their wheels, so make them even more stable, more more stable I say, go 19", heck 20.
 
buckoW

buckoW

Turbo Monkey
Mar 1, 2007
3,787
4,733
Champery, Switzerland
Udi said:
For those that have tried similar bikes with different CS lengths, or preferably the same bike in various settings, which numerical setting do you prefer and why? I'll leave a template as a guide if you need ideas:

CS length:
Rear traction: (poor/good/excellent)
Ease of initiating drift: (poor/good/excellent)
Ease of controlling/predicting drift behaviour: (poor/good/excellent)
Riding style/position: (rear-heavy/centered/front-heavy)

Some caveats:

- The longer setting (on a multi-setting bike) will result in more wheel travel and more sag, thus better feeling suspension unless you correct spring/damper rate - obviously the travel change remains but bump performance will be similar. Chances are not many do this, so I prefer if bump absorption is factored out of comparisons, as well as the obvious change in wheelbase.

- High pivot bikes have a huge amount of dynamic variance in CS length (thus rear wheel weighting, thus rear traction) so I'm not largely interested in anything with more than 15-20mm of CS extension. Before someone gets offended, it's not that these designs have no merit, it's just that I can't learn anything from subjective data when you have a 16" CS that could be anywhere between 16" and 19" depending on corner type and corner/other loading. Even 20mm blurs the results a bit but that should cover a decent selection of bikes.

- I have my own take on this but am curious to hear what others have experienced, will chime in after some replies.
Click to expand...
Udi, try the short stays for now and put it in the long hole when you are flat out and needing a little more hook in flat fast corners. Traction is dependent on a lot more than CS length, IMO. Brendan runs the long hole in PMB and Leogang with a steeper HA by the way. It is another tool in the toolbox and should be used to dial in the bike for the track.
 
saruti

saruti

Turbo Monkey
Oct 29, 2006
1,169
73
Israel
had a Sunday for 5 years.
loved it
got a Turner DHR DW for a year.
the first thing I noticed was the longer CS. it was harder to corner and play with the bike...
after cracking the frame in Morzine this year, I got me a Sunday again.
wow. I really love the feel of the bike in corners.
my body seat on more toward the back of the bike now. and I really fell faster coming out of turns.
I even get out of turns on the back wheel if I want with not much effort.
I'm 1.70cm high. so maybe I like shorter CS just because I'm short...(?)
 
Mo(n)arch

Mo(n)arch

Turbo Monkey
Dec 27, 2010
4,441
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Udi is gambling I think...:clue:
Pics please.

Riding a bike with adjustable chainstays, I came to the conclusion that I like the short CS setting way more than the long setting.
I find it way easier to ride the bike in tight berms and on technical terrain. Manualing the bike is also way easier that way.

CS length: 430mm (measured)
Rear traction: (poor/good/excellent): good
Ease of initiating drift: (poor/good/excellent): good
Ease of controlling/predicting drift behaviour: (poor/good/excellent) good
Riding style/position: (rear-heavy/centered/front-heavy): centered to rear heavy

I am a fairly tall rider nd ride a bike with a nominal reach of 440mm. The shorter CS make for a more nimble feel of the bike which I definitely prefer.
 
Leppah

Leppah

Turbo Monkey
Mar 12, 2008
2,294
3
Utar
Please, carry on. I've never actually thought about the differences my bikes would have when talking about chainstay lengths. I just hop on and ride. Please, carry on.
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
4,915
1,200
Monarch / saruti -
Thanks! Can I ask what the WB was on all those bikes, if you measured them?

gemini2k -
Do you think taller guys on longer bikes like yours need longer stays to match? What's your WB?

Ben -
I'm locked in short here as the WB would be excessive otherwise, pretty happy with the setup - also found it hard to lift the long front in the long setting, but I'll try it again sometime. Just keen to hear others thoughts. I've run a few ~16.8 and ~17.3 bikes in the past and the changes I've felt have been consistent over all of them.

Definitely agree that traction is based on many factors, but the CS vs. FC length does play a large part in the normal force generated under the rear tyre, and thus the frictional force. Biasing the rider's static COM isn't a small factor when the rider's mass is ~80% of the vehicle. Obviously riders move around to compensate but I think there's noticeable differences in predicting the limit of traction and predicting/managing a drift as a result of CS length. There's also a noticeable difference in outright rear traction, but I find it's a tradeoff with predictability.
 
Sandwich

Sandwich

Pig my fish!
Staff member
May 23, 2002
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Everybody likes to make fun of me because I buy and sell so many bikes, but this is exactly the reason.

Sunday
CS length: 17.2
Rear traction: Excellent
Ease of initiating drift: Poor/good
Ease of controlling/predicting drift behaviour: good
Riding style/position: Centered

The sunday is kind of the gold standard of modern geometry. I ran a medium, at 5'11, with both a factory and angled headset. I always felt like that bike was both super playful and planted as well. The rear traction was always pretty good, making for less of a drifty bike and more of a direct feeling handler. I felt pretty centered on the thing at all times. It was very easy to kick the back end out, and felt pretty natural.

Yakuza
CS length: 17.2
Rear traction: Poor/Good
Ease of initiating drift: Excellent
Ease of controlling/predicting drift behaviour: Excellent
Riding style/position: Rear heavy

I only had the kuze for a brief period of time before I discovered more cracks than a bad part of detroit. The geometry is pretty similar to the Sunday, but I switched to a large with a short stem and an angleset, putting my weight further back. I loved it. It was playful when I wanted it to be, because of the shorter stays, but had stability at high speeds. It jumped really well and was totally predictable, despite being undersprung. It didn't quite have the terrain tracking of the sunday, so it drifted a bit better and initiated easily.

More wood Izimu
CS length: 17.7
Rear traction: Hard to define
Ease of initiating drift: Poor
Ease of controlling/predicting drift behaviour: Good
Riding style/position: Front heavy

The morewood was a weird bike. I liked it's simplicity and light weight. it worked OK with the air shock. I feel like it made me a faster rider, as absolutely bombing sections through the woods was no problem. It was a weird handler though (and may not work for your high pivot exclusions), because of the length of stays and weight balance (and a host of other factors I'm sure). It wasn't radically different in design than the kuze, but the handling was. I felt like the longer stays were much harder to initiate drifts, and the higher pivot probably didn't help either. Rear traction was hard to define. The longer stays kept it planted, but it liked to skip with the brakes on, chuffing over dry terrain and into hard turns. The longer stays, air shock, and slightly shorter front end pushed my weight forward and made the bike feel very front heavy, even with the same cockpit as the kuzi.

I'm not sure if any of this helps or hurts or is completely irrelevant. I think my favorite was certainly the yakuza. That bike felt long and lean and just wanted to go, or disintegrate. The geometry felt natural without being skittish or overly planted. I loved the longer top tube and huge wheelbase. No matter of speed seemed to phase it set up like that. I don't think I would want CS any shorter than 17, as I feel like I'm fighting the bike a bit, even at low speeds on my xc steed, instead of feeling connected with it, but I haven't tried a crazy short setup with a longer FC.
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
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Excellent, definitely what I was looking for. I do feel there shouldn't be as large a difference between the Sunday and Yakuza as what you experienced though - were they fairly similar in suspension / sag and tires / pressures? Interesting if so. Everything else roughly lines up with what I've experienced.

Also I added wheelbase to my template since I'm asking everyone anyway. Feel free to add the numbers if you ever measured them.
 
Sandwich

Sandwich

Pig my fish!
Staff member
May 23, 2002
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The difference between the sunday and yakuza is hard to justify, so I'm just going off of memory. The sunday was equipped with excellent components, the right spring rate, but a shock that was poorly tuned and had too much rebound and thus packed up. The s'kuse had a fair shock with no compression adjustment and a spring rate 50-100lbs too light. I didn't realize that it was undersprung until I also realized it was cracked. Tires were similar, DHF/DHR 2.5 3c on the sunday, DHF fr/rr 2.7 ST on the koozy. Extra inch in the top tube, and the kooz was probably a degree/1.5 slacker, as it had a 8.75 (instead of 9") shock and -1/-1 cups, instead of -1.5/0. So, it was slacker/longer, undersprung and I had it two years after the Sunday....I'm guessing most of the differences between the two are the advancement of my riding ability and the suspension, as well as the geometry.

I think the bigger take home that I wanted to convey was the difference between the morewood (half inch longer stays) and the yakuza, which actually felt like quite a bit on the trail, and much of it came from those chainstays, I felt, since it was something I was paying close attention to. I wouldn't hesitate to buy a large sunday, had I the time and money, since I got along with that geometry so well....or another nice single pivot like the yakuza with a similar setup to what I was running (63.5*, 13.8"bb, 17.2 stays, 24.5" ett).

I didn't measure the wheelbases on any of the bikes besides the yapooza, which was like 46.8" or something.
 
norbar

norbar

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Jun 7, 2007
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buckoW said:
Udi, try the short stays for now and put it in the long hole when you are flat out and needing a little more hook in flat fast corners. Traction is dependent on a lot more than CS length, IMO. Brendan runs the long hole in PMB and Leogang with a steeper HA by the way. It is another tool in the toolbox and should be used to dial in the bike for the track.
Click to expand...
That's really interesting. Since Leogang is steep in parts and quite bermy in others I would have thought he would have preffered slack and short cs compared to other tracks. Is it because both of them are quite flat (leo is 50/50) and he wants more front wheel traction?
 
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demo 9

demo 9

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Jan 31, 2007
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not totally relevant to your question, since none of the bikes are similar, but i always found that the longer chainstay bikes i owned were much easier and more predictable to drift, compared to my demo 8 which ripped corners, and slid easily, but always seemed to get more "hung up" in the corner. I found that the tighter stays seem to "square up" the corners more-which ****s you if you arent on something steep
 
saruti

saruti

Turbo Monkey
Oct 29, 2006
1,169
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Udi
I didn't measure the DHR, but it was a M with a headset that made the bike shorter by 1.5cm.
the Sunday is a S (16) with 2 degree headset (63HA)
 
Udi

Udi

RM Chief Ornithologist
Mar 14, 2005
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demo 9 said:
not totally relevant to your question, since none of the bikes are similar, but i always found that the longer chainstay bikes i owned were much easier and more predictable to drift, compared to my demo 8 which ripped corners, and slid easily, but always seemed to get more "hung up" in the corner. I found that the tighter stays seem to "square up" the corners more-which ****s you if you arent on something steep
Click to expand...
I agree almost completely, glad you chimed in with that. The only small difference I found from what you say is that the short chainstay bikes (16.9 or less) actually don't start sliding easily and have more absolute rear grip until the point at which they let go.

It's harder to get them to slide because there's more weight over the rear wheel, but it's also noticeably harder to pick the point of maximum traction on a corner, and if you push past that region what you get is a very abrupt slide. I find this is more noticeable on higher grip surfaces than really loose stuff.

At that point I feel the same way as you - the drift is less controllable, much more of a square off, and not particularly smooth. The return back to traction is just as sharp, which completes the "hang up" feeling you describe. It doesn't feel good at all.

I raced a demo 8 for a season as well which is where I first really noticed this (combined with a long frontend), but have since ridden other short-CS bikes that have replicated the feeling.

With that said, these bikes (in my case) have also been longer (FC and WB) than the others for whatever reason, and I've found them to be quite fast bikes overall even though they feel lousy in tight corners. The other interesting thing is, I haven't noticed a loss of front traction that correlates to the increase in rear traction on these bikes. Theoretically something like that should happen, but I haven't found it.

Potentially I've felt faster on these bikes mostly because they've had a longer reach / FC, but I think once you add that to a long(er) CS as well, they end up being unreasonably long and become hard to manual - so the short CS mitigates these issues.

On a more open track with less sharp corners and more steady state ones I think you could have both (long front and ~17.2 rear) and enjoy more predictable slides, but for tighter ones the short CS settings are still useful on long bikes I think.
 
O

Optimax150

Monkey
Aug 1, 2008
208
0
Japan
I have a banshee scythe, with -2 deg cups. The setting I run it in has a wheelbase of 1180mm and a chainstay of 440. If I change it to shorter wheelbase and shorter chainstay I definitely feel the difference. I notice the rear wheel is tucked more under the seat. I dont like it, I feel it breaking loose easier and uncontrollable before entering a turn.
This has me worried because I kike the wilson and the undead but there geo numbers has a shorter wheelbase than the scythe.
 
Gary

Gary

"S" is for "neo-luddite"
Aug 27, 2002
7,659
5,575
UK
Like my chainstay length as short as possible, this has nothing at all to do with cornering performance tho.. I just spend far moar time riding a DJ hardtail (or BMX for that matter) than a DH bike so find long bikes way harder to turn, even my roadbike is shorter than it should be for my height.

folk get far too hung up on the addad stability a super long bike gives, unless you're super tall or Damien Spagnolo I wouldn' worry about the stability so much and given the choice simply choose a CS length that plays towards your own cornering strengths

Sometimes you want a hatchback, other times a limo..

http://mpora.com/videos/AAdo1vx6cyqi
 
Mo(n)arch

Mo(n)arch

Turbo Monkey
Dec 27, 2010
4,441
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Nah man.

Udi is a "Mad scientist bike builder guy" and one of the few guys in all the mtb forums who knows his ****.

I was refering on Gwins "sizing problems".
 
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Mo(n)arch

Mo(n)arch

Turbo Monkey
Dec 27, 2010
4,441
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Italy/south Tyrol
Monarch / saruti -
Thanks! Can I ask what the WB was on all those bikes, if you measured them?
Click to expand...
It took me a while to get home.
And I had to shred tons of pow.
WB is 1220mm in the short setting.
CS length: 430mm
FC (BB to front axle): 790mm
 
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