Fit changes to improve bike handling?

Discuss light weight issues concerning road bikes & parts.
wintershade
Posts: 242
Joined: Mon Apr 16, 2018 7:12 pm
Location: San Francisco, CA

by wintershade

Alexandrumarian wrote:
Wed Jun 05, 2019 5:42 pm
Your current position is not preventing you from having bent arms. Just lean forward and your arms will bend. How low and for how long depends primarily on your flexibility and core. If the bike is too small/short reach, you will feel the bars under your neck and want to push your butt over the saddle. As for the saddle position, I happened to settle very close to the kops thing. I didn't search for it, it happened in years of tinkering with the position. More forward I get all sort of knee issues, more backward I feel too closed to put down the power.
Yes, well that's basicly how I ended up where I am. We positioned my cleat such that my foot was in the correct place over the spindle, then moved my saddle such that my knee was directly over the spindle and adjusted saddle height to get knee angle in the established range of ~145-150 degrees, and then picked a cockpit/stem length that got me to the right back angle and allowed me to get as low as I could get without running into hip flexibility issues so my pelvis wasn't rocking on the saddle.

I am tight through the hips but have good back and hamstring flexibility.

Anyhow, I think it's worth just moving things back about 2cm and testing out the shorter stem for a couple rides before I sell the bike for 1/2 what I paid. Other than handling, the bike is pretty nice otherwise.

by Weenie


mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

So your fitter set you up using KOPS?

wintershade
Posts: 242
Joined: Mon Apr 16, 2018 7:12 pm
Location: San Francisco, CA

by wintershade

Yes, I think KOPS was how fitter set me up. He made this whole big deal out of the process of starting at the foot and working up and everything sort of magiclly falling into place ("brining the bike to my body... not bringing my body to the bike"). He noted that he also moved my foot / cleat position a bit further forward (I think it was forward) because apparently this was somehow better for my knees given I have a history of patellofemoral syndrome, and would be more similar to optimal triathlete cleat position and riding position.

If you look at the picture, you can see my knee is pretty much right over the spindle.

mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

Probably time to go and see someone a bit more up to date and explain the problems clearly and accurately! (Maybe print this thread off ;) )

TobinHatesYou
Posts: 4185
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

KOPS is so inane. You can achieve it with any number of x,y coordinates.

aeroisnteverything
Posts: 193
Joined: Fri Aug 24, 2018 4:43 pm

by aeroisnteverything

TheRich wrote:
Wed Jun 05, 2019 2:32 am
TobinHatesYou wrote:
Wed Jun 05, 2019 12:25 am
Did you just decide to ignore that part where I mention loose gravel/sand, ice, standing water, etc? I’ve ridden my road bike in those conditions in the last week. Shifting my weight forward in those conditions makes amplifies otherwise minor steering inputs. That can lead to a loss of adhesion in what is otherwise a balancing act of keeping the CoG directly over the bike at lower speeds.
I was hoping that you would realize the contradiction. The question is what makes the proper weight distrubution change when the grip level is high?

Hint: It doesn't, you can just get away with it on pavement.
Yeah, but being able to "get away" with it is important. I don't need to ride, or set up my bike, in such a way so as to be able to push the limits of adhesion. I am not a machine that can calibrate a steering input so precisely as to keep the bike "just about" upright, and I want forgiving and less nervous handling when traction is low. When traction is high, tolerances are higher, and so I am not so concerned with what THY identifies as a squirrelly front end.

If we were racing motorbikes, this might be another story. But even in motorsports, at least the 4-wheeled one, drivers tend to prefer understreery set ups in the wet - which is the equivalent to having less load on the front and more on the back for a bike set up.

TobinHatesYou
Posts: 4185
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

aeroisnteverything wrote:
Wed Jun 05, 2019 9:32 pm

Yeah, but being able to "get away" with it is important. I don't need to ride, or set up my bike, in such a way so as to be able to push the limits of adhesion. I am not a machine that can calibrate a steering input so precisely as to keep the bike "just about" upright, and I want forgiving and less nervous handling when traction is low. When traction is high, tolerances are higher, and so I am not so concerned with what THY identifies as a squirrelly front end.

Right, and when we put more weight on the front, we end up magnifying our subtle inputs so they aren't so subtle. That's why in slower, looser stuff, while it seems counterintuitive to sit back and upright, we do it anyway. We give up "grip" on the front because we're basically teetering at or even slightly past the limit of grip anyway, but we gain balance and finer control.

Karvalo
Posts: 737
Joined: Fri Aug 10, 2018 6:40 pm

by Karvalo

wintershade wrote:
Wed Jun 05, 2019 6:37 pm
...adjusted saddle height to get knee angle in the established range of ~145-150 degrees...
Interesting you should mention that. If you look at the picture you posted from your fit you'll see that the line going through your hip is kinda ok, but the centrepoint of the angle measurement is nowhere near the marker denoting the centre of your knee and with the blurring from the slow shutterspeed the line through your ankle is basically a guess. As such in this case the given angle measurement doesn't really show the final angle of your leg, just the number the fitter wanted you to see.

IMO.

Karvalo
Posts: 737
Joined: Fri Aug 10, 2018 6:40 pm

by Karvalo

wintershade wrote:
Wed Jun 05, 2019 7:18 pm
If you look at the picture, you can see my knee is pretty much right over the spindle.
The picture shows your foot at the bottom of the pedal stroke. That's not how KOPS works.

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Lewn777
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Joined: Thu Mar 09, 2017 5:35 am

by Lewn777

TobinHatesYou wrote:
Wed Jun 05, 2019 9:49 pm
aeroisnteverything wrote:
Wed Jun 05, 2019 9:32 pm

Yeah, but being able to "get away" with it is important. I don't need to ride, or set up my bike, in such a way so as to be able to push the limits of adhesion. I am not a machine that can calibrate a steering input so precisely as to keep the bike "just about" upright, and I want forgiving and less nervous handling when traction is low. When traction is high, tolerances are higher, and so I am not so concerned with what THY identifies as a squirrelly front end.

Right, and when we put more weight on the front, we end up magnifying our subtle inputs so they aren't so subtle. That's why in slower, looser stuff, while it seems counterintuitive to sit back and upright, we do it anyway. We give up "grip" on the front because we're basically teetering at or even slightly past the limit of grip anyway, but we gain balance and finer control.
Having too much weight on the front of the bike will amplify so many handling problems. We sit basically over the rear wheel on any kind of bike because overloading the front wheel can easily lead to the bike low-siding, also we need a light front end to enable us to control the bike. Any kind of bike shares a lot in common with a unicycle, where the unicycle is the only wheel, that's your rear wheel. The front wheel is for extra balance and to enable you to do all those high speed weight shift, countersteering and steering things a unicycle can't do. When we wheelie, manual or ride no handed on a bicycle we can see how rear baised a bicycle really is. The idea that somehow a front and rear tire are sort of equal in the game and require a similar amount of grip and loading is a disaster waiting to happen.

Too much weight over the front end will restrict your control and even fairly mild corner braking can cause low sides. In wet or dirt this is even worse. You can load the rear tire because your weight is over it, and you have to load it the rear to really excessive amounts before you high-side. Also it's really easy and sometimes quite fun to control a rowdy rear end.

Of course during straight-line braking you can happily load the front tire almost to your hearts content in the dry and make the bike endo, but that braking has to be feathered gradually until zero at the the apex or again you're going to low side. But don't confuse braking with handling.


youngs_modulus
Posts: 575
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

TobinHatesYou wrote:
Wed Jun 05, 2019 9:49 pm

[W]hen we put more weight on the front, we end up magnifying our subtle inputs so they aren't so subtle.
I’m afraid I don’t quite follow this sentence. In what sense does putting more weight on the front wheel “magnify subtle inputs?”

TobinHatesYou
Posts: 4185
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

youngs_modulus wrote:
Thu Jun 06, 2019 12:24 am
TobinHatesYou wrote:
Wed Jun 05, 2019 9:49 pm

[W]hen we put more weight on the front, we end up magnifying our subtle inputs so they aren't so subtle.
I’m afraid I don’t quite follow this sentence. In what sense does putting more weight on the front wheel “magnify subtle inputs?”
If I hit a patch of ice, a rock on a gravel road or a pothole, having all my weight on the front will cause me to lurch forward pretty hard. Being bucked forward like that can cause one to accidentally steer, that's all I'm saying.

youngs_modulus
Posts: 575
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

OK...that makes sense. I thought you were saying that the inherent steering response of the bike changes depending on how much weight is on the front wheel, which sounds specious to me. But you weren’t saying that at all. I see how a surprise bump could lead to unintended steering inputs.

by Weenie


youngs_modulus
Posts: 575
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

Lewn777 wrote:
Thu Jun 06, 2019 12:00 am
Too much weight over the front end will restrict your control and even fairly mild corner braking can cause low sides.
The only thing that “causes” low-side crashes is a loss of adhesion at one or both tires. Excessive front braking while leaned over for a corner will cause your front wheel to wash out regardless of weight distribution. If you lose adhesion in the front on pavement, you pretty much get dumped immediately (as we all know). That’s a low-side crash.

If you lose adhesion at the rear tire, you can low-side as well as long as you don’t “catch” the slide. Deliberately laying your bike down (say, to avoid hitting a chain stretched across the road and three feet above it) usually involves locking your rear wheel as part of an intentional low-side crash.
Lewn777 wrote:
Thu Jun 06, 2019 12:00 am
In wet or dirt this is even worse. You can load the rear tire because your weight is over it, and you have to load it the rear to really excessive amounts before you high-side.
Your use of the term “load” is pretty vague here, but high-sides are the result of a stick-slip condition, not weight distribution. A sliding tire that suddenly grips (like when transitioning from glare ice to adjacent dry pavement) will pivot about the newly-grippy contact patch and throw the rider. That’s a high-side crash.

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