Understanding Descending Mannerism of Bikes

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RyanH
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by RyanH

A few things on the SuperX that I should qualify or caveat my feedback on. I did not put a lot of miles on that bike. I probably rode it 10 times total of roughly 15 to 20 miles each. I had the crappy stock alloy wheels on it and Vittoria Terreno (I think) tires on it. Further, my setup on the bike wasn't identical to my road bike setup so I was higher up, less weight on the front. Mine was a 51 2018 version which was 71 HTA with 55mm rake fork. Cannondale calls this their OutFront steering geometry and my recollection was that the bike felt like it wanted to self correct when turning. It also felt slow and ponderous when riding on the road. A lot of this could have been the tires and wheels. I didn't spend much time trying to figure it out.

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RyanH
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dcj10 wrote:I've soaked up the comments on this thread, as the question asked has occupied me for years. What are people's thoughts on weight distribution playing a significant role in this topic? When comparing the subjective handling of different bikes, did all the components affecting rider weight distribution occupy the same position relative to the other machine? Second thought: assuming a persons bikefit has taken into account their physical limitations, what necessary sacrifices to perfect weight distribution were consciously made to get there (for example: perfect saddle position achieved, but the rider lacks flexibility and so needs a shorter reach and more upright hand position)? Mostly I wonder if not having enough rider weight low over the front wheel might lead to vague handling, but that is just my theory. I've no knowledge to back it up. Interested if there are any thoughts on these aspects.
Over the years I've modified my fit to longer and lower. I've found that your position makes a huge difference on a bike. I've had bikes that changed from okay to good based on swapping stem lengths. I've also found that if the reach increases without you adapting you feel like you're steering behind the bike and gives the impression of a tendency to go wide. Also, I've had bikes that were nervous or downright scary due to a stem (looking at you Extralite).

I have an outlier fit as I really need a bike with like 530mm stack and ~395mm reach to be able to run a 120 stem. So, instead, I often run a 130 or 140 stem on small bikes.

If USPS didn't drop the ball on my Fair Wheel package, I would've been able to report back if 5mm change in trail is noticeable but that'll have to wait until Tuesday.

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by Karvalo

Lucendi wrote:
Sat Dec 04, 2021 9:34 pm
The agility vs stability tradeoff has mostly to do with the caster angle (all other things equal).
All other things are not equal. Leaving aside ultra-steep mountain bike descents, caster angle on a bicycle is important because it creates trail, and trail is the source of the self-correcting factor. But fork offset also plays a major role in trail figures and there are reasons to play around with the two.

Quite some time ago Mike Burrows played around with prototypes that could replicate up to a 90 degree head angle but with trail (some kind of caster wheel system I guess) and came to the conclusion that trail was the single dominant factor in road bike geometry that governed handling characteristics.

More recently companies like Cervelo and Cannondale have both started using different fork offsets and head angles throughout the size range with the goal of keeping the same trail figure for each size of frame within a certain model, again because they now believe it's the best way to maintain consistent handling traits for every rider.

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by dcj10

RyanH wrote:
Sun Dec 05, 2021 4:00 pm
Over the years I've modified my fit to longer and lower. I've found that your position makes a huge difference on a bike. I've had bikes that changed from okay to good based on swapping stem lengths.
Thankyou for posting this feedback. So then it's by accident I've recently found the same thing to be true :thumbup:
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Mr.Gib
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by Mr.Gib

dcj10 wrote:
Sun Dec 05, 2021 1:22 pm
I've soaked up the comments on this thread, as the question asked has occupied me for years. What are people's thoughts on weight distribution playing a significant role in this topic? When comparing the subjective handling of different bikes, did all the components affecting rider weight distribution occupy the same position relative to the other machine? Second thought: assuming a persons bikefit has taken into account their physical limitations, what necessary sacrifices to perfect weight distribution were consciously made to get there (for example: perfect saddle position achieved, but the rider lacks flexibility and so needs a shorter reach and more upright hand position)? Mostly I wonder if not having enough rider weight low over the front wheel might lead to vague handling, but that is just my theory. I've no knowledge to back it up. Interested if there are any thoughts on these aspects.
I think weight distribution is mostly a non-issue and perhaps a "red herring" when trying to understand causes of good or bad handling. At least in high speed descending, the majority of weight will be on the pedals and the basic handling characteristics of the bike will be revealed. True, the rider can adjust the amount of weight on the bars by shoving the torso forward or back, but a good athlete will instinctively find the optimal amount of weight on the bars which won't be a lot regardless. Further, with fundamentally sound bike fits, there won't be much variation from one rider to the next. It's all about the bike (but longer stems do add stability).

Your point about the rider that has the seat in the correct location but can't reach the bars so must comprimise the cockpit - thats just someone on the wrong bike. In theory you should be able to locate that person's center of mass correctly between the two wheels - you just need to design a bike for it. In general, assuming fundamentally sound fit and weight distribution, I don't think putting more weight on the front end to solve some frame design induced handling problem is a good idea. When I hit terminal velocity I get low and move my weight back. Same in high speed corners.
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by Marin

Tires also make a huuuuge difference. Pressure obviously, size too, but type is really important. Handling really changed when going from Pro One to Corsa Race recently.

Also, geometrically, bar width and stem length probably have more of an influence on percieved handling than trail has.

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by jadedaid

Going off of to changes made to a single bike over the last few years I have found position (or perhaps more accurately, weight distribution within the bike) to make the biggest difference. I've got long legs and found the further forward I move, the better the bike descends. If I compare running 2cm setback versus running a straight post it's the difference between a bike that I hate descending on to one I'm ok with. With reference to the comment about the weight being on your pedals, you might have your weight on the pedals but where your center of gravity is relative to the wheels still matters. Your position on the bike will affect those force vectors.

I changed from cheap chinese carbon to Roval Rapide's this year and it has also improved the descending of the bike. My theory being that the cheaper wheels flexed more, resulting in more movement of the bike within a turn?

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by DHG01

jadedaid wrote:
Mon Dec 06, 2021 4:17 pm

I changed from cheap chinese carbon to Roval Rapide's this year and it has also improved the descending of the bike. My theory being that the cheaper wheels flexed more, resulting in more movement of the bike within a turn?
Very much agree with that last comment - all things being equal, I ve noticed a significant improvement in handling by swapping to stiffer wheels.

CR987
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by CR987

Lucendi wrote:
Sat Dec 04, 2021 9:34 pm
The agility vs stability tradeoff has mostly to do with the caster angle (all other things equal).

Image

More positive castor angle => heavy steering (stability)

Less positive castor angle => easy steering (agility)

At high speeds more of a castor angle is preferable as road imperfections won't take as much rider input to compensate for.

At low speeds less of a castor angle is preferable as steering will be easy and thus quicker.
I'm sorry this is completely incorrect. You cannot compare car geometry with a bikes

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by Lucendi

CR987 wrote:
Mon Dec 06, 2021 5:26 pm
I'm sorry this is completely incorrect. You cannot compare car geometry with a bikes
I'm not talking about automobile wheel alignments, I am specifically talking about caster angles and I chose to illustrate what castor angle is with the simplest picture I could find.

Car, motorcycles, bicycles, even shopping carts all have caster angles.

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by TobinHatesYou

Lucendi wrote:
Mon Dec 06, 2021 8:19 pm

Car, motorcycles, bicycles, even shopping carts all have caster angles.

Yes, we just always refer to it as rake.

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by Karvalo

Lucendi wrote:
Mon Dec 06, 2021 8:19 pm
CR987 wrote:
Mon Dec 06, 2021 5:26 pm
I'm sorry this is completely incorrect. You cannot compare car geometry with a bikes
I'm not talking about automobile wheel alignments, I am specifically talking about caster angles and I chose to illustrate what castor angle is with the simplest picture I could find.

Car, motorcycles, bicycles, even shopping carts all have caster angles.
Right, but as I pointed out bicyles also have fork offsets, therefore steering stability isn't predominantly to do with caster.

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by Karvalo

TobinHatesYou wrote:
Mon Dec 06, 2021 9:48 pm
Lucendi wrote:
Mon Dec 06, 2021 8:19 pm

Car, motorcycles, bicycles, even shopping carts all have caster angles.
Yes, we just always refer to it as rake.
I think in cycling we refer to it as head angle, because we use the word rake differently to everyone else.

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by RyanH

Yeah, cars have rake as well but car alignment and setup is fairly well understood whereas bicycles not so much. Adding in concepts from cars just muddies the waters further.

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by Lewn777

It is different. Caster angle in cars is more like fork offset or trail, whereas a bike head angle is just that. You can use caster in a car to demonstrate the idea of fork angle, but really only bikes can be compared and that means moto, MTB etc are all relevant.

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