Descending, bike fit, weight distribution

[andreas]

I find the bikes where I have more weight distributed over the rear wheel more confidence-inspiring for descending. On my current main race bike, the geometry is such that I have to ram the saddle all the way forward, which makes it feel more unstable both when descending and when riding without hands on the bars. Also, it complicates descending "sitting" on the frame, since the saddle nose gets more in the way.

Of course, you should never prioritize setback for descending over getting a correct setup for knee-pedal axle positioning on your current bike, but I will probably try to downsize on my next race frame to gain back more confidence in descending again.

[dcorn]

Seat position really makes no difference for descending. I'm never in a normal spot on the seat (sometimes not even on the seat) when descending. I'll either slide way back and have the seat under my thighs with pedals at 3 and 9, or I'll sit on the top tube in a supertuck.

I'd say slightly longer stem would be better so the handling isn't as twitchy. There is no reason to have super fast steering when flying down hills.

Honestly, the bike should fit you when riding normally. Unless you are starting up downhill road cycling, there's no reason to change a bike fit specifically to go down hills.

[mattr]

So what is better for descending, more weight on the back wheel, or a longer stem to have more fine grained control ...

Within the restrictions of the frames geometry, it'll make no measureable difference at all. External factors will swamp any changes you make to position.

It's you who can't descend. You need to practice more.

[GrumpyOldPizza]

Honestly, the bike should fit you when riding normally. Unless you are starting up downhill road cycling, there's no reason to change a bike fit specifically to go down hills.

Perhaps I should have added more background then ... I am developing a spine issue. My normal fit that I had for the last few years does cause me a good amount of pain ... Turns out that a slightly more stretched position is more comfortable (perhaps it's better on a pressure point, who knows). So I suddenly have 10mm more reach in my working setup. Initially I was experimenting with a longer stem and a different handlebar (less drop to stay comfortable). So the question is now in which direction to do trial and error first. My main weakness (besides consuming way too much ice cream) is descending. So I'd love to mess perhaps first with the dominant item that would most likely help me there. I just need to know which one that is, which I why I posed the question.

[JKolmo]

Stem length and saddle setback has nothing to do with it. Relaxed body, shoulders and arms, hands in the drops, look way ahead where you are going not right in front of you, learn how to distribute your body weight and lean your bike, weight on outer pedal six o’clock, find apex in the bends, learn correct braking technique, practice and practice and practice. There is no tech gear short cut out of it.

Again, all of that is irrelevant. I have 2 bike setups that are equally good in terms of speed on the flats, climbing and all other aspects I can think of. What you mention are questions of technique (other than the distribution of body weight). All I am asking whether there is an advantage in having the saddle 10mm further back with a shorter stem, or saddle further forward with a longer stem (simply assuming that the reach is the constant here (tip of saddle to center of bar for simplicity).

Whoops, sorry! I thought you wanted to be a faster descender. Moving your saddle or getting a different stem will not help you at all in that respect, that was my point. I am out.

[GrumpyOldPizza]

Whoops, sorry! I thought you wanted to be a faster descender. Moving your saddle or getting a different stem will not help you at all in that respect, that was my point. I am out.

That was perhaps a good enough answer. The spine issue just triggered a radically new setup ...

[Js2]

If you have a buddy who's really good at descending you can ask him for some pointers, maybe also follow his line. Work on your technique and slowly progress, it will build up your confidence. Or you can have him tail and record you with a gro pro, that way you can analyze it even further.

Weight distribution and stem changes might change the feel a little bit but I don't think its a big issue. I've ridden different bikes with different setup and you can adjust the setup base on preferences but minor change here and there wouldn't make a huge difference (unless your bike fit is totally crazy off) as long as your basic technique is solid.

[Mr.Gib]

I started reading the replies and became infuriated so I quit after about 4 or 5. Apologies then if I repeat what subsequent replies already covered.

To the OP - the engineer in you should have known not to ask about what saddle position is best for descending. You have to ride your bike and as such there is (with very minor latitude for personal preference) a correct postition for your saddle based on the proportions of your body. Move it 10mm in any direction and it's wrong. You won't pedal as effeciently, you will be less comfortable, and you may injure legs, knees, hips, etc.

OK, so now that we have the saddle out of the way, what about the stem? The stem length should be chosen to achieve your desired balance between comfort and performance. It is possible that a person could get on quite well with a stem that is a 10mm too long or 10mm too short. But if you can settle on the one that feels the best, that is your stem length - period. Forget about the impact on descending - there really won't be any. Remember with your saddle fixed, your entire body except for your arms is in the same place no matter what the stem length. And if we are talking about a difference of 10mm, really just a tiny change in shoulder and elbow extension - that will be almost nothing in terms of weight distribution. A full or empty water bottle will have a bigger impact on weight distribution.

Yes, longer stems result in a bike that responds less to steering inputs, but you will adjust instantly to any difference and end up with comparable steering performance. You bike will not suddenly become unstable because your hands are 10mm closer or further away.

And most importantly, I assume that your issue is not your ability to go fast in a straight line, but rather to corner rapidly. If that is the issue then the location of the saddle and handlebar (within the parameters discussed here) is almost irrelevant because you won't be on your saddle! Your weight will be divided (mostly) between your feet and hands so that your body can move and be positioned to give you the best ability to control the lean and traction of the bike while carving turns. Often this means moving your body (center of mass) back a bit. Bottom line - if you descend with your ass planted on the saddle, expect to be slow, shakey, and to crash when you try to push it. (Exactly what happened to Michael Woods when he crashed in front of Thomas earlier in the tour - he said a much in an interview.)

Alternately you could just be content to descend slowly and have your bike set up any way you desire. For some people that works just fine.

[gurk700]

I don't know if all the math and people's ideal setups will answer it for you.

IMO, bike handling is a very complicated subject and there's no one size fits all kind of answer. It's very personal too.

I LOVED my Cervelo R5 but it felt twitchy AF. I was fast enough on it descending but never felt like I was as fast as my potential. I'm confident with speed as I come from moto racing so I chalked it up to pedal bikes not feeling the same so I need time to get used to it.
Then I bought a Cervelo S5. I was immediately faster on it on descends and felt VERY confident going downhill. Handling felt more stable. It didn't turn as easy but it felt planted to the ground.
Went back to R5 a few months later as I missed the light weight and the nervousness came back.
Now on an S-Works Tarmac. It feels planted on cornering and confidence inspiring.

So that's just one part of the equation. Some bikes feel more confidence inspiring than others.

The other part of it is preference. What I call twitchy, some people will be faster on and prefer. It's very similar on motorcycles. I jump on a friend's moto and while they LOVE it, I hate it. Can't turn the thing. And vice versa. They hate my setup.

So yeah.. Gotta find what you gravitate towards and go from there. Bike fit to me is a whole different thing. Get a comfortable fit that you can ride on and put the power down for hours.

[Stueys]

I’ve an r5, wouldn’t say it’s a rock solid bike at speed but I wouldn’t describe it as twitchy. I rented an SL6 and noticed the lower bb made it feel more stable on sweeping bends at speed but the front end felt lighter than my r5 and that made it feel more twitchy than my r5. It was a rental so quite likely I didn’t have the position as dialled in as my r5.

To the op, I look for longer wheelbase, a lower bb and slacker HT angle to get a sense for how nailed a bike feels on a descent, I used to regularly faff with stem lengths and, to me, 10mm more or less made no discernible difference to steering feel. And as everyone has said I think saddle position is pretty much irrelevant, you’re moving around on a descent. Get the fit right for comfort and biomechanics.

The first suggest made was a good one, wider tyres make a big difference to how stable a bike feels. Well worth a try.

[Karvalo]

For this questions's shake, lets assume both fits are equally good, no noticable differentce.

Let's also assume that with both setups I could move my body weight around that same way, just with one 10mm further to the back than the other, but not being limited in any other way.

So what is better for descending, more weight on the back wheel, or a longer stem to have more fine grained control ...

Why not assume they're both equally good?

But seriously, it depends. Unless someone has all possible information about your position, the answer is always, it depends. Further back isn't better if you're already further back than optimal, and further forwards isn't better if you're already further forwards than optimal. And what if your absolute optimal weight distribution is bang in the middle of the two?

[Karvalo]

I’ve an r5, wouldn’t say it’s a rock solid bike at speed but I wouldn’t describe it as twitchy. I rented an SL6 and noticed the lower bb made it feel more stable on sweeping bends at speed but the front end felt lighter than my r5 and that made it feel more twitchy than my r5. It was a rental so quite likely I didn’t have the position as dialled in as my r5.

Keep in mind that only the 58 and 61 R5s have (slightly) higher BBs than the SL6. Every other size is the same or a fraction lower.

[Multebear]

Again, all of that is irrelevant. I have 2 bike setups that are equally good in terms of speed on the flats, climbing and all other aspects I can think of. What you mention are questions of technique (other than the distribution of body weight). All I am asking whether there is an advantage in having the saddle 10mm further back with a shorter stem, or saddle further forward with a longer stem (simply assuming that the reach is the constant here (tip of saddle to center of bar for simplicity).

I'd definitely choose a stem as long as possible. You´ll put more weight on the front wheel which stabilizes steering and overall bikecontrol. I ride 140 mm stem, and my Evo1 is very stable, and makes me feel very confident in all situations including descending.

[Mr.Gib]

I'd definitely choose a stem as long as possible. You´ll put more weight on the front wheel which stabilizes steering and overall bikecontrol.

Is this what you want when you have the bike leaned over at the limit? Just about anything works going in a straight line, but the ability to corner at speed without feeling like you are going to slide out is what makes the difference. How does loading up the front end help in this situation?

[basilic]

Gib is right, in any technical part you' re off the saddle, and the F/R weight distribution is more 70/30 than 40/60, which you adjust by extending your arms. The arms give you a lot more adjustment than a 1 cm stem change.
A frame with a lower bb will definitely be felt and give confidence, it'll feel like you are "in" the bike, not "on" the bike