horizon wrote:531colin wrote:horizon wrote:..... To accommodate my legs I shift the saddle back - you have to do this or you just sit off the back of the saddle....
This is the bit that worries me.....Generally, you set the saddle HEIGHT for your leg length (with various caveats)
Preamble (warning - maybe TLTR!)I've tried to limit myself at times to talking only about frame proportions. This thread viewtopic.php?f=5&t=118634&hilit=spa+titanium+brushed almost exactly parallels many of the problems I faced in simply understanding how a frame fits together and changes dimensions and angles according to make and size. I'm happy that I can now (almost) buy a bike knowing what it is I am buying in terms of size and fit.
So that's the frame but it leaves all the other variables of body proportion, flexibility and riding style i.e. the rider. It also leaves the possible adjustments - cleats, stem and saddle. As I said upthread, most of "me" is totally happy on a bike but it leaves the niggling problem of reach. This is caused principally by my moving the saddle back further than normal and thus putting the bars out of comfortable reach.
The conclusion I came to is that my overlong legs led me to buy bikes that were generally too large (and coincidentally had usefully long top tubes) but actually not too far wrong for my height. A smaller size would have solved the reach problem (despite the shorter head tube) and that is where I am now heading. I'm going to test one by buying a cheap second hand touring bike in a smaller size and giving it a good trial. I'm also currently using my Dawes Horizon without a VK adaptor to see what that really feels like. It has a 73.5 deg seat angle and I'm thinking that 72 deg might clinch it. I must emphasise though that most of the time I am almost 100% OK - it's just that i cannot really test it out. And I also find that my needs change over the course of a ride - as they do for anyone.So back to your point: I agree. I had actually come to the same conclusion (it may have been something in this thread). But that leaves me completely in the dark as it might be one of several factors - my leg proportions, upper body flexibility, foot position on the cleats etc. But I reckon you still need to be behind the pedals sufficiently in order to complete the pedal cycle - you cannot bend your knees enough without being able to push you body back. So I still think that seat angle is critical if you have long legs for you height - remember, I am not tall (5'10") but I have long legs for my height (34" inside leg). This, as I see it, throws the balance between saddle height and reach - as you accommodate your legs (by moving your bum backwards, you lose your arm position in relation to the bars. BTW I have plenty of height adjustment on all my bikes. I accept that if I were very flexible that wouldn't be a problem but I like a fairly relaxed upright position - mind you, I still like the bars nearer even when my back drops (bending my arms).
QUESTION EVERYTHING......and question again until you are sure that you understand what they are saying, and why they are wrong (or, sometimes, right.)
For example, your squatting man with the caption "the longer your thighs, the further back your bum must go" ......while its true that if you have long thighs your bum must go further behind your knees, the caption could have been "the longer your thighs, the further forward your knees must go"......because when squatting you have to be in balance, that is your centre of gravity (centre of mass) must be over your feet, otherwise you will fall over. And that is the function of saddle fore and aft adjustment.....push the saddle only as far back as it needs to be in order to have a comfortable (small) amount of weight on your hands.
For actually pedalling and propelling the thing, if you had said you need to be far enough behind the pedals to get your heels down, I would agree. If you can't flex (bend) your knees enough to get the pedals "over the top" that sounds like the saddle is too low.
Seat angle is critical for getting the saddle far enough back to reduce the weight on your hands....just watch all the people on fashionable road bikes with fashionable steep seat tube angles....they all pedal toe down all the time. If you are racing, even if its only "racing" your mates on a Sunday morning, then an aerodynamic position is not only worth having, its worth a little bit of effort to achieve. The steep seat tube angle pushes your bum forwards, which makes it easier for the average Joe (Joanne) to achieve an aerodynamic position....the bum goes forwards and up, the hands go forward and down, the weight of the torso falls increasingly on your hands. (I'm not talking about the world-class athletes who ride like this...... the fact that world-class athletes can achieve a particular riding position doesn't make it a "given" that middle-aged recreational cyclists should strive for the same position) I can't remember who it was, somebody referred to this as the rider's body "rotating around the pedal spindles".....and I think thats an accurate analogy. As your bum comes forward, your toes go down, and the saddle needs to go up to reduce knee flexion. Watch the professional riders in the international events....only a handful ride with their foot level, very few get their heels down like Froome.....the majority ride toe down all the time.
Recreational riders, however, need their saddle far enough back to limit the weight on the hands, and low enough to reach the bottom pedal with the foot flat. If you need to be on tiptoe to reach the bottom pedal, you are just one step away from over-extending your knees with every pedal stroke. (If you are looking for that knee extension to give maximum power for your muscle work, its perfectly simple to slide back in the saddle for whatever proportion of the ride you are seeking maximum power....not much for me, I'm mainly enjoying the ride!)
That thread about titanium bikes started soon after I moved house, and I thought there was enough nonsense in it without me joining in.
For example, its pointless measuring the top tube length if you take no notice of seat tube angle. A degree on the seat tube is worth about 10mm on the top tube for an average rider. A short top tube doesn't translate into a short reach if you have to push the saddle way back.
"Reach" measured in front of the bottom bracket will tell you just exactly that....but the "reach" of a frame doesn't matter at all if you can't get your bum in the right place.
And "weight distribution".....my favourite red herring. ....look at all the bikes that use the same chainstay length for all the sizes......look at all the big frames with short front centres where they increase the reach by steepening the head angle and reducing the fork offset. I even came across somebody who reckoned the seat tube angle should vary if the rider has a fat ass, in order to keep the weight distribution "correct".
When buying a bike, the usual trade-off is you can go for a smaller size, this should give a shorter reach (as long as you avoid the trickery where they steepen the seat tube in order to reduce top tube length) at the expense of a shorter head tube, which means you have to work at getting the bars high. If you go for a bigger size, you are likely to get a taller head tube at the cost of a longer reach, and sometimes a slacker seat tube angle as well.
73.5 deg seat tube angle is too steep for me to be comfortable, at least it is with a Brooks saddle.
), I don't think i have a back/posture/reach issue. I've artificially moved the saddle back further than it is designed to do using a VK adaptor. That was in order to accommodate my legs and make my position on the saddle right (remember, I moved the saddle back not forwards). Of course that has knock-on effects on reach - as it would do I presume on your own bike if you moved your saddle back 4 cm.