Thorn Cycles Forum

Technical => General Technical => Topic started by: Inbred on January 14, 2019, 08:17:43 PM

Title: Calculating saddle & handlebar position.
Post by: Inbred on January 14, 2019, 08:17:43 PM
I've had my saddle and bars in the same position for many a year, but recently I've started to doubt whether I've got it right...
The seems to be a plethora of ways to determine the saddle layback and handlebar reach, but no one definitive method.
How do you calculate yours?
Just wondering....
Title: Re: Calculating saddle & handlebar position.
Post by: mickeg on January 14, 2019, 08:55:50 PM
When it felt pretty good and I stopped having lower back pain, that meant I pretty much had it right when I could go 100 km without any problem, day after day on a long tour.  Height of saddle was largely based on lack of knee pain.  Sometimes I tweak handlebar height by 5 or 10mm with spacer changes.  I use drop bars on all but my errand bike.  And I have them all setup nearly identical. 

At one time I was using an adjustable stem (adjustable angle) so I could make quick adjustments during a ride to see how I liked the changes.  And a bunch of steerer tube spacers.  And that was how I determined what worked best for me.  I have over the years loaned that stem out to several friends so they could try different bar positions to see what worked best for them too.

My rando bike has a bit more reach than I wanted, when I built it up I did not realize that the bars I bought had a longer reach than most of my other handlebars, thus I got the stem length slightly off.  But that bike I just live with it.

Every once in a while I adjust saddle height, but I only make adjustments by 5mm at a time.  I leave a piece of tape on the seatpost so that there is about a 5mm gap between the tape and frame, if the gap disappears that means the seatpost moved and needs to be fixed.  I have several bike shoes and I suspect some shoes have a different sole thickness.

When setting up a new bike, I get the saddle set at the right height based on measurements from other bikes, saddle set back about the same as other bikes but maybe a bit more forward if for shorter faster rides.  Then from measuring other bikes figure out how long the stem has to be to give me the right reach.  That was where I got it wrong on my rando bike, the bars were a deeper reach bar than the other bars.  After getting that one bike wrong, I no longer measure from the saddle to the bar distance, I now measure the saddle to the brake hood distance so that I can take into account bars of different reach.  I put a stick on the hoods and measure to the center of the stick from the tip of the saddle.

Bar width, that is simple, I buy the widest bars I can find without them being those odd extra wide angled bars like some of the bikepackers use.

There is one deviation, my folding bike has a much shorter reach, so on that bike my bars are much lower so that my lower back has about the same amount of forward lean angle as my other bikes.  I have my adjustable stem on that bike so if I want to make a tweak to fit, I can easy tweak it.
Title: Re: Calculating saddle & handlebar position.
Post by: Inbred on January 14, 2019, 09:11:29 PM
Thanks Mickeg.
How did you get to your basic starting positions?
Title: Re: Calculating saddle & handlebar position.
Post by: jags on January 14, 2019, 11:14:56 PM
there's no point in guessing get a pro fit done and be done with it ;)

Title: Re: Calculating saddle & handlebar position.
Post by: energyman on January 14, 2019, 11:35:03 PM
Trial & error, after a couple of years trying I have finally got it just right.  Thanks to Thorn comfort bars, adjustable stem thingy and a 35 saddle from my LBS and a tape measure.  All my bikes are identically set up.
Title: Re: Calculating saddle & handlebar position.
Post by: Inbred on January 14, 2019, 11:43:37 PM
I was really after finding out how people work this out.
Title: Re: Calculating saddle & handlebar position.
Post by: jags on January 15, 2019, 12:21:07 AM
when i got the probike fit done for both my bikes he changed saddle height/  tilt of saddle/ new stem/ new bars / shifted the cleats , basically everything different than i had them set up.

i can't ride my lovely bike now because of lower back pain, i done myself a lot of damage riding a bloody tandem that was way to big for me but being the gobshite i am i couldn't refuse the guy..

honestly get the bike fit done it takes about hour cost 100 quid or there abouts but you will ride in comfort.

Title: Re: Calculating saddle & handlebar position.
Post by: Andre Jute on January 15, 2019, 01:44:01 AM
All my bikes are set up the same to within one millimetre at the contact points of saddle, handgrips and pedals. No, the bike frames aren't precisely the same, but I've effectively made them the same by precise setup.

Before you even consider doing what I do, you should know I sit very upright, and I'm fanatical about ergonomic angles for knees, wrists and handgrips. I have no interest in deforming my body to cycle faster, so I don't use drops but North Road Bars, which are by far the most ergonomic bars you can get, regardless of the fact that some ergonomically wretched bars have "ergonomic" in their name. There's possibly a weight penalty to setting up the bike as a I do. My process works amazingly well on bikes from three manufacturers and of very different frame sizes though the angle-geometries are relatively close.

First of all, I set up the seat height so that the instep (not the ball of the foot as for proper athletic cycling) of my thick rubber-soled street shoes rest comfortably on the pedals with the knee just slightly crooked and the knee slightly in front of the instep-pedal position at the bottom of the stroke; if your legs are not the same length, you may have to compromise by setting seat height halfway between the correct positions for the two legs. The slightly bent knee at normal max stroke permits a modicum of extra power when necessary by very slightly going light over the saddle (rather than fully posting -- no daylight between my bum and the saddle will be visible). All this must be done with my back in the proper riding position, which is just slightly bent forward, say 15 degrees off the perfect vertical because perfectly vertical (right angles to the ground) would not only be uncomfortable and painful but could do your vertebrae permanent damage. Practically I start with the seat height right and the saddle tilted ever so slightly backwards or even perfectly horizontal. Then I slide the saddle forwards and backwards to position the knees over the pedals. There may need to be a further millimetre height adjustment of the seatpost to realign the knee over the instep if you're really finicky, and perhaps another millimetre of saddle adjustment as a consequence. When the adjustments are down to one millimetre, I generally call it near enough for my back.

So now two points are adjusted and I haven't yet added any weight to the bike, unless the frame is so undersize that an enormously long seatpost is required. The next step is trickier because we need to arrange two fixed points, the handgrips, in three dimensions with a given fixing point, the steering tube exposed length above the head tube, and available components, handlebars and stem, of fixed lengths and arcs.

Generally, since I sit so upright, the first three things I do is fit a long steering tube extender and fix it in the headset with a clamp lock of some kind (I use a seatpost clamp) so that it the bearings are correctly loaded without depending on the stem to hold everything together, stack spacers on top of that purely for cosmetic purposes, and fit an adjustable stem to the very top of the increased-length steering tube. Then I fit North Road bars, of which I have a selection with various rises though most often I use a cheap and common type Uno-Kalloy with a splay and downturn of the grips of which I approve. I rotate the whole handle bar inside the stem-clamp so the ends of the handlebar grips are about the level of the saddle nose or above it and fix it lightly in the handle-bar clamp of the stem. I loosen the stem's swivel clamp until it just holds the weight of the handlebar grip in place. Now I have a complete articulated steering assembly.

The next operation is to sit on the saddle in my preferred position with my feet on the pedals, and arrange the articulated steering assembly in three dimension to suit the length of my arms and the preferred angle of my wrists. Clearly everything must depend on one's reach with elbows slightly bent. So I grip the handlebars (which are fully assembled right down to the Brooks leather-ring grips I like, including controls and cables) which are splayed outwards at an angle that is natural to the tube through my fingers and thumbs enclosing the grips and turn the handlebars in the stem-clamp to point downwards at an angle that will straighten my wrists. I almost always use the Uno Kalloy 600-620mm wide North Road Bars, which make this process easy as the rise, grip splay and grip vertical angle are perfect for me. This usually brings the handlebar grips to above the saddle and quite a bit closer to the rider than is common today. It's a fair way from an old-fashioned gentleman's bicycling position, but it is equally far away from being on the drops too.

Troubleshooting. The entire handlebar pulls the adjustable stem in an arc, up and down, so there's usually no great problem caused by the desired ergonomic arrangement in three dimensions of control radius (arm length), straight wrists, and handhold splay and downturn. But if you can't satisfy all three at once, the first thing to look at is the position of the stem on the steering tube (or extension): you could move the stem down or get a longer steering tube extension (not so easy if you've already fitted the longest available). The next thing is to get a longer or shorter adjustable stem, but generally it shouldn't be necessary to go this far. Or you could get a handlebar with a different rise, but most of the ones available bring different geometric problems with them, and only the Uno-Kalloy comes with adequate length of handgrips: they're intended for you to saw bits off, but I have wide shoulders, plus a lot of controls I need under my thumb.

Now you can substitute a fixed stem of the correct length and angle, if you can find one, for the adjustable stem. I don't bother because the adjustable stem permanently on the bike allows me to make further adjustments as time goes by, and I am compulsive about forearm ergonomics because a writer is a sort of manual worker who operates a keyboard.

The key to giving yourself a proper bike fit -- rather than something some fellow thinks will suit a much more powerful athlete -- is the adjustable stem. You can do it with a solid stem, as when I fitted a non-adjustable n'lock, with the further complication of being closed on top so it has to fit at the very top of the steering tube, by having the correct length of steering extension tube, but it's a tricky conceptual and arithmetical problem not recommended for newbies, unless they actually like frustration.

It gets easier every time you do it, until I can now do it in less time than it takes to read this description of what I do.
Title: Re: Calculating saddle & handlebar position.
Post by: jags on January 15, 2019, 01:56:35 AM
Thats what you call a reply,take me a week to type that mind you I haven't t he brains for such a reply. :'(
Title: Re: Calculating saddle & handlebar position.
Post by: mickeg on January 15, 2019, 02:11:11 AM
Thanks Mickeg.
How did you get to your basic starting positions?

Trial and error about 50 years ago.

Saddle height is pretty easy, put your heel on the pedal with your leg straight and set your saddle at that height being careful that you are not leaning one way or the other, pedal at the bottom of the pedal stroke.  That gets you in the ball park for starting position.  Pain in front of knee, saddle too low and pain in back of knee, saddle too high.

I recall seeing something about KOPS for fitting, but I do not recall what it said.  Perhaps an internet search? 

One other thing - saddle shape varies for how much lean you have.  I find that a B17 works well for me in a fairly upright position but if I am using the drops it is too wide and too flat.  Thus I use a Brooks Pro or Conquest on my bikes with drop bars.

Saddle can be more forward if you are riding more aggressively.  I was at my nieces house for christmas and I asked her how she could ride her bike that way, the seatpost was turned backwards, the saddle clamp was in front of the seat tube axis, not behind.  She said she had forgotten all about that, they set up the saddle much further forward when she had time trial (or triathalon) handle bars on her bike a few years ago but now she should put the saddle back in the position where it belonged.
Title: Re: Calculating saddle & handlebar position.
Post by: Andre Jute on January 15, 2019, 07:09:50 AM
Thats what you call a reply,take me a week to type that mind you I haven't t he brains for such a reply. :'(

You're far to humble, Anto. All it comes down to is:

1. Start where you have already reached, with a sitting angle at which your back is comfortable.. You can't start anywhere else, anyhow, as we used to say Down Under.

2. Move the seat tube up and down and the saddle back and forth until your knees are slightly bent at the bottom of the stroke and just in front of the pedals.

3. Put two hinges in your stem, one near the headset, one by loosening the handlebar clamp.

4. Slide the stem up and down the steering tube and swivel the handlebars on the hinges described in 3 above until your arms, wrists and hands are as comfortable as your back.

5. Torque everything up and ride in comfort.

It's not rocket science. Ha! It took me only about thirty years to work out...
Title: Re: Calculating saddle & handlebar position.
Post by: B cereus on January 15, 2019, 07:53:59 AM
The most critical adjustment, and probably the easiest to get correct, is the saddle height. The well known advice here is to have the leg with a slight bend at the knee with the pedal at the bottom of the pedal stroke. There are various ways to achieve this and they will all get the saddle height close to optimum. Having the leg fully straightened with the heel on the pedal is probably as good a method as any other.

Saddle setback is a much more controversial subject and is probably least suited to the application of rules or formulae. Much depends on style of riding and the proportions and flexibility of the individual. Moving the saddle fore or aft primarily effects weigh distribution, in other words the percentage of weight on the front and rear wheels. It importantly also effects how much weight is on the hands. The further aft the saddle the less weight will be on the hands and the more will be taken by the saddle. The other way of relieving weight on the hands is to pedal harder, when more weight will be reacted through the pedals. If you habitually pedal hard with a stretched position and the bars significantly below the saddle, then a forward saddle position will suit you and will have the additional advantage of opening out the angle of the bend in your trunk and alleviating the sensation of the knees colliding with your chest. If on the other hand you pedal less vigourously, as many cycletourists do, you will probably be more comfortable with the saddle pushed rearwards, and with the bars a little closer and level with or a little higher than the saddle.