Witterings

Don't know if anyone can help with this and you know when you over think things you start questioning if you're actually working something out correctly or not.

If I have a 29er that theoretically my knee has been forward of the "perfect" knee over spindle position but I've always been comfortable with it ...

If I then buy a gravel bike, take a plumb line and drop it so it falls in the middle of the pedal spindle and measure the distance from that to the front edge of the saddle and the distance between the 2 is now 4cm less on the gravel bike .... is that going to put my knee even further forward than it was on the 29er ... I'm guessing it is but was wondering if one has drops if it'd make any difference and have been thinking about it to the extent I can't see the wood for the tress at the moment.

Also if I'm trying to set one up to feel similar to the other, is measuring from the nose of the saddle to the center of the bars a good way to do this so when you're on the flat's on the drop bars it's similar to the MTB but more aero if you go onto the hoods and more again in the drops or are there other things to take into consideration between the two .... interestingly if I measure the difference between the two there's 4.5cm which pretty much correlates to the difference in distance between the center of the spindle and the nose of the saddle.

Maelochs

Most important relationship is where you sit on the saddle (not the nose---every saddle is shaped differently) and the BB/spindle. I often use (as a starting point) the extension of the seat post up to the top of the saddle ... because as i note, the two saddles could be radically different in shape, and the nose of one might be two inches forward of where I normally sit to ride. And with noseless saddles .. ??

Everything, for me, is just a starting point ... or just the next step. Theoretically I could set up all my bikes with all the contact points and control surfaces in exactly thew same proportion, but in reality every bike is a little different--and I want it that way. I have a couple endurance-frame bikes---why would I set them up like my racer/climbing frame? Why buy different frames then?

And also, i have some bikes with 175 cranks and some with 170 .....

I start with about the same relationship between everything, and tweak as I go. And I do that only when analyzing geometry before buying.

Once i have the bike in my garage, i set it next to the washer/dryer with a footstool on the other side, so i have plenty of support and can get into a riding posture and even rotate the pedals. Then I see where i want to start .

i often get the seat right on, or withing a couple millimeters up.down-fore-aft right out of the box. The rest depends on the bike, its weight distribution and road feel and how I plan to ride it.

But it all starts with the saddle/BB relationship--or saddle/pedals, more accurately. For me.

Witterings

Maelochs,

Cheers for that and some really useful points ... I can't seem to work out at the moment though if having the saddle more forward or aft and which direction to try 1st ... although there are some limiting factors potentially.

They "measured me" before ordering the bike and then fitted a shorter stem before I picked it up ... the one comment I picked up on though (I'm guessing that was based on what they thought was the ideal KOPS) they weren't sure if they could get the saddle far enough back without a lay back seat post.

The one it comes with has none and the saddle is currently set in it's most rearward position combined with if I was to try and move the saddle forward I'd feel like I was really cramped into a ball which would exaggerating what it feels like at the moment and kind of the reason for posting the thread.

The bikes not far off due it's "New" service so I may raise my currents concerns as they're a very reputable LBS who do proper bike fits and maybe I've just ridden in a certain position for a while and anything else including the change to drops is a bit alien ... despite having clocked up about 300 miles since I've had the bike.

Maelochs

Try a plumb line from where you actually sit on your old bike---or wherever the extension of the seat tube hits the top of the saddle---and see how far forward the BB is from that. measure form where the seat tube hits the saddle to the pedal at longest extension---measure Something which shows where you sit on the bike relative to the BB ... and not some random part of the saddle.

Sounds like you need a set-back seat post.

Don't necessarily distrust your body and trust the "experts." Event he best "experts" were trained with certain assumptions about the "right:" way to fit a bike.

I have a tiny torso and long limbs, but a huge belly. A lot of people put me on a much longer frame than i prefer, and have me riding stretched and low and also in pain after an hour. They don't understand my limited shoulder flexibility, breathing issues, and odd proportions. They follow their charts and their education, but aren't any better than i when it comes to altering those charts and standards to fit a non-average body.

That is why I always start from sitting on the bike with my feet on the pedals. Screw KOPS---it is a guideline for starting, not a goal to be reached. I have NEVER used it.

KOPS is an easy way to get a general fit for most riders on most bikes---but if they have unusually proportioned limbs, it is meaningless. And even a person with an "average" build would need fine-tuning.

Start sitting on the seat and see where your feet fall. See how far back and how far above the BB the seat is on the bike you ride comfortably. I have used big sheets of cardboard )boxes from bike frames and wheels,) taped them to the bike, and traced. I have made giant right triangles out of cardboard to help me measure. Whatever it takes. Figure out the relationship in two dimensions (how far above and how far back) your ischeal loops are from the BB spindle when you sit comfortably on the bike that fits. That is probably about the relationship you will want with All your bikes.

Stem is the Last thing to look at. if you are sitting in the right place, you just lean forward and see where your hands comfortably and naturally fall and get the stem length and angle (and bar shape and size) to put your hand on the control surface where you prefer to ride.

No one can regularly and accurately decide who long a stem you need until they know where your hips should be ... measuring form the tip of the saddle is great,. so long as you always use exactly the same saddle, and so long as you have the same set-back on your seat posts, and so long as the head- and seat-tube angle is exactly the same on all your bikes. but those things are never the same.

Some folks just see numbers--"Oh, the top tube is 58 cm versus 57 cm, and the reach is 15 cm more than on his other bike, so lengthen the stem by X amount"---but the angle of the stem, the length and angle of the head tube, the length and angle of the seat tube ... those number matter, too. Top center of the saddle to top of the head tube is good to know--but you also want to know the drop. Top center of the saddle to the middle of the bars is useful, but again, what's the drop? What is the angle from horizontal of the line connecting the two? because if the drop is more, the angle is steeper, the line is longer ... and if the head tube angle is different between two frames adding a spacer has a slightly different effect on reach on each frame. If the seat tube angle differs, raising the seat also displaces it more or less for and aft.

A lot of people look at stack and reach and make up the difference with a longer or shorter stem ... but All numbers on a frame are relative.Everything moves in two planes when you change one dimension.

The things that don't change? Your legs, your hips, how flexible you are and how much you like to bend (and even those things can change as you ride more or less.) But at a given time, the Body is the constant. And for most bodies there is one relationship between BB and seat--not saddle, but Seat--where you actually Sit on the saddle---that gives the best compromise between comfort, power, aero, and avoiding potential injury. Get the seat/BB relationship right in two dimensions, and everything else is dictated by your body based on you sitting comfortably on the bike.

Well, that's how I do it, and the ways I learned to fit myself to my bikes. I may be totally wrong.

Still ... break out the big sheets of corrugated cardboard ans start tracing and measuring.

JohnDThompson 

KOPS is a starting point, not the ultimate goal. If you've found a position that works for you and isn't KOPS, more power to you.

Witterings

Got to actually measure as suggested and the difference is pretty much the same about 4cm so kind of backs up the need for a lay back seatpost ..... coincidentally the 29er has a lay back post which is about 4cm and the same size so an easy option is just swap them for a bit and see how it feels.

That said I spoke with the LBS today and they were just bring it in with measurements from the 29er ... I asked if it'd be beneficial to bring the 29er with me and they said even better still and they've put a lay back post to the side as well so going to take it down there tomorrow.

Thanks again for all the input is much appreciated!!

12boy

I have often wondered about the relationship between knee stress, power delivery and fore and aft saddle position relative to the bottom bracket. On my Brompton I am way back and on other bikes further forward. No pain with any of them, although I do set up saddle height so my heel barely reaches the pedal at max extension. Anyone understand the relationship between those 3 things?

Maelochs

Sounds like a proper shop. Good for you and them.

Witterings

Must admit they're a really good shop which is probably one of the reasons I bought the bike from ... got lucky with that find but they are about 45 mins drive each way.

@12boy .... don't understand the relationship between them but at the beginning of the summer I put my saddle up to pretty much about the same height as you describe, I'd only moved it about 5 mm from comfortably having my heel on the pedal to a bit of a stretch and thought I'd absolutely destroyed my knees.
Pretty quickly worked out what it was which coincided with a weeks holiday when they settled down, put my saddle back down and no more problems in the knee department.

Funny how each of us is different although it could also bear some relation to how fore / aft our saddle is.

bruce19

This.

Maelochs

Knee pain, as far as i understand it, is generally hyperextension or insufficient extension. Straighten the leg too far, it hurts a lot and lasts for a week. But if you push too hard without straightening the leg enough, you are using too much power inefficiently and are likely to strain the muscles trying to go faster than the inefficient leg geometry allows.

For and aft brings different muscles into play---triathletes tend to be pretty vertical, I hear, because ti gets the back of the leg involved more so they have more leg left for running, and time trialers tend to be pretty far forward to get a lot of weight on the pedals---but they only ride for an hour in that position.

For general riding, everyone has a best compromise. Sit back more, put more weight on the saddle, your buttocks will tire but your legs will last. Sit on the nose, the legs will tire sooner. We all find the balance---and it changes as our bodies change, through a season or through the seasons.

Also ... if a person doesn't ride to fatigue limits---if a person just rides around---a wide range of set-ups will work. it is when you have to ride out toward the edges of your personal envelope, either in speed or distance, that you start to feel where things aren't quite right. Then it is a matter of tiny changes---five millimeters is a lot---until either you feel right, or your body progresses to a new level of performance and you keep adjusting.

Witterings

Just been back into the shop and they re-iterated exactly this and saying their pre-purchase sizing is just to make sure they get the right size bike and to give a starting point for set up from which to "tweak" as necessary.

What a great place as well, they let me choose if I wanted different tyres than came with the bike when I bought it and changed the stem with no extra charge, he's just re-measured and compared it to my MTB and agreed the seat could go back so has given me a lay back seat post as well as the old one in case I don't like the new position and wanted to revert.
H felt he wanted to give me a riser stem as well but he'd only make one change at a time and said to go and try it for a couple of weeks and then go back and they'd swap the stem as well if the new saddle position felt better..

Seriously what a brilliant place, highly professional and with excellent customer service above and beyond ... if anyone's UK based and is thinking of buying a bike and isn't miles away it's Owens Cycles in Petersfield although I think they have a branch in Four Marks as well.

Kapusta

DaveSSS 

If you want to know the position of the knee relative to the pedal, put the bike on a level floor and use a plumb bob to take a measurement. Don't rely on measurements from the saddle nose to the BB, unless both bikes have the same saddle. I'd never ride with the knee ahead of pedal. Further back usually works to reduce the weight on your hands and better recruits the hamstrings and glutes.

Pay attention to the seat tube angle on your bikes - that alone tells you if the saddle will need to be positioned further forward or backward to achieve the same position on a different bike.

ddub

Maelochs is spot on. In essence the best fitter is the one riding the bike. A professional fitter can get you very close in one session but ultimately you will find your sweet spot if you put enough time in the saddle. Don't be afraid to do a little adjustment if you can't get comfortable.