Is the plumb line from knee down to pedal axle still a valid thing on MTB?
Just checking on my t130 and was 1.5-2″ out from that with seat too far back based upon it.

It was never a valid thing.

It is a good starting point as are the seat height calculations but only needs a ride around the block to see if it actually feels right and adjust from there.

It was never a valid thing

Elaborate, plenty of websites would disagree, hence my question.

If it’s not, then what is?

How long have you been riding a mountain bike? Do you really need some imaginary formula to set up your own bike for your own comfort?

How long have you been riding a mountain bike? Do you really need some imaginary formula to set up your own bike for your own comfort

Many years. I’ve been having knee issues and calf issues so reading up more.

Why are we being arseholes over a simple question?

If it can stop being a valid thing, it never was a valid thing. Seat tube angles have gotten a lot steeper over the last few years, which means that riders are sitting much further forward, which means it’s not longer a valid thing, which means it was never a valid thing.

I don’t see how it can be more than a general starting point, length of back and appendages must have a greater effect.
OP, is it just old age creeping in? Perhaps less mashing up hill and smashing the gnar on the way down?
Does your stem length affect the angle you sit at? I found a shorter stem on one bike helped reduce soreness in the front of my knees when climbing.

Why are we being arseholes over a simple question?

Sunday afternoon, nothing else to do?

OK, the simple answer is No.

From my own recent knee issues, I found it more important to have approx 30 degree leg bend between hip/knee/ankle at bottom of pedal stroke. 10mm of saddle height will change this angle by approx 10degrees.

Currently have knee above pedal axle on Wazoo, above Crank end on road bike, 175mm and 172.5mm cranks respectively.

This is KOPS, it’s always been a good starting point, but it’s always only ever been a rule of thumb that seems to work reasonably well.

As with most of the old road-derived rules of thumb, it’s becoming less relevant the further MTB geo separates from Road, and there’s the argument about how you plan to be positioned on the bike also. Rear suspension is going to play hell with it too.

Just as with getting the saddle around the top of my hip bone, I’d probably use it when first setting a bike up and then see where things ended up after a ride or two. Everyone is likely to have a different view though…

You shouldn’t be rocking your pelvis at full stroke (saddle too high).

But also you should be able to almost extend your leg at the bottom of the stroke, but not quite.

That’s the most efficient pedal position.

I guess that’s more for road racing though! Mtb may be different as a high saddle will get in the way.

After years of plumb-lining I now shove my MTB  saddle as far forward as it will go.

Makes a massive difference to my climbing.

All those wasted decades!

It’s a start point and not much more. Remember it’s also a start point from the perspective of a road bike with a 73 degree seat angle.
No harm trying it but don’t expect it to solve all issues.
Have a look here for more details.
https://bikedynamics.co.uk/achesandpains.htm#1

Thanks fellas

“Is the plumb line from knee down to pedal axle still a valid thing on MTB?”

It can’t be because the seat angles on MTBs have changed hugely in recent years. It was either valid then but not now or vice versa or it was always irrelevant.

KOPS worked for average proportion riders on square geometry road bikes. It seems to be an effect of other things rather than the cause of good fit. Won’t work so well or even be possible on a bike with 76 STA and an inline dropper post. But the reason it was about right for road bikes (general balance over the bb) is partly why steeper seat angles plus inline posts can be a problem for mountain bikers who ride along as well as winch/plummet, or ride longer distances, as it can put more weight forward than is ideal. Like all these new geo things there’s no all-win for all. Some might not be bothered by that 50mm shift forward, others are.

Some where there is a famous article debunking the one y over spindle thing.

I can’t say I found the article a.y more convincing than the theory on the first place

My knee problem check list would be in no particular order

1. Seat high enough

2. Nothing bent or twisted. Cranks or pedals

3. Hamstrings not too tight (stretch)

4. Cleats (where applicable) not aligned correctly

5. Q factor. Most find feet closer is better. I’m not sure I could ride a fat bike

6. For role. Needs professional help

I’ve had 1-5 create/solve a knee problem

I had terrible knee problems and then by rushing a new shoe on rode with cleats way back nearer heal than toe. Solved all pain.

Flat pedals or cliped in?

I find I have to be really precise with my cleat placement if cliping in to avoid knee issues. Alsosaddle too low causes issues. Not relevant during DH runs but when doing more pedaling style riding.

“5. Q factor. Most find feet closer is better.”

Q factor should scale with hip width and also depends upon joint geometry. I prefer ebike width over MTB and to road bike by far!

Yes.

Further back for epics and touring, further forward for fun and shorter rides.

But basically, yes. It just seems to work.

Don’t forget to change height to compensate.

Would you ever want the knee to be behind the pedal spindle, with the foot reaching for the pedal?

Would you ever want the knee to be behind the pedal spindle, with the foot reaching for the pedal?

Why not? You push a lever around the BB axle and get effective power out for 90 degrees or so from each leg. It doesn’t really matter where that 90 degrees is in relation to the vertical or horizontal as long as you’re in a good position to apply it.

It doesn’t really matter where that 90 degrees is in relation to the vertical or horizontal as long as you’re in a good position to apply it.

It’s much easier to apply it from above than from behind, especially on long climbs. If you try riding an old school DH bike uphill, you’ll find you spend half your strength pulling yourself forward so you don’t fall off the back of the saddle.

recumbents?

Did 30km locally this morning and felt fine. Never actually noticed after about the first 2 minutes. Time will tell how all of this works out with saddle height and position.

Flats only here, fiveten

Search for Keith bontrager and Sheldon brown and the myth of KOPS

^ True on the old bikes uphill, the Marzocchi ETA lock-down forks were brilliant for climbing on them, had the effect of an adjustable +3 degrees STA. Some of it’s being in balance on the bike and some of it’s pedalling efficiency for the individual. I tend to be able to push a bigger gear more easily when pushing down and slightly forward than down only, or can spin a gear more easily when sat on top of it. Power is just work done over time and some spin, some mash. The 10-15 degree change in all that from riding on the flat to going uphill is what makes it tricky to get right in all situations, a long time since I read the Keith Bontrager article but that was the gist of it.

A lot of this is why I prefer saddles that let you move fore-aft easily, less reason to worry about a degree or so on the STA when you can move more than that in comfort.

recumbents?

They have the huge advantage of bracing your back against the seat so you can push the crank at that angle, but yes.

Ongoing question then.

Still been having a few minor knee niggles. Today I did 55km in the slip on the t130. No knee issues afterwards.

So I checked saddle height and nose position.

Parkwood was 2cm higher than t130.
But also the nose on the saddle of the Parkwood was 2.5cm further back than on the t130.

So the question is. Do you set the saddle in relation to the cranks even on different angle seat tubes?

“Do you set the saddle in relation to the cranks even on different angle seat tubes?”

In simple BB to saddle distance yes but the angles (or horizontal offset) have to change.

I generally set up seat height and fore/aft to what I think is right then tweak it over a few rides until it feels natural. After around 5 or ten rides of little changes the middle of the saddle on 3 bikes is within 3mm over all bikes – just by feel

All measured from the centre of the bottom bracket so seat tube angle doesn’t really matter and ultimately my knees end up where ever they end up – once cleat position is sorted.

All bikes have 170mm cranks and the same pedals, so they remain constant.

I used to set up my mountain bike this way and still do my road bike. Now I have realised where I live (NE Scotland) most of my pedalling is done uphill, so to get the same position over the pedals, the saddle needs to be further forward. I basically just have the saddle as far forward as it goes, climbing is easier, I’m off the saddle on the descents and I just accept I’m a bit too far forward on the flatter parts of the ride.

Depends on whether you are an up and down pedalled i.e quad dominant or like I am more of a push over the top and down pedaller using more of your hamstrings. Further back your saddle is seems to help with the push over the top type pedalling.

I’m the latter due to various bio-mechanical issues including two bulging discs, but I definitely more of. a deadlifted in the gym than a squatte, though that might be due to my separated shoulder due to OTBs and weight of the bar on my shoulders is painful.

Depends on STA and steepness of climbs
Forward enough that front wheel is weighted going up should be the criterion
Mtb fit is determined by the bike
Road bike fit ( ideally) is dictated by the body