This is my 19” Kona Lava Dome I got 2nd hand and fairly beat up, I’ve swapped the generic gym bike style saddle for a spare Bontrager road saddle I had lying around, but it feels as though I can’t get it far back enough. My knees seem to be too far forward ahead of my toes. Am I just too used to road bikes or am I missing something I can change? My road saddles tend to be about halfway along the rails, and I ride 56’s.
It also has a 90mm stem I’m tempted to swap for something like a 50/60
That is a slammed back position with a setback seatpost and rail position.
Can you measure the setback to your saddle with normal fit measurements and compare between both bikes?
You sure the bike is the right size for you? Seems unlikely that you can’t get the saddle far enough back relative to the BB, so I would guess the issue is more likely to be distance from saddle to bars isn’t long enough and that’s what’s making you feel like you need to get further back.
In which case swapping in a shorter stem will make things worse.
I agree with longer stem, what length do you run on your 56 roadie? Also how tall are you? You might just need to size up on mtb. I ride a size or 2 down on road bikes compared to my mtb size.
Looks like the bike might be a bit small! But it seems huuuuge 
think I have 100mm on my road bike stems, I have the measurements of a fit written down somewhere to I’ll look at that thanks.
Stop being such a roadie eh.
How tall are you?
Frame sizing generally isn’t going to have that much of an effect of this specific aspect of bike fit.
Knee position relative to the BB is largely dictated by seat tube angle, which doesn’t change a whole lot between two adjacent sizes, if at all. Seat post extension has an effect, but of course that’s easily adjustable.
Crank length has an effect, but again you won’t see much if any difference between two adjacent sizes.
Cleat position can have an effect, but you’re using flat pedals.
If you’re feeling “cramped”, raise the seatpost by 5mm and see what happens. The effect of having a saddle further back is mostly going to help you push the cranks over the top of the pedal stroke (12 o’clock).
The pedals are flat one side for my commute with spds on the other. I haven’t used he spd side much so perhaps it’s a case of getting used to it and experimenting
6 foot
My cleats are slammed all the way back on all of my pedals. As a result, I like having my saddle pretty far forward. On the road bike, this helps with my aero position, and on an MTB, this helps keep my weight forward on steep climbs.
I have this problem on all of my bikes and had to swap out the specialized Roubaix bendy seatpost for a normal one.
I have short legs relative to my body which is my main problem.
I find that the newer MTB’s with the longer reach are better…older ones like your Kona have steeper geometry and less reach.
At that height, even by 1990’s standards with long stems, you should be on a large size MTB, which would have been a 19" to 21" sized bike back in the day (seat tube measurement).
These day’s you would most certainly be on something with a reach around 460-470mm.
Geo between road and MTB is not comparable as the bikes are too different these days, eg my TCR has a reach of 400mm (and feels good with a 80mm stem)…my smallest MTB reach is 430mm (which feels small), and the average of my other 4 bikes is 455mm (which feels perfect) with 40mm and 50mm stems.
I am 5’10" / 178cm.
If you feel scrunched up on the Kona, and you’re thinking of a longer stem to compensate, then I hope you have a good dentist as s/he might be needed from all the OTB’s you might experience!
I would agree with most of the above people that the frame is just too small for you.
The other thing to take note of in MTB fit, is that the key is to be sitting more central to the bike than what you do on the road. This is for when you are standing and moving around, which you will do well over 50% of the time (or you should be if you’re riding anything above a beginners trail or a fire road).
Just take it as a sign that you need a new bike…the universe has a way of telling you these things… 
As a roadie turned MTB’er I’ve learned that positioning on a MTB is a very different thing. I support @handynzl opinion, but I want to add an another factor. On a MTB you want to get back behind the saddle under some circumstances. If the saddle is to far back this can be difficult, not to mention getting back up.
Also since the speed during mountain biking usually is comparably lower, a more upright position won’t be much of a problem, bike separation is of greater importance. I guess that is why dropper-posts are so popular.
I race XCO and I sit 95% of the time because it’s generally more efficient. I don’t agree outside of descending.
Your particular bike has a fairly similar seat tube angle as compared to a road bike, so you should be able to get the two fairly close.
Given that I would go ahead and measure the saddle setback from the bottom bracket for this mountain bike as compared to your road bike and then set them identically. Given that this is a hardtail, that should be fairly straight forwards to accomplish.
After you get the setback dialed, then fine tune your stem length independently of your saddle position. You really shouldn’t be compensating at all for the saddle position by modifying stem length.
If you feel cramped, one thing you could also try is flipping and slamming that stem as that will effectively make the bars farther away from you.
Once you determine that none of that is working for you, rest assured that you got a hot deal on this bike and can make do with the poor fit while you save up for a bike more suited to your own personal dimensions.
At the end of the day, I find mountain bike sizing to be a bit of a dark art as compared to road bike sizing and there’s really no “right” answer. All one has to do is look at bike checks for various pros to see how different everyones setups are. Even online, you’ll read general advise, but it never references what type of riding is happening. There’s huge differences in the way a XC bike is setup as compared to a Enduro or even Trail bike gets setup.
I have had a road bike fit and saddle set up for the tip 6.5cm behind BB (Selle San Marco Shortfit). 70cm saddle hight.
On my MTB I can only get the same saddle 4cm behind the BB fully setback with an inline dropper post. If I had it in the centre of the rails it would be about 2cm. Should I be concerned with this or is this common? I do not feel as though I am as efficient on the MTB and wondered if setback could be the reason.
TL;DR I fully expect that modern road and MTB fit will NOT match in many cases.
With the change in MTB geometry in the last decade (particularly in the last 5 years), these bikes have steeper seat tube angles than in the past. Much of this is a change as a result of dropper posts gaining wider acceptance and use, coupled with improved geo that makes MTB more stable and capable.
MTB’s of old shared lots of geo cues with road bikes, and in those cases, matching a roadie fit setup on the MTB might have made sense. But with the changes above, and considering the very different pattern of use on MTB, having a unique fit setup seems more than practical to me.
It might be nice to cut and paste the fits in a simple sense, but I don’t think the two really have much to do with each other. Bike pitch changes quicker and more drastically on the MTB for one thing. Add in the more frequent transitions between seated and standing riding and you really get a different demand on the rider. Handling in various terrains also plays a huge part.
Cheers chad, really useful information. I guess it is more about playing about with fit and seeing what works rather than going off the road measurements.
Out on the trails I do not notice it too much but the 30-45 minutes on the road to get there or steadier climbs it does seem harder to get the power down or hold a certain wattage i.e holding zone 2 on the road sections feels like more of an effort where on the road bike you can turn the pedals without thinking too much about it.
I just thought matching the setback/height would get me in the ballpark for steadier efforts but as you say the geometry of modern XC bikes doesn’t allow it.