[Closed] Bike fit issues on one mountain bike but OK on the other

saddle height and set back are the normal culprits for knee pains.
height is easy with a tape measure, but you'll need a level
surface and a plumb bob to check and the setback.

Look up reach and stack and how to measure, see if any differance there. Also pick a point hip, knee and ankle when on the bike (need someone else for this) and try and check relative angles against each bike when on them.
Could be something as simple as seat tube angle putting you more toward or back from the bb. Check where the front of the knee is in relation the the pedal spindle. Loads on the web re what to look for here.
Hope helps.

Regardless of bike geometry/stack or reach which are probably super important for how the bike rides for bike fit(from a pain point of view) the three contact points need to be in the same place ie.saddle/bars and pedals.If you have a bike fit it is normally on a jig and not a bike.With MTB's other variables are bar width and crank length which could create a problem.As therevokid said make sure your saddle height is the same/the distance from the nose of the saddle behind the bottom bracket and from the nose of the saddle to the bars plus the difference in height between the top of the saddle and the top of the bars.The last thing is the q factor of the cranks but less important IMO

Thanks for the information so far. I've managed to get the sadal heights the same & the distance between the sadal and the stem the same. I think I've got the nose of the saddle behind the bottom bracket the same as far as I can tell (not an easy one to measure). The fit still doesn't feel great though.
As far as I can tell the only difference now is that the stems are very different. On the Spec camber the stem is short & raised to give a more up right position, on the Spec Crave its longer and not raised, giving more of a stretched out position. Obviously this changes the handlebar position and height. Would this make a difference in relation to knee/leg pain ?

Obviously this changes the handlebar position and height. Would this make a difference in relation to knee/leg pain ?

Can do, as if I am understanding you correctly, you've got the same horizontal distance between saddle and stem on both bikes but the bars are much lower on the Crave?

the distance between the sadal and the stem the same

This needs clarifying through, do you mean distance from saddle to [b]stem [/b]or saddle to [b]bar[/b]?

Obviously if you've measure saddle to stem then the length of the stem is relevant too as you'll be stretching to reach the bars with a longer stem and that's not the same fit at all!

Likewise if the bars are a lot lower, if that's the case then you're asking your body, and hips especially, to work at a much more acute angle to the other bike, and hip angle can be critical to comfort and efficiency on the bike, being tighter there can have knock-on effects elsewhere like knees legs as the muscles are all working under different degrees of tension.

Can do, as if I am understanding you correctly, you've got the same horizontal distance between saddle and stem on both bikes but the bars are much lower on the Crave?

Yes this is exactly right. Previously I only assumed leg/knee issues were related to the saddle in relation to the pedals.
Now that I've found that the position of the sadal in relation to the handlebars could also cause issues I'm going to try and get that sorted by getting the same stem.

try and get that sorted by getting the same stem

Make sure you look at the bigger picture, just buying [i]exactly[/i] the same stem may not get you in the same position due to top tube length, stack heigh, headtube length, head angle etc.

Drastically changing the stem length can also affect handling (along with bar width) so just be ready to experiment!

Getting the [i]exact [/i]same position may not be necessary as differnet bikes often get ridden in different ways; more standing on HT, more sitting on FS, or just a different way of weighting the bike or used on different terrain so it is normal to have [i]some [/i]difference between bikes used for different things, but extreme changes can cause discomfort and some people are more sensitive to different aspects of fit.

Take a photo (using a tripod) of both from the side, it may be really obvious.

Do some stretching.

I've managed to get the sadal heights the same

with sag?

with sag?

saddle hight (from BB to top of saddle) will not change with sag*.

If OP is measuring from floor then that's a damn silly way to do it anyway due to variance in BB heights/tyres sizes etc.

* unless you have a URT or other design where the BB moves with the suspension (i-Drive, Maverick etc.) which his bike does not.

The stretching advice does have a lot of merit, it makes a huge differance in the ability to cope with differant positions.