Like many (it would seem) my front squat technique is much better than my back squat technique, even when the weight for the front squat is heavier than the back squat. In particular, my knee - toe tracking is really good on the front squat without even trying that hard. Yet with the back squat I put in as much effort as I can to keep the knees tracking the toes, but they still cave in!
Any advice is much appreciated
First question: what shoes are you wearing?
Could it be that your posterior chain is weak compared to your quads? So when you do a back squat, your knees come in to allow your quads to take up the slack from your weak link.
Posterior chain weakness is definetly a possibility, and I am working hard to fix that with lots of assistance work, so we’ll see if that makes a difference.
Shoes - the problem occurs when I do it bare footed, in trainers, and when I wear Olympic lifting shoes (Adidas).
Are you actively pushing the knees out when you go down? My experience with front squats is that this happens more natural than with back squats.
It could also be that you try to stay to much upright with your torso, this limits the amount of tension you can get in your legs (in a low bar squat) so that you can not keep your knees out. When you have this tension right you can also feel that you are pushing your feet out against the floor which helps to keep your knees out.
They’re two different movements. Keep working the form on the back squat.
I do push my knees out on the front squat and knee tracking is fine. On the back squat I put in as much effort as possible to push them out, but they still cave in.
im still doing both exercises tom63, but thanks for the advice 
[quote]tom63 wrote:
They’re two different movements. [/quote]
Absolutely.
Try to push out your knees on the ascent and the descent, also be aware of the position your feet are in… You can check the video below or PM me and i can help you there…
Do band hip abductions.