Can I put insoles in my cycling shoes?

If you wear spin shoes then you can certainly add insoles to them. Due to biking on different surfaces, your feet take stresses consistently through uneven areas, so injuries could happen. But after adding insoles in your spin shoes, it should give you better balance and it might minimize the chances of any major or minor injuries.

Yes, you can. However, insert the insole towards the forefoot where the bodyweight concentrates. Alternatively, it could extend from the heel to just behind the toes (or be full length). It'll aid in effective pressure distribution in the foot. An example is the cycling metatarsal pad.

Yes, an insole will help spread the body weight over the entire surface area of the heel, making cycling shoes more comfortable. The best orthotics for cycling will provide support and cushioning for the feet even through bumpy rides. Upstep orthotics come highly recommended for use in this regard.