As above, I have a theory about lack of wind resistance I developed years ago.
When you have a bike that is perfectly comfortable outside, and then leads to problems when ridden inside, I feel it is important to look at what is different. When you do, there are two key differences.
- Lack of wind resistance on the body riding inside. That is a difference that I find because you end up with slightly more weight on the hands and arms, because you don’t have the wind pushing your upper body back.
- To compensate for that, I recommend that people raise the front axle about 1"-2" [25mm-50mm] higher than the rear axle. This shifts the weight slightly back onto the saddle and off the hands and arms.
Additionally, that leads into my typical rocker plate discussion, but will leave that out other than to mention the typical inside riding practice. Most people tend to “lock in” when they get on a trainer inside. They don’t stand or move around on the bike nearly as often as they might when riding outside. This includes hand positions on the bars. We might end up staying in a single position far longer than we do outside.
So, make sure to be “active” and make a variety of position changes (body and hands) to alter the loading on your body. Most of what you describe sounds like a blood flow restriction (numb and cold) which means you are likely pinching the flow of in your hand. Move around and get the weight off the hands (via higher front axle compared to rear) and see how that works.