Long time ago I had a wrist injury. Just trying to find something that will help a little.
Bike is a Giant TCR. Fit is really good. I played with tire pressure, bar angle and have
the stem up. Numbness starts around 35 mile mark. Would like to get another 10-15
miles before this happens.
Would changing the stem length help?
How does going 10mm longer or shorter change things?
Thanks

1. Shorter stem and corresponding increase of saddle setback to reduce weight on your hands.
2. Increase bar drop. Consider drastically lowering the bars. The lower you go the shorter the stem has to be to maintain the same reach. Use an online reach calculator. It's counter-intuitive but increasing bar drop can reduce weight on your hands by shifting more weight into your body core, spine, and legs.
3. Consider the possibility you're developing peripheral neuropathy as a pre-diabetic condition. Half the population is prediabetic, but fortunately it's easily reversible by changing to a low-carb diet. Symptoms of prediabetes and "metabolic syndrome" include hindered circulation in your legs and hands, feelings of coldness, numbness, feeling exhausted after eating meals especially a mid-afternoon crash, frequent urination, and weight gain. If these symptoms apply google metabolic syndrome and low-carb diet. Nip diabetes in the bud before it destroys you. It's easy to reverse.
4. It's also possible your stem is too short and inadequate reach causes back-pressure against your hands cutting off circulation, but that's a fairly obvious situation.

Thanks.
I found a thread with the info I was looking for.

What thread was that (a link might help people who come after you, since this comes up every so often)?

Also, mild carpal tunnel syndrome is a possibility. That's based on my being diagnosed with moderate CTS with numbness after 10-15 miles.

Numb Hands

You might also check the positioning of your brifters, yo see if you are "breaking" your wrists. Do you arms flow naturally from your shoulders to the bars?
Padded gloves and/or padding under your bar tape can help.
Carbon handlebars can reduce harshness if your roads are not the best.
Practice frequently moving your hands to different positions. Top of bars to brifters to drops.
Try flexing your hands frequently.
Do you unconsciously have a tight "death grip" on the bars?

I went into my LBS this year and finally had them do a basic fit for me. The resulting fit is much better, and numbness is much less. It was a very worthwhile $40 exense.

I have no idea if this helps: A downward tilted seat of 6mm/ 1/4", or more is a real hand killer.