I regularly suffer from numb hands on longer bike rides. The tingling sensation occurs from the wrist forwards and is sometimes so bad that I have to reach across with my ‘other’ hand to change gear. Obviously this is dangerous as leaving a numb hand just resting on the bars is a never a good thing, very much like trying to stand on a dead leg.
The Ergon oversize grips are anatomical in shape and feel very comfortable in the hand. Initial impressions were good, no loss of feel in the fingers at all ( I always ride in full finger 661 gloves, which are lightly padded)
Over a few rides the conclusions I have come to are a bit ‘curates egg’ i.e. good in parts. By being of a larger diameter they make it less comfortable to hold the grips tightly. It’s hard to get your fingers around the grips with your outside 3 digits. This makes pulling on the bars harder work, so lifting the front wheel to clear logs etc is harder. However by not gripping the bars so tightly I think that blood flow is increased to the fingers, thus stopping numbness setting in.
I found on a 45 km fast paced ride last weekend I could ‘mimic’ the hand that didn’t have the Ergon grip by opening my fingers to rest on the brake lever / resevoir, leaving the thumb to do more of the control on the bars. I compared a Race Face Lock-on grip with an Ergon, over 3hours on the bike.
Control in technical sections is decreased, but at least you can feel what your fingers are doing.
I think its like trying to grip a large diameter pipe, rather than a small one, the more you can wrap your fingers around the greater the purchase, which will affect the blood flow. The larger pipe is harder to hold, but blood flow is increased.
The answer seems to be if you suffer from numb hands adjust your hands on the bars to a more open posture, covering the levers, whenever possible on climbs or fireroads then revert back to ‘death grip’ when riding fast downhill or single-track sections