I was training for a century and crashed and broke my right wrist quite badly. I really want to do the century and my doctor said I can start riding again in a few weeks but only if I put zero pressure on my wrist.

I have a road bike and a gravel bike. The road bike is obviously quite bent over and puts a lot of weight on my wrists. It also has those fancy brake/shifter combos where you press to the left to shift and pull in to brake. My gravel bike is more upright and might be easier to modify. It has regular brakes and twisting shifters in the handlebars.

Can I modify either of these bikes so I can resume training for my century?

Yes, buy a recumbent

That's quite a bit more money than I have....

There are lots of extreme stems that raise the bars quite a bit, but I can’t think of any stem and bar combo that’s going to put you upright enough to keep all pressure off your hands and wrists. Maybe just wait out the recovery period.

Your gravel bike sounds like it might be a more practical choice for this. What kind of bike is it? If it uses a 1" threaded fork, Soma makes a really tall threadless adapter. If it is threadless, there are steerer tube extenders that can help raise the stem, but are not suitable for rougher riding. Buying a new fork with an uncut threadless steerer tube can get a quite a bit of height on some bikes, though if you do get something that adds a lot of height, a steel steerer tube is likely safe, an aluminum steerer tube is less likely to be safe depending on how hard you ride it, and adding a bunch of height with a carbon steerer tube will likely end in disaster.

Nitto Bosco bars make a bike considerably more upright and are relatively narrow. Beach Cruiser handlebars also give a lot of height, and tend to be quite wide.

Once you have the parts installed, I would plan on having to replace all of your cables, housing, brake hose, etc before it is ready to ride. With a bike that is considerably more upright, you might find that you need a different saddle or a suspension seatpost to comfortably ride longer distances.

I would be concerned about twist grip shifters will actually be pain free and allow for the sopport you need for healing of bones and of related soft tissues. I had a Colles fracture about 10 years ago, and surgery was done to connect all the bits back together. Riding was restored, but while the bones were healed to full strength after a few weeks, but occupational therapy to restore strength and flexibility. Twisting the wrist involves a lot of little pieces being in place and moving correctly. Total recovery was about 3 months.

It helped that my bikes, while using drop bars, use Ergopowers rather than
any twisting controls. I managed hand pressure by positioning the saddle
fore and aft

Nerve damage in my left hand left some of those muscles atrophied, to the point where using the left Shimano trigger shifter on my flat-bar commuter bike was almost impossible, especially in cold weather. I replaced the trigger shifters with a set of Grip Shifts. Problem solved.

Operating a decent pair of Grip Shifts (i.e., models selling for $30 or more) imposes no more strain on the hands than twisting the top off a new jar of peanut butter. My only regret was not having made the switch much earlier.

time trial (TT) bar add-ons might work well....they shift the load to your forearms.

How about joining a gym, training on a recumbent indoor trainer until your wrist can handkerchiefs some weight?

Instead of modifying the bike modify how you ride.

As an extreme example, if you ride a unicycle there is no pressure on your wrists. It would also be hard and unlikely to do a century ride on a unicycle.

Hold the grips llightly. Keep the meat of your hands above the bars and use extended fingers. The easiest way for me to accomplish this is on a flat bar. Preferably a flat bar with grips that turn way back towards me. North Roads bars as used on old Raleigh three speeds. Also the bars that were used on old Schwann balloon tire bikes.

Pull on the bars instead of resting weight on bars.

For extreme braking or for long step descents it is likely you will change your grip and take solid hold of the bars and put weight on them. I would suggest avoiding the steep downhills altogether until the wrists are stronger. Always try to ride so extreme braking in an unusual event.

You may not be able to do a long complete ride only holding the bars lightly, you can certainly give your hands some rest.

Interesting

0 pressure? Can you ride without holding bars ? (risky as you cant steer)
Modify bike, yes remove the bars.
Sorry, just being anal

Some recumbent bikes use steering via levers to either side (which pull bars that pull the steering column left or right, I assume). Some front loader cargo bikes also have a separate column for the fork vs. handlebars and connect the two with a rod.

Maybe you could take a normal bike, then add levers to either side, or even behind you, and just control the steering that way.

Can't feel pressure on your wrists if you are grabbing a steering bar behind you and leaning forward. 😁

I recently purchased a Fuji with broken a handle bar. Maybe I'll just remove them, I can brake with my feet. Though shifting maybe a issue?

If this is serious:
Please don't ride anywhere near anyone at anytime for any reason. Skidding and slowing down slightly and wearing out shoes is not braking and a broken handlebar just needs to be replaced and if broken levers just get new levers or find a bike that isn't broken.

If a joke:
Hahaha. You can do what LarrySellarz does and just kick your derailleurs and use your fingers...LOL

I'm not likely to get anywhere on this forum but will try once more before walking away and leaving you to it.

This is supposed to be adaptive cycling. I've put together a couple bikes for cyclists with one hand/one arm. Think about that one a minute. Just not good idea to put much weight on the one good hand. It's going to cause control problems. Excess weight on one side only is going to cause stress and then injury. And these are people who do not have an extra hand to spare. So they ride light.

A death grip on the handlebar is never a good idea.

I routinely see brakeless fixie riders doing 20mph in heavy traffic while texting. One hand to hold phone, one hand to type. I can't do it and would not if I could. But it can be done. I see them stopping quickly and stopping to a track stand while they type away. It's stupid and it's scary - it is possible.

What I have done is snap a stem clean in two and not fall. Downhill with weight on bars. And then proceed to ride home twenty miles. One hand with grip on steerer, the other hand holding the now loose handlebar that still has the brake connected. Don't know for sure if I would try that one again but yes, it can be done.

Do not ride with a death grip. And if you can't much ride a bike quit making fun of those who can. Goodbye.