A few years back, as my body settled into complete recovery from a broken hip with two titanium rods inserted, I got a professional fit from an awesome PT. My primary goal was to eliminate left knee pain - the broken hip was on the right. Along with some other tweaks and exercises, we decided on a shim under my right cleat, to counter the fact that my right leg was now shorter than the left by a fair bit. I've been riding pretty much pain free since. There are a lot of issues specific to my riding posture due to the fact my left arm is missing at the shoulder that have taken a bunch of years to straighten out, but I feel I'm pretty much there.

In preparation for an upcoming gravel bike build, I recently bought some mountain bike shoes and SPD pedals, and started running them on my Domane to get used to them. I did not put a shim in or try to set up the cleats to mimic my road shoes (wouldn't know how anyway). No issues over three or four rides until yesterday, when a fairly hard solo effort - 40 miles at 19 mph average - brought back the left leg pain. The first 20 was into a headwind and I spent the vast majority of the ride in the drops.

Once the gravel bike comes in, is it necessary/advisable to go back to my fitter for a bike-shoe specific fit?

Short answer: yes, it is advisable. I'm going to go out onto a limb (just a little) and say that the gravel bike geometry is different enough from the road bike that you would absolutely get a benefit from it.

It can't hurt to go. But even if you don't go now, you can always go later if it proves to be an issue.

What will that accomplish? The leg length differential will still be present, and unaddressed. Lowering the saddle might get the shorter leg in "position," but then the longer leg is out of "position." The fix without another fitting is to shim the cleat on the shorter leg to get the pedal/cleat to saddle length equal.

Many people deal with leg length discrepancies, without using clipless pedals, and without the ability to use shims. Setting seat height for the shorter leg can work for them.

It is quick and easy, and it is how some people deal with leg length differences, and adapting fit to the shorter leg is a far better solution than to the longer leg...but, the OP asked a very specific question that this doesn't answer.

As a reminder:
And I will reiterate, yes. Especially in the context of the specific physical issues the OP needs to ensure are accounted for and addressed in his bike fit. I think it is borderline irresponsible to be telling him to start playing around with his seat height.

All - very grateful for the posts, which were uniformly insightful and well intended, so no quibbling please. Cubewheel's comment pretty much nailed it - first hard effort in the drops had the longer leg working harder.

The last fit followed a few years of me making minor adjustments with the cumulative effect of making things worse. So short term, although I'm pretty sure there would be no harm in lowering the saddle a touch, I think I'll move the SPD set-up down to the trainer and add the shim.

When the new bike comes, I'll head back to visit my favorite PT.

To the OP, it seems to me your shoe-shim solution made your two legs functionally more equal, hence you should have been able to fine-tune your saddle height, tilt, and setback as does one with normal legs. Forgive me if my thinking here is too mechanistic, and for neglecting the effect of your arm challenges. In my experience regardless how carefully I set me saddle, if it is too low I feel excess pressure where my feet meet the pedals. There is a sense I’m driving my feet through the pedal at bottom trying to extend my legs even though there is not enough room. The stress also shows up as knee pain and I haven't noticed any effects in my hip joints.

What I do then is raise the saddle a millimeter at a time, revisit tilt (because tilting nose-up lowers the saddle at the rear and I’m back in the soup!), as well as setback. A micro-adjusting post is essential. After a few iterations I’m back to hood balance, pedal reach and saddle support.

So, can you use your previous set of adapted shoes and compatible pedals on the new bike? If you lower the saddle to adjust to your shorter leg, I worry that your longer leg may become constrained and stressed.

Considering that you have a set of physical issues, probably the best thing is to go back for another fitting. But does the gravel bike really need to have different contact points than the road bike, below a professional level of performance?

What do you mean by “professionally-accepted?” And does that term mean it must be a good fit? It’s odd to see such an authoritarian sounding term here on a bike site.

This is a stop gap. If there is known leg length differential, addressing that properly is not a matter just "getting the saddle height right." So to speak. Doing that can certainly get one by...but back to the OP's original question. Yes, in a case where leg length difference is known, and changing from one bike to another with a different (enough to matter) riding position, and different pedal system (with known different stack height), a new fit is recommended.

Internet experts can certainly offer their opinions, it's why Bikeforums exists, just so long as everyone involved understands that they are just opinions, and short of a fit, are at best short term solutions.

The shortages are a drag for sure. In my case, between me on the internet, the LBS' supply resources and parts I have sitting around, the full GRX di2 group set was accumulated between early December and late January. The frame, originally due in December, had an ordering glitch. When the order was resent, the delivery slipped to March, now May.

A buddy ordered a bike from a direct to consumer company in January. April delivery, confirmed three weeks ago when the parts arrived in port, is now June. In his case, it appears to be Shimano short shipping orders - likely to spread the pain and pleasure as equitably as possible - forcing companies to build the oldest orders first.

I was in a LBS a few weeks ago. Across is 5 stores it was one of the largest Trek retailers in the country. 15 lonely bikes in inventory. A woman came in looking for a Mtn. bike. The salesman said they are not taking orders or deposits, predicting a one year lead time.

Great video, thanks! I'm not sure it exactly addresses these points, but a lot of good ideas are in there.

To me, "professionally-accepted" means there are a lot of experts who can be identified, they routinely discuss and formalize agreements on key points in professional practice, and their views and conclusions can be discovered by normal users (meaning cyclists) with reasonable effort. AND they actually do agree on the point in question. I can accept that one expert can agree with you. I've been on this subforum since it started and it has been mainly about cyclists saying "my butt/hands/back/glutes hurt, what do I do?" Of course fitting is often a recommendation, but we just as often have, "got a fit, >$150 fee, now I'm worse off, what do I do?"

If "professional fitter" means someone who will take my money, then I do not want to ever meet a professional fitter. I had an excellent one, and several that were not positive and productive, and did not improve my comfort and performance. The best fit I have ever had was developed by me while training for a tour. I don't see the need to see one at this point, for myself. If it could ever mean someone was registered, licensed, and carried societal endorsements of successful work, I would have a lot more respect.

The best I can do is try to understand the actual complaint the poster of a message has, and share how in my experience I have resolved (or not!) similar matters. I think I made that clear in my post, which you responded to. And I never advocated cranking up the saddle drastically. I suggested raising it a millimeter at a time to reduce what for me is a source of joint stress. I intended for him not to go past or even to the point of hip-rocking or any such destructive condition. It takes some patience and methodical approach to do this, but it's not impossible. I assume the OP has enough sense to ignore my input if s/he does not have the same complaint or a similar one.

I don't believe fitting or "a fitting" is a hobby kit you can hook up to the rider, turn the switch, and then it will work, elininating all problems and discomforts.

If a rider is complaining of numb hands, I would first try to reduce the weight on the hands. The most direct approach to that is to move rider center of gravity back away from the 'bars. The ideal case of this is to make the rider take on the tuck of a champion downhill skier or cross-country skier while in a glide. In a tuck over skis, your CG is above the feet somewhere. For a cyclist that might be too extreme. I don't know a general rule, in these terms. I do know that for me it is possible to have too much setback, in which case my butt tends to move forward on the saddle and the sitbones fall off the platforms - causes perineal abrasion!! So while I set back the saddle to reduce hand pressure I try not to set it back past the point where pressure reduces to an acceptable level.

After succeeding with this adjustment you might find you are reaching more forward than you like, in a trainer test or road test. At this point the stem could be changed for one with less extension, or the 'bars changed for one with less reach. If like me you have usually a 9 cm stem with long-reach MAES or Nitto 115 bars, you could get some nice compact-pattern bars to pull the grips closer to your body. Less drop, but, there are other solutions as well, such as keeping the original old-school long reach rando or touring bar (the MAES) and getting a stem that is a cm or two shorter. If you need a stem extension less than about 5 cm, parts availability can be a problem.