I’d be very suspicious of the overall fit before blaming the pedal system.
Lake makes great shoes and you could probably switch from MX-242 to CX-242 and get things back close. I ride MX238 with SPD and CX238 with SPD-SL and my fit is within a millimeter between the two pedal systems. The mountain shoes do allow a more rearward cleat position but there’s an overlap as well so you can get both to fit the same as long as you’re not at an extreme. I have my cleats almost all the way back on my CX shoes and very much in the middle on the MX shoes.
But things like cleat fore aft changes require looking at saddle height and setback in conjunction. Achilles strain can often be caused by some combination of the saddle height too high and/or the cleats too far forward. You don’t want to pointing your toes down with a history of Achilles injury.
It would be really easy to switch to road shoes and mess this up. If all the rest of the fit is improved it could be better, but it’d be the fit more than the pedals, if the fit changes you should be able to fix the fit with the SPD setup as well.
Ironically I got my MX 238s first, when I got my CX238s I strained my Achilles. Nothing to do with the shoes or pedals but just from not having the fit right with that setup.
Replacing cleats on SPD-SL is important too. They loose stability quickly as they wear. SPD offers less at the beginning but changes more slowly.
Thought I would chime in on this, as someone who has gone back and forth on this several times over the years.
I don’t have any tendon injuries, but have suffered with foot pain at times (maybe a Morton’s neuroma?) and have very high arches.
When I have gone to spd pedals, it has been for livability, particularly when commuting. A bit easier in stop start traffic and walking. I can get good comfort and support, but everything needs to be ‘right’. Ie. look xtracks for broader platform, shoes in good nick, Sidas high arch slim insoles that are not worn (last a year or so).
SPD sl obviously don’t have same livability but my feet cope way better. When my insoles wore out earlier this year and couldn’t get a new pair, resulting in bad foot pain, I put my spd SL pedals on, used old shoes and insoles and did a range of different rides. No issues or pain at all.
Stayed on spd SL since just invested in fresh shoes/insoles.
I have the MX-2s and me700s. The me700s are much more supportive and 90% of the way to my looks. Definitely would recommend trying some other spds with a platform (does your fitter have loaners?) Though I also wouldn’t think twice about switching to SPD-SLs for road use
I can probably help here, since I’m using both the Lake CX201G on the road and MX21G for gravel/mtb (the lace up version of the 242’s), wide, also with Favero MX pros (and Pro SL on the road). Only difference is I’m using the SH-51 cleats, which supposedly feel the same as the MT cleats. For road I’m using the 2 degree blue cleats.
Also worth mentioning, I have a surgically repaired Achilles on one side and tendinopathy on the other side, since I grew up with competitive tennis destroying my body. Both bother me occasionally, though the surgically repaired side less so.
Quick answer: changing won’t help… The feel between the two setups is very, very similar. To the point that I’m on a 5 week trip with my gravel bike and a second set of road wheels–and while I brought my road shoes and pedals, I’m not bothering to change them. I feel just as stable on the MTB pedals/shoes. The shoes themselves are identical, except for the rubber glued to the sole. The interface with the SH-51’s feels very similar to the blue Shimano cleats, with just a bit more float. There’s no side-to-side rocking at all, and the shoes are stiff enough that the size of the contact area just doesn’t seem to matter.
There is one advantage to the MTB set-up though for those with Achilles issues, and that is that you can get the cleats farther back, which can alleviate some of the stress on the Achilles. I did this for a while but moved my cleats back to a more neutral position, as it was causing some plantar fasciitis to run the cleats too far back. You may want to experiment with that, as it does seem to take stress off the Achilles, and you can get the cleats pretty far back on the MTB set-up. But yeah, I see zero benefit to switching, based on my own experience.
No idea why, but this thread came back to me when out riding, and couple of things suddenly occurred to me.
Unless you can replicate your foot position exactly with the new pedals (fore/aft and stance) you are changing more than one thing, so if it has an effect (positive or negative) you won’t know if it was the different pedal system or the different foot position that had the impact.
Unless you can have exactly the same shoe, but in SPD-R version, you’ll be changing three things, muddying the waters even further.
SPD typically allows a more rearward cleat position, which asks less of the archilies and calf muscles, and thus may be better for you.
So, before you blow the money on different pedal bodies, cleats and shoes, why not try the free things first.
Does simply lowering your saddle a little help?
Are your SPD cleats all the way back? If not, push them back (you’ll need to drop the saddle a little too, as moving the cleat back has the same impact on total leg extension as raising the saddle). Do a decent ride and see if that helps.
Consider G8 or similar customisable insoles, as the instability might be the foot in the shoe, not the shoe on the pedal. Even if it doesn’t solve the problem, it should make an improvement more generally, and if you do switch to SPD-SL, you should be able to just transfer the insoles across so the investment isn’t wasted.
The Achilles\calf isn’t responsible for stabilising your foot, that’s the job of all the smaller muscles in your lower leg like Tibialis Anterior and Fibularis Longus&Brevis. (Try standing on your tip toes on one foot and see which muscles are twitching to keep you stable)
The Gastroc and Soleus that connect to your heel through the Achillies are there to provide power.
My first thought when reading your intial post was that your cleats are too far forward and the saddle may have also been too high, but the cleats would be my first guess.
I hope you can find a solution to get you riding pain free again!
Rather timely for your question is This video on cycling shoes from BikeFitJames. Yes it’s specifically on wide feet and wide fit cycling shoes, but it touches on subjects that cross over with things likely related to your issues.
Chiming in supporting that the shoes are the bigger differntiator. I ride SPD and SPD-SL and use essentially the same shoes for both (shimano s-phyres XC and RC) and to be honest in a totally blind test I probably couldn’t tell you which shoe/pedal combo was which.
it was mentioned earlier to move your cleats rearward…regardless of whether you think your cleats are correctly positioned or not, if you are experiencing the symptoms you describe, then put your cleats back as far as you can. It makes a substantial difference on your Achilles.
You also mentioned a PT routine. I can’t emphasize this enough - if you aren’t doing weighted eccentric heel drops, you are wasting your time. Those are the single best exercise for Achilles rehab. Not heel raises, heel DROPS. You can start with just your body weight, but you will need to add more weight…i think I got up to 30lbs in a backpack when I was rehabbing my Achilles.
To do them properly, stand on a stair step and raise up on your good leg, switch to your injured leg and then slowly lower down on the injured leg. When you heel goes past horizontal, switch to your good leg and riase bag up. Repeat.
Also consider flat soled shoes. This is counter-intuitive as most will tell you you want to use heel cups or a show with a decent heel-to-toe drop. Once I switched to flat-soled shoes, I had almost immediate relief. The shoes I used were from a company called Sanuk, but there are many similar ones out there now.
I was seeing a PT to rehab a knee pain issue and he mentioned in his research/reading speedplay pedals allowed the greatest control for addressing fit issues. Mentioning them as an option since no one else has yet.