I started on 5 string a few months back and despite my love for the low B, I found most of what I was playing didn’t utilize that extra string, though it sure made a good thumb rest!
So I bought a 4-string - SBMM Ray34!
But, I’ve been noticing when I’m playing more on the low frets and low strings that I get a weird little friction “burn” on the side of my left index finger?
It’s kind of callous-ish, but not in a way that is definitely not as enjoyable and does not elicit the pride that I’ve felt with the ones developing on the pads of my fingers.
So, I’m wondering - why?
I’ve got big-small hobbit hands - largeish palms with stubby fingers- less than optimal for bass. In addition, I have issues fully supinating my hand because I’ve got a brutish history that involves spending too much time bench pressing, so accessing and navigating to the lower frets, especially on the lower strings is a bit uncomfortable- almost as though I have to force my wrist unnaturally.
BUT- I never had this hand issue when I was playing 5 string or even when I played guitar.
The only thing I can think of is that the smaller radius of the 4 string (9.5”) compared to the 5 string (according to Yamaha the TRBX305 has a 23.625” radius) is making me have to bend my hand at a more acute angle, causing side of my left index finger to rest against the bottom of the fingerboard/D-string?
Any ideas on how to mitigate this?
Do I need to work on that hand/wrist flexibility or am I just hosed?
I’ve got a video demonstrating what I’m talking about but unfortunately it’s too large to attach inline. I uploaded it to a streaming site, but am not allowed to post links. So, best I can do is an attached screenshot from the video showing what happens with my index finger when accessing lower frets/ lower string. I’m not actually fretting with the index finger here (not purposefully, anyway) so this seems to be an occurrence when transitioning - maybe using my index as leverage? Just thinking aloud, but hopefully someone has a solution for this annoying habit.
The side of your index finger should not come in contact with the neck. To fix this situation, try bringing your hand further forward over the neck than it is indicated in the photo, and arch your fingers so your fingertips come down onto the strings.
I have a unique perspective on this situation as my fretting hand fingers are shorter than normal due to losing my fingertips in an industrial accident when I was 16, a very long time ago.
I’ve played guitar, sax, piano and bass since then. For bass, I must bring my hand over the neck more than the average player, and I arch my fingers down onto the strings. It works.
Your very close to your answer…
Think about it until you know from the inside out.
That which we figure out ourselves is that which we remember the longest.
If anyone would have insight into this question, its gotta be you MikeC…
The seemingly worst answer you can get is, ‘Think about it’.
But its the best answer. 
Here is a valuable video from Talking Bass. Mark Smith presents a great exercise for whipping your fretting hand into shape. The exercise is really good unto itself, but Mark also points out proper fretting hand position and finger arching.
In particular, check out Technique Tips starting at 5:43 in the video. Extremely worthwhile fretting info here.
Yes this^^^
I seriously need to sign up for a course or 2 from Mark 
TY for sharing this Mike
Along the lines of @MikeC - your fretting hand thumb is pushing your hand and fingers away from the neck.
See if you can get your thumb to relax, and drop down instead of pushing back. That way your fingers have space between your palm and the neck, and you will - hopefully - not have your index being dragged around.
Fretting hand position and comfort can be really hard to develop as it takes a while for the fingers to get the strength and coordination to play with comfortable technique.
Dr. it hurts when I put my hand on a hot stove element, what can I do?
Don’t put your hand there…
Think about it…
What would Yoda say?
Put it there, do not, hmm?
That is the type of question that he who asked it looks back on after a dozen or so more hours of thinking about it and practicing and then realizing, ya, just don’t put my finger there…
My favorite Yoda-ism… “Do or do not. There is no try.”
I posted it at my practice station as inspiration for getting back to bassing and a starting a band after a 50 year swerve from music.
Musta helped… after 8 months and 8 rehearsals, our fusion band’s concert happened December 8. Recording studio booked for January 25. Thanks Yoda.
Do or don’t, there’s no try.
Oh someone just posted that. 
I really appreciate this video, I think I’d seen it in my YouTube feed previously and checked out his “BEHS” learnings briefly but never got too deep with it. It seems like my overall answer comes down to just reprogramming my fretting hand/wrist to get more “in front of” the neck. Unfortunately I’ve been stuck at work since I posted this, but am looking forward to getting home tomorrow afternoon and putting this into practice.
Really glad you liked Mark’s video. But he is not the “BEHS” guy. That’s some other dude.
Yeah, I couldn’t think of the other dude’s name - was just referring to the accent lol
I mean you’re on the money. I haven’t lived in the UK for quite a while but they’re both Yorkshire accents (I think) to my ear?
Leeds / Bradford maybe?
I find it super charming that England has so many accents, considering the entire country is about the size of Texas
(actually Texas is bigger!)
The US has like one accent from the Pacific to as far inland as maybe Colorado.
I don’t know the answer but my guess would be that Britain is a very old country. Add into the mix that centuries ago you’d be born and live within a small geographical area.
So regional idiosyncrasies such as accent and slang would be perpetuated.
I grew up with slang words that are only used in a relatively small radius 