Anyone have informed thoughts on this?

I want a suspension seatpost to be a bit easier on my nagging back. I cannot find one in 26.8mm other than an old Rockshox from 20 years ago for almost new price.

I can get a used 27.2 Thudbuster or similar that is still supported with replacement parts for nearly the same price.

I don't  see where shaving off .0157" the diameter would make it dangerous but I don't know.
I would put a big radius in the corner where the cut ends. I would turn the minimum length needed so if it does break, it does so at the clamp so I don't get 7" of post up my ass.
I could even press a sleeve into the ID to reinforce it.

I am not finding 25.4s to shim up to 26.8.

This is an old used bike that I bought specifically to do a 20-30 minute "sprint" in the morning before my workout. It isn't a hobby or for pleasure so I don't want to spend $120-250 for a new seatpost. Before doing that I would just get a trainer.

In google searches of the bike forums on this question the answer tends to be don't do it but these people might be idiots. I trust arfcoms volume of knowledge more than some unknowns so I ask here.

If you've got the equipment to do it, go for it. Worst case it breaks, which it doesn't sound like you care too much about.

What's the bike and the type of terrain you are riding on? Might be able to fit a larger volume tire and go tubeless to run lower air pressure. You do know to stand up over rough terrain, right?

Buy a bike with rear suspension.  I doubt you will find a seatpost shock that doesn't bind.

A rear suspension bike cured my lower back issues and most of my sciatica.  My back hurt continuously for about 6 months and then gone.

It took a dip, a collapsed seat post, and a pinch flat to make me realize where the issue was.

Well I don't want to get injured but as I said I doubt it would be a problem with taking .008" away from the wall thickness.

I am basically using it as an on-road bike now.
It's an early 90s mountain bike, the wheels are narrow, 21.5mm. They measure .850" outside on the braking surface. It has 26x2.100" tires now.

Yes I know to stand, I had a mountain bike many moons ago and dirt bikes and currently a DS cycle.
I plan on trying tubless on these wheels to see if it will work.

I am just riding the streets/bike paths now which are relatively smooth. Biking seems a lot rougher than I remember it being 30+ years ago lol.

I have 12acres in AZ, which is hilly with washes and mostly gravel like ground. If I decide I want to get into it more there(after I move) I would probably try to find something with FS.

Quote History

I didn't want to spend that much if I didn't plan on making a hobby out of it.

The Thudbusters are well reviewed, they work by using linkage rather than a tube inside a tube.

I didn't either.  I went into a bike shop and talked to a mechanic. We walked out to the parking lot and he sold me his Cannondale Fox Alps frame with some XTR things on it.  Cheap.  The rest of the mechanics were pissed.  They didn't know it was for sale.

Too bad that it is a bad time to buy a bike right now.  Wait until January if you can.

I'd order the unit, then measure the wall thickness. Calculate the new wall thickness. Calculate the change in bending strength of the tube. If it's 25% or less (and you're near the max weight limit) I'd go for it since most things are engineered for 2x safety factor at the rated maximum weight. Worst thing is that it bends on you. Not really dangerous.

Yeah, if it just bends that's ok and as I said can make an insert to press into the ID.

Now to find one used for a decent price. Used bicycle shit on ebay seems to hold value.