I was looking at solutions for greater setback without changing the seatpost. I came across old threads about the M2racer Power Module which gives you an extra 4cm of setback, but the company closed a long time ago.
So then I came across the Rinsten Spring from Ukraine, but made in China. It's a simple U shaped rail made out of spring steel which is supposed to serve as a form of suspension. Looks like you can get up to maybe 8cm of setback, but you'll get a lot of bounciness if you're that far back. Supposedly reviewers say it feels pretty good, but some people worry about it being too bouncy, or about too much lateral deflection and torsion. This might also cause the clamp to slip backwards. I thought maybe if you stuck a piece of TPU or rubber block between the upper and lower rails, you'll get some dampening. If you also clamp the open ends with a second set of clamps, you might get less torsion.
Here is a video:
It goes for $60, but there are some similar products on ebay or Amazon from Chinese sellers for $20, although I don't know who came first. One difference appears to the the angle between the upper and lower rails. Rinsten claims 8 degrees. Superimposing the product images, I estimate the Chinese versions are probably 10-12 degrees, so you might have problems not being able to level the saddle if you run out of tilt adjustment on your clamp. The smaller angle of the Rinsten might have a better chance of leveling. Rinsten started as a Kickstarter campaign, and they claimed that the first batch was bad and had to be tossed. I guess from poor manufacturing tolerances, probably non-parallel rails or spacing. So I don't know if the version from Chinese sellers would have a similar problem. Rinsten claims that their next batches were closely watched and checked for quality control.
Rinsten also seems to have only partially shipped units to the campaign backers. The latest update says in order to ship to the remaining backers, they need to sell 3 units for every 1 backer. But I guess if you're buying one from their website, they're probably happy to ship it to you.
https://rinsten.com/
One reviewer on Amazon for the Chinese version says it snapped while riding.
Oh, I found a thread on Bikeforums where someone tested a prototype of the Rinsten, but it broke after 800 miles.
Although the kickstarter page says they're testing different materials and doing stress tests, so the production version might use a different material than the prototype.
Rinsten saddle spring
I was thinking about using this on my Brooks because I'm 2-3cm too far forward. But I have sprung B17 Flyer Imperial, which already has some tilting deflection from the springs, in addition to my thudbuster, so I would only use these additional U springs on an unsprung saddle.
But anyway, if I were to use this, I'd set the clamp as far forward as possible and then back it off to achieve the desired setback, as the main purpose for me is for the setback and not for the suspension.
Above: Rinsten
Below: Chinese variations on Amazon and eBay
