Josh Poertner from Silca wrote an article a few years ago (before gravel really took off), talking about vertical frame compliance. I assume it can still be found somewhere on their website,
This was about ‘comfort’ road bikes, but the same can be applied to mtb’s. The gist of it is that since springs in series are dominated by the softest one, the (relatively) soft tire has much more effect than the small variation in (much stiffer) frame.
Of course, there is more flex than just vertical compliance, but it is a good reminder to keep things in perspective.
Then there is the matter of frame material. Steel as a material is way stiffer than aluminum.
The only reason I can think of why steel frames would be more flexible is if you use skinnier tubing. But , like Andrew says, that hasn’t been true for a long time:
My first US bought bike was a cheap Fischer mtb’ish thing, in 1996. Steel frame, but tubing the same size as aluminum frames, and I am confident, had no butting or anything. I am sure that was way stiffer than any aluminum frame of the time.
In 2010 my friend bought a steel hardtail frame, that does ride with a more flexible feel. Guess what? Skinny tubes, open drop outs, long chainstays. If you did the same frame in aluminum, it would be a noodle!
May 26, 2023, 8:01 a.m. - Tjaard Breeuwer
Josh Poertner from Silca wrote an article a few years ago (before gravel really took off), talking about vertical frame compliance. I assume it can still be found somewhere on their website, This was about ‘comfort’ road bikes, but the same can be applied to mtb’s. The gist of it is that since springs in series are dominated by the softest one, the (relatively) soft tire has much more effect than the small variation in (much stiffer) frame. Of course, there is more flex than just vertical compliance, but it is a good reminder to keep things in perspective. Then there is the matter of frame material. Steel as a material is way stiffer than aluminum. The only reason I can think of why steel frames would be more flexible is if you use skinnier tubing. But , like Andrew says, that hasn’t been true for a long time: My first US bought bike was a cheap Fischer mtb’ish thing, in 1996. Steel frame, but tubing the same size as aluminum frames, and I am confident, had no butting or anything. I am sure that was way stiffer than any aluminum frame of the time. In 2010 my friend bought a steel hardtail frame, that does ride with a more flexible feel. Guess what? Skinny tubes, open drop outs, long chainstays. If you did the same frame in aluminum, it would be a noodle!