I was looking at getting a new frame, the Stromm Raktt. They are local and the bike looks amazing, to me, and the Tour numbers are awesome. I wanted to get a frame with a steeper seat tube and a longer front center. Im not a sprinter nor a climber. a bigger rider @ 190-210 lbs depending on time of year, and amount of ice cream in the off season. Looking at the bottom bracket numbers on the frame made me cancel my order. They list the Stromm @ 34nm. I know I dont need crazy stiffness for a non sprinter but that seemed super low in comparison to most frames. I thought it may be a noodle and at the price of the frame I was put off. Im no expert, but does this seem rather low?
My general sense is that outside of sprinting, it will make zero difference. I’ve never actually seen that measured before. Do you have other comparable bike stats?
I’m not even sure what that means. I assume “nm” is newton meters, which is commonly used as a torque value. Without the context of how much the frame is flexing under a given load (which could be measured in Nm), I’m not sure how that torque value could be used in isolation to measure BB stiffness. Are you sure you aren’t just looking at the torque spec for the threaded BB insert?
I asked Grok and it spit this out…
N/mm in Tour Magazine (TOUR) bike tests stands for Newtons per millimeter.
What it means
It measures stiffness (Steifigkeit) of the frame, fork, bottom bracket, etc.
- How it’s measured: They apply a known force (in Newtons) to the bike on a test rig and measure how much it deflects/bends (in millimeters).
- N/mm = Force ÷ Deflection → Higher number = stiffer (less flex).
Common values from Tour tests
- Lateral fork stiffness: Often 50–60 N/mm (higher is better for steering precision).
- Bottom bracket stiffness: 60+ N/mm is very stiff.
- Overall frame + fork stiffness: 9+ N/mm is considered very good; top bikes can reach 10–11 N/mm.
Tour uses these objective lab measurements (along with weight, aero, etc.) to give grades in their bike tests. A bike with high N/mm values feels more responsive and efficient under power, especially when sprinting or climbing out of the saddle.
My TT bike is a 2018 Giant Trinity, very well known for being a “flexy” bike. Its the only bike I’ve ever owned that I could really feel the bottom of the triangle being flexy. Even then, I only feel it when putting out 500w+.
Its not a confidence inspiring bike to sprint with, but I’ve done plenty of sprints on it and never had anything close to a durability problem with almost 10k miles on that bike.
That’s interesting, I’ve never seen that stuff reported before. And including the context of how much it moves for a given force makes it a meaningful metric I guess. I personally wouldn’t eliminate the bike based on that lower value, but I’m not a big sprinter and I think BB stiffness is more about feel than actual performance. If you like the way a stiff bike feels, maybe it’s important, but I can’t see it having a meaningful performance impact.
Personally, I’d start with fit, you want a bike that fits you and suits you. E. g. whether you want a more aggressive bike, a longer or a shorter bike, that’s also a matter of taste. I hated how my endurance road bike felt when cornering and I couldn’t dial in my position. My aero road bike (a 3T Strada) fits much better. It completely eliminated the rear end problems I had, a regular saddle with no cutout just works. That’s where I would start. If that’s the Stromm Raktt for you, then get that. But if you are just looking at Tour’s numbers and buy a frame based on that, I’d strongly discourage you from that.
I thought it was widely accepted that engineering for Tour’s stiffness numbers lead to a generation of badly riding bikes.
I’m very concerned about the simplistic stiffer = better. The bike frame is like a spring, so even a flexier frame won’t lose the energy you put into it (for the most part), but release it again. Of course, a very stiff frame might feel faster in some circumstances, but keep in mind that in all likelihood, a stiff frame is also less comfortable.
Ditto for frame drag numbers: by now it is clear that this is a minor gain compared to making aero positions more usable and comfortable. So start with fit and go from there.
I have my fit dialed. My saddle is well forward now, and run a 130 stem. I want a geometry that suits that. Moving the BB back is essentially what they are doing, I figure you need more front center to distribute your weight better. So the Raktt, Noah fast3 and the Factor one are all on the list. Raktt offers a seat post that is adjustable. You can get pretty well over the BB with it. Its just the number listed in this test is so much lower then every other frame by a large margin. That fact had me question it. Tour numbers help but Im buying more for fit with the three frames im looking at, all things equal on the fit I look at things like this. I dont mind a bike with a mid stiffness BB, but I know I dont want a noodle. Im close to them, sent them an email. They say I can ride one. So Im going to do just that. If its too flexable then Ill look at the One or Noah.
Test riding bikes is always the best option. Lots of bikes that are great on paper felt meh or bad to me (e. g. my old Cube Attain GTC SL, Cannondale’s SuperSix or Trek’s Domane).
Make sure to ride a different, but similar bike for direct comparison. Otherwise there is a good chance for a confirmation bias, i. e. you will look for flex in the BB area but focus less on how that bike rides.
If they’re local, can you test ride one?
That said, I’ve had a bike with a flexy BB, and it wasn’t fun to ride. Only used it for commuting, but sold it. (It had other things I didn’t like about it too.)
Well I got the answer for anyone questioning the same metric. Stromm says they sent Tour a non production frame. The layup isn’t what they are using for retail. They told me the BB stiffness is 50-60 N/mm so right inline with other frames in the category.
I’m not familiar with Tour’s test protocols, but directionality matters greatly.
But you touch on another point: a bike can be objectively “worse”, yet more fun. My light MTB hardtail is at a disadvantage compared to modern fullys, yet I really like the feel of a hardtail. I reckon light wheels and a reasonably stiff frame are similar.
I know nothing about the bike and don’t wish to discredit all its good aspects, but that explanation… doesn’t pass the pub test.
Mere mortals aren’t likely to notice much of a difference between racing frames WRT BB stiffness. Most all of them are going to fall in the “stiff” range.