NSMB - 2020 - Hardtail Thread

Posted by: JBV

so since you guys are the HT experts, riddle me this: i read a lot of comments about how stiff this that and the other HT frame is. lots of grumbling. i'm confused. aren't hardtails stiff and boardy in the back end? like, all of them? what am i missing?

are some of them 'plush'? are some smooth riding and forgiving? the one i'm considering, Commencal HT in plump wheel size is aluminum and i imagine, very stiff. with fat tires and inserts ridden at low pressure, i would think that the stiff factor would be well mitigated but i don't have experience first hand.

so is it the frame, the tires, the wheels, or something else that makes an awesome hardtail?

The frame makes a big difference, but other factors also contribute.

I've got two (now somewhat vintage) hardtails, both with 140mm forks, 26x2.35s. and have primarily run Syncros 27.2 Ti seatposts (until recently :( ) whose flex makes a big difference vs. aluminum posts for seated pedaling over chatter. Although both started with Kenda Nexcavators, the Blizzard has moved on to Schwalbes (MM up front, Nic in the back because MMs won't clear the chainstays) Both started with WTB Silverados (Ti rails on the Obed, CroMo on the Blizzard) the Blizzard has also had several different vintages of Chromag Trailmaster DTs.

Titanium Litespeed Obed aka Cove Hummer (18")

4130 Rocky Blizzard LT (19.5")

I think the steel Blizzard LT actually has a smoother ride. The square-swaged seat/chainstays may contribute to the Obed's rear end being vertically stiffer than usual for a Ti bike. Other possible contributors:

• Blizzard - plush coil Marz 44 vs. Obed - very linear Magura Thor air

• (I've put enough miles on both bikes that the Blizzard is on its second 44 and the Thor is awaiting bushing replacement)

• Blizzard - 31.8 butted Ti bars vs. Obed - very flexy 22.2 straight-gauge Ti (which may take some of the edge off the Thor)

• Blizzard - bladed spokes in the rear wheel vs. Obed - straight-gauge spokes

• Blizzard - North Shore XS cranks on square taper BB vs. Obed - M970 XTR

As a super-nerdy aside:

The cranks are a form of suspension that I think is overlooked for hardtails. I don't think you want crank-arm flex (worst case, arms hitting chainstays, but also losing energy to lateral flex that can't be recovered), but I think torsional flex (not bending) of the crank spindle might not be such a bad thing. Picture yourself riding with your pedals even on rough terrain and torsional wind-up of the spindle allows the crank arms to go from being parallel to each other ( - -) to a subtle inverted V shape ( / \ ) damping out some of the force of an impact and preventing it from being transmitted into your feet. If the torsional flex was large enough, it might also even out pulsations in peak pedaling force by winding up only to spring back and release some of that energy in the dead part of the stroke. The challenge would be to get the torsional flex without getting bending flex (which would be hard on bearings) A smaller spindle with outboard bearings might give a good torsional wind-up while limiting bending and keeping shear strength up (the weak point of my square-taper). A possibility for a Chromag Crank Concept... XD?

After all that, I don't think it's possible to build an aluminum hardtail with nice compliance but good fatigue resistance. I haven't ridden a ton of aluminum hardtails, but every one I have ridden was a filling-removal machine.

Posted by: WeTYC...

As a super-nerdy aside:

The cranks are a form of suspension that I think is overlooked for hardtails. I don't think you want crank-arm flex (worst case, arms hitting chainstays, but also losing energy to lateral flex that can't be recovered), but I think torsional flex (not bending) of the crank spindle might not be such a bad thing. Picture yourself riding with your pedals even on rough terrain and torsional wind-up of the spindle allows the crank arms to go from being parallel to each other ( - -) to a subtle inverted V shape ( / \ ) damping out some of the force of an impact and preventing it from being transmitted into your feet. If the torsional flex was large enough, it might also even out pulsations in peak pedaling force by winding up only to spring back and release some of that energy in the dead part of the stroke. The challenge would be to get the torsional flex without getting bending flex (which would be hard on bearings) A smaller spindle with outboard bearings might give a good torsional wind-up while limiting bending and keeping shear strength up (the weak point of my square-taper). A possibility for a Chromag Crank Concept... XD?

In my personal experience and perception, I rarely have my weight completely evenly spread between the two pedals when riding over bumpy terrain -- I'd say this is due to the cranks being roughly horizontal but my legs being in different positions, of slightly different strength, and so on. So when I absorb hits from the rear with my legs, the cranks will move around anyway. I don't know if your suggested torsional flex approach would make a noticeable difference in that situation. That said, I tend to push more of my weight into the fork than on a FS bike when riding the hardtail, and it's steel, with outboard bearings and a 24mm spindle. Regarding pedaling, from your description it sounds like oval chainrings try to solve the same issue (successfully in my opinion, my hardtail is easier to pedal on steep, loose surfaces in 32:18 with an oval).

Posted by: WeTYC...

After all that, I don't think it's possible to build an aluminum hardtail with nice compliance but good fatigue resistance. I haven't ridden a ton of aluminum hardtails, but every one I have ridden was a filling-removal machine.

I agree completely.  Steel or Ti is really the way to go.  

Btw, awesome bikes!

Unfortunately flex characteristics are very hard to gauge without actually riding the bike in question. I'm a fan of steel bikes because they can be both affordable and flex nicely, but they can also be super stiff. Bike reviews can be helpful if the reviewer is a similar weight as you, similar riding style and is knowledgeable/aware about the subject of frame flex. Other than my custom Daambuilt I've just made the best educated guess I could about hardtail frames and then accepted the fact I'd try and sell some of them. Over the years I can recall 3 frames that were unpleasantly stiff so they lasted a few months before I moved on. I feel like I am getting a bit better at figuring this out remotely since most of the frames I am interested in are not available for test rides. Although after my experiences with getting a custom hardtail made part of just wants to keep going that route so I can just spec exactly what I want and not have to compromise.

While we are talking about compliant steel frames what would be the best design for a complaint frame? Would this style of rear end be compliant?

Or would this be a more rearend be more complaint?

The classic "S-bend" seat stay

Posted by: heathen

While we are talking about compliant steel frames what would be the best design for a complaint frame?

The length, shape, wall thickness and diameter of the tubing plus geometry of the frame are all important. As well as any butting and any bracing. It's a complex thing to analyze and not something you'll easily deduce from a photo.

Posted by: Vikb

Posted by: heathen

While we are talking about compliant steel frames what would be the best design for a complaint frame?

The length, shape, wall thickness and diameter of the tubing plus geometry of the frame are all important. As well as any butting and any bracing. It's a complex thing to analyze and not something you'll easily deduce from a photo.

I didn't personally give any of this much thought until I had a frame custom made that was too compliant in both directions. It was really interesting to understand what that feels like. My subsequent frame nailed the feel through a careful combination of those factors and now I've limited the lateral flex nicely but still get good vertical compliance.

I believe all steel Chromag share a tube set. My Wideangle is super stiff

OK. My Stylus was way more compliant than any aluminum hardtail I have owned so big wheels on the Rootdown will be just fine.

I question the dedication to steel frames. With big volume 29” tires (and inserts), proper geometry that get you more over the fork on the descents, I think I’d rather save the 2 pounds of weight an aluminum frames offers over steel. It won’t have the lifespan of steel for sure tho.

Posted by: flattire2

I question the dedication to steel frames. With big volume 29” tires (and inserts), proper geometry that get you more over the fork on the descents, I think I’d rather save the 2 pounds of weight an aluminum frames offers over steel. It won’t have the lifespan of steel for sure tho.

It won't ride like a nice flexy steel frame either. Weight is 100% overated [within the +/- 1-2 lbs range]. Ride quality is far more important for comfort and performance. I've owned fatbikes and currently own two 29+ bikes - frame quality/feel is still very important even with big tires and nice suspension forks.

Posted Vikb

It won't ride like a nice flexy steel frame either. Weight is 100% overated [within the +/- 1-2 lbs range]. Ride quality is far more important for comfort and performance. I've owned fatbikes and currently own two 29+ bikes - frame quality/feel is still very important even with big tires and nice suspension forks.

100%

Posted by: craw

Posted by: Vikb

Posted by: heathen

While we are talking about compliant steel frames what would be the best design for a complaint frame?

The length, shape, wall thickness and diameter of the tubing plus geometry of the frame are all important. As well as any butting and any bracing. It's a complex thing to analyze and not something you'll easily deduce from a photo.

I didn't personally give any of this much thought until I had a frame custom made that was too compliant in both directions. It was really interesting to understand what that feels like. My subsequent frame nailed the feel through a careful combination of those factors and now I've limited the lateral flex nicely but still get good vertical compliance.

What was the two makes of frames?