What Fork To Get, and/or Other Parts (for a weight weenie low power fs eMTB)

[Catalyzt]

As many of you know, I ride an XCish 46ish pound Class 1 FS eMTB with a 250 watt 40 nm motor and 34mm Suntour middle-of-the-road front fork.

I break 30 MPH fairly frequently and occasionally break 40 MPH, but do that only very briefly on pavement that is smooth. On the trail I'm usually on novice trails with intermediate segments, and occasionally on intermediate single track with a few very short advanced segments. Generally, I ride 75% terrible pavement, gravel, broken glass, and junk, and 25% dirt. Hills where I live are steep.

This bike used to weigh about 49 pounds. I dropped it to 46 by going to Maxxis Ikons 2.2s (I was coming from Riddler 2.3s) and going tubeless and getting a CF seat. And-- for many reasons, not only weight, also decreased rolling resistance-- it made a HUGE difference. I was able to get to another range of hills and ride much more interesting terrain. It's easier to carry down stairs or over gates or obstacles, and safer-- less risk of losing my balance and falling, etc.

My first decision was, whether to upgrade and retrofit my other bike -- a 42 lb. hardtail w/ a TSDZ2B that has a cracked motor housing. I believe, with a variety of mods, this could be a 40 lb. 80nm+ class three monster, and I really want to do that project, BUT, if I'm going to spend $2,000 to $2,500, I think the money may be better spent on the FS than the hard tail.

That is not the question I'm asking at the moment, but I'm open to thoughts on that. My decision is not finalized. The main reason I'm more likely to invest in the FS bike is because it is so underpowered, and for that reason, everything is likely to last longer, from the motor itself to the chain, the crank, the gears, the battery, etc. That makes investing in the FS bike a better investment, I think, particularly if the economy goes to hell and I have to retire before I really want to. I'm 67.

What I'm trying to figure out is how much weight I can lose on the FS bike and where to lose it. There is, as @PedalUma noted, a point of diminishing return. However: There is a long, mild upgrade on the way to my favorite trail that I could probably do with less assistance if I could shave a little more weight, and that could mean more riding on the best terrain w/ less range anxiety.

But I'm not sure I'm getting great advice from my LBS on this. They say things like, "you need a 36mm Fox Float Fork if you replace the fork, the 34mm Fox Float is not as robust as your Suntour and not for an eBike." This doesn't make sense to me. My bike is very, very underpowered, and it's already pretty light and I only weigh 155 pounds, so what about my bike being electric makes it less suitable for the 34mm? I don't do big drops, nothing bigger than riding of a medium-height curb. I'm on blood thinners, have no reason to take that risk.

They also say things like new wheels would cost me $2,000 and would only save me a pound, or that it's pointless to replace the pedals, and that it won't save significant weight. I think they're not thinking it through-- that's rotational weight, and actually, I could lose half a pound by going with CF pedals. (It is true that I could, potentially, crack one, but that's unlikely to cause an accident or keep me from getting home. I think.)

Anyway, what do we think would be my priorities for saving weight and staying within my budget? Here are the items I'm considering:

Wheels - 1 to 2 lbs (I think my current wheels are heavy for what they are, my LBS says it's impossible to figure out wheel weights. My hunch is, I could shave a half pound or a pound just going with better allloy rims, maybe 2 lbs if I went CF. Pedal has some ideas about lightweight, low-resistance CF wheels and hubs I need to follow up on.)

Tires - .5 lbs (options here are VERY limited, because my tires are light already. I'd be going with 2.0 inch Schwalbe rocket whatever. That's as thin as I probably want to go for intermediate trails-- and could be a mistake. Maybe the Maxxis Ikon 2.1s are already in the sweet spot. If I can replace them, they are down to 15%.)

Pedals - .5 lbs

Bars - .25 to .5 lbs.

Fork - 1 to 2 lbs. LBS is claiming 1 lbs, but I think he's looking at the 36 and ruling out the 34 unreasonably.

Seat post - .25 to .5 lbs

Obviously, what's most expensive would be the fork -- probably just over a grand -- and the wheels. And obviously best to use rotational weight first, and weight low on the bike second, weight high on the bike makes a lot less difference.

Thanks, I can supply more detailed info about my current fork, etc. Pedal, I know I gotta call a guy about a horse-- or a wheel-- but there are other items on the list as well.

 

[jabberwocky]

Changing the tires to something lighter and faster rolling is the low hanging fruit, and you've already done it. Beyond that, you're quickly throwing money into a hole to make the bike ever-so-slightly lighter. Its your money, but I'm not seeing a lot of benefit, really. At least if your main concern is just weight. Dropping a 46lb bike to 43lb by removing 3lb of non-rotating weight is barely going to be noticeable IMO.

For the fork, look at axle to crown of the current fork and what you're thinking of replacing it with. The argument for the 36 may be that its actually a drop in replacement for whatever is on there now and the 34 is not. You do not want to change fork geometry on a FS MTB.

There may be an argument for some of this stuff on a performance basis (i.e. I imagine the Fox 34/36 outperforms the Suntour in pretty much all categories, carbon bars can get you some vibration damping, a higher end drivetrain also shifts smoother, etc).

 

[Jeremy McCreary]

And obviously best to use rotational weight first, and weight low on the bike second, weight high on the bike makes a lot less difference.

Why reduce weight low on the bike before weight high? The latter contributes more to the bike's rotational inertias in roll and pitch, thus reducing nimbleness.

 

[BlackHand]

Why reduce weight low on the bike before weight high? The latter contributes more to the bike's rotational inertias in roll and pitch, thus reducing nimbleness.

Rotational weight impacts acceleration and climbing more than static weight. To what degree and how much it is offset by loss of inertia on downhills seems to be one of those neverending debates.

 

[Jeremy McCreary]

Rotational weight impacts acceleration and climbing more than static weight. To what degree and how much it is offset by loss of inertia on downhills seems to be one of those neverending debates.

Agreed. I was talking more about static weight distribution, which affects how the bike resists changes in attitude — i.e., rotations of the entire bike in roll, pitch, and yaw directions. This goes directly to handling.

 

[BlackHand]

Agreed. I was talking more about static weight distribution, which affects how the bike resists changes in attitude — i e., rotations of the entire bike in roll, pitch, and yaw directions. This goes directly to handling.

Somehow, I missed the original context of what you were replying to.

 

[Catalyzt]

Changing the tires to something lighter and faster rolling is the low hanging fruit, and you've already done it.

Yeah, that may be for the tires, but I do have to replace them in the fall, and if I can find something that rolls a little faster and is a little lighter, why not? I'm not even sure I can find Maxxis Ikons in 2.1 anymore.

As for wheels, I'm trying to get a fix on how much my current wheels weigh vs. how much they would weigh with lighter rims-- even aluminum rims-- and what the LBS says is it's impossible to figure out. I think it should be possible to make better guesstimate.

Beyond that, you're quickly throwing money into a hole to make the bike ever-so-slightly lighter. Its your money, but I'm not seeing a lot of benefit, really. At least if your main concern is just weight. Dropping a 46lb bike to 43lb by removing 3lb of non-rotating weight is barely going to be noticeable IMO.

If nothing else, it will help with carrying the bike down stairs or pushing it up brief stretches that are too steep and loose to climb-- like on Hell Hill. My 42-lb bike was much easier to carry downstairs at my Saturday night meeting. Four pounds lighter = huge difference.

But I'm seeing if I can drop at least a pound of rotational weight via pedals and slightly lighter tires, possibly more with rims. And that's absolutely not my only concern. Decreased rolling resistance, whether due to better tires of better hubs, is definitely of interest for my long, slightly uphill traverses when I'd love to use less motor.

For the fork, look at axle to crown of the current fork and what you're thinking of replacing it with. The argument for the 36 may be that its actually a drop in replacement for whatever is on there now and the 34 is not. You do not want to change fork geometry on a FS MTB.

I don't think my LBS checked that measurement, but that's a great point. I will try to harvest that metric. Thanks!

There may be an argument for some of this stuff on a performance basis (i.e. I imagine the Fox 34/36 outperforms the Suntour in pretty much all categories, carbon bars can get you some vibration damping, a higher end drivetrain also shifts smoother, etc).

Yeah-- I had totally forgotten about vibration dampening, but with stage III osteoarthritis in both hands? That's very important. I think CF bars definitely are going on the Christmas list! Thanks again, super helpful comment.

 

[Catalyzt]

Agreed. I was talking more about static weight distribution, which affects how the bike resists changes in attitude — i e., rotations of the entire bike in roll, pitch, and yaw directions. This goes directly to handling.

These are great points, as is Blackhand's response, which brings me to something I haven't mentioned: I love the way this bike handles and corners. That's an argument for going slow with changes to the weight high on the frame. The bars are a worthy gamble-- if I hate them, I've only gambled two or three hundred bucks. Serious money, but not the same level of risk as getting a new fork!

 

[jabberwocky]

Yeah, that may be for the tires, but I do have to replace them in the fall, and if I can find something that rolls a little faster and is a little lighter, why not? I'm not even sure I can find Maxxis Ikons in 2.1 anymore.

As for wheels, I'm trying to get a fix on how much my current wheels weigh vs. how much they would weigh with lighter rims-- even aluminum rims-- and what the LBS says is it's impossible to figure out. I think it should be possible to make better guesstimate.

You should be able to estimate wheel weight. Its hub+rim+spokes(number of spokes for your lacing pattern)+nipples(same). Theres variance in all those parts so the shop may not want to commit to a weight but you can come up with a working estimate. I did weight weenie wheels on my road bike back in the day (kinlin rims on CK R45 hubs with Sapim CXray spokes and alloy nips) and I learned that while they are nice for acceleration, they took a lot of maintenance to keep them true and I had to replace spokes occasionally. When I built wheels for my gravel bike (that doubles as my current road bike) I definitely went heavier and don't regret it in the least.

Wheels are a nice plate to save some weight; they are rotating so you feel it a lot more than static weight on the bike, but its also easy to over-weight-weenie and create a lot of headache for your future self. Just keep that in mind. The really light stuff... isn't durable. And wheels that aren't durable suuuuuuuuck.

For tires you may look to the gravel world for something lighter and faster rolling, since it sounds like most of your riding is rough pavement and not trail.

 

[Catalyzt]

Thank you so much for that formula! (hub+rim+spokes etc.) I think your breakdown of why the shop doesn't want to help game that out sounds dead accurate. If I were them, I'd be thinking about it the same way.

Your point about maintenance for lighter rims is well taken, too. I do have a good LBS, and I trust them for everything that's safety related, their prices are decent, and overall, I've learned a ton from them-- and they do take time to teach me stuff. (This visit, they showed me a bolt for trigger shifter I had completely ignored, it was loose enough to be near breaking.)

But they are over two miles away, and I don't like bugging my wife to pick me up there. And while there is some work I can do myself, and I like to pick up a few new maintenance skills every year, wrenching on bikes is not my passion. Truing wheels can be a PITA, and the WTBs have been bomb-proof so far. And yes, good point about gravel tires. Pedaluma had some thoughts along the same lines for the 29er, which runs on similar terrain, though when I have it back on the road, it's less suited to intermediate single track.