Question about frame choices with 170mm rear dropout spacing

[Mclewis1]

I'm looking at another ebike build that would offer more traction for occasional rougher trail conditions (mostly year round, but not too much deep snow use). I currently use a Surly Bridge Club with a 500w Shengyi hub motor and 27.5 x 2" tires/wheels. This has been a great upgrade over a 700c setup that was used for years for occasional commuting and grocery getting on urban streets and MUPs (plowed conditions but with lots of slush and ice).

The new bike would extend that type of riding (more stability in those winter conditions) as well as be a more comfortable ride on rural trails (but no serious MTB use). One option I've been looking into is just adding a new limited suspension fork to the Bridge Club but the 2 - 2.4" rear tire size limits on the BC are a concern in the winter.

What I don't want is a full on fatty (don't hate, just don't like them and want to keep the overall weight down) or a new mid drive (to much $$$ configured the way I like it). I'm considering staying with the same type of setup but with both a power and wheel width upgrade. Specifically using a 750w Bafang G62 hub motor with it's 170mm drop out requirement and 4" rear tire (keeping the front down to a 2-3" width). Yes this also means going down to a 26" wheel in the rear (need a wider rim), and that's fine.

One frame that appears to meet my requirements is the Surly Wednesday with the addition of a new suspension fork. Any other choices that I might look at? Some of the basic requirements are ~170mm dropouts, steel tubing or a very robust Alu setup with proven solid rear dropouts (but no thru axles), geometry that accommodates a suspension fork, and will fit a 6' 2" guy. It must also accommodate fenders, rear rack, and have room in the triangle for a downtube battery.

 

[amberwolf]

One frame that appears to meet my requirements is the Surly Wednesday with the addition of a new suspension fork.

Just a note: Since a typical suspension fork (because of it's extra length so it can travel) is longer than the original standard nonsuspension fork on bikes like that, changing that to a suspension fork (unless perhaps if you reduce the wheel diameter to match the added fork length), will change the steering geometry, and will affect the handling of a bike (often negatively, but you'd have to try it out to see what it does to any particular bike in your specific usage).

 

[AHicks]

I THINK maybe some shopping around may show that there are quite a few who bought into this "Fatty" idea by mistake. Thinking one these bikes might be purchased pretty reasonable.

I bought one, hated the fatty wheels and tires (feels huge, because it IS huge!), but loved the rest of the bike. It wasn't cheap, but I ended up lacing a new 27.5x38mm rim to the original (170mm) rear hub, scrapping the boing boing springy front end for a hydraulic with 135mm spacing (not as expensive as it sounds), and set that up with a new hub/rim to allow me to run 2.8" Schwalbe Super Moto's front and rear. Bike is now the perfect "hybrid" set up exactly for how I use it.

 

[E-HP]

...changing that to a suspension fork (unless perhaps if you reduce the wheel diameter to match the added fork length), will change the steering geometry, and will affect the handling of a bike (often negatively, but you'd have to try it out to see what it does to any particular bike in your specific usage).

Whatever change you make to the head tube angle, it will have both pros and cons, so the negative is usually offset by a positive, and depending on what you're trying to achieve, could be net positive. When suspension forks first came out, I swapped out the rigid forks from both my mountain bike and my wife's. Although we used to do a lot of mixed riding; single track, fire road, downhill, etc., we got the forks specifically for the descent down Mt Tam across the bay, that we'd ride twice a month. Downhill was pretty brutal on a rigid fork, so we couldn't go too fast. The slacker head tube angle from adding the suspension fork made our bikes more stable for the higher speed descent. They were only 80mm, so they didn't have too big of a negative impact on single track riding, but with faster, smoother, downhills, I think they were a net positive benefit. I used the same bike for my initial ebike conversion. Old school, but it still handled the offroad stuff nicely.

 

[Mclewis1]

First off, thanks everyone for the comments.

I'm pretty sensitive to front end tracking (rake angle, trail, etc.) so I need to be careful on the specs for a suspension fork ... but with somewhat bigger (wider and softer) front tires the need diminishes to be too particular about the specs. The good part is that my suspension needs are also pretty minimal so 70-100mm forks will be fine (so less effect on stack height etc.). I'm also already resigned to working with different size wheels (26" rear vs. 27.5) so also going with a 26" wheel in front is a possibility if I find I really need to drop the front end height a bit.

It turns out (if it wasn't already blatantly obvious to everyone else) I'm really looking for a unicorn ... something with fat tire clearance and dropout spacing but also with 10mm axles for the non thru axle setup on the hub motor. After looking at a lot of bikes online the Surly Wednesday with a suspension fork still seems to be the closest I've come to my unicorn.

Interestingly there is a somewhat comparable commercial setup (Aventon Adventure.2 and some lesser known brands of essentially the same bike - https://electrek.co/2023/01/23/denago-fat-tire-step-thru-e-bike-review/ ). Still not exactly what I want, but closer ... they don't come with as good a quality groupo (7spd Shimano Tourney) and are quite heavy (in the high 60s to high 70s lbs depending on the battery size and accessories). On the plus side the latest versions of this type of bike are also coming with a torque sensor (dropout based) and a simple change of tires would certainly help some of the weight and ride. What I'm debating is that since I'm shifting away from the bikes I've ridden for years (road and lightweight hybrids) is whether or not something like the Aventon will satisfy me. It will certainly do the job in rougher conditions (winter, rougher trails, etc.) but will I also be happy with the heavier, less responsive bike on the roads around town?

I'm really looking to extend the capability of my Surly Bridge Club (with it's narrower tires and smaller lighter but more limited 500w motor) in some rougher conditions but I don't want to entirely give up the ride quality and enjoyment of this somewhat lighter more bicycle like setup (vs. an assisted "fatty").

Decisions decisions decisions.

 

[ZeroEm]

Decisions decisions decisions.

It's great to have endless options, better than this is the only one take it or leave it.