24 Inch Suspension Fork on 26 Inch Frame ?

[LewTwo]

OK ... so maybe this is a stupid question.

If one replaces a rigid fork on a bike with a suspension fork then it normally raises the front of the bike and screws with the ride geometry. This is a picture of a 26 inch crank forward "630" bike.

My question is:
Could one replace the front fork with a 24 inch, short travel, suspension fork/wheel and maintain the ride geometry?

 

[Tommm]

yes.

 

[LewTwo]

Bounce ...

I have not had much experience with Suspension Forks.

The first one I had was on a Schwinn Sierra. Its handlebar was so far up in the air that I felt like I was mounted on a sea-horse. I sold it off faster that I had purchased it.

I was really hoping for a bit more feedback on this question.

 

[Chalo]

Yes, you can substitute just about any combination of fork + wheel that gives you the same ride height. Depending on the fork offset and wheel size, you might end up with more or less trail than you had to begin with, which isn't usually a big deal.

One of my bikes started life as a ten-speed with 27 inch wheels. It's now a chopper with a 20 inch front wheel, 24 inch rear wheel, and 25 inch (axle to crown) fork. Not only does it ride just fine, but the original kickstand still works.

 

[qwerkus]

Could one replace the front fork with a 24 inch, short travel, suspension fork/wheel and maintain the ride geometry?

Forget about the 24" and go for a 26" suspension fork with a 20" wheel. Should net you exactly the same height and allow you to use hub motors more efficiently.

 

[2old]

That bike looks like it has a 1" threaded fork, so good luck locating a fork for it, no less a 24" fork. Possibly a low end (very low end) one from a bso unless you're fortunate and find a good used one from the early 90's. Then it'll have aluminum lowers and if you install a motor make sure your insurance is paid up.

 

[TNC]

OP, I take it that the bike you pictured is not necessarily the exact bike you're asking this question about...correct? Is it the kind of bike you're considering or something quite different? What do you plan on using the bike for?...or is this more of a generic question about how hypothetically a 24" suspension fork will affect any 26" bike?

If your question involves a bike like the one pictured...like a Trek Electra Townie or such...then you probably won't have a big issue as far as handling goes. You're talking about a cruiser where you won't be riding rough off road or hucking off curbs and loading docks. However, you are talking about an ebike I presume, and that will at least raise speeds to probably much higher than the normal operating envelope of a cruiser bike. At that point a 24" front wheel may indeed become somewhat noticeable with a little less stability and how the tire/wheel size reacts to bumps, potholes, etc. Things could get "hinky" depending on where/how you're riding it and how the actual frame geometry design/numbers shake out. Ebikes usually bring speed to the mix, and it has to be considered.

If your question involves a mountain bike application, it is absolutely bad juju to go to a 24" front wheel on a 26" or bigger designed MTB in "most" all cases. That wheel will want to hang up in and on every obstacle and will make front wheel stability and handling super funky. But I'm guessing you're not really looking at a mountain bike application here...are you?

 

[Chalo]

That bike looks like it has a 1" threaded fork, so good luck locating a fork for it, no less a 24" fork.

Like most comfort bikes these days, it appears to have a threaded 1-1/8" fork. The stem quill being a little fatter than the handlebar is a giveaway.

LewTwo: It might be a little tricky to find a suspension fork with a long enough steer tube, and it's unlikely there are any threaded ones in the right length. Expect to change the headset and stem for threadless versions if you swap the fork.

Is the point here to use a smaller wheel, or just to add suspension? Because front suspension is of negligible value on a bike like this. Almost all the rider's weight is on the rear wheel, so there's little to be gained in return for the tradeoffs. A parallelogram type suspension seatpost would be a much better addition to this bike.

If the point is to use a smaller wheel to enhance the performance of a hub motor, well then you'll want that wheel to be mounted in a steel fork with good strong tips. There are many longer forks to choose from, including suspension corrected forks and 29er forks, which can be up to about 3-1/2" or 90mm longer than the one in the picture.

 

[LewTwo]

TNC:
Actually the bike pictured is a one of two candidates I have identified:
https://www.amazon.com/dp/B079YYQ35C
https://www.amazon.com/dp/B08NFG8TSR I do NOT like the color

The things those two have in common are they are 26 inch size wheels that will mount wide tires (i.e. SCHWALBE Big Apple), rim brakes, 7 speed derailleur, aluminum crank forward frame, double tube step through .... and about 38 pounds stock

Then there is this one that already has a suspension fork and a steel frame but it is also about $300 higher cost:
https://www.amazon.com/dp/B07TBYVXRR I do like the color

I am NOT obsessed with having disk brakes. I am obsessed with IGH rear hubs. All of the above would need a new rear wheel or at least a relaced with an appropriate hub (which I probably already have).

The idea is to replace my 'weight weenie bike' with something a tad bit more practical. I am 70+ years old with joints that no longer operate with peak efficiency and resilience of a teenager. I no longer operate a cage as well. The E-Bikes are my ONLY form of transportation. I have zero interest in trail riding. However with modern municipal budgets, neglect, heavy trucks and Texas heat, some city streets have turned into something that can best be described as broken asphalt washboards. Come to think of it, the grass covered ground next to the some drainage canals might offer a smoother ride.

Chalo:
All three of those bikes appear to have 1-1/8 steerer tubes and long ones at that. While I agree with your opinion that most of the seated rider's weight is on the ass end of the bike. I am interested in the possibility of hedging my bet by being able to replace the front end with a suspension fork.

That fork on the Schwinn does not to appear to be an high end product (despite the extra $300).
***EDIT***:
Per specific Cycle (Schwinn Distributor): "The suspension is a coil fork without any adjustments."
I believe Chalo calls these "pogo sticks".

My main concern is winding up with another 'sea horse' .... I really hated that Schwinn Sierra. The other problem of course is most modern consumer bikes are built for short people (5 foot 6 inches or less). I only tip the scales at 135 pounds but that is stretched over a six foot tall stack of bones.

Cloud 9 seat and a thudbuster are also required bits.

 

[markz]

I am riding casual cruiser rigid fat bike with 5" riser handlebars and a front hub and a front suspension fork will be nice to lessen the jarring action of bumps. I've noticed on my long rides yesterday and the day before that even cracks in the 30 year old pathway's asphalt are noticeable. There's slight cracks and there's bigger cracks with some that are huge, on a 26x2.25 wheel (front) with hub. The jarring action would be less with a 26" fat tire (29" OD) and squishy psi. A cheap front suspension fork might do, I can't remember when I had my Townie with stock front suspension how the jarring action was on the cracks. No need to drop tons of money on a front suspension fork for the riding I do, and might have to revert to rear hub and deal with broken spokes and flats all the time again, or just go with mid drive and deal with wear and tear.
Nice cushy fat tire bike with plus sized tires that have squishy psi on rigid frame is my next change-up.

Cloud 9 seat and a thudbuster are also required bits.

Good choices, but thudbuster is expensive. I'd probably collapse that Cloud 9 seat's rails within 6 months. My Bell is holding up, but 380lbs breaks stuff on bicycles, thankfully I have lost a ton of weight. The big seats with the elastromer cushions are good, the seats with the big springs never lasted for me. But at 135lbs you shouldnt have to worry. Thats thin for a persons thats 6'1"ish. I used to eat that much in food at a sitting :wink:

 

[LewTwo]

... my Townie with stock front suspension ...

I can not recall ever having seen a an Electra Townie with a suspension fork ...

I used to eat that much in food at a sitting :wink:

LOL ... In my younger days I once complained that Crystal (aka White Castle) hamburgers were so small that I needed at two dozen to make a full meal. My friends father laughed and said that he would pick up the tab if I could eat two dozen of them in one sitting. He was a CPA and was not in the least happy about having dig out his wallet. 8)

When I was in AF Basic training the TI ran me through the Chow line twice at every meal ... wasted effort.

Geez ... now I am hungry.

 

[markz]

I bought my Townie Electra 21D used for a great deal, and it was barely used.
I still have the fork, bike is long gone to the dump with broken top bar which could have easily been welded.
My bike has the exact same fork as many on search engine picture results, fork labeled Electra.
Townie is made by Trek.

2013 model - https://www.rei.com/product/813222/electra-townie-21d-step-through-womens-bike-2013

SR Suntour XCT

Sticker labelled Electra on the fork itself
https://duckduckgo.com/?q=Townie+Electra+21D&t=ffab&iar=images&iax=images&ia=images
https://bikemarkt-images.mtb-news.de/ls/51/5193/5193696-large.jpg

It was a good bike, the frame cracked right at the cable hole by the seat. The battery had many different configurations and weight but was taped, hose clamped and zip tied to the top bar. I still like to have 3x7 gear train, as I find 1x7 just isnt enough for cruising at speed and pedaling and just a tad off on gearing for climbing hills.

... my Townie with stock front suspension ...

I can not recall ever having seen a an Electra Townie with a suspension fork ...

 

[2old]

Sorry, that looked like a 1" fork to me. Since it's 11/8, as stated above, you could use a threadless system which would allow many fork possibilities. You might consider a 26" fork and 24" wheel to minimize the influence of the smaller tire, and ebikesca has a front hub motor that's compatible with suspension forks.

 

[Chalo]

The last conversion I did was a Townie that had originally come with a crappy suspension fork. I ditched the fork, but I was unable to find a suitable replacement that had a long enough threaded steer tube. So I grafted a longer steer tube onto a fork that was too short otherwise.

The axle to crown length of this rigid fork is identical to the uncompressed height of the stock squishy fork.

 

[LewTwo]

One thing I never liked about the Townie was the pregnant bump in the top tube. Too bit too "Picasso" like for my tastes :-(

OK, the Schwinn Suburban Women's Classic Comfort Bike is a loser: have to scrap the fork, handlebar and both hubs right out of the box. Much too dear a price for a frame. Moving on I found a specification page for the Schwinn Sivica 7 Comfort Cruiser Bike. https://www.schwinnsivica.com/

I removed the top tube and added some information (dimensions in inches):


The I downloaded the best side view picture I could find. I used it as an overlay in my CAD system to try and extract some more dimensions. I used the wheelbase length of 47.60 inches as the control dimension.

One should realize that there is a margin of error when working with photographs but I think that this is fairly close. Note that the seat tube angle on the spec page is bogus. FYI: I buy blue jeans with 32-33 inch inseams. I calculate about 80% of the seated rider's weight on the rear wheel (plus cargo and/or trailer weight). Perhaps a 2.5 wide Big Apple would fit in the rear??? I also wanted to see how much room there might be for a battery between the tubes (green rectangle).

I am still guessing 1-1/8 steerer tube but it is kinda hard to tell for certain ... at least for me it is.


Thoughts, comments and/or flames .... fire!

 

[markz]

Yeah but the Townie Electra's had a huge amount of space in the triangle for the battery. Though some other bikes, including older Electra's had the stupid 2nd top bar which limited battery placement in the triangle. My Santiago cruiser bike was like that.
http://www.bikeroar.com/products/norco/santiago-2015

Is that green shaded area where your battery will be?
I'd try to build a battery to fit in the V-shape between the seat post and the top bar, then that defeats the step-thru design of the bike.

 

[LewTwo]

Is that green shaded area where your battery will be?

It is one possibility ... a most likely one but it would likely require a custom battery. Could possibly stick a flat Rack battery in there. It might be forward enough not to interfere with the riders legs.

I'd try to build a battery to fit in the V-shape between the seat post and the top bar, then that defeats the step-thru design of the bike.

Exactly .... I do not need a big battery. If for some reason I did then I would probably load it on my Burley Travoy Bike Trailer.

 

[markz]

18650
L = 65mm is 2.559055"
W = 18mm is 0.7086614
Add in spacing for 18650 holders makes it probably 21mm (0.8267717")
So you'd have plenty of breathing room from the top top bar to the lower "top" bar, 3.26"-2.56" = 0.80" of space
Just a matter of how wide you want the pack to be sticking out from each side along the top bars.
15.93" / 0.827" = 19 hopefully you could stuff an extra one in there to make it an even 20 so you can have two 10S lengthwise, from bb to headset. Then its a matter of how wide you want it

Then its a matter of figuring out which 18650 to buy, 25R, 35E.... depends on what discharge capabilities you want.
@3P and say 40A controller, you'd need a cell to do 13A so make it 15A
@4P and 40A controller, you need 10A so make it 15A.
@6P and 40A you'd need 6.5A
@8P you'd need 5A

35E is 8A but 3.5Ah
25R is 20A and 2.5Ah
Sony VTC6 18650 3000mAh 15A
Samsung 30Q 18650 3000mAh 15A
LG HG2 INR 18650 3000mAh 20A

Remember you dont want your cells to work hard so round up generously. @8P being 5A just skip the 35E and find a 10A 18650
Sanyo NCR18650GA 3500mAh 10A
And say for 6P 6.5A go 15A 18650.

I will jive together a pic, as you can see the 18650 are standing upright on the bottom top bar.
Thats why you'd kinda want to fit 20S in there.
Then its a matter of how wide you want it, how many Parallel which gives your Ah.
So 1P would basically be a bit smaller then the width of the frame tube.

3 wide is 10S6P (60-18650's) sticking out 15mm each side.
5 wide is 10S10P (100-18650's) sticking out 33mm each side.
7 wide is 10S14P (140-18650's) sticking out 51mm each side.

Of course cost of 18650 cell will play a role in what you choose, along with the research others have done.
I like the 25R at 2.5Ah and 20A but would be overkill for your 10S6P and pack when your using 40A controller. But they'd wouldnt be stressed at all either. Unlike if you go 35E with 8A.

Lots of work to build your own battery, but it will be a nice sleek, stealthy look to shove the battery between the two top tubes.







Bettery config, where is says 10S1P thats your center of the frame tube. To me it would seem a bit imbalanced, because the cells at the far end the electrons have a longer way to travel (top right) then the cells at the battery leads to the controller that you see on the bottom right. I'd try to connect a few wires at evenly spaced lengths along the same power rail and connect them all together, then have it go out as your main battery wire. I will try to do another pic for ya.





Crude I know, but its evenly spaced out. Tapping into the + rail at even lengths, same for - rail. Of course all my handiwork, goes out the window if you want 20S voltage, but I doubt your into that kind of speed. You could do 52V 14S or 48V 13S for a smaller pack with much more room above and below, then no connecting wire on the left hand side

 

[LewTwo]

Personally I prefer LiFePO4 chemistry. Less energy density but a lot longer lifetime. I also happen to have some salvaged A123 (26650) cells. A 2P16S pack would give me 5 Ahrs @48 volts or a 3P16S pack would be 7.5 hours which might just be adequate for the neighborhood. Hmmm.... two each 2P16S packs would be 10 Ahrs and about 4.25 wide by 2.25 high by 16.5 long. That would actually fit and would also give the option of running one pack or two depending on the distance needed. The maximum continuous discharge rate for 2P is 100 Amps.

I guess what I am saying is that there lots of possibilities :wink:

 

[markz]

What kind of range are you looking for out of your battery pack?
Will you be forcing yourself to pedal with pedal assist?

https://ebikes.ca/learn/batteries.html

Motor Type Rough energy usage
Minimal Assist (using motor only on hills, slower ~30kph setup) 6-8 Wh/km 9.6-12.9wh/m
Typical Assist (~40 kph with pedaling, motor on all the time) 9-12 Wh/km
Power Hungry (either no pedaling, or hauling a load, or going really fast) 14-20 Wh/km

Minimal Assist 9.6-12.9 wh/m
Typical Assist 14.5-19.3 wh/m
Power Hungry 22.5-32 wh/m

I dig the sleek look of stuffing the battery between the two top bars. But the legs do hide lots of area from people looking from the side at you.

I find my riding with my batteries I get 55km, out of 52V 14.5Ah (750wh) and 36V 15Ah (540wh) = 1290wh total/55km = 23wh/km so 35wh/mile. Winter I get 40km total. Pedaling is minimal, hills I pedal.

26650 at 3.2V and very high discharge rates.
Would need 12S to get 38.4V or 11S 35.2V to get same as 18650 10S 36V.
Bulky indeed.

 

[LewTwo]

What kind of range are you looking for out of your battery pack?
Will you be forcing yourself to pedal with pedal assist?

https://ebikes.ca/learn/batteries.html

Motor Type Rough energy usage
Minimal Assist (using motor only on hills, slower ~30kph setup) 6-8 Wh/km 9.6-12.9wh/m
Typical Assist (~40 kph with pedaling, motor on all the time) 9-12 Wh/km
Power Hungry (either no pedaling, or hauling a load, or going really fast) 14-20 Wh/km

9.6-12.9 wh/m
14.5-19.3 wh/m
22.5-32 wh/m

LOL ....
This is Houston .... the closest thing to a hill is a bridge over a drainage canal .... maybe a 4 foot rise side to side.
At 20MPH I can not pedal fast enough to keep up with the motor.
I do not even bother to install the PAS hardware.
My two main destinations are less than 5 Miles round trip.

Longest trip would likely be 10-12 miles round trip. I also have a 48 Volt 17 Ahr (20 pound) battery I can put in the trailer. I am a bit conservative. I figure a 1Ahr gets me 1 mile dragging the trailer with 50 pounds of cargo... even after the battery is several years old ... I think that is about half your 'Power Hungry' rate.

 

[LewTwo]

I dig the sleek look of stuffing the battery between the two top bars.

Perhaps a bespoke fiberglass cover on each side between the downtubes???
That would be a 'round-to-it' project if there ever was one. :|

 

[Hillhater]

I calculate about 80% of the seated rider's weight on the rear wheel .......

I dont think so , no with those handlebars anyway.
Even though the seat is well back , the riders arms, legs, head, and a fair bit of the body,.. will be well infront of the seat.
What are your main objectives for this frame ?....step through ?... low seat height,?..upright ride position ?.. cost?..
There are other frame options, depending on your priorities.

 

[LewTwo]

I calculate about 80% of the seated rider's weight on the rear wheel .......

I don't think so , no with those handlebars anyway.
Even though the seat is well back , the riders arms, legs, head, and a fair bit of the body,.. will be well in front of the seat.

A lot of that depends on riding position and if one is actively pedaling (not to mention body type .. i.e. bear belly). I do not clown pedal and I do not tuck. A fair bit of my leg weight is hanging from my hips.

About the handle bar .... turn the stem around 180 degrees ... bring back closer to the rider.

What are your main objectives for this frame ?....step through ?... low seat height,?..upright ride position ?.. cost?..
There are other frame options, depending on your priorities.

1) Upright seated riding position.
2) Ease of mounting (i.e. do not have to throw a leg over rear wheel/rack or the top tube)
Remember I am an OLD FART and the joints do not bend as well as they did 30, 40, 50 years ago.....
3) Low seat height, flat foot technology, whatever you want to call it: put my feet on the pavement when I stop.
4) Cost ??? Not hardly. A crank forward framed bike is generally harder to find and more expensive.
5) Comfort would really sum it up.

 

[LewTwo]

What kind of range are you looking for out of your battery pack?
Will you be forcing yourself to pedal with pedal assist?

Now I can better answer you question. I accidently ran the rack battery until the eBikeling shut down ... ooops. I put an inline meter on it when I charged it backup. Managed to stuff 438 watt hours into a six year old Golden Motor 36 volt, 12 AHr LiFePO4 pack.

Then I used that freshly charged battery to go to the grocery store:
Top speed = 20 miles per hour
Distance to grocery store = 2.4 miles one way
To store = 57 watt hours used = 23.8 watt hours per mile
From store = 67 watt hours = 27.9 watt hours per mile
Ambient Temperature = 85 degrees
Motor Temperature = 94 degrees
Controller Temperature = 101 degrees