Belt drive in a full suspension bike question

[MrCaspan]

so the new bike that I'm getting is a chain driven mid drive bike, but it is a full suspension bike. I know if I want to convert this to a belt driven there would have to be cut in the frame somewhere so that the belt can go through it.. with a full suspension bike is it possible to use the rear suspension points and disconnect them to get the belt in there and then you don't have to have a frame with a cut in it?

the bike I'm getting is a Juggernaut Ultra FS2 by Biktrix. I know in the past people have said don't get a belt driven because you have to get a bike frame that has a cut in it which weakens it and just thinking about a full suspension and the fact that it has to pivot means there has to be a break in the frame. I'm guessing it would depend on your full suspension setup but based on this bike is it possible to get a belt inside the frame because there's a break for the rear suspension?

 

[Marci jo]

Wow, I googled the picture and that’s a beautiful bike. Congrats.
I’m a little confused. Are you talking about cutting the frame on your new bike?
Why not ride and enjoy it?

 

[AHicks]

You might also look into the need for taking up the slack/stretch that will be required for that belt to maintain tension as the suspension moves through it's travel. You can install an idler wheel possibly, but that just another layer of complexity/weight. I could be wrong for sure, but my understanding is that's one of the bigger reasons you don't see FS w/belt drive.

 

[Mr. Coffee]

Don't do it, you'll just ruin what looks to be a perfectly good bike.

That bike has an aluminum frame. If you break the frame like that you'll necessarily put in parts to un-break it. Unless you do some very serious engineering on those parts (and fussily check before every ride that the bolts are still properly torqued) chances are flexing will wear away the softer aluminum frame over time and it will likely fail at a very inconvenient time and place. This is even more true in an FS bike because there is going to be a lot more flexing of that whole connection.

 

[Mike TowpathTraveler]

Yes, the rear suspension pivot points could act as the frame break to install a new belt. With that out of the way, your design, engineering and build fun is only just starting......

As in engineering-up a front ring spider to fit the Gates front ring. You'll have to go with the super expensive Rohloff rear Internal Gear Hub because they are the only game in town that makes a 197mm rear hub. And of course, a means of belt tensioner that allows the belt to maintain tension as the suspension flexes up and down. My opinion, we're basically just bicycle riders here, not engineers. And there is a whole lot of thought put into a dual suspension bike, more with a rear IGH and even more when you mix in the Carbon Drive System. And figure on that Bafang motor shredding the Rohloff internal gears in short order when full power is applied.

Still serious about maybe trying this? I'd call Cycle Monkey out in California and see what they say. They are one of the big US distributors of the Rohloff/Gates Carbon Drive system. Let us know how it works out as it can help the next person coming along who wants to do the same thing.

That Biktrix has a super nice Sram Eagle NX derailleur system. As @Marci jo said, I agree: Best to just ride and enjoy that bike as-iswhen it arrives at your doorstep.

Some reading on converting a Bafang to the Carbon Drive: https://www.electricbike.com/gates-belt-bbs02/

 

[m@Robertson]

I would think the belt tension issue would be the real stumbling block on this project. That and belt alignment. Do you know whether you can get the precise front-to-back straight line a belt requires? I'd think you have to buy and affix a Gates 'chainring' as a first step in measuring that.

Kindernay does a 197mm hub. And its rated for more torque than the Rohloff. 150 Nm vs. 130. And neither of those matches up to the 160 that Ultra is putting out.

 

[MrCaspan]

These are all great points and why I wanted to ask the question if it possible. I'm going to ride it as is to see if I like it of course. It was more just curiosity because so many people say don't do it because you have to break the frame, but in rear suspension you would not have to do that so it would take out that argument. With rear suspension I already have an engineered break in the frame I can use...

Some good points were made about how you pick up slack on the belt and if there is a straight line from the hub to the crank..

I might some day just update to a IGH once they have been out for longer and can handle the stress of that much torque.

Don't do it, you'll just ruin what looks to be a perfectly good bike.

That bike has an aluminum frame. If you break the frame like that you'll necessarily put in parts to un-break it. Unless you do some very serious engineering on those parts (and fussily check before every ride that the bolts are still properly torqued) chances are flexing will wear away the softer aluminum frame over time and it will likely fail at a very inconvenient time and place. This is even more true in an FS bike because there is going to be a lot more flexing of that whole connection.

I'm not breaking the frame its Rear suspension so there is already a engineered brake in it or the rear suspension

Wow, I googled the picture and that’s a beautiful bike. Congrats.
I’m a little confused. Are you talking about cutting the frame on your new bike?
Why not ride and enjoy it?

I'm not cutting it read above and it is a beautiful bike no way i am cutting that LOL, I cannot wait!

 

[MrCaspan]

You'll have to go with the super expensive Rohloff rear Internal Gear Hub because they are the only game in town that makes a 197mm rear hub.

Can you explain this a bit more please why do you need 197mm hub. Is it for the width of the tires they are so fat its hard to find a IGH that supports that wide?

 

[scrambler]

Two mechanical issues to be solved:
1- The IGH
You need to check what is the width of the dropout on that bike, and you need to know what the Chain line is (distance between the center of the bike and the center of the front sprocket)
Based on this info, you can review if an IGH (Rohloff or Kindernay) can be fitted with their Belt line matching the bike's Chain Line. In order for the belt to work, you must be able to get perfect alignment. There are ways to shift the front chain line in or out a bit with spider orientation and spacers, but that can only go so far.
If there is no IGH that fits the dropout width and chain line as is, you may be able to engineer an adapter, but feasibility will depend on the exact geometry of the bike.
If interested, I did such a project recently on a much more complicated case

Boxxbike Valkyrie : 12kw crank concentric mid drive with left hand motor drive

Boxxbike Valkyrie : new 8kw mid drive with pedals and left hand motor drive .. customizable from 250w to 8000w up to 250Nm torque.. https://evnerds.com/ev-album/your-ebike/the-performance-e-bike/ facebook.com/boxxbike boxxbike.com

endless-sphere.com

2- The belt tensioning
This can be a lot more complicated, as on a full suspension bike, depending on the rear travel, as well as the offset between the Bottom bracket and the Swing arm axis, the variation in belt path length can be significant. This means a tensioner would need to take a lot of slack.
The problem then is that you need to have enough clearance under the swingarm for a tensioner to have enough range to take all the slack.
Often what you find out is that a single wheel tensioner simply does not have the space to move to take all the slack. In that case a dual wheel tensioner could be considered but there is nothing available out there so you would need to design from scratch and fabricate (I know as I did exactly such project a few month back for another FS bike)

 

[MrCaspan]

wow this post you linked yo is super comprehensive, half of it is way over my head!! I'm going to read through this just for the education alone!!

 

[AHicks]

wow this post you linked yo is super comprehensive, half of it is way over my head!! I'm going to read through this just for the education alone!!

ES is like that!

 

[scrambler]

Below is an example of the first calculation needed, to evaluate how much slack a tensioner would need to take

In this case it shows the longest belt path is 1459mm
BUT the closest (as long or longer) Gates center drive belt is the 137th which is 1507mm
This means the tensioner will have to take 48mm of slack at the minimum (1507-1459), and 106mm at the most (1507 - 1401)
You then try different tensioner size and position and see if you can get the path of the belt to reach 1507mm when going around the tensioner
And in this example there was no way to absorb 106mm with a single wheel tensioner without the tensioner wheel interfering with the swing arm...

 

[PedalUma]

Split Belt Pro™ - Bicycle Belt Drive Kit

Veer's durable, robust bicycle belt drive kit lasts 3x Longer than traditional chain components and is just as strong and more efficient. Our bicycle belt drive kit is the next generation of belt drivetrains that enhances a seamless cycling experience without needing a split in your bike's frame.

www.veercycle.com

This is a Veer Split Belt. No cutting the frame.
You are IMHO far better off with the new KMC chain.

 

[scrambler]

Things to keep in mind with the VEER is that it is not quite strong enough to take the power of a Bafang ultra, and because the belt is larger they only work with the Rohloff but not the Kindernay.

That said the Bike the OP is mentioning appears to have a bolt on the swingarm that would allow to open the swing arm to pass the belt. So that is not an issue for him.

 

[Mike TowpathTraveler]

Can you explain this a bit more please why do you need 197mm hub. Is it for the width of the tires they are so fat its hard to find a IGH that supports that wide?

On the Biktrix page for your bike, the specs show a 197mm rear hub. My Haibike Full FatSix and Specialized Fatboy feature 197mm wide rear hubs. Pretty much an industry standard for fatbikes.

Yes, the width of the rear hub is to accomodate the width of the tires in conjunction with a proper chainline that will not interfere with the sidewall of the rear tire.

As I mentioned earlier, the Rohloff IGH is the only game in town that features a 197mm rear IGH hub made for fatties. Kindernay USED to, but no longer.

Fwiw, I considered a Gates Carbon Drive on my Full FatSix. Splitting a rear suspension frame to slip in the belt is intensive as it is, but doable. But considering everything else that needs to be re-engineered to accept a belt drive, it's beyond the scope of this shadetree bicycle mechanic!

 

[PedalUma]

I agree @MikeTownpathTraveler, Knowing when to pass on a project or to delegate some portion of it to an expert is difficult to learn and is highly important. I am working on a fatty today with about 200mm OLD. It is a Specialized Fat Boy with 4.7 inch tires. I had some parts made for me at a pro machine shop including asymmetric cups to fit the bottom bracket. It is getting a 750W torque sensor with 90Nm so I don't need to worry about the conventional drivetrain disintegrating. The inner diameter of the frame's BB shell is 45.9mm, hence the asymmetric cups to hold the motor. I am installing the secondary motor mount now and doing through frame wiring.

 

[PedalUma]

Yes, I know, "No photo or it didn't happen." I just got the motor set.

 

[Mike TowpathTraveler]

Yes, I know, "No photo or it didn't happen." I just got the motor set.

@PedalUma: I hope you can do some pictures of the Fatboy build when you are all done. Knowing how your workmanship is top-notch, that owner will be getting a very nice e-fatbike.

Regards to the Fatboys: Be aware of the rear hub. If this is an early Fatboy (and I believe it is, based on what I see are red graphics), the rear bearings in the hub failed on a heck of alot of Fatboy owners who were thrashing their Fatboys. As the bike was new and in-warranty, Specialized covered these hubs under warranty with a Hope Fatsno rear hub, a big upgrade from the in-house hub that failed on those bikes. Mine is a 2015 model, also prone to those hub failures, but I've never had an issue, maybe cause I never beat the bike up like I suspect these folks did with theirs.

I believe the press fit bottom brackets were prone to "creaking under load", another minor issue with some Fatboys. I figure that 90nm will put it to the test!

My Fatboy, 2015 model. I wanted a front rack to accomodate pannier bags as well as for mounting a dyno hub powered headlight. But the factory carbon fiber fork could not accept a rack mounted to it. I managed to find an aluminum Fatboy fork, from which I had the local LBS install riv-nuts to accept the 5mm screws that hold the rack onto the fork. Stripped the paint, applied epoxy primer and a 2k gloss black urethane and there we have it!

Unfortunately, she has collected dust since April 2017, when the Haibike Full FatSix entered the scene!

 

[PedalUma]

Thank you. I will tell the owner about the hub problems. I polished out my asymmetric press fits and put them in with grease. The originals did not have grease and the bearings were tinny, fragile. It is a 2014. The guy is heavy but will not be jumping. He wants a throttle so I need to use the larger display. Your bike is beautiful.

 

[JRA]

Seems like your attraction to a IGH belt drive is contradictory to the fact that you just ordered a bike that is known to be hardest on chains in the ebike spectrum that has no chance of ever being a belt drive. Or have an IGH because the torque an Ultra puts out will spin a Rohloff's axle right out of the dropouts, I've seen it happen with a BBSHD that has similar power on tap. Good luck.