MBc-Member Product Review: GruBee Solid Hub Heavy-Duty Axle Kit

[alesterfeind]

Ok, I got my new axle, hub and sprocket yesterday by FedEx from bicycle-engines.com. I called them on Tuesday and got it on Saturday. This is the 2nd order I have made with this vendor, and they have been very quick to deliver both times.

Now, about the hub:

It's HUGE! The picture on the website does not really give you an idea of the size of this thing. I had planned on threading and building my own wheel. After getting it, I realizd the diameter is bigger than my other axle, so I have to replace the spokes as well. I took it up to the bike shop along with my wheel to talk to the techs about it. And, just so everyone knows, the guys at Bicycle's Plus here in Flower Mound were really cool about it being a motorized bike. One guy mentioned, "I have seen a guy riding one of these going north on FM-2499." I said, "That was me!" They can't wait to see the bike once it's put together.

After talking about options, I decided that if I am going to put any more money into this, then I am going to do it right. I purchased a heavy duty rim, (2 ply), new spokes, and I am letting a tech build it so it will be true when I put it on. It was $35 for the rim, $18 for spokes, and $45 for labor. So, it's going to cost about $100 to build the wheel around this new hub, and the hub cost about $50 with S/H. I really think the end result will be worth it in the long run. This new wheel should last forever and run much smoother compared to using the assembly kit we get with our engines that compresses and bends the spokes.

One great thing about this hub is how easy it will be to interchange different size sprockets since it just screws onto the axle. My hub kit came with a 44T. When Andrew gets his, I am sure he can come up with some custom sprockets to fit. I really want a 36T or 32T for my bike.

I should have it ready by this next weekend, and I will post pictures of the parts and the final result.

 

[Demosthenese]

saw the post about disk brake bolt on application, just a warning, I've done that twice. Both times, i've managed to tear out the bolts while riding normally. I have a 65cc going to a 36t sprocket, and there was power to literally pull the mounting bolts out of the steel threaded holes. The second time it happened, i had purchased the strongest most expensive rim available and was using special disk brake bolts. The bolts didnt break, they just tore out.

It seems like an ideal solution, but they're not built for it.

 

[ocscully]

saw the post about disk brake bolt on application, just a warning, I've done that twice. Both times, i've managed to tear out the bolts while riding normally. I have a 65cc going to a 36t sprocket, and there was power to literally pull the mounting bolts out of the steel threaded holes. The second time it happened, i had purchased the strongest most expensive rim available and was using special disk brake bolts. The bolts didnt break, they just tore out.

It seems like an ideal solution, but they're not built for it.

Would you mind sharing with us what hub/hubs it was that had the failure? And do you by chance have any photos of the failure that you could post?

ocscully

 

[alesterfeind]

Disk brake mounted sprocket

I got a custom made sprocket from Kings that would allow me to install it on the disk brake hub or use the spoke assembly that we get with the kit. I was leary about using it on the brake hub because it didn't seem like the bolts would hold. Now I know thanks to Demosthenese. I really would hate to ruin the disk hub, or worse, have the sprocket rip off while at high speed and do who-know's-what kind of damage. I will probably stick with the assembly. At least the sprocket I had made will work with that and it's a nice one.

 

[Demosthenese]

i'll try and get some pics of the dead hubs, but i'll at least elaborate.

I first installed my 44 tooth onto the original hub that came with the bike; just took off the disk brake rotor and swapped it for the sprocket. It worked quite well, but i was foolish to use hardware store bolts. After a month it failed; the bolts either tore out of the hub, or the bolt heads came off in one quick catastrophic DING. No injury or problems apart from that. I redrilled and retapped that hub and used larger more heavy duty bolts. THe second time, they ripped out more metal, leading me to believe that that hub simply wasn't strong enough. I went to a mountain bike store and grabbed the strongest disk brake hub they offered (200$) and some disk brake bolts (3$ each) to be sure. It worked just fine for 2 months, and i thought i had the problem licked. I was careful to check them every ride, and even with locktight they would work themselves loose. One day i was just motoring along slowly when DING, they ripped themselves out of the hub again. Don't know how or why. But there is no way for me to increase the strength of this setup, so i have to conclude it's not really viable.

I have pondered the issue at great length, and the only other factor i can think of is this. When i look straight down at my engine, i can see that the chain is not PERFECTLY straight from the engine to the sprocket, relative to the frame. There is a very slight, like 2-3 degree angle to the chain; closer to the frame at the engine, farther out from the bike at the rear sprocket. The result is that i guess when tension is put on the sprocket, there is a slight outward force trying to pull the back side of the sprocket off of the bike, putting extra tension on the bolts. If you're motor is mounted so that the chain is perfectly straight, then the force is would all go into turning the wheel, rather then even a tiny bit going into pulling the sprocket out . This may have contributed.

This problem bothers me, because it seems like if a disk brake can last through slamming on brakes at 40km/h (and i'm sure they're tested for higher speeds, and have a huge safety factor too probably) then it should be able to take the power of the engine just fine. I still don't know for sure why it failed; logically i don't see why it did. Maybe someone else has an insight?

 

[BoltsMissing]

This problem bothers me, because it seems like if a disk brake can last through slamming on brakes at 40km/h (and i'm sure they're tested for higher speeds, and have a huge safety factor too probably) then it should be able to take the power of the engine just fine. I still don't know for sure why it failed; logically i don't see why it did. Maybe someone else has an insight?

Maybe someone else has an insight?

I think it seems like a "laws of physics" type of thing.
Take a look at where the ripped bolts are, where it's sheared as you explained.
Then think about a coat hanger wire if you bend it and straighten it enough times it will get hot at the bend, and eventually snap. That's a basic demonstration of fatigue.

If human power is doing 40Mph and nothing happens to the disk brakes, that's because there is no engine to wilt the bolts back and forth with each compression stroke as you are slowing down.
If you ride the same way using the same disk brakes set-up etc. with an engine doing the work, then this MIGHT be doing fatigue issue in the same principle when you bend a coat hanger wire.
This is as you asked, insight

 

[HoughMade]

Also keep in mind that the disk brake is not constantly under stress. When you power the bike through the same hub, the sprocket and hub is under stress every moment the bike is moving, not a few seconds at a time separated by long periods of non use.

 

[Demosthenese]

yeah both of those things make sense. I think it's probably a combination of lots of factors really, i'm more surprised that if this solution doesn't work, how is it that the spoke attachment does... anyway, i'll be getting my hub from b-e soon, there was a mixup with the mail but it's on its way. once i have that i won't be worried anymore.

i in fact have tried one more time with this solution. I went to a local bike shop and grabbed a new second hand hub for my 200$ rim and then respoked the new hub onto the old rim. Saved almost 80$ over buying a new rear wheel, woot
I'm using strong bolts again, and i'm now tightening them well before and after every ride, religiously. At least if it fails again, i'll be able to definitively pronounce this idea dead, because there's nothing more i can try.

The rear HD hub will be for my current bike, but my next build, i want to use ghost's up and coming right power transfer kit!

 

[azbill]

I may have solved this problem
I took a normal sprocket, cut the center out (dremelled from hole to hole)
bought a normal mtb disc rotor and bolted the sprocket to the rotor with 2 nuts as spacers, then bolted rotor to my rim
now the sprocket is 1/2" closer to spokes
gave me a perfect chain line
have approx 300 miles on it so far
if it fails I will let everyone know

I will post pics soon

 

[Demosthenese]

all right, so i got my b-e hub today with the key'd solid hub. I spoked it to a rim i all ready had this afternoon.

The sprocket mount isn't threaded; it just slides on and a small key fits into it to hold it in place. I did the same thing as alaskavan and hammered out the bearings and turned the axle around, which was the easiest mod ever. I now have a 7 speed freewheel on the right hand side and the 44 tooth sprocket and strap brake mounted on the left, hopefully with plenty of room to mount on the bike. I haven't tried that yet, that'll be tomorrow's project, but it looks like it will fit just fine. I'm going to have to swap it to a 36 tooth in the long term, but i've spent enough money recently, and since i installed a new spark plug wire the 44 tooth is seeming much faster .

In terms of spoke tension, does anyone know how this thing should be dished?

edit: also, even though i tightened the bolts on my disk-brake hub adaptation every time using anti vibration washers and locktite, they come loose every ride, and today, on a 45 minute ride, one of them fell out, even though it was completely tightened before the ride began. I am more and more convinced that the issue is mostly that the bolts will work their way out over time and then own the hub when a couple have fallen out or the play in the sprocket rips them out. So it's probably possible to do it, you just have to make sure of keeping the bolts tight, and maybe swap them every couple months if your scared of fatigue. I'm gonna stick with the hd hub though

 

[Mike S]

I installed the HD axle without the strap brake because I am using a 3 inch dia. tire and it all just would fit right unless I super bent the frame which I didn't want to do. So I designed a mount for a cantilever brake for the rear wheel and it works great. Mike S