Evaluating a Bike for GEBE-ification

Discussion in 'Rack Mounted Engines' started by smapadatha, Dec 9, 2007.

  1. smapadatha

    smapadatha Guest

    In this ranticle, I assume you’ve read “How Does the GEBE System Work?” and you understand what the GEBE/kit comes with. I also assume that you've made the decision to buy a GEBE/kit and now you need a bike to go with it. My suggestion is that it's a bleep load easier if you buy the kit first, and then find a bike that is compatible with the kit; rather than the reverse. Of course, if you already have a bike, the information in this article may help you figure out if your bike meets the requirements for GEBE-ification.

    1. When I say “GEBE/kit”, I mean an engine from GEBE and the GEBE mounting kit.
    2. The information here is specific to putting a GEBE/kit on your bike. If you are going with a different vendor for the engine or the mounting kit, this document will be largely useless to you.
    3. The info in this article is based on my research and experience with the GEBE/kit. Opinions on the best way to do things vary, so consider this article a list of suggestions.
    4. Putting a GEBE kit on a bike is usually not a one-evening project, regardless of what the GEBE website leads you to believe. I recommend that you read a bunch of posts at motoredbikes.com, think it all through, then proceed with caution.

    [size=+2]The Easiest Way to Put a GEBE/Kit on a Bike [/size]

    1. [size=+1]Buy an engine with mounting kit from GEBE. [/size]

      I would recommend at least the 32cc 2-stroke Tanaka or the 35cc 4-stroke Robin/Subaru. If you live in an area with small hills, or no hills, or if you don’t plan to tow any kind of cart behind your bike, you might get by with a smaller engine. I’ve done a few side by side comparisons between the Robin/Subaru 25cc and the Robin/Subaru 35cc (one person on each bike) and I’ve learned that the R/S 25cc is a pretty pathetic hill climber. It does okay on flat roads though.

    2. [size=+1]Buy the rear 26" wheel from GEBE with the 12 gauge spokes. [/size]

      GEBE has already done the work to get a decent rim, heavy spokes, and a hub that not only has a solid axle, but with an axle long enough to support the lower mount strap (the main bracket). Getting this rear wheel from GEBE solves about 90 percent of the problems you will have. I tried to build the wheel myself and ended up spending (literally) 3 times as much for a wheel that I'm not sure is even as strong as the one GEBE sells. IMHO it's a good idea to buy a front wheel from GEBE as well. Most bikes that sell for under $600.00 have crappy Chinese wheels on them.

    3. [size=+1]Attach the GEBE drive ring to your rear wheel.[/size]

      GEBE will do this for you if you buy the kit and rear wheel from them. It’s a little more difficult to put the GEBE drive ring on 12 gauge spokes than it is to put it on 14 gauge spokes.

    4. [size=+1]Identify potentially suitable bikes in your area.[/size]

      Most standard “road” bikes will have rear forks that are too narrow to handle a rear wheel with the GEBE ring on it. Your best best is a mountain bike, cruiser, or hybrid.

      I recommend larger stores. A larger store will have a return policy in case your bike fails to GEBE-ify. Staff at a large store don’t really give a **** if you bring a bike back because they get paid the same regardless. Smaller shops are totally motivated to push bikes out the door. The are not happy when bikes come back, and returning a bike to a small shop may be impossible, no matter what you were told when you bought the bike.

      I bought the bike that I eventually GEBE-ified from REI. They have a “no questions” return policy. If you bring the bike back in the form of an aluminum cube, they’ll still refund your money. The downside is that they don’t have stores in every state, and they don’t have a large selection of bikes. IMHO, REI stores also have excellent bike repair staff. They seem to enforce high standards on the bike mechanics that they hire, pay them well, and give them decent resources to work with.

    5. [size=+1]Go to bike stores in your area and find a bike that passes the following tests: [/size]

      TEST #1: Does the bike have a derailluer with external gears?
      Opinions vary on this, but IMHO, it’s a mistake to try and put a GEBE/kit on a bike with an internal hub. If the bike has an internal hub, I would look at other bikes.

      TEST #2: Make sure the bike has at least 1 1/4” of clearance between the rear fork and the spokes. See the section below “Clearance on your rear fork” for horrifyingly clear instructions. If the bike fails this test, look at other bikes.

      TEST #3: Is this a bike you’d be happy/comfortable with in general?

      You should not rely on the average bike shop mouth breather to sell you an appropriately sized or adjusted bike. There is a good discussion of getting a bike that fits you in the book “Urban Bikers Tips and Tricks” by Dave Glowacz


      mainly in “Chapter 1 - Choosing a Bike”.

      Note that many people hate the Glowacz book because it does contain some pretty demented advice - like how to grab onto passing trucks and get a free bike ride. However, I still recommend it because it also contains a *ton* of useful information about riding in urban environments.

      TEST #4: Does the store have a return policy? If your bike fails to GEBE-ify, you want to be able to get your money back. It’s best to get the return policy in writing before you buy. If they don’t have one, look at other stores.

      TEST #5: Does the bike have front and rear brakes? You need both if you’re going to have a motorized bike. See “GEBE Requirements for Your Bike” below for more info.

      TEST #6: Does the bike have a front suspension? A cheap front suspension fork is nice to absorb road vibration from a motorized bike. It’s also useful when you whack into a pothole at high speed. A fork with 50mm of travel is ok, 100mm is better. If the bike doesn’t have a front suspension fork, measure the space between the front fork arms. If the space between the fork arms is wide enough, you’ll be able to put a 2.35” or even a 2.5” wide tire on your front wheel, which can also absorb a lot of road vibration.

      For example, the Big Apple tire from Schwalbe (http://schwalbetires.com/node/61/ok) is 2.35” wide and needs about 60mm of space between the fork arms.


      The bike in the picture above has a 1.95” (about 50mm) tire in it at the moment and there’s plenty of room. The fork is about 70 mm wide, which would *barely* be enough for the Schwalbe Big Apple tire. This is a suspension fork, so I’m not that worried about getting a fat tire in there.

      However, If the bike doesn’t have front suspension, and isn’t wide enough for at least a 2.35” tire (60mm), I would reject the bike and move on to other candidates.

      TEST #7: Does the GEBE wheel (with GEBE drive ring on it) fit onto the bike?

      Tell the manager that you are thinking of buying a particular bike, but you want to see if it will fit your wheel (with the GEBE drive ring on it). If noone asks what that weird plastic ring on your wheel is, don’t volunteer information.

      You’ll need someone at the store to remove the existing wheel, and replace with your wheel that has the GEBE drive ring on it.
      Make sure your wheel is on the bike correctly.​
      Make sure there is AT LEAST 1/8” of space between the GEBE drive ring and the upper and lower arms of the rear fork. See the section “Clearance on your rear fork” below for details.​


      If the bike passes all of the tests in this section, buy it, take it home and see if you can put the GEBE/Kit on it. If you can’t put the GEBE/kit on, you can always return the bike and get your money back.

    [size=+2]Appendix A: GEBE Requirements for Your Bike[/size]

    These are things that GEBE recommends your bike have before you put an engine on it. On the GEBE website, this information has been cleverly distributed across 6 or 7 different pages, so I’ve collected it here for yer edification.

    1. Clearance on your rear fork.

      The GEBE drive ring mounts on the "left" side of your rear wheel. ("Left" as though you were sitting normally on your bike.) Because the drive ring sticks out from the wheel, your rear fork must have AT LEAST 1 1/4" between the rear fork arms (upper and lower) and the spokes of the *original* wheel.


      EXAMPLE: Here’s an Elektra Townie 21 speed that’s been parked outside a Pete’s Coffee in Bethesda, Maryland, since 11:00 am this morning. While the owner, a corpulent woman with bad hair, is inside waiting for the next batch of scones to come out of the oven, let us stealthily approach and see if this bike can pass the GEBE rear fork clearance test.


      1. Stand on the left side of the bike (“left” as though you were sitting on the bike).

      2. Measure 8 1/2” from the center of the rear axle along the rear fork, and put a piece of masking tape there. Do this on both the “upper” fork arm and the “lower” fork arm.

        We measure 8 1/2” from the rear axle because that’s where the GEBE drive ring will be when you install it. (This bike has a quick-release rear axle, which is a GEBE no-no, but we’ll deal with that later.)


      3. Now, at your tape marks, measure the clearance between the spokes and the inside of the fork.

        This bike has a bit more than 1 5/8” of clearance on the lower rear fork, and about 1 3/4” clearance on the upper rear fork. That is plenty of room to handle the space needed by the GEBE drive ring.

    2. 26" REAR wheel with 36 12 gauge spokes

      Rear wheels with 32 spokes are very common now, and GEBE does make a drive ring for 32 spoke wheels, but you are better off with a 36 spoke wheel. All of your weight, plus the weight of your bike is being supported by those spokes. The more spokes you have, the less weight each spoke has to support. Sheldon Brown has a very good rant about modern wheels having fewer and fewer spokes.

      There are people who have 14 gauge spokes on the rear wheel of a GEBE bike and they don’t have problems. However, for most people I think the best idea is to buy the Velocity rim from GEBE with the 12 gauge spokes.

      The dimensions of the FRONT wheel are less critical since there's less weight on it, but a 26 inch 36 spoke front wheel is good too.

    3. Solid axle in the Rear Hub

      You can have a quick release hub on your front wheel, but GEBE recommends a hub with a solid axle for the rear. If you’ve already got a rear hub with a solid axle, go to the next step to see if it’s long enough to support the GEBE lower mount strap.

      If your rear hub is a quick release type (like almost every bike sold today), you’ve got several choices:

      1. Buy a rear wheel from GEBE.

      2. Put together a rear wheel yourself. The problem here is that it is tough to find a solid axle rear hub these days. I searched high and low and only found 2: one from Atom Labs (backordered), and a DMR Revolver. I bought the DMR for $80.00, which is $9.00 less than GEBE sells their entire rear wheel for. What I also did not know at the time is that there is a difference between a “bolt-on” hub and a hub with a solid axle. I assumed they were the same. The DMR hub I bought has a reputation for strength, but it is actually a hollow axle. It is “bolt-on” because it has two hex cap bolts that thread in from each side. But the center of the hub is hollow. In my experience it is incredibly tough to find a decent quality bolt-on hub these days. That hub has been almost totally replaced by the quick release hub.

        A slightly simpler solution is to do yourself what GEBE does. Buy a cheap, but decent quality quick release hub, like the Shimano Deore (or more expensive, the Shimano XT) and replace the skewer with a solid axle. You can buy solid axles from GEBE, but Harris Cyclery also sells them. You will either have to replace the axle yourself, or pay someone to do it.

        Axles from GEBE
        scroll down to Axles.

        Axles from Harris Cyclery

      3. You can also make your own axle. I’ve never done this, but it doesn’t look too hard. I ordered a replacement axle from GEBE and it turns out it is:

        10mm threaded rod ​
        Hardened steel​
        1 mm thread pitch​
        8” long​

        As I said, I’ve never made my own axle, but I don’t see why you couldn’t make your own axles as long as you are using 10mm threaded rod made of hardened steel.

    4. Rear Axle is Long Enough to Support the GEBE Lower Mount Strap

      The GEBE lower mount strap is about 3/16” thick. If the axle on your rear wheel isn’t long enough to support the lower mount strap and still give the axle nut enough to grab onto, you have several options:

      1. Buy a rear wheel from GEBE which will include an axle that is long enough to support the lower mount strap.

      2. Buy just an extra long axle from GEBE.

      3. Make your own extra long axle.

      4. Bolt the GEBE lower mount strap to your bike frame. This has the advantage that you can remove the engine without removing the rear wheel, and remove the wheel without removing the engine; and believe me, that’s handy. The downside is that you have to a little bit of careful measuring and cutting to get the GEBE lower mount strap directly to the frame of your bike.



        [post=75008]More details here...[/post]

    5. Front and Rear Brakes

      1. The rear brake could be V-brake, caliper, drum, or disc.

      2. The front brake could be V-brake, caliper, or disc with a bolt-on hub. Many people, including Sheldon Brown, have noted that a front drum brake has very little stopping power. The Sheldon Brown site also has a link to an article where some folks raise serious concerns about using a a disk brake with a quick release hub.


        But see also:

        Sheldon Brown -> Good braking and turning technique can save your life!

    6. Clearance Between the Drive Belt and the Rear Tire


    [size=+2]Appendix B: Reasons Why You Shouldn’t Try to GEBE-ify an Internal Hub Bike[/size]

    First, don’t get me wrong. I *love* good quality internal hubs, especially the Shimano Nexus line. I just think that trying to GEBE-ify a bike with an internal hub is terrible, terrible mistake that you’ll regret. Maybe not today. Maybe not tomorrow. But soon and for the rest of your life.

    1. Many bikes that come with internal hubs have more narrow rear forks and won’t be wide enough to take a wheel that has the GEBE drive ring on it. (To my knowledge, most internal hubs are more narrow than externally geared hubs, which is why the fork is also more narrow.

    2. Some internal hubs have a slightly modified spoke pattern that is going to require you to perform surgery on your GEBE drive ring. First, you will have to get instructions from GEBE on how to do this. Second, I’m against making mods to factory parts unless I have absolutely no choice.

    3. Putting an engine on a bike adds a lot of stress to that bike. If you bust a Shimano Deore hub (with a swapped out solid axle) on your GEBE-ified bike, that’s about 40$ to replace. If the stress of having an engine on your bike causes your internal hub to break, that’s a **** of a lot more.

    4. The GEBE site says that you should not put their kit on a bike with a internal hub that has a coaster brake. I don’t know why GEBE says that, but these are the least expensive type of internal hubs.

    5. If you use an internal hub you probably won’t be able to get a Velocity rim from GEBE with the 12 gauge spokes. This wheel from GEBE is a great value. If you wanted to use your internal hub with this wheel you would have to relace it (and pay for labor, unless you can build wheels) and you might have to drill out the internal hub to take the 12 gauge spokes. I’d be against that for reasons I’ve already discussed in this article.

    6. The GEBE website has 53 reviewers. ONE of those people GEBE-ified a bike with an internal hub. It’s true that internal hubs are less common than hubs with external gears, but I have to believe there are other reasons why the internal hub bikes are outnumbered by 52:1.

    7. Even though you may have a nice internal hub, the spokes and rim it came with are probably crappy, Chinese quality. Using the Velocity rim from GEBE solves so many problems: decent wide rim, super tough spokes, and a solid axle that is wide enough to support the GEBE lower mount strap. If you get a bike with a derailluer, and you buy the rear wheel from GEBE, all you have to do is transfer the cassette from your new bike’s wheel to your GEBE wheel and you are done. In my case, I had to buy a new 7 speed cassette, which cost $15.00. Big whoop.

    IMHO, it is just not worth the headaches and hassles to try and GEBE-ify a bike with an internal hub.

    Attached Files:

    Last edited by a moderator: Dec 10, 2007

  2. azbill

    azbill Active Member

    very informative
    well written post !!!!
  3. kenspice

    kenspice Guest

    Nice job Smap, I put the 035cc GEBE on a Schwinn aeromax and got the solid axle from GEBE. Very easy setup. But there is one important item that you may have overlooked, IMHO. That is whether the bike you buy has rear suspension or not. A mistake is to mount the front mounting strap to the seat tube or seat clamp on a bike with rear suspension. The reasons are multiple. It will not allow the suspension to operate properly. It will put undue pressure on the strap, seat post, Engine mount bolt, or lower engine mount. You can mount the fwd strap to the fender mount or any part of the rear suspension that moves with the rear wheel. That will usually mean a weak mount or a modification of some sort. I mounted the strap to the seat clamp but made a modification that allowed it to flex. That lessens the pressure as the bike suspension operates. A bike without rear suspension eliminates this problem. The afore mentioned problem may show up quite a while after installation as verified in several posts on this web site (broken front straps, lower engine mounts and seat posts). Just another thing to be aware of but easily fixed. Otherwise I am extremely happy with my GEBE/Schwinn mountain bike. Very nice and a useful post for new purchasers and I am sure they will thank you for that.
  4. Scottm

    Scottm Guest

    What an excellent post. When and if I upgrade from Happy Times to GEBE I'll know what I'm in for.
    Thanks for your hard work and time in putting this together.
  5. smapadatha

    smapadatha Guest

    Thanks guys for the kind words. It took me forever to bang that article into shape. I know there are some serious gear heads on MBc who can literally build a bike starting with a stack of chro-moly tubes. Those guys probably put a GEBE/kit together during a lunch break. But for those of us who don't have that background none of this is simple and obvious.

    Those two articles: How Does the GEBE System Work, and Evaluating a Bike for GEBE-ification, are what I wished I'd had when I wrote my first rant on MBc last summer. They would have made life so much easier when I first stumbled across the GEBE website.

  6. uncle_punk13

    uncle_punk13 Guest

    Very good!!! I've been riding and building M/B since 1998, and NOTHING was available back then; it was a matter of build it, test it, break it, figure out why it broke, back in the shop, try some more... And so on.
    I'm so glad we now have this resource, not only for ourselves as experienced builders/riders, but also to be able to better help those who are new, and make their builds that much easier. Good on ya' for that article!
  7. larymor

    larymor Guest

    Excellent Sam
    Not enough is said about the need for a longer rear axle especially....I struggled for hours before I finally whacked off the ends of the axle mount and frame mounted....Maybe you will save someone hours of frustration!!
    Dakotey Lars
  8. sabrewalt

    sabrewalt Guest

    Bike Choices

    I also concur. My GEBE install was fairly straight forward because of the bike choice. To me that is 80pct of the challange and I tell folks that when they show an interest in my bike. It took a long time to find the right bike setup. This tutorial should probably be a sticky.

    I ended up with two bikes because I rejected the first one and will probably just donate the second one to Goodwill.
  9. JemmaUK

    JemmaUK Guest

    Very good - and I agree with most of it...

    I would disagree regarding drum brakes. I had one on the front of the old bike with a 25c Zenoah and it was more than enough to handle a top speed of over 30mph..

    I am myself pondering the wisdom of putting this together on a machine with a nexus hub - it seems as if there is a straight through axle - so there shouldnt be a problem but the thing is slipping I think...

    On the issue of coaster brake it seems to be ok and working fine... although its something that takes alot of getting used to...

    I have to say however that I am much less keen on the new GEBE mount in some respects - namely that of getting the engine off the thing for a start... while it is much more compact and in alot of ways more solid its alot tighter and difficult to work on.

    on a sidenote - whoever it was said that the Tanaka motor is not suitable as a naked engine is right - the airflow is different and there is no cooling to the cylinder as there was on the Zenoah w/out casing... although it has to be said that the vanes on the cylinder for the T32cc are much larger than the Zenoah..

    Jemma xx
  10. uncle_punk13

    uncle_punk13 Guest

    Again, I revisited this thread, in searching for the right frame. I'm not happy with what I have on hand- I'll have to do some brazing/gusseting to get the frame strength to where I want. BUT thanks to this tutorial, my build will be soooooo much smoother once I really get rippin. If not for this, I'd have been building, discovering that the rear stays wouldn't be wide enough, cursing, tearing it back down, throwing the frame across the yard onto the parts pile, and grabbing another. As I have something specific in mind for this build, these measurements are sooooooo helpful. It's gonna be fun to find what I want/need to do it properly, but the end result will be rockin'...!
  11. kenspice

    kenspice Guest

    I again concur with your thread Sam, and agree it should be a sticky. Getting the correct bike by following your instructions and then treating it according to what you have built is essential. There are so many different combinations of rider weight, engines, bikes and gears that can be used with the GEBE system. Because of this, it can be very confusing to a new builder as each combination has its own inherent problems. Your riding style can dictate to a degree what you need to build. After you ride it for a while you will no doubt make some modifications. Reading this web site and especially this thread will save you time and money. Always consider safety first. The engine power and bike strength will depend on the terrain and your physical condition (how much you intend to assist). Spoke size and wheels will depend on total weight and how aggressive a rider you are. If you are going to be on long trips or in the backcountry, a good set of tools will be a necessity. Regular maintenance and inspections will add to your enjoyment and longevity of your build. Break your engine in correctly. I weigh about 200 lb.s and have the wheel and spokes the bike came with. I have ridden it up some really steap hills with the R/S 035 and have about 1000 miles on it. No bent wheels or broken spokes. The engine is getting more powerful with each ride. The wheel gear is tracking true and the tensioner is not too tight but still barely moves. The belt is not wearing that I can tell. The bike is not fancy but is reliable. I give most of the credit to this web site and threads like this one. Ride often and enjoy your New Year!
  12. uncle_punk13

    uncle_punk13 Guest

    Well said sir. I also believe this should be a sticky. I've never run a GEBE set-up, (many different other types though), and already this tutorial has been the first thing I do when wrenching. I open up this thread on the laptop, then I open the toolbox. Finding a frame that fit within the parameters of my vision and this engine kit has proven to be somewhat a chalenge, but I found what I needed. The rest I have on hand, and will begin the build in ernest soon (maybe I'll work on the frame tonight), and it should go fairly smoothly and quickly now, again with the help of this thread. I will also build with the help of the other threads, but this one is the stuff!!!