With about a month left before the races I’ve got quite a lot of work to do. I’ve been making progress but you know how these things go. I’m working on the hobbit engines first so the Tomos is in planning and parts ordering phase. Last time I talked about the rules as I read them and were planning to interpret them but I also know that as they are written is not exactly how the class is run. Stock is more “stock” and unmodified frame is more “this was a moped once”. I had a conversation with Jake Cain about them, who is helping the planning and organizing, and he explained in more detail the allowable creativity. That’s great but I want to build a stock bike, so I am going to keep it as actually stock as possible.
My philosophy for this build will be fairly basic. I will allow myself some machining ability on some parts but not cnc (which is what I do for a living so I can do some silly stuff, but that’s pretty unattainable for most people, best kept to the hobbit build), I will restrict myself to only parts that would have come on a tomos or can be purchased from Treatland (except a couple special parts). I can modify the forks internally but not externally and I can run different rear shocks. I can try to maximize the stock motor and drivetrain as much as possible with only basic tools available to most people (except a little bit of lathing and welding), but otherwise it will be pretty bare for mods.
First step is to take notes on the bike and do some research. I have my usual stock A55 around town bike as my comparison to use and I know what I’ve done to that and how it runs. That’s my base of comparison for this build. Now I know that my red tomos makes a little over 4hp (because of the dyno day) but that only came with the 17mm carb. The stock carb ran at 3.1hp and since that is my limit on this bike I’m going to have to do some work to get this as fast as my daily. Now since I am limiting myself to treats for the moped specific parts I don’t have many options for pipes. In fact they only had the biturbo, the MLM peoples pipe, and the Treats black pipe, I already use the black pipe on the daily so it made my pipe choice pretty simple. The rest of the motor is going to be stock so all that’s left for me to do is to port the cylinder and modify the head. The intake, carb, airbox, will be run without mods but with my velocity stack of course. The stock motor runs around 8400-9000 rpms with the factory porting so the plan is to increase the port timings to closer to 120 transfer, 140-150 intake, and 170 exhaust then increase the compression to around 160psi measured. That should increase my rpms ceiling to 10k rpms easily and give me back that lack of power from the smaller carb. I’ll gear it shorter than the daily to 26:24 to keep the same top speed range and hopefully increase the acceleration. If I can get this bike to be faster in a strait line than the daily tomos then I know I’m doing pretty good.
The transmission on the A55 is basically the same as the A35 as far as I know with no changes in gearing or basic design so I don’t think there is any advantage in tracking down different parts so I’m just going with the stock parts. I will attempt to lighten and balance as much as I can on the gears. I weighed everything and inspected what I can remove and they didn’t make it easy. All of the gears are solid with no relief holes so the easy solution is to punch a bunch of holes in them, but without using a mill that’s pretty hard to do accurately. If you drill holes in them but they are not perfect the imbalance of the parts will make the bike terrible to ride so my plan it try and turn as much weight off them as possible with a lathe. The clutches themselves will only be modified by springs and oil type and volume so not much to do there. I will try to balance them as best I can with a scale but not much else.
Stock A55 forks are 30mm, standard dampening rod forks and for the moped world are pretty nice. But dampening rod forks don’t perform great in general so I bought the smallest fork diameter Gold Valve cartridge emulators they make. So basically forks have two main functions, the springing and the dampening. Spring is the force to return the suspension to neutral based on the wheel position, and dampening is the force feedback based on the rate the suspension is moving. A fork with no dampening is basically an oscillator and if you have ever ridden in a car with blown shocks that never stops bouncing that’s the feeling. So the dampening is very important in how the forks feel but the way a dampening rod fork works is not particularly refined. They tend to be soft at low speed movements and way too stiff with larger bumps, basically the opposite of what you want. The Gold Valve system is designed to give you much better dampening response with great tunability while not requiring a lot of modification to old style forks. Sounds perfect and I can’t wait to try them out.
The rear shocks will be upgraded from treats but also using slightly longer shocks. The stock shock length is 280mm but I want a steeper fork angle for cornering. You can’t really move the fork tubes up very far because of the handlebars so the only option without frame modification is longer shocks. I tested a set of 310 shocks on the daily and really liked the change in handling. There is no room for longer shocks either since the swingarm contacts the pipe mount with that length already so the adjustable length treats progressive shocks should be perfect.
I weighed the stock spoked rims and they came in at a hefty 7.2lbs for the rear. Just the steel rim itself weighed 3 lbs by itself. So I emailed treats and asked how much their aluminum 16″ rim weighed and they responded with 2.5lbs. I had a set of A35 mags and the rear weighed 6.4 lbs total, so even if I used the aluminum rims on the spoked wheels they would still be heavier than the older mags so mags it is then. I also plan to install valve stems into the rims and run them tubeless, cutting even more weight off the wheels. Tire selection is pretty slim and really only leaving me with the 2.5 GP1’s so guess that’s what I’m running. My favorite moped tire is the Heidenau K56 but they are not available in 16″, so it goes.
The rest of the bike is really just removing anything that’s not needed to reduce weight. Honestly it’s a pretty simple build but I think I can extract a lot of speed from it. It’s going to come down to little changed and tuning. Stock class is a very rider dependent class so hopefully I can make up some ground by just riding better. But that’s never been my strength so we will see.