MotorCycle Gearing

[jraice]

Hey guys, anybody know a bit more then the average joe about ideal motorcycle gearing?

As some of you know, my currect situation is that Ill be getting my first bike, a classic rare 1982 Honda MB5 in just three short days, and that I plan to modify it a good bit over the next month or so...

Besides a few cosmetic parts to add to the racing look it will get...
Sprockets (subject of this thread)
66cc Airsal Big Bore Kit
20mm Mikuni Carb Kit
Techno Racing Exhaust
Olympia Carbon Reeds

Clearly it will still be a small CC motorcycle but I hear these sort-of mods can make a good deal of a difference, and they are all bolt on parts with just a few adjustments (carb's) that need to be played around with...

Anyways, I plan to leave the rear sprocket at 43, why? Its the more expensive of the two so I'd rather replace a less expensive front sprocket to alter my gearing.

Stock it has a 13 tooth sprocket. With modifications and stock gearing this bike would have tremandous torque (again, this is all relative to most 50cc bikes, not a 600cc Middle Weight sports bike), probably a bit higher end speed then stock (can achieve redline in 5th gear easier) but would not generally get me to my goal and would require shifting pretty quickly...

My goal is to get the best medium of power (for climbing hills) and top end speed (to keep up with traffic).

On the flats this wont be an issue, its more on the hills.

16 tooth front sprocket is often used for all out speed but I dont believe it will give me the torque I desire.

So really its a choice between 14 and 15.

Thoughts?

I have been playing around with some online gearing calcs and clearly the 15 will have higher top end speed... But its hard to find a good medium... And Ill likely have to just try one out and see how it feels but I cant decide where to start, 14 or 15.

If you guys would like I can give you specifics on the bikes gearing ratio's, tire dimensions and powerband...

Lastly, what should I look for in the riding of the stock bike in terms of helping me make this decision? If the stock bike readily nears redline in top gear, would that be enough evidence to say I should go all the way from 13 to 15 with the mods (and vise versa, if the bike lags in top gear I would know to do a smaller step in gearing)

[Easy Rider]

Originally Posted by jraice

Hey guys, anybody know a bit more then the average joe about ideal motorcycle gearing?

Well yes, as a matter of fact, the manufacturer usually knows a LOT about it!

The first problem is finding sprockets that will FIT that particular bike.
If you can find them, I would only go ONE tooth at a time.
Small sprockets like that are relatively cheap.

If I were doing it, I'd try the stock ratio first.
You still don't seem to get the reality that an extra 16 cc isn't going to make that much difference........a couple of tenths at the track maybe but on the highway, not much to notice.

I admire your enthusiasm and this project will be worthwhile because you will no doubt learn a LOT (some the hard way) but whether the end result will be what you hope for is another question.

Good luck!

[themeatmanlandry]

Originally Posted by jraice

Besides a few cosmetic parts to add to the racing look it will get...
Sprockets (subject of this thread)
66cc Airsal Big Bore Kit
20mm Mikuni Carb Kit
Techno Racing Exhaust
Olympia Carbon Reeds

Clearly it will still be a small CC motorcycle but I hear these sort-of mods can make a good deal of a difference, and they are all bolt on parts with just a few adjustments (carb's) that need to be played around with...

Question: Since when do they make bolt-on big bore kits?

I'd suggest following ERs advice about moving one tooth at a time, and not expecting a world of change from the modifications.

[jraice]

I had a feeling I get responses like this ...

Yes yes I am aware its not going to make a world of differece but I think it will be a fun project and a fun bike I will keep for a while, even after I get a "real bike"...

The big bore kits are bolt on and I would guess maybe its a two stroke thing or possibly a small CC engine thing, because almost every two stroke big bore kit I looked into was the same design... I even found an interested you tube video of somebody putting a 28.5cc kit on a 23cc RC car.

I dont expect it to suddenly become some sort of racing machine but I have heard that these mods do make a noticable difference and I just feel that it would be a very fun experience to do this many mods to a bike (would be much to expensive on a larger bike, all of these parts will cost just about what a slip-on exhaust costs for a larger bike) and tweak it, and maybe learn a few things along the way such as carburator jetting etc...

Alrighty so Ill likely ride the $#%@ out of the bike stock, get a good idea of the performance. Then do all the mods (no sprocket) and see how it compares... And then start throwing sprockets on there...

Maybe Ill just "waste" $15's and get a 14 and a 15 in my order.

[Easy Rider]

Originally Posted by themeatmanlandry

Question: Since when do they make bolt-on big bore kits?

I've never looked into it but.......on a 2 stroke, why not?

No real "heads" to worry about so then you've got the cylinder with valve ports bulit in and a new piston/rod. If the stroke doesn't change, the old crank will do.

While it doesn't match the common understanding of "bolt on", technically I think it would be.

[DrBob]

Wow, haven't seen one of those things in years!

A buddy had one back in the day. He put a big bore kit in it, but it still would not do more than about 55 or 60 MPH, maybe 40 with a passenger. Fun little bike though- that motor would rev sky high and never blow. Had that classic two-stroke buzz- definately the coolest moped ever made!

[Uncle Bob]

Jraice, think you're going to become our expert on modding 50cc bikes.

So just go for it and keep us posted !

You'll theoretically increase your max top speed with a larger front sprocket but this will put more strain on the engine, it's going to be to some degree like taking off from a standstill in second or maybe third gear all the time.

I'm guessing it'll take forever to get to your new max speed and midrange power will suffer because for any given speed the engine will be below it's power band max output.

[jraice]

Uncle Bob...

Those are good points and is why I dont want to put the large 16 tooth sprocket up front...

However, the bike comes stock with a 13 and works well.. Considering Ill be getting a bit more performance front the engine, if I moved up to a 14 tooth front I could end up with the same torque, engine running in the same power band except it would slightly race my top end speed... No?

Most people say the bike does about 50mph stock in most cases, a bit faster if you are really trying...

However a few people, one person for example, say its a bit faster then that. I am talking to one MB5 rider who says he routinly takes it on the freeway and at redline (10,500rpm) it 5th gear he can fly away at 60mph forever (he does pretty long rides like this) and said even uphill or in the wind he can maintain 50-55mph... Now thats a stock bike...

I think Ill order a 14 tooth sprocket but leave it at the stock 13 after the mods to see how it performs...

Alrighty guys!

Bike comes in 2 days... Hopefully ordering my service manual tonight. Ill order performance and cosmetic parts sometime next week and lastly I need to pick up some other goodies inluding transmission oil, engine oil, maybe some brake fluid...

Eventually (probably when I add the performance parts) I plan to give the bike a slight overhall by replacing all the fluids and inspecting brake pad wear...

Also I was thinking about getting a new spark plug (bike only has 4,000 miles) or is that total overkill? I have heard you can use the color of the plug to diagnos how your engine is performing, and I know its recommended to change them closer to 20,000 miles then 4,000 , but it is a 25 year old bike...

[Easy Rider]

Originally Posted by jraice

Also I was thinking about getting a new spark plug (bike only has 4,000 miles) or is that total overkill? I have heard you can use the color of the plug to diagnos how your engine is performing, and I know its recommended to change them closer to 20,000 miles then 4,000 , but it is a 25 year old bike...

I don't know this for that particular bike, mind you, but experience with some 2-cycles about that vintage tells me that you've got it backwards. My guess is you'll be lucky if a plug lasts 1000 miles. You ARE burning oil WITH the gas remember. That tends to leave deposits in the chamber.....and on the plug.
And anyway, plugs are cheap.

[jraice]

I think I saw on the MB5 site that they recommend every 22,500 miles..

But they are cheap... If I can find one locally Ill put it in when I do the other mods.