Gearing a 125 for motorways

[Paul2129]

Hi guys, I'm looking for some feedback from someone who's done what I'm suggesting, I have a CG125 which I'm using for motorway work. I have no problems with the actual bike, actually I really like it, and I have no intention to replace it for anything bigger to do the same job. I do also realise that there are limitations here, there is only so much power, and in this respect it's very different to asking the same question of something without the same limitation of power and top speed... Actually I don't want to go faster, I want to maintain roughly 62mph. It seems to have little problem with this... But it revs it's little nuts off. Clearly, it had 5 gears, but I wondered if it could be re-geared so that 4th 'felt' to the bike like 5th, ie it was similar gearing, giving me a final gear for flat motorways at slightly less revs. I'm not worried about acceleration, or having to change from 5th to 4th on inclines, more that on the level, on motorways, that I could use 5th (as a sort-of 6th) for slightly less frantic 62mph.... If it'll pull it (on the flat)

Does anyone have any experience of this on a similar bike, and can they tell me the sprocket sizes ? I know that Mr Honda was smart, and I know that when I've ridden the bike on motorways, I sometimes change my mind and agree that things can't be improved, I just wondered

Paul

[Ste]

Why the 125?

If you change the gearing in order to make it slightly quieter, you'll still only be doing 62mph and you'll still be getting in everyone elses way.

[stevo as b4]

The CG engine Revs to probably 9000-9500, but will never normally reach this in top. The usual indicated top speed on the flat is about 62-65mph depending on how good an example it is.

On typical motorway uphill gradients you should be able to manage an indicated 50-55mph, but maybe a bit more.

Downhill you can get them to indicate just about 75mph on std gearing, but it will be past peak power Revs.

I think your going to lose more than you'd gain by upgrading, ad you only have 10-11bhp to propel you along on an unfaired naked bike.

Mine used to be able to hold an indicated 60mph most of the time on the flat and gentle up hills. Long motorway gradients could get it below 55mph, but not by much really.

By doing what your suggesting, youd only have four accelerating gears, and one mainly useless overdrive top for ideal conditions or downhill etc.

A std CG can get away at the lights and keep most cars behind it until 35mph, if ridden properly. You will lose the ability to get off the line and have a useful bike in most situations.

[MCN]

The limit is the power output.
You are near the peak power at 55. Possibly over.

The front sprocket may be able to be changed for a tooth less. but since there is very little margin of power you would then struggle on hills.

BIGGER BIKE.

Or suck it up.
60 odd is fine on a CG125.

Edit: 1 tooth less on the front sprocket is not a toothless sprocket. You only get that with abuse.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[Rogerborg]

Speed = power = torque x revs.

You're limited by power and you need revs for that. There's no magical solution to get the same speed out of lower revs without adding more capacity.

Fit a 150cc kit, gangsta.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[stinkwheel]

If you gear it taller, you'll land up constantly changing between 4th and 5th and probably spending more time in 4th with the revs higher than they were before every time you come to a hill.

One thing that would probably help, but which would be very difficult to do without a whole lot of very technical stuff, would be to make the top couple of gears a closer ratio THEN up the gearing. This would make the gap between 4th and 5th smaller so you'd be shifting up into a more powerful part of the rev range and stand more chance of pulling that gear (how many times do you go for 5th to find it wont actually pull it).

Trouble is, you'd need to fit different gear clusters to achieve this. I'm not saying they aren't out there (honda made a lot of bikes and many parts will fit other models) but you'd be looking at totally dismantling your engine and fitting gearing out of another bike which you'd first have to identify.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Paul2129]

That's really great advice. It seems to have little trouble maintaining 62mph. I went to Hamburg Germany last year, and, being (honestly) an experienced biker, I don't expect too much, or particularly push it too hard, but as the journey went on, my cruising speed of 55ish went up to 62 or more. I didn't feel any lack of power, genuinely, until I was back in the UK, heading home from the ferry, and was on the climb from Dover, I couldn't get past the wagons despite slipstreaming them thinking that I could shoot past.
I know these things are tough, but would you expect that constant high speeds on a 125 will cause any damage, there's a 1250 mile 2 day ride planned for this year. Part of the fun (yes, honestly, this is the kind of thing I do for fun) for me, is seeing if this tiny bike can make it to the places I point it at. It's super light, ludicrously frugal, and has a 275 mile fuel range. It makes not a half bad little tourer (perhaps in a 'rather you than me sense) than some more 'made for the job' machinery that I have in my garage.
Can I continue that 62mph torture, and assume that it won't explode ?

[Paul2129]

I'm really impressed by your replies, thanks very much for taking the time on what's not the most interesting of threads.
I found that to get the top speed up for overtaking, getting a low riding position really allowed more speed in top gear, you just do this naturally when you're desperate to get past something, however there isn't much space on this bike, and the natural relatively upright position is hardly aerodynamic, had the position been a bit lower, I could have perhaps added 5 to (maybe an unrealistic) 10mph to the top speed, and therefore talked about re-gearing that might have worked

[stinkwheel]

[Paul2129]

I put a screen on this bike once, it was a relatively tall one, it make no difference to the wind blast.... You just don't get wind blast at these speeds..... And no difference to the top speed.

[Rogerborg]

No argument about the aerodynamics, but a 150cc barrel and piston is both cheaper and less obvious.

https://pbs.twimg.com/media/CMNFmlLUEAALKG_.jpg
____________________
Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[Paul2129]

There has been some pretty beautiful cafe racers made from CG125's, with very low riding positions, weirdly these 'racers' (we can use the term loosely) never seemed to report any increase in top speed, unless they were mainly interested in the cosmetic look of their machines... Which, doing this to a 125 is likely.
I'm tending to use the pillion pegs for my feet when on the motorway, I'm wondering if changing the handlebars would be worth it. I'll have a quick look at fairings, but this is our secret

[stinkwheel]

[Paul2129]

I think that so many cans of soup would be beyond the loading capacity, unless I was to start eating the soup on the way, problem is, I don't like soup

[Paul2129]

It's not a good look riding a CG, and it's hard to contemplate what being caught by someone you know with a 'slippery fairing' attached. If Honda were to actually design something, and for people to use it for this purpose, I think there are bikes such as the Yamaha YZF125 which can crack fairly close to 75 or 80mph, that's slippery, with more power.... And probably the price of a small car !

As it is, I'm gonna enjoy my next bit of touring, and probably set off 10 minutes earlier

[stinkwheel]

[Paul2129]

Re the hand behind the back thing, would it be best to cross the fingers, or give the finger with that hand ?

[Paul2129]

Thanks for the chat, really enjoyed it

Paul

[MCN]

I took a CG125 from Bradford to Hull along the M62. I recorded 72.3MPH on my GPS with my big head and vast posterior tucked in behind the speedo. The prone position makes a hoorova/massive difference and you can nap in that position too on longer runs.

60 MPH on a CG will do no longterm harm. It is not going to melt the piston to the barrel like an Aprila 50.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[talkToTheHat]

Don't mess with the gearing. Tight fitting leather not an advenure parachute jacket and get your chin on that tank. Or a bigger bike.
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Bandit. does. everything.

[MCN]

[The Shaggy D.A.]

[woo]

ive increased the gearing on my honda msx 125 by 1 tooth on the front sprocket going from 15 to 16, the rear sprocket is standard.

Also got an o ring chain instead of the standard non o ring chains as these are stronger and require far less adjustment, the non o rings chains are a pain.

I prefer this set up as i can cruse on the motor way at 60mph at 6.5k rpm instead of 7.5k rpm (redline is 8.1k rpm)
64mph is now 7.1k rpm

real steep hills require me to drop down into 3rd gear but thats fine as overall this feels better for me, bike only has 4 gears

also got a healtech speedo healer to correct my speedo readings

you could try this set up and see how you get on

my bikes not designed to be the quickest off the mark just to do its job

Im taking taking this little bike touring from south east london to north west scotland in the summer and using the motorways from london to glasgow so my average speed should be 60mph
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Elen sila lummen omentielvo!

[Alpineandy]

I really don't understand why you wouldn't get a bigger bike. Even a 250 is more stable on the MWay and doesn't have to be ridden any faster than 62mph. What's more (assuming you have a full licence) you could probably buy a bigger bike for less than your 125 would sell for...
Odd.
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The above comment isn't necessarily the truth and anyone that says it is, is only correct if it's the truth or they're bigger than me.

[woo]

250 wont give you 100 mpg best ive seen from my research is between 60 mpg and 75 mpg

my 125 does 100 mpg using motorways or 130 mpg just town riding

dunno if thats what the OP is after but thats what im after, as i can live with 60 mph on the motorways
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Elen sila lummen omentielvo!