Centre of gravity

[kaz]

I'm still looking for something a bit bigger but not sure whether a scooter (a Gilera VXR200 or maybe even a Vespa GT200) or a motorbike (possibly a Honda VTR250). My main purpose commuting 15kms total each day but also keen to have some weekend fun.

Anyway during my search I have come across mention of "centre of gravity" but I don't understand how it works and why it is important. For example, I have heard good things about the Vespa GT200 centre of gravity but don't know anything specific about what's good about it.I sort of imagine that if CoG is low, it would make cornering easier (and if it was high, you might feel you could tip over)...?

Is it good if it's low? What if it's high? And can you tell by the kind of bike it is, by looking at it, or by its style? Or is it not obvious until you actually ride it?

If anyone can help I would really appreciate it.

[Dave Lobster]

Low isn't necessarily better. Ideal centre of gravity is just above the middle.

[davereid]

Low center of gravity is handy if you have short legs, as the bike can get more off central while you are stopped with a footdown without you dropping it. So if you have trouble holding the bike up at the lights, a bike with a low COG may be handy.

[kaz]

Hi and thanks to both Daves - as it happens I have really long legs so holding up a bike is no issue. I get the idea now that low isn't necessarily what you need. So it is something to do with how the frame is made? Or where things like petrol tank, engine, etc sit on the frame?

[scootnz]

try understanding this:

http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=137

[kaz]

try understanding this:

http://www.msgroup.org/forums/mtt/topic.asp?TOPIC_ID=137

Thanks Scootnz. A very interesting article thought it stretched my attention span for very technical stuff! Also the main forum itself had heaps of other interesting articles which I read so thanks for the referring me to the website.

What I didn't get from the article is a clear and simple (for simple souls like myself) understanding of WHY centre of gravity is important. And if there is any way to gauge something of it by simply looking (rather than riding) a specific bike.

[Pwalo]

FWIW go around a few shops and try sitting, or better still, test riding a few different types of bike.

Buy the one you like most. COG is not important unless you're racing.

[scootnz]

yeah I think actually sitting (and riding) different bikes will help you understand COG in a more real sense, rather than theoretically. I'm used to older style vespas with a pretty low COG - start adding luggage and you soon find out what changing the COG does to handling. You learn to put stuff as low as possible (on the floorboards). Slightly off topic sorry.

I find most bigger motorbikes daunting just to look at, wondering if I could actually hold one up let along ride one, but I expect most are well designed in terms of COG. Surely for most riders things like height, and more so leg length, is what you need to consider when choosing a particular bike.

[Grub]

There's a couple of issues, handling/safety and lifestyle

Scooters are pretty unstable. That 'responsivenes' and 'nipping around town' ability is achieved by an inherant instability which is not something that you need for your weekend riding. The instability in a scooter is a whole bunch of things but CoG and wheel size play a part. Because a scoot is small and light the instability doesn't make them unsafe around town, only when touring. I was very very worried when Nasty was considering a scoot to commute 15km on Wellington's motorway - after getting a bike instead, she agrees.

Lifestyle is a different thing. If you like the idea of going out on the weekends and exploring places outside the 'burbs, then I would stay away from scooters and look at a 150/250 of some sort. A 'real' bike has the ability to tour and see the countryside. It gives you the ability to ride with others and it gives you the ability to join KB functions.

Nasty bought a Suzuki FXR150, it's a brilliant bike. I rode it from Gisborne to Wellington at a 100kmh and loved it, no chore at all. We both then commuted on it for ages and only found the Wellington headwinds an issue. With that bike we 'found our wings' (and KB). I wouldn't recommend any other way.

[scootnz]

A lot of what you say is most likely correct. But I still choose to tour by vespa - and have managed some extensive tours in this way. It is possible to do a 2000km trip on a scooter - it can take a bit longer, but it takes way longer on a bicycle, which is another mode of transport many people choose to tour NZ on. Off topic again.

But anyway, I wasn't promoting a scooter as an ideal choice for the OP, just pointing out that my personal experience is of scooters and not motorbikes. I don't think scooters suit everyones needs and I don't push them to everyone.

[sinned]

CoG is not an issue once the bike is rolling at a reasonable speed. The G forces in balance through the body seat and frame is what makes riding a bike and cornering in particular such a pleasure. In a car, hard cornering is a chore as the sideways G forces are variable and tiring. This is what cage drivers don't understand or appreciate about the joy of 2 wheels. Let's keep it a secret?

[UberRhys]

There's a couple of issues, handling/safety and lifestyle

Scooters are pretty unstable. That 'responsivenes' and 'nipping around town' ability is achieved by an inherant instability which is not something that you need for your weekend riding. The instability in a scooter is a whole bunch of things but CoG and wheel size play a part. Because a scoot is small and light the instability doesn't make them unsafe around town, only when touring. I was very very worried when Nasty was considering a scoot to commute 15km on Wellington's motorway - after getting a bike instead, she agrees.

I disagree, I used to commute 50km each day on Auckland's Southern motorways, have been all around the central north island on my Vespa and find it solid as a rock.


Lifestyle is a different thing. If you like the idea of going out on the weekends and exploring places outside the 'burbs, then I would stay away from scooters and look at a 150/250 of some sort. A 'real' bike has the ability to tour and see the countryside. It gives you the ability to ride with others and it gives you the ability to join KB functions.

I ride with others all the time and I have friends with bikes and scooters. I won't win a race against the big chaps but they have never lost my yet. Mind you I haven't lost them yet either...

The main point I would like to point out is that all 2 wheeled transport is different and your own opinion is everything. Learning to ride on a GN250 then jumping on a HD are miles apart. Just like the difference from a classic Vespa and then jumping on a modern one - poles apart.

As mentioned above by others, go and try them out. Sit on them and feel the weight and then take it for a ride and you will see what I mean.

[scootnz]

Actually I agree about the worries of commuting on the Wellington motorway - its the main thing that stops me moving out to the Hutt - I flatly refuse to commute by scooter on that motorway. But my partner wouldn't hesitate - the difference is the attitude, not the bike. I wouldn't feel safe. I feel much safer on open road, although it takes a lot of focus and mental preparation for me to get started on a tour. I get really nervous. That makes the achievement of getting out there all the more rewarding. Mind you, the issues I face are those of a vintage bike, so its a little different.

[Pwalo]

I learnt to ride on a Vespa 150 SuperSport way back in the 70's. I thrashed that to school and back (J'ville to Wellington Coll) for a few months before I bought my first bike.

I didn't have any issue with the Vespa (apart from that naff combined clutch/gear change left grip), but I much preferred my Suzuki for travelling on the motorway. If your riding was mainly around town then a scooter is amazing fun, and I'm sure that you could travel around the world on one, but in my humble opinion a modern bike offers a whole lot more potential.

[Nasty]

The thing to realise that, what you will learn from this thread, is that each riders ride is different. We all have our preferences for what and how we ride. I considered a scooter and spoke with a few scooter riders prior to completely closing to that idea, in Wellington they found the winds on the 250 scooters still forced them to the backroads, which are not that good. I chose the FXR and it was good as mentioned by the Grub ...

Take you time ... test ride lots of bikes .. and take them out on the motorways if that is where your riding is done .. make sure that the fit for you is right ... as its your body riding it. :yes:

:scooter::scooter::scooter:

[kaz]

Thanks for all the replies about CoG. I am starting to see that I was thinking it was more important than it is (for my needs).

Riding on the motorway is a major reason why I have been seriously looking at a Gilera VXR200 Runner. The wheels are a bit bigger than many scooters (at 14 inch front and 13 inch rear) - still not as large as a bike but still small enough for good manoeuvreability and easy parking round town.

I don't need to go near the open road or motorway for my main purpose - commuting from about 7kms out into town. But I have friends to visit further out of town at the weekend (in Porirua for example) and other places I could go...

I have been a bit puzzled as to why people think the FXR150 is better than, say, a Vespa ET4 150. But from reading the replies on this thread, I think it must be to do with stability (as well as feeling more "at one with the machine"). And I'm learning that engine size is not important on its own and that there's this thing called horsepower that's important here too (ET4 is about 12hp and I imagine the FXR is more than that. The Gilera Runner is 21hp).

So can anyone explain horsepower?

[Pwalo]

Kaz. There isn't any way that someone else can give you a solution.

Have you ridden a motorbike yet? You really need to try one to see how it compares to a scooter.

The larger modern scooters perform pretty well, and you'll have no trouble keeping up with traffic on the m/way. It all comes down to what you feel most comfortable on.

Besides it's a good excuse to take a few test rides.

[Rosie]

A small engineering diversion about Horsepower:
The hp figure quoted for a bike is the amount of power it will produce at a certain number of engine revs. Usually this is the maximum amount of power the engine will produce. So, theoretically, a bike/scooter with 20hp would have more acceleration, go faster etc than a bike/scooter with 15hp.
Because the engine isn't producing maximum power most of the time, hp figures aren't going to tell you very much about the way the bike is going to handle on the road (will it accelerate sluggishly in 50km/h traffic? Will it get to 100km/h going uphill? etc). For small bikes (and maybe scooters too, I've not looked) it can be hard to find data on power output anyway.

And continuing your original motorbike-or-scooter dilemma:
Test ride as many different bikes and scooters as you can. Even styles of bike you don't think you'd want to own. Take them around the sorts of roads you'd normally ride on, and try a few new things as well - maybe go out into the country, since you normally use your scooter to commute.
This gives you a good idea of what is out there, how different bikes/scooters are going to perform under various conditions, and, most importantly, you'll be able to figure out the things you like and dislike about each.

[kaz]

Thanks Rosie. I just found this on the relationships between torque and horsepower http://www.straightdope.com/mailbag/mhorsepower.html
I got a little lost at first the but example near the end (where they graph Car A and Car B's torque and hp as a curve) is really good. It fits with your explanation about taking in to account what you are actually wanting to do (how you use the bike) - e.g. to accelerate quickly, to get up hills, etc.

[mbazza]

I believe a 15km commute on a scoot needs to be evaluated not only in terms of CoG, comfort or safety, but also in terms of driver attitudes towards the rider.
On my scoot I get NO respect from drivers as evidenced by them not seeing me in a lane or at an intersection.
On my bike (probably because of size) I get more respect from drivers.
I ride defensively on the bike and paranoically ( is this a word? ) on the scoot. I love riding both.
Can you get a test ride of a scoot on the motorway to get a 'feeling' of whether you loke it or not? Cheers.:Punk:

[delusionz]

Not to mention respect from fellow bikers too, Scooters get no nods & no thumbs.

[UberRhys]

Not to mention respect from fellow bikers too, Scooters get no nods & no thumbs.

Speak for yourself, when out on the open road I get a heap of nods and waves from bikes. Those that generally don't are Sunday HD riders who may be too busy trying to keep upright or remembering what gear they are in.

I think it is great how those on 2 wheels regardless keep an eye out for others and say gidday in there own ways.

[delusionz]

Speak for yourself
I am, I've had both, I know.


I think it is great how those on 2 wheels regardless keep an eye out for others and say gidday in there own ways.
Nobody gives 2 squirts about scooters, as for HD riders, most of them are gang members anyways

[kaz]

Nobody gives 2 squirts about scooters, as for HD riders, most of them are gang members anyways

So if you don't give two squirts, what are you doing getting aggro about scooters on the scooter part of this forum? We don't criticise bikers for riding bikes. Some of my best mates are bikers and none of us have a problem with each other's rides. We are even secure enough as people to hang out with bicycle riders sometimes :sunny:

[merv]

Scooters, mopeds, and bikes - I happily wave at them all as I ride by.

You're all bikers to me - enjoy!!

[kaz]

Scooters, mopeds, and bikes - I happily wave at them all as I ride by.

You're all bikers to me - enjoy!!

:niceone: We have more in common than we have differences. And if we have differences too, well that just makes for a more interesting world.

[Jantar]

I am, I've had both, I know.


Nobody gives 2 squirts about scooters, as for HD riders, most of them are gang members anyways

Wrong, (don't they teach logic in school any more?)

Most gang members do ride HDs. But that doesn't mean that most HD riders are gang members.

Its a bit like saying "All female motorcyclists wear helmets -- delusionz is a motorcyclist who wears a helmet, therefore delusionz must be a female."

It is a an unfortunate and common mistake in logic to reverse a statement and claim something different.

[UberRhys]

I am, I've had both, I know.


Nobody gives 2 squirts about scooters, as for HD riders, most of them are gang members anyways

Hey no worries, you must be in the group that don't give the nod or wave at scooters. Next time a 2007 Kawasaki Ninja 250R refuses to return the salutation I will know it is you.

[delusionz]

Hey no worries, you must be in the group that don't give the nod or wave at scooters. Next time a 2007 Kawasaki Ninja 250R refuses to return the salutation I will know it is you.

Hey if you nod, I'll nod back, I'm not a snob, all I'm saying is when I was on a scooter I got no nods. I'm not getting agro in this thread I'm just stating what I've experienced with scooters and bikes.