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/to...p?TOPIC_ID=137

[kaz]

try understanding this:

http://www.msgroup.org/forums/mtt/to...p?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.