Sportbike World banner

1 - 18 of 18 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
Why would a person want to lower a bike. Other then the main reason of making it easier for a shorter person. A friend of mine lowered his 2004 gsx600r. The thing is, hes 6 foot. What are the advantages and disadvantaged of doing this???
 

·
Registered
Joined
·
6,400 Posts
I can see lowering the front end to possibly raising the rear end for better set-ups in handeling. Though have never done it.

Still I to have read of people 6', in my case 6'2" & 240lbs lowering the bike. Crumbs I only stand 5'10" when I can staighten up & weight around 175 lbs though more once I put on my riding gear. Also I am a bit short in the arse for my inseam trouser measurement is 29.5".
 

·
Premium Member
Joined
·
3,059 Posts
Well, if it's not for drag racing..it's for the Bling effect....Personally, I think lowering a sportbike is a waste..unless your short..:D
 

·
Registered
Joined
·
1,820 Posts
More like disadvantage, supposedly it keeps wheelies to a minimum and delivers power efficiently to the rear wheel if the swing arm is also stretched. But it seriously handicaps sportbike's handling to more like stretched choppers and HD.
 

·
Registered
Joined
·
6,400 Posts
Hammer gave the correct answer being "--Bling effect...".
 

·
Registered
Joined
·
3 Posts
Discussion Starter #8
How much of a handling hit does it give you. Does it make the bike harder to handle, or just not allow agressive handling. For example if you didn't ride the bike hard, would you notice that it doesn't handle, turn, as well as a non lowered bike??
 

·
Registered
Joined
·
8,798 Posts
Hard to say if you would notice or not. I know I would notice right away. You can do a simple test. Take one of you suspension components (doesnt matter which one) mark the settings, then turn all of them as far as they would go to either side. The effects of dropping the bike are going to be much more pronounced, so if you notice that, you will notice.
You are basically rubbing yourself of ground clearence to lean into, and you are lowering the center of gravity, so you will have to lean the bike more to corner (and you are already low on grounclearance to lean it into)
 

·
Registered
Joined
·
1,820 Posts
Hey Vash, let me just stray off the topic and nit pick a little, there seems to be a clash of opinions here. Your track day Buell buddy suggested that bikes with low center of gravity (his Buell for example, as well R6) allows to carry more speed into the corner, though I'm not sure about this, but wouldn't carrying more speed into corner mean the bike is far more nimble? Thus allow arrays of lines to choose from while going into the apex, so leaning most is not necessary than a bike with higher center of gravity. 600 CCs bikes have lower center of gravity compared to 1000 cc, though not as pronounced, but if we take Ninja 250, which is very low, it becomes apparent that bike is very easy to handle, even if it has ground clearance issues. I always figured things with lower center of gravity allows it to "hug" the surface as oppose to higher center of gravity, which is more stable but not as nimble, like cars VS SUV. Anyway, I could be way off, but what's your take on this?
 

·
Registered
Joined
·
8,798 Posts
You know its one area I'm not entirely clear on. But here is what I know.
The bikes turning ability, is a function of the distance of the CG in respect to the line of the wheels. The further off the line the CG is the more the bike turns. Of course the limit to this is the traction provided by the tires. From this you can see that a bike with a higher CG will move the weight farther away from the line and thus turn more, or so goes the theory. If you ever tried turning a cruiser you will see that at work.
Here is what I think is happening in the case of buell and r6 (well partly anyway) The lower CG requires the rider to lean the bike more, however it also allows the rider to be abit more smooth with inputs (since the same lean moves the weight abit less) being more smooth allows the tires to grip abit better (since transient loads are hardest for tires to deal with) so in effect it makes it abit easier to ride faster. Of course this is just a theory.

What R6 and Buel are famous for is not lower CG but rather mass centralization. That means that most of the mass is right around the CG. I'll have to use a few examples to explain why thats usefull.
Consider throwing a hammer. It would be damn difficult to determine exactly how its going to be twisting end over end in mid flight. However if you track the CG of the hammer you will have a perfect parabolic curve.
So the CG travels in a near perfect curve, while the other weight dances around it. The further away it is, the more it will dance. which on a bike is a bad thing.
If you own a truck, try putting a big heavy weight in the bed. Drive around with it all the way next to the cab, and all the way back to the tailgate. With the weight farther off away from CG you will fishtail all over the place. The other way its not too bad.

Buell's are generally pretty radical bikes. Just consider the rake (21deg) and the wheelbase (51in) Those are considerable more touchy than their japanese counterparts (ussually 23-24deg and 54in) I would guess that an r6 with a 21 deg rake will be unridable by most of us. Perhaps the higher rakes compinsate for the increased rotational mass? or the lower CG? I just dont know.
 

·
Registered
Joined
·
1,820 Posts
Not sure about valid, but that's a pretty sound explanation. I guess lower center of gravity in bikes is not necessarily associated with speed taken into the corner. It could be how effective mass centralization, weight of the bike, and how radical the rake angles are. I can picture a taller bike able to lean more, but it doesn't weed out the possibility that a shorter bike (low CG) with limited leaning capability having to lean more than the taller bike to make a hypothetical turn would be considered less agile. I guess it's very hard to explain without putting the theory at work. But take a pocket bike for example VS a regular 600. It's obvious 600 can lean more, but take it to a turn maintaining 40 mph, I have a feeling the pocket bike could lean in that much quicker and exit out of it. Of course all the weight and steering geometry makes it diffcult to predict. Whether bike has to lean more or less is not the only issue, but I guess how fast it can lean and reach the maximum degree from the line of wheels, a bike with higher CG should take longer. Perhaps we should lower a bike (not stretch) and take it to a track and find out. :D But we'd probably be right to assume that normal bike could lean better than a lowered bike.
 

·
Registered
Joined
·
8,798 Posts
Like I said this is really starting to scrape the edges of what I understand about motorcycle suspension. If we could get a pro tuner in here (if we have any on the board) perhaps than we could get a better explanation.
I'm not entirely convinced on the whole one bike being able to cary more speed thru a corner than another. Assuming they are of simular weight, and the lean is not limited by some hard frame part I dont see why one bike will be able to carry any more speed than another, seems like it would be a function of tire traction.
Oh crap this is going to get complicated as I start to think out loud. Really need some numbers to plot this out.
Ok a bike with a taller CG will have to lean less for the same turn (since the cg moves farther form the line of the wheels) If it leans less, the tires are further off the edge and traction should be increased. I think.

A few more factors in the equation. Wheelbase and trail both affect the flickability of the bike, or how long it will take the bike to lean in. However they do this in different ways. Wheelbase adds a static resistance that the bike has to changing lean angle, wether its from streight to lean, or lean to streight. Trail will always try to stabalize the bike, and bring it back to streight.

Then you have to consider the front brake on the buell. Using one outside rotor allows it to bolt to the outside of the wheel, and less strenght is required in the spokes, since they do not have to transfer braking loads, and thus the wheel can be made lighter. Lighter wheel allows for quicker changes of direction becouse of lesser gyro forces, and it helps grip since the wheels weight is unsprung, or unaffected by suspension.




Can you tell I really want to be doing this for a living?
 

·
Registered
Joined
·
8,798 Posts
I believe we discussed that before, buddy. Even if I could pull out of my ass the ammount of money it would take to get the education (takes alott of cash without being able to take a student loan, much less grants/scholarships) I still couldnt talk anyone into hiring me...

Alas, I dont get to have the same dreams as those around me.
 

·
Registered
Joined
·
525 Posts
With the U.S. having a murder of multimillionaires it is a shame that none of them venture into this market. REally the only thing you need to do is reverse-engineer one of the top Jap bike for the intro-year, and then improve it from there. There are plenty talented engineers here to get this started. How do you think most competitors come up with their models?

Vash- So when you say, "The further off the line the CG is the more the bike turns." Are you trying to say the bike has to be leaned over more to make the raduis (turn) or it's easier to tip the bike in to make the turn??
 

·
Registered
Joined
·
8,798 Posts
leaned over less with a higher CG.

A lower cg will make it easier and quicker to turn but you will have to lean it more. Of course wheelbase and trail has much mroe to do with speed of leaning, than cg height.
 

·
Registered
Joined
·
4 Posts
Z_Fanatic said:
More like disadvantage, supposedly it keeps wheelies to a minimum and delivers power efficiently to the rear wheel if the swing arm is also stretched. But it seriously handicaps sportbike's handling to more like stretched choppers and HD.
That really depends on how low you put it. I lowered mine an inch so I could touch down with more than a tippy toe. I actually had trouble backing out of or into parking spaces. The 1" lowering I did has had little effect on the handling. I am sure there is some but nothing like those streched busa's or those POS chopper/hardley's. Don't go that far pleeeeease..... I needed it lowered to give me better odds at not dropping it. I like it and am used to it know (I haven't grown any more) so it will stay lowered.

Later
B
 
1 - 18 of 18 Posts
Top