Revs vs speed

[surferbikerdude]

Howzit  

I've got an australian 2002 gs500. (not that austalian version should be any different in terms of the gears and engine)

Awesome bike.

Anyway,
I was wondering what speeds I sould expect at what revs.
These are sum of the speeds vs revs I get:
60km/h at 4000 rpm in 4th gear.
60 km/h at 3500 rpm in 5th gear.

80km/h at 4000 rpm in 6th gear increasing at 20 km/h for every 1000 rpm
(ie 100km/h at 5000 rpm, 120km/h at 6000 rpm etc)

Also, I was wondering why in 4th gear, speep increases proportionally to revs until 4000 rpm, where I can increase revs but speed doesn't increase at the same proportion.
ie, I get
40 km/h at 3000 rpm,
50 km/h at 3500 rpm,
60 km/h at 4000 rpm,

65 km/h at 5000 rpm,
70 km/h at 6000 rpm.

Is this normal? I've only noticed this in 4th gear..
Shot guys

[superted666]

Sounds like the clutch slipping , maybe wrong though. what does anyone else think?

[Kerry]

I don't know about the non-linear ratio, but the RPM vs kph figures sound like they're in a reasonable range.

I started keeping informal track of this kind of info when my 1999 still had the original Exedra tires.  With those tires, 5th gear was the "magic" gear where the two needles (speedo and tach) "tracked" each other:

4000 RPM = 40 mph
5000 RPM = 50 mph
6000 RPM = 60 mph

However, when I replaced the original rear tire with a 130/90 Cheng Shin, the ratios changed.  All of a sudden, 6th gear was the "magic" one where the needles tracked each other.  Huh?  It took me a while to figure out that the larger diameter of the rear tire caused the difference.

At the moment I'm riding on a mostly worn 130/80 Metzeler, and the "magic" gear would be somewhere between 4th and 5th.

Bottom line? Assuming that the bike is running well (and your 2002 shouldn't be worn out yet!) the ratios you get depend on two things: the size of your rear tire and (more importantly) the tooth counts on your front and rear sprockets.

The figures I stated above were all observed while using sprockets with the stock ratio of 16 front / 39 rear.

[Richard UK]

RPM/speed is fixed by gears/sprokets/tyre size, but bear in mind that the dials (speedo and tachometer) are only a 'good enough' guide to what's going on.  

In particular, their accuracy varies at different parts of the gauge, e.g. good around 60kph, much worse around 120 kph.  

They work using magnetic drag - a spinning magnet on the end of cable (speed or tach) tries to pull around an iron cup to which the needle is attached.  The faster the magnet spins, the harder it tries to pull the cup around.  A spring is used to stop the cut spinning right around.  Most of the inaccuracy is due to the spring's response, which is not completely linear.

[Michael]

The motor and gearing are no different on our Aussie versions than the rest of the world.  The only real differences are in the wiring- eg we don't get a switch to turn off the headlight.  The figures you quoted are pretty much the same as I got on my '01.

[pujmonkey]

This is the first time i've posted on this message board, though i troll it often.  I've been studying engines for the past few months and i think i can answer this question.  or at least explain what's going on.

First, its brand new.  i highly doubt that the clutch is slipping.  so lets assume its not.  
if you have complete contact to the ground, no tire or clutch slippage, then the following is true:
in any particular gear, at a certain speed, you will always have the same RPM (or vise versa), whether you're coasting or accerating.  for example, if in 4th, at 40, RPMs at 4000, then no matter what, if your going 40 in forth, you will be revving 4000.  
that seems simple enough, but now look at something else:  at 0 RPM in First, you're going 0 mph, at 0 in 6th, you're also going 0.  in other words, as you slow down in any gear, rpms will approach 0 as your bike approaches 0 mph.  we all know you can't take off in 6th gear (@1000 RPM you should be going 12ish mph already), or stop your bike with 6th engaged, but you see what i'm saying.
therefore,
each gear is going to have an exact rpm to mph ratio, and sometimes it seems like there's a magical gear that follows your rpms.  what happens though is this.  my fourth in 4000 at 40, probably has a ratio something like 931 RPMs per 10 mph (example, cause i don't know).  and starting at say... 35 mph, it seems to match RPMs until around 50, where it seems to stop.  basically all that's happening is the rates are simalar enough to fool your brain into making a calculation that its exactly 100RPM per MPH, and the equipment innacurate enough for it to appear that way.  something like this happens to me a lot when i'm waiting at stoplights.  i'll be in a turning lane and i'll watch the blinkers of the cars in front of me, and for a few seconds i'd swear they were blinking perfectly in unison, but then its chaotic again.  same idea there.  (but that works well because of something called critical flicker fusion, light stays in your eyes for a fraction of a second longer than it actually transmits, which is why we can handle watching a movie in the theater)

on another note, you could logically make a gear that followed perfectly, however, because i doubt there would be an exact rpm to mph ratio made with gears, as those are exact ratios, and 100rpm to 1mph is unlikely.  however, because of the variable diameter of tires, you could get damn close.  but then, that's a LOT of math.  heh.

all in all, its exactly as Kerry says, but hopefully i explain why it seems the way it does.

[TheGoodGuy]

it seems normal.. my 2001 GS500 does the same.. 60km/h (40mph) at 4000 rpm is right.. the same speed in 5th is 3500 or so.. so your bike is running fine.

On the top end I normally get 65mph(62mph = 100kmph) at 5500 rpms and 75mph (120kmph) at 6500-7000

Ofcourse my bike has 6000+ miles on teh clock. If I remember right when I first got it brand new and i finished breaking it in, it was about 5000 rpm for 65mph

I think this is normal.

By the way if I remember right the power curve vs. speed ratio is NOT linear.