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gear ratio rpm's messed up...mystery.

  • Thread starter Thread starter Guest
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My current secondary redution ratio with 17/47 is 2.765. with a 17/45 it is 2.647.

Even with the 47t I should be under reving by a hair, not over reving by 400? as I am currently 4400rpm @ 100kph and the numbers say I should be 99.7kph @ 4000rpm

This is where the applesauce comes in....my tach/speedo dispayes the correct numbers but I am only actually going 90kph. The theory with my tire and sprogs show correct on my clocks but in reality I am going 10kph slower??????

MY BRAIN HURTSSSSSS.........
 
I did some math...going to a 45 tooth rear and keeping your 17 tooth front, you will go 66mph at 4k rpm's. Given the tire circumference quoted here.

I'm figuring your primary drive and 5th gear ratio the same as an 1150. That math worked with your 17/47 sprockets now.
 
Thanks Bill,

My 5th gear ratio is .961:1 (25/26)

The math all works out with what my clocks are dispaying BUT.. my actual speed is only 90kph or 56mph so I am over reving by 400rpm?
 
I would be happy with that math. That is what I have determined as well but my bike seems to be in the twilight zone.

I must be missing something simple....it is always something simple...
 
How are you determining actual speed?

Do you have a GPS device? that works real good..over a long distance...

.961 is ame as an 1150
 
pacing with my grand prix GT

I have produced a chart of speeds @ 4000rpm in each gear to see if maybe someone has altered the tranny gearing and I will be checking my tach correction with a meter to see if it is out and by how much.

Maybe I have a coil problem. I have just got her on the road after a rebuild and put on some used dyna S. The flatslides are running a little rough too as I am trying to dial them in as well.

Few things going on at once.
 
Does your GT have the stock tires on it...Exact size? Makes a difference..I think the car is off...
 
Also, what is the exact circumference of the tire on the bike right now? Run a string around it and measure the string.
 
Well, the formula I gave you should help you get to a target zone...within a few mph.
 
my math says I should be running 62.7mph @ 4000 but I am only getting 56mph

Thanks Bill for the help
 
THE rpm mystery was a simple deal..the cars speedo is way off. I paced some bikes on the hwy and my speedo is bang on.....oooooops.

thanks for the help and sorry for not double checking my sources....
 
on my 81 GS1100 with GSXR wheels and 530 chain I like the 17/39 gearing. A bigger motor with more Torque likes taller gearing.
 
wow your speedo was useless.

17/47 gives a correct speed at 60mph. 39 is considerably tall....

180mph gearing.
 
speedometer and gearing

speedometer and gearing

Hi Katman. Your reference to the speedometer being useless with 17 39 gearing in your last post leaves me confused. On gs or 90ish GSXR the speedometer pickup is on the front wheel. I don't see where gearing has anything to do with it.
 
I use the GSXR USD front end witht he stock wheel and speedo drive. I assume it's right but I have not checked it. I hope to run 170 in the 1/4 mile with it this summer.... with the Turbo setup.
 
Big_T said:
I use the GSXR USD front end witht he stock wheel and speedo drive. I assume it's right but I have not checked it. I hope to run 170 in the 1/4 mile with it this summer.... with the Turbo setup.
Click to expand...

LOve the turbo's.....
 
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