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

[katman]

according to my calculations the 530 gears are as follows:

front is 3.8% smaller than the stock one
rear is 6.6% smaller than the stock one.

That should make a drop in rpms? not a rise....

The gixxer rear tire is 2% smaller than stock which should offset the smaller rear sprocket so rpm's should not be affected by much.

Correct me if I am wrong????

[Anonymous]

Hi KAtman!

You have too high gearing. If you measure the org. 15-42 it is 2,8:1
With 17-49 you get 2,88:1. When I went from org. wheel to a modern 160/60-17 I had to go up one teeth in the front = 42/16 wich gave me 2,625:1. That was as close to the org. rpm/speed I had. If you want to use your 17 front sprocket, a 45 in the rear would give 2,647:1 in ratio.

The 180 tire is a bit higher than a 160 so the small difference in ratios should be eliminated by that.

Go for the 45, thats my suggestion -for what it is worth....

/Chris

[katman]

a 45t will only bring my rpm down 150 revs. I am still way over. the 2.88 vs. 2.8 is only 50rpm. That I can live with. it's the 100's of rpms I am trying to sort out and can't.

My mind is apple sauce.

thanks for your reply..

[Anonymous]

a 45t will only bring my rpm down 150 revs. I am still way over. the 2.88 vs. 2.8 is only 50rpm. That I can live with. it's the 100's of rpms I am trying to sort out and can't.

My mind is apple sauce.

thanks for your reply..

You?re welcome Katman.

The thing is, if you run a 17-45 combination with the R-wheel you will get as close to the org. ratio as you did with the 130-90/17 baloon. When I rebuilt my rear wheel I started out with ratio 2,88:1. That meant 5000rpm at 120km/h, close to 65mph. changing ratio to 2,8:1 meant app. 130km/h or close to 70mph. Not a big difference you might think when looking at the numbers, but difference in feel -enormous. Note that all measurements were done with the org. speedo after 20some years...
Hmmm, a lot of repeating it feels like...If you want it to go a little faster than org. go for a 44teeth.

My current project will use 16-42 with a 180-55/17 tire, same as before but the diameter of the rubber is 10mm larger than the 160-60/17.

44 or 45, you can?t miss, and btw: Leave the applesauce on the table for the children instead, no good up where you keep it...

[gsbill]

This worked for us racing..It may not directly help your gearing concern, but here ya go

RPM x Rear Tire Circumference X Front Sprocket Teeth
______________________________________________

Primary Ratio X 5th Gear Ratio x Rear Sprocket X 1056

Will yield top speed at given rpm..

Your gearing can also be simplified by dividing rear sprocket by front sprocket

15 front 42 rear =2.8 ratio

17 front 47 rear= 2.76 ratio...higher gear, less rpm per mph

[katman]

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.........

[gsbill]

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.

[gsbill]

I got 69.5 mph...115kph at 4400 rpm. Clutch slipping?

[katman]

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?

[katman]

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...

[gsbill]

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

[katman]

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.

[gsbill]

Does your GT have the stock tires on it...Exact size? Makes a difference..I think the car is off...

[gsbill]

Also, what is the exact circumference of the tire on the bike right now? Run a string around it and measure the string.

[katman]

yeah, she is all stock

tire is 1985