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

[katman]

Ok boys,

I need a circumferance of a stock gs1100 rear wheel. I am running 4000 at 60mph. with a 47t rear and a 17 front on my katana. I was running a 49 but wow way tooooo big. I didn't account enough for the smaller gsxr 17" wheel I guess.

thanks guys.

[Anonymous]

Hey Rob,

Check out:

http://www.motorcycle-karttires.com/

It is Bridgstone's site. Go to Motorcycle/ATV tires, then Street Tires, then look up the Sport Touring tires, then BT-45's. They are bias ply and come in close to the original sizes. The mounted diameter is listed for all sizes. You can also track down radial sizes if you go to the radial models.

Mark

[katman]

BOY...it has been a long time.

I did a search of gsr and have found my RPM's aren't that far out of line.

60mph is 3900 with my 47t sprog and about 4200 (a no, no on brake in so I am guessing) with my 49t sprog. The science specified a 48t to keep stock ratio of 15/42. I am now running 17/47.

[Hoomgar]

My 1000 ran at close to 5000 when doing 55 mph when I dropped to a 14t in the front with my stock setup. I am going back to stock now because although it gave a noticable jump at launch I didn't like it for highway riding.

And me being the avid rider I am, I don't just ride one type of road. I ride everywhere so I need my bike to be a bit more "all purpose" than it was. I think 4000 @ 60 is good. I can only hope for that with my new setup.

[Robert Corrie]

My 1150's run 3k at 50 mph. The Kat is the same. The 1260 is 2900 at 50,and thats right on the edge of the warp engines coming on line.

[katman]

I have had a few dudes tell me there stock kats and gs11's are 4k @ 60mph

[Dink]

You guys must get good drugs over there, both my 1100's run stock ratios and run at 3500rpm @ 100 kmh.
Dink

[katman]

You guys must get good drugs over there, both my 1100's run stock ratios and run at 3500rpm @ 100 kmh.
Dink

15/42 Dink?

Very strange how all these stock bikes are pulling different rpms?

I wish I could remember what mine used to run????? I do remember a buzz at 60mph I thought it was around 35k but too many guys are telling me 4k
although my 530 17t is about the same size as my stock 15t 630 on the front..my rear cog at 49 is smaller than my stock 42t yet my rpm is higher?? since the rear cog size is smaller it should be taller gearing.

I guess with all the figuring I have had to do with this project I finally broke something.....

[katman]

Here is a simple gear ratio calculator. It is for bicycles but works just as well when you plug in front and rear sprocket sizes, rpm's and speed.
then plug in a new set of cogs and it will calculate the differences.

http://www.metroyamaha.com.au/Tools/tools.htm

this one looks better....

http://www.rbracing-rsr.com/gearspeed.html

[katman]

Ok,

here we go. I found the numbers...

http://www.cbxclub.com/davespage/mcy80-11.html

It would still me nice if someone could get me the circumference of a stock 1100 rear tire.

[Jethro]

I can tonight when I get home. My bike has a stock size Metzler on it.

For the record, I get about 4k at 60mph. I have a 530 conversion with a 42 on the rear- not sure about the front.

[Anonymous]

It would still me nice if someone could get me the circumference of a stock 1100 rear tire.

OK Rob, you're going to make me do it...

A close approximation of the original tire size is either a 130/80-17 or a 130/90-17. Perhaps someone can enlighten us as to which one is closer. Bridgestone lists the respective diameters as 25.1" and 26.2". To get the circumference, simply multiply by Pi (3.14159). So we get a circumference of 78.9" for the 80 series tire and 82.3" for the 90 series tire.

For your 180/55-17 Bridgestone list the mounted diameter as 24.7", which gives a circumference of 77.6". Not really much difference from the 130/80 listed above. This tire will give you revs that are 1.7% higher (78.9/77.6=1.017) than the 130/80 and 6% higher than the 130/90. So if the stock revs are 4000rpm at 60mph with the 130/90, then your revs would be 4240rpm at 60mph with the 180/55. Not really much difference at all, in the end. If your gearing is messed up, you can't really blame the back tire...


Mark

[katman]

OUTSTANDING MARK,

it doesn't seem like much but it equates to 2.5 teeth on the rear. combined with an extra tooth or too already it all adds up to high rpm. I am going to back down my rear sprog a couple more teeth so I am running 17/46 instead of 17/49

thanks again

[katman]

I checked with a dude with a gs1100 and his rear tire is 80". so I am off te buy a 45t sprog.....

anyone want a brand new vortex polished alum 49t 530 sprog? 65.00.?

[katman]

Ok, I am stumped or burned out or something...

My rear wheel is 1995mm circumference. my front cog is 76.3mm and rear is 227mm and stock is 79.3 and 243mm

76.3/227 530
79.3/243 630

according to the gearing calculator the diff between an 80"(stock kat) and 78.5"(gixxer) is only 70rpm.

The 17t 530 front cog is 3mm smaller than the stock 630 15t cog, BUT my rear cog is 16mm smaller than the stock (243mm) sprog.

Currently my speedo is reading 100kph @ 4000rpm with an actual speed of 93kph. So that would make an actual speed of 100kph close to 4800rpm

So I am lost for an explanation for the high rpm's.