13T Front Sprocket Speed?
#21
05-03-2012, 11:48 AM
I posted this in another thread some time ago.
42/14 = 3 or 3 to 1. This is the stock gearing ratio. Meaning for every 3 full revolution the front makes the rear sprocket will make one full revolution.
42/13 = 3.230 or 3.230 to 1. Meaning for every 3.230 revolution the front makes the rear sprocket will make one full revolution. Or 3.230 divided by 3 (Stock Gear Ratio) = 1.076 or 7.6% gear reduction over stock. So if you are going 40 MPH at say 5000 RPM with stock gearing. With the 13 tooth front the engine will have to be running at 5380 RPM to go the same 40 MPH. 5000 RPM x 7% = 380 + 5000 = 5380 RPM.
So it is a ratio on the RPM change not a set amount like 500, but close.
14t at 60= 7,000 RPM then 13t at 60= 7,532 RPM
14T at 70 = 8500 rpm then 13t at 70 = 9,146 RPM
42/14 = 3 or 3 to 1. This is the stock gearing ratio. Meaning for every 3 full revolution the front makes the rear sprocket will make one full revolution.
42/13 = 3.230 or 3.230 to 1. Meaning for every 3.230 revolution the front makes the rear sprocket will make one full revolution. Or 3.230 divided by 3 (Stock Gear Ratio) = 1.076 or 7.6% gear reduction over stock. So if you are going 40 MPH at say 5000 RPM with stock gearing. With the 13 tooth front the engine will have to be running at 5380 RPM to go the same 40 MPH. 5000 RPM x 7% = 380 + 5000 = 5380 RPM.
So it is a ratio on the RPM change not a set amount like 500, but close.
14t at 60= 7,000 RPM then 13t at 60= 7,532 RPM
14T at 70 = 8500 rpm then 13t at 70 = 9,146 RPM
You remove 1 tooth out of 14, so the change is 1/14=0,07 which is 7%!
#23
05-03-2012, 11:24 PM
I've been using a 13 T for a while now and like it. 60mph is a good cruising speed at around 6,500 rpm, at 70 it's around 7,000 +. It's raining now or I'd give you a more accurate reading. With the KLX red lining at 10.5 I don't think it harms it to run at 6-8,000 rpm.
#24
05-04-2012, 02:14 AM
I've been using a 13 T for a while now and like it. 60mph is a good cruising speed at around 6,500 rpm, at 70 it's around 7,000 +. It's raining now or I'd give you a more accurate reading. With the KLX red lining at 10.5 I don't think it harms it to run at 6-8,000 rpm.
RPM = (Speed in MPH + 10) * 100
You're saying yours runs 70MPH at 7000 RPM? ...with a 13T on it? That sounds *WAY* low! Are you talking about a 250S or SF? Has your speedo been corrected from the +9.7% the stock speed is off?
Last edited by rgoers; 05-05-2012 at 03:48 PM.
#25
05-04-2012, 02:59 PM
I watch my speedo a lot... it's been corrected, and accurate to the tenth. With the stock 14T, my RPM is roughly:
RPM = (Speed in MPH - 10) * 100
You're saying yours runs 70MPH at 7000 RPM? ...with a 13T on it? That sounds *WAY* low! Are you talking about a 250S or SF? Has your speedo been corrected from the -9.7% the stock speed is off?
RPM = (Speed in MPH - 10) * 100
You're saying yours runs 70MPH at 7000 RPM? ...with a 13T on it? That sounds *WAY* low! Are you talking about a 250S or SF? Has your speedo been corrected from the -9.7% the stock speed is off?
#26
05-04-2012, 08:41 PM
Quit raining and the roads dried
so I went for a ride. Observed
RPM's at 60--6,500, at 70--7,800
uncorrected speed.
so I went for a ride. Observed
RPM's at 60--6,500, at 70--7,800
uncorrected speed.
#27
05-05-2012, 03:47 PM
Should have been:
RPM = (Speed in MPH + 10) * 100.
So... when I'm going 60 I'm turning @7000 RPM, 70 = @8000 RPM, etc. (speed plus 10) times 100).
I checked it again on Thursday... 7000 RPM at 63 MPH.
My speed is corrected (-9.7%), and you're running the 13T (+7%), so that's why the numbers on your 13T look so close to the numbers with my 14T. The two pretty much cancel each other out.
Stock - my speedometer used to read 9.7% high, which is actually a LOT! That's roughly 7 MPH high at 70 MPH.
So when you *think* you're going 90 MPH, you're really just touching 81.3 MPH... Bummer.
Last edited by rgoers; 05-05-2012 at 03:50 PM.
#28
07-14-2012, 08:39 AM
Join Date: Dec 2011
Location: Cheshire, in between the Welsh hilly bits and the Peak district hilly bits - just about in the North
Posts: 78
I have just installed a 13T and went for a run to see the difference - also realised my GPS gives a speedo reading and appears to show the bike speedo is around 10% optimistic. How / What / Cost - is a Speedo Correction ~ magic box of wires that are programmable or just some numbers stuck on in the right place?
Oh and a quick run up my nearest muddy lane suggested the 13T lets you run the engine / choice of gear at a more optimal range ~ I have a big bike for long road runs, so top speed not as critical.
Oh and a quick run up my nearest muddy lane suggested the 13T lets you run the engine / choice of gear at a more optimal range ~ I have a big bike for long road runs, so top speed not as critical.
#29
07-14-2012, 08:43 AM
Join Date: Dec 2011
Location: Cheshire, in between the Welsh hilly bits and the Peak district hilly bits - just about in the North
Posts: 78
I have just installed a 13T and went for a run to see the difference - also realised my GPS gives a speedo reading and appears to show the bike speedo is around 10% optimistic. How / What / Cost - is a Speedo Correction ~ magic box of wires that are programmable or just some numbers stuck on in the right place?
Oh and a quick run up my nearest muddy lane suggested the 13T lets you run the engine / choice of gear at a more optimal range ~ I have a big bike for long road runs, so top speed not as critical.
Oh and a quick run up my nearest muddy lane suggested the 13T lets you run the engine / choice of gear at a more optimal range ~ I have a big bike for long road runs, so top speed not as critical.
#30
10-28-2012, 12:30 AM
13t sprocket
I put a 13 tooth sprocket on my 2012 bike today. Well worth the $9 from Rocky Mountain. Took the bike to work and used an impact on the nut, borrowed a fancy torque wrench. All went smooth. Appreciated all of the warnings I found on this site.