What does the number represent for a gear ratio?
For example, with a 38 rear and a 13 front the gear ratio is 2.92.
You can get damn close with different sprocket combinations.
For example a 44 rear and a 15 front gives me a 2.93 gear ratio.
What does the 2.92 and 2.93 #'s mean?
Thanks ALot
I also understand that going up one in the front is like going down 2.5 or 3 in the rear and going up 3 in the back is like going down 1 in the front, I'm just curious from an engineers stand point what the # means.
I prefer gearing numbers as rear sprocket/front sprocket (some do it the opposite way). The 2.93 tells you how many times the front sprocket rotates for one rotation of the rear sprocket. A larger number is shorter gearing, shorter gearing means more rpms for a given speed. Shorter gearing gives better acceleration, but less top speed. Tall gearing does just the opposite. How big of a change is noticeable depends upon the bike. Gearing for an RC51 is not quite as critical as for a TZ125.
I use gearing charts to pick a ratio and change wheelbase. For my TZs I have 4 front sprockets and 6 rear sprockets, as you noted, some combinations overlap (same or close to same ratio), these can be used to alter gear ratio and wheelbase. I tend to experiment quite a bit with gearing.
Things get a bit more complicated when you also have different internal gears from which to choose.
It means the front sprocket must make 2.92 revolutions to equate to 1 revolution of the rear sprocket.
As for different combos equaling almost the same ratio, remember, you have a chain on the bike. Different combos may not fit that chain. And it can/will dramatically affect wheelbase which will affect handling as well.
Thanks for the explanation, that helps me.
How does changing the gear ratio alter the wheelbase. ??? Pease explain.
QuoteIt means the front sprocket must make 2.92 revolutions to equate to 1 revolution of the rear sprocket.
As for different combos equaling almost the same ratio, remember, you have a chain on the bike. Different combos may not fit that chain. And it can/will dramatically affect wheelbase which will affect handling as well.
AH HA!!! So if you put a larger sprocket on the rear the chain brings the rear wheel closer to the front causing a shorter wheel base.
I get it! ;)
But, how big of a difference can it possibly make on a SV650. I know you don't have much to play with when it comes to moving the rear wheel foward or back. How big of a difference does an inch or two make?
It can play a HUGE difference. The biggest difference you will notice is turning. A short wheel base will turn quicker (too short will be very twitchy), and a longer wheelbase will seem to be more difficult but smoother to turn.
For Road A, I try to have a longer wheelbase than any other track.
"How does changing the gear ratio alter the wheelbase. ??? Pease explain."
I currently have a 15/42 sprocket combination yielding a 2.8 ratio. I wanted a 16/45 sprocket combination to gain more clearance between the chain and the swingarm pivot(1/4") The 16/45 yields a 2.81 ratio. With the 16/45 sprockets it caused the rear wheel to move forward by approximately 1/2", but I didn't have enough chain length to allow the fitment of the different sprockets.
When you ride a motorcycle that has limited horespower there are times that the gearing won't affect the top speed. Case in point, my stock GS1100 back in the 80's had 15/45 sprockets, I changed to 16/43 sprockets and the result was a slower top speed with nothing else done. It did however allow me to run a better 1/4 mile time due to the one less shift needed. I would match the ET of the then current GSXR1100.
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Also many bikes if you set up the rear end geometry to ideal then you have a radical downslope to the swingarm and need a larger front sprocket to keep chain from riding on the swingarm.