pegscraper Posted January 21, 2007 #1 Posted January 21, 2007 (edited) Here is a chart some of you may find useful, since this question gets raised occasionally. It compares the engine rpms of a stock 2nd gen Venture against what they become when a V-Max rear gearset is installed. Mph is down the side, gear number is across the top, stock gearing rpms are on the bottom of each box, and the rpms with the V-Max rear gear is on the top of each box. To make things a bit more readable, the rpms are rounded off to the nearest 10, which isn't detectable on most tachometers anyway. If you're one who doesn't like math, then don't bother to read the rest of this. The stock gearseat has 33 teeth on the ring gear and 10 teeth on the pinion gear, where the V-Max rear gear has 9 teeth on the pinion gear. Basically, the V-Max rear gear will raise the engine rpms about 11% over stock: (33/9) / (33/10) which simplified goes more like this: 10/9 The numbers in the chart are calculated figures based on the results of one of my dyno runs, which eliminates the speedometer error (about 10%) inherent in our bikes. The dyno indicated an engine speed of 6610 rpms at a road speed of 87.33 mph in third gear with a V-Max rear gearset. Then I calculated out the miles per hour and the transmission ratios to get the rpms at other road speeds and in other gears. Since my bike is a Royal Star which has a different primary gear ratio as well as different transmission ratios then the Ventures, I had to calculate through all these different ratios to get what rpms in a 2nd gen Venture would look like. For starters, at 90 mph in third gear it goes like this: 6610 / 87.33 x 90 / (29/25) x (30/25) / (85/51) x (87/49) = 7510 where (29/25) is a Royal Star third gear, (30/25) is a Venture third gear, (85/51) is a Royal Star primary reduction ratio, and (87/49) is a Venture primary reduction ratio. And that is with the V-Max rear gear since that's what I started with. To get the rpms with stock Venture gearing, multiply by 9/10. Clear as mud? You were warned. I drew a few different charts showing rpms with various transmission and rear gear ratio combinations on both Royal Stars and Ventures. I made them for myself quite a while back, partly because our bikes don't have tachometers and I wanted to know what rpms I was running without spending the coin it takes to buy one, and partly because I wanted to know what would happen with different transmission and rear gear ratio changes. Edited February 7, 2016 by Freebird
Squeeze Posted January 22, 2007 #2 Posted January 22, 2007 Hi Pegscraper, nice Chart you made, really ... If you're gonna take yourself more on the engineering Side of this Questions, google for Geardata. It's a free Programm, in which you can see any changes of any Gearratio takes it's Consequences. very small, very simple, easy to use.
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