| Author | Message | ||
     Lovedabueller |
whats the difference at the wheel number wise with the different gearing setup. ive seen the stock r dynos but no cr dynos. help please | ||
| Ccryder |
I think there is an 8% difference in gearing b/t the r and cr. Engine performance numbers may change but only relative to RPM, not absolutes. | ||
| Naiguy |
Being that the change is on the final drive. The way a dyno works would not see the change. Excelleration from stop to 150 is where the difference is. | ||
| Xl1200r |
Won't be a difference on a Dyno, assuming it's set up correctly. The lower gearing means the CR multiplies the torque more than the R, so it can only be felt when riding. | ||
| Ccryder |
Mark: Please help educate me. Will the peak torque number change or, will the location of the peak torque number in the rpm range change, or both? I can get my brain around the location in the rpm range changing but, not the magnitude of peak torque changing with just a final drive gearing change. Pls help clear up my fuzzy brain. Thx Neil S. | ||
| Spike |
This might get ugly as dyno threads often do, but I'll give it at shot anyway.
The torque number reported by the dyno should not change at all aside from the normal variance between different bikes and different dynos. The torque reported by a dyno is a bit misleading. An inertia dyno will measure how much power was delivered to the roller. It then uses the engine RPM to calculate the torque output of the engine across the RPM range. The torque figure displayed on the dyno chart will be the engine torque as measured at the rear wheel. This is not the same as the actual torque delivered to the rear wheel, which will be different depending on the gearing. With the 1125R and 1125CR the engines are in the same state of tune, so they should produce the same horsepower and torque. The CR has shorter gearing and thus will deliver more torque to the rear wheel (and the roller of the dyno), but since the dyno is calculating torque at the engine based on the power delivered to the rear wheel, the amount of torque it displays on the chart will be the same. | ||
| Xl1200r |
Neil - Spike is pretty close, at least in my understanding. The only thing I would want to add is, AFAIK, the Dyno knows what the trans and final gearing ratios are. Spike is right about the misleading figure - the torque delivered to the rear wheel is a much larger number than what a Dyno reports because everything between the crankshaft and the tire acts as a torque multiplier - the higher the overall gear ratio, the higher the multiplication factor. That's why you can accellerate at a faster rate in 1st gear than you can in 6th. And that's why a CR, with it's shorter overall gearing, would outaccelerate an R up to the CR's top speed. The peak numbers and the shape of the curve would not change between the bikes. The Dyno is aware of the force being put on the drum vs. the engine RPM. But it also is aware of the RPM of teh drum, and therefore, in a roundabout way, is aware of the overall gear ratio of the bike. The CR may be able to spin up the engine RPMs faster in a given gear than an R, but the Dyno knows that the drum speed is less on the CR, so that's taken into account. The gearing difference would show up on the dyno if you were to use Time or MPH on one of the axis. You would see lower MPH on the CR, but faster times to get through the rev range. | ||
| Ccryder |
Thx, that's what I kinda thought. I have seen some dyno charts with MPH versus RPM and that chart might show up the difference. That difference would be reflected by an offset of the torque versus the MPH between the two bikes. Too much play and not enough work, BACK TO WORK, Neil LOL!!!! | ||
| Xl1200r |
Yeah, MPH would be lower both bottom and top end for the same gear on the CR vs. the R. | ||
| Buelldyno_guy |
There are two major differences in how the Dyno manufactures give you a TQ and HP numbers. Some use "Mass X Acceleration" They know the drum mass so they measure how long it takes to accelerate it up to speed, basic physics. On those the final drive ratio as affected by gear choice, tire diameter even as it changes due to heat, so as the final drive ratio changes so do the "Numbers" Other company's measure the TQ using a load cell and calculate the HP by using Watt's calculation of measured TQ * RPM / 5252. On those the final drive ratio has little affect on the numbers. Ours actually discounts out three types of inertia. Inertia "A" which is the engine and drive line, inertia "B" which is the manufactured inertia of the drum. Our drum is 16 inches by 64 inches and has it's inertia of 7.750 stamped on it. the final is inertia "C" or the inertia of the eddy current brake. These are all used in a formula by the control software. One big difference in how ours works compared to others is that I chose the inertia "A" from a pull down menu, so when running a 600cc-IL4 I chose 0.082 and if it is a 2 cyl 1200 I use 0.088, then those values are used in the formula. Again the most common Dyno is a plug and play that uses the "Mass X Acceleration" method so final gearing becomes important. Hope this helps. Terry - www.jtsperformance.com | ||
| Boltrider |
Further info to back up what Terry said can be found on this streetbike website under the "gear ratios" section. This is probably why the whp numbers of the CR seem a little low in comparison to the R if the dyno pull was done on a Dynojet. Nothing to worry about really. http://www.hotbikeweb.com/tech/0808_hbkp_dyno_tuni ng_for_engine/dyno_testing_and_gear_ratios.html I think we can also say that the same principles apply to cars/trucks. I don't see why they wouldn't. (Message edited by boltrider on June 21, 2009) | ||
| Rsh |
The streetfighter shootout from 6/09/2009 at Motorcycle.com has dyno numbers for the CR, scroll to the bottom of the article. http://www.motorcycle.com/shoot-outs/2009-streetfi ghters-shootout-aprilia-tuono-1000-r-buell-1125cr- triumph-speed-triple-87798.html |
