Apparent proof that tire weight affects Dynojet results
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Stellar HDF Member
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From: Lethbridge, Alberta Canada
Now I agree that it is NOT a perfect correction, since real world engines do not get the "best" they can out of any given combination of temperature, barometric pressure, and humidity. But, it's the best we've got, and it's error is normally much smaller than the 2.5% and 3.5% changes we are seeing here in power and torque.
Furthermore, the previous peak power and torque numbers were the BEST that Mike was able to get up to yesterday. Yesterday beat those peaks, and did so using only ONE run and absolutely no changes other than the new tire (positive effect) and the over-oiled air filter (negative effect
).Jim G
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Stellar HDF Member
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From: Lethbridge, Alberta Canada
Racing teams do not specifically try to reduce weight of rotating components but to reduce the weight of the whole system (vehicle).
The marginal differences you noticed when dynoing your bike may as well be primarily caused by the different/better traction provided by your Pirelli tire.
The marginal differences you noticed when dynoing your bike may as well be primarily caused by the different/better traction provided by your Pirelli tire.
They focus on reciprocating weights (like connecting rods, pistons, valves) because their moments of inertia would otherwise tear the engine apart as rpm goes higher.
They focus on rotating weight because lower weight means lower moment of inertia which means less power is diverted to "spinning up" the rotating components when the bike is accelerating.
Ask any actual race team. Like Lozano Brothers. Mike tells me that reducing rotating weight is especially valuable.
And no, provided that the tire was no "slipping" on the dyno on previous runs (it was not), and that the tire was at correct operating pressure (it was), there is no gain via merely a different cross-sectional profile.
Jim G
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I thought everybody knew that it takes more energy (or power) to move or rotate larger or heavier mass. Why do you think drag bikes and drag cars use the lightest crankshaft, pistons, rods, driveshaft, flywheel, rear wheel and tire possible? The heavier an object is the more power it takes to move it.
The lighter your rotating mass, the more power to the ground. That is old news
The lighter your rotating mass, the more power to the ground. That is old news
To my knowledge, no one has ever before specifically proved this. Dynojet of course would like people not to know this, since it highlights a weakness in its design - an uncontrolled variable on a component that IS indeed likely to be changed over time, especially on race bikes which change tire brand/model whenever even a tiny performance improvement is promised or noted.
I have suspected this weakness for some time, but never before had the easy no extra cost opportunity to test for it. My recent change of tire, with its dramatic weight reduction, and Mike's willingness to try the test, finally provided the real world data.
Jim G
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This reduction in gap at the higher rpm MAY be due to the air intake being slightly choked by the grossly over oiled air filter. Mike thinks so. The amount of pink K&N oil we found on the exhaust and rear of the bike was ridiculous, but it would have taken a lot of time to remove the filter, wash it with some sort of non-hurtful solvent, relubricate properly, and reinstall, and neither of us had the time. I'm sure I'll get more dyno opportunities in the future though.
Jim G
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Actully, it means that if you make a change in your engine tune, but also change the rear tire before dynoing the bike again, you won't know if any change is due to the tune change or the tire change.
Jim G
Jim G
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If you made no adjustments to the tune after installation of the lighter tire, then the statement that it means nothing is accurate.
Road Warrior
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From: Triune, TN
You missed the point. The point is that the reported torque and power on a Dynojet dyno can be increased or reduced, WITHOUT ANY CHANGES TO THE ENGINE'S ACTUAL POWER AND TORQUE, simply by using a lighter or heavier rear tire.
To my knowledge, no one has ever before specifically proved this. Dynojet of course would like people not to know this, since it highlights a weakness in its design - an uncontrolled variable on a component that IS indeed likely to be changed over time, especially on race bikes which change tire brand/model whenever even a tiny performance improvement is promised or noted.
I have suspected this weakness for some time, but never before had the easy no extra cost opportunity to test for it. My recent change of tire, with its dramatic weight reduction, and Mike's willingness to try the test, finally provided the real world data.
Jim G
To my knowledge, no one has ever before specifically proved this. Dynojet of course would like people not to know this, since it highlights a weakness in its design - an uncontrolled variable on a component that IS indeed likely to be changed over time, especially on race bikes which change tire brand/model whenever even a tiny performance improvement is promised or noted.
I have suspected this weakness for some time, but never before had the easy no extra cost opportunity to test for it. My recent change of tire, with its dramatic weight reduction, and Mike's willingness to try the test, finally provided the real world data.
Jim G
Do a dyno run with 90 weight oil in your primary and trans, then do a run with 50 weight and you get an increase in rwp because the 50 weight has less resistance.
Do a dyno run in an automobile with an automatic, then install a manual transmission...wow, you gained roughly 5% rwp. Then replace the stock driveshaft with a lightweight shaft...dang, I just gained 3.5% rwp. Lighter brake components...more rwhp....lighter wheel tire combo more rwp.
You missed my point. This is old news dude. You did not increase the hp of the engine at the crank...only at the rear wheel, and there are many ways to do that.
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Stellar HDF Member
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From: Lethbridge, Alberta Canada
Did you make any tune adjustments or are you only realizing what appears to be a gain in torque/HP across the board by installing a lighter tire?
If you made no adjustments to the tune after installation of the lighter tire, then the statement that it means nothing is accurate.
If you made no adjustments to the tune after installation of the lighter tire, then the statement that it means nothing is accurate.
HOW in The World does the gain in power mean "nothing"???
Jim G
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Stellar HDF Member
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From: Lethbridge, Alberta Canada
That's not old news. It's confirmation of a theory I have long held.
Jim G