Tony Posted September 4, 2008 Report Share Posted September 4, 2008 As most know i'm "underprivileged" in the engine department but seeing the dyno sheet from the Supra has my little brain wondering this..... If the dyno is on a rolling road would the software need to know the wheel size?.... Reason i ask is on the printout it says everything including tyre pressures but nothing about the wheel size Quote Link to comment Share on other sites More sharing options...
JamieP Posted September 4, 2008 Report Share Posted September 4, 2008 The Bigger/heavier the wheel the more power is needed to turn them and it does effect the numbers imo, next time im on the dyno i may test the theory. http://www.turbomagazine.com/tech/0106tur_...ower/index.html Quote Link to comment Share on other sites More sharing options...
jammy Posted September 4, 2008 Report Share Posted September 4, 2008 Could you do two runs.one on standard rims and the other with the ones you have now Quote Link to comment Share on other sites More sharing options...
JamieP Posted September 4, 2008 Report Share Posted September 4, 2008 Just thinking about it and no i cant test the theory, I have 14" brembo's on the rear and no chance any smaller wheels will fit. Quote Link to comment Share on other sites More sharing options...
magic919 Posted September 4, 2008 Report Share Posted September 4, 2008 The reason for the tyre pressures being recorded is that it affects how wheel the torque gets transferred to the rollers. I can see no valid reason for wheel size forming part of the calculation. Bit of a minefield, rolling roads and comparisons. And don't get started on so-called flywheel HP... :-) Quote Link to comment Share on other sites More sharing options...
jammy Posted September 4, 2008 Report Share Posted September 4, 2008 Just thinking about it and no i cant test the theory, I have 14" brembo's on the rear and no chance any smaller wheels will fit. Just looked at the pics again and yeah dont think you'd get smaller rims on there thay are some big stoppers you got there Quote Link to comment Share on other sites More sharing options...
Tony Posted September 4, 2008 Author Report Share Posted September 4, 2008 The Bigger/heavier the wheel the more power is needed to turn them and it does effect the numbers imo, next time im on the dyno i may test the theory. http://www.turbomagazine.com/tech/0106tur_...ower/index.html I confess to not knowing how a dyno works, i assume on a rolling road the rollers measure by their revolutions? but inertia is in there somewhere as well..... To my little brain any form of measuring that uses rotational inertia would need a transient scale as reference, wheel weight would impact the inertia but it's the measuring that leaves me in the dark. Quote Link to comment Share on other sites More sharing options...
jammy Posted September 4, 2008 Report Share Posted September 4, 2008 In throry there must be a diffewrance in final readings? When i had my 17s on the astra it wasnt as punchie as with the stock 15s on as the waight difference in the rim would make it react slower so wouldnt the torque atleast suffer a reduced reading Quote Link to comment Share on other sites More sharing options...
Tony Posted September 4, 2008 Author Report Share Posted September 4, 2008 The reason for the tyre pressures being recorded is that it affects how wheel the torque gets transferred to the rollers. I can see no valid reason for wheel size forming part of the calculation. Bit of a minefield, rolling roads and comparisons. And don't get started on so-called flywheel HP... :-) So actual "revolutions" of the rollers is beside the point? Quote Link to comment Share on other sites More sharing options...
NickT Posted September 5, 2008 Report Share Posted September 5, 2008 I don't see how the new Dynos that attach to the drive flange direct can take into account rolling losses of the tyres. NickT Quote Link to comment Share on other sites More sharing options...
Bazza Posted September 5, 2008 Report Share Posted September 5, 2008 I don't see how the new Dynos that attach to the drive flange direct can take into account rolling losses of the tyres. NickT they dont and are not meant to the tyres can cause an inconsistant reading, pressures and temperatures all make a difference from one run to the next, by using the hub mounted dyno you can get a far more accurate reading Quote Link to comment Share on other sites More sharing options...
Bazza Posted September 5, 2008 Report Share Posted September 5, 2008 The reason for the tyre pressures being recorded is that it affects how wheel the torque gets transferred to the rollers. I can see no valid reason for wheel size forming part of the calculation. Bit of a minefield, rolling roads and comparisons. And don't get started on so-called flywheel HP... :-) So actual "revolutions" of the rollers is beside the point? correct as far as my basic knowledge, the dyno applies a force to the wheel/hub and measures the torque applied to maintain the rpm, which is then measured the horsepower is calculated from the torque measurement Quote Link to comment Share on other sites More sharing options...
Sagitar Posted September 5, 2008 Report Share Posted September 5, 2008 The reason for the tyre pressures being recorded is that it affects how wheel the torque gets transferred to the rollers. I can see no valid reason for wheel size forming part of the calculation. Bit of a minefield, rolling roads and comparisons. And don't get started on so-called flywheel HP... :-) So actual "revolutions" of the rollers is beside the point? correct as far as my basic knowledge, the dyno applies a force to the wheel/hub and measures the torque applied to maintain the rpm, which is then measured the horsepower is calculated from the torque measurement . . . . and of course the r.p.m. Quote Link to comment Share on other sites More sharing options...
Tony Posted September 5, 2008 Author Report Share Posted September 5, 2008 The reason for the tyre pressures being recorded is that it affects how wheel the torque gets transferred to the rollers. I can see no valid reason for wheel size forming part of the calculation. Bit of a minefield, rolling roads and comparisons. And don't get started on so-called flywheel HP... :-) So actual "revolutions" of the rollers is beside the point? correct as far as my basic knowledge, the dyno applies a force to the wheel/hub and measures the torque applied to maintain the rpm, which is then measured the horsepower is calculated from the torque measurement . . . . and of course the r.p.m. So the rim size would matter. Quote Link to comment Share on other sites More sharing options...
Sagitar Posted September 5, 2008 Report Share Posted September 5, 2008 The reason for the tyre pressures being recorded is that it affects how wheel the torque gets transferred to the rollers. I can see no valid reason for wheel size forming part of the calculation. Bit of a minefield, rolling roads and comparisons. And don't get started on so-called flywheel HP... :-) So actual "revolutions" of the rollers is beside the point? correct as far as my basic knowledge, the dyno applies a force to the wheel/hub and measures the torque applied to maintain the rpm, which is then measured the horsepower is calculated from the torque measurement . . . . and of course the r.p.m. So the rim size would matter. Not if you measure torque at the axle. The beauty of using torque is that it makes the measurement independent of radius. Torque is a force times the distance at which it is applied. 10lbs on the end of a two foot spanner gives twice the torque of the same force on the end of a one foot spanner. The work done is the force times the distance moved by the force. The distance moved is two pi times the radius. So, if you double the radius, the distance moved doubles, but the force required to produce the torque is halved, so you can ignore the radius. The work is measure in foot-pounds (forcexdistance) and horsepower is the rate of doing work i.e. how many foot-pounds in a minute, so torque times rpm is horsepower. All this is delightfully old fashioned and I am more used to power being measured in watts, which is nice because James Watt is credited with defining horsepower, based upon what weight of coal a horse could pull up a mine shaft. Quote Link to comment Share on other sites More sharing options...
Tony Posted September 5, 2008 Author Report Share Posted September 5, 2008 I've come over all educated..... Nice explanation. Quote Link to comment Share on other sites More sharing options...
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