Dyno Questions

[mustanger]

Question 1. If you change the diameter of your wheels , say 20" down to 18", will you get a higher or different reading on the dyno. Everything else remains the same .

Question 2. If you change to a lower diff ratio on your car , will you get a higher or different reading. Everything else remaining the same .

Please keep it on topic and thanks in advance....Cheers John

[Delco]

Tyres size , diameter , dif ratio should not change the dyno readout if the dyno is operated properly

[Oztrack Tuning]

Lighter wheels i have been told can make a big difference.

[Delco]

Lighter wheels i have been told can make a big difference.


like anything you can trick a dyno

[Oztrack Tuning]

I guess its more the heavy 20" wheels that hold people back. Because usually light wheels like Welds might not be good because they usually have race sticky tyres on them which might have too much friction.

[Wonky]

Lighter wheels i have been told can make a big difference.

Makes sense - if you take it to the extremes and imagine a super light rim and tyre vs. one weighing say 200kg (for the point of the argument) then obviously a lot of the cars power is going to go into rotating such heavy wheels.

It then becomes a question of at what point does comparative mass affect power when you are talking normal wheels and to what extent? :confused:

[CROSSEDUP]

Yep,interesting.
Less Unsprung weight better handling. On dyno ?
Just like Heavy vs Light flywheel.Ones good for holding revs, other good for quick reving . Does it make a difference on dyno?
Answers pls

[iamhappy46]

Depends on which gear your in. A lower ratio(1/2/3) usually give a small gain for a lighter rim. Less moment of inertia is the key.

Also, as a larger diameter rim has more mass further from the hub, they usually suffer in the Nm output on a dyno, as the crankshaft torque needs to get this mass moving. Nm = force(N) x distance(m)
Most dyno operators test in a higher gear to neutralise any affect of inertial gains.

Essentially, two rims both weighing 10kg each on the scales, one a 17" rim and another a 20" rims will having a different 'inertial mass' under acceleration.

There is a comphrehensive article I will find and link.

[Ahyeah]

not sure about dyno figures, but 18's on a subaru rx make a HUGE difference from the stockies!! both acceleration and braking!!

[iamhappy46]

OK, this is a brief article on a Nissan flywheel that is worth reading, then use some of the formulae to work out how your wheels can influence your figures.
Notice that the PAR flywheel weighed more than the Fidanza, yet had a slightly better MOI due to it having more mass located closer to the centre.

http://www.neoed.servaus.net/Pdf/FlywheelComparison.pdf

There is another in depth article on wheels with similiar formulae that I am trying to find.


not sure about dyno figures, but 18's on a subaru rx make a HUGE difference from the stockies!! both acceleration and braking!!

That would also be from the change in rolling diameter.