Dyno Results And Wheel Sizes

[Cobra]

how about trying a 19" on one side and a 17" on the other side ??

watch the car cork-screw off the dyno

all about traction .... I've watched altered results if the rear wheel is allowed the ride up to the top of the dyno roller (I.e. the car wasn't strapped down properly)

oops ... another pandorra's box

tyre pressures anyone ??

[DrewBytes]

I know my wagon's power varies depending on what tyres I run. Same 17" stock wheels with sticky tyres lost 10-15rwkw over the standard factory tyres (same day, same dyno- just a quick tyre change). Been told by a few shops that the type of tyre affects the power reading (can't tell youthe technical reasons why) and from what I've seen it does.

[ktford]

less than 5% hey Drew

Scotty

[Mustang D]

If anyone truely believes that running 17" wheels instead of 19s is going to suddenly give their car and extra 7 or 8% increase in power then how about we all go out and get 12" mini wheels?

<{POST_SNAPBACK}>

This can be proven mathematically, and it does happen in practice. Nobody said that the ENGINE will have 7-8% more power, the fact is though, a lighter wheel/tyre combination with LESS INERTIA will produce higher figures on a Chassis Dyno.

Look at what happens on a Dynpack Dyno, the numbers are significantly higher, because the wheels are removed altogether, less rotational Inertia means more power that it measured by the Dyno.

[geea]

Would anyone know which of the following would give the highest reading. I'm asking because I'll be running my car up on the dyno at easter nats and would like the highest reading the car can get.

1) 275/30/19's with normal road tyres

2) 235/45/17 with new dunlop 3000A's

3) 245/45/17's with Nitto NT555R drag tyres.

Appreciate any imput.

Geea.

[TBO240]

Would anyone know which of the following would give the highest reading. I'm asking because I'll be running my car up on the dyno at easter nats and would like the highest reading the car can get.

1) 275/30/19's with normal road tyres

2) 235/45/17 with new dunlop 3000A's

3) 245/45/17's with Nitto NT555R drag tyres.

Appreciate any imput.

Geea.

<{POST_SNAPBACK}>

using a gear calc program I have 275/30/19=DIA 25.5in

235/45/17=dia 25.33in

245/45/17=dia 25.68in

[ktford]

I'd use the Dunnies Craig as I think the Nitto's will peel badly strapped down on the steel

Scotty

[slapnut]

Tyre circumference MUST influence that RWKW.

The question is .. by how much?

It depends on the difference in the overall circumference of the tyre.

Here is a link to a tyre size calculator that may help.

http://www.miata.net/garage/tirecalc.html

<{POST_SNAPBACK}>

well, using that argumenat so does diff ratio, gearbox ratio, etc etc so come on - answer the Qs - why don't dyno operators need to know these things in order to calculate their results???

<{POST_SNAPBACK}>

Hey Turbo6man

I am not a dyno expert, just a hack, so back off man.

But everything behind your flywheel MUST affect the RWKW.

auto versus manual, - diff ratio - what grease and sh*t is in there - if your handbrake is on or not...

I don't believe that dyno dudes will ever give you an actual figure for fly wheel KW.

If they do give you a figure for FWKW, it is an estimate based on experience and factory claims for FWKW.

The only accurate way to measure FWKW is at the flywheel not at the wheels.

<{POST_SNAPBACK}>

You've obviously missed the point - when was the discussion about FWKW? We've only been talking RWKW so don't make it any more complicated than that eh? So far no one can show even how the RWKW figures are determined or why they vary with different wheel sizes so don't get into FWKW at this point.

If you go back over what I've said - it is that the figures presented mean J@CKSH!T.

If anyone truely believes that running 17" wheels instead of 19s is going to suddenly give their car and extra 7 or 8% increase in power then how about we all go out and get 12" mini wheels?

<{POST_SNAPBACK}>

Turbo6man

I haven't missed the point at all.

It is all to do with Year 9 mathematics - moments to be precise.

If the wheel you are using has a smaller circumference (,with everything else being equal) it will read more power on the dyno.

QED

[slapnut]

I dare anyone to prove this wrong - mathematically of course.

Go for it Brian!!

Edited 24/03/05 10:42 AM by slapnut

[Mustang D]

Would anyone know which of the following would give the highest reading. I'm asking because I'll be running my car up on the dyno at easter nats and would like the highest reading the car can get.

1) 275/30/19's with normal road tyres

2) 235/45/17 with new dunlop 3000A's

3) 245/45/17's with Nitto NT555R drag tyres.

Appreciate any imput.

Geea.

<{POST_SNAPBACK}>

Option 2 most definately.