Dyno Results And Wheel Sizes

[PASHEN]

Do wheel sizes affect the dyno result? I mentioned that they do to Scotty last year and he pissed himself laughing. Would like to hear from people who:

1. ARE dyno experts

2. HAVE had their cars dyno'd, especially if on 2 different wheel sizes

My car was tuned to 333rwkw on 17 in tyres. Fitting the 19's showed the power figure to be 310 rwkw.

I had the power de-tuned back to 310rwkw on 17's. A recent dyno with the same power level on my 19's showed the power to be 285rwkw.

Have others found the same thing? If so, for brag value, obviously everyone will be quoting power figures from dyno runs with smaller wheels?

Would appreciate a discussion on this.

[geea]

Do wheel sizes affect the dyno result?  I mentioned that they do to Scotty last year and he pissed himself laughing.  Would like to hear from people who:

1.  ARE dyno experts

2.  HAVE had their cars dyno'd, especially if on 2 different wheel sizes

My car was tuned to 333rwkw on 17 in tyres.  Fitting the 19's showed the power figure to be 310 rwkw.

I had the power de-tuned back to 310rwkw on 17's.  A recent dyno with the same power level on my 19's showed the power to be 285rwkw.

Have others found the same thing?  If so, for brag value, obviously everyone will be quoting power figures from dyno runs with smaller wheels?

Would appreciate a discussion on this.

<{POST_SNAPBACK}>

After listening to a discussion on the possible effects of wheel size on dyno results I'll definately be using my 17's at the Easter Nats.

Geea.

[Geeseman]

Im 317 on 19's. Had 19's for a while so can't do any comparisons. On the same point I think that the same applies to drag racing - smaller wheels for better speed?

[FPV TRANNY]

Sweet!!!! I was 284 rwkw with 19"s. Must run willowbank on 17"s then

[PASHEN]

Im 317 on 19's. Had 19's for a while so can't do any comparisons. On the same point I think that the same applies to drag racing - smaller wheels for better speed?

<{POST_SNAPBACK}>

Steve, if that's the case, then fitting 17's and doing a dyno run will show in excess of 335 rwkw....

Not saying your figures are wrong...just making an observation mate. Can someone please confirm the relationship bw wheel sizes and dyno results?

[Cobra]

if the rolling diameter is the same then there would be no change in gearing and you'd think no influence on rwkw figures

I've heard the more rubber the more grip

figures ranging 10%-15% are seriously significant ... be interested in founding out myself ... my trouble is that I only use bigger rims to allow for bigger brakes ... 17s won't go there anymore

need a powered up car with stock brakes for next dyno day

[PASHEN]

My last 3 dyno runs have been done by 3 different but credible tuners. All 3 have said that wheel sizes will DEFINATELY affect the dyno result. One even said that a customer wasn't happy with a recent 285 rwkw power upgrade. They told them the problem was easily and cheaply fixed - simply fit a set of 17's and get it re-dyno'd.

I'm like you Cobra...my brakes wont allow for standard 17's to be fitted.

[Geeseman]

Im 317 on 19's. Had 19's for a while so can't do any comparisons. On the same point I think that the same applies to drag racing - smaller wheels for better speed?

Steve, if that's the case, then fitting 17's and doing a dyno run will show in excess of 335 rwkw....

Not saying your figures are wrong...just making an observation mate. Can someone please confirm the relationship bw wheel sizes and dyno results?

I may do that in future if I ever buy 17's for track work or the occasional drag.

Anyone with drag experience report better results from using 17's over 19's?

[PASHEN]

If wheel sizes DO affect the dyno result, would the tyre profile also make a difference?

[Turbo6man]

The dyno measures tractive effort at the rollers. It doesn't matter what sort of car it is, what size wheels or what diff ratio or gear ratio. It doesn't even care who the driver is.

The dyno doesn't measure driveline losses, wind resistance, tyre resistance or weight.

Any figure taken from the dyno has to be manipulated by the software/operator in order to make figures the customer can relate to and is happy with.

People who use dynos to extrapolate absolute power figures are kidding themselves. It is a tuning tool ONLY.

I don't know how many times this has to be explained before it will be accepted as THE TRUTH.

I suppose however, that without dyno figures to talk/argue about, this forum would be a pretty boring place so ... ALL POWER TO THE DYNO!!!