Tire size/weight a factor?

[TheBac]

Just curious if running heavier tires affects dyno numbers like they would affect track times. Im thinking more mass = more power to get moving.
Never gave a thought to this before, but got to thinking about it due to the rather large weight differences between what I run.

The truck is shod with 285/70/17 Hankooks/07 GMC wheels on the street @ almost 80lbs per tire/wheel, and with 275/70/16 Toyos/PY0s at the track at 53lbs per tire/wheel.

Just trying to get an accurate picture.

 

[Whitetail Addict]

I would think the overall circumference would come into affect as well. It would, in theory at least, change the final drive ratio. That would then have an effect on the gear selection in the transmission to get the perfect 1:1 trying to get back to the original gear ratio of 3.73:1

Maybe I'm way off base though.

 

[TheBac]

Hmm...didnt think about tire size changing the gear ratio. Good point.

 

[lotsofmiles]

i have been wondering about the height of the tires myself. van came with 245's, but I now have 265's, almost an inch taller.

 

[Whitetail Addict]

Thanks Tom.

Another factor, I could see, of the weight difference would be the fact that the heavier combo would be harder to get moving initially...but then once in motion I would think it would retain the speed with less effort. That is if the excess weight is in the tire.

I believe its Newton's Law that states "An object in motion tends to stay in motion, until acted upon by an outside source". The outside source would have to have the same energy to stop the tire from spinning freely...therefore it would take more to stop it completely.

On a dyno that may affect the numbers...probably not very much though.

Just another theory for discussion.

 

[TheBac]

Inertia.


I was bored today while on the road, and the result is ideas like this....

 

[Whitetail Addict]

Inertia.


I was bored today while on the road, and the result is ideas like this....

Thats it...the word itself never came to mind though

Glad to see I'm not the only one that thinks of subjects like this when they're bored.

I've been thinking alot on the subject lately, mainly for daily driving purposes though, because I'm putting tires on my PYOs and am torn between 265/75/16s or 285/75/16s.

 

[JoshH]

Here's another thing to keep in mind, the further to the outer edge of the tire the center of mass is, the more inertia it has. Meaning, you can have two wheel/tire combos that weight the same, one with a heavier wheel and lighter tire and one with a heavier tire and lighter wheel, and the one with the lighter tire will have less inertia (making it easier to accelerate).

 

[12secondhandshaker]

Tom, just for sake of argument......

I lost 20hp and 50tq by switching to a heavier 20" wheel/tire combo 07 vs. 08

I asked Dunbar about this and he said the curves looked the same and there was little difference in temps and humidity one year vs. the next. tuning was the same and I added some additional bolt on's in 08 yet dynoed less.

I think rotating mass will affect both dyno numbers and E.T.'s more than people think but what do I know....I drive a manual

 

[NWTDIESEL]

Ive thought about this several times.........

Isnt the rule of thumb (in drag racing) every 1lb lost on the drivetrain is equivelant to losing 4lbs off the truck?? If that is so, i think tire weight would effect dyno numbers to a certainy.

 

[SteveFord]

Anytime you can get the rwhp closer to the hp at the flywheel done by less rotating mass you should see an increase in mph. Et might not be effected as the lighter wheel and tire might not hook as well. The right combo should net you both better mph and et. The question is whats the right combo?

 

[IdahoRob]

Here is another thought that I have put into use. No matter what size/weight tires you are using, try to get the roll out of the front to back the same. Do this by using tire pressure.

Think about what the transfer case does and if you had two different gear ratios in the front and back....they would be fighting each other. Well if your roll out is different between the front and back, you are fighting all the way down the track, thus losing mph and et.

Little things help:hug:

 

[SteveFord]

Here is another thought that I have put into use. No matter what size/weight tires you are using, try to get the roll out of the front to back the same. Do this by using tire pressure.

Think about what the transfer case does and if you had two different gear ratios in the front and back....they would be fighting each other. Well if your roll out is different between the front and back, you are fighting all the way down the track, thus losing mph and et.

Little things help:hug:

I thought about this also but never measured. Rob I've seen you posted before that you was a brick layer by trade.......Did you design the bricks , as your one smart mofo.

 

[TheBac]

I wonder if the same factors that go into proper track setup also are factors when dyno-ing.
The axle will probably still wrap under load from the dyno. Incidentally, this should give me a great shot at video-ing the snubber working.
Inertia is in play when the power is applied to get the tires moving, but would the larger tires then be easier to roll once they get moving?

Just random thoughts....

 

[TrentNell]

also something to note , when i dyno they calibrate the machine and test the rolling resistance before the dyno is done. this has never been done on my truck at dyno events . my freind matt says my truck has the least amount he has seen , so it must affect correction factor . dont know if it matters but something to bable on about anyways :rofl:

 

[SmokeShow]

wasn't it huckstorf who said to run 315s if you want higher numbers on DP? or am I all wet?? :spit:

 

[IdahoRob]

Shoot, I just noticed this was a dyno thread, sorry my bad. I hit "new posts" and didn't read the heading.

 

[McRat]

While I saw a lot of difference on cars, I haven't seen as much on Dmaxes. But heavier tires appear to lower the readings.

 

[TheBac]

So maybe the smartest thing to do is to dyno in the config that you use for racing?

Apples-to-apples type thing?

 

[TheBac]

So is the consensus to run the Toyos and see what happens?