if I was to dyno my truck would I have to put stocker sized tires on it first?

 

My understanding is that you will put down the most power with close to stock size street oriented tires. The 39" tires are a bit more mass to turn than the stockers

 

Yes, size will affect the numbers since it affects your gear ratio. A trick I've heard of some people using to get better numbers is to slightly overinflate the rear tires to increase their rolling diameter slightly. That trick is supposedly good for around 5 rwhp on a Corvette. This only works to a point though...you can only increase size slightly before you start to lose power.

 

What if you re-gear your truck?? Does that help any?



~Nick

 

Yup...

they might get you a higher top speed, but to get them turning its simple math, a heavier tire needs more power to turn and will eat up a few more horses than stock tires for that reason...

Rick

 

Speaking from working with jeeps...

Well, watchin that is... If you regear the truck, it will use the power that you already have, but it will get it to the wheels at a much smoother rate per say. Lets suppose, with a jeep you run stock 31's at a 3.55 ratio, for a 35 inch tire, to bring it up to speed and make it feel like it did with the stock tires, you would need like a 4.56 gearing or so..

The gearing will compensate for the tire size gains, and thus it will help you out, but your top end speed will suffer, cause more RPMS with the combination of deeper gears will better suit the power you already have, but they will hurt you on the top end, you will run out of RPMS and speed much quicker..

Like anything else, its a tradeoff..

Tx

 

On an inertia 'dyno', large tires and/or very heavy large steel wheels can drastically lower your indicated HP and torque. On a loading dyno, while making a steady state pull, or one with a very slow ramp rate, the difference will be very very slight and only as a result of the slightly higher rolling resistance. But if you use a rapid ramp rate on a loading dyno, then it too will indicate greatly lower hp/torque when using large/heavy wheels and tires. Its all a result of the increased rotational inertia of the large tires and wheels. The roational inertia only comes into play when you are either accelerating or decelerating the rotation.


KP