HP and TQ

[PrecisionBoost]

So, gearing also makes a difference then?

I dynoed my car with a long 3rd gear (around 180 kmh at 7000 rpm)... now i have a shorter 3rd gear (around 150 kmh at 7000 rpm)

last time i got 135 whp, and it was a bit scary reving the hell out of it on the dyno. but i did felt the engine kinda pushing too hard with that long 3rd gear.

Yes.... gearing makes a huge difference..... changing from 180Km/h to 150Km/h should make your car quite a bit quicker ( roughly 17% in 3rd gear acceleration )

Now having said that the Dyno allways calculates to a 1:1 ratio so allthough you will be putting more force to the dyno roller it will offset by the change in RPM vs Speed.

So in real life.... your acceleration in 3rd will be much quicker due to the fact that your engine is putting down 17% more power to the pavement.

[PrecisionBoost]

Actually most people disagree that if you have two wheels, one 15" and one 18" the same weight/design that the 15 will give you more power. But i know better! lol
Also more weight towards the outside means not as good braking.

Yes.... the weight distribution and total weight of the wheel will affect both acclereration and deceleration.

I'm not going to get into the exact formulas as I need to use calculus to express the weight per cubic centimeter vs radius.

The correct terminology for this effect is "rotational inertia"

Basicly.... I don't want to get too technical.... so I will just simply state that the energy sucked from the engine is proportional to the mass of the object times the square of the radius.

So if you had two objects of the same weight..... one with a 12" diameter (6" radius ) and one with a 20" diameter (10" radius) you would find that the 20" diameter mass would require about 2.78 times more power to spin it up.

Having said that there are a number of things that affect this number.... density of the alumium, width of the spokes, width of the wheel, thickness of the material throughout the rim.

The actual calculations required are fairly lenghthy and my calculus isn't that great..... otherwise I'd figure out the exact amount of power it sucks off the engine.

Perhaps I will torture myself and do the math sometime but at this point it's just a matter of "best guess

[PrecisionBoost]

Things you want to look for in a wheel to decrease losses due to rim weight.

1) Overall weight
--> this is obvious so I won't explain further

2) Diameter of rim
--> this is what we've been talking about in the last few posts
--> if you have two rims that both weigh 20lbs but one is 16" in diameter and the other is 18" in diameter the bigger rim will cause more power loss.

3) Width of rim
--> since the section of the rim is the furthest out it will be responsible for the most loss of power
--> if you have two rims that both weigh 20lbs but one is 7" wide and the other is 8.5" wide the wider rim will cause more power loss.
--> if they both weigh the same the odds are that the 7" rim will have more weight towards the center of the hub

4) Pattern of spokes
--> if you had two 17" rims both 7.5" wide that weigh exactly the same you would find that they would create different levels of power loss due to the spoke pattern.(distribution of weight)
--> a spoke pattern where the spoke is larger near the hub and thinner near the outside rim will have less of an impact on performance than one where the spoke is larger near the rim and thinner near the hub.


Spoke patterns won't make all that much difference..... most of the power loss is on the outside of the rim so the rim width and diameter will account for 95% of the losses.