Weight and Horsepower
07-19-2016, 12:17 PM
#31
I'm in....
Rennlist Member
Rennlist Member
While we are at it, what about changing wheel diameters. I used the app that ProCoach pointed to in the 'when to shift' thread (I think that's where he referenced it) and calculated my speed at shift points with 20" and 19" rims.
As an engineer it seems that if the same car has a lower top speed due to a smaller radius wheel then it is getting there quicker thus feeling like more HP. Is this correct? If so, then the resulting ratios change my 400HP to 415HP when I change from 20" rims to 19" rims (similar tire profile on each 295/30/R19 or R20).
Does this math work?
As an engineer it seems that if the same car has a lower top speed due to a smaller radius wheel then it is getting there quicker thus feeling like more HP. Is this correct? If so, then the resulting ratios change my 400HP to 415HP when I change from 20" rims to 19" rims (similar tire profile on each 295/30/R19 or R20).
Does this math work?
07-19-2016, 12:19 PM
#32
Three Wheelin'
While we are at it, what about changing wheel diameters. I used the app that ProCoach pointed to in the 'when to shift' thread (I think that's where he referenced it) and calculated my speed at shift points with 20" and 19" rims.
As an engineer it seems that if the same car has a lower top speed due to a smaller radius wheel then it is getting there quicker thus feeling like more HP. Is this correct? If so, then the resulting ratios change my 400HP to 415HP when I change from 20" rims to 19" rims (similar tire profile on each 295/30/R19 or R20).
20" rim (27" tire), 3rd gear max calculated to 112.8mph
19" rim (26" tire), 3rd gear max calculated to 108.7mph
(108.7 / 112.8) = 0.96365 (I got this same ratio regardless of the gear)
(400HP / 0.96365) = 415.087HP
Does this math work? Or is it the other way around and I get less horsepower (intuitively it seems like it should be more)? Less torque results in more HP.
As an engineer it seems that if the same car has a lower top speed due to a smaller radius wheel then it is getting there quicker thus feeling like more HP. Is this correct? If so, then the resulting ratios change my 400HP to 415HP when I change from 20" rims to 19" rims (similar tire profile on each 295/30/R19 or R20).
20" rim (27" tire), 3rd gear max calculated to 112.8mph
19" rim (26" tire), 3rd gear max calculated to 108.7mph
(108.7 / 112.8) = 0.96365 (I got this same ratio regardless of the gear)
(400HP / 0.96365) = 415.087HP
Does this math work? Or is it the other way around and I get less horsepower (intuitively it seems like it should be more)? Less torque results in more HP.
Now you're getting into gearing. The observation that lower gearing (or smaller circumference wheels/tires) results in better acceleration is of course true, but that's really a whole separate topic.
07-19-2016, 02:05 PM
#34
Rennlist Member
(disclaimer: this is for straight line acceleration)
if the track is real smooth, the unsprung weight is less of a factor, but now we are talking about handling, not raw acceleration.
07-19-2016, 02:18 PM
#35
Rennlist Member
So does the change in gearing (or in this case tires) give a perceived HP gain similar to losing weight?