This question is a bit out of the box but is relevant, I’m not a Physics Professor but this has been driving me crazy trying to work out why this happened.
I have owned and restored over 150 cars and bikes and i have never had this problem come up before now.
I have a small hatch which my daughter drives, it’s an 100k automatic 1.3 DOHC VVTI F/I 2006 model, it went like a cut cat before i changed the wheels over (well as fast as a 1.3lt auto can go anyway), since i changed the wheels over its lost its acceleration and performance.
The standard wheels are 14” x 5.5 steel/plastic hubcaps running a 175/65 x 14 tire which has an overall diameter of 583mm with sidewall height of 4.48 inches
The factory mags i fitted up are 15” and run a 195/50 x 15inch tire, overall diameter of 576mm and sidewall height of 3.84 inches.
I would have thought that the mags i just fitted with a smaller overall diameter would accelerate faster because of less torque required causing less inertia being required to moving car forward during acceleration, EG: I believe that as you increase the diameter of the wheel you increase the inertia required (Inertia = 1/2 mass * radius ^2). Hence the same amount of torque applied to the two different size wheels should cause the wheel with the smaller overall diameter to rotate quicker give that the 15’wheel has a smaller diameter overall than the 14” wheel (aprox 7mm) difference.
I can’t believe how much difference that made in acceleration from standing start, even hills that we travel on all the time are now almost requiring a downshift to keep up with traffic flow.
I thought it may have something to do with the weight of the 14” steel wheel and tire VS the weight of the 15” mag and tire (15” is 9.7KG heavier) , but if weight were an issue then when we had 2 extra people in the car (say an extra 130 kgs combined) the car running the standard 14” wheels still maintained its performance etc, even with the extra passengers, so what changed.
When i used to ride 2-3 day enduro’s back in the 70’s in the NT and outback QLD, if ever we wanted to change our gearing (lower it) we would always fit a smaller sprocket to the front shaft and if we still needed a bit more we would change the rear sprocket to a larger size. So why does this seem to be defying all logic that i have been using all my life given that the cars drive is from the front wheels so dropping overall diameter (similar to dropping 1 x tooth on the front sprocket of a enduro bike) should cause increase in acceleration???
Just to prove to myself i wasn't dreaming i refitted the standard 14 inch wheels and everything is back to normal.
I don’t know if i am going crazy or what, but can someone explain why this is so, is it something so simple that i have missed it?
I have owned and restored over 150 cars and bikes and i have never had this problem come up before now.
I have a small hatch which my daughter drives, it’s an 100k automatic 1.3 DOHC VVTI F/I 2006 model, it went like a cut cat before i changed the wheels over (well as fast as a 1.3lt auto can go anyway), since i changed the wheels over its lost its acceleration and performance.
The standard wheels are 14” x 5.5 steel/plastic hubcaps running a 175/65 x 14 tire which has an overall diameter of 583mm with sidewall height of 4.48 inches
The factory mags i fitted up are 15” and run a 195/50 x 15inch tire, overall diameter of 576mm and sidewall height of 3.84 inches.
I would have thought that the mags i just fitted with a smaller overall diameter would accelerate faster because of less torque required causing less inertia being required to moving car forward during acceleration, EG: I believe that as you increase the diameter of the wheel you increase the inertia required (Inertia = 1/2 mass * radius ^2). Hence the same amount of torque applied to the two different size wheels should cause the wheel with the smaller overall diameter to rotate quicker give that the 15’wheel has a smaller diameter overall than the 14” wheel (aprox 7mm) difference.
I can’t believe how much difference that made in acceleration from standing start, even hills that we travel on all the time are now almost requiring a downshift to keep up with traffic flow.
I thought it may have something to do with the weight of the 14” steel wheel and tire VS the weight of the 15” mag and tire (15” is 9.7KG heavier) , but if weight were an issue then when we had 2 extra people in the car (say an extra 130 kgs combined) the car running the standard 14” wheels still maintained its performance etc, even with the extra passengers, so what changed.
When i used to ride 2-3 day enduro’s back in the 70’s in the NT and outback QLD, if ever we wanted to change our gearing (lower it) we would always fit a smaller sprocket to the front shaft and if we still needed a bit more we would change the rear sprocket to a larger size. So why does this seem to be defying all logic that i have been using all my life given that the cars drive is from the front wheels so dropping overall diameter (similar to dropping 1 x tooth on the front sprocket of a enduro bike) should cause increase in acceleration???
Just to prove to myself i wasn't dreaming i refitted the standard 14 inch wheels and everything is back to normal.
I don’t know if i am going crazy or what, but can someone explain why this is so, is it something so simple that i have missed it?
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