power to weight or just more HP????
07-08-2008, 01:16 PM
#91
Rennlist Member
Those factors are actually very large. (15% larger to make up for a 50% diff)
A e36 to a e46 might have to have its width go from 65" to 75" to keep the same mechanical grip for a given turn at a given speed with tires that could also keep grip. Thats like m3 vs corvette as far as width. length would be 100" going 15" larger and same thing for hight.
you also missed the point that its not just the tires that are fixing the problem of equalization. its the cars dimensions and CG. Another point and question woudl be are the larger tires getting a larger contact patch. in most cases, no. generally most race e36 m3s you see at the track weight 2800lbs with driver while e46s will weigh near 3100lbs with driver. They will be sporting 235s and 275s respectively. This is a very small tire size change. Ive seen tires that are large and dont even use 1-2" of a particular edge of the tire, vs using all of the tire with a smaller size. (these are all set up considerations)
So, "theoretically" the heavier car CANNOT develope the same handling characteristics by just putting on a larger set of tires. its CG has to be lowered, its length has to rise and its width has to go up. These are not insignificant factors.
A great example of this was in World Challenge GT with the Audi. It already was doign well at a plump, 275 rewards weight added, 3500lbs/550 + hp , but when they widen the track by 2" and put on 305s vs 275s, it was a monster and near unbeatable. 2:14 at Road America . This is a case of a heavy car beating the near equal weight/hp ratio of the porsche. And it did it based on power overcoming aero drag on long courses, and mechanical grip due to its MUCH larger width and length. Quite the opposite happens with the GT3RS vs the Cup car in WCGT. Its wider, has bigger stickier tires and is lighter. (without that much of a power difference). It is MUCH faster at any track, by near 10 seconds at RA.
So, in order for a heavier car to handle as well as a lighter car, it better be wider, longer and have a lower CG. Some of this can be traded off on a long course where HP/drag ratios can assist the disadvantaged, handling heavier car if nothing else changes. There are basic corning force, and load transfer formlas to see the impact of weight and g loading capabilities. just plug in the weights and dimensions and see if a tire change could make up the difference. usually, it cant.
mk
A e36 to a e46 might have to have its width go from 65" to 75" to keep the same mechanical grip for a given turn at a given speed with tires that could also keep grip. Thats like m3 vs corvette as far as width. length would be 100" going 15" larger and same thing for hight.
you also missed the point that its not just the tires that are fixing the problem of equalization. its the cars dimensions and CG. Another point and question woudl be are the larger tires getting a larger contact patch. in most cases, no. generally most race e36 m3s you see at the track weight 2800lbs with driver while e46s will weigh near 3100lbs with driver. They will be sporting 235s and 275s respectively. This is a very small tire size change. Ive seen tires that are large and dont even use 1-2" of a particular edge of the tire, vs using all of the tire with a smaller size. (these are all set up considerations)
So, "theoretically" the heavier car CANNOT develope the same handling characteristics by just putting on a larger set of tires. its CG has to be lowered, its length has to rise and its width has to go up. These are not insignificant factors.
A great example of this was in World Challenge GT with the Audi. It already was doign well at a plump, 275 rewards weight added, 3500lbs/550 + hp , but when they widen the track by 2" and put on 305s vs 275s, it was a monster and near unbeatable. 2:14 at Road America . This is a case of a heavy car beating the near equal weight/hp ratio of the porsche. And it did it based on power overcoming aero drag on long courses, and mechanical grip due to its MUCH larger width and length. Quite the opposite happens with the GT3RS vs the Cup car in WCGT. Its wider, has bigger stickier tires and is lighter. (without that much of a power difference). It is MUCH faster at any track, by near 10 seconds at RA.
So, in order for a heavier car to handle as well as a lighter car, it better be wider, longer and have a lower CG. Some of this can be traded off on a long course where HP/drag ratios can assist the disadvantaged, handling heavier car if nothing else changes. There are basic corning force, and load transfer formlas to see the impact of weight and g loading capabilities. just plug in the weights and dimensions and see if a tire change could make up the difference. usually, it cant.
mk
Cheat???
We are not dealing with the extreme and unreal 3:1 weight and size factors. What we are discussing is the 2000 - 3500#s range of real track cars. Also, check your notes b/c weight is proportional to mass and mass is proportional to dimension^3. Therefore, 50% more weight translates into just 14.5% larger on any dimension (length, width or height), which is very likely to be the real life size difference between a 2200#s car and a 3300#s one.
Look around at any DE or Club race. A E36 M3 most likely fits 245 or 255 tires, and a E46 M3 will fit 275 or 285. That more than corresponds to the weight difference between the two cars. Nevertheless, theoretically the heavier car could generate the same grip on the slightly narrower tires for a short periodof time (grip = weight x friction coeff, tire width size just help with handling characteristics and grip degradation due to heat, flex, etc. aggravated by the heavier car)
We are not dealing with the extreme and unreal 3:1 weight and size factors. What we are discussing is the 2000 - 3500#s range of real track cars. Also, check your notes b/c weight is proportional to mass and mass is proportional to dimension^3. Therefore, 50% more weight translates into just 14.5% larger on any dimension (length, width or height), which is very likely to be the real life size difference between a 2200#s car and a 3300#s one.
Look around at any DE or Club race. A E36 M3 most likely fits 245 or 255 tires, and a E46 M3 will fit 275 or 285. That more than corresponds to the weight difference between the two cars. Nevertheless, theoretically the heavier car could generate the same grip on the slightly narrower tires for a short periodof time (grip = weight x friction coeff, tire width size just help with handling characteristics and grip degradation due to heat, flex, etc. aggravated by the heavier car)
