Okay, not really, but it's certainly grist for the mill. And I just love a gristy mill.
I'm in midst of picking out some aftermarket tires/wheels for my not-yet-delivered MCS. I've narrowed it down to a very lightweight 17" wheel from Centerline, or perhaps a freakishly lightweight 16" wheel from SSR. Like most everyone else, I like the look of the bigger, heavier wheel more, so I'm trying to get a feel for how that last few pounds of weight will influence may car's performance.
Well.
I went over to the i-club forums and discovered that they debate that concept at least as much over there, as we do over here. (They even quote Garfield's MINI thread where he G-Tech'd a couple different wheel sizes.) Anyway, in my searches I happened across this thread.
If you follow the link in the first post, you can download a spreadsheet that purports to calculate the (average?) torque required to spin a wheel up 60MPH. (You plug in how long it takes your car to reach 60MPH "normally", and then it figures out how much torque is required to just get the wheels spinning that fast. i.e. How much torque would it take to spin (all four of) the MINI's wheels up the 60MPH, while the car was up on jacks? (I'll leave it up to the reader to figure out how you get the rear wheels spinning at all in such an experiment.)
Better yet, the spreadsheet calculates all this for two different tire/wheel combos, and displays the difference between them. Cool, cool, cool.
I went ahead and plugged in the specs for the standard 17" S-Lite <cough> wheels and runflats, as well as those for the super lightweight 16" SSR Competitions shod with lightweight (and smallish) Toyo T1-S tires. I've attached that spreadsheet for your enjoyment. Check out lines 30-34. That's where the 'output' is. (Hmmph. I see the attachment didn't work. I'll try to attach it in the next post.)
The results? Oh. My. God. Unless I've messed up something somewhere, it takes almost 25 ft/lbs less torque to accelerate a 30lb tire/wheel package, as compared to the 50lb stockers. 25 ft/lbs. That's a lot. Like fully 16% of the peak torque the MCS is capable of. If the MCS doesn't have to spend that torque spinning (and accelerating) its wheels, it can spend it accelerating the rest of the car. To give a feel for that number, if the whole car was to accelerate 16% faster, (it wouldn't, quite) a 7.2 0-60 time would improve to near 6 seconds flat.
(That wouldn't happen in real life since you'll always be traction limited down in the 0-20MPH range.)
The spreadsheet also says my wheel-change is equivalent to dropping 399 lbs off the chassis. I don't know if I believe that, but yike. Oh, that's just 16% of the MINI's 2500 gross weight. Makes sense, I guess.
Yes, I entered pretty "extreme" lightweight wheel and tire values, and my 16" tire has a pretty small diameter. 23.2" vs the stock 24" of the recommended tires. But I think the main factors that contribute to these glorious improvements on the MCS are that:
One concept I had trouble with when interpreting the spreadsheet was, "What does it mean when it say it takes x amount of torque to accelerate the wheels?" Accelerate it how? When?
I believe what the spreadsheet does is take the amount of time it takes for the car to accelerate to 60MPH. (i.e. 7.2 sec.) It then figures out the "average" acceleration experianced during such a run. Then it figures out how much torque is required to accelerate just the wheels at that same "average" rate, and bases the rest of the figures off of that. In real life, we accelerate really quickly in the lower gears, and more slowly in the higher gears, so the amount of torque required to spin up the wheels varies a lot. The moral? Light wheels help a ton when accelerating quickly, but don't help much at all when accelerating slowly. Frankly, I'm only interested in what happens when accelerating quickly!
Anyway. Discuss!
-Dave
I'm in midst of picking out some aftermarket tires/wheels for my not-yet-delivered MCS. I've narrowed it down to a very lightweight 17" wheel from Centerline, or perhaps a freakishly lightweight 16" wheel from SSR. Like most everyone else, I like the look of the bigger, heavier wheel more, so I'm trying to get a feel for how that last few pounds of weight will influence may car's performance.
Well.
I went over to the i-club forums and discovered that they debate that concept at least as much over there, as we do over here. (They even quote Garfield's MINI thread where he G-Tech'd a couple different wheel sizes.) Anyway, in my searches I happened across this thread.
If you follow the link in the first post, you can download a spreadsheet that purports to calculate the (average?) torque required to spin a wheel up 60MPH. (You plug in how long it takes your car to reach 60MPH "normally", and then it figures out how much torque is required to just get the wheels spinning that fast. i.e. How much torque would it take to spin (all four of) the MINI's wheels up the 60MPH, while the car was up on jacks? (I'll leave it up to the reader to figure out how you get the rear wheels spinning at all in such an experiment.)
Better yet, the spreadsheet calculates all this for two different tire/wheel combos, and displays the difference between them. Cool, cool, cool.
I went ahead and plugged in the specs for the standard 17" S-Lite <cough> wheels and runflats, as well as those for the super lightweight 16" SSR Competitions shod with lightweight (and smallish) Toyo T1-S tires. I've attached that spreadsheet for your enjoyment. Check out lines 30-34. That's where the 'output' is. (Hmmph. I see the attachment didn't work. I'll try to attach it in the next post.)
The results? Oh. My. God. Unless I've messed up something somewhere, it takes almost 25 ft/lbs less torque to accelerate a 30lb tire/wheel package, as compared to the 50lb stockers. 25 ft/lbs. That's a lot. Like fully 16% of the peak torque the MCS is capable of. If the MCS doesn't have to spend that torque spinning (and accelerating) its wheels, it can spend it accelerating the rest of the car. To give a feel for that number, if the whole car was to accelerate 16% faster, (it wouldn't, quite) a 7.2 0-60 time would improve to near 6 seconds flat.
(That wouldn't happen in real life since you'll always be traction limited down in the 0-20MPH range.)
The spreadsheet also says my wheel-change is equivalent to dropping 399 lbs off the chassis. I don't know if I believe that, but yike. Oh, that's just 16% of the MINI's 2500 gross weight. Makes sense, I guess.
Yes, I entered pretty "extreme" lightweight wheel and tire values, and my 16" tire has a pretty small diameter. 23.2" vs the stock 24" of the recommended tires. But I think the main factors that contribute to these glorious improvements on the MCS are that:
- The stock wheels are pretty darn heavy.
- The stock tires are ridiculously heavy, and that weight is out on the "edge" where it hurts the most.
- The MCS is fairly light.
- The MCS is not overly endowed with torque to begin with.
One concept I had trouble with when interpreting the spreadsheet was, "What does it mean when it say it takes x amount of torque to accelerate the wheels?" Accelerate it how? When?
I believe what the spreadsheet does is take the amount of time it takes for the car to accelerate to 60MPH. (i.e. 7.2 sec.) It then figures out the "average" acceleration experianced during such a run. Then it figures out how much torque is required to accelerate just the wheels at that same "average" rate, and bases the rest of the figures off of that. In real life, we accelerate really quickly in the lower gears, and more slowly in the higher gears, so the amount of torque required to spin up the wheels varies a lot. The moral? Light wheels help a ton when accelerating quickly, but don't help much at all when accelerating slowly. Frankly, I'm only interested in what happens when accelerating quickly!
Anyway. Discuss!
-Dave
