Weight loss program

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silverstrom
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Re: Weight loss program

#16 Post by silverstrom » Thu May 04, 2017 6:00 pm

At some point it becomes cheaper to make HP than it does to drop weight.

I use this bit of info I found online a while back to help make sense of it. I would credit the author, but unfortunately don't have those details.

Horsepower Gains

Have you ever wondered what 10 or 20 extra How to Compare Weight Savings to horsepower might "feel" like in your car?
Maybe you've wondered how removing 100lbs will affect your car in terms of how much horsepower you'd have to gain to accomplish the same thing.
These questions are wise to ask because they can be used to make significantly better modification choices and frankly it can be fun to "simulate" different modification scenarios.
For example, if I could buy a carbon fiber hood that weighs 20lbs less than factory, it'd be nice to be able to view that weight loss in terms of horsepower. In other words, how many horsepower would I need to gain in order to accomplish the same thing as losing 20lbs? (Hint: it's pathetically little)
What if I wanted to determine if a dual exhaust system is worth while? How much more power would I have to make to offset the extra 20lbs? (in a 3500lb car with 215 hp, not even 1.25hp, so probably do-able)
Can someone on the forum claiming to feel a 1-2hp gain on their butt dyno really do so? Well, using this formula you'd see that they'd have to be able to feel the difference between having groceries in the car vs not having groceries in the car to "feel" that supposed gain.
What about if I wanted to see how much weight I'd have to lose to compete with the same car with 50 extra horsepower?
All of these kinds of questions can be answered with the simple math in today's article.
Weight to Power
You've probably heard power-to-weight more than weight to power, they're the same thing but one has nicer numbers and a better visual representation so I'll be using weight to power for this discussion.
Weight to power is one way to get a general idea of acceleration performance. For example, if I have a 3500 lb car with 215 horsepower, I simply divide 3500 by 215 to get a weight to power ratio of 16.28 lbs per horsepower. The same car with 250 hp would have a weight to power ratio of 14 lbs per horsepower.
To give you a really over simplified visual, imagine that each "horsepower" is a horse. The fewer pounds the horse has to drag with it, the easier it is for it to run.
The Bugatti Veyron with 987 bhp and a curb weight of 4,162 lb has only 4.12 lbs/hp and thus is significantly faster than our example car.
Great, that's all very simple. So how is this useful beyond comparing vehicles to one another?
Well, let's go back to the 3500 lb car with 215 horsepower example. Let's say I want to know how losing 100lbs would translate into horsepower gained, because let's face it, most of us think in terms of horsepower gains.
So we take 3500 lbs (the original weight) and divide by 215 to get 16.28 again (rounding for simplicity, you'll want to use the full number to get accurate results).
We take 3400 lbs (the new weight) and divide by 215 to get 15.81 lbs/hp. That is better of course, but what would that mean in terms of horsepower? Well, we do some simple Algebra to see what horsepower we'd have to have with the original weight to get the same weight-to-power. Stick with me as this is really cool/useful:
3500 / x = 15.81 (Non-geek translation: original weight divided by some unknown horsepower would give us the same power-to-weight ratio as 3400 / 215). Solve for X (which I have done for you below)
"Weight loss" to "Horsepower" Formula
Old weight (3500) / New Power-to-Weight Ratio (15.81) = 221.38 hp
So that means that by taking 100lbs out of the 3500lb car, we would have had to gain ~ 6.38 hp (221.38-215, (the new-original horsepower) to accomplish the same thing WITHOUT taking out the 100lbs. Thus in this situation, 100lbs is roughly the same as if we had done something to gain 6.38hp. So to some extent, this means that something like an intake that adds +6hp would FEEL kind of like losing 100lbs (or a very skinny passenger) in this particular vehicle. In another car with different weight and power numbers, this figure would be different but calculated in the same way.
"Weight Gain" to "Power Loss" Formula
You can also use this same method to determine how adding weight is hurting you in terms of theoretical power loss. So if I add 50lbs of stereo equipment to the same car, it's
Old Weight (3500) / New Weight-to-Power Ratio (16.74) = 209.08 hp
So that 50lbs of equipment is LIKE losing a little under 6 hp as those horses will now be dedicated to hauling that 50lbs.
This will give you a new way to think about weight and power. You can also go the other way and see how power gained changes the car in theoretical terms of weight, though I find this less useful. To do that, you say a 3500 lb car with 215 horsepower has a 16.28 lb/hp power-to-weight, and let's say we gained 50hp to get up to 265 hp. That's a power-to-weight of 13.2 lbs/hp. Now it's simple Algebra again to figure out how much weight I'd have to lose off the car to make up the same amount of power:
In formula form:
New Power to Weight (13.2) * 215 (old horsepower) = Theoretical Weight (2838).
So 50 horsepower in this particular vehicle would be roughly the same as shaving off 662 lbs. As you can see from this math, this is why losing weight is rarely as useful as gaining horsepower, or at least, horsepower gain is significantly more practical and cost effective than weight loss in a production car.
Of course, this is also if we only take into consideration the acceleration effects of weight and power. In road racing or in a daily driver, weight loss is more useful than in drag racing. Of course, regardless of our goals, the least amount of weight necessary is best.

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two-stroke-brit
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Re: Weight loss program

#17 Post by two-stroke-brit » Thu May 04, 2017 6:40 pm

Very detailed but easy to grasp explanation.
She might not be pretty but always a fun ride !!

RC45
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Re: Weight loss program

#18 Post by RC45 » Thu May 04, 2017 8:40 pm

My car used to weigh 3190lbs and made 385bhp (340rwhp).

Currently weighs 2990lbs and made 660bhp (600rwhp) before the mild cam swap.

The 200lb weight loss cost about $8000 in replaced/upgraded parts and a number of removed bits.
The 260rwhp gain cost about $18,000 in engine build out and required drive train upgrades.

When I went to a milder cam (got tired of engine rebuilds) the 60rwhp loss of power (currently 590bhp (540rwhp)) was very noticeable, especially at those higher uhm, freeway speeds when you uhm... you know sometime need to beat a Viper or 911 Turbo to the next Toll Booth ;)

I added a 90lb pushbar to my Tahoe PPV that is rated at 380bhp on E85 and I felt that 90lb immediately in the handling more than the acceleration - all the weight is in front of the front axle.
When I fill up with regular unleaded the power rating drops to 355bhp and the extra 90lbs helps to make the truck feel even more like a snail trying to pull a beached submarine than it normally does on regular gas.

Given the choice I would try lose weight first to aid handling then go after as much power as I could afford :)
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Re: Weight loss program

#19 Post by johannes factotum » Thu May 04, 2017 8:51 pm

Adding power to compensate for overweight only works with drag racing. Sport machines need 'inertial' qualities in order to be truly great. That said, it's also true to say that a bike ceases to be a sportbike if the power to weight ratio is greater than a certain point. Kevin Schwantz had said to Matt Oxley a while back that the last gen 250cc GP two stroke was the greatest sport/racing motorcycle ever devised, owing to its overall balance. Now, mind you, a last gen 250 had a similar horsepower to weight ratio to the first gen R1.... So what he was saying that was 95hp in a light weight bike was the best you could do. He's also saying that the 500GP was only a superior bike, laptime wise because of long straights. Light weight is king.

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Re: Weight loss program

#20 Post by johannes factotum » Thu May 04, 2017 8:55 pm

Oh, and Steveho, what can I say, .... carry on. Pretty.

silverstrom
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Re: Weight loss program

#21 Post by silverstrom » Thu May 04, 2017 9:55 pm

You can only lose so much weight. At some point you are out of options. That was my point.

RC45
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Re: Weight loss program

#22 Post by RC45 » Thu May 04, 2017 10:05 pm

silverstrom wrote:You can only lose so much weight. At some point you are out of options. That was my point.
True - and beyond the few easy low hanging weight savings, the costs start to add up quick.

I supposed for bikes the easiest to achieve weight savings are wheels, tanks, bodywork, remove street gear and go on a personal diet.

After that it is on to the tiny expensive bits.
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TZ250B 3YL
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steveho
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Re: Weight loss program

#23 Post by steveho » Fri May 05, 2017 1:27 pm

To quote Colin Chapman of LOTUS fame, "the first thing to add is less weight".

To be fair, I think pre-F1, he was generally talking about taking unnecessary parts off, rather than spending sh*t loads on exotic materials.

Still, the sentiment is the same, less weight helps everything (apart from top speed), i.e. Acceleration, braking, cornering, changing direction etc..... , So why not.....:cool:

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Re: Weight loss program

#24 Post by johannes factotum » Sat May 06, 2017 7:52 am

For sure. You have to add as much less weight as possible. The two stroke already has vastly superior mass centralization and C/G, but making it a bit lighter really makes the bike fantastic. I might take the pains to build an aluminum tank.

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Re: Weight loss program

#25 Post by pstamper » Sun May 07, 2017 9:10 pm

Trying to strip weight as RC45 says can get expensive. I think my track bike is around 389 or so. I picked up some magnesium wheels at the Austin GP and there is a huge weight savings. I only have 90 reliable horsepower and can run against liter bikes at my level. Nice to have a light bike but I go back to my roots, ability, tires, brakes, and suspension in that order. Oh finess does not help and why I personally could lose 10 pounds myself.

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Re: Weight loss program

#26 Post by pstamper » Sun May 07, 2017 9:34 pm

A video of a contractor I know. He is way more successful than I am. I can say I do all my own work and also get to enjoy my passion. Big pocket book will buy you most anything.
https://m.youtube.com/watch?v=-t_0diZ3gpY" onclick="window.open(this.href);return false;

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