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post #1 of 35 (permalink) Old 12-21-2009, 04:53 PM Thread Starter
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Power to Weight Ratio - why it's important in choosing a bike!

This information is targeted toward those who will be seeking to experience the upper capabilities of whatever bike they ride or race on the track, not as much for those who are just out for a spirited cruise around the track on the highest Horsepower bike they could find. By "upper capabilities" I'm talking about being within 110% of the fastest Expert Racer's lap times on that same track by a Racer who's using approximately the same Power to Weight Ratio (P/W/R) as yourself. Due to the numerous variables that effect motorcycles on a race track, the P/W/R numbers I'm going to give in this article are not hard and fixed points, they are approximate ranges that I've personally experienced (and observed many other racers experiencing as well) since I started racing in 1996. Brand new tires are of course going to spin later than used tires and in turn will be somewhat of an exception to the ranges I list, this advice is going to be aimed more toward tires that have some use on them already since most people don't use new tires for every session they do on the track. Also don't think you can't ride a certain bike with a certain P/W/R because of what I've written, this is simply a guide to assist you in making more informed decisions about motorcycle's that will be used on a Road Race course (whether for Track Days or actual Racing).

Power to Weight Ratio effects many different aspects of everyone's lives on a daily basis, yet many people are oblivious as to what it is and how it effects all of us. Everything from lifting/dragging/pushing something, to sports, to driving, to the Space Shuttle, are all effected by P/W/R.

Believe it or not, how much Power you have isn't nearly as important as your ability to use it. All too often with Motorcycle Road Racing and Track Days many people start out thinking they need the most Horsepower (Hp) possible, but then as they evolve into being an experienced racer the realities of P/W/R become much more obvious or restrictive (even if they don't realize it's P/W/R causing it) and many racers will end up choosing to race lower Hp bikes as a result. Why? Because controllable power is able to be applied sooner and much more effectively, usually resulting in better lap times. Excessive Hp is often times used as a crutch for lesser experienced riders who want to believe their fast - when in reality many are just racing from corner to corner and parking it in the turns. Even experienced riders who have reached a plateau in their ability (a plateau that others have surpassed with the same P/W/R) may think it's due to a lack of power, when most likely it's suspension set-up and/or corner speed/technique that actually needs to be improved. Does that mean that's always the case? No, but those 2 situations are true more often than not.


What is Power to Weight Ratio?

A slingshot is a great example I thought of that describes P/W/R in a way that's relatively easy to understand. A slingshot will produce a certain amount of Power based on how far it's been stretched, if you pull the rubber tension bands back the same amount every time you'll have a predictable amount of power available over and over again. If you were to make a fixture to hold a slingshot in a fixed position, and provide a mechanism that would pull back on the tension bands the same amount every time, it would provide a situation that was able to be repeated predictably. To show the various effects of P/W/R all you need is some Ping-Pong balls to shoot from the slingshot fixture I described. Take a Ping-Pong ball and shoot it from the slingshot 3 times and the ball will go apx the same distance every time. Now fill one of the Ping-Pong balls with foam to add a little weight to it and shoot it 3 times, again it will travel apx the same distance every time - but it will be different than when the hollow Ping-Pong ball was used. Now try this with several more Ping-Pong balls filled with increasingly heavier materials inside each of them with the heaviest being filled solid with metal. I used a Ping-Pong ball as a constant in this example because the outside size and surface material would remain the same so the effects of aerodynamics wouldn't be a factor.

What you would see as a result of that test (using the same amount of tension on the slingshot every time) would be that the hollow Ping-Pong ball would go a certain distance and as you start to use the Ping-Pong balls filled with increasingly heavier materials you would see them shoot farther and farther, but only up to a point, then you would see the distance start getting shorter and shorter till you get to the metal filled Ping-Pong ball which would go the shortest distance. When comparing this example to motorcycles the engine would be the slingshot and the combined bike and rider weight would be the Ping-Pong ball. The motorcycle is going to have a predictable amount of power available, no matter how much the rider weighs, the difference will be the ability of that fixed amount of power to propel the various weights. The heaviest Ping-Pong ball would represent a very heavy rider (350 lbs for example), in this situation the motorcycle (I'm going to say a GSXR 1000) is only going to be able to do so much with the power it has available. The hollow Ping-Pong ball would represent the lightest rider you can find (100 lbs for example), in this situation the tables are turned, there's now not enough weight to stop the rear wheel from spinning on acceleration.

Two other VERY important aspect's of P/W/R are acceleration and top speed, the slingshot example is an excellent example of both of these as well. Each of the different weight Ping-Pong balls explained in my example would accelerate from the slingshot at different rates and ultimately each would reach different maximum top speeds as well - the heavier an object, the less top speed it can achieve given a fixed amount of power and the longer it will take to accelerate to that top speed. As a result, if a lighter object is able to accelerate at a rate of only 1 mile per hour faster than a heavier object, the acceleration difference is equal to 1.466 feet per second! In bike terms that means if someone can accelerate at a rate of only 1 mile an hour faster than you they will pull away from you at a rate of 1 bike length every 5 seconds - on a straight away allowing 15 seconds of acceleration that equals about 3 bike lengths! In a 9 lap race that 1 MPH difference in acceleration (on just that 1 section of the race track repeated 9 times) means the lighter rider could potentially gain almost 200 ft by the end of the race! Both acceleration and top speed are greatly effected by P/W/R, this is why the antiquated system of requiring VEHICLE ONLY minimum weights in many different forms of racing is being replaced by the much more accurate system of COMBINED RACER & VEHICLE minimum weights.


How do you figure P/W/R?

Power to Weight Ratio is actually fairly easy to figure if you know your bikes Rear Wheel Horsepower (R/W/Hp), all you need is 2 bathroom scales and a calculator. Your going to need to figure out your combined Rider and Bike weight: weigh yourself wearing all your safety gear head to toe, then weigh your bike using 2 bathroom scales making sure all fluids are in the bike (some people like to use a 1/2 tank of fuel in their bike as a basis for figuring weight). As a suggestion for not ruining your bathroom scales, make sure they are both rated for at least 250 lbs each (if it's a Busa or something similar you may need heavier scales) and it's not a bad idea to put a piece of wood on top of the scale to help distribute the bikes weight across the scale (not just focused in a small spot by the tires). Another suggestion is to lay down some wood next to each scale to act as a step up, this will help to stop your scale from trying to tip over or push away. I personally like to have the weights of the rider and bike separate so it's easy to calculate the P/W/R of different power and weight combination's.

Earlier I gave an example of a GSXR 1000 and different extreme's of weight between 2 riders, I'm going to continue with those numbers for an actual P/W/R example. Let's say that the bike has 160 R/W/Hp and weighs in at 410 lbs in race trim with apx a 1/2 tank of fuel, the rider weights (100 & 350 lbs) include all their safety gear. What we need to do now is calculate the combined rider and bike weight, then divide that number by the Rear Wheel Horsepower. Here's the numbers:

410 lbs + 100 lbs = 510 lbs ***** 510 lbs / 160 Hp = 3.188 lbs per Hp

410 lbs + 350 lbs = 760 lbs ***** 760 lbs / 160 Hp = 4.750 lbs per Hp


What's the desired P/W/R range for different skill levels?

There's people out there that understand what P/W/R is, but so many people don't seem to grasp the significance of various P/W/R number's and the massive effect it has on a riders capability to be competitive. I personally have done a lot of number crunching concerning this over the years and found some interesting trends, trends that are too obvious to ignore, yet some will deny that they are relevant (ironically it's almost always lighter weight riders).

Horsepower varies based on the amount of work done to the engine, but for the most part the following are the 4 basic classifications of bikes (with some examples) and their approximate ranges of Rear Wheel Horsepower (there will be some bikes which fall out of these groups slightly, usually older models or highly modified new bikes):

Lightweight (LW) under 100 Hp (650 V-Twin's & 2-stroke 250's)
Middleweight (MW) 100 to 125 Hp (up to 640cc I-4's, 980cc Triples, & 850cc Twins )
Heavyweight (HW) 125 to 150 Hp (up to 750 cc I-4's & 1000cc Twins)
Unlimited (UL) over 150 Hp (1000 cc I-4's & almost anything else)

Today at most tracks the Middleweight bikes seem to dominate, as a result many people are quick to say that 600's are awesome. I personally believe it has ALOT more to do with the P/W/R of most of the winning racers on those bikes. Ironically many of the same racers who place well on MW bikes don't show much (if any) improvement in lap times when getting on a higher Hp bike, which doesn't seem to make sense till you factor in P/W/R. The following is an example of some Expert racer & bike combination's:

Modified 600cc MW bike / 390 lbs wet bike weight / 120 Rear Wheel Hp / 160 lbs racer with gear

390 lbs + 160 lbs = 550 lbs ***** 550 lbs / 120 Hp = 4.583 lbs per Hp

Now compare that to the same racer on a GSXR 750 with 140 Rear Wheel Hp and 395 lbs wet weight:

395 lbs + 160 lbs = 555 lbs ***** 555 lbs / 140 Hp = 3.964 lbs per Hp

Now compare that to the same racer on a GSXR 1000 with 160 Rear Wheel Hp and 410 lbs wet weight:

410 lbs + 160 lbs = 570 lbs ***** 570 lbs / 160 Hp = 3.563 lbs per Hp

Based on what I've seen, if you want to be a front running Expert level Racer (on a bike without a really good traction control system) you want to shoot for the 4.25 to 4.50 lbs per Hp range in all categories except for Lightweight - in LW you want to get the lowest possible P/W/R you can. I have a name for the power delivered around 4.25 pounds per Hp and below, I call it "Chaos Power", because once you get truly 'fast' out on the track that kind of Power gets exponentially more difficult to deliver to the ground (especially if the bike doesn't have a really good traction control system). That last example of the racer on the 1000 is a great example of 'Chaos Power', 3.5 lbs per Hp on the track is a waste for anyone genuinely wanting to go fast (other than a Top Expert or Pro Racer which will most likely be using a high-end aftermarket traction control system to help tame that power for them).

For new people to the track who truly want to learn I highly suggest something in the 6.0 lbs per Hp and higher range, this range will see a far greater chance of the tire not spinning under acceleration. In my opinion the 5.0 to 6.0 lbs per Hp general range (this is very dependant on your individual situation and could be higher or lower for you personally) is somewhat of a transitional range where your leaving the safety of not really being able to spin the rear tire very easily and reaching a point where tire spin will be somewhat random. Back when I raced my 1999 GSXR 600 I was around 5.75 lbs per Hp and I personally hated it because tire spin seemed somewhat random & unpredictable for me on that bike even though I was using the same suspension upgrades and tires as my GSXR 750's. The 5.0 to 6.0 lbs per Hp range will provide new challenges if your pushing hard, including some tire spin on acceleration out of some turns and possible head shake from the front end being light under some acceleration situations.

From what I've seen 5.0 lbs per Hp seems to be somewhat of a general range where controlling your bike reaches a different level (that is if your within 110% of the fastest Expert racers lap times with that same P/W/R). Going much below 5.0 lbs per Hp will allow you to spin the rear tire under acceleration out of some turns (pretty much at will) and even lift the front wheel (sometimes unintentionally) under power. Below this P/W/R your now having to regulate your power delivery more carefully or your going to be learning very quickly what high-siding a motorcycle is all about.

Getting down to the magic 4.25 to 4.5 lbs per Hp range will be great for Experienced Racers who are trying to win at the Top levels of Regional racing, a blend of power with some slight remaining limitations to help them not get too awful far over their head. But going much below that 4.25 lbs per Hp threshold seems to be a major hurdle for most everyone who rides under those circumstances, at that point it's not about going fast anymore, it's about not crashing while trying to go fast!

As you may notice I'm not making suggestions about what bike each individual should get, I'm suggesting a Power to Weight Ratio. For me on my 2002 GSXR 750 I'm at apx 4.9 lbs per Hp, If I bought a new GSXR 750 with about 10 more Hp than I have now, and I personally lost 10 lbs, I would be at apx 4.45 lbs per Hp. Your individual situation is far more important than what someone else is doing because their overall situation is probably different than yours. You may also find that you personally like a certain P/W/R range based on your personal experience, riding style, and the amount of risk your willing to take. There's not any single P/W/R range that's going to be perfect for everyone, instead what I've given here are some basic categories where the majority of riders & racers at different levels will find different degree's of difficulty.

Hope this helps out with choosing a bike for the Track!

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post #2 of 35 (permalink) Old 12-22-2009, 11:51 AM Thread Starter
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Here's a sample of some different rider & bike combination's and how changes to weight and power progressively change the Power to Weight Ratio.

SV650

A stock Suzuki SV650 is roughly about 70 Rear Wheel Horsepower and 400 lbs wet weight (all fluids including a full tank of standard fuel). I'm going to use 6 different rider weights (including safety gear): 140, 160, 180, 200, 220, & 240 lbs.

400 + 140 = 540 lbs ***** 540 lbs / 70 Hp = 7.71 lbs per Hp
400 + 160 = 560 lbs ***** 560 lbs / 70 Hp = 8.00 lbs per Hp
400 + 180 = 580 lbs ***** 580 lbs / 70 Hp = 8.29 lbs per Hp
400 + 200 = 600 lbs ***** 600 lbs / 70 Hp = 8.57 lbs per Hp
400 + 220 = 620 lbs ***** 620 lbs / 70 Hp = 8.86 lbs per Hp
400 + 240 = 640 lbs ***** 640 lbs / 70 Hp = 9.14 lbs per Hp

Modify the engine, fuel delivery, exhaust, and use the good race fuel and the R/W/Hp could potentially be about 85, here's what the difference is:

400 + 140 = 540 lbs ***** 540 lbs / 85 Hp = 6.35 lbs per Hp
400 + 160 = 560 lbs ***** 560 lbs / 85 Hp = 6.59 lbs per Hp
400 + 180 = 580 lbs ***** 580 lbs / 85 Hp = 6.82 lbs per Hp
400 + 200 = 600 lbs ***** 600 lbs / 85 Hp = 7.06 lbs per Hp
400 + 220 = 620 lbs ***** 620 lbs / 85 Hp = 7.29 lbs per Hp
400 + 240 = 640 lbs ***** 640 lbs / 85 Hp = 7.53 lbs per Hp

Start shedding weight from the bike and only run a 1/2 tank of fuel during sprint races and you could potentially drop your bike weight down to 375 lbs, here's the difference:

375 + 140 = 515 lbs ***** 515 lbs / 85 Hp = 6.05 lbs per Hp
375 + 160 = 535 lbs ***** 535 lbs / 85 Hp = 6.29 lbs per Hp
375 + 180 = 555 lbs ***** 555 lbs / 85 Hp = 6.52 lbs per Hp
375 + 200 = 575 lbs ***** 575 lbs / 85 Hp = 6.76 lbs per Hp
375 + 220 = 595 lbs ***** 595 lbs / 85 Hp = 7.00 lbs per Hp
375 + 240 = 615 lbs ***** 615 lbs / 85 Hp = 7.24 lbs per Hp

Looking at those numbers and figuring that both riders were similarly experienced racers, a 240 lb rider on a stock SV650 (9.14 lbs per Hp) would have absolute no chance what-so-ever against a 140 lb rider of similar ability on a race prepped 85 Hp SV650 (6.05 lbs per Hp). So what would it take to equal out the P/W/R of those 2 riders? Figuring that the 240 lb rider gets a similarly modified bike as the lighter rider (same suspension, tires, etc) here's what the Hp would need to be for him to be on a level playing field and have the same P/W/R (divide the heavier riders combined bike & rider weight by the lighter riders P/W/R to come up with the required Rear Wheel Horsepower the heavier rider would need):

375 + 240 = 615 lbs ***** 615 lbs / 6.05 lbs per Hp = 101.65 R/W/Hp

So in order for the 2 riders to have an identical P/W/R of 6.05 lbs per Hp the heavier rider would need 101.65 Rear Wheel Hp. But even if such an SV650 existed, what would the P/W/R be if the lighter rider was on that bike?:

375 + 140 = 515 lbs ***** 515 lbs / 101.65 Hp = 5.07 lbs per Hp

At 5.07 lbs per Hp the lighter rider on that SV650 could actually be somewhat competitive in the Middleweight classes.


GSXR1000

At the opposite extreme of an SV650 would be a stock Suzuki GSXR1000 which has roughly 160 Rear Wheel Horsepower and weighs about 450 lbs wet (all fluids including a full tank of standard fuel). Again I'm going to use 6 different rider weights (including safety gear): 140, 160, 180, 200, 220, & 240 lbs.

450 + 140 = 590 lbs ***** 590 lbs / 160 Hp = 3.69 lbs per Hp
450 + 160 = 510 lbs ***** 610 lbs / 160 Hp = 3.81 lbs per Hp
450 + 180 = 530 lbs ***** 630 lbs / 160 Hp = 3.94 lbs per Hp
450 + 200 = 650 lbs ***** 650 lbs / 160 Hp = 4.06 lbs per Hp
450 + 220 = 670 lbs ***** 670 lbs / 160 Hp = 4.19 lbs per Hp
450 + 240 = 690 lbs ***** 690 lbs / 160 Hp = 4.31 lbs per Hp

Modify the engine, fuel delivery, exhaust, and use the good race fuel and the R/W/Hp could potentially be about 185, here's what the difference is:

450 + 140 = 590 lbs ***** 590 lbs / 185 Hp = 3.19 lbs per Hp
450 + 160 = 510 lbs ***** 610 lbs / 185 Hp = 3.30 lbs per Hp
450 + 180 = 530 lbs ***** 630 lbs / 185 Hp = 3.41 lbs per Hp
450 + 200 = 650 lbs ***** 650 lbs / 185 Hp = 3.51 lbs per Hp
450 + 220 = 670 lbs ***** 670 lbs / 185 Hp = 3.62 lbs per Hp
450 + 240 = 690 lbs ***** 690 lbs / 185 Hp = 3.73 lbs per Hp

Start shedding weight from the bike and only run a 1/2 tank of fuel during sprint races and you could potentially drop your bike weight down to 410 lbs, here's the difference:

410 + 140 = 550 lbs ***** 550 lbs / 185 Hp = 2.97 lbs per Hp
410 + 160 = 570 lbs ***** 570 lbs / 185 Hp = 3.08 lbs per Hp
410 + 180 = 590 lbs ***** 590 lbs / 185 Hp = 3.19 lbs per Hp
410 + 200 = 610 lbs ***** 610 lbs / 185 Hp = 3.30 lbs per Hp
410 + 220 = 630 lbs ***** 630 lbs / 185 Hp = 3.41 lbs per Hp
410 + 240 = 650 lbs ***** 650 lbs / 185 Hp = 3.51 lbs per Hp

Looking at these numbers the situation is quite different than with the SV650, with the SV650 the lowering of P/W/R as it was modified was a welcome addition, with the GSXR1000 the ever decreasing P/W/R is actually a handicap for all but a very small percentage of the top racers. I'm an example of a 240 lb racer, for me a STOCK GSXR1000 would put me at 4.31 lbs per Hp - right in the 4.25 to 4.50 lbs per Hp range I spoke of earlier. In a road racing application I wouldn't even consider racing a bike if my P/W/R was 2.97 lbs per Hp (like the 140 lb rider with 185 Hp), that would require an impressive traction control system just to be able to even attempt to race that thing for a Top 5 finish as an Expert level Regional Racer.

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post #3 of 35 (permalink) Old 12-22-2009, 11:52 AM Thread Starter
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There's some other things I want to emphasize about Power to Weight Ratio.

P/W/R is a factor in track performance when pushing a bike to it's limit's, but that doesn't mean you still can't do well with a less than desirable P/W/R, it just means your job's going to be more challenging than for others you may be racing against. Also there's another very important issue, weight in itself. An excessively low P/W/R may result in constant wheel spin under even moderate acceleration, but heavier weight in itself can also test the limit's of traction when turning and braking and cause faster tire wear (that's on top of the restrictions of having a higher P/W/R).

A shopping cart can be used as a great example of how weight effects acceleration, turning, braking and top speed. If you push an empty shopping cart you'll find it's fairly easy to accelerate, turn, stop, and push the cart pretty fast - you may even be able to run while pushing the cart. As you add weight to the cart you'll find it gets increasingly more difficult to accelerate, turn, slow down, and push as fast as you could when the cart was empty. I encourage anyone questioning the effects of P/W/R to try this simple test with a shopping cart in a parking lot - but if you do try it don't be an idiot, at least be safe about it.

A real ego destroying statement I've made in the past was as follows: "If a heavier rider on similar equipment is keeping up with you, the heavier rider is actually the better rider". For people who truly understand the significance of P/W/R (including weight's additional effect on braking, traction, and tire wear) that statement will be undeniably obvious, but sadly that's a tough pill for many others to swallow. The exception to that statement can be when you get into the 'chaos power' range I described before, in that unique situation a heavier rider will have a higher P/W/R (even if it's still in that 'chaos power' range) which can possibly be of benefit in trying to control and use that power because the extra weight tames that power down a bit (especially at tracks with limited straight line acceleration and less top speed sections).

I've mentioned that I'm a heavier racer, for the last several years I've been about 240 lbs, as a result I experience the negative effects of having a higher P/W/R (compared to most others I'm competing against) every time I get on the track. The places I really notice the P/W/R differences are on acceleration (especially on longer straights) and less Top Speed, the heavier weight issue is especially noticeable when braking hard - I have to start braking earlier because it takes me longer (than it does lighter riders) to get down to corner entry speed.

An example is a situation I had the last time I raced at Road America against a racer who was literally less than 1/2 my weight and had a higher Hp bike as well. I previously mentioned my P/W/R is about 4.90 lb per Hp on my '02 GSXR 750, I estimated the other rider who was on a new GSXR 750 was somewhere around 3.5 to 3.7 lbs per Hp. This racer was in many of the same race classes I was in during the event so the effects of the differences in our weight and P/W/R were repeated over and over again. The situation was always the same, they either passed me on the brakes approaching a turn or could accelerate faster than me. Even though this racer was able to get by me on the inside during braking (because they could brake REALLY late due to their low body weight), they would almost always totally blow the race line and park it in the turn. The one time this happened was in Turn 3 at Road America, a 90* right hand turn that exits onto a Top Speed straight. This racer shot down the inside of me approaching the turn on the brakes hard, but even for them they braked too late, the result was they ended up going straight until they almost stopped at the outside edge of the track (about mid-turn) and then had to make a very slow hard turn to get going again. I saw what was happening so I slightly adjusted my line thru the turn to avoid them, but I didn't lose any corner speed as a result and blew by them as they did their slow recovery turn. As I'm accelerating as hard as I can away from the turn I'm thinking ahead to the end of the straight away and planning on running a defensive line more toward the inside of the track as I approach Turn 5, but it turned out it didn't matter. I didn't make it more than a few hundred feet down that straight and the rider that had screwed up that last turn blew by me like I wasn't even trying, then continued to run away from me at a rate that just amazed me! The times I was near this rider in a series of turns which didn't involve straight line acceleration (for example from Canada Corner thru Turn 14) they were actually in my way and holding me up, but as soon as they hit the Front Straight it was time for the disappearing act again.

Blackhawk Farms Raceway is my Home track and also the one I've turned the most laps on, I estimate that I easily have more than 5,000 race miles on that track alone. Blackhawk is one of those places where I'm decent at gaining ground on some racers in a couple spots, so much so that I have to brake extra or back off ahead of time to avoid hitting them in the turn. But just like the example I gave before, as soon as we hit a straight they run away from me, even if I carry more corner speed and pass them at the exit of the turn. To be on a GSXR 750 and not be able to out accelerate other racers on a straight away that are on 600's is frustrating to say the least, but I also understand why the situation exists.

The intention of me telling you all of this isn't to try and make excuses for me not being a front runner (I'm well aware of what it would require for me to do that again), I'm simply offering examples of situations that all of us will encounter from one side of the equation or the other. For racers it's not a bad idea to figure the apx P/W/R range that your competitors have, that can be a huge reality trip and also help you in realizing what type of bike(s) you'll probably have the most success racing!

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post #4 of 35 (permalink) Old 12-23-2009, 02:17 AM
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My bike has the random sliding thing too, and that's kind of annoying. It could be from the massive amount of odd tires I've been running, to just not quite being as consistent as i like.

But it could be because I am in that zone right now, were you have to slide a little bit to get the most out of a corner. Well I am pretty much right before that, and it's scary sometimes. haha
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I'm glad you include the rider's weights in calculating the P/W. Too often they are left out, which makes the differences between bikes seeming much larger and more significant than they often are.



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Quote:
Originally Posted by inpayne View Post
My bike has the random sliding thing too, and that's kind of annoying. It could be from the massive amount of odd tires I've been running, to just not quite being as consistent as i like.

But it could be because I am in that zone right now, were you have to slide a little bit to get the most out of a corner. Well I am pretty much right before that, and it's scary sometimes. haha
Slides can be caused from so many different things, but the main ones are:
-bad lines thru a turn
-body position on the bike
-tire condition / tire type / tire pressure
-suspension set-up

Power to Weight Ratio is responsible more for tire spin when applying throttle, whether it's while your still leaned over or already vertical.

The following is just a suggestion, not ridicule or anything like that. In your case, and without actually seeing you ride and going purely by what you've said, I would imagine your traction issues might be a combination of suspension set-up (as you change between different tires), varying your lines, and body position - P/W/R may be a factor as well if your experiencing slip under acceleration. When I first saw your avatar photo it reminded me immediately of a racer freind of mine who use to have an almost identical body position in turns. Some racers/instructors worked with him on his body position and he got faster and smoother. The issue was he was getting off to the side of the bike a little too much and it messed with the handling characteristics of the bike and also didn't allow him to 'feel' what was going on with grip as well.

I had a somewhat similar issue, just not as pronounced as his. I was told to try and keep my head closer to the center line of the bike when turning (that doesn't mean ON the center line 100% of the time). What that does is give you a better perceived 'feel' for what the bike is doing, especially for rear tire traction (which is where I was have an issue). There's 2 current threads going on here in the 'On The Track' section concerning racing/track pictures, go thru those pictures of some of the fastest racers in the World and notice that in most of the pictures their heads are usually not too far off of the center line of the bike - usually within several inches.

Next time your at the track give that a try and see if that helps.

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post #7 of 35 (permalink) Old 12-24-2009, 12:33 AM
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That is my "normal" positioning. In that picture was one of the last sessions I was fooling around. haha

But a AMA rider has pretty much taught me how to ride this past year, and has helped a ton. Most everyone has told me I have pretty excellent body positioning, and what not.

It could most definitely be suspension, my rear suspension is 100% shit really. I hope to at least get it rebuilt before I hit the track again.
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post #8 of 35 (permalink) Old 12-24-2009, 09:46 AM Thread Starter
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Body position in those pics definitely looks a lot better!

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post #9 of 35 (permalink) Old 12-24-2009, 05:08 PM
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Thanks.

I am getting my rear suspension re-done, so hopefully that will help. It's not bad at all, it's just starting to happen.
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post #10 of 35 (permalink) Old 12-25-2009, 10:26 PM
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now i want to get all dressed up and see how much i weigh

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post #11 of 35 (permalink) Old 12-26-2009, 11:19 AM
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now that it has had a chance to digest...How do you account for changing of Gear ratios? power and weight still stay the same??

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post #12 of 35 (permalink) Old 12-26-2009, 02:32 PM Thread Starter
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Quote:
Originally Posted by binx_19 View Post
now that it has had a chance to digest...How do you account for changing of Gear ratios? power and weight still stay the same??
It's like a teeter-toter, on one side you have acceleration, on the other side you have Top Speed. If you gain on the acceleration side you'll sacrifice Top Speed, and respectively if you gear your bike for more Top Speed you'll sacrifice acceleration (extremely noticeable at Tracks like Road America, Daytona, & the original configuration of Brainerd).

I use to gear my bikes much more aggressively (for acceleration) than other people I was competing against to compensate for my weight, for example when others were using +3 overall gearing at a specific track (-1 in the front OR +3 in the back) I was using +7 overall gearing (-1 front / +4 rear). That would allow me to accelerate better, but each gear was very short lived and I was constantly shifting around the entire track. On a straight I was having to shift more times at lower speeds than other riders, every time you shift you lose a little bit to your competition. Shifts at lower speeds cost you more distance on your competition because that's during your highest rate of acceleration, so any brief loss of acceleration at that time costs you more - but as you get going faster your acceleration curve flattens out and each shift costs you less distance on your competition.

When I was using very aggressive gearing I would usually shoot away from a turn quickly, but then when I was about 1/3 to 1/2 of the way down the straight the competition would have caught me, then pass me, then pull away - a little more each time I shifted. I also had a tremendous risk of high-siding out of the turn due to spinning the rear tire on acceleration when geared very aggressively, running overly aggressive gearing can make racing overly hectic and stressful. Another issue is that I would start to get into the upper capabilities of the engines power production sooner, in other words I would run out of power sooner on a straight due to being in the upper most gears of the transmission sooner. There's a bit of advice out there that says to gear your bike so you top out in your upper most transmission gear at (or just before) the end of the fastest section of a track. When I did that I would end up shifting into 6th gear when others were still in 4th, as a result I was in a much flatter portion of the engines power curve when my competition was still climbing up their power curve and now pulling away from me. For those with a lower P/W/R they could actually skip using 6th gear all together on some tracks and stay in each of the more aggressive harder accelerating gears for longer.

I did a lot of trying different gear combo's trying to find that blend of acceleration and top speed that worked best for my situation, but what I found was that it was always a compromise. A fixed amount of power is only capable of doing so much work, as you add weight the capability of that power is now reduced due to having to do more work to achieve the same end result. Think of it like this: if you took a GSXR 1000 engine and put it in a fully loaded Semi you could probably eventually gear it down enough to move the truck, but in exchange your never going to have any speed capability because of your P/W/R. All your doing with gearing is compressing (or extending) the duration of time that the fixed amount of power you have available is going to be used.

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post #13 of 35 (permalink) Old 12-26-2009, 03:25 PM
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hmmm funny what bike holds the only record at deals gap?lol
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it is kind of confusing, because you could technically gear a GSXR1000 to act like a GSXR600, but you would still have the same power to weight ratio. my thought is that you some how have to consider Gear Ration into that power to weight ratio theory of racing.

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post #15 of 35 (permalink) Old 12-26-2009, 04:29 PM Thread Starter
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Quote:
Originally Posted by yellow_wolf View Post
hmmm funny what bike holds the only record at deals gap?lol
Though this article is meant in a helpful way for those who wish to use the upper limits of a motorcycles ability on a racetrack, and to the best of my knowledge Deals Gap is a curvy road and not an actual race track, would you like to elaborate as to what the 'only record at deals gap' is that you speak of and it's significance as related to P/W/R?

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