Rear/Front track width

[marcush.]

of course I was assuming you were at or near something like a balance to start with,and sorry for exagerating a bit I should have specified 5mils

Of course if the setup/layout of the car is wayout one mil is not changing anything but if you are near the sweet spot 1lbs of load transfer will definitevely do something,at least for a capable driver.

[Jersey Tom]

Of course if the setup/layout of the car is wayout one mil is not changing anything but if you are near the sweet spot 1lbs of load transfer will definitevely do something,at least for a capable driver.

According to who or what? Prove it

1 lb of weight moved from one tire to another, with vehicle load probably on the order of 7000 lb at top speed...

[Conceptual]

Of course if the setup/layout of the car is wayout one mil is not changing anything but if you are near the sweet spot 1lbs of load transfer will definitevely do something,at least for a capable driver.

According to who or what? Prove it

1 lb of weight moved from one tire to another, with vehicle load probably on the order of 7000 lb at top speed...

I've noticed (in rFactor at least) when I am dialing in the tyre temps, that sometimes very, very small adjustments such as this do go a long way. Especially when you look at Left to Right weight distribution. I have dialed in the 1991 F1 mod for several circuits this way, and it ALWAYS comes down to minute changes in load transfer, so why is 1lb so unimportant in the real world?

[Jersey Tom]

and it ALWAYS comes down to minute changes in load transfer, so why is 1lb so unimportant in the real world?

Quantify "minute."

Also, rFactor tires != real tires. Their tire model is particularly poor IMO.

I'm just saying, if 1 lb is indeed a definitively big deal, it should be easy to prove.

[Conceptual]

and it ALWAYS comes down to minute changes in load transfer, so why is 1lb so unimportant in the real world?

Quantify "minute."

Also, rFactor tires != real tires. Their tire model is particularly poor IMO.

I'm just saying, if 1 lb is indeed a definitively big deal, it should be easy to prove.

I have been educated several times on this board about the fact that in race car engineering, there are no free lunches. I always took that as with the level of controlled tolerances on a racecar, that there is no such thing as an insignificant amount of weight, regardless how minute.

Now, I don't exactly know how much it will do per se, but I do know that if that 1lb is the crossing point between front-rear balance, it would be a HUGE participant in the overall handling of the car.

Maybe I am looking at this wrong? Or don't understand what your point is fully?

I am open to be educated, as always!

[Jersey Tom]

Removing mass is one thing. And in that case yes, pulling any amount of mass out of a component is good, since the sum of many small changes (be it a gram per component) does sum to a significant quantity. Though even then there's the question of how significant a difference it will be, in order to justify the time and money to spend on it.

Just seems a lot of the time folks make blanket statements about how finely tuned these cars are, without anything to back it up. If someone is going to say that a 1mm (0.040") change in track width, or a 1 lbf change in load transfer distribution is significant, then they must be able to prove that. In the realm of pure physics, sure, any non-zero quantity is a change in the system. In the realm of engineering though, there's the question of significance and what resolution is required to make a change that you can definitely see.

I don't buy that a 1 lbf change in LLT is significant, and you wouldn't be remotely able to see that level of detail in any kind of real world DAQ. From the plot I'm looking at right now.. from a top-tier racecar.. you'll easily get 30-70 lbf of variation in corner loads, on back to back laps with identical setups and < 0.1 variation in laptime.

Plus, I don't think of balance in terms of crossover points or anything. At the simplest, it's a 3-d map as a function of Ax, Ay, and speed. Is a 1 lb shift enough to mean anything to a driver? Highly doubt it.

[Conceptual]

Alright, I see your point, and with the plot that you spoke of, that does seem insignificant.

[Ciro Pabón]

I think this is the proof JerseyTom asked for (you know my mantra: "don't give me opinions, give me numbers").

If I assume that the CG is at 1 feet of height, the wheels are 7 feet apart and the load is the 7000 pounds someone assumed, then, when the car is going in a straight, we have this:



If the car takes a curve at 1G, then we have this:



The torque around the CG is equalized (as you all know) by a lateral weight transfer, like this:



Thus:



Then, the left wheel (I'm assuming we're looking the car from the front) "weighs" 4.500 pounds and the right wheel (to the left in the image) "weighs" 2.500 pounds.

Now, if we increase, let's say, 0.1 feet (that's 3 cm, give or take) the front width, we get:



Thus:



That's around 30 pounds of difference. So, we get the 30 pounds "asked" when the change in width is 3 cm, not 1 mm.

Anyway, I don't think that 30 pounds is going to make any difference at all in the feeling: it's like 0.5% of the weight...

Now, if this change in weight of 0.5% "translated directly" in laps 0.5% faster, this would mean that for a 1:30 lap you'd get a difference of 4 or 5 tenths (I don't think this is the case, but...).

Is this the case?

However, if we move just the left wheel 0.01 of a foot (that's like 3 mm) I find a change in force of 7 pounds... which is around a fourth of the change "required".

Same goes for Center of Gravity height: a change of 0.01 foot equals 10 pounds.

So, a change of 1 mm in width is no big deal, as JerseyTom correctly states. A change in the position of one of the wheels could be felt at half the distance "required". A change of 1 cm in the CG height gives you 30 pounds more weight on the external tyre. Perhaps that's why Alonso has lost weight...

Conclusion: when you race, check the "width" of both tyres. The distance of both tyres to the CG must be equal to the centimeter or less, or you are changing the attitude of your car in a significant amount, even for small movements of the tyres.

[Conceptual]

Ciro,

Is the CoG directly related to ride height?

Thank you!

[mike]

im not entire sure about your interpretation of weight transfer%
2000lbs of weight differences is 1000lbs of transfer thats 14.29% compare to 1971lbs of weight differences and 985.5lb of transfer 14.08% and if u work out the difference thats 1.45% and in a 1:30lap the difference is 1.305s with the assumption that it is in a circle pulling 1g constant or on average, i agree totally with you that change of 30mm makes hardly a difference since cars dont travel in a curve for that amount of time in real life.

i think this topic is about comparing the track width ratio of the front and the rear, my own interpretation is that wider front comparatively to the rear will give you understeer since the rear trasfers more weight to the outside than the front and wider rear track will give you more oversteer, however the width of the tyre can give you such affect.
For example you wouldn't expect a car with 50:50 balances on 295 tyres and 1500mm track on the rear, 205 and 1300mm front to have extreme oversteer since the front is more proned to slip

[MReggio13]

As a race engineer, I've never had the good fortune of working with somebody that can feel 1 lb or weight change on any one corner. If he/she is out there, I'd like to work with them. There are many times that when a car comes back from a session that the corner weights have shifted slightly by a few lbs. This is almost inevitable, and the driver does not notice a balance difference from right to left. Also, because we don't deal with perfectly smooth tracks, any small undulation in the track will cause some amount of weight transfer, even in a straight line. This will be very pronounced if you are running very stiff ARB's.

When tuning a car, you have to look at percentages, and it does take a significant track change, usually restricted by the rules, to alter the amount of load transfer happening.

While I'd like to think that an F1 car is a hyper-sensitive machine that requires the slightest of adjustment to make a huge difference, I have seen from every car that I have worked on, from F2000 to Indy Lights, that this just doesn't happen in the real world. There are also times when the driver bounces off a wall, and the car goes quicker..... Maybe that just means I'm not doing my job correctly.....

Mike

[Ciro Pabón]

Welcome, MReggio13. It's a pleasure to read your post, I hope you stick around.

I agree with you. However, as the legend goes, "... it is said of Tazio Nuvolari, one of the greatest racing drivers ever, that he knew at all times while driving the weight on each of the four tires to within a few pounds."

"Nuvolari ha cinquanta chili d'ossa Nuvolari ha un corpo eccezionale...", that is, "Nuvolari has 50 kilos of bones, Nuvolari has an exceptional body..." --Lucio Dalla's Nuvolari song --
[youtube]http://www.youtube.com/watch?v=KbKYiwzSSmc[/youtube]

Sorry, I couldn't resist posting that video. I know that for english speakers, the song has no attractive, but for an italian or spaniard, the lyrics are clear. It's also clear that Lucio Dalla is crazy for racing: "Three plus three for him always are seven".

Me, I'm not that good, of course. In Colombia, cars have to pass an annual inspection, that includes a measurement of the weight of each tyre and of the braking force. Here you have the numbers for my car weight:

Front right/left weight (Newtons): 3309/3214
Rear right/left weight: 2156/2159

That's like 10 kilos of difference in the front axle, give or take. I had no idea until I got the measurement...

Chap, simple: yes.

Of course, the CoG is "sum" of the CoG of all the parts of the car, so you could think of a car with a lower ride height but that somehow has a heavy gadget on top, which could move you back to the same CoG height. For example, if you lower your car but add a spoiler, a turbo on top of the engine, many dials, roll reinforcement, etc. you could end with the same CoG height.

Incidentally, using the same equations I posted, you can understand that the CoG height influences the braking ability even more than the turning ability of a car. That's why SUVs are so lousy at braking, I think...

[tarzoon]

Is the track width in any way related with the modifications to the rear wing?

I'm wondering what is the influence between the dirty air behind the rear wing (especially in width) and the wider track, presumably less affected by car ahead.

[Conceptual]

I have a question for Karts, since my kids are starting to get into them...

Can the track width on a Kart be changed by putting a spacer between the tyre rim and the mounting point on the chassis? I mean, if the car is understeering, I could put a 5mm washer on both rear tyres to increase the track width by 1cm, or vice versa? Can someone explain in a bit more detail the major effects concerning the balance between front/rear track width? Is it like 100%F/105%R? Is there a key, or a slope that is best to follow? So maybe 102%F/108%R (increasing both to keep a ratio). I am really interested in this. I have ordered Competition Suspension (as well as the Aero, Electrical, Controls, Chassis and Tyre companion books) so I hope that book covers this exact thing, but it would be great to get some feedback from the Karters on the forum.

Thanks!

[Jersey Tom]

Increasing rear track width will increase limit understeer as you will have less load transfer. The relative difference between front and rear plays into balance.. and global track width plays into ultimate lateral load transfer and grip.

I don't know what the suspension adjustment is on a kart, but your best bet is probably to try adjusting balance with air pressure split. Higher in the rear to free the car up.