losi xxx

[bigred5765]

without over complicating thing blow a feather then try it with a brick it sticks better mass/weight in the right place,without over doing it helps.IE why tricky and Danny McGee add weight to a over weight car

[Northy]

So then Carl, is that why all the F1 teams spend millions making their cars light? They make their cars lighter than the weight limit, then add weight where they want it, but keep the car just over the limit. They don't just add weight to the car and say bollocks to the weight limit. Or am I wrong?

[paulj]

Originally Posted by Northy

So then Carl, is that why all the F1 teams spend millions making their cars light? They make their cars lighter than the weight limit, then add weight where they want it, but keep the car just over the limit. They don't just add weight to the car and say bollocks to the weight limit. Or am I wrong?

As far as I was aware F1 teams don't have drivers standing at the side of the track to drive the car and with a minimum weight of 600kg they have a little bit more weight than a 1/10 buggy to juggle with

Don't forget that weight effectively increases with speed due to the downforce at least as far as the tyre is concerned.

There is more to be gained by reducing the unsprung weight on the car compared to the overall weight too, so lighter wheel/tyre combinations or wishbones/hubs should have more effect than simply replacing all the screws with Ti or alloy but if you get the thing so light it's not staying in contact with the ground over bumps then it ain't going to do well in the corners

[paulj]

Oh and I bet an F1 aero package is a lot more effective at creating downforce and grip than your pred

N.B. Honda's current effort excepted

[Dunc]

I suspect the point of adding mass is to calm the behaviour of the car. Particularly nowadays with the high speeds we are able to achieve, which translates to kinetic energy, when we hit a bump some of this energy causes unwanted movement of the car as the suspension tries to compensate. Increasing the mass will help dampen any such response and therefore, as paulj touched upon, help keep the vehicle in contact with the ground, which is where you want it.

It would appear the amount of mass people typically add is insufficient to significantly upset the other handling characteristics, as outlined on the webpage Northy linked to previously. From a brief skim of the webpages in question I suspect this is because the increase in mass of the car is not a significant percentage compared to its total mass (typically 2-5%) and I doubt the CG position is radically altered either.

[bigred5765]

well said and 1700 grms works differently than 600kg on gravity

[bigred5765]

Originally Posted by Northy

So then Carl, is that why all the F1 teams spend millions making their cars light? They make their cars lighter than the weight limit, then add weight where they want it, but keep the car just over the limit. They don't just add weight to the car and say bollocks to the weight limit. Or am I wrong?

and u still havent explained the oil thing ae vs losi

[Northy]

If people are adding mass to keep the car in contact with the ground over bumps do you think the shocks might not be set up correctly?

G

[Dunc]

Originally Posted by bigred5765

well said and 1700 grms works differently than 600kg on gravity

Thank you, glad you liked it!

Originally Posted by Northy

So then Carl, is that why all the F1 teams spend millions making their cars light? They make their cars lighter than the weight limit, then add weight where they want it, but keep the car just over the limit. They don't just add weight to the car and say bollocks to the weight limit. Or am I wrong?

Again, paulj has pretty much answered this already, but just to expand a bit:

A Formula 1 car does weigh a lot when you consider the aerodynamic downforce acting upon it. This equates to an increased contact force at the wheels and hence more grip.

It is advantageous to generate increased (vertical) force on the wheels via aerodynamic aids because it will not affect the mass of the car or the CofG (assuming your reference point is on the chassis). Therefore the desirable handling characteristics afforded by having a light vehicle with a low CofG can be maintained whilst still generating prodigious amounts of grip.

You could achieve the same level of vertical force by drastically increasing the mass of the car, but as the link you posted suggests, this would have numerous detrimental affects on the handling characteristics.

The amount of aerodynamic downforce an F1 car is able to produce far outstrips that due to its mass alone, i.e. there is little benefit in saying "bollocks to the weight limit."

[Northy]

Some quick sums......

2wd weight limit: 1474g

A 2wd car weighing 1700g is 15% over the weight limit.

I don't know of any proffesional class of racing where they would dream of running a car that is 15% over the minimum weight limit if they could do something about it. OK, F1 might not the the best example, so lets go to WRC. When Ford first released the Focus WRC car they spent a fortune making it lighter as it was far too heavy!



G

[Cockerill]

OK, lets forget F1 cars for a moment.

How about WRC cars, do they add weight to make their cars go over bumps better, or do they try to get as close to the limit as possible, I wouldn't know, best person to ask would be Jim Dixon as he prepares rally cars, I have a feeling he might say no.

[Dunc]

Originally Posted by Northy

If people are adding mass to keep the car in contact with the ground over bumps do you think the shocks might not be set up correctly?

G

A fair point, but I think the added mass is largely to help cope with hitting perturbations at speed. This is not a dominant requirement in setting up a car; stability in corners is where it counts. These two criteria are likely to be at odds with one another so you've got to try and compromise somewhere.

[Northy]

Originally Posted by Dunc

What Dunc said......

Good post Dunc. Let me just point out here I'm not trying to say I'm right and everyone else is wrong. This is a discussion and I certainly don't want it to end up as a flame war we're all friends here.

F1 was not a good example, which is why in the post above I have mentioned WRC cars which are more like our toys.

Next time I speak to Jim I'll ask if he's ever added weight to a WRC car to make it handle better

EDIT: Tom beat me to it!

[super__dan]

In fairness G, not many motorsport classes have the same power to weight ratio as us though do they.

Also speak to any chassis designer about a class where they deliberatly run a soft plastic chassis as flex is prefered here rather than in the suspension setup and I guarantee they will think you'r insane, trust me I've done this and he thought I was a simpleton!

I could think of a few more things that make no sense in bugy racing given time

[Northy]

Don't even get me started on flexible chassis's Dan, they're only for lazy people who can't be arsed to set thier shocks up!

JOKE!!!! (Sort of)

G

[Dunc]

Originally Posted by Northy

Good post Dunc. Let me just point out here I'm not trying to say I'm right and everyone else is wrong. This is a discussion and I certainly don't want it to end up as a flame war we're all friends here.

F1 was not a good example, which is why in the post above I have mentioned WRC cars which are more like our toys.

Next time I speak to Jim I'll ask if he's ever added weight to a WRC car to make it handle better

EDIT: Tom beat me to it!

Northy, no flame war (or offence) intended!!

I just enjoy a good to and fro of intellectual thoughts, but often get a little over exuberant!

I think it's hard to make real comparisons, even with similar classes such as WRC, as the way our vehicles behave is quite unique.

Imagine a full-sized vehicle doing correctly scaled speeds and jumps to our buggies! The forces involved from landings and the like would be immense, I'm not even sure it could be done.

[jimmy]

weight adds stability and slows the reactions - which on our crazy-fast cars is a good thing for lesser drivers like myself

[elvo]

Jimmy hit the nail on the head there.

The reason some add weight here or there is the same reason a dog licks himself: BECAUSE WE CAN :-)


Not to be disrespectful, but power-wise, WRC are pussies. As Northy might put it: we've got power coming out of our ears. And F1 is more about aero stuff than anything else. So no fair comparisons there.

I think it's just a case of the gains out-weighing (hehe) the losses: a few grammes at the front or back can be enough to bring balance to the force - or a race car, with liçttle ill effect. I've won races with a 2WD car that was 200 grammes overweight. It's not 'quick', not nimble, but 100% controllable and consistent.

And besides, making comparisons is even more difficult, I think, because we rely on a totally different sort of grip than most 1:1 racing classes. We have itty bitty little pins biting into the ground, not knobs or grooves or slicks or anything that looks remotely like a 1:1 tyre.

[xx4-nutter]

I raced my Losi xxx BK2 last night at a local club on a tight track using 4wd fronts with no weight on the front end running an 11x2 and it was awsome, i was into corners so tight and spot on, in the final keeping an X10 behind me until the last lap which i was happy about lol

last time out i was alot slower with it whilst racing with 2wd fronts, comapred to last time what a difference.. also does any one have a good starting point set up for grass for the xxx BK2 ?

Garry D.

[_sleigh_]

If it's the standard BK2 with no mods done to it, then try this.

Front

Losi 27.5wt / Red Piston / Green Spring
Shock - Middle on tower / Middle on Wishbone
Camber link - Middle on bulkhead / Outer on Hub

Rear

Losi 27.5wt / Red Piston / Red Spring
Shock - 3 on Tower / Inner on Wishbone
Camber Link - Middle on tower / Outer on Hub

Wheelbase - Medium

Anti-Squat - 1 shim under front

Ride height - set back at driveshaft level and then the front should be set so the chassis is straight (front to back)

25g in front bulkhead



If you are thinking of modding the car, then certainly look at cutting the brace between the cells and the servo out. Then dremel the area to allow the cells to move right upto the servo. That really helps gain on-power steering.

Another mod that would be worth looking at is swapping the steering to the XXX-CR rack. Again this helps smooth and equal out the steering through the corner.