handling gain

[lotus]

Hi Can anyone tell me if there is any gain in handling if both front wheel base and back wheel base are the same,my car has smaller front wheel base than the back, it would be possible to put wheel spacers on so front and back are the same but is it worth it thanks.

[Goran Malmberg]

Originally Posted by lotus

Hi Can anyone tell me if there is any gain in handling if both front wheel base and back wheel base are the same,my car has smaller front wheel base than the back, it would be possible to put wheel spacers on so front and back are the same but is it worth it thanks.

No, that small change dosent make any difference noticable. It also changes the scrub radious to a probably worse situation than plus factor of the track gain.
Goran Malmberg

[graham bahr]

the only real benifit i can think of is if your rallying on a loose or muddy surface, then it might benifit you as the rear wheels will follow in the cleaner tracks left by the front

[Chucky]

It is always preferable to have a wider front track than rear track.

Have you ever tried to corner a tricycle hard?

[THR]

FRenault cars use diff sets of wheels to alter the under of over steer of the car.
if you make the front wider youll make it over steer more, and it loads the tires quicker too!!

[MGDavid]

as has been intimated above, I think you mean track not wheelbase; the latter is fore-and-aft and is usually the same on both sides unless you've had a shunt!

[dtype38]

Originally Posted by Chucky

It is always preferable to have a wider front track than rear track.

Don't karts all have a narrower front track

[Goran Malmberg]

Well, I dont have eveerything straight about the influence of TW. Right now I am working on the influece of Rc and the mecanical versus spring transfered weight distribution. I will be back when I get some better knowledge. The old truth is somewhat questioned today. A trike has its problem with a "narrow" front track, but so does a "reverse" trike with two front wheels and one wheel at the rear. Both tilt at about the same static cornering force.
Now, a gocart have a Rc very much given by the driver practically sitting over the rear axle together with the engine.

I understand that "Lotus" was asking for 1/2 inch or so in Tw change, and this is not of very much influece, more than the % number of change. Of corse we want large front Tw, but not really at the expense of scrub, depending on the number allready used on the car.
Goran Malmberg

[dtype38]

Interesting ideas Goran. As you know I don't go in for a very mathematical approach, but lean more towards a holistic view with some axle separation to relate suspesion to chassis stress. In the case of track, I think it's valid to use a similar approach to that of corner loading. Ie., if the corner loadings on one axle are significantly higher than the other due to weight distribution and effective COG height, then a valid approach would be to increase the track on that axle. Hence on a kart where the weight is predominantly to the rear and high up, then with no springs to play with, a wider track is a simple solution to even out tyre loading. On most closed wheel cars, like mine, the limiting factor is usually wheel arch clearance and in general the widest track possible will give the best results. :-)

[greenamex2]

Wider track is generally good idea but keep in mind -

- Greater wheel offsets may cause additional stresses that will break things sooner. They can also cause handling difficulties all of their own. (Says the guy with an additional 1.5 inches of offset on his wheels!)

- Using longer wishbones may also suffer from additional flexing or breakages or have to be appreciably heavier.

- Making the suspension pickup points further apart is also difficult and will either make the car heavier or effectlively less stiff.

Once again we are playing a balancing act with many variables.

The best example I can give is the difference between my Corolla race car, my old Corolla road car and my kit car. The race car has large wheel offsets and is pretty good round corners but has awful steering, so bad that I would never drive it on the road. The road car has nice steering but falls over going round bends. The kit car has a properly designed wider track and feels fantastic (once the self induced bump steer was removed, the castor was corrected to the design amount, the steering linkage was made straighter, a decent link was fitted, the right springs were fitted to stop the dampers bottoming out etc etc etc).

Back to original question, I would leave things as they are, I doubt if Lotus got things that wrong when they designed the car in the first place. I would spend the time and money on a more track orientated set of springs, dampers and tyres.

[BrettFrancis]

Originally Posted by dtype38

Don't karts all have a narrower front track

Yes, but to make a kart go around a corner, aren't you also trying to lift the inside rear?

[Goran Malmberg]

Originally Posted by BrettFrancis

Yes, but to make a kart go around a corner, aren't you also trying to lift the inside rear?

Of course, the weight transfer is Weight transfer=(cgh*weight*g-force)/track width. So both front and rear inside wheels is reducing weight to the ground.
Goran Malmberg

[Goran Malmberg]

I am picking up this "old tread" again since I have made up an counter in excel
to calculate the influence of front and rear track width relations. The formula is backed up with a physical experiment with a "car model".

Now, if we think of a car with 2,5 meter wheelbase, 1,6 m front and rear track
cornering at 0,5g steady state. No acc or retardation forces present.
Cornerweight is Lf 175, Rf 325, Lr 275, Rr 425kg.
If we rise the frot track to 1,6m (4") we will get Lf 175, Rf 325, Lr 280, Rr 420 kg.

As we can see there is no change in front wheel loads, but a more even rear tire load, representing the whole reduction in weight transfer from the increase in average Tw.
I can put in any number of Tw,Wb,Weight front to rear axle, CGH, Acc and brake forces in G, even a 3 wheeler, If anyone is interested.
Goran Malmberg

[Red Dog]

So by increasing front track, the load on the outer rear is decreased? Does this mean that if you have a car tending to oversteer, the tendency will be reduced by increasing front track?

I imagined it worked the other way round.

We recently got a kart for my son to drive and it has a lot of track adjustment available so I'm very keen to understand how this works and how the track/wheelbase relationship affects handling.

[tzei]

Thanks Goran! It all makes sense to me - now. I've been thinking these geometry-things (sort of) and now I understand my cars behavior a little better.
BTW is the formula calculating cornerweights difficult? Would be interesting toying with it...

[Goran Malmberg]

Originally Posted by Red Dog

So by increasing front track, the load on the outer rear is decreased? Does this mean that if you have a car tending to oversteer, the tendency will be reduced by increasing front track?

I imagined it worked the other way round.

We recently got a kart for my son to drive and it has a lot of track adjustment available so I'm very keen to understand how this works and how the track/wheelbase relationship affects handling.

As the average Tw is increaced we could see a little more cornering power capacity which then should be gained from more rear grip. I do remember reading this also in a cart-setup site somwhere.

But I also have read the opposite theory elswhere. So there obviosly is different opinions here. If you have all the info about the car I could put the numbers in the formula to see what we end up with. Just mail it to me in private at hemipanter@brevet.nu

Put your son in the seat and axleweight the car. Measure Tw front - rear and wheelbase. We could estimate the cgh.
Sorry, the increased front Tw should be 1.7m in my previous message.

Cheers
Goran Malmberg

[Goran Malmberg]

Originally Posted by tzei

Thanks Goran! It all makes sense to me - now. I've been thinking these geometry-things (sort of) and now I understand my cars behavior a little better.
BTW is the formula calculating cornerweights difficult? Would be interesting toying with it...

I did put out a formula earlier concerning another matter. A few off my expressions ended up with "smiles" as they probabley used the same caracters. Ok, it was sort of funny.

Ill try an explanation. You are having an overturning moment comming from cgh*wheight*g-force. The same force is present at 0,5*Tw of 2m. If the front Tw is 1,8m then we got 0,5*1,8=0,9m. The rear is 1,6m, 0,5*1,6=0,8m.
We know the Mot = cgh*w*g, and thereby the same at Tw2m/2.

Now we must know the Mr (motion ratio ) which are easy as we use 1 meter. Then 0,8/1=0,8 and 0,9/1=0,9. So, the Sr=spring ratio become 0,8^2 *Sr at the front and 0,9^2*Sr at the rear. Add those two and we know the springrate at 1m arm. Then cgh*w*g/Sr@1m=the number of deflection (D) in mm at 1m arm. If D=20mm at 1m, then D at 0,9m is 0,9*20=18mm.
And 0,8*20=16mm. So the front springs will be compressed 18mm and the rear spring 16mm. Then weight transfer front is 18*Sr and Wt r =16*Sr.

The reason for this way of counting is that I put in other factors in my excel sheet. Such as braking, acc forces and weight distribution.

Dunno if it makes sense as I fabricate my own math.
Kind regards
Goran Malmberg

[dtype38]

Goran.. correct me if I'm wrong, but the math you give assumes the chassis and tyres are rigid compared to the springs. This means the only deflection is by the springs. In the case of a kart, there are no springs and the tyres compress and chassis flex due to cornering loads. You might be interested that I watched a programme about kart racing once where one of the top drivers was complaining that he'd chosen too stiff a chassis for the bumpy track he was racing at. He said he couldn't tune it in fully using the tyre pressures and track width and was losing time because he was bouncing too much over the bumps. From that I would guess that for karts tyre pressure and track width are used to adjust the effective "springing" for rough and smooth tracks, but that this only works within the limits of the chassis you have. :-)

[Goran Malmberg]

Originally Posted by dtype38

A
Goran.. correct me if I'm wrong, but the math you give assumes the chassis and tyres are rigid compared to the springs. This means the only deflection is by the springs.
B
In the case of a kart, there are no springs and the tyres compress and chassis flex due to cornering loads. You might be interested that I watched a programme about kart racing once where one of the top drivers was complaining that he'd chosen too stiff a chassis for the bumpy track he was racing at. He said he couldn't tune it in fully using the tyre pressures and track width and was losing time because he was bouncing too much over the bumps. From that I would guess that for karts tyre pressure and track width are used to adjust the effective "springing" for rough and smooth tracks, but that this only works within the limits of the chassis you have. :-)

A.
Let me start off by saying that what I whant to show is purley load distribution in relation to track width and wheelbase. In fact not even the springs is needed to be taken in to account. And if tire rate is added it should not really affekt the utcome of the numbers. Tire rate should then be added in series with wheel rate.
The reason for the Sr to be used in the formula is to be able to use it combined with different springrate front to rear. And we could also add a bar.
If the springrat is raised or lovered by the same ammount front and rear, the loas otcome will be identical and only D (deflection) will change.
B.
Bad torsional stiffness will uppsett this calculation. But "framespringing" can be used for carts as they do not have regular springs. This was also used in speedway bike racing. However, for regular racing cars we should presume using a totally rigid chassis.

On a bumpy track we must use more wheeltravel not to make the whole car go upp and down.
So, when the cart is driven on a bumpy track we may use a softer chassis.
The sideffect is that we will soften steering balance at the same time.

On a regular "stiff" racing car we can soften the springs while keeping the
load distribution the same. We only alter the deflection.

The difference is that the softer chassis acts as a spring in between the axles.

C.
Another factor that for the same reason is left out here is "jacking".

Hope I am not expressing myself to "hazey".
Goran Malmberg

[dtype38]

Your express yourself very well Goran... its just my brain that is a bit "hazey" at understanding sometimes :-)

Re: point A, I wasn't trying to suggest that your maths was "too simple", only that it was more representative of a race car with a rigid chassis and relatively soft springs rather than a kart.

Re: point B, Agreed, a "softter" sprung kart chassis makes for better handling over bumps but less precise cornering. What I was suggesting was that increasing track would have a similar effect to softening the chassis springiness, because the lever arm would be increased. But now I'm not so sure, because although the lever at the wheel increases, the moment correspondingly reduces. Hmmm... would it lower the effective spring frequency I wonder?

Maybe I'll leave all this difficult stuff to people who understand it...... like you!

[tzei]

My brains are also a bit hazed, but i'll try to figure this one out...
Like to keep it simple (and stupid - uh?)(Don't take this the wrong way Goran, I'm not referring to your math but my brain) - to have some sense to the basics, later on I should propably take account tyres & springs etc.

I know - World is grey, But making a bit of it black and white can help sometimes...

[Goran Malmberg]

Sorry,guess explanations like this IS a bit tricky, very much depending on the lenght off formula. There is also much of a help beeing able to sitt by a table with pen and paper, making drawings.
Dont be alarmed by not getting everything straight at once, I have been sitting with chassis stuff a number of years....
Goran Malmberg

[Alex Hodgkinson]

Originally Posted by dtype38

In the case of a kart, there are no springs and the tyres compress and chassis flex due to cornering loads. You might be interested that I watched a programme about kart racing once where one of the top drivers was complaining that he'd chosen too stiff a chassis for the bumpy track he was racing at. He said he couldn't tune it in fully using the tyre pressures and track width and was losing time because he was bouncing too much over the bumps. From that I would guess that for karts tyre pressure and track width are used to adjust the effective "springing" for rough and smooth tracks, but that this only works within the limits of the chassis you have. :-)

With karting the chassis is tuned to go around the corners as quickly as possible usually. I've not, at any circuit ever, had to alter my track/tyre presures to cope with bumps. With a kart the rule is generally front wheels out, more front end grip. However this is due to the lifting the rear's and cannot be applied to vehicles with diffs.

[dtype38]

Originally Posted by Alex Hodgkinson

I've not, at any circuit ever, had to alter my track/tyre presures to cope with bumps.

Have you ever met anyone who does, or was the bloke I saw talking cow droppings??

I only ask this because on my race car I've not, at any circuit ever, altered my track, tyre pressures, spring rates, damper settings, anti-roll bar settings or anything else, wet or dry, bumpy or smooth. Not because it doesn't make a difference... just because I'm bone idle

[Goran Malmberg]

Originally Posted by dtype38

Have you ever met anyone who does, or was the bloke I saw talking cow droppings??

I only ask this because on my race car I've not, at any circuit ever, altered my track, tyre pressures, spring rates, damper settings, anti-roll bar settings or anything else, wet or dry, bumpy or smooth. Not because it doesn't make a difference... just because I'm bone idle

Funny you say so, you know the moost important part is the DRIVER.
I have an priority list here....
1. The Driver.
2. Tires and camber angle.
3. The seat.
4. Weight and CGH.
5. Aero.
6. Springs, dampers and rollbars.
7. The rest......
So if the car is working fair, you may do quite well by beeing a good driver.
Goran Malmberg