Rear/Front track width

[Conceptual]

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.

There isnt much in the way of suspension setup at all on a kart that I have seen. That is why I was thinking of using the shim as another dimension of control. The tyre pressure I understand, so thank you for your info!

[Jersey Tom]

You could try it, with the spacers... though then you start to put more load on the wheel bearings, etc. Track width is generally not used as a chassis tuning tool.

[RH1300S]

I have seen Kart chassis where you can adjust track width. Normally spacers at the front and moving the hubs on the axle at the rear.

As a kart chassis is also the spring - would not a wider track also "soften" the chassis at that end? So you get less load transfer due to greater track width, but also the softer (as the wheel sees it) chassis should also give more mechanical grip at that end.

I think Kart setup is quite complicated (anyone know?) - look at a kart and the front castor angle lifts or drops a front corner as the wheel is turned - which MUST affect how the back behaves on corner entry. So, a wider track might exagerate the castor effect and lift a rear wheel more. So the kart might turn in better - which might feel like less understeer, but is in fact less rear grip - I'm already confused

[Conceptual]

I'm taking my 8 year old to Motorama in Harrisburg in 2 weeks. Whe wants to look at the Karts, and since you can walk through the pits, I will make a special point of asking some of the karters there.

Thanks for the info!

[marcush.]

everyone in karts uses track width as a tuning tool.On the rear with the solid axle you just slide the rims in or out ,the hubs are slotted and clamped by setscrews.
As for the momentary load variations I´m aware of this but in setup terms you have to filter out noise or try to find a better setup to minimise the load fluctuations.Sure this dependends on your sampling rate , maybe more confusing than helpful if youre not into optimising high speed damping.
Forget about the 1 mil,I went overboard on that statement,but on the cars I work on and the guys I have the pleasure to work with ,6mil in track does get noticed and has a small effect on tyre temps.

[Jersey Tom]

When you have +/- 1000 (or more) lbf of load variation, that becomes lost very quickly Even if you're logging at 100, 200 Hz or so.

Plus, with tire deflection your true track width and offset is probably going to change 25+ mm through cornering. Maybe even considerably more.

[Belatti]

Interesting thread.

Of course karts uses track width as a tuning tool. The lack of suspension maybe make people think there is not much to tune there but nothing in the world is as wrong as that. Kart tunning is as difficult as any other race car tunning. The rear axle works as a beam, flexing between the wheel and the bearings. You can choose what diameter and thickness of axle use and also how many bearings youll use (2 or 3) and how they are going to be fixed. You can change rear wheel hubs to make that working axle shorter or longer, you have got torsion bars in the front and in the rear



etc, etc, etc...

Heres a very cool Kart setup guide by Arrows:

http://www.dpeng.com.au/files/arrow/arr ... manual.pdf

Jersey Tom is wrong not only because he believes track width is not generally used as a chassis tuning tool, but also because he thinks that you can balance a kart with air pressure split. At least with the rubber we use arround here, you cant use other tyre hot pressures than 13 to 14 psi. They are used to balance nothing. Tyre compounds are very sensitive to temperature and the over pressures make tires work in an undesired temp range. Overpressured tires literally turn into a "glass" appearence in matter of few laps, while very underpressured tires have walls not rigid enough and there is always the danger of loosing the tire.

Also, take a look at that manual for wet setup advices and you´ll see track width setup is fundamental there.

[RacingManiac]

I think Jersey Tom's comment about track not being a tuning tool is aimed at normal car chassis.....

[Jersey Tom]

Correctamundo! I have never seen track-width as a test day tuning tool in pro openwheel or pro stockcar. I'm not really concerned with karts.

[RacingManiac]

Mind you, our FSAE car had messed with track width before...historically we've had spacers to let us run different year's rim on the same car, and we've tried to wider track in investigate the effect...the thing they say about you nailing the cone with inside rear wheel is true...

[Jersey Tom]

True, true.

Now, even if 13-14psi hot is truly the only possible place you could run your kart tires.. I'd bet 13F/14R handles noticeably different than 14F/13R. Depending on the car and setup, as little as a 0.25 psi change is noticeable. If you aren't currently using pressure split as a tuning tool, perhaps you should try it.

[Belatti]

Correctamundo! I have never seen track-width as a test day tuning tool in pro openwheel or pro stockcar. I'm not really concerned with karts.

Oh sorry!

Still, here "pro stockcar" (we call that TC) uses track width to tune chasis. Rims or spacers, depending the case.

[Ciro Pabón]

... I'm not really concerned with karts.

Oh, Taraxippus, enlighten him!

[DaveW]

Forgive me, but my thoughts on the subject are:

Assuming a good & balanced mechanical starting point, increasing front track will cause more of the cornering roll moment to be carried by the front axle. This will move lateral balance towards understeer.
Understeer can be corrected by reducing front bar or (better) reducing front springs.
Reducing front springs will (generally) allow a reduction in rear damping.
Reduced springs & damping should mean that the vehicle will be disturbed less when taking kerbs.
This should allow more kerb to be taken in low speed corners, thus opening up the corner & increasing exit speed.
On many tracks increased low speed corner exit speed will improve lap time significantly.

[Jersey Tom]

Assuming a good & balanced mechanical starting point, increasing front track will cause more of the cornering roll moment to be carried by the front axle. This will move lateral balance towards understeer.

Sure you don't mean the opposite?