Albuquerque Speedway Karting Forum Index Albuquerque Speedway Karting
ASK tries to keep this a user friendly site. The site management team can and will delete or ban any posts or users deemed non-constructive.
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Best explanation about cross.

 
Post new topic   Reply to topic    Albuquerque Speedway Karting Forum Index -> Tech Talk
View previous topic :: View next topic  
Author Message
Don Kruse



Joined: 16 May 2007
Posts: 437
Location: Albuquerque

PostPosted: Sat Jan 23, 2010 7:20 am    Post subject: Best explanation about cross. Reply with quote

Kart takes too long to come in or RR is cold, take cross out

Kart goes away too quickly or RR is hot, add cross
--------------------------------------------------------------------------
Makes sense to me. You want both those big right side tires gripping to the max, evenly, when hitting the apex of the turns. If set up correctly both would come in at the same temps.

Maybe?
--------------------------------------------------------------------------
Would this mean, set up the kart to turn then adjust for cross or cross first?

DK

PS, I hate winter.
_________________
Buy it used, buy it cheap and have fun!
Back to top
View user's profile Send private message
karter43



Joined: 04 May 2007
Posts: 265

PostPosted: Sat Jan 23, 2010 8:18 pm    Post subject: Reply with quote

Well, sort’a, kind’a, not really, maybe! I think with this reasoning you’r walking a knife edge.

If the kart is loose and eventually “comes in” ,,, yea, taking cross out will help, but the real question might be ‘why did the tire need to come in?’ Old tire, too hard ?
So the kart “goes away”,,,, add cross weight ,, but that promotes the first case. Perhaps the compound is too soft to go the distance …..

Now, as for the big right front, it don’t make cense from a “math/science” standpoint. When F1 could go crazy with their tires (1970s) you’ll notice the front is relatively small and the rear is HUGE. The math is, for a “neutral” set up, (rear weight %) X (front tire coefficient) = (front %) X (rear tire coefficient). Now this is REALY simplified but,

Rear tire = 8” width
Front weight = 45%
Rear weight = 55%
8 X 0.45 = (front tire width) X .55
Front tire = 6.5”

Using the big tire on the front has 1 BIG advantage, the rubber is still fresh, rotate to the back occasionally.
[/img]http://www.motoringpicturelibrary.com/preview_image.asp?fleID=6309
_________________
Stephen Spiak
Back to top
View user's profile Send private message
Don Kruse



Joined: 16 May 2007
Posts: 437
Location: Albuquerque

PostPosted: Sun Jan 24, 2010 9:05 am    Post subject: Reply with quote

Hey Steve: Your theory lends itself to straight up sprint karts more so than a LTO but still doesn't wash. Two big differences: the karts live axle and the short almost square wheelbase.

You will have to agree the goal is to get the absolute maximum grip at the apex of the corner allowing the maximum speed through it. After all to get down the straight fast you must get through the corner fast. With all the dynamic adjustments of the LTO chassis; your goal is to drive the kart in faster, hit the corner harder and come out faster.

Cross is the fine-tune adjustment used to balance the kart at the apex. Cross will set the balance between the tires when the centrifugal forces of the center of gravity of the kart. When the cross is tuned to the chassis exactly the tires will carry the weight equally. The indicator is the temp at the scale.

Keep in mind all this doesn't mean a hill of beans if you aren't close on the setup that turns you into the corner and tires that are close.

DK.
_________________
Buy it used, buy it cheap and have fun!
Back to top
View user's profile Send private message
karter43



Joined: 04 May 2007
Posts: 265

PostPosted: Sun Jan 24, 2010 10:07 am    Post subject: Reply with quote

My veiw on the whole thing with karts is: the entry to the corner is the most important. My experience is that if you get in good all else will follow, if you push going in the driver will most likley over correct and the kart will be losse in the middle or off,,,, Too lose going in and the kart will never recover and will drift up as the driver tries to catch it.

Most of the time cross weight is a adjustment when you have run out of adjustment on stagger, track width and weight distribution. All of these affect steady state cornering equaly as well as entry and exit. Entry is affected more by how the kart loads up fron static (in the pits sitting on the scales) to dynamic (steady state cornering). The change (entry / exit) is governed by things like frame flex and tire sidewall flex. HP is also an important factor in exit but, karts don't have enough (except duals or opens) as usually your wide open from at or before the apex.

I don't think LTO or short wheel base or live axle affect cross weight adjustment function. They do chang the sensitivity of it though.
Back to top
View user's profile Send private message
Don Kruse



Joined: 16 May 2007
Posts: 437
Location: Albuquerque

PostPosted: Sun Jan 24, 2010 3:23 pm    Post subject: Reply with quote

When your baseline setup is close and you have the near correct tires rear stagger gets you into the corners front gets you out. The right side grip maximizes at the apex and then releases on the way out. Doesn't it makes sense you want both with equal grip at the maximum?

Steve: I understand you may get your son in a kart this year. It will be good to see out at the track again.

DK
_________________
Buy it used, buy it cheap and have fun!
Back to top
View user's profile Send private message
karter43



Joined: 04 May 2007
Posts: 265

PostPosted: Sun Jan 24, 2010 5:46 pm    Post subject: Reply with quote

Front tire stagger is a myth! If the tires are not locked together (as on the rear axle) it has no effect. Different tire diameters do change the cross weight but, if you were to adjust it back the net change would br ZERO.

Grip needs to be maxamized very soon after turn in, unless you are able to drive the corner like a parabola.
Back to top
View user's profile Send private message
Don Kruse



Joined: 16 May 2007
Posts: 437
Location: Albuquerque

PostPosted: Mon Jan 25, 2010 2:52 pm    Post subject: Reply with quote

To a degree it is true but, I think in the modern LTO chassis the designers are accommodating the front stagger into the front end. I believe they do this to set the base-line setup to the kart without having to use excessive adjustments to get to the numbers they want.

Getting back to the original statement of the post, assuming you are close on tires for the track and your setup is close, if you are heating up the RF and the RR is cold you have too much cross. I would take out 2% (a large amount) so as to feel the difference.

DK
_________________
Buy it used, buy it cheap and have fun!
Back to top
View user's profile Send private message
karter43



Joined: 04 May 2007
Posts: 265

PostPosted: Mon Jan 25, 2010 4:06 pm    Post subject: Reply with quote

I totaly agree that you need the small LF to be in the chassis adjustment set up range......

Here is what we need to do:

Time all laps, do 5 laps per session, toss the high and low, average the remaning three.

Set rear of kart as narrow as possible, adjust cross for best handeling (lowest lap time)

Set rear of kart as wide as possible, adjust cross for best handeling (lowest lap time)

We could also do this matrix with stagger, but that is not as easly adjusted. I also think that most Bullers will not be able to adjust cross enough to maxamize the two test conditions (but, it would be fun to try)

Go back to the original set up and retime (to baseline a graph of performance (that is eliminate changes in conditions))...

A radar gun would be nice, that way we could quantify handeling in, at the apex and off.......

I guess my bottom line is that Stagger, track and cross all add up to the same handeling. I've never been able to identify if one of thoes three matters more for turning in ,apex or exit.
Back to top
View user's profile Send private message
karter43



Joined: 04 May 2007
Posts: 265

PostPosted: Mon Jan 25, 2010 4:19 pm    Post subject: Reply with quote

Gee Don, I hope we're not givin all the secrets away .... I was going to start in about stagger and how to best use that Twisted Evil
Back to top
View user's profile Send private message
Don Kruse



Joined: 16 May 2007
Posts: 437
Location: Albuquerque

PostPosted: Mon Jan 25, 2010 4:44 pm    Post subject: Reply with quote

I'm seeing a trend for high cross (58-66) with lots of rear stagger (1.5"+) in the setups of some of the new chassis'. Not seeing this in the baseline from the manufactures but from the tuners looking for something; I don't know what but something. I think this might apply on small tight tracks where the tuner want to rotate around the RF quickly for small radius turns. I don't know.

I do know in Phoenix at the Classic once I found the tires that worked for me (Vegas) my RR was hot and the RF was cool. I dialed in more cross (1/2 turn on the screw jacker) and the RR temp dropped and the RF went to warm. The kart really handled much better with this change and neither tire was being overworked. I didn't make any further adjustments to cross but now feel I could have gone a little further.

DK
_________________
Buy it used, buy it cheap and have fun!
Back to top
View user's profile Send private message
karter43



Joined: 04 May 2007
Posts: 265

PostPosted: Mon Jan 25, 2010 4:59 pm    Post subject: Reply with quote

When I first started we used as low as 48% cross and 1/2 to 3/4 stagger.....

Last kart I worked on was 62% and over 1 on the stagger Very Happy

Put cross in it till it pushes! HHHHhhhhmmmmm I wonder if you could put enough to get it to lift the LF Question


Hey Don, I found the plate to press apart Yamaha cranks, you want it?
_________________
Stephen Spiak
Back to top
View user's profile Send private message
Don Kruse



Joined: 16 May 2007
Posts: 437
Location: Albuquerque

PostPosted: Mon Jan 25, 2010 7:00 pm    Post subject: Reply with quote

Sure that would be great. I'll call you tomarro.

DK
_________________
Buy it used, buy it cheap and have fun!
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    Albuquerque Speedway Karting Forum Index -> Tech Talk All times are GMT - 6 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group