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Ambrose Buldo
Joined: 06 Jul 2009
Posts: 263
Location: United States, New Jersey, Old Tappan
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 Posted: Fri Dec 28, 2012 12:01 pm Post subject: Scaling a Kart - How to get rid of cross wt and balance it |
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Had some time today, so I took the Intrepid Silvertone with KPV3 (Sprint Racing) out of the trailer today and put it on the scales for the first time. Was very unhappy with the way both Karts handled. This kart had way too much rear grip, could not get it loosen up, effect of setup changes were not what I expected.
I've never scaled a kart, so looking for some input on how to proceed now that I have numbers
With race toe, camber, caster, 15 PSI air all around, 1.75 Gallons gas, driver in race gear, front wheels straight, on level pad, Front spindles with equal # of shims, I got the folowing:
LF 82 RF 69 ttl frt 151 Frt 40%
LR 102 RR 124 ttl rear 224 Rear 60%
Total WT 375
Obvioulsy I got serious cross wt issue and I have too much rear bias ( I was told target is 43/57).
Should I lift/Tweak the LF a little to get rid of corner wt? Then if need wt in front should I move the seat forward about a CM? Not sure how I go about getting balance without adding weight as I am above class min (There is no ballest on kart).
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Ambrose Buldo - AKA Racer27
Old Tappan, NJ 07675
Current: Citation FC2000 (For Sale), Madza RX8, VW Eos
Kart for myself: Intrepid Silverstone Pro w/HPV3 --- With a ROK TAG engine waiting in wings
Kart for Daughter: 2001 Birel ARC-100
Last edited by Ambrose Buldo on Fri Dec 28, 2012 12:51 pm, edited 1 time in total |
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Benn Herr
Joined: 18 Jul 2001
Posts: 1580
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| Posted: Fri Dec 28, 2012 12:37 pm Post subject: |
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Ambrose,
With the kart on the scales, slip a thin piece of plastic or plywood under the right front wheel. Something like an old number panel will work. Stack them up until your front weight is equal side to side. It will help your rear weight also. The thickness of the shims needed will tell you about how far you have to adjust your front spindle height. You might need to take some off one side and add some to the other. You also may need to raise/lower one of the rear axle cassettes in its mount.
If the amount is too great handle with the adjustment, your frame may have a slight tweak in it. There are clip on YouTube of people "adjusting" frames.
As for too much rear weight, about the only thing you can do is sit up and mount the seat farther forward.
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Ambrose Buldo
Joined: 06 Jul 2009
Posts: 263
Location: United States, New Jersey, Old Tappan
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| Posted: Fri Dec 28, 2012 12:50 pm Post subject: |
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Thanks for the reply... So it is better to have unequal # of shims for spidle on each side or better for me to Tweak the frame?
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Ambrose Buldo - AKA Racer27
Old Tappan, NJ 07675
Current: Citation FC2000 (For Sale), Madza RX8, VW Eos
Kart for myself: Intrepid Silverstone Pro w/HPV3 --- With a ROK TAG engine waiting in wings
Kart for Daughter: 2001 Birel ARC-100 |
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Benn Herr
Joined: 18 Jul 2001
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Ambrose Buldo
Joined: 06 Jul 2009
Posts: 263
Location: United States, New Jersey, Old Tappan
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| Posted: Fri Dec 28, 2012 2:35 pm Post subject: |
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With the numbers I have you suggest tweaking frame first and fine tuning with the shims.
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Ambrose Buldo - AKA Racer27
Old Tappan, NJ 07675
Current: Citation FC2000 (For Sale), Madza RX8, VW Eos
Kart for myself: Intrepid Silverstone Pro w/HPV3 --- With a ROK TAG engine waiting in wings
Kart for Daughter: 2001 Birel ARC-100 |
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Benn Herr
Joined: 18 Jul 2001
Posts: 1580
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al nunley
Joined: 13 Nov 2006
Posts: 3038
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| Posted: Fri Dec 28, 2012 5:53 pm Post subject: Re: Scaling a Kart - How to get rid of cross wt and balance |
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| Ambrose Buldo wrote: | LF 82 RF 69 ttl frt 151 Frt 40%
LR 102 RR 124 ttl rear 224 Rear 60%
Total WT 375
Obvioulsy I got serious cross wt issue and I have too much rear bias ( I was told target is 43/57). |
I’ve heard that number before, but it’s not always correct. You need to set the weight balance for the engine class and the kart.
I stood and watched a friend move a seat forward on his kids kart and it worked good, better then before, but when they went to an engine class with a lot more HP, they had to move it back. No scales so I can’t tell you the difference in weight.
I was watching a driver once. On a practice day, and saw that the kart was pushing. I went over and was looking at the kart. There was a lot of lead on the back end. I suggest moving some of the lead to the front. I was told, very curtly, that the weight was correct, (as I remember, the same weight % as your’s, or close.) and the driver said, “what can I say, it’s an Emmick, they push.” I just walked away.
You know, changing the track width can change the handling a lot. Narrow the front, widen the rear, that can stop a push. Still, you’re right, the weights could be better.
Moving the seat is a good option. Maybe forward and to the right. Not much, go slow.
I think most karts are a little heavy on the right because of the engine being over there. I’m not sure the rear makes all that much difference in sprint race as far as balance is concerned because the inside wheel is off the ground in the turns. The front is a different story.
Sometimes they get bent. In that case, you put the heavy wheel on a gas can, have two people stand on the rear tires and a third person jump on the light front side. Use caution. Go slow. This is what I did and we had no scales, we just stood over the front end and lifted one tire, then the other, to see if they felt the same. The old mild steel Margays would bend real easy. The new chrome molly karts are much harder.
Good luch with the kart.
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If the data does not support the theory, get a new theory. (Al Nunley)
All else being equal; Compression is the Holy Grail.
45 years, in and around karting |
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gregg boyce
Joined: 27 Jul 2004
Posts: 1143
Location: United States, Tennessee, nashville
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| Posted: Fri Dec 28, 2012 5:54 pm Post subject: |
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I'd move the seat to get your ft/rr percentage first, THEN double check the alignment and see where you're at. Having the steering off by a tiny amount will throw off your weights.
BTW, with those numbers you should have been loose to the left and tight to the right.
GB
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George Young
Joined: 22 Aug 2003
Posts: 32
Location: United States, California, Salinas
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| Posted: Sat Dec 29, 2012 8:02 am Post subject: scaling kart |
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| Ambrose, Start out right when scaling. Are your scale pads perfectly level, and equal tire pressures do not equate to equal tire diameters. Level your scale to the penny, and measure the outside circumference of each tire and match the fronts by adjusting the pressure. same with the rears. Then follow some of the advice you're receiving. fyi, I don't use shims, a small tweak on the corner of the kart the good old fashioned way works fine. Stick a tire under the rear wheel on the same side of the chassis that is light (get the light spindle in the air), have your biggest friend sit on the rear tire without the wheel under it, and jump up and down on the front spindle carrier of the light corner of the chassis. Highly technical! |
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Chris Reinhardt
Joined: 29 Aug 2002
Posts: 2933
Location: United States, New York, Ossining
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| Posted: Sat Dec 29, 2012 8:20 am Post subject: |
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That chassis has adjustable rear height also? If the rear axle height isn't even on both sides, that will also through the cross weight off.
CR
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Ambrose Buldo
Joined: 06 Jul 2009
Posts: 263
Location: United States, New Jersey, Old Tappan
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| Posted: Sat Dec 29, 2012 11:24 am Post subject: |
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I went out there today to work on the kart and checked the tire circumfernace. The front circumferance was equal side to side @15 PSI, the RR was almost 2 CM smaller the left rear. In order to get the rears close the Left rear was set tp 8 PSI and the RR was set all the way up to 60 PSI. I put it back on the scales and the cross wt % did not change much (actually got slightly worse)
With tire pressures being in such an unnatural state made no sense to continue with scaling excersize.
Since it is snowing outside, and I have limited room in my unheated garage, I am going to dissasamble kart and move it in my heated basement. After disssambiling, cleaning and re-assableing, I will rescale with either new slicks or use brand new rain tires who's circumferance is more equal.
Thanks for your assistance.
Just from an education perspective, I tried Bens approach of putting tiles under the light front tire of Kart. I needed 2 tiles to gets front weight even. That is a little more about 1/4".
Let me get this thing cleaned, stripped and re-assambled before trying scaling again.
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Ambrose Buldo - AKA Racer27
Old Tappan, NJ 07675
Current: Citation FC2000 (For Sale), Madza RX8, VW Eos
Kart for myself: Intrepid Silverstone Pro w/HPV3 --- With a ROK TAG engine waiting in wings
Kart for Daughter: 2001 Birel ARC-100 |
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Benn Herr
Joined: 18 Jul 2001
Posts: 1580
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Dan Haynes
Joined: 17 Sep 2007
Posts: 2372
Location: United States, Pennsylvania, Ellwood City
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| Posted: Sat Dec 29, 2012 11:41 am Post subject: |
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I hope you realize that if you have to disassemble it to get it in the house...you will also have to disassemble it to get it back out 
Make sure your steering wheel is perfectly straight. That will make a huge difference.
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Blaise Haynes
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Mike Unger
Joined: 18 Jul 2001
Posts: 308
Location: United States, Ohio,
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Chris Parks
Joined: 09 Sep 2001
Posts: 1504
Location: Australia, not USA state,
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| Posted: Sat Dec 29, 2012 9:23 pm Post subject: |
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The best thing you can do is pack up the scales and go back to the track. Drive the kart then move the seat, it does not matter whether to the front or back, just move it and drive again, better or worse? Now you know what that change did you have the knowledge of which way to move the seat. BTW it should be level with the bottom of the chassis rails to start with as a height reference. Once you are happy with the turn in and exit you can play with height if needed. A quick way to do this is sit on something to raise the verticle CoG. If that is the wrong way you can try lowering it, karts as a rule don't need a lot of grip as it slows them down, they need to change direction quickly be be able to be steered with body weight, throttle and wheel and you can't do that with a grippy kart. We used to run the seat so low that it wore the bottom out of the seat and we kept repairing it from the top until it stopped hitting, at that point it was right.
After you get the thing handling then put it back on the scales, I bet that it will weigh totally different to all the advice you have been given. Every kart has its sweet spot and there is no one recipe, if there were it would be easy. After you get the seat right you then have another twelve months of trying to figure out the rest. Go back in this forum and read some of the stuff that used to be written and be prepared to actually do some study. Anything that John Learmonth was involved in is worth reading.
PS, just read your post and it is snowing! I guess you might have to wait a while or go on a long trip! We don't have that stuff here and I always forget you guys do.
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understeer happens on road courses and usually is pronounced with a British accent. Push happens on ovals and usually is pronounced through a wad of chew. Other than that, I don't think there's a difference - Jim Derrig
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