R30 tight in hot weather

[pedro]

We have an R30 running Yam Sr. Can (335 lbs) on Bridgstone YHC tires at NCMP. When we run in the heat of the summer we always have a problem getting tight in the slower corners that exceed a 90 deg turn. The chassis starts out ok, but gets tight about halfway through the race. We are running around 14 psi cold pressure on used tires, so I don't think the tire pressures are too high. We run short hubs on the rear and the softest Freeline 40 mm axle. We run one seat strut per side. On the front we run 2 mm toe out and 1/2 deg negative camber. We run caster approx 1 deg less than standard.
Do you have any suggestions to help our situation.

[Marc Miller]

You can try to take the camber out (we rarely run negative camber) as well as using the pill you are currently using for camber and try taking more caster out.

Even in yamaha - we have run as low as 10-12 lbs in tire pressures. The toe might be fine but is the 2mm out while you are in the kart on the ground or set on the stand?

Tim & Chris might not be in this morning, but I will make sure they see this so they can expand on these details.

[Garry Lobaugh]

In my view the pressures are a little high. The race tech group will attempt to give you further suggestions.

What I determined over the weekend is as follows: Some racers get so involved mentally in the race mode that they over drive the corners and in fact build in a tightening affect on the kart. The harder you race (over drive the corner) the more the driver is going to contribute to a tightening condition. Others may disagree, but until we watch you drive, it is difficult to stipulate what is the cause of the tightening.

I'm sure the techs will have additional helpful ideas. Thanks for asking the question.

[Chris Lobaugh]

You will need to check your tire pressures hot after a 7-10 lap run. Not to beat a dead horse but I feel that your tire pressures are too high for the summer months. 13.5 to 14psi should be your hot tire pressure when the ambient temperature is over 75 degrees. There is also a point at which the rear of the kart can be too soft and this is further compounded when you "deaden" the front of the kart by removing caster and adding negative camber. If the kart has an exit push more than likely you have the rear of the kart too soft and not enough grip in the front to keep the inside rear tire off the ground. Are you running the middle bearing on the axle tight or loose?

[pedro]

We run the middle bearing out. The 2mm toe out is on the stand. And it is 1 mm per side, set using sniper gages.
We run negative -1/2 to -1 on camber, the driver has always preferred some negative camber.
Also, we run air in our tires. Are you running nitrogen?

[Marc Miller]

Pedro-

Is your set-up really wide and really soft? We assume you might have a 40mm "B" axle.

2mm on stand is perfect, though we suggest you steer clear of negative camber unless the rear of your is sliding - and considering you have removed the caster too, it is defeating the purpose.

Air pressure - we all here still think you are running too high for pressures, especially considering you are running air. It is typical the folks that run Newcastle run higher pressures and if there is rubber on the track, the kart gets tight very fast. Try starting 10-11 - even as low as 8-9.

[pedro]

Marc,
We run run the rear aroung 53.75 in with the softest "B" axle and short hubs in the rear. We have had to run lock collars to prevent the hubs from slipping, thus we are not as soft as the axle would normally be. The front has been run anywhere from 3 large spacers down to 1 large spacer this past weekend. There seems to be pretty good agreement among the experts that our tires pressures are too high. But, as you mentioned in your response, sometimes you need a lot of pressure to run fast at NCMP (especially in the spring).
What are you suggesting on camber, zero degrees or some positive?
Thanks for your help.
Pedro

[Chris Lobaugh]

Pedro,
I would put the caster back to 0 (central pills) and run 2mm positive camber on the stand. Keep your toe at 2mm out like you have been. If you are using the sniper gauge 1 dot equals 1mm and 1 box equals 2mm. Hope this helps.