Tyre pressures?????

68northantsdart · Post by **68northantsdart** » Fri May 09, 14 9:21 pm

Any one hive me any tips on what pressures I should be looking to run in my slicks? I have a pair of 28/11.5/15 and some 28/13.5/15 both mts. I know they will differ on track, temp ect but just after some good starting points??

Les Szabo · Post by **Les Szabo** » Fri May 09, 14 9:59 pm

Depends on your chassis set up/weight and how hard you hit the tyres...but start at say 10psi for a 28" tall tyre and see where you are, you only want to see a slight wrinkle in the sidewall on the hit without wrapping them up too much, that'll get you out of the whole for best 60fts/ET.

Les

Pete · Post by **Pete** » Fri May 09, 14 10:23 pm

I think different makes react differently to pressure.
However, as Les says - start at 10 PSI and work downwards

68northantsdart · Post by **68northantsdart** » Fri May 09, 14 10:43 pm

Could explain poor 60ft times then ??!! We were running 5 or 6 and the tyres were really screwing up. Cars running ss rear springs, trans brake, 727,383 bb, not sure on weight but will look into it this week

Pete · Post by **Pete** » Fri May 09, 14 10:48 pm

You need to "read" the tyres and ensure that you are getting full width contact across the tyres on a run.

I tend to reduce the pressure progressively until the groove is the widest possible whilst still remaining stable(ish) at the top end.............

Dave-R · Post by **Dave-R** » Sat May 10, 14 12:37 am

If it is a heavy car I think you will probably find 10psi ideal.

My heavy Challenger would feel "light" at speed with 8psi without going any faster than it did at 10psi where it drove much more stable.

Les Szabo · Post by **Les Szabo** » Sat May 10, 14 10:12 am

68northantsdart wrote:Could explain poor 60ft times then ??!! We were running 5 or 6 and the tyres were really screwing up. Cars running ss rear springs, trans brake, 727,383 bb, not sure on weight but will look into it this week

This is the Big Bopper Dart......12.2 at 120mph.......think you got more of an issue there than just low tyre pressures.

Les

Pete · Post by **Pete** » Sat May 10, 14 10:28 am

Good point. What is the tyre height and rear gear ratio? Sounds like highway gears....

68northantsdart · Post by **68northantsdart** » Sun May 11, 14 2:00 pm

Tyre height is 28 inch?? As for gears I need to try and work them out

68northantsdart · Post by **68northantsdart** » Sun May 11, 14 2:47 pm

Any helps appreciated les as I'm new to this so feel free??

Pete · Post by **Pete** » Sun May 11, 14 2:49 pm

Need to know the rear gear to work out the art of the possible.
Also get the car weighed....with and without driver!
Corner weights will tell a lot - suspension load and bind, etc.

mopar_mark · Post by **mopar_mark** » Sun May 11, 14 6:08 pm

68northantsdart wrote:Tyre height is 28 inch?? As for gears I need to try and work them out

Jack the car off the ground, support axle on axle stands.

Mark the prop shaft & mark the tyre/rim. Then rotate the wheel for one full rotation & at the same time count the number of revolutions of the prop shaft.

Then divide one by the other, this will be close enough to give you your rear end ratio. Plus, there is only a certain range of rear end gearing available & unlikely it would of been fitted with custom gears/pinion.

68northantsdart · Post by **68northantsdart** » Sun May 11, 14 11:00 pm

Cheers mark I'll do that tommo

Kev · Post by **Kev** » Mon May 12, 14 10:05 am

mopar_mark wrote:
68northantsdart wrote:Tyre height is 28 inch?? As for gears I need to try and work them out
Jack the car off the ground, support axle on axle stands.

Mark the prop shaft & mark the tyre/rim. Then rotate the wheel for one full rotation & at the same time count the number of revolutions of the prop shaft.

Then divide one by the other, this will be close enough to give you your rear end ratio. Plus, there is only a certain range of rear end gearing available & unlikely it would of been fitted with custom gears/pinion.

WARNING! Not applicable for you "Peg Leg" blokes!

Les Szabo · Post by **Les Szabo** » Tue May 13, 14 1:11 pm

What did you end up with...3.55?...what gear are you going through the finish at and at what rpm?

Les