For those of you that run a roadster I am struggling with the right amount of tire pressure in a Goodyear 16 33 15 slick. The car leaves good with a 1.29 60 ft but will start drifting left at about 200 ft out. Then you have to start to drive the car to correct. I have started out at 6.5 now almost at 7 3/4 doesnt seem to make any difference. I have a friend that runs a slower et than mine and is at 9.5 he shifts on rpm Im shifting on time. car has a 115 inch wheel base with 4 link with wishbone and antiroll. any input would be appreciated. The usual advice is to keep going up on pressure until car wont hook. I have been a door car guy for years before I bought this ride. Previous owner sold it rolling so no info as our combinations were different

I run a roadster, it's 2200 with my fat butt in it. 52% of the weight on the rear. 115 inch wheelbase with 4 link with wishbone and antiroll. I run 14.5 32-15 Hoosiers. Which is not apples to apples. I run 5.45 Psi. My target is 5.50 high and 5.40 low. I slow the car down to run a 1.19 60 foot. If I ran 7 PSI, I would be skating all the way down the track, at 5.7 it gets "interesting".

Joe

Something is up other than tire pressure. I have ran 16.5x33x15s Hoosiers on my car before at 5.5lbs and zero problems. It was slower then only 1.33-1.35 60' times and 6.20s.

I switched to 14x32 Goodyears running 6.75lbs and 1.30 60'. Moved to 14x32 Hoosiers and end up running 1.25 60' and 5.80s at 7 3/4lbs pressure.

As I got quicker the car got more unpredictable as to where it might go. LOL I built a swing arm for it and now it's pretty deadly. I have Mickey's on it now running 6.0lbs and 1.20-1.22 60' depending where I am racing. 5.66 et 107" wheelbase, a-arm front, four link @2000lbs with me in it.

200' out and drifting I don't believe is tire pressure. Sounds like something my be in a bind, out of square or the front might be the problem. Have you videoed the car to make sure it's not crabbing? Also have you scaled the car to make sure you aren't really heavy on one side?

I'm 483 484
552 481
Corner weights

quote:

Originally posted by CURTIS REED:
Something is up other than tire pressure. I have ran 16.5x33x15s Hoosiers on my car before at 5.5lbs and zero problems. It was slower then only 1.33-1.35 60' times and 6.20s.

200' out and drifting I don't believe is tire pressure. Sounds like something my be in a bind, out of square or the front might be the problem. Have you videoed the car to make sure it's not crabbing? Also have you scaled the car to make sure you aren't really heavy on one side?

I don't run a roadster, but I agree with Curtis.

2BKING

Thanks guys for all the input and info. I will add this info It has a 4.10 gear glide with 1.76 and leaving off SLE at 3400.
I think I will try lowering the air pressure and see what happens.
The car is a round tube built by PK race cars in Ohio. It was scaled and all that checks out. I have vids of it from previous owner and its straight as an arrow with his combo.
Im going to be on a learning curve for sure from the door car. I will add this I won't forget to put my helmet visor down before I leave again I think I may be an inch taller now the way it stretch my neck anyone of you have that happen. Just had a thought before I close message. I have not checked the roll out I had a set of Goodyears 14 32 once that did same thing found out roll out was almost an inch between tires ran different air pressure in each tire and it corrected it. Take care

quote:

Originally posted by SR6223 Monza:
I will add this I won't forget to put my helmet visor down before I leave again I think I may be an inch taller now the way it stretch my neck anyone of you have that happen.

LOL, First time I ever drove a roadster at about half track I was looking through the bottom of my helmet. Helmet was to big (borrowed full face helmet) so air got inside and forced my head back..LOL

On the subject. Check to make sure you don't have any rear steer in the rear.

Dave

2150# Roadster with a 582. 4.29/1.80 Hoosier 16-33/15's @ 6.5-7 pounds on 15 inch rims. Four link, anti-roll, track bar, usually leave between 4400- 4500 with 37# ballast on the nose (to help reduce the wheel stands) and drop 8* out from 36* at the hit.

Essentially not a lot different than your car.

Check to see if it has any rear steer, a broken engine mount or mid mount, how much pre-load is in the four link?

Any decent local circle track racer can help you measure / identify any rear steer.

Bob

drop tires to 5.5 see what happens with a 1.29 sixty foot i assume it has a low power engine and tire pressure is more of a bandaid to a setup issue or suspension problem. what are the scale values.