What would 5lb pressure difference make in rollout….I haven’t raced my altered for about 3 years and thinking about increasing pressure by about 5lbs..should it slow down RTs or increase them and by approx how much….altered weighs around 1850 with ladder bar rear solid front and ET front runners…small block 383….launch rpm is 4600

based on your avatar photo, playing with front tire pressure won't do anything for your reaction times.

That’s an old photo..it now drives out and just Carrys the fronts and drops them down under full power

What’s your current front tire pressure and are you transbrake or footbrake launching?

Transbrake and 30 psi

Tire pressure changes on my roadster, which is 2000lbs with me in it and 51.5% on the rears, makes almost no difference unless I go so low I worry about them.

I was wondering about this also. I run a 28x4.5 front tire at 35#. I'm going to run some .5 pro tree no box index stuff. I'll need to slow down the leave, I've been running 1.07 in the box when leaving on the top bulb. I plan on lowering the launch RPM, but was also wondering how much tire pressure would change things.....

Thanks….over here in Australia we don’t get that many times in the year to try things out so it just helps to ask those who have a lot of tracks to get plenty of runs in a year..

Almost did not bother to replay because Mr. no it all 1290 love to tear up anyone who doesnt agree with him but.. what brand tire do you use . I have used Goodyear-very stiff wall tire almost no change however Hossier and M/T will but not at 30lbs. Have run those at 24-28 and you can fine tune R/T there but try starting line RPM first-works much better 200 RPM is about .01 on my 100 inch W.B. door car that runs 8.80s in 1/4

i have played with this some. i normally run around 35 to 40 psi in the front on any given day. i typically have 1080 to 1085 in the box for a long tree. when i 6.0 index race on a .4 tree i have to stiffen my rear shocks some and will go to 50 psi in the front, that combined will be worth about 010 to 015 in react. front tire pressure is probably only worth 4 or 5 thou maybe per 10# of pressure. at least that is what i see on my stuff.

ep

quote:

Originally posted by vetman:
Almost did not bother to replay because Mr. no it all 1290 love to tear up anyone who doesnt agree with him

You shouldn’t of and only ass holes like you that only reply to debate my over 3 decades of track proven advice, who think they know yet ain’t done shyt nor have shyt worth talking about.

Let’s us know when you have a car on par with either of these which are 2 of the best on the property where ever we compete and their driver one of the best in the country under 30. This is just the past 3 weeks…

This message has been edited. Last edited by: 1320racer,

Whitey234, are you trying to shorten your R/T, or slow it down? Raising pressure in the fronts should either make your lights quicker, or make no difference at all. Long list of variables involved, but the basic concept is that increasing the tire pressure will make the tire more round, (shorten the footprint / distance between the stage beam and back of the tire). Less FORWARD travel required to clear the beam. As Ed hinted in the first reply to your question, if your front tires clear the beam by traveling vertically, tire pressure will likely make no difference in R/T.

most alterds(center steer) I see bracket racing don't work well. That said, 30 psi is low. My suggestion would be lower the launch rpm to get a competitive reaction time window then raise the front tire pressure to dial it in.

To make RT slower, you'd need to lower the pressure. I agree with other posters that you might be looking at .010 difference between the low and high in the 'safe' range.

I'd be decreasing launch RPM first. Bringing your rear tire PSI down as far as you are comfortable would likely help more than anything you can do to the fronts.

Thanks for your replies..as it was midnight here with my last post I only just got back on..I’ll try the tire pressures at 30 and go with lowering startline…..last time I raced in Sydney was before the track was ripped up and relaid with new concrete….I was averaging 020 reaction time and that was getting me rounds but with the new surface I have noticed that people are regularly going in the 010 range

quote:

Originally posted by WHOMPWHOMP:

quote:

Originally posted by pauley:
i have played with this some. i normally run around 35 to 40 psi in the front on any given day. i typically have 1080 to 1085 in the box for a long tree. when i 6.0 index race on a .4 tree i have to stiffen my rear shocks some and will go to 50 psi in the front, that combined will be worth about 010 to 015 in react. front tire pressure is probably only worth 4 or 5 thou maybe per 10# of pressure. at least that is what i see on my stuff.
ep

BUT….you a bad man….

quote:

Originally posted by WHOMPWHOMP:

quote:

Originally posted by WHOMPWHOMP:

quote:

Originally posted by pauley:
i have played with this some. i normally run around 35 to 40 psi in the front on any given day. i typically have 1080 to 1085 in the box for a long tree. when i 6.0 index race on a .4 tree i have to stiffen my rear shocks some and will go to 50 psi in the front, that combined will be worth about 010 to 015 in react. front tire pressure is probably only worth 4 or 5 thou maybe per 10# of pressure. at least that is what i see on my stuff.
ep

BUT….you a bad man….

VERY Bad ….On Jegs Allstars Roster for US Nationals

Very impressive! Congrats on the Jegs All Stars!

Congrats EP.

I learned a lesson with changing front tire pressures the hard way. My son and I went to T&T on a Friday night and his RT's were good. Dad got a little concerned with the car hiking the front tires with the new Weld 2.0's and the Hoosiers deforming on landing. So, Saturday morning when he wasn't around, (we have a rule that I don't mess with the car on race day), I went from 32psi to 35 and kind of forgot about it. Well first time shot RED, second time shot RED, first round RED and now he is PO. We were talking at the trailer, and it dawned on me what I had done. He scowled at me and reset the pressure to 32 like we had always run and won the by back (I paid) and a few more rounds. Lessoned learned and the valve stem caps are Loctite now. LOL