progressive vs 1200 spring

[ambonci21]

currently running a 1200 pound pull bar spring with 1/2" preload as per chassis builder. Only getting 1 1/4" travel at the absolute most I check it after every heat and feature. Car is pretty fast but always trying to improve it. I have read some information on this site about the progressive spring and I'm getting mixed reviews. usually run on a track with short straightaway's. the next two races are on tracks with longer straights. chassis builder told us since we are on IMCA tires we should take the 1200 out and put the progressive in. real nervous to do that because we have been a top 3 car all year long. would like to hear from you guys on here.Thanks

[Fox_hunter42]

it will soften the bite when back on the gas. put a little preload into it and you should be ok.

[MM90]

That's what I noticed the most when I went from a straight spring rate to progressive. On a hooked up track where you might be off throttle and then wide open you will notice it hooks up slower, I call it lazy. Like mentioned above, adjust preload to help that.

[ambonci21]

What is a good starting point 3/8-1/2? So that may not benefit us at all off the corner without playing with preload. I think we will try it tomorrow and see what happens. Still need an idea on where to start with preload. What kind of travel is normal for a pull bar or does it matter on spring rate? Thanks guys

[oldtrackchamp4x]

I run a 1200-2000 with 3/8 preload and get about the same travel as you're getting.JMO.

[ambonci21]

track champ, what are you trying to tell me lol you will to dumb it down for me please. Thanks

[JustAddDirt]

Start with 5/8 preload. That will get you close, adjust from there to get back to your travel you want
But I didn't see were you mentioned the start and end rate of the progressive spring you intend to run

[oldtrackchamp4x]

Sorry for the half a s s e d response. Just saying i don't get any more travel with a progressive spring than you do with a 1200 lb spring. I've ran a 1050 spring with 5/8 in preload and a biscuit bar with a 1/2 in preload , and they all get about the same travel, with hardly any difference in forward drive between all three. I don't go by how much travel i get any more, i go by how much drive the car gets. I also run the IMCA G60 tires, and with them tire prep is VERY important. Back to you changing your pullbar spring. If you are that competitive i would really think hard about changing your pullbar and look at other small changes in your car setup or your driving. As always, this is JMO.

[dereksehi]

Trackchamp what do you usually do for tire prep if you don't mind me asking?

[JustAddDirt]

Pull bars are not magic, like I have stated before on posts about them. I have broken one on around lap 82 of a 100 lap race leading, finished and won, with no difference in the car's traction. even on restarts, the car still had the same amount of traction it did with the pull bar hooked up. I just had to keep pinion up so it would not be slamming around in car with just the 90/10 shock holding it in.

[oldtrackchamp4x]

On new tires i first wipe off the mold release with lacquer thinner then i sand off the nubs with a 40 grit sanding disc. I then sipe straight across rear tires and from 8 oclock to 2 oclock looking from the back of the tire on the RF. I sipe 1/2 the tread depth with an 8 blade siper. I do this the day of the race, if not, be sure you wrap them in plastic wrap so the oils in the tire don't dissipate. After the race i pressure wash and sand the right side tires from inside to outside to remove any feathering and do the left side the opposite. Once again do the day of the race or if earlier be sure to wrap. JMO

[ambonci21]

Thank you all. we ran last weekend and stuck with the 1200 and the car was a rocket ship had a fast car. I agree with others I think we will stick with the 1200 and put the progressive in the backup car. Very interesting tire prep trackchamp. I usually pressure wash the feature tires then grind them and let them sit inside, I usually do the feature tires on Tuesday and heats on Friday and race Friday. do you wrap right after grinding every week? another question, whats better for the rubber grind or sand? Thanks very good info here.

[oldtrackchamp4x]

Do either one, but use a 40 grit disc with a firm backing plate. I use a variable speed grinder set at 1000-1200 rpm. You don't want to remove a lot of rubber, just open up the surface of the tire and remove feathering. After sanding/ grinding i blow off the loose rubber and immediately wrap tightly with wide plastic wrap and stack them up on top of each other out of the sun. Put on new tires after you get down to the bottom of the sipes or sooner if you have a big tire budget. JMO