What Exactly Does the 4th Rail Do?

Chris M Johnson · Joined: 14 Oct 2005 Posts: 568

I have heard that it adds front grip, but I dont necessarily believe this.

I suspect that it makes the chassis more resistant to twisting/jacking and would actually increase rear grip. This is what i suspect from trying it.

Anyone with experience using the 4th rail?

I have an intrepid explorer with a CR-125. 200lb 6'1" driver.

Rick Blood · Posted: Thu Aug 09, 2007 10:23 pm Post subject:

It balances the chassis so that the flex is equal in either direction. It should not be removed except in extreme conditions.

Now comes the flood of contadiction claiming everything from changing scrub radius to increasing horsepower. Shocked

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Brent Harper · Posted: Fri Aug 10, 2007 6:16 am Post subject:

Are you refering to the side or rear rail... I ask this because I have heard people calling both of these a 4th rail..
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John M. Skowron · Joined: 18 Jul 2002 Posts: 444

The 4th rail actually is the second left side rail. Since the right side of the kart has two rails for the motor, some karts have a second rail on the left side to balance it out. Usually only on chassis design for high horsepower applications like shifter and tag. It changes how much the chassis twists.
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Brent Harper · Posted: Fri Aug 10, 2007 10:37 am Post subject:

I questioned which rail because when I tell guys I am running without the 4th rail a lot seem to think I mean the rear bar. We have actually been testing quite a bit and the 4th rail gives my whole chassis more bite in the slower corners but seems to make it a little skatey in very fast sweepers/banked corners. Chassis is less compliant with it in..
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Bernie Adamson · Joined: 20 Jun 2003 Posts: 3001

Brent,
you need to add in what configuration....

Road Racing or Sprint...and which Chassis
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Chris Wehrheim · Posted: Fri Aug 10, 2007 11:19 am Post subject:

No its just that your wrong Rick. Drivers have different feelings with the bar in and out. This is my opinion. With the 4th rail in you will get more front bite on entry and more rear grip on exit. With it out you will have less front grip on entry and less rear grip on exit.

Rick Blood · Posted: Fri Aug 10, 2007 12:01 pm Post subject:

OK Chris, what did I say that was wrong? It doesn't balances the chassis so that the flex is equal in either direction?
and
Why would you need less front grip on entry and less rear grip on exit? An extreme condition?

That's the wonder of karting. Mention chassis tuning and everbody see's things in a different way and everybody is right. And people ask why there isn't a chassis setup book. Confused

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Chris Wehrheim · Posted: Fri Aug 10, 2007 12:44 pm Post subject:

The it should not be removed except in extreme conditions.

Marshal Vortriede · Posted: Mon Aug 13, 2007 4:30 pm Post subject:

Rick Blood · Posted: Mon Aug 13, 2007 7:12 pm Post subject:

Chris, I only got that from Bill Talley and lord knows he doesn't know what he's doing.
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Shawn Campbell · Posted: Thu Aug 16, 2007 6:34 pm Post subject:

Its a stiffener like other bars. It probably depends on a number of factors like track conditions, weight, engine choice, tires, ect. Test it with it in and test it with it out. That is the best answer.
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