Tires, Rear Alignment info for Drag Racing - A limited compliation of info regarding suspension setup, drivetrain mods and some limited tire information for maximum traction in a straight line.

Post Date:    Tue, 27 Mar 2001
Subject:      Re: Drag Radials
List:         xr4-hardcore@yahoogroups.com




Chad wrote:

> last year i ran 245/50 15 kumho
> auto cross tires (they were free)

I don't believe any DOT approved autocross tire would be 
worth using in a drag race situation, compared to a tire 
designed with drag racing in mind.  I know my "racer" XR 
will melt BFG R1's in 2nd gear (coming out of a turn), and
traction was always a joke in a straight line in first 
gear.  The car is only putting out about 220hp, if that.  

I've always been amazed at how R-compound autocross tires 
don't hook up as much as you think they would.  I was 
concerned I'd be replacing my 5-year old Motorsport 
clutch as soon as I bolted on the R1's last year.  Well, I 
suspect they'll live through this season of the Kumhos too.

As I recall, this thread started with Tim asking about what 
else he could do to hook his car up.  Maybe it was someone 
else.  Anyway, I'll add my $0.00.

Get an LSD.  We've discovered how cheap it is to get a 
viscous LSD from a Sierra XR4x4 out of England.  I'm going 
to be installing mine this coming weekend if all goes well.  
You can see my write-up to date in the install progress at 
my "Archived Tech Articles" page.

Also, I don't think I've ever heard mention of it among the 
XR drag racing crowd, but do NOT forget about the importance 
of a rear alignment.  Rear camber especially, and toe 
somewhat, have a HUGE effect on straight line traction.  
Maybe this has been talked about and I just wasn't paying
attention.

My "racer" had a standard-lowered-XR rear negative camber of
about -2.75°.  In a straight line, with street tires I could 
bark 3rd gear on command and smoke them as hard as I wanted 
going into 2nd.  I reset my rear camber to about -0.75° and 
I could no longer get any tire noise out of 3rd gear and the
car prefered to hook up much faster going into 2nd.

Shim the rear suspension until you get the desired camber.  
There is another "Archived Tech Article" on rear suspension 
shimming as well.

I'd suspect that the really hardcore XR drag racers could 
benefit from even a tad bit of positive camber at the rear 
tires (I can't believe I just typed that)  When the XR is 
launching, accelerating, the rear suspension squats, 
increasing negative camber (I'm sure most of you know this, 
just covering this for clarity).  This reduces available 
traction.  If the tires are vertical, you'll get better 
traction.  This holds even more true on wider tires.  
Slightly positive camber would turn to zero camber or maybe 
less negative camber when traction counts the most.

Finally, I'm not a pro or even a regular drag racer.  There 
may be better info, but I think I'm barking up the right 
tree.