Autocross Forums

PrevPrev Go to previous topic
NextNext Go to next topic
Last Post 06/22/2006 9:06 PM by  root
what psi to use, and what handling to expect with over-width tires
 2 Replies
Sort:
You are not authorized to post a reply.
Author Messages
root
New Member
New Member
Posts:


--
06/11/2006 8:11 PM

    I am getting 225/45/17 RT615 tires for the stock 17x6.5J wheels on the mazda3.  The tire size is a bit too wide for the rim, but I see many people using tires that are waay too wide for the rim at autocross events, so I assume the effects of this sort of mismatch are well understood.

    My questions are:

    what pressure should I run the tires at for autocross?  For the stock tires (205/50/17) I was watching rollover, and ran the lowest pressure that would not allow any (41 psi for eagle RSA).  Does the same rule of thumb apply to the wider tires?

    what pressure to run on the street ?  I am planning on using the same wheels and tires on the street since I am not ready to swap wheels all the time just yet.  lucky for me, our region has a "road tire" class, which means I have to use stock wheels.  Any recommendation for street pressure for safety and tire life are appreciated.

    Camber setup: with normal tire sizing my front camber goals would be max negative within factory allowance: -1°40' , how about with the oversize tires -- do I still want max camber?

    Are there any peculiar handling characteristics that I should expect?  the gut tells me the breakaway should be more sudden, is that correct?

    any help would be appreciated.

    Lynn
    Veteran Member
    Veteran Member
    Posts:1733


    --
    06/12/2006 10:22 PM
    Run the lowest pressure you can without rollover just like any other tires for autocross.  For street, you may need to run less pressure, because you are pinching the tire and that may cause the tread to bow a little.  Just  don't go too low.  I wouldn't go any lower than what the car maker says, and maybe not even that low.  Just be prepared to wear out the middle of the tread.  I'd run the most camber I could get. 

    Since the RT615 will have shorter and stiffer sidewalls than your previous tires, breakaway will be more abrupt, possibly much more abrupt.
    root
    New Member
    New Member
    Posts:


    --
    06/22/2006 9:06 PM

    update: ran 45psi hot in the front, worked out great, great slip angle curve, and the load sensitivity is much improved.

    The side with -0.9° camber wears perfectly to the wear mark, and the side with -0.7° wears 1/8" beyond... 

    About the pressures, is there any way to decide whether I need to raise it or lower based on the amount of deflection in the picture?

    rollover on falkens

    You are not authorized to post a reply.


    If you have any questions about Solo2.org please feel free to email us. [email protected]