Page 1 of 2 12 LastLast
Results 1 to 30 of 39

Thread: Larger tire and caster

  1. #1
    Join Date
    Aug 2018
    Posts
    34

    Larger tire and caster

    Insight welcomed.
    We run a class with Carlisle 13x6.5-6 being largest tire.
    The diameter of tire is significantly longer than that of typical slicks. Assume I'm running + caster in front.
    Dynamically the caster would effect camber change and load transfer on or off corner More dramatically than a smaller diameter tire; would it not? I'm not so much looking for suggested settings rather affirmation "or not" of my thinking. What say you?

  2. #2
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    No, from one tire to the other, you'll have to reset the front end settings.
    Both will change with different height tires, in fact it will change all of your chassis settings except for maybe toe.
    Your changing the rake of the chassis.
    But degrees are degrees doesn't matter the tire that's on it.

  3. #3
    Join Date
    Aug 2018
    Posts
    34
    Rate of rake.... maybe a better way to phrase it? I realize i needn't mention camber though i would change it respectively with caster change.

  4. #4
    Join Date
    Oct 2013
    Location
    iowa
    Posts
    6,205
    I'm reading this a little different .
    I believe your asking will the turf tire being taller then a standard slick, will that affect scrub radius.

  5. #5
    Join Date
    Aug 2018
    Posts
    34
    Yes.... seems like it would unload or load corner at different rate than smaller diameter tire with same degree setting.
    ??

  6. #6
    Join Date
    Aug 2018
    Posts
    34
    I suppose I associated scrub radius more with wheel offset and or spindle/hub spacing....I'm really glad you mentioned it in that way!

  7. #7
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    What your talking about is progressive camber gain, diameter discribes the height of a tire not the width, and only a width change to the contact patch and or the kingpin inclination changes scrub radius.
    And the answer is still no, a tire diameter change doesn't change progressive camber gains

  8. #8
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    Quote Originally Posted by Nesloney View Post
    Yes.... seems like it would unload or load corner at different rate than smaller diameter tire with same degree setting.
    ??
    If you don't reset cross, camber, caster, LS% and nose that tire will cause less weight transfer

  9. #9
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    Quote Originally Posted by Nesloney View Post
    Yes.... seems like it would unload or load corner at different rate than smaller diameter tire with same degree setting.
    ??
    The rate would be the same, you can't change that without changing camber, caster or KPI..
    Camber and KPI adjustment change the scrub radius

  10. #10
    Join Date
    Aug 2018
    Posts
    34
    With a taller tire "diameter". The point at the end of the caster line in front of the kart would be further away from the Front/rear center of the chassis. When turning the steering wheel I don't understand how it could be the same rate of load change as with a smaller diameter tire with the same caster setting. Regardless of any other setting....I'm not talking about camber change...I mentioned it in my first post and was quickly set straight on that. I'm here to learn, but I'm hung up on this one.
    Last edited by Nesloney; 12-06-2018 at 12:02 AM. Reason: Changed from acronym F/R to front/rear

  11. #11
    Join Date
    Oct 2013
    Location
    iowa
    Posts
    6,205
    The chassis is designed for 10" diameter tires putting a 13" tire surely would change the scrub radius.

  12. #12
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    Quote Originally Posted by Nesloney View Post
    With a taller tire "diameter". The point at the end of the caster line in front of the kart would be further away from the Front/rear center of the chassis. When turning the steering wheel I don't understand how it could be the same rate of load change as with a smaller diameter tire with the same caster setting. Regardless of any other setting....I'm not talking about camber change...I mentioned it in my first post and was quickly set straight on that. I'm here to learn, but I'm hung up on this one.
    Caster angle changes when you put the taller tire on to more positive, if you reset it, it will be the same caster.
    It wont load any differently because you still will have X Amount of caster

  13. #13
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    Quote Originally Posted by flattop1 View Post
    The chassis is designed for 10" diameter tires putting a 13" tire surely would change the scrub radius.
    Only a wider tire, not a taller one, it will change with just that swap, if he doesn't reset.

    He said change, reset

  14. #14
    Join Date
    May 2015
    Location
    north central nebraska
    Posts
    1,300
    By definition, unless KPI is zero, scrub radius will change with a taller tire.

  15. #15
    Join Date
    Aug 2018
    Posts
    34
    I'm leaning towards what flattop and Shaw are saying.
    Scrub radius would be different with taller tires.
    My plan is to try a little less +caster than what I see recommended from chassis manufacturer, or others on same chassis running 11 inch tires.
    Trial and error is all I have.....well not all....I have a string, 4 bathroom scales, an uneven shop floor, and a stopwatch!

  16. #16
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    Quote Originally Posted by 95 shaw View Post
    By definition, unless KPI is zero, scrub radius will change with a taller tire.
    How when the contact patch doesn't change.
    Scrub radius is a line through the kingpin bolt to the ground and the center of the contact patch.

  17. #17
    Join Date
    Oct 2013
    Location
    Jacksonville Beach, Fl
    Posts
    341
    I believe their point is with a larger front tire, the contact patch says in the same location. The higher chassis height causes the kingpin point where it intersects the ground to move further outward and that would decrease the scrub radius.

    Bottom line is the contact patch stays the same but the kingpin inclination intersect point at the ground changes.

  18. #18
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    Quote Originally Posted by 01ron View Post
    I believe their point is with a larger front tire, the contact patch says in the same location. The higher chassis height causes the kingpin point where it intersects the ground to move further outward and that would decrease the scrub radius.

    Bottom line is the contact patch stays the same but the kingpin inclination intersect point at the ground changes.
    That's only if he don't reset camber.
    He said putting the taller tire on was all he wanted to do to his current setup.
    Putting the taller tire on changes camber, caster, cross, LS% and nose weight.
    If he resets all those adjustments back to what they were before, scrub radius will be the same.

  19. #19
    Join Date
    Oct 2013
    Location
    SW Va. Where Tenn,Ky and Va meet
    Posts
    3,855
    I think I have an idea of the problem he's trying to fix, and a taller tire isn't the solution.

  20. #20
    Join Date
    Oct 2013
    Location
    Marysville, Pa
    Posts
    6,285
    So if I'm reading this right IF all he does is put on the taller tires and makes NO other changes it will change everything Including scrub radius ?
    However IF he puts on taller tires and RE-SETS all other adjustments back to same numbers before the taller tire change then scrub radius stays the same ?

  21. #21
    Join Date
    Oct 2013
    Location
    Jacksonville Beach, Fl
    Posts
    341
    I'm wondering if this is even on a regular kart. 13" wheels? Does it have springs and shocks also like some yard karts? That would throw all kinds of other issues into the equation.

  22. #22
    Join Date
    May 2015
    Location
    north central nebraska
    Posts
    1,300
    With a heim frontend, changing camber does not change the tires relationship to the kingpin, unless the center of tires contact patch moves.

    Simply putting a taller tire on and resetting the front end settings, the scrub radius changes. Certainly not a large amount, depending on the situation.

  23. #23
    Join Date
    Oct 2013
    Location
    Jacksonville Beach, Fl
    Posts
    341
    And I can see the issue with raising the front of the kart. It changes the caster as you raise the front of the kart which changes the camber setting (but not sure if it's really a large change). This will also probably change the kingpin intersect point with the ground.

  24. #24
    Join Date
    Oct 2013
    Location
    Jacksonville Beach, Fl
    Posts
    341
    After thinking about this further, I now can envision that changing the rear ride height would also affect the adjustments we are talking about WITHOUT changing the front tire sizes. Maybe not enough to matter but definitely affects caster/camber somewhat.

  25. #25
    Join Date
    Aug 2018
    Posts
    34
    OK.... I'm already running 13"tires all the way around..... I'm not making a tire change to try to fix anything. How can i rephrase this? Our class runs these tires. When I research other people's caster setting recommendations online per say, they are almost always folks who run 11" tires. I don't run 11" tires. At All. My thinking suggests that my caster settings "amongst other settings" won't directly relate to 98% of the people on this forum because we as a "class" have larger diameter tires all the way around the kart.
    There are all sorts of quirky things caused by this tire rule.... in this case I'm just talking caster.
    My thinking is I should run less +caster than what many recommend on here because the intersection point is further forward causing a more rapid load change under steering thanks to the scrub radius difference. Obviously I'm new to karting so my vocabulary of terminology isn't helping this discussion much. I am very thankful for the feedback whether it's philosophy or physics.

  26. #26
    Join Date
    Aug 2018
    Posts
    34
    Quote Originally Posted by 01ron View Post
    I'm wondering if this is even on a regular kart. 13" wheels? Does it have springs and shocks also like some yard karts? That would throw all kinds of other issues into the equation.
    12 Phantom Triton

  27. #27
    Join Date
    Aug 2018
    Posts
    34
    Quote Originally Posted by XXX#40 View Post
    That's only if he don't reset camber.
    He said putting the taller tire on was all he wanted to do to his current setup.
    Putting the taller tire on changes camber, caster, cross, LS% and nose weight.
    If he resets all those adjustments back to what they were before, scrub radius will be the same.
    Not what i said
    Thanks

  28. #28
    Join Date
    Oct 2013
    Location
    Jacksonville Beach, Fl
    Posts
    341
    If you have to run 13" tires, I would recommend you just try more caster and/or less caster and see what works best on your stopwatch. Also widen track and narrow track. When you get the best times on the track, then try to analyze why. I doubt Phantom designed that chassis with the idea that 13" tires would be run on it ever.

  29. #29
    Join Date
    Aug 2018
    Posts
    34
    Quote Originally Posted by 01ron View Post
    I would recommend you just try more caster and/or less caster and see what works best on your stopwatch. Also widen track and narrow track. When you get the best times on the track, then try to analyze why.
    Of course I'm going to do that.
    That's what we do!
    Can't run hot laps Thursday on the internet.... but we can talk about it

  30. #30
    Join Date
    Aug 2018
    Posts
    34
    Quote Originally Posted by 01ron View Post
    I doubt Phantom designed that chassis with the idea that 13" tires would be run on it ever.
    Exactly!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •