Front Wheels (to use with 8.50/8.80 (depending on brand) 15" and Rears 10" or 12" wide

[Jammer75]

I have been using 5.5" width 15' wheels (with an Apex 8.80-15). I will be upgrading my wheels and tires and wondering if I should go to a 7" wide wheel or stay with the 5.5"?

Same with the rear. I think I run a 10" wide now, will have to measure. I use 33" Blasters. 

Pro's/Con's?

 

[Fullthrottleguy]

I have been using 5.5" width 15' wheels (with an Apex 8.80-15). I will be upgrading my wheels and tires and wondering if I should go to a 7" wide wheel or stay with the 5.5"?

Same with the rear. I think I run a 10" wide now, will have to measure. I use 33" Blasters. 

Pro's/Con's?

Here is my take there are serious consequences in handling and steering when changing the scrub of the tires - 

There are great books on suspension theory - My favorite is by my Friend Herb Adams  "Chassis Engineering", its older and you can find excerpts online free - its still accurate and smart - but here is what I have learned building cars.

Offset is key  Most 5" and 5.5" wheels are Zero offset  so they basically place the scrub of the tire over the spindle in the way the car was designed for.  when you go wider you likely cannot use zero offset since the wider wheel (tire actually) will likely rub on full lock on the steering  so you end up pushing the wheel out  and this screws with geometry and can cause bump steer, erratic handling in turns and a host of other issues including changing the shock valving characteristics.  I have see great handling riding cars ruined just by changing wheel and tire combo.

Its also REALLY hard on the spindles and Rod ends (if your car has them and no uniballs)

  Like bigger tires  its like changing from a short wrench to a Leverage bar on the spindle and front end parts .  Big tires look cool but they are hard on parts  not to mention sprung weight. The farther you get away from centered wheels the more issues you impose on bearings and spindles -  hence the reason most people all of a sudden break a Combo spindle that worked for 10 years and no fatigue - they go from 8.50's to 12.50's and that big lever snaps the Combo spindle like a twig  and they go to 2" hollows and bad mouth combos ...

In the rear its not going to effect the handling to the same degree and sometime a wider stance is preferred, but its way harder on the bearings and the trailing arm bushings If you run Microstubs (unit bearings) it will wear they out faster  - assuming the new wheels have a farther out offset - which 99% of the time they will have to

Its not as hard on Midboard or outboards, but it's still a bigger lever out there.  The trailing arm inner pivots always seem to "wallow" out the holes  after you go bigger on the tires and wider on the wheels, for the same reason (but this also happens when the bolts come loose).  And like the fronts, it can affect the shock rate (valving) although to far less a degree - if the tire wheel combo is heavier the sprung weight changes and the you need to add more control (mostly rebound).

To be fair most sand cars (not all the name brands)  handle pretty bad and most people cannot tell until they drive something that handles really well (think FUNCO)  and most Funco owners don't mess with wheel and tire combos on their cars.   It seems every car I work on comes in with poor wheel alignment.. fixing thet is the first place to start.  If you change up wheel/tire combos without proper planning. you may make your car worse or its already pretty bad you don't notice,  or its looks bitchin' now and you live with it ...

FWIW

 

[lincster]

I run 15X6 with 2.25" backspace in the front with 35" Bajas mounted to them

I run 15X10 with 2.25" backspace in the rear, with 33" Blasters.

I like the 10" rear because I can leave my paddles on when I load my car into my Warrior.  I know there are other factors to fitting in trailer, but it works for me.

The 10" wide wheel gives the paddles more "balloon" affect and is not as hard on the drive train due to more spin.

I like the 6" wide front because it just "looks better" for me and you have a little easier access to the valve stem.

Here is a decent pix of my front.

My car is the black one.

 

[Bobalos]

There are great books on suspension theory - My favorite is by my Friend Herb Adams  "Chassis Engineering", its older and you can find excerpts online free - its still accurate and smart - but here is what I have learned building cars.

Does this book have much in it specifically about off road stuff & longer wheel travel or is it mostly focused on "suspensions"?

thanks

Bob

 

[Jtmoney714]

Here is my take there are serious consequences in handling and steering when changing the scrub of the tires - 

There are great books on suspension theory - My favorite is by my Friend Herb Adams  "Chassis Engineering", its older and you can find excerpts online free - its still accurate and smart - but here is what I have learned building cars.

Offset is key  Most 5" and 5.5" wheels are Zero offset  so they basically place the scrub of the tire over the spindle in the way the car was designed for.  when you go wider you likely cannot use zero offset since the wider wheel (tire actually) will likely rub on full lock on the steering  so you end up pushing the wheel out  and this screws with geometry and can cause bump steer, erratic handling in turns and a host of other issues including changing the shock valving characteristics.  I have see great handling riding cars ruined just by changing wheel and tire combo.

Its also REALLY hard on the spindles and Rod ends (if your car has them and no uniballs)

  Like bigger tires  its like changing from a short wrench to a Leverage bar on the spindle and front end parts .  Big tires look cool but they are hard on parts  not to mention sprung weight. The farther you get away from centered wheels the more issues you impose on bearings and spindles -  hence the reason most people all of a sudden break a Combo spindle that worked for 10 years and no fatigue - they go from 8.50's to 12.50's and that big lever snaps the Combo spindle like a twig  and they go to 2" hollows and bad mouth combos ...

In the rear its not going to effect the handling to the same degree and sometime a wider stance is preferred, but its way harder on the bearings and the trailing arm bushings If you run Microstubs (unit bearings) it will wear they out faster  - assuming the new wheels have a farther out offset - which 99% of the time they will have to

Its not as hard on Midboard or outboards, but it's still a bigger lever out there.  The trailing arm inner pivots always seem to "wallow" out the holes  after you go bigger on the tires and wider on the wheels, for the same reason (but this also happens when the bolts come loose).  And like the fronts, it can affect the shock rate (valving) although to far less a degree - if the tire wheel combo is heavier the sprung weight changes and the you need to add more control (mostly rebound).

To be fair most sand cars (not all the name brands)  handle pretty bad and most people cannot tell until they drive something that handles really well (think FUNCO)  and most Funco owners don't mess with wheel and tire combos on their cars.   It seems every car I work on comes in with poor wheel alignment.. fixing thet is the first place to start.  If you change up wheel/tire combos without proper planning. you may make your car worse or its already pretty bad you don't notice,  or its looks bitchin' now and you live with it ...

FWIW

Define scrub for us and how it would affect sand cars. 

 

[Fullthrottleguy]

Define scrub for us and how it would affect sand cars. 

I think of it like this  - caution some math involved  to do it right, but I'll leave that out ...

If you draw a line top to bottom through the upper and lower Rod ends or Uniballs (ball joints on regular cars) where they attach to the spindle and down to the ground  (vertical)

In a well designed front end it would touch the ground under the center of the tire where the tire touches the ground (center of the Contact Patch) like drawing line top to bottom through the center of the tire

Think of the tire turning on a single point like the point of a nail that what a centered scrub would be like  - when is not set like that the Tire "scrubs" the ground as it turns

If you move the tire out then the two points don'r match (same is if you move the tire in)  when you move the tire out  thats Positive scrub, if you move it in thats negative scrub

 If you have too much positive scrub the car will feel a bit more stable  going straight (like positive caster)  but when you turn its very hard on the steering rack and given we are in sand and, sand pushes against the tire, it will tend to push the tire to turn in or out harder (accelerated the turn) -  If you have PS you will just feel the car fighting a bit, if you let go of good grip on the wheel in a turn the car goes full lock really fast (aka roll over) but the steering rack mounting and tie rod mounting on the spindle takes a lot of pressure (the reason guys put big tires on the Spindle breaks the tie rod mount off  (J Alper posted those pics alot in past)

If you go negative the car will resist accelerating turning in or out, so high speed stable or if you get a flat the wheel won't turn as hard and you probably won't roll over.  So a little Negative is better than a little Positive, but too much negative makes steering slow and unresponsive (like a 1980's Mercedes if you ever drove one of those)

On road cars getting all that wrong makes the car handle like crap - sand is forgiving, but way easier to break stuff (spindles, rod ends, tie rod mounts on spindles, wheels, bearings, steering rack)  when its set up wrong and greater possibility of flipping the car 

Some cars you see never break stuff  - thats partially why ...

Hope this helps ...

 

[Bobalos]

like this?

 

[Fullthrottleguy]

Does this book have much in it specifically about off road stuff & longer wheel travel or is it mostly focused on "suspensions"?

thanks

Bob

Unfortunately not.. Robbie Gordon needs to write one  :classic_biggrin:

The best source I have for that is an article I saved from Larry Rosevear the original owner of Suspensions Unlimited - I should try to scan it - it's about 10 pages and has drawings  and great info

 

[Fullthrottleguy]

like this?

yes like that  - I probably should have googled a Pic and posted it  - I basically see that in my head when I think about scrub

Its really amazing how little changes can make such a big difference 

 

[Bobalos]

Unfortunately not.. Robbie Gordon needs to write one  :classic_biggrin:

The best source I have for that is an article I saved from Larry Rosevear the original owner of Suspensions Unlimited - I should try to scan it - it's about 10 pages and has drawings  and great info

I think he is kind of busy right now.  LOL

that would be great.  If I can help, let me know.  we have a copier @ work that does a pretty bang up job of scanning. 

yes like that  - I probably should have googled a Pic and posted it  - I basically see that in my head when I think about scrub

Its really amazing how little changes can make such a big difference 

agreed.  When I read your description, I read into it that Where the Tie Rod connects to the spindle in relationship to the CL of the wheel also has an affect on it, but in my mind that does not Jive.  a picture of that relationship would be uber helpful.....

 

[Mike E]

like this?

This is the perfect picture for the question the OP posted because in this diagram the only thing that has changed is the offset of the wheel. The left is a positive offset and the right is a negative offset. You can also adapt the lines to see what happens with Larger diameter tires. 

Each manufacture builds them differently, so you really need to check your angles and measurements. 

 

[Fullthrottleguy]

I think he is kind of busy right now.  LOL

that would be great.  If I can help, let me know.  we have a copier @ work that does a pretty bang up job of scanning. 

agreed.  When I read your description, I read into it that Where the Tie Rod connects to the spindle in relationship to the CL of the wheel also has an affect on it, but in my mind that does not Jive.  a picture of that relationship would be uber helpful.....

All I was alluding to is that where the spindle connects to the tie rod is generally strong enough..  but often fails when excessive  strain is applied by the lever action of a bigger tire and outbound wheel offset

 

[Jammer75]

Thanks!

I think I’ll just stick with what’s been working for 14 years. 
 

(if it ain’t broke don't fix it)