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effect of tire width on steering effort

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bajavit View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bajavit Quote  Post ReplyReply Direct Link To This Post Topic: effect of tire width on steering effort
    Posted: 2012-Mar-14 at 4:19am
Last year we used tires having width of 7.5inch.In order to reduce the scrub radius we are planning to use 10 inch broad tires.I have less idea on its effect on steering effort.any suggestions?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-14 at 6:18am

There are other variables involved in scrub radius than just tire width.  Consider your wheel width, offset, and steering knuckle geometry.  If everything stays the same but you use a wider tire, the geometry and "calculated" scrub radius will be the same... you may have more rubber on the ground though, so steering efforts could increase. 

You can think through any other changes and figure out the effects in a similar manner.
Kyle Collins
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bajavit Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-14 at 12:43pm
thnx for reply...we have tried all the possible cases for reducing scrub radius nd the best we could come up was changing the tire width from 7.5 inch to 10 inch.And this time we are using a rack and pinion of ratio 6:1 hence steering will be a lot easier.Since we don't have any expression for calculating effect of tire width on steering effort nd its based on friction,plz tell whether it can be a concerning factor on steering effort or we can simply go through it?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-14 at 1:24pm
Your forearms woun't like 10" tires after a few hours. What is your scrub?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-14 at 1:32pm
Changing tire width without changing wheels will NOT change your scrub radius.  Have you changed wheels too? 

My team ran 9 or 10 inch wide 24 inch mudlites on the front 2 years with a Dan's rack and pinion... I'm no body builder, and didn't have a problem, so I wouldn't worry about it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-14 at 1:35pm
And what do you mean by a 6:1 ratio rack and pinion?  Racks aren't typically referred to by ratios like that...  

Do you mean 6 turns lock to lock?  Talking in those terms still isn't very clear, since rack length can vary.  Unless your rack is very very long that seems like a pretty slow steering car.  
Kyle Collins
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-14 at 1:44pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote OctoberSky Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-14 at 3:20pm
Most stock rack-n-pinions list ratios like that.  Still haven't figured out what the ratio is, but I can tell you that 12:1 is easier (more degrees turned per inch traveled) than 6:1.  Our 6:1 is maybe 270 degress lock to lock, and it takes a decent amount of muscle to use.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-14 at 6:58pm
In the steering industry racks are spec'd by mm/revolution
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Post Options Post Options   Thanks (0) Thanks(0)   Quote OctoberSky Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-15 at 2:04am
Well you would definitely know!  That helps a ton for future reference, although I guess chassisshop has decided to do whatever the hell they want.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akron 1998 to 2004 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-15 at 8:41am

So you're using bigger tires to reduce scrub radius. This plan will only work if you're also using wider rims. Why would you do this, people might ask? Because you can only buy a rim with so much back spacing. for the 7.5" wide tire you could use a 5" wide rim with 1Nx4B spacing or for the 10" wide tire use a 8" wide rim with a 1Nx7B spacing to reduce scrub radius by about 1.5"; which may very well completely eliminate your scrub radius. The width of the tires will only affect your steering effort if your rolling resistance goes up. I'm SWAGing steering effort for you.

7.5" tires with 1.5" scrub 6:1 rack = 4 lbs normal driving effort. about 50 lbs when you hit something on the track

10" tire with 0" scrub 6:1 rack = 0 lbs normal driving effort and 0 lbs when you hit something on the track.

So why wouldn't you go for zero scrub radius? Because a zero effort steering wheel feels like a limp d!ck in your hands.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-15 at 8:46am

Such an eloquent way of putting that...

LOL
Kyle Collins
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bajavit Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-15 at 10:03pm
I think i got it...see what we are actually doing is  increasing tire width so that we can increase kingpin inclinaton(which was not possible in earlier case in which increasing the inclination of kingpin was making the upright to go out of the rim..hence we may lose some points for design) which will make the scrub much lesser...along with wheels too..and talking about the rack and pinion,the pinion gear travels 3/4 of a turn from center to lock(270 degrees) or 1.5 turns from lock to lock and the rack travels 4.5 from lock to lock.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bajavit Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-15 at 10:07pm
ya...although 12:1 is much easier but in case of a bumpy ride we need more control over vehicle on turning which done by using 6:1...
abhi
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: 2012-Mar-16 at 7:17am
Originally posted by bajavit bajavit wrote:

see what we are actually doing is  increasing tire width so that we can increase kingpin inclinaton(which was not possible in earlier case in which increasing the inclination of kingpin was making the upright to go out of the rim..hence we may lose some points for design)


How did you figure that out?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akkino Quote  Post ReplyReply Direct Link To This Post Posted: 2013-May-09 at 12:46pm
What is the meaning of 12:1 (or 6:1) rack and pinion?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cujdubs Quote  Post ReplyReply Direct Link To This Post Posted: 2013-May-09 at 9:53pm
6:1 means fewer turns lock to lock than a 12:1...it also means more steering effort with the same setup. I am unsure how it is actually calculated but I have been trying to figure that out so I can make a rack with a ratio somewhere between the two

if anyone figures it out i would love to hear about it
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bajavit Quote  Post ReplyReply Direct Link To This Post Posted: 2013-May-11 at 12:33am
steering ratio={360/sin inverse (C factor/steering arm length)}
where C factor=rack travel in inches/pinion rotation.
and pinion rotation=total pinion rotation in degrees/360 degrees

considering the rack travel of 1.25 inch and pinion rotation=1
taking the length of steerin arm=2 inch
Steering Ratio = 360 / sin-1( C factor / steering arm length )  = 360/ sin-1(1.25/2) = 9.3:1 ~ 9:1
which is what u require....Smile
abhi
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akkino Quote  Post ReplyReply Direct Link To This Post Posted: 2013-May-11 at 2:09pm
I have seen this formula in RCVD by Milliken but I didn't get the concept.
Say, I have a rack travel of 5 inch with 1 lock to lock turn and a 4 inch long steering arm.
So to find the steering ratio I would need sin inverse of 5/4 which isn't possible.
So how do I calculate the steering ratio?

Also, is the rack and pinion ratio which you've mentioned same as the overall steering ratio of the vehicle?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cujdubs Quote  Post ReplyReply Direct Link To This Post Posted: 2013-May-11 at 7:46pm
I feel stupid now for not looking in RCVD sooner. and we have a copy right in the shop too....Akkino this would give the ratio for the entire steering system. 
I understood how steering arm length and rack ratio effected steering effort before but its nice to have a formula that goes along so I can improve some things and have numbers
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bajavit Quote  Post ReplyReply Direct Link To This Post Posted: 2013-May-12 at 12:31am
1 lock to lock turn? that's gotta be wrong..its more like a F1 car......it should be around 2 to 2.5 in our case...
abhi
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akkino Quote  Post ReplyReply Direct Link To This Post Posted: 2013-May-12 at 5:24am
Abhi, 1 lock to lock was just an example.
Even with 2 lock to lock turns, 5 inch rack travel and say a 2 inch long steering arm, the formula doesn't hold true.
You would then need to calculate sin inverse of 2.5/2
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ahmed Quote  Post ReplyReply Direct Link To This Post Posted: 2013-Jul-17 at 8:09pm
does anybody know what may be the tire and vehicle dynamic characteristics that should help in selecting the suitable tires and rims sizes?
Thank you in advance
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Post Options Post Options   Thanks (0) Thanks(0)   Quote zglazer Quote  Post ReplyReply Direct Link To This Post Posted: 2013-Jul-18 at 1:11am
That isn't an appropriate question to ask, nor is this the correct place for it. There are already at least a few threads on this forum that discuss tire and wheel selection. Take a look at those threads and do some research of your own about the different options available to you.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote bajavit Quote  Post ReplyReply Direct Link To This Post Posted: 2013-Jul-18 at 6:53am
ahmed,the size of the wheel you choose depends upon your wheel base,track and suspension and the rim width you select  depends upon how much scrub you are getting and therefore the mounting points of steering arm.Design the knuckle first and then you will get to know what type of tires suits you.
abhi
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