Track Tac

Circumference vs wheel width?

N

Nickp

Member
Aproximately how much bigger is the Circumference if you were to mount the tire, measure, and then re-mount the same tire but on a 1/2" narrower wheel?
 
Rough guess.....like mentioned lots of variables. I'd say 1/8"-1/4" (+/-) bigger in circumference......I know some that have 8.5 & 8.25 LR wheels to play with stagger without swelling or shrinking tires.

Again.....big pile of variables at play here.
 
jaymancds said:
Lot of variables at play here.
Click to expand...
I understand that. Just looking for an "approximate" value. I figured it wouldn't be much.

Slick27 said:
Rough guess.....like mentioned lots of variables. I'd say 1/8"-1/4" (+/-) bigger in circumference......I know some that have 8.5 & 8.25 LR wheels to play with stagger without swelling or shrinking tires.

Again.....big pile of variables at play here.
Click to expand...
Thank you Sir. That's what I was looking for.
 
Depends on tire brand as well.
Some mount up bigger than others on narrower wheels.
We've been mounting sets of Burris 33s and Hoosier D30As on 9 1/2" wide wheels (simply out of necessity - ie lack of 10" wheels) and they have been rolling out 34 1/4." After cutting and a little shrinking, they're right back at 34" where we want them.


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
32 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Nick also remember if you start swapping wheel widths to keep an eye on your rear tread width measurement.

Very easy to try and gain stagger but not move the wheel to where you want it. Simple mistake trying to find a gain can send you in the wrong direction. Just a heads up.

We are a 2 man team so I try to eliminate all the things I could overlook while we wrenching.
 
Nickp said:
Thanks for all the help everybody!
Click to expand...
I made drawing in my CAD/CAM program.

8 inch tire on an 8 inch rim, sidewall straight up and down. 8 inch tire on a 8 1/2 rim, the sidewalls are at an angle. The difference in overall height is .011". That's the radius, the diameter would be twice that. If I mount that same tire on a 9 inch round, the height of the sidewall is now .050" less in height, versus straight up and down

Real world numbers might be different, but that's how it plays out in my CAD/CAM program.
 
So I did a drawing just to prove it to myself.
 

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CarlsonMotorsports said:
Depends on tire brand as well.
Some mount up bigger than others on narrower wheels.
We've been mounting sets of Burris 33s and Hoosier D30As on 9 1/2" wide wheels (simply out of necessity - ie lack of 10" wheels) and they have been rolling out 34 1/4." After cutting and a little shrinking, they're right back at 34" where we want them.


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
32 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Click to expand...
Brian does that change the spring rate of the tire much with a narrower wheel? Like mounting a tire on a 9 3/4 inch wheel instead of a 10 inch? White Vega tire.. thanks
 
atwoodracing20 said:
Brian does that change the spring rate of the tire much with a narrower wheel? Like mounting a tire on a 9 3/4 inch wheel instead of a 10 inch? White Vega tire.. thanks
Click to expand...
I know you asked Brian, but yes going to a narrower wheel changes the spring rate of the tire. Lowers the spring rate.
Brian i believe is only doing it out of necessity with 10" wheels so hard to get.
 
There are times when I prefer a narrower right side wheel - ie temporary track surfaces like fair racing, very sandy / porous surfaces like horse arenas, or on grass and ice. 99% of the time, you want 10" right sides.
If you need more side-bite, a narrower right side wheel will help.
Some of our new customers have no wheels and tires at all, and for what the price of used are going for, we outfitted them with 1/2" narrower right sides which will work just fine for their application (no bite track, etc.)
It definitely changes the spring rate as Earl explained. Some brands significantly more than others, depending on the sidewall construction.
Keep in mind, you can accommodate some of this with air pressure, but it's still a band-aid in my opinion.
 
SoCo Tire Treatments said:
I know you asked Brian, but yes going to a narrower wheel changes the spring rate of the tire. Lowers the spring rate.
Click to expand...

This is a question, not a statement.
Then it means when you lower the spring rate at a tire, the tire then needs less weight to compress.

The reason you need a lower spring rate in a tire, as my mentor "out east" explained to me during our first meeting around 15 years ago:

When track conditions warrant a lower spring rate it's because grip has gone away from the track.
And when track grip goes away the only thing that always happens is you will be going slower.
Because your going slower there are less on-track forces available to you to operate your chassis (the tires per this discussion).
Simply put lowering the spring rate makes it easier for your chassis to work as it did before track grip was reduced.

Then this offering brings up another question which is do you relate needed spring rate to your speed or track grip?

Another answer to my offering is because were talking about low hp karts with adjustable grip at the tire, when track grip goes away we may be able to compensate for it by changing tire grip and there will be no loss of speed. and ????????

But then again if you increase the tires ability to grip won't it still take more effort from going fast because to get the tire with more grip to work it will take more of your available hp or built up momentum. and lots of ?????????'s on that one. ... :)

Might it be more about how much effort it take to operate a tire changed spring rate then either speed or grip????????

dang you all cause me a lot of questions to thunk about ... :)
 
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Nickp said:
Aproximately how much bigger is the Circumference if you were to mount the tire, measure, and then re-mount the same tire but on a 1/2" narrower wheel?
Click to expand...

I think and hope you already got your question answered making my wonderings about the replies ok. and ???????
Did you?
 
paulkish said:
This is a question, not a statement.
Then it means when you lower the spring rate at a tire, the tire then needs less weight to compress.

The reason you need a lower spring rate in a tire, as my mentor "out east" explained to me during our first meeting around 15 years ago:

When track conditions warrant a lower spring rate it's because grip has gone away from the track.
And when track grip goes away the only thing that always happens is you will be going slower.
Because your going slower there are less on-track forces available to you to operate your chassis (the tires per this discussion).
Simply put lowering the spring rate makes it easier for your chassis to work as it did before track grip was reduced.

Then this offering brings up another question which is do you relate needed spring rate to your speed or track grip?

Another answer to my offering is because were talking about low hp karts with adjustable grip at the tire, when track grip goes away we may be able to compensate for it by changing tire grip and there will be no loss of speed. and ????????

But then again if you increase the tires ability to grip won't it still take more effort from going fast because to get the tire with more grip to work it will take more of your available hp or built up momentum. and lots of ?????????'s on that one. ... :)

Might it be more about how much effort it take to operate a tire changed spring rate then either speed or grip????????

dang you all cause me a lot of questions to thunk about ... :)
Click to expand...

paulkish said:
This is a question, not a statement.
Then it means when you lower the spring rate at a tire, the tire then needs less weight to compress.

The reason you need a lower spring rate in a tire, as my mentor "out east" explained to me during our first meeting around 15 years ago:

When track conditions warrant a lower spring rate it's because grip has gone away from the track.
And when track grip goes away the only thing that always happens is you will be going slower.
Because your going slower there are less on-track forces available to you to operate your chassis (the tires per this discussion).
Simply put lowering the spring rate makes it easier for your chassis to work as it did before track grip was reduced.

Then this offering brings up another question which is do you relate needed spring rate to your speed or track grip?

Another answer to my offering is because were talking about low hp karts with adjustable grip at the tire, when track grip goes away we may be able to compensate for it by changing tire grip and there will be no loss of speed. and ????????

But then again if you increase the tires ability to grip won't it still take more effort from going fast because to get the tire with more grip to work it will take more of your available hp or built up momentum. and lots of ?????????'s on that one. ... :)

Might it be more about how much effort it take to operate a tire changed spring rate then either speed or grip????????

dang you all cause me a lot of questions to thunk about ... :)
Click to expand...
We been doing this all along, changing spring rate, just been doing it with internal treatments.
As Brian pointed out, theres times where a narrower wheel would work, but 99.99% of those times a wider wheel, proper internal is the way to go. This is also the reason why theres a 10" wheel width rule. Have you ever seen how much faster a kart is with a 10.5" wheel on a good track, dont have to be a great track, its a difference :)
Right now wheels are very hard to come by, new ones arent available (mines been on order since beginning of January), but there are folks who have oddball sizing, the 9.5" and so on. At times you just got to make do with what you have, unfortunately.
 
I can't speak AT ALL about dirt racing with any significant knowledge (I drove in one dirt race in my life... probably 25 years ago), but....

In sprint racing, I've always had the feeling that it wasn't simply the spring rate of the tire that changes, but also the "natural frequency" and spring rate of the axle/chassis/tire combination. As I'm sure many of you know, swapping the axle on a sprint chassis is method of tuning the handling, with axles often being classified as "hard", "medium" or "soft". Interestingly, this does not necessarily correlate to stiffest, less stiff, and least stiff. More often than not, the wall thicknesses can be the same. I believe these "labels" that have been applied have to do with how they "feel", (and technically, I believe it has something to do with what's called: "loss coefficient" -- roughly meaning "internal damping of the material"). Changing material type can make the axle be "livelier" or "deader" (for lack of better terms).

I have an interesting document on this subject, if anyone is interested.

(side note): Hub width is also a tuning method on a sprint kart, which I "suspect" ties into changing the stiffness and/or damping of a greater or lesser portion of the axle.

Do not mean to derail this thread about tire OD at all (I can start another topic if preferred), but since this moved from wheel widths / tire OD / to: spring rate, I thought I'd toss this in.

PM
 
Sign me up Pete, I am mainly a sprint racer and have been straightening all types of axles for over 10 years with a hydraulic jack jig.
I use a dial indicator to tell me how much movement I need to get a response which does corollate some with hardness of the axle I am working with yet it would also be interesting if my jig read pounds of pressure too.
 
Yes: hardness changes the tensile and yield, but will not alter Youngs Modulus (the amount of flex for a given force within its yield limit).

Shoot me a private message with your email and I'll send you the document I mentioned. :)
 
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