8.3 vs. 9.5 X 24 tire OD's?

[JohnnyJohnsoninWI]

Hello,
This is my first post here. I've been lurking and it looks like a lot of nice people hang out here.
I have a question about tire size. Does anyone know the outside diameter of a new 8.3X24 ag tire? I have a set of 9.5X24's on my cub right now and have been wondering how much I could "gear down" by going to the smaller tire. I'm expecting some where between 2-5%.
Thanks,
John

[Eugene]

John:

I don't know the answer to your question. I suspect you wouldn't notice the difference in the tractor's ability to "pull" with either sized tire.

Couple of things I do know. The same sized tire from different manufacturers - one will be slightly larger than the other. Wear reduces the circumference of a tire.

My operators manual lists the ground speed in first gear @1800 RPMs as 2.4 mph with 8X24 tires. I have one of the F Cubs and @1200 RPM in 1st a person walking is quite a bit faster than the Cub.

Eugene

[Steve Butram]

John, My experience with tires tells me that a 9.5- 24 is only 1" wider than a 8.3-24 . So by only being wider and not taller there is no gearing difference just a wider tire profile The 8.3-24 tires are the standard but are getting harder to find so you will see the 9.5s more on the cubs. I hope this answers your question.

Steve

[Bigdog]

Actually, the wider tires do stand a slight bit taller. But I believe the difference is very slight and at cub speeds it definitely would not be noticeable.

[johnbron]

When the 2 of My Cubs are parked side by side I notice a big difference in heighth between the 2 tire sizes mentioned.

[JohnnyJohnsoninWI]

Hi Guys,
Thanks for your replies. I have to agree with johnbron and bigdog. In many photo's, the tires size varies quite a bit when compared to the rear fenders and rim diameter.

My Goodyear 9.5X24's with ~80% rubber are 40.5" in diameter. Assuming a similar aspect ratio (height/width) I expect the 8.3X24 diameter to be 1 to 2 inches smaller in diameter. It's only my estimation, however, because aspect ratios vary from 82 to 88% on the tires I've measured.

Although we would never notice a 5% ground speed reduction, I believe, that it does translate into 5% more power available for running the mower or what ever.

I've been searching though these archives and have found threads about getting more power from a cub. Suggestions were given such as removing the generator belt and replacing the oil bath air filter with a foam motorcycle filter. In light of these suggestions, I believe a 5% increase by tire size reduction is significant.

Take care,

John

[johnbron]

OK Folks, I just went out and measured both tires from ground to the tops of tires and this is the results.


[8.3 X 24] is (37 & 1/2") high.
***********

[9.5 X 24] is (40") high.
***********

2 & 1/2"s is quite a difference.

[JohnnyJohnsoninWI]

Hi Johnbron,
Can I ask a favor and have you measure once again? If you measure from the ground up, you will introduce some measuring error due to the weight of the tractor causing a flat spot at the bottom. Try measuring horizontally or from the center and double it. I try to line up both tires with my tape measure to eliminate any paralax error.

Of course it would be really neat if you had a 4-foot dial-caliper laying around.

Thanks,
John

[Jim Becker]

OK, you guys finally shamed me into trying to look it up. Here is information distributed by IH in 1939, when the wide base 8-24 and 9-24 tires were a new thing. This is based on a 7" rim for one tire and 8" for the other. On a Cub, they are both mounted on a 7" rim, which will slightly change the numbers for the 9-24. But it will mostly change width measurements and not do much to height. 8.3 and 9.5 are the newer size designations and also have little effect on the diameters. Also, beware that physical size will vary some from brand to brand and even different styles of tire within one brand.

8-24 overall diameter 39" loaded radies 18.1" sectional diameter 8.40".
9-24 overall diameter 41" loaded radies 19.3" sectional diameter 9.50".

[johnbron]

Hi Johnbron,
Can I ask a favor and have you measure once again? Thanks,
John

OK, Just measured from center axle to rearmost tread surface on both and got these results.

8.3 X 24 is (19 & 1/4")

9.5 X 24 is (20 & 1/2")

Man, You is giving this Ol`Man his morning exorcis/ism!!.

[Don from Indiana]

I have two cubs, one with 8.3 and one with 9.5 by 24. To me there is a noticable difference. With the 8.3, I mow in 2nd. With the 9.5 I mow in 1st.
Don in Indiana

[Eugene]

Interesting topic. I measured my Cub tires. 8.3 x 24 = (90%+ tread) 37.5" and (100% tread) 38.0" in diameter. Measured an unmounted 9.5x24 = 38.25" dia. All 3 different brands.

Took the medium 8.3 diameter and the medium 9.5 diameter from all of the measurements and came up circumference difference of 4.346%.

I don't believe I would replace my 9.5 x 24 tires with 8.3 x 24 at a cost of $300-.

What I did find interesting is that my 9.5 x 24 was smaller than one of the 8.3 x 24s listed.

Eugene

Good topic though.

[Lurker Carl]

Yikes! Does this mean I'm gonna have to change the speedo gear in the tranny?

[JohnnyJohnsoninWI]

Hi Guys,
Thanks for all your help.
No, I don't think the difference is worth $300 to make the change. However, if your tires are worn out, this is worth considering before making your new purchase.

Lurker Carl, I didn't know that the cubs came with a speedo option. Cool!

Seriously though, unfortunately, I have a set of Firestone on the back of my JD 1520 and ever since that Firestone high speed blow-out scare a couple years ago, I've been afraid to shift that tractor into road gear. Well, not too seriously.

Thanks,
John

[Larry in IN]

Johnny -
You are SAFE on your Firestones
If you followed that story, you may remember that all the problems happened in relation to FORDs!
So much so that the old family alliances between the Firestones and Fords went down the tubes in all the resulatant finger-pointing and CYA.
All the time that circus was going on, we were mounting thousands of Firestones per day on GM pickups at Fort Wayne and never had a blurb about safety. G M spec'd their own tires, thank goodness.