tire sizing hurts my head

[69C10@16]

sumbody plz help me b4 my head explodes.
ok. my tires right now are 235/75/15.
according to the little calculator that means they r 29 x 9.25 x 15
ok. i know the 15 is wheel diameter.
is 29 the tire height?
and is 9.25 the width?

because if it is then the cragars i want will not be wide enough for me. the cragars are 17x9's. and if my current tires are 9.25 inches wide then i want to go like 11 inches wide.

what size tires would you recommend and can i go wider with the tread than 9" with still decent sized tires and no rub. Man this makes me confused.

I think i want 31 inch tall tires. ive been told 33's will fit without rub but im also lowering the truck 2/4. so i figured 31's would be my max.

Thoughts? Comments good/bad?

[powerbench]

I think i'am reading your post right , but here it goes.The sizing you are doing is for your rims (17x9) ? I find (and this is just me ) usually , in your case you probably have a seven inch rim on those tires now..15x7. I have eight inch rims on my wifes 88, it has 275/40/17 on the back. Now i don't know the width of the tire, but in you tire calculator i bet it's close to 11 inches wide. Most of the time , you(or in my case me) would choose a rim smaller in width than the width of the tire. As far as for height or profile , it will depend on the tire , i know with our 17 wheels finding say a 50 series tire is harder than say a 40. Now 18 or say 20 inch rims have a bigger selection of profiles and widths. And to recap...and man i hope i'am remebering this right,in your case 235= width /75= % of 235 for sidewall profile/15=rim size...

[68K20 x Drill]

29 x 9.25 R 15 = 235 76 R 15
as per THIS CALCULATOR at www.dakota-truck.net

now that we know that, try the OTHER CALCULATOR from www.miata.net, and plug in the new value, and try to find a size that matches up....
245/60R17 converts to 29X9.65R17, essentially the same as you have now.
295/60R17 works out to 31X11.65R17 and your speedo will read 7.1% slower.

[cdowns]

if you have the 235X75X15 tires now why do you need a calculator to tell you how big they are?? dont you know how to use a ruler?

[scatesracing]

Originally Posted by 69C10@16

sumbody plz help me b4 my head explodes.
ok. my tires right now are 235/75/15.
according to the little calculator that means they r 29 x 9.25 x 15
ok. i know the 15 is wheel diameter.
is 29 the tire height?
and is 9.25 the width?

because if it is then the cragars i want will not be wide enough for me. the cragars are 17x9's. and if my current tires are 9.25 inches wide then i want to go like 11 inches wide.

what size tires would you recommend and can i go wider with the tread than 9" with still decent sized tires and no rub. Man this makes me confused.

I think i want 31 inch tall tires. ive been told 33's will fit without rub but im also lowering the truck 2/4. so i figured 31's would be my max.

Thoughts? Comments good/bad?

its all metric 235 is the width 235 x .03937 = 9.25195 inchs...... the 75 is a percentage 75% that is side wall 9.25195 x .75 =6.9389625 take that times 2 for the top side wall and the bottom side wall x 2 =13.877925 now add the rim dia (15") and you get 28.877925 28 7/8 inchs tall ( uncle ownes a tire shop) I have found that calculators very from site to site they are all "close"....... tape measure works good too lol.............................................wow now my head hurts

[scatesracing]

Originally Posted by powerbench

I case 235= width /75= % of 235 for sidewall profile/15=rim size...

sorry powerbench i should have read closer you beet me to it.

[powerbench]

no prob

[c10addict]

http://www.discounttiredirect.com/di...foTireMath.jsp

here you go my man.... I use this all the time..

[68Stepbed]

Are you just trying to figure out what size tire to run on 17" rims? Will you have 17x9's all around or just in the rear? A 275/60/17tire is 30" tall with about a 10.5" section width. A 285/60/17 will be just a bit taller and wider, but either of these sizes will be too much tire for the front if you plan to lower the truck.

[69C10@16]

ok. after reading all those posts my head really does hurt and i read my first post and realized it must have hurt awfully bad then too cuz its kind of confusing.

Plans changed ever so slightly since the first post

I want to run 18x10's in the back and 18x8's in the front and i need to know what size tires i should run AFTER a 2/4 drop.

i HAVE 15x?'s. I dont even know. Im assumin 8's. can i measure tire width and get the right size? i want to go with lower sidewall profile but not complete low profile's.

Hope that helps you guys answer my question.

[powerbench]

hey bro check out this thread in the faq's http://67-72chevytrucks.com/vboard/s...d.php?t=143835 this will give you some pic's to choose from,and tires selections and ideas ...i think there is even a set of cragar's..good luck shake and bake

[68Stepbed]

Check out SactoJim's build thread. He's running 18's on his ride. I believe he has 255/50/18 front, 275/55/18 rears. He has a 4/6 drop but the tire size should still look good with a 2/4 drop.

[Brock]

I started stockcar racing this year and everybody was talking stagger by using the "65 or 75 or 55...". I didn't get it. So I looked it up and turns out THEY didn't get it. That number is the height of the sidewall expressed as a PERCENTAGE of the tire width. So a 235/55 was actually shorter than a 275/50. A 235 has a tread that is 235 mm across, the sidewall height is 55% of that or 129.25mm; while a 275 has a tread of 275mm and a height of 137.5mm. Confused yet??? You can convert to inches if you want by dividing those #'s by 25.4. Then my racer buddies started talking circumference so I grabbed a calculator, tapped a BUNCH of numbers

235x.55=129.25/25.4=5.0885826X2=10.177165+15=25.177165(the diameter)x3.14=79.056 inches as circumference

as I was doing all that a guy was measuring (yes I did get done first) and said it was just a smidge over 79 Inches. (I guess .o5 inches is a smidge)

Yes I do teach math and science...

Here's a pic that might help

[69C10@16]

68stepbed - would you mind posting a link. I checked the members list and couldnt find SatcoJim.

Brock, that diagram is going to help me with a lot of stuff. I appreciate it. I can tell youre a teacher. You remind me a lot of our math teacher at school.

Thanks Guys!
Newton

[724x4a/cchevy]

This is an overall tire diameter calculator i made for an engineering project. It will tell you the overall diameter. I made it so that you can compare two tires against each other and see the % difference. You can use this to make speedometer changes and topspeed calculations and all kinds of cool stuff. Its a really simple program. It uses Microsoft Excel.
Overall Tire calculator.zip

[c10addict]

Not to confuse anybody anymore Back in the day there were L's N's G's and more!! A L60 was wider than an L50.. That was a big deal.... People would say I got L60's on my car/truck And you know they were packin a wide tire... THey still sell them http://store.summitracing.com/egnsea...5&autoview=sku

I being 32 only remember hearing all the talk in the garage but dont know how they measured out...

Brock I bet thats what the other racers were talking... Alot of race tires are still sold using the old measurements.... Theres more for you to think about....

[Brock]

Thanks...I was starting to get a little clearheaded!!!

[ERASER5]

My truck sports 31x10.5x15 tires. Let's see that's calculates to uh 31x10.5x15. 31" -15" = 16". 16"/2 =8" side walls. What is so hard about that? The metric/aspect ratio rating serves only to confuse the public. Many tire sellers could not explain it if thier lives depended on it. I couldn't when I was a tire monkey, and I had to tell the boss about the "aspect ratio" thing because he did not know.

[Alvin]

http://www.wheelsmaster.com/rt_specs.jsp

Best dam tire calculator on the 'net!

Also, for quite awhile I was under the impression the first number (275/xx/xx) was the tread width.. but it's not, it's the overall width of the tire. See "Section Width" on this page: http://www.tirerack.com/tires/tirete....jsp?techid=46

The 225 indicates this tire is 225 millimeters across from the widest point of its outer sidewall to the widest point of its inner sidewall when mounted and measured on a specified width wheel.

So that means a 275/45/20 is approx. the same overall width as a 275/60/15. The difference is the 15" tire has taller sidewall and it "balloons" more than the 20" tire, so the 20" tire actually has a wider contact patch/tread width (it has to since it doesn't balloon as much).

Like my friend's Camaro running 315/35/17's, they appear MUCH wider than a 305/50/20 I had on hand, because his section width consists of nearly all tread while mine has considerably more sidewall. Wish I had pictures.

Does any of that make sense?

[69C10@16]

Alvin. I LOVE YOUR CALCULATOR!!!!! Thats wut I wanted.....i love it.....thanks a million....i now know i need 295 55 18s in the front and 235 70 18s out back....i dont know why that was so hard for me to figure out b4 but that calc is awesome. THANKS A MILLION

[c10addict]

In that case your front tire will be 2.36" wider than the rear???? Is this really what your after??

[69C10@16]

woops....i SO reversed those numbers....lol....

295/55/18s out back
and
235/70/18s in the front

Sorry about that....lol....i bet that was confusing

[TR65]

69C10@16,

Just for interest,

I have the Tire and Rim Association Handbook (tire industry standards organization) on my desk. The recommended rim widths for P235/75R15 tires are: 6, 6-1/2, 7, 7-1/2. The permitted sizes are 8, 8-1/2. I typically run 8 (wider is better within the permitted sizes) Wider than permitted starts to give mounting, un-seating and other problems.

If you need the permitted widths for other tires, let me know.

TR

[69C10@16]

Thanks TR65!
Maybe I shouldve thrown in that i plan on running 18x10's out back and 18x8's in front. so i should be ok. thanks for the future offer because I havent found the rims yet unless i can find my cheap way to convert to 5 lug which i started a new thread for. THANKS AGAIN!