Tyre size

[younglion]

is a 19" rim and tyre 235/40/19 physically bigger/wider than a 18" 235/40/18

[shiftySLE]

yes, by 1 inch in diameter, the width depends on what widthe the wheels are, that tyre will fit on probably anything from 7-9 inch wide

[Scooter79]

A 235 tyre on a 7" rim? I'd hate to see that.

Use this link if you want to compare tyre sizes Tire size calculator

[shiftySLE]

not real smart idea but i've seen it, maybe I should have started with 8 inch. BTW whats the tyre size calculator for, the wheel is one inch bigger and the tyre size is the same except one inch bigger

[ducker85]

is a 19" rim and tyre 235/40/19 physically bigger/wider than a 18" 235/40/18

NO it is the the same outside diametre spot on!! it's perfect when compared to the stock 15's.

AND will not affect your speed

[shiftySLE]

NO it is the the same outside diametre spot on!! it's perfect when compared to the stock 15's.

AND will not affect your speed

????? How is it the same diameter outside, one wheel is 18" and the other is 19", and 15", where di that come into it.

[M01ST]

Mate had 18 inch rims 245 wide and The tyre factory fitted 235's instead of 245's, the result was rims with bad gutter rash because the tyre didnt protect the rim at all.

[shiftySLE]

Why do so many people rely on the tyres to protect the rims these days. DON'T HIT THE GUTTER = NO GUTTER RASH!. The Tyre isn't there to protect the wheel, its there to drive on.

[HoldenOnn]

Total Tyre Height Comparison (from ground to top of tyre when installed on rim);

235/40/19 = 67.06cm (tyre width = 23.5cm)
235/40/18 = 64.52cm (tyre width = 23.5cm)
205/65/15 = 64.75cm (tyre width = 20.5cm)

Obviously the first figure gives away the width of the tyre.

Also, yes its true that some tyres have rim protectors. The rim protector does very little if anything to help protect the rim. The best thing to protect the rim is not to hit or scuff alongside a kerb in the first place. Do not buy tyres based on their rim protector feature.

[| evaN |]

^^^ he never said it was the same. He listed the overall diameter and the list the widths.
for the first two, the widths are the same but the overall diameter is different.

[shiftySLE]

^^^ he never said it was the same. He listed the overall diameter and the list the widths.
for the first two, the widths are the same but the overall diameter is different.

you are right mate, i read the post wrong

[Scooter79]

not real smart idea but i've seen it, maybe I should have started with 8 inch. BTW whats the tyre size calculator for, the wheel is one inch bigger and the tyre size is the same except one inch bigger

I posted the tyre size calculator so you can see how different size tyres can accomodate different size rims, therefore keeping the same rolling circumference (or at least very close) and not throwing the speedo out.

[shiftySLE]

I posted the tyre size calculator so you can see how different size tyres can accomodate different size rims, therefore keeping the same rolling circumference (or at least very close) and not throwing the speedo out.

fair enough, its a good tool too, its made its way to heaps of threads

[ducker85]

????? How is it the same diameter outside, one wheel is 18" and the other is 19", and 15", where di that come into it.

yea and the OUTSIDE diametre of the TYRE is the same. The wheel size mean jack, only when you get 20's the OUTSIDE diametre of your TYRE change it's all about tyres not WHEEL DIAMETRE

because to make it legal it has to be the same OUTSIDE diamtre to your factory 15's which were engineered for that car at the drawing boards of Holden

and the width doesn't come into it unless your talking track width so dont worry about it as long as you have to correct offset for your car. 245 or 195 it doesn't matter nor affect your speedo

[shiftySLE]

yea and the OUTSIDE diametre of the TYRE is the same. The wheel size mean jack, only when you get 20's the OUTSIDE diametre of your TYRE change it's all about tyres not WHEEL DIAMETRE

because to make it legal it has to be the same OUTSIDE diamtre to your factory 15's which were engineered for that car at the drawing boards of Holden

and the width doesn't come into it unless your talking track width so dont worry about it as long as you have to correct offset for your car. 245 or 195 it doesn't matter nor affect your speedo

OK, read the following CORRECT fact about tyres, then comment.

Width is in mm, 245 tyre is 245mm wid
Profile is a % of the width 40% x 245mm is 98mm
Wheel dimater= 18" which is 45.72
TOTAL OUTSIDE DIAMETER IS 65.32cm = the wheel + the profile X 2--top and bottom of the rim
Now again with the 19"
If the tyre is still 245 so 245mm
Profile is still 40 so 40% x 245mm = 98mm
Wheel diameter is 19" = which is 48.26
TOTAL OUTSIDE DIAMETER IS 67.86 = THE WHEEL + THE PROFILE X 2--TOP AND BOTTOM OF RIM.
The only reason it would change for a 20" is you would generally need wider rims, which is more tyre for tyhe same profile ie. a 275/40/20 then turns inot 40% of 275mm.
A 40 profile 235 will have a bigger side wall than a 205 with a 40 profile which is why when we get wider tyres, we get lower profile.

Test it out, a stocky 205/65/whatever will be 65% x 205mm side wall = 135mm + the diameter of the wheel approx inches x 2.54 will give cm.
What state are you saying the outside diameter has to be the same as stock, not Vic

All these measurement were done on tyres already fitted to wheel wheras the tyre size relate to full tread tyres before fitting, including the bead

[ducker85]

OK, read the following CORRECT fact about tyres, then comment.

Width is in mm, 245 tyre is 245mm wid
Profile is a % of the width 40% x 245mm is 98mm
Wheel dimater= 18" which is 45.72
TOTAL OUTSIDE DIAMETER IS 65.32cm = the wheel + the profile X 2--top and bottom of the rim
Now again with the 19"
If the tyre is still 245 so 245mm
Profile is still 40 so 40% x 245mm = 98mm
Wheel diameter is 19" = which is 48.26
TOTAL OUTSIDE DIAMETER IS 67.86 = THE WHEEL + THE PROFILE X 2--TOP AND BOTTOM OF RIM.
The only reason it would change for a 20" is you would generally need wider rims, which is more tyre for tyhe same profile ie. a 275/40/20 then turns inot 40% of 275mm.
A 40 profile 235 will have a bigger side wall than a 205 with a 40 profile which is why when we get wider tyres, we get lower profile.

Test it out, a stocky 205/65/whatever will be 65% x 205mm side wall = 135mm + the diameter of the wheel approx inches x 2.54 will give cm.
What state are you saying the outside diameter has to be the same as stock, not Vic

All these measurement were done on tyres already fitted to wheel wheras the tyre size relate to full tread tyres before fitting, including the bead

Also im talking from an engineers point of view not state laws



it's the overall that affects the speedo tho. The width of the tyre/wheel DOES NOT CHANGE THIS MEASUREMENT! So I would think your trying to work out the load rating there.

I have owned 15's 16's 18's 19's and stood them all side by side are there all the same height/diametre, and only changed in width/load rating.
A set of 15's with 85 series tyres will through your speedo out without changing wheel diametre or width. Same goes for a 15's fitted with 45 series tyres or for that matter just bald tyres

I just ran my tape measure over my 15's and there somthing around 636mm overall with 65=127mm side walls on a 15 inch wheels (205 wide) on brand new tyres
My 16" SV5000's are 631mm overall with 50=145mm side walls on a 16inch rim (225mm wide) 80%tread

use your maths to work out some 18's fitted with 235/45 and then the same for 18's with dish say fitted with 285/45's the outside diametre is the same only the width and load rating change (load rating is heigher) so you should get the same answer for overall dismetre. Correct?


using this http://www.miata.net/garage/tirecalc.html I got 205/65/15 are 647.5mm heigh and 245/35/19 are 654.1mm heigh which is different to my tape measure so i would surguest getting your facts from a tyre place not the net,
Like I have from my shop Wheel Worx

[shiftySLE]

?? no one is talking about width, he is asking if they are bigger, diameter, height from floor to top of tyre. the only reason I spoke of widths are that this is the ONLY way you can work out the profile.
A 85 series tyre on a 15" rim can only be matched in diameter by a wider tyre with a lower profile. I dont see what it so difficult about this, it is just maths, width = mm, profile = % of width, thats as easy as it is, the only way your 15,16,17 and 18 can retain the same rolling diameter is if the profile is reduced each wheel size increase. Do you agree?

[STEALTHY™]

Your missing one key point ducker.


You would be right, however you didn't read the original post right.

he is using 40 walls on both the 18in rim and the 19in rim. If the 19 was smaller (not exact here but say 35) walled then yes, the overall rolling diameter would be the same or closer.

[shiftySLE]

Your missing one key point ducker.


You would be right, however you didn't read the original post right.

he is using 40 walls on both the 18in rim and the 19in rim. If the 19 was smaller (not exact here but say 35) walled then yes, the overall rolling diameter would be the same or closer.

This is the key factor, I'm not just trying to be right, it is just the maths of the situation

[STEALTHY™]

This is the key factor, I'm not just trying to be right, it is just the maths of the situation

Quite a simple thing to miss, considering 'most' people choose a lower profile when getting a bigger rim.

[shiftySLE]

true, and its Friday

op - I think you have your answer to your question too.

[ducker85]

Your missing one key point ducker.


You would be right, however you didn't read the original post right.

he is using 40 walls on both the 18in rim and the 19in rim. If the 19 was smaller (not exact here but say 35) walled then yes, the overall rolling diameter would be the same or closer.

Your right I did miss that bit. Sorry, I just dont know why you would do that it's like your 195/65/15 and goin i want 245/65/20 which is stupid in my opion because of all the other factors

sorry mate (shiftySLE)

[shiftySLE]

yeh no stress, its all just talk here but dont get me wrong, I've been corrected too on things, its just when some people are presented with the facts they still push their point, I've worked on heaps of engines of a few types and there is nothing worse than someone making a mistake you've made in the past when all you are trying to do is help so they dont waste their money and time from bad advice or info. But as you said ducker85 which I think I did a few days ago in another thread, sometimes you just miss that one key word which changes your opinion, anyway shit happen, its all fun and cars related

[| evaN |]

Also im talking from an engineers point of view not state laws



it's the overall that affects the speedo tho. The width of the tyre/wheel DOES NOT CHANGE THIS MEASUREMENT! So I would think your trying to work out the load rating there.

How does the width not affect the total measurement? The profile is calculated from the width.
eg 235/40/18 means the sidewall is 40% of 235. so 245/40/18 has a larger overall diameter because it's sidewall is 40% of 245.

And this isn't just rumors and made up crap from the net. It's what those numbers mean.

[shiftySLE]

How does the width not affect the total measurement? The profile is calculated from the width.
eg 235/40/18 means the sidewall is 40% of 235. so 245/40/18 has a larger overall diameter because it's sidewall is 40% of 245.

And this isn't just rumors and made up crap from the net. It's what those numbers mean.

yeh all true evan but in this case, the width is the same, the profile is the same, the only change is the 18" or 19" rim. Width doesn't affect speed if all other factors are the same.
Refer to the last few posts, all seems to be sorted