tyre's tyre's tyre's .......what why upsizing etc......read

[DrRubber]

another sticky perhaps ??

where to start, this is the obvious component of your car that connects you to the road, I could go on with a manufacturers blurb but they change their tyres every few years and wouldnt be that helpfull so ill start of with upsizing

If you are looking to put larger wheels on your car then getting the correct tyre size is imperitive, using tyres that are too large can result in rubbing on the cars body or suspension, also it can alter your turning circle and wheel alignment.
So to keep it simple lets go through what the size of your tyres mean. The example tyre size we will use is 205/50/16

the 205 is the width of the tyre so in theory it should be 205mm wide, however different manufacturers seem to design their tyres differently and the width may vary 10mm or so either way (dont ask why i dont know)

now the 50 refers to the tyres height which is a percentage of the tyres width, in this case it would be 50% of 205mm :wink:
(this also varys between manufacturers and product design)

and of course the 16 is relitive to the size of the wheel that the tyre is to be fitted to....its irish because the wheel is mesured in inches (imperial) and the rest in milimeters (metric) but thats the way it is

so now you know what they mean lets take a look at upsizing.
An easy way to figure out a basic upsize is like so

205/55/15
205/50/16
205/45/17
204/40/18 (never seen that size but you get the idea)

however when you change widths etc it becomes more complex...there is a formula that can be used but its much easier to use this link and it will show you what happens when you change tyre size and how much it could affect your speedo.

if I put lower profile tyres on my car it makes it look lower au

bullshit, if anything it makes it look higher because there is more gap between the tyre and the wheel arch.......use the correct size tyre and it wont look undertyred or overtyred........ :wink:

also using a tyre too small can result in premature bending of your rims and adverse tyre wear.....

air pressure.........normal passenger tyres are reccomended to run 32psi and on small cars id agree....commadores, falcons, diamantes etc id run like 36-38......any low profile tyre on whatever car I reccomend 38-40psi or you might as well just drive around with no tyres on
This also helps to stop your wheels from bending 8)

I guess the next thing is a quick lesson on tyre types......most of you are familiar with non-directional type tyres that come out on regular cars from the factory and also directional type tyres that we see on most performance applications.......but wait theres more

asymmetric tyres

An asymmetric tyre has different tread patterns on its inner and outer sides, giving it a distinct performance advantage over a tyre with a symmetrical or directional tread.
The tread pattern on the inner side of a typical asymmetric tyre has more grooves giving better grip on wet roads
The outer side has a higher plain surface area, the benefit of which becomes apparent when cornering at speed on a dry road.
Unlike a directional tyre, an asymmetric tyre can be used in any position on the vehicle. It is very important however, to follow such wording as 'inside' and 'outside' on the tyre's sidewalls to ensure that the tyre is fitted 'the right way round'. As with directional tyres, incorrect fitment can seriously impair performance.

an asymmetric tyre may look similar to this



Directional Tyres

Designing a tyre tread which will operate equally well rotating in either direction inevitably involves compromises which limit ultimate performance in some respects.
Directional tyres, on the other hand, are designed to rotate in one direction only (indicated by a conspicuous arrow pointing in the direction of rotation on the sidewall along with the word "rotation"); so performance - wet grip, directional stability and handling - far from being compromised, is optimised.
Obviously, a directional tyre can deliver this improved performance only if it is correctly fitted to ensure that it rotates in the direction indicated on the sidewall.

A dirctional tyre will look like(or similar) to this



Im not gonna give anything on normal tyres as really all you need to know about them is that they are black and round

As always you get what you pay for when it comes to a tyre and value for money, just be sure anyone you deal with in the industry is someone you trust and is selling you a product that suits your needs as well as budget.

I will update this as I think of things 8)

[EVIL DA]

how about some approxiamate prices of not just performance tyres but some economy tyres and stuff aswell for people out of the know...

i say this coz i mate of mine just payed $140ea for 185/60/14 unidirectional tyres...which i think is a bit of a rip off, but i could be wrong, hence the reason to put it in this thread..

[Horny_Devil]

Originally Posted by CRX001

how about some approxiamate prices of not just performance tyres but some economy tyres and stuff aswell for people out of the know...

i say this coz i mate of mine just payed $140ea for 185/60/14 unidirectional tyres...which i think is a bit of a rip off, but i could be wrong, hence the reason to put it in this thread..

tire prices change its probably better if u PM him

[DrRubber]

tbh it depends what tyres he got ???

I do three tyres off the shelf in that size which retail for $99.....$130 and $159 respectivly........so at the end of the day you get what you pay for :wink:

sounds to me like your mate got upsold from a budget tyre to a mid range He would have made an informed decission at the time and he's probly better off for it in terms of comfort, tyre life , and performance 8)

so yea like jase said tyre prices change....and its like petrol..........so you cant really sticky something like that....hence the reason I said to deal with someone you trust....not just the cheapest backyard garage you can find :idea:

[Horny_Devil]

or he got a parelli tires aye greg

[DrRubber]

maybe only half of one :!:

[EVIL DA]

yeah i knew that...... ops:

[creative]

Ive been running 36psi on my 205/40/17 - you say thats a little low?

Sure many on here have been running around the same. I did a bit of search and all i can find is around the 36psi mark... :?:

[DrRubber]

imo more is better.......but were only talking about 2 psi so whichever floats your boat I reccomend 38-40 psi for low profiles 8)

[nitrous]

What would you call low? (these days)

Anything less than 50 Aspect-ratio or way less? Just trying to get an idea of the sliding scale of A/R vs suggested inflation pressure. And is it more to maximise tyre geometry in the corners even wear?
It's just that my 50's seemed to wear a little more in the middle at 32-34PSI which the old books always used to point at and say "over-inflation"

Appreciate your input. Cheers.

[DrRubber]

well id call low.......anything lower than a 50 series....however I seems strange that at that pressure they would wear through the centres more.....did they wear right to the bottom of the tyres tread ??? if so and the shoulders just had a little bit of meat on them then thats fantastic !!!

you basicly got the full life out of your tyres its only really overinflated if the middle wears out and the shoulders are stil like 4-5mm tread 8)

[Shadow Sol]

according to that calculator i got the right size tyres even though my parts department told me i was wrong!

stock 185/65R14
now 205/55R15

speedo reads low by 1.017% ie so when speedo says 100Kmph its 101.7Kmph

not bad really - if i had used 205/50R15's the speedo would read fast by 1.017%

[2slow]

Originally Posted by Shadow Sol

according to that calculator i got the right size tyres even though my parts department told me i was wrong!

stock 185/65R14
now 205/55R15

speedo reads low by 1.017% ie so when speedo says 100Kmph its 101.7Kmph

not bad really - if i had used 205/50R15's the speedo would read fast by 1.017%

If your speedo only reads 1.017% out then it's probably more acurate than most of the cars on our roads, regardless of tyre size!

As for pressures in low profiles, I'd say anywhere from 34-40psi depending on size and weight of the car.
For example, I have a CRX with fully stripped interior on 205/40/17's, I run 35psi up front and 32psi in the rear. The tyres are wearing fine.
When I ran the rears at 35psi they ran around all over the place trying to slow down for corners (not racing, just sidate road driving).

Also running too lower pressures wont buckle your rims, driving into curbs does that!!!'

Other that that, very simple yet informative write up.

[DrRubber]

Originally Posted by 2slow

If your speedo only reads 1.017% out then it's probably more acurate than most of the cars on our roads, regardless of tyre size!

As for pressures in low profiles, I'd say anywhere from 34-40psi depending on size and weight of the car.
For example, I have a CRX with fully stripped interior on 205/40/17's, I run 35psi up front and 32psi in the rear. The tyres are wearing fine.
When I ran the rears at 35psi they ran around all over the place trying to slow down for corners (not racing, just sidate road driving).

Also running too lower pressures wont buckle your rims, driving into curbs does that!!!'

Other that that, very simple yet informative write up.

yea very true....it does depend on the application totally........sometimes you just have to own a car for a while and find out what pressures work best........as for the other bit about bending wheels....your right there too, but in auckland (and heaps of other places) the roads are shit and potholes > wheels :wink:

[crx_bob]

Good to see a nice simple write-up on tyres to many people dont understand sizes and ratings.

You should do one on the downsides or putting to tyres that are to large for the car on, excesive grip can kill, sometimes sliding is good

[DrRubber]

Originally Posted by crx_bob

Good to see a nice simple write-up on tyres to many people dont understand sizes and ratings.

You should do one on the downsides or putting to tyres that are to large for the car on, excesive grip can kill, sometimes sliding is good

thanks bob, There is more to come outlining more stuff.....just in between work ya know :wink:

[Colza]

I have a question *raises hand politely*

If you take that assymetrical tyre youve got up there. When you put that tyre on the other side of the vehicle, dont you end up with the old situation of the tread pattern being backwards on one side of the car? The thing they were trying to get rid of with directional tyres...

Ive tried to illustrate what i mean but paint > me.



But you can see what i'm trying to get at.

[Matty]

It depends on if the asymmetrical tyre is also directional. An asymmetrical, non-directional tyre can be swapped between sides no problems, as long as the tyre is mounted correctly so (for instance) a groove intended to be on the inside of the tyre is still on the inside on the other side.

Asymmetrical directional tyres can only go on one side. For cars like the NSX that use them and different sizes front to back each tyre can only go on one wheel.