Tire Size Upgrading and Downgrading

[jaydenn]

Hey Guys,

Thought this be useful to most of the OH members here!

http://www.1010tires.com/tiresizecalculator.asp

Basically you just slot in your Tread width/Profile/Diameter and compare with the Tire Specs you want to get! It will tell you if it falls within the 3% diameter height of the original tire.

It is recommended staying within the 3% as if you go any higher you face the risk of brake failure.

[JohnL]

Hey Guys,
It is recommended staying within the 3% as if you go any higher you face the risk of brake failure.

How so? I fail to see how a larger wheel diameter can cause brake failure.

A real issue is that changing the wheel diameter also affects the accuracy of the speedometer reading.

[jaydenn]

if you fail to see how a larger wheel diameter can cause brake failure then you should try it and find out.

And yes another issue is the accuracy of the speedometer reading, your correct JohnL

[chargeR]

if you fail to see how a larger wheel diameter can cause brake failure then you should try it and find out.

I also don't understand how a larger diameter tyre can cause brake failure, could you explain for us simpletons please? My new tyres are 2.5 % taller than my stock tyres is my car going to spontaneously combust?

[geeang]

Only thing I can see leading to brake failure is if your overall rolling diameter was drastically larger than stock, making your top speed higher and the rolling distance for braking much longer (hence you'd need to brake harder to stop in the same amount of time).

So it's probably not as much brake failure, as potential brake wear/fade.

[chargeR]

Yeah. Also the ABS system might not deal to well with significant changes in rolling diameter, I can't see that causing brake failure though.

[SPL_K]

That calculator aint too helpful considering you can't pick what kind of tyres you're running since semi's are slightly larger then street tyres even tho they are supposed to be the same size but physically the size is actually different due to certain characteristics.

Also the width of the rim is another variable in this situation. What if you're running low profile tyres that are stretched or what not.

I also fail to see how this could cause brake failure. It will only cause more inertia which means the car needs more braking power.

And Tom... whats ABS? It doesn't exist on my dc.

[mocchi]

ABS = A Bullsh*t System

Carbible site for rolling diameter sizing.

I was kinda wondering too how rolling diameter can lead to brake failure. SPL K, that makes senses i guess.

[TALEB TYRES]

big changes in rolling diameter (ie limit is 15mm above or below original size according to nsw RTA), have a few consequences, just quickly,

depending on where you are, it is illegal to go over a set limit, thus also voiding insurance as well if you have to make a claim and its spotted, also may mean that your tyres are not load rated for the car as a smaller tyre will usually have a lower load and speed rating.

I know alot of newer cars have systems that measure rolling diameter, so if you change your tyres to a different rolling diameter, the car may think you have a flat or something, it happens!, people wonder why the car wont let them go over 40km/h after doing so!

also take into mind, as was said above, 2 tyres of the same size but different brands, can also have fairly different rolling diameters, magnified when your talking about semi's.

Havent had any experience with brake failure as a consequence, depends on what vehicle and what kinda change your talking about, everything has its limit.

[gumbs]

I think the increase in weight would have a much bigger effect on "brake failure" apparently the rubber I'm running now is just right, and the rubber I had before that was out of range but was actually a better drive and the speedo was more accurate.

[Huggyb]

I think the brake failure comes about because you simply require more torque to stop the wheel at the same speed. As you should all know, torque is force x distance so if you increase the rolling diameter, with the same required force to stop the car, you increase the amount of work that the brakes have to do to stop the vehicle. Ultimately i think the site is just keeping itself safe in giving this warning, as there may be cars which have underengineered brakes (which im sure is not the case with a quality honda).

[migoreng]

sounds a little silly..
so when you're carrying 3 people in your car with groceries or whatever in the boot do you need bigger brakes??
that's at least an extra 200kg in the car...
so bigger wheels won't cause a prob at all.