Tire size

I am looking at going to a tire/wheel combination that is approx. 2 inches smaller in overall diameter than stock (purely for looks). Some online tire sites state you should not change your tire diameter by more than 3% or you can be at risk of brake failure. Any rhoughts?

And those 2 inches make up more than 3% for your wheels?

Balley,

I DEFINITELY got some thoughts on that !

You're a LOT more likely to get a reduced effect in Braking, from having a larger Tire than on a smaller (lower profile) one !

The only problem I can foresee which would cause more stress on your brakes, whould be if you used a Rim, that really restricted the Air Flow around the Disk or Drum. Usually, newer rims give you more air flow than did the originals, if you're going to use some new Mags or "Designer" types.
And if you're using your original Rims, then no problem!

Now understood, that any change in Rolling Diameter*, will effect your Speedometer, but it's usually minor, and you can do a Stop Watch on a given distance (Mile/Kilometer) to calculate just what effect they have.

Have a good Day !
S.W.

PS Jeffie,
Yes, 2" would be more than 3% on most, other than very large Tires.

* = Rolling Diameter:
Measured from the Center of the Axel, to the Ground, on a mounted tire, correctly pressurized, with the weight of the vehicle on the Wheel Assembly.
This measurement X2 = Rolling Diameter.

PPS: Mith "BUSTED" !

The reduced outer diameter of the tire causes less available torque to be available for stopping before the wheel would lock up from braking force changing the vehicle's braking distance.

An increased outer diameter of the tire causes more stress to be applied before the wheel would lock up from braking force. Some of the braking parts may not be able to handle this additional stress.

This is why the tire companies don't recommend moving either over or under by that much. It also may make it impossible for the vehicle to pass inspection in your state.

The speedometer would change relative to the diameter as previously explained. Note the rim diameter is very different from the wheel diameter and wheels are typically measured by inner or rim diameter.

Once you have the wheel diameter before and after you can do a mathematical proportion and can figure out the exact speedometer shift in percent.

Post edited by: jmborchers, at: 2008/08/13 02:06

Thanks. The outside diameter change I am looking is 7.6% smaller than stock. The wheels are 17" Mustang Cobras with 235 / 45 17's. No problem with air flow to the brakes. Would the ABS be affected?

Balley,

The first time I put set of low profile Tires on one of my vehicles, was in about 1956, on a 1940 Ford 2 door, and on several other vehicles I’ve owned, and many more, when I worked at a Speed Shop in Odessa Texas.

In the numerous years, thousands of miles that I have personally used these, I have never had a problem with my brakes, nor have I herd of any other person who had! Additionally, if this had been a problem, the Feds would have moved in on it, and Goodyear, Michelin, Firestone and the Rim manufacturers, would have dropped this like a hot potato!

Today, there must be thousands here in Houston, as well as millions of vehicles in the US, which have these Custom Rim Low Profile Wheel Assemblies on them, and are reliable and safely operated, insured and inspected.

This “Custom Procedure” is well beyond a fetish, it’s an INDUSTRY!
So, you go right ahead and put those on your car, enjoy, and
this will not effect the operations of your ABS what so ever.

Also, if you had a 75 profile Tire on it to start with, I bet that changing to a 45, is going to improve the handling a LOT more than 7.6%, it'd be more like 1000% better!

Have a good Day !
S.W.

PS: I think that’s going to look SO cool, you just got to take a picture and let us see it !

A FYI:
Balley,s Tire number would be written 235-45R17 (probably)
The 235 is the Tire WIDTH.
The 45 is the HEIGHT of the Tire Sidewall.
The "R" would indicate that the Tire is a Radial.
And the 17 is the Rim Diameter which it fits (in inches).

Post edited by: SWHouston, at: 2008/08/13 15:32

Absolutely the ABS would be affected because the computer no longer knows the correct vehicle speed.

Balley,

You were going to put 4 identical Rims/Tires on it weren't you ?
And, if that's the case, proceed !

Have a good Day !
S.W.

See: http://www.tiresafety.com/images/Tire%20Replacement% 20Manual.pdf

Read page 4 "Never select a tire with a smaller size, or with less load carrying capacity, than the tire specified on the vehicle tire placard"

Post edited by: jmborchers, at: 2008/08/19 03:19

Don't give me that lawsuit xxxx. These forums are about freedom of speach. If I do something that gets me hurt I take full responsibility. I'm glad you posted the tire safety document. It contains good informaion. When I first posted my question I was ready for all feedback good or bad. It's up to me to look at all the information and make a decision.


EDIT: Language

Post edited by: SWHouston, at: 2008/08/20 18:23

It's good that you would take the responsibility but there's many people today who come back later to sue the one's that helped them do something wrong. And if they don't get the poster they sue the web site who broadcasted the information.

With that said, I'm surprised SW who's a retired eng would be recommending something that's clearly wrong to do without other modifiocations and not recommended unless you fully understand the risks and account for them.

Can you provide us with one actual case where someone successfully sued a "poster" or message forum?

WOW !,

I'm going to have to go along with Balley on the Suit issue. Forums (all) are "Reader beware", and this one is no different.

We clearly have two schools of thought here (gees that's an understatement if I ever said one), JM, by the book, and I, offering my practical experience.

Thanks for the article JM, it's good stuff, didn't read it all, but it's clearly "play it safe", and given they are a Manufacturer, they couldn't put it any other way. They're the ones with the warranties.

The article clearly addresses the Load Bearing abilities, and I admit, at the onset of this Topic, I had no idea what weight vehicle Balley was talking about, but, when he mentioned the 235, it really was a mute point. Those guys are for Cadillac and Lincoln (some light trucks/SUV's too). So, I don't think he's in any major jeopardy there from overloading them.

JM offered Page 4, and I counter with Page 16, the article clearly indicating that they expect Low Profiles to be installed, and are courteous enough to tell you what they think of them, listing those aspects.

I don't agree with them about the Winter Performance, that would depend on which Tread Model was used on a given Tire. The statement is just too general, but, that's what the article is all about.

I'd be glad to view any other information/URL's that someone might offer, but I kinda need to move on here. I've put a lot of time in on this Topic, and need to do some other things on this Website.

So, I've said what I want about this issue and if "anyone" needs to contact me, do it via PM.

Have a good Day !
S.W.

When they are calling out low aspect ratio tires they don't mean you simply are changing the size of the OD.

Take for example my car a 2006 Sentra SER - Spec V. It has low profiles on a 17" rim as standard option where the regular car has 14" rim.

But both OD's are actually the same. So when you go to low profile you are supposed to size up the rim accordingly and keep the OD the same or within 3%.

I agree load is not a big factor. Heat, suspension and braking are the biggest factors I see.

The 7% decrease in OD will cause more tire heat to maintain the same speed. Not to mention the camber with decreased OD will force the tire and ride it on it's edge. The suspension might not have enough adjustment for proper alignment.

See Nascar blowing tires right and left lately because of the camber issues? It's the same thing.

Of course he can do it but he needs to understand the risk and take careful attention to the tires and wear.

Thanks for all the input so far. I should give you some information to explain the method to my madness. I have an 07 Ranger XLT and I'm planning to install a 4/5 drop kit to get a lowrider effect. The guy who will be installing the kit says I need to go to a smaller diameter tire or the fronts will rub in the wheel wells. He reccomends a 2" smaller diameter up front and says the backs would be okay but would look kinda funny being so much taller. He says the backs should be kept close to fronts but they can be 1" taller with no problem. He says camber adjustment is no problem. ABS is my main concern but I have talked to other guys with various tire wheel combos who say it's not a problem. I guess I'll give it a try and see what happens. This seems like one of those questions where there is no clear concensus.

This seems like one of those questions where there is no clear concensus.

Yes You are right...