Tire Help

[phuk]

Hi guys,

I'm a noob so I need some help.

I have a 2003 P5 and stock tires on there are 195/50/R16. I have a set of winter tires from an '04 camry that is 205/60/R15. Now I called up mazda and they use 195/65/R15 for their winter tires. I am wondering if the 205/60/R15 will fit.

If i compare the 205/60/R15 to what mazda uses for their winter tires (195/65/R15), the difference is in height, the ones mazda uses (25" height) are 0.3" taller than the 205's (24.7") so I can assume that the height wont be an issue (correct me if I'm wrong). My concern is the width. the stock tires and snow tires mazda uses for the car is 195mm but their heights vary. My 205's are right in between with height but wider of a tire. My thoughts are 10mm difference is only 5mm per side and I figure mazda wouldn't have that small of a tolerance. The only way I dont see them fitting is if the wheel well tapers significantly as the height raises.

Any thoughts from anyone? anyone who has tried to put on 205/60/R15 or any 205's that are relatively tall for that matter?

Any help would be great.
thanks in advance

[dwpeek]

You should be fine.

[Tom03es]

I had a set of 205/60/15 snow tires on my car last year. They were Semperit Sport Grips. I had no issues on my Protege ES. I know the P5 has slightly different fitment issues, but I think you'll be fine.

[phuk]

I was told of possible transmission damage from a local goodyear shop. Can anyone educate me on this or is he just trying to sell me new tires?

Please keep the advice coming, I'm wondering if anyone has tried this with their p5. thanks so far guys!

[YelPro03]

I was told of possible transmission damage from a local goodyear shop. Can anyone educate me on this or is he just trying to sell me new tires?

Please keep the advice coming, I'm wondering if anyone has tried this with their p5. thanks so far guys!
The guy at the goodyear shop is full of it. My wife is driving on 205-40/17 tires in the summer and there's no rubbing issues of any kind. Mind you her Protege 5 is at stock height (not lowered).

[Tom03es]

I was told of possible transmission damage from a local goodyear shop. Can anyone educate me on this or is he just trying to sell me new tires?

Please keep the advice coming, I'm wondering if anyone has tried this with their p5. thanks so far guys!

The only reason why I could think someone would say such a thing is that if you had 2 drastically different sized tires on the right and left sides of the car at the same time. Some transmissions don't like to be spun at different speeds and can cause the differential to give out (Saturn S-series are known for a weak $.15 roll pin to shear in the differential when one tire is spun more than the other- like during a burn out). But if you have 2 of the same sized tires on the front, the transmission is happy. It doesn't really care what size the tires are, just as long as they are the same. Your speedometer/odometer might be off slightly if the tires have a different outside diameter than what the ECU is calibrated for, but other than that, no issues.

I have some 195/50/15 winter tires on my car right now and a set of 215/45/17 summer tires in the basement. I think there is something like 4-5% difference in overall diameter between the 2 sets. Oh well.

[CTt3P5]

Plugged the stock tire size and the tire size you want to go with into http://www.1010tires.com calculator and came up with this:

Speedometer Difference: - Speedometer Difference: 4.271% too slow
Diameter Difference: - Diameter Difference: 4.1%

According to them, anything over 3% difference you are risking 'brake failure'. Not sure how true that may be....maybe Josh could help out there?

[Tom03es]

That brake failure warning is interesting. My only guess as to why they say that is a larger diameter tire also has a higher rotating inertia and therefore is harder to change its velocity (accelerate/brake). But if a 4% change in tire diameter is enough to overwhelm your car's braking system then your car is a POS. While Protege brakes are small, they are big enough to handle the a small change like this.

I would say that 1010tires.com puts that warning on there as a CYA (cover your ass) for that one instance for when someone tries to come back and sue them for something.

[CTt3P5]

Gotcha. Makes sense in our litigious society. One issue I can foresee is possible rubbing in the rear due to the hatch not having as much room back there like the sedan does.

[antiblazed]

DONT USE the 205 60 15, i got on now 205 55 15 and the overhang (buldge) out the side of the tire rubs on the wheel well now could also be because i havent changed my stock Springs but alas they do feel nice on the ride till i hit a large Philly dip or CAVE HOLE (you know how philly is) Like road Frogger


anyways hope you get your sizes good befo the winter Hits

[MazdaSpeeder]

[quote=phuk;3546949]I was told of possible transmission damage from a local goodyear shop. Can anyone educate me on this or is he just trying to sell me new tires?
[quote]

What a moron (smash)...they'll say anything to get you to buy their crappy, overpriced tires, pay for repairs you don't need or just to try and look like they are smarter than they are. When buying tires I have saved the last two times buying online...tirerack.com, onlinetires.com, discountiredirect.com. Even after installation, it's still cheaper!

As far as % too fast or slow, I am running 215/40/16s on stockers, and 1010tires says that I have a 3.81% diameter difference from stock...no "brake failure" yet, just lots of really fun grip!

[JoshP5]

That brake failure warning is due to the additional torque on the brakes, not rotational inertia.

Torque is proportional to radius, so larger radius tire = more torque on the brakes.

In any event the 4% difference won't mean much especially in winter when there's far less traction available anyway.

For winter tires, you should stick with stock-size or slightly narrower, wider won't help.

[Tom03es]

That brake failure warning is due to the additional torque on the brakes, not rotational inertia.

Torque is proportional to radius, so larger radius tire = more torque on the brakes.

The funny thing is that you just contradicted yourself. Larger diameter tires carry with them higher inertia which puts additional torque on the brakes when the brakes are applied- thus changing that higher rotational inertia.

[The Short Bus]

The funny thing is that you just contradicted yourself. Larger diameter tires carry with them higher inertia which puts additional torque on the brakes when the brakes are applied- thus changing that higher rotational inertia.

Agreed, but the tiny amount of added rotational inertia pales in comparison to the inertia of the entire car, which makes itself known to the brakes via torque, which is now measurably increased.

[JoshP5]

Hey Tom, you have been on my ass for a while now, I think it's time you gave it a rest. I'm not on here to instigate drama or stroke my ego. I know a few things and I do my best to support the Mazda enthusiast community by proliferating factual information.


My only guess as to why they say that is a larger diameter tire also has a higher rotating inertia and therefore is harder to change its velocity (accelerate/brake).

That brake failure warning is due to the additional torque on the brakes, not rotational inertia.

The funny thing is that you just contradicted yourself.
No contradiction--the effect of increased torque is far larger than the nominal increase in rotational intertial of the larger diameter (and maybe slightly heavier) tires. That's a fact. You're a mechanical engineer, do the math. The reason for the warning is the increased torque, as I indicated.

You're obviously a well-educated guy, I respect that. But I don't respect your hostile responses when I challenge your comments. It's ok to disagree and discuss these issues. No need to get defensive. :)

[Tom03es]

Hey Tom, you have been on my ass for a while now, I think it's time you gave it a rest.

I'm going to continue to drop some science on you (and everyone else)anyway. You actually agreed with me without knowing it too.

We all know (or should anyway) the equation Force=mass*acceleration which is good for straight line motion. However, for rotating systems, that same equation can be expressed:

torque=Inertia*angular acceleration

And since both torque and inertia are in the numerator on each side of the equation, that makes them directly dependant on each other--> if you increase one the other one also increases if you hold angular acceleration constant.

And BTW, I never got defensive.............

[JoshP5]

Are you claiming that when you hit the brakes, the majority of the work is done reducing the speed of the rotating wheels?

Dude, that is insignificant compared to the work done reducing the linear momentum of the whole car. Get it?

That ME degree doesn't make you right. Apparently it just makes you arrogant.

[Tom03es]

My response was directed at the 1010tires.com warning for 3%+ oversized tires.

But thanks for your input Josh. Valued as always.

[JoshP5]

Likewise, a pleasure.

[slave600]

not that i'm an engineer.... but i kinda am. a common response from my rim shop buddies is as follows.
"i have bigger rims/tires on my car." which yeilds " how much more do they weigh than OEM?"

maybe the reason Goodyear claimed brake failure is the illogical leap to larger rims/ tires= greater weight!!!! alot of ppl think that brakes will fail under these conditions. i've seen failure happen but not over the slight weight difference in wheels and rims! i repeat "i've never seen failure from rims/tires alone!"
i have seen failure from a combination of this and towing a boat... behind an suv w/ dubs on it!
and by the way, my ford ranger has 22" on it and has a 14% difference but i NEVER tow w/ it... and i've never had any issues even w/ the rear drums!
the dr.

[tonybonekhang]

Isn't rotational inertia pretty much the same as torque?

[P5inder]

Try this -

http://www.miata.net/garage/tirecalc.html

According to this, the tire you're planning on putting on your car (205/60/15) is actually smaller than the "OEM" size tire that Mazda recommends for winter.

Your speed will be different though. You'll be traveling at 59.3 MPH while your speed will read 60 MPH.

Not an issue...

[JoshP5]

Isn't rotational inertia pretty much the same as torque?
Nope.
Rotational inertia is an object's resistance to change its rotational speed (aka angular velocity).
Torque is the amount of work required to rotate an object.

[YelPro03]

Are you claiming that when you hit the brakes, the majority of the work is done reducing the speed of the rotating wheels?

Dude, that is insignificant compared to the work done reducing the linear momentum of the whole car. Get it?

That ME degree doesn't make you right. Apparently it just makes you arrogant.

Just out of curiosity how do you reduce the linear momentum of the whole car? I’m also a Mechanical Engineer and the only way I can figure is the linear momentum of the whole car is transferred to the wheels when you’re trying to reduce its speed… unless you crash into something. So if the brakes aren't doing most of the work in slowing or stopping a car then what is?

[Tom03es]

OK, I'm going to come clean. Josh was right about both- me liking to yank his chain and about the larger tire issue creating more torque (but the inertia of the larger tire also plays a part- a small one at that). I'll see if I can explain it better since Josh hasn't.

Torque is a force applied at some distance (hence the unit ft-lbs).

The weight of the car (or you can think of it as inertia) is carried into the wheels at the hubs. And then the reacting force to slow/accelerate the car is done at the contact patch of the tire. If you increase the distance from the hub to the contact patch by going to a larger outside diameter tire you create more torque at the hub (bad for your CV joints/transmission for accelerating and bad for your brakes for braking). But honestly, I think 1010tires.com is just saying that about the brake failure to cover their ass "just in case".

[JoshP5]

^Well said. (group)

Since force = rate of change of momentum, in this case it may help to think of it as

torque = rate of change of momentum imparted at some distance.

[tonybonekhang]

Nope.
Rotational inertia is an object's resistance to change its rotational speed (aka angular velocity).
Torque is the amount of work required to rotate an object.

What I meant is that in this application the rotational inertia increases the torque resulting in demand for more power from the brakes. So the argument over whether it was increased to either over the other was invalid.