Tire experiment, what if

[PandaBear]

I'm planning to drive this car only when it is not raining, and I have a dedicated rain day car (baby sitting my friend's car for a year, he paid for insurance under my name). So wet traction is not an issue.

The front is on matching pair of H rated tire at 5/32 (Bridgestone HP50). The car is a FWD Honda, local commute or once in a while highway commute only, driven conservatively (around speed limit).

I plan to ask my local gas station to replace my rear, bald tires (1/32, 195 60 14) with not so bald tires of non matching sizes (3/32, 195 60 14 and 5/32, 175 65 14). Why gas station? Because a real tire shop wouldn't touch any tire with less than 5/32 left. The diameter of the 2 size based on my calculation should be the same:

195 * 60% = 117 + (3/32 * 25.4) = 119.38
175 * 65% = 113.75 + (5/32 * 25.4) = 117.72

Since it is on a non driving wheel, the 1.5mm difference shouldn't matter in diameter. What I'm concerned about, is the traction difference during braking. The 175 is a T rated tire (no name brand that I took off from my inlaw's junk car) and the 195 is an H rated tire (Dunlop SP A2).

Will moderate braking on a FWD car cause the car to pull to one side under dry condition? I figure it should be significantly better than running on donut spare for sure, but what about slightly different width (175 vs 195) and different traction type (H vs T)?

I've done something similar to a Corolla once, by putting the same wider/more traction tire on only 1 of the rear, and it seems to work fine for me other than making the car feels heavier.

 

[AuthorEditor]

Why?

 

[oilboy123]

I did a used tire kind of a thing many many years ago and won't do it again. All I can say is good luck. It can get nasty with rain at times out of nowhere just about anywhere.

I try to run pretty decent tread on all vehicles. Hydroplaning can get really scary and I like to have pretty decent tread for that reason. The tire contact to the road is one of the most critical things involving a car.

 

[PandaBear]

Originally Posted By: AuthorEditor
Why?


1) To not waste natural resources (the 2 less bald tires)
2) So I can replace all 4 tires at once when the front wear out
3) Curiosity

 

[IndyIan]

With the 2 decent tires on the front, I doubt you could tell which side the small tire was on, for even maximum braking on the street. Maybe you could tell on a skid pad but on cars like a stock corolla the rears are really not doing much. Either braking or turning, the fronts are doing atleast 2/3 of the work.
I bet the car will tend to want to wander one way on the freeway but nothing scary.
If you ever lend the car to someone I would just get a used tire of the right size at least.

 

[d00df00d]

1. That difference in diameter might affect ABS. Does this Honda have it?

2. Speed ratings (H vs. T) are about the construction of the tire, not traction. A higher speed rating means the tire will hold together at a higher speed. The narrower tire will have less traction because it is narrower, not because it's T-rated.

3. Your front wheels will be doing almost all of the work under braking. I don't think the traction difference between the rear tires will make the car hugely unsafe.

4. That said, don't cheap out on tires. They are important. Do it right.

 

[PandaBear]

1) No ABS

2) It is not just the speed rating, but tire design with traction AA temperature A vs traction A temperature B

4) It won't be cheap out, consider I can get a good tire for my size for only $60 and I'd need to mount tires sooner than later with the experimental setup. I'm just doing it to satisfy my OCD and curiosity.


I won't lend the car to anyone, and I won't drive it in the rain.

 

[d00df00d]

Alright then. Enjoy.

 

[HTSS_TR]

"I'm planning to drive this car only when it is not raining". It's okay for dry roads as long as you don't drive very aggressive, keep a good distance from the car on front. As you already knew, compact spare is much smaller than full size and can be driven up to 50 MPH.

 

[CivicFan]

OP, please don't endanger your life for the sake of curiosity and experimentation. Either get good tires or don't drive the car at all.

 

[IndyIan]

Keep in mind that his corolla will still out handle most SUV's even with a mismatched set of tires...

 

[berniedd]

Hmmm, it's better to take an actual circumference measurement with a tape measure than rely on mathematical computations based on claimed tire diameter. If it's within 4 mm of each other,I wouldn't worry about it. Heck, my 4WD Honda is allowed a 2.5% mismatch/difference in tire sizes.

 

[crinkles]

will you pass y our state's registration inspections? I doubt i'd be able to register a car with odd size tyres in new south wales.

 

[CapriRacer]

PapaBear,

I hope your realize that the narrower tire also has less load carrying capacity. That increases the risk of a load related tire failure, which sometimes has tragic results.

But what originally came with your Honda? On every vehicle sold in the US - and I understand this is a worldwide practice as well - there is a sticker – commonly called the tire placard - that lists the original tire size and the proper pressure for that size. The placard is usually located on a doorpost or in the glove box – but sometimes it is located in the trunk or on the fuel filler door.

BTW, it doesn't matter who makes the tire or what pressure is listed on the tire's sidewall, if the tire size is the same as the placard, then the pressure listed on placard is also appropriate.

Also, how old are your tires? Recent bulletins from the tire industry indicate that tires degrade simply due to time. The age of a tire is important even if the tire is unused. There some disagreement over how to best express this age limitation, but my take is:

If you live in a hot climate (AZ, CA, NV, TX, and FL) then the limit is six years. If you live in a cold climate (MN, ND, WI, MT, etc), then the limit is 10 years. States in between are ..... ah ........ in between.

Here's how to tell how old the tires are:

First locate the letters "DOT" on the sidewall of the tire. Nearby will be the DOT code. DOT codes are 10 to 12 digits long. BTW the digits can be numbers or letters.

The first 2 digits are a code for the manufacturing plant.

The next 2 digits are a code for the tire size.

The next 3 or 4 digits are a code for the type of tire.

The last 3 or 4 digits are the date code. The format is week/week/year/year or week/week/year. These are always numbers.

Starting in the year 2000, the date coding used was 4 digits. That means the largest number you should see for the year is 10. Before 1999 the format was 3 digits. 1999 and 2000 are transition years, so you will find both 3 and 4 digits.

The date code only has to be on one side – and it is permissible for there to be a partial DOT code, so long as one side has the complete code.

 

[mrsilv04]

You know... anyone can play any type of "tire russian roulette" that they want. Who really cares, right?

It's not until they lose control for some reason and hit another vehicle or a pedestrian, that it becomes a problem.

Get it now?

Drive safely...

 

[onion]

Yeah Panda, you will surely die and burn in [censored] if you dare try something unconventional around here.

Seriously though, it will probably be a non-issue. The rear tires of a fwd car just don't do a whole lot. Until quite recently, I had odd-sized tires on the rear of my nasty old '94 Corsica. Had a 17-year-old 185/70/14 snow tire with no apparent brand name on one side, and a 195/65/14 Bridgestone Potenza on the other side. Had these tires on the rear of the car for roughly 7 years and 60,000 miles- driven daily in all kinds of weather. Not a single problem to report... until the snow tire grew a lump just the other day.

I put these tires on the car back around 2003-ish... I was broke at the time and just needed to keep the car rolling... had several mismatched used tires available. I originally put these two tires on the front- their calculated diameter is within 1%. THAT was a mistake- the car was all over the road at highway speed... bad idea. So I switched them to the back. And they worked so well that even years later when I could afford a decent set of tires, I just saw no reason to replace them. For about a year there, I had a complete set of four mismatched tires on the car (the front two were the same size and type, though... a goodyear and a michelin). Never caused a problem.

Sure, it's not ideal. It can under some circumstances compromise handling and/or braking. It certainly won't get the BITOG stamp of approval. But even with mismatched tires, a small car will still stop and handle better than dozens of trucks, vans, SUV's, and assorted beaters that you pass every day. Personally, I have more immediate problems to worry about.

I have 5 used tires left in the garage that I need to wear out on the ol' Corsica (two pairs and that oddball Bridgestone). By the time I wear out these tires and any leftovers from the wife's Lumina... it'll probably be time to get rid of the Corsica. If that car could talk, it'd say something along the lines of "For the love of gawd- just let me die!"

 

[d00df00d]

Originally Posted By: onion
Yeah Panda, you will surely die and burn in [censored] if you dare try something unconventional around here.

Did you bother to read the responses in this thread?

 

[HTSS_TR]

Originally Posted By: crinkles
will you pass y our state's registration inspections? I doubt i'd be able to register a car with odd size tyres in new south wales.

California doesn't care about safety equipments, the only test every other year is smog.

 

[PandaBear]

There's no safety inspection here mainly because there's no snow in the major population area. The original size of this vehicle is 195 60 14, which 3 of the 4 tires are sized at, the remaining one is a 175 65 14.

Prior experience of a very similar rear setup on a corolla (stock 175 65 14 but with 195 60 14 / 175 65 14 pair on the rear) doesn't make a difference to handling other than fuel economy (slightly lower), not even pulling, not even in the rain.

I personally found that camber wear (nearing 1/32) on front tires (especially worn outer edge on the front tires) make the car most dangerous, much more so than mismatched rear tires that still has thread.

The second most dangerous handling problem I've found is actually low quality tires (like low rolling resistance OEM tires) and pads (like the $15 after rebate Monroe pads).

I'm probably one of the safest driver in my age and gender group, and I'm probably more aware of tire condition than 99.999% of the people out there (I check on a daily basis). Having to throw out tire into the landfill before they are bald makes me feel irritated (OCD), that's the whole purposes about wearing out the old tires before getting new one.

Those tires are 3 and 5 years old, spent 1 year sitting in my garage wrapped in plastic bags.

 

[HTSS_TR]

Originally Posted By: PandaBear
Having to throw out tire into the landfill before they are bald makes me feel irritated (OCD), that's the whole purposes about wearing out the old tires before getting new one.

Me too. Since we don't have any rain in summer from May until November in So Cal, I had bald tires on all my cars during summer months. How bald it was ? Less than 1/64" on the outsides and no tread left on the center. The performance/handling of the bald tires is actually better than full tread on dry roads. But I changed those bald tires out late October before any chance of rain in early November.