tire size change, effect on engine/transmission

[ahoier]

If I plus size accordingly, I won't be "taxing" my automatic transmission or engine will I?

Really considering going a tad bigger, likely "plus-zero" only, since I don't think I'm quite ready ($$$) to change out my stock rims (they aren't bent yet lol)....

right now I got 185/70R14 on it....if my calculations are right, I should be able to go with 195/65-14 195/70-14 or 215/60-14 (which are likely out of the question....have a feeling those may stick out too far...plus, many searches found "truck" type tires....and this is a passenger car

For "kicks and giggles" I put those sizes into 1001tires calculator and here's what they said:

Click to reveal..



(hidden, since the chart didn't copy right...

But basically, the speedometer readings are within ~1mph of each other...60.5 mph,58.6 mph ,60.0 mph,61.3 mph accordingly.

How will it affects the transmission/engine/revs though? Or none at all?

 

[dparm]

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


Well, it is affecting the transmission/engine/revs. It's miniscule, as you said. For trucks that move up to very big tires (or some cars, I suppose), it would generate additional heat in the transaxle.

 

[IndyIan]

From your tire size, I assume you've got an older car? 4spd auto? Any tire within a couple mph at 60, you won't notice much or hurt the car. You might get slightly better or worse mileage but nothing major.
I don't run tires any bigger than stock but I run smaller diameter tires all the time and they just add a bit of acceleration and a 100 or 200 rpm at 60mph. The car couldn't care less. I'd run bigger too say up to 10% difference without worrying about it.

 

[mechtech2]

No tranny problems should ensue.
But the speedometer and odometer may be off.
Also consider how much tread is on the tires - used large tires will be smaller than new small tires.
http://www.1010tires.com/TireSizeCalculator.asp?action=submit

 

[ARCOgraphite]

You need the actual tyre circumference to run the calc. Tyre sizes are all over the place manufacturer to manufacturer. I went from a 65 to a 50 aspect on my old Suzuki Aerio SX and couldnt believe what a diff it made in effective final drive ratio. Phunny that the actual tyre (FALKEN) measured more like a 40 aspect.

 

[ahoier]

Originally Posted By: IndyIan
From your tire size, I assume you've got an older car? 4spd auto?
Yep, it's an 88 Dodge Aries, with the 3 speed, A413 transmission.

Originally Posted By: mechtech2
No tranny problems should ensue.
But the speedometer and odometer may be off.
Also consider how much tread is on the tires - used large tires will be smaller than new small tires.
http://www.1010tires.com/TireSizeCalculator.asp?action=submit
Yep, that's the calculator I used actually. I did compare the readings with that of miata.net, but found the 1010tires calculator a bit more "user friendly" and if say, you go wayyy out of range, it'll give you a huge warning, that you could create braking problems, etc...but yea, the readings hidden behind the spoiler tags are from 1010 tires, they just don't put the chart in a copy-paste friendly manner

Originally Posted By: ARCOgraphite
You need the actual tyre circumference to run the calc. Tyre sizes are all over the place manufacturer to manufacturer. I went from a 65 to a 50 aspect on my old Suzuki Aerio SX and couldnt believe what a diff it made in effective final drive ratio. Phunny that the actual tyre (FALKEN) measured more like a 40 aspect.
Good point, and yes, I've heard of stories about that, comparing exact same size tires, side by side, say; in a tire shop show room, and there be "noticeable" differences

Guess it's similar to that of clothing, one size from one manufacturer may not fit the same way from another manufacturer

But yea, the readout from miata.net is basically the same:
Code:


Specification Sidewall Radius Diameter Circumference Revs/Mile Difference

185/70-14 5.1in 12.1in 24.2in 76.0in 834 0.0%

195/65-14 5.0in 12.0in 24.0in 75.3in 841 -0.9%

195/70-14 5.4in 12.4in 24.7in 77.7in 815 2.3%

215/60-14 5.1in 12.1in 24.2in 75.9in 835 -0.2%

175/70-14 4.8in 11.8in 23.6in 74.3in 853 -2.3%



My guess, all the "plus size calculators" adapted from miata.net's formulation anyways

 

[JHZR2]

My 318i had 195/65R-14 tires on it. There werent any good options so I put 195/60R-14 tires on it. No noticable difference in any way. Speedo is slightly off, but they all are compared to GPS (which is off in and of itself, so who knows what is correct).

Make sureyour weight rating is OK.

 

[Sonic]

From the tires you have listed the only one that is actually a smidge taller than what you have now is the 195-70-14. The rest are shorter which I don't think you'd want. I changed out the stock size tires on my Subaru (215-60-16) for a 215-65-16 and it made absolutely no difference that I can tell. Whatever the speedo is at is exactly what the GPS is reading with either size tire (on my car anyway). Going up a size (15-20mm in height) really isn't enough to make a real difference. I think the only way to actually see a diff would be to add a few inches in tire height. I went up a size on my car cuz the stock tires looked small and I also thought that maybe it would run less rpm's cruising the highway. It winds pretty good at 70mph+. Honestly though, I can't tell if it helped but it does look better with a bigger tire.

 

[ueberooo]

Sonic, how much of an effect on handling did you notice, going to the higher profile 65 tire??

By going to the larger diameter tire (3.2%) you'll likely somewhat improve your highway mpg (remember to adjust your trip odometer mileage by 3.2% when calculating the mpg).

As for the OP, I think he will get noticeably better handling by going from the 70 profile tire to the 195 65 tire; though at the cost of maybe up to half a percent loss in highway mpg's because the engine revs 0.84% higher, and you will be cruising at a slightly more restricted throttle than the optimal nearly wide open throttle.

I went from a tall profile tire 75 to a squatter 60 profile and had a very noticeable improvement in the handling. it was something like 195 75 r14 to a 205 60 r15 if i remember right. (I think the fuel economy may have dropped though due to the wider width and different tire brand, but it's still too early to tell, esp with the winter switch in fuel.)

 

[01rangerxl]

In my experience, the effect is very small, practically unnoticeable.

1995 Explorer 4.0 4x4 4-speed automatic...went from 235/75R15s (29") to 31x10.50s. It was slightly slower with the larger tires, but still drove perfectly good. I tested the speedometer against a handheld GPS unit and it was actually dead on after the tire change. No regrets about upsizing.

2002 Ranger 3.0 2WD 5-speed automatic...went from 225/70R15s (27") to 235/75R15s (29"). Really no noticeable difference in performance. The truck accelerates and drives pretty much as it did before. I actually feel the larger tires are a more appropriate size for the truck than the small stock tires. I have had a ScanGauge in the truck for years and the engine and trans temps did not change at all with the larger tires. I didn't do the GPS test with this truck, but when the cops put up those roadside speed displays it always matches the speedometer pretty closely. It doesn't seem like it's off at all.