A question for anyone who knows stuff about tyres
 

Hi all.


Today i went to buy new tyres, and for some reason the pirelli 175/75R14 tyres that were ordered in didnt eventuate, and the mechanic fitted four 185/75R14 tyres instead.

my car is an old one (13 years old), and my question is, will this have any adverse effect on the vehicle? or should i just be happy that i got tyres that are $20 more expensive for the same price?

Basically, you got tires that are slightly wider, while the profile is similar at 75.

It's difficult to comment without knowing the car, but older cars are finiky in such matters.

Your new tires, owing to greater contact patch, will provide greater amount of grip, although this will not be noticable. Rolling resistance will also increase slightly, and fuel consumption could also increase, marginally, but I don't think that's gonna be observable in olden carz.

If the tires are too wide, they affect the handling. Car may tramline at certain speeds. The 75 profile will ensure you have a plush ride. My carz have 60 oe lower, sporty, but harsh. Better load index as well. Good choice overall. If the dealer was remotely competent, he wouldn't fit a wrong size. Oh well, enjoy.

Those tyres are also a larger diameter, your speedo will be reading wrong, although not by much.

That was the wrong way to upsize the tyres. Idiot dealer, methinks.

Well, techincally, wheel well clearance could also be an issue.

175/75R14

Let's break this down a bit, shall we?

175 = The tire tread. This is how much tire is in contact with the road, and in this case it is 175 mm.

75 = The "Profile" of the tire. As you know a profile in any case is a side view. So when looking at the tire from the side you would measure the amount of rubber that you see. 75 mm.

R = Radial

14 = Diameter of the entire tire from the side.

No more false claims please?

wheel, not tire

This is the most clusterfucked explanation of tire size I've ever heard! LOL.

Just make sure your tires don't rub the wheel well when you turn and hit bumps.

It will not affect your speedomoter reading, it will not do any damage other than hitting your fender or wheel well.

BAAAHAHAHAAAAA LMFAO

yes bones, in the magical land of America where Colour becomes color, connexion becomes connection, and organise becomes organize.

some people spell stuff differently in other parts of the world =)

oh, and thanks everyone... i've checked, and there seems to be plenty of clearance.

Your speedometor is calibrated by a cable that connects to your transmission, so unless you got a new transmission, don't worry about the speedo ;)

If the dealer put them on your car and somethings wrong, i'm sure you can just take them back. Those tyres (tires where i'm from :P) should fit with your car with no problems. If something feels funky, go to the dealer. I seriously doubt it will eat your gas mileage. It would do that if the tire was taller, not wider. If it downed it at all, it'd be an insignifigant notice. Good luck sir.

Not even remotely close. The "75" in this case refers to the sidewall height as a percentage of the tread width. In this case, the 175 is the tread width in millimeters, the 75 is the height of the sidewall as a percentage of 175, and the 14 is the wheel diameter in inches.

And, Newman, this tire is taller. It's wider as well. The height hasn't changed much, but a little. His speedo will read about 1.5mph slow at 60mph. In other words, 60mph = 61.5mph.

Idiots - the speedo will effectively be reading wrong with bigger tyres.

The speedo calibration is based on the circumference of the tyres - bigger tyres go further for each revolution.

Therefore, with a slightly bigger tyre (say 5% bigger), with the speedo registering 50 mph, you'll actually be doing 52.5 mph. Which isn't a big difference, but I know that some of the police forces (farces?) in the UK will nail you for speeding with that sort of difference .... and possibly do you for driving with a car thats dangerous/not legal/something else.

DEI37 - thanks about the 75 being the percentage, I was 99% certain of that.

"Your speedometor is calibrated by a cable that connects to your transmission, so unless you got a new transmission, don't worry about the speedo "

whoops. not correct. Well, the speedo does run off the tranny, but the tranny rotates faster or slower depending on the total diameter of the drive wheels. So if you make the wheels bigger or smaller than stock, you need to recal your speedo.


Actually, the main problem with these tires, and the reason I'd march 'em right back to the dealer, is that they will throw your odometer off. Not overly much, but if you ever sell it you'll have to mark down that you know the odo reading is inaccurate.

The speedo will be wrong IF the tire is any taller than you stock tires and your gas mileage will probly be hurt if the tire weighs more than your stock tire, but jumping from a 175 to a 185 you won't have any issues on your gas mileage.

75 = The "Profile" of the tire. As you know a profile in any case is a side view. So when looking at the tire from the side you would measure the amount of rubber that you see. 75 mm.

uhm... as far as I understand, 75 is the relation between tirewidth and tire height. So 75 means the sidewalls are 75% the height of the tires width...
Feel free to correct me if I'm wrong.

I feel like we are in the ghetto

Tires not Tyers !

185/75R14 tyres, WHEEL RIM DIAMETER IS 14INCH.WIDTH OF TYRE IS 185. PROFILE IS 75% OF THE 185 WIDTH. EASY! WILL CHANGE SPEEDO ACCURACY, WILL CHANGE TOTAL DIAMETER OF TYRE. OH AND I LIKE THE ONE ABOUT THE SPEEDO CABLE CALIBRATING THE SPEEDO. IF YOU ARE THAT WORRIED YOU COULD PROBABLY BUY A SPEEDO GEAR WITH A DIFFERENT RATIO TO OVERCOME THE INACCURACY.

This thread is sooooo funny!!! lmfao!!!

Guys, just for future reference, there is a website that I found when I was dealing with switching rim size and tire sizes.

Check out the Tire & Wheel Calculator

As far as the 2 tires in question, @ 60 mph (96.54 kph) according to your speedometer will actually be 61.42 (98.83 kph)

If you don't like my answer, do the research yourself. This information is as accurate as I could find on the net (Verified by my mechanic also).

Funny this thread came along right now. I just put 225's on my car, it had 215's on before, and it says 215 on the VIN sticker; I was told this isn't a problem; is it? 1989 Pontiac Bonneville SSE.

0001 - the important thing is the overall diameter of the tire. For example, my car came with 185/75R14 and I now have 215/45R17. The two sets are very close in overall diameter. My speedo is 1.2% to fast. You could easily have 225 tires on a car that came with 215's as long as the aspect ratio changes accordingly. This tire chooser works really good if you're not sure.