Different Tire Sizes

[mello555]

Hi All,

I have a March k-12 which i purchased 3 months back. Its front tires are Bridgestone 165-60-R14 and rear tires are Chinese with sizes of 175-70-R14.

My question is:

Will having this different tire sizes affect badly to car structure?...eg: transmission, front suspension.

I have not come up with any transmission or engine issue so far and car does about 13.5 km per litre.

Pls comment..

[MrCat]

The difference in tire sizes should not effect anything mechanical. It`s just that your rear tires are 10mm wider and 10mm taller than the front ones, that's all.

[heavyD]

It may affect the ABS system. Different tyre speeds and all that.

[terrabytetango]

Not to be a stick in the mud, but the tire profile size calculation is slightly more complicated than that. It's actually a percentage of the tire width, so in this case the difference in the mentioned sidewall heights would be (175*.70)-(165*.60)=122.5-99=23mm in diameter. Ideally, his rears should be 175/55 14 to more or less maintain the same overall sidewall height. But other than that, yeah what everyone else said. If anything, you'll be blessed with better rear end grip and passenger comfort.

Edited November 22, 2011 by terrabytetango

[CARBON B4]

Have a look at this , it will show how different it is. Just run with it for now but in the next replacement just put the same tyres. Preferably the smaller ones as my guess if that seems the original tyre

http://www.kouki.co.uk/utilities/visual-tyre-size-calculator

[mello555]

I have a doubt as car's rear end is a little bit higher than the front which is against the original engineering of the car. This will lead to weight shift to the front with the car tilted to front. As the weight shift to front, won't this add extra weight and stress to frontal area(parts)?

Will this affect the "center of gravity" of the car?

Pls correct me if I'm wrong. I'm not an engineering guru. Just trying to apply my understanding here.

[mello555]

.

Edited November 22, 2011 by mello555

[terrabytetango]

No shift in weight, only the ride height is different. Therefore, no change in COG either.

[Sifaan]

  On 11/22/2011 at 11:52 AM, terrabytetango said:

No shift in weight, only the ride height is different. Therefore, no change in COG either.

center of gravity is a point. it won't change (except insignificant amount because the tyre mass is different) but because the car is slightly tilted forward the weight will appear to act at a point slightly forward of usual. as to whether this makes a real-world difference or not, sorry, I have no clue!however, manufacturers chose particular tyre sizes for some very valid reasons, and it's probably better to stick with it; so it would make sense to go back to the original size when next changing tyres

[mello555]

I found following articles related to above from below links:

1)

http://www.turnfast.com/tech_handling/handling_weightxfr

  Quote

The "Roll Center" is the line through which the vehicle rolls. It is not necessarily parallel to the ground. Weight distribution, and roll coupling distribution can create a roll point at the front of the car which is lower to the ground that the roll point of the rear of the car. This creates a sloped line. The angle of this line has influence on how much weight is transferred, and where it goes.

http://www.miracerros.com/mustang/t_rollcenter.htm

2)

http://www.icrewchief.com/CrewChief101/02_Aerodynamics_and_Ride_Heights.htm

  Quote

The ride height of you car affects two things, weight transfer and aerodynamics. For the best mechanical grip, you want your car as low as possible, to get the center of gravity down low. For best aerodynamics, you want to get the front of the car as low as possible. This prevents air from going under the car, creating a vacuum that actually sucks the car to the ground, creating downforce.

3)

Weight transfer formula

http://www.hipermath.com/cars/front_tire_diameter

[CARBON B4]

Thanks for sharing Melo555,

Its a good article, from whats mentioned wrt the ride hight its actually better if the rear is slightly raised than the front. Therefore having slightly bigger ( taller) tyres at the back maybe ok. At least good till his next tyre change.

But I think in the case of a AWD car this should be avoided.

[slcamel]

Guys, yesterday I have replaced my tyres from a reputed direct inport agent and got to know from them that most of the tyre importers will be increase their prises by 15% to 20% at the end of this month due to the $ rates. Just wanted to keep you guys posted the info.

Better to check with your tyre shop soon....