Correct Tyre Profile Affects?

PJB

Hi

Just called my tyre dealer (as in the rubber bits on the wheels, tyre is not a new legal high! That i'm aware of anyway!).

I have 205/40/17's on the alloys that were on the car when I bought it. I wanted higher profile replacements and asked his advice and he said his advice is always the same, put the same as were originally on there as the car is tuned etc to that size, by going to a lower profile (I wanted a higher profile) you are making the engine work harder and may adversely affect your fuel economy as well as your engine etc long term.

On reflection this does seem to make sense but I am a novice when it comes to things like this, anyone know whether he's correct or not?

thanks in advance

s_b

tyre man covering his buttocks
he fits larger profile you have an accident attributed to tyres he get in trouble
of course a higher profile could jam on full lock /roll conditions affect stability control abs etc as well as nulling your insurance if not advised
if you want to keep your fillings flog the car

marlot

Car manufacturers have an obsession with low profile wheels which look great but are pretty useless in everyday life.

If you want a tyre with a taller sidewall, look in the handbook to see if your car was available with 16" wheels, and look to swap your 17" for 16" - perhaps advertising on an owners club forum for your make.

If you go to size not specified by the manufacturer you can have problems with insurance.

Nearly_Old

Similar questions crop up fairly frequently on car forums - usually with people wanting to reduce the size of the tyre!

Going from your current 205x40x17 to 205x45x16 makes very little difference to the rolling circumference: -0.82% so there would be no issues with the speedometer reading.

The 205x40x17 has a tyre height of 82mm (40% of 205)
The 205x45x16 has a tyre height of 92.25mm so a gain of 10mm

If it was an option fitting 225x40x17 would increase the tyre height by 8mm and only affects the rolling circumference by 2.69%

s_b

Nearly_Old wrote: »

Similar questions crop up fairly frequently on car forums - usually with people wanting to reduce the size of the tyre!

Going from your current 205x40x17 to 205x45x16 makes very little difference to the rolling circumference: -0.82% so there would be no issues with the speedometer reading.

The 205x40x17 has a tyre height of 82mm (40% of 205)
The 205x45x16 has a tyre height of 92.25mm so a gain of 10mm

If it was an option fitting 225x40x17 would increase the tyre height by 8mm and only affects the rolling circumference by 2.69%

some cars you cant get a fag paper in between the strut cup and the tyre so that 10mm could lock it all up
saw a pewgot 806 last week the spring had broke and what a beauty it was,you want the tyre as far away from that spring as you can get because it had slid down the cup just waiting to spear the tyre

forgotmyname

Fitting a higher profile to the standard width means the tyre will be taller.

It may foul on full lock or when the suspension is on full bump/rebound.

If you fit a higher profile you should go down a rim size. Instead of 17's fit a 16" wheel. etc.

Obviously covering the brakes etc maybe a problem with smaller wheels and your insurance will need to be informed.

Nearly_Old

s_b wrote: »

Quote:
Originally Posted by Nearly Old
Similar questions crop up fairly frequently on car forums - usually with people wanting to reduce the size of the tyre!

Going from your current 205x40x17 to 205x45x16 makes very little difference to the rolling circumference: -0.82% so there would be no issues with the speedometer reading.

The 205x40x17 has a tyre height of 82mm (40% of 205)
The 205x45x16 has a tyre height of 92.25mm so a gain of 10mm

If it was an option fitting 225x40x17 would increase the tyre height by 8mm and only affects the rolling circumference by 2.69%


some cars you cant get a fag paper in between the strut cup and the tyre so that 10mm could lock it all up
saw a pewgot 806 last week the spring had broke and what a beauty it was,you want the tyre as far away from that spring as you can get because it had slid down the cup just waiting to spear the tyre

There is an increase in the height of the tyre sidewall by 10mm not the width so as the tyre is still 205 and assuming that wheels with the correct offset are used then the clearance to the spring does not change. The overall diameter (that determines the rolling circumference) needs to be kept as close as possible to the original to avoid introducing unacceptable errors in the speedometer reading.

In effect: bigger wheel / smaller sidewall height = harsher ride but probably better roadholding and smaller wheel / higher sidewall height = more comfortable ride but can compromise the handling. The wheels on our Z3 and Z4 have the same offsets and between us we've got sets of 16", 17" and 18" wheels. However the 16" won't fit the Z4 as they don't clear the brake calipers which is a shame as we were going to use these as winter wheels. There is a very marked difference in handling on the Z3 between the 16" wheels (you can feel the higher sidewall lurch over when cornering) and the 17" and 18" wheels. All other clearances are identical between any of the sets.