Queries re increasing alloy wheel size

baz003

Hey,

I have got Focus with 205/55 R16 alloys on at present and was thinking of upgrading to set of ST 205/50 R17 replicas. I know that 205/50 R17 was extra option when buying car.

My question is will upgrading to 17s affect the handling, comfort, fuel economy, braking - ABS, ESP, etc in your opinion/experience?

I presume one doesn't have to recalibrate the speedo as change in circumference is minimal or what slight increase in circumference is acceptable. If slight difference in the circumference - does this meaning you are going faster or slower than speedo. Where can you get calibration done if needed?

Also has any one advised their insurer before re the above and what did they say or charge?

Many thanks for your help - sorry about all the questions.

mickdw

If the size you plan to get were a factory option, then there are no issues.
You might lose a small bit of comfort and gain a degree of handling sharpness but no issues.

Be careful to ensure that the wheel offset is correct for your car. This offset dictates how far the wheel sits inward/outward.

Nonoperational

The issue wouldn't be the size but the potentially poor quality and heavy replicas. They can be quite inferior to genuine alloys so be careful.

coylemj

The change in geometry will be minimal so no need to worry about recalibrating your speedo.

Your existing tyres (205/55 R16) have a circumference of 1,985 mm. The proposed replacements (205/50 R17) have a circumference of 2,001 mm which is an increase of less than 1% so I wouldn't worry about the speedo.

However since you specifically asked about the change in circumference and the effect on the indicated speed...... if you've previously calibrated your speedo with a GPS, the new tyres will involve fewer rotations for the same distance travelled so the indicated speed (on the speedo) will drop by 0.78%. Assuming your speedo was deadly accurate before, it will indicate 128 kph when you're actually doing 129 kph, that's the point where the difference on the speedo will be exactly 1 kph because of the new tyres so I wouldn't worry too much about it.

Disclaimer for the pedants: I am not encouraging the OP to break the speed limit.

If you're travelling over lots of city streets you may notice more bumps from the ruts the cable companies and the folks from the waterworks leave behind thanks to the lower profile tyres but you will gain a bit of handling just like mickdw said.

Anan1

My car came from the factory on 215/55 R17, it's currently on 215/60 R16 winters. It's noticeably more comfortable on the smaller wheels, to the point where i'm considering replacing the factory 17"s with a set of lightweight 16"s for summer use. Turn-in is a little softer, but the extra compliance lets me go faster over rough surfaces and the car feels happier overall.

mm_surf

mickdw wrote: »

gain a degree of handling sharpness

Just a quick Q (and for Coylemj too)

Why do you think there will be a handling improvement?

Bigger wheels are heavier, and unsprung weight is (usually, rule of thumb) thought to be 4 times worse than sprung weight, i.e. adding 10kg to the wheels is like adding 40kg to the chassis.

Contact patch size remains the same (assuming same tyre pressure)

Bigger wheels means bigger torque to turn them (assuming wieght is primarily at the rim, rather than around the centre?

Nissan doctor

You would get more grip(if using equivalent tyres) with the larger/wider wheels due to less flex in the sidewall of the tyres but the weight of the wheel would determine any handling improvement.

Genuine lighter alloys would improve the handling, heavier replica's would reduce the handling......but neither by an amount that most people would ever notice.

Lower profile tyres would reduce the comfort over bumps but the focus factory size(205/50) is far from the lowest out there so shouldn't be too bad.

Keep in mind also that replica wheels tend to be very easily damaged by poor road surfaces.

mm_surf

Nissan doctor wrote: »

You would get more grip(if using equivalent tyres) with the larger/wider wheels due to less flex in the sidewall of the tyres but the weight of the wheel would determine any handling improvement.

Genuine lighter alloys would improve the handling, heavier replica's would reduce the handling......but neither by an amount that most people would ever notice.

Lower profile tyres would reduce the comfort over bumps but the focus factory size(205/50) is far from the lowest out there so shouldn't be too bad.

Keep in mind also that replica wheels tend to be very easily damaged by poor road surfaces.

But the tyre contact size is the same regardless of the wheel size.
Car weight is unchanged, tyre pressure is unchanged. Therefore, contact patch size is the same. It's counter intuitive, I know - but that's physics.

For any wheels, assuming the same brand, I'd expect the bigger wheel to weigh more - hence affecting unsprung weight. Cheap alloys can be very heavy, as you say.

Alloys Vs. steelies - less weight, better handing.

I've never found sidewall stiffness to have anywhere near as big an affect as wheel weight though.

Nissan doctor

mm_surf wrote: »

But the tyre contact size is the same regardless of the wheel size.
Car weight is unchanged, tyre pressure is unchanged. Therefore, contact patch size is the same. It's counter intuitive, I know - but that's physics.

For any wheels, assuming the same brand, I'd expect the bigger wheel to weigh more - hence affecting unsprung weight. Cheap alloys can be very heavy, as you say.

Alloys Vs. steelies - less weight, better handing.

I've never found sidewall stiffness to have anywhere near as big an affect as wheel weight though.

The same contact patch yes, but a lower profile tyres will have less flex, keeping the contact patch level on the road.

The lower profile tyres give better grip, not handling....two very different things.

mm_surf

Ahhh, gotcha. My bad.

DieselPower

I had a set of them st replica wheels on a focus before, two front ones cracked on a back road, welded them and put them on the back of the car. Tyre centre said that theyre made from poor metal with imperfections hence the weakness. However the improvement in looks was well worth the hassle.

mm_surf

mm_surf wrote: »

........ but that's physics..............

Physics would consider the profile :pac:

Pulsating Star

Would the profile have to change though? Say if there is ample space and the larger wheels are primarily to enhance the aesthetics re arch gap?

Anan1

Pulsating Star wrote: »

Would the profile have to change though? Say if there is ample space and the larger wheels are primarily to enhance the aesthetics re arch gap?

If you increase the overall diameter of the wheel/tyre by much then you'll make sh1t of the car's gearing, not to mention handling.

tossy

mm_surf wrote: »

tyre pressure is unchanged..

Tyre pressure would need to be changed as you change the size and lower the profile of the tyres.

Nothing wrong or necessarily bad about going down the route of larger wheels.A lot of people in this country do it wrong i.e heavy replica wheels and budget tyres and then complain about how sh!t it was and try to frighten people of it.