Changing tyre size

[Biomecanoid]

Hello,

My car came with 175/65/R14 tyres can i go with bigger sidewall ? Like 185/65/R14.

As i understand things tyres are a part of the suspension so a bigger sidewall would give me a tiny bit more ground clearance and a softer more cushioned ride.

Is my assumption correct ? What more details would you need to make sure i can fit bigger tyres ? I have a 2006 Daihatsu Sirion

Thank you
 

[FROSTYBALLS]

Need to check the effect on the speedometer - it is illegal to show a speed less than the true speed. There are a number of sites where you can input the tyre sizes of the original tyres and the proposed tyres, and the effect on the speedometer reading is calculated for you 

[Stivino]

The 185 figure refers to the width of the tread.  The 65 refers the the percentage the sidewall is in regards to the tread width.

[Biomecanoid]

8 minutes ago, Stivino said:

The 185 figure refers to the width of the tread.  The 65 refers the the percentage the sidewall is in regards to the tread width.

I know so 185/65/R14 would be both taller and wider that 175/65/R14. So that's fine

[Stivino]

6 minutes ago, Biomecanoid said:

both taller and wider

Correct.

[Biomecanoid]

1 hour ago, FROSTYBALLS said:

Need to check the effect on the speedometer - it is illegal to show a speed less than the true speed. There are a number of sites where you can input the tyre sizes of the original tyres and the proposed tyres, and the effect on the speedometer reading is calculated for you.

I went for an MOT like 2-3 months ago and they DIDN'T check that. They checked the fluids, the brakes, emissions, lights, and inspected the underside of the vehicle. So pretty basic stuff.

But despite what MOT does i try to keep my cars in top condition even if they are not supercars.

So the conclusion is that nobody cares or tests if the speedometer is off. So its OK to go bigger on tyres. 

The question remains Is my assumption correct that more side wall will cushion the ride.?

[FROSTYBALLS]

I didn't imply that checking the speedometer reading was part of the MOT. 

Nonetheless, it is still illegal to have a speedometer that under-reads, and also it won't help you judge speed when approaching speed cameras, average speed cameras, etc, but it is your risk.

 

[Biomecanoid]

26 minutes ago, FROSTYBALLS said:

I didn't imply that checking the speedometer reading was part of the MOT. 

Nonetheless, it is still illegal to have a speedometer that under-reads, and also it won't help you judge speed when approaching speed cameras, average speed cameras, etc, but it is your risk.

The speedometer will be off by 1.7% which is negligible.  My question was more of a mechanical nature and not about legality which is just fine where i live.

[Stivino]

1 hour ago, Biomecanoid said:

The question remains Is my assumption correct that more side wall will cushion the ride.?

 I suppose that in theory, the answer will be yes.

But, I also suppose that tyres from different manufacturers will have different strength sidewalls.  So, the answer could be no.

🥴

 

 

 

[Catlover]

How much taller would a 185/65 be over a 175/65 ?      Is it worth the change?

[Stivino]

I make it 6.5 mm so nothing really as it’s only 3.25 more as it would be all the way round. I.e. measured at the top and the bottom as it were.  It’s only the difference between a new tyre and a worn tyre.

[Biomecanoid]

2 hours ago, Catlover said:

How much taller would a 185/65 be over a 175/65 ?      Is it worth the change?

Look here:

https://tiresize.com/tyre-size-calculator/

 

Size	Diameter	Width	Wheel
165/65R14	-2.6%569	165	14 x 4.5-6"
185/60R14	-1.3%577	185	14 x 5-6.5"
205/55R14	-0.4%582	205	14 x 5.5-7.5"
225/50R14	-0.4%582	225	14"
175/65R14	Equal584	175	14 x 5-6"
195/60R14	+0.9%589	195	14 x 5.5-7"
185/65R14	+2.2%597	185	14 x 5-6.5"
175/70R14	+2.6%599	175	14 x 4.5-6"
205/60R14	+3.0%602	205	14 x 5.5-7.5"

 

 

[Catlover]

If there is a13” wheel that fits your car, and a tyre that would give an approx same outside diameter, then you would have a deeper side wall and potentially more “suspension”.

[Biomecanoid]

3 minutes ago, Catlover said:

If there is a13” wheel that fits your car, and a tyre that would give an approx same outside diameter, then you would have a deeper side wall and potentially more “suspension”.

Yes you are absolutely right, but my wheels are just fine they don't need to be changed. On the other hand its about time to change my tyres so i am researching what are my options keeping my current original wheels.

[Catlover]

15 minutes ago, Biomecanoid said:

Yes you are absolutely right, but my wheels are just fine they don't need to be changed. On the other hand its about time to change my tyres so i am researching what are my options keeping my current original wheels.

Ah right, I thought your priority was for a softer ride.

[Biomecanoid]

25 minutes ago, Catlover said:

Ah right, I thought your priority was for a softer ride.

Yes i would like a softer ride but nothing wrong with my current wheels. If they were damaged i would change them with 13'' steel ones. So what are my options while keeping my existing wheels ?