Tyre widths

[NAYLAD]

Hope I havent missed this in earlier posts.
Seems logical that wider tyres would help roadholding.
I have standard 17" wheels, whats max width possible, or would I have to change wheels to gain width?

[Gsi3.2]

you could stretch it to 235's.. but no wider on standard 17's...

we run 225's on the vec and siggy..

[m8internet]

Ironically, wider tyres don't always lead to better roadholding

Compare :
205/55R17
215/50R17
225/45R17

All three should fit the standard VX alloy wheels, and they all pretty much have the same surface area on the road
The 55 aspect tyre will have a more relaxed feel on general driving
The 45 aspect tyre will have a more firmer feel on general driving

As the aspect decreases the ride quality deteriorates, as does the risk of kerb and road surface damage

[nutron]

Depends on the width, most Vx 17" wheels are 7" width. The 235/45 R17 are not recomended but will fit fine and I've run that size in three different tyres with no fitment problems. The 235/50 R17 is recomended down to 6" width so you could go for them but they are larger and so would put your speedo out slightly (no more than 2&#37.

The wide the tyre, the more grip you will get but the more feed back you will get from the road. You will probably find torque steer increases, if you have some now. Also, if you go into the slow lane on the Motorway, the big ruts left by HGVs will make the car pull all over the place.

Another thing to think about is tyre pressure, you may have to increase the pressure slightly as you increase width to achive uniform wear (more rubber = more flex obviously).

And if you don't have mud flaps, expect stone chips on the side of the car.

[Duncan]

Compare :
205/55R17
215/50R17
225/45R17

All three should fit the standard VX alloy wheels, and they all pretty much have the same surface area on the road

How do you work that one out? The 225 width tyre will have more surface area (10% more) on the road than the 205 width tyre as it's a wider tyre by 20mm.

[m8internet]

That's just the way it is
With the 205/55R17 tyre the tread has greater flex
With the 225/45R17 tyre the tread has less flex

As a result they both have the same % ratio of road surface area, and as a result do not affect the speedo reading
If they did have then the speedo reading would also be affected
The air volume in the tyre would also be different and not only would you need to work out the ratio of tyre you needed but also the comparative speed rating, but as it is you don't

Take actual measurements of the surface area for all three tyres and compare

[Faz]

eg 225/45/17

The tyre width i.e. 225 refers to the width in mm. Therefore 20.5cm

The tyre height i.e. 45 refers to the height as an aspect ratio of the width. i.e. 45% of 225 = 101.25cm

This is why not all '45' height tyres are the same height, as it depends on the width.

[Duncan]

That's just the way it is
With the 205/55R17 tyre the tread has greater flex
With the 225/45R17 tyre the tread has less flex

As a result they both have the same % ratio of road surface area, and as a result do not affect the speedo reading
If they did have then the speedo reading would also be affected

I think you're getting mixed up here? The overall diameter and circumference of different width/profile combinations can indeed remain the same and not affect the speedo - but that's not what I was saying.

I was referring to the amount of surface area of rubber that met the road - that's what determines grip - and with a wider tyre it's a simple linear relation. The wider the tyre, the more rubber that is one the road. The profile has nothing to do with how much rubber meets the road.

D

[nutron]

It pains me to agree with Duncan.

[john_k_sri]

I was referring to the amount of surface area of rubber that met the road - that's what determines grip - and with a wider tyre it's a simple linear relation. The wider the tyre, the more rubber that is one the road. The profile has nothing to do with how much rubber meets the road.

D

Am I ignorant, but am I right in saying that if tyres are under-inflated, then more of the tyre than is advisable is in contact with the road, and if over-inflated is not the reverse true? Surely correct tyre pressures would affect/limit the amount of flexing in all types of tyre.


I am a simple soul and to change from 215/50 to 225/45 assuming that the profile is the percentage of the width, would simply mean an increase in ride height of 6.25 mm on the 215's, and that would affect the speedo reading slightly.

Please tell me if I am talking bull****. We are all here to learn.