E46 Tyre Help please

[KH]

2001 3-series 330i SE Touring.

Currently running 45 profile tyres all round and I find the car quite bumpy over uneven road surfaces.

My question: can I go to a larger profile to make the ride a bit more comfortable? There is space in the arches. Has anyone done this? I notice that the model before this has 60 Profile tyres on smaller wheels.

Thanks! Kim

[soda]

Smaller wheels won't be an option with a 330, requires 17"s to clear the brakes.

SE should surely be comfortable enough though? Is the suspension possibly past its best, new dampers could see a big improvement. And check tyre pressures, maybe experiment a bit with them.

[KH]

Suspension should be okay as it's only 63,000 miles?

I reckon it's the low profile tyres that are the problem. Car is a family cruiser and I want it to feel more like a Lexus than a Golf GTi.
Upping the profile will definitely help but I'm not sure how far I can go.

[4rephill]

First thing is, are you on runflat tyres?, as these have a very stiff sidewall to resist deflation from punctures and can make the car very crashy on the UK's crppy roads.

Also, be aware that if you change the profile of your tyres, you have to alter the width accordingly to keep the aspect ratio correct, otherwise your speedometer will be miss reading.

[tgr]

If it's bouncy I would suspect shock absorbers - but cheaper is to experiment with tyre pressures at least to start with. After 60k and 10 years they won't be great

[KH]

I'm on Bridgestone Portenza, 225 x 40 x 17.
I've lowered the pressures by 5psi all round and it didn't make any difference. Should I go more?
The ride isn't bouncy, more crashy. When you hit uneven roads, you certainly know about it. Maybe the roads are just getting worse?

Edited by KH on Wednesday 15th June 22:12

[PJ S]

Bridgestones are a firm sidewalled tyre - 5psi is too much of a drop, assuming you were on recommended pressures front/rear.
Softer tyres like the Falken FK452, and moreso the Toyo T1-R will change things, but not necessarily all for the better.
You've an SE - reasonably softish, so what's likely is the bushes or the dampers (depends what sort of life they've had in the intervening years, not just mileage - motorways tend not to work them hard, but speed bumps will!) are past their prime, and the tyres are exacerbating it somewhat.

Get it up on a ramp, and have the bushes looked at, and check rear springs on the shocks too - known to break on the 330 Coupes & Saloons - but I doubt your symptoms point to that, more just while your there, you may as well.

Edited by PJ S on Thursday 16th June 10:10

[KH]

Many thanks, I'll do that.

[ghibbett]

4rephill said:

Also, be aware that if you change the profile of your tyres, you have to alter the width accordingly to keep the aspect ratio correct, otherwise your speedometer will be miss reading.

Not wishing to nit-pik, however surely the aspect ratio has nothing to do with speedometer readings. If the profile of the tyre is increased, whilst keeping the same rim, then the speedo will under-read irrespective of what tyre width you have?

[PJ S]

http://www.carbibles.com/tyre_bible_pg4.html

[Gaygle]

My Continental tyres made the ride so much better than when i had the Potenza's. Also look to make sure your bushes don't need changing - the ride improved quite a lot after i had the FCAB changed too.

[KH]

Thanks!

[4rephill]

ghibbett said:

Not wishing to nit-pik, however surely the aspect ratio has nothing to do with speedometer readings. If the profile of the tyre is increased, whilst keeping the same rim, then the speedo will under-read irrespective of what tyre width you have?

The aspect ratio most definitely does have something to do with the speedometer readings as it's the tyre wall height as a percentage of the width of the tyre, the two are interlinked!.



Try using the link provided by PJ S for some homework:

PJ S said:

http://www.carbibles.com/tyre_bible_pg4.html

In the Current wheel/tyre size try putting in: 245/40/17 and in the New wheel/tyre: 245/60/17 and see what the difference is when you click on the calculate boxes.

You'll find that your actual speed at an indicated 70mph on the speedometer is @ 80.93mph.

Now try it with the New wheel/tyre set to: 225/60/17.
When you re-do the calculation for an indicated 70 mph, the actual speed is @ 78.25mph.


Increasing just the aspect ratio of the tyre will cause the speedometer to under read because the tyres are physically bigger and therefore travel further for every wheel revolution.


When it comes to tyres, the width, diameter and aspect ratio are all related in order to keep the rolling radius of the wheel/tyre correct so that the speedometer reads accurately.

[ghibbett]

Yes fully understood, however I think I worded the first part of my post poorly. My understanding from the OP was that he was asking to increase the profile (I read: outer diameter) of the tyre with no mention of changing the width, i.e. increasing the overall height to give more of a cushioning effect. Most likely my just not understanding the OP fully.

[4rephill]

ghibbett said:

Yes fully understood, however I think I worded the first part of my post poorly. My understanding from the OP was that he was asking to increase the profile (I read: outer diameter) of the tyre with no mention of changing the width, i.e. increasing the overall height to give more of a cushioning effect. Most likely my just not understanding the OP fully.

That was My understanding as well but the OP needs to realise that you can't simply increase the aspect ratio and keep the same width and diameter as it will affect the speedometer reading due to the larger rolling radius.

(Sorry if it sounded like I was having a go at you BTW )