Comfort wheels and tyres

[Greny]

After a horrible skiing accident last year I can finally start riding my car (sportsback from 2015 , standard suspension with 18" wheels and Hankook tyres) again since 2 months . Before I found the car a bit harsh but ok. But now my back hurts in it. My doctor says it's going to stay like that. Luckily in daily live , I'm fine.

In my van my back doesn't hurt. Was thinking of getting a pair of 17 " wheels with Michelin Primacy 4 (I heard very comfortable).

But on 17 wheels what is highest I can fit 225/55/17 ? or only 225/50 ?

Anyone knows ?

[Magnet]

Hello Koen,

Sorry to hear of your skiing accident. I’m sure there is room for inprovement in the ride quality of the car by fitting smaller wheels and then increasing the profile of the tyre to give you more cushioning between the wheel and the road. 

In order to help us to give you more helpful advice, could you let us know the size of the tyre fitted to your standard 18 inch wheel.

Once we have that, it should be possible to calculate the maximum profile tyre you can fit on 17 inch wheels, since the theory is that the outside diameter of the wheel and tyre together must be the same as your current 18 inch wheels and tyres. 

Congratulations on your good English. 

Kind regards,

Gareth. 

[Greny]

Hi Gareth,

 

Ty for the kind reply.

The car is now on 245/40/18.

Regards

Koen

[Magnet]

Hello Koen,

Thanks for the additional information. 

If you now have 245/40/18 then the depth of the rubber on these will be 40% of 245mm which equals 98mm. 

I notice you are now considering a narrower 225 tyre and is so, the depth of rubber will be as follows:- 

50 profile gives you 112.5 mm (an extra 14.5 mm). 55 profile would give you closer to 124 mm ( an extra 26 mm) .

My maths points me to your current 18 inch wheels with 40 profile tyres having an outside diameter of just over 653 mm. 

To retain that outside diameter using 17 inch wheels, and using 225 tyres you would need to use 50 profile tyres which would result in an outside dia. of just under 657mm , which is close enough to your current 18in wheels with 40 profile. 

Worth bothering to buy new wheels and tyres for just another 14mm of rubber?? 

Of course, Koen, the suspension set up will remain the same, and I’m not sure what the end result of changing the wheels and tyres would be - you may not notice much difference. 

Other things to consider is whether the car currently has run-flat tyres fitted - if so, these are going to give you a harder ride. Also if it is perhaps fitted with ‘extra load’  XL tyres - which again are less flexible. 

Not sure how much of this will be of practical help.

Kind regards,

Gareth.

[Greny]

Ty again Gareth

It's an extra load tyre , just had a look.

I did my maths wrong . I thought 17 " wheel is 2.5 cm smaller then an 18 inch wheel , so I could at the 25 mm to the height. Add the 25 mm to the 40 mm tyre of the 18"inch wheel.

So a 225/65/17 wheel /tyre combo .

Pity I'm wrong...

[Dan3222]

Not trying to throw a spanner in the works here but if 225/65/17 are available for the same speed rating as the ones you currently have fitted, which I doubt, are you aware they are designed for SUVs? This would change the whole dynamics of the car and I believe not in a good way.

I wonder if anyone close enough to you from the forum had a spare set of 17’s with tyres that they could lend you for a week. To see if the ride does feel different.

If you should go down this route could I suggest 225/50R 17’s, there would not be a massive difference in overall diameter in fairness and you might see a small change in comfort, how much I am not sure. I strongly recommend sticking with XL’s though, low profile tyres need them!

I guess in fairness if the local councils actually sorted the pot holes ur back would cope better anyway.

To other members on here, what size tyres do you have on your 17’s. this info could be helpful for this chap.

 

hope that helps?

[Magnet]

I’m with you on anything like a 65 profile tyre Dan, and in an ideal world, the opportunity to try the 17in wheels with 50 profile before committing would be great, since I too wonder what the overall benefit may be. 

Only thing I would perhaps query would be the need for XL tyres if using 50 profile, since I wouldn’t have thought that 50 would be considered low profile. 

Kind regards,

Gareth. 

[Dan3222]

Hi Magnet, it’s because of the power and size of the A5. Not the smallest of car. But maybe your right.  (My English is terrible once again)

Let’s hope some people post on here what they have currently. Might be interesting to see.

[Dan3222]

One more thing I should have said. If any car goes down slightly in size or tyre circumference you will notice that at 60mph you will actually be going a little slower in real time. You can check this with a Sat Navthat gives current speed readings.

E.g, when I take the 18’s of the T5 and put the winters on, 16’s, the Sat nav says I am going 61 when the speedo says 65. With the 18’s the Satan’s says 64mph. Something to be aware of.

As for the OP, maybe changing the A5 for a Q5 might actually provide the ride comfort he requires!?!

[Magnet]

Hello Dan,

’......going down in wheel or tyre circumference ....’ and effect on speed indication. That’s why I overworked my brain! - with the maths, to ensure that the overall outside diameter remains as close as possible to the original specification wheel and tyre set up. 

Re. extra load (XL) tyres, my initial interpretation of the need for these was for estate cars etc. where weight carrying may be a regular occurrence. I could be wrong. 

Kind regards,

Gareth.

[Greny]

can pick up this weekend for cheap a pair of 17 with 225/50 on them.

I keep you posted , thx again 🙂

[Greny]

Got a second option .

Near me are 2 options

4 wheels Audi 245/45/17 Or

4 wheels Audi 225/50/17

both priced at 450€

Which is most comfortable , don't care about performance :)

 

[Magnet]

Hello Koen, 

You are talking a theoretical difference of less than 3mm of rubber between the two different tyres (assuming they are new and not part worn - which you don’t tell us). Nothing in it then, but I would  again point out the consideration of XL tyres and harsher rides, or indeed the possibility of them being even run-flat, which do not have comport in mind.

Please respect Dann’s comments on the overall dia. of wheel and tyre and the effect on speed indication. It’s the end of a hard day for me, so I’ll leave it to you to do the maths, although I think I had previously worked it out for one of the tyre sizes. 

Kind regards,

Gareth.

[Dan3222]

Hi Greny, 

What did you go for?

You have very little to loose whichever you get because if the ride feels little different then you can always sell on the wheels easily enough. TBH, I doubt it will make much difference as it’s the suspension that is most responsible for how the car feels on the road. Hence my suggestion for changing to a Q5 perhaps!?!

I would be tempted to go for the 225 tyres as there is more wall height to help in your quest for comfort. The less width than the 245’s also means less stress on the steering of the car. Particularly at low speed parking etc.

Woukd be very interesting to see if you feel the difference in ride comfort. Be useful for others in the future too.

Final comment is I am surprised not one forum member posted their 17” tyre size!! A shame because that’s what these forums should be about.

Best of luck

[Greny]

tried an a5 at the garage , with 17" , very small difference.

A Q5 is a great car but I don't like the looks of it , not just a q5 , more SUV's in general.

going for a test drive of an a6 Allroad later this week :)