Changing down alloy size instead of replacing?

[lesteph]

I've been told one of my C-MAX's 18 inch alloys is cracked, so I'm looking to replace it as getting it welded seems like a bit of a headache.

The ride has always felt a bit harsh (2008 diesel Titanium model), so I'm weighing up whether to replace the damaged wheel like-for-like with an 18" one and transfer the tyre, or try and improve the ride by switching down to whole new set of wheels, maybe 17" or 16". It's looking like the difference between about £200 and nearer £900 with the tyres but apart from the ride I really like the car.

Any views on how much I'd be likely to notice the difference in ride between 18" and 17" alloys, or whether it's worth going to (cheaper) 16" ones if I'm looking to soften the ride? Anything I need to bear in mind? Thanks in advance.

[jkh112]

What size tyres are fitted to the 18 inch wheels? If they are very low profile then it would make a difference, if they already have a decent sidewall then the gain will be less.
You will need to be careful of fitting smaller diameter over large brakes as well as the usual offset etc.

[B'stard Child]

jkh112 said:

What size tyres are fitted to the 18 inch wheels? If they are very low profile then it would make a difference, if they already have a decent sidewall then the gain will be less.
You will need to be careful of fitting smaller diameter over large brakes as well as the usual offset etc.

Good point not sure how big the brakes are on a C-Max but my money is on they will fit under a 16 steel

[lesteph]

They're not ultra low-profile - here's a pic http://postbureaucrat.com/bits/cmax.jpg

I was thinking of sticking to replacement alloys for a 2007-10 C-MAX anyway, so I'd hope that brakes etc would fit OK on 16 or 17 inch wheels?

[V8forweekends]

I've had mixed results - going from 19" with a 40% profile to 17" with a 55% improved grip, ride and fuel economy on my Jag.

Changing from 17" 45% to 16" 50% didn't help with the utterly appalling ride on my A3, in fact it made it bouncier without being significantly less harsh.

If I were you, I'd want to try an example of your car fitted with the "other" wheels before laying out - you might be disappointed.

[Matt UK]

I changed the 17s on my Mini Cooper S 15s with winter tyres.

The ride is so improved I've kept the 15s on all year round.

Unless you drive a touring car on race tracks, big wheels are a curse of the devil. Fact.

[Jaguar steve]

Google TRC Tyre Calculator. It'll automatically calculate rolling radius, speedo error and comfort rating for for your current tyre and wheel diameter compared to the proposed replacements.

[lesteph]

Jaguar steve said:

Google TRC Tyre Calculator. It'll automatically calculate rolling radius, speedo error and comfort rating for for your current tyre and wheel diameter compared to the proposed replacements.

That's great - thanks. Looks like a 'tyre suspension comfort' difference (out of 10) of 2.9 on the current 18" wheels to 6.5 on 16" - that sounds worth doing

[gizlaroc]

What tyres are you running?

That will make more of a difference.

I swapped the 17" wheels on my ML 235.65.17 Michelin Latitude Tours for 19" wheels running 235.55.19 Goodyear EfficientGrips and the comfort is the same.
I had Continentals on the 17's before and they were very hard and crashy, and also really noisy, the jump to the Michelins was impressive, the jump to the Goodyears on 19s even more so.


I have got Pirelli P7s on the X3 and they are a very comfy tyre, if anything a bit too soft, but very comfy.


Camskill list the noise and noise class ratings for each tyre, and generally anything in the 67/68db range with noise class 1 will also be comfortable, the two 99 times out of 100 go hand in hand.