going from 18' wth 40's to 17' with 45's will it make a difference

flyaway

Hi guys on a drive to nite with changes to the car (see other post about a mfsw)

I have 18' mcv2's on the car with 40 tyres,
If I move to same alloys in a 17 with 45 tryes will it make much of a difference comfort wise on reasonable to bad roads?

.Longshanks.

Not a whole lot, but you'll notice it. Road noise might slighly reduce but depends on how wide the tyres are in the first place. Cats eyes in the centre of the road (or potholes etc) will still he felt but not as bad.
Oh & the car might feel a tiny bit quicker!

bazz26

You can check the difference here and the effects it will have on your speedo reading:

http://www.miata.net/garage/tirecalc.html

Anan1

It depends on the width of the tyres, the 40 and 45 figures are the sidewall height as a percentage of the tyre width.

.Longshanks.

Yeah the 17" tyre with a 45% profile will have a taller side wall than an 18" with 40% profile so there will be more rubber between the wheel and road so should be more comfortable but it totally depends on the thickness of the tyre in the first place.
If sized correctly the speedometer should still be correct (they are always over calibrated a tiny bit anyways).

Anan1

The sidewall needs to be taller by 1" to compensate for the reduction in rim size, so comfort should definitely be improved. The car isn't an E90 on RFTs by any chance, is it?

robbie99

Anan1 wrote: »

The sidewall needs to be taller by 1" to compensate for the reduction in rim size,

1/2" would be more correct. Wheel sizes are diameter rather than radius

flyaway

Thanks for all the help so far
should have said it is an e46 320 (standard suspension)
at the moment have
225 40 18

am thinking of moving to

225 45 17 (provided can find same alloys in a 17)

AM I reading from the responses so far that it is unlikely to make much difference confort wise?

Anan1

robbie99 wrote: »

1/2" would be more correct. Wheel sizes are diameter rather than radius

You're dead right, silly me!

mickdw

I think it will make a huge difference. 40 profile tyres are a disaster on country road. 45 profile is a fair bit better(keeping the same width). You are gaining 11.25mm of tyre (radius) or overall in relation to diameter, you are gaining 22.5mm tyre & dropping 25mm due to rim reduction so overall rolling diameter is only changing by less than 3mm which is fine is relation to speedo etc

Big Nasty

Will definitely be a smoother ride - end of!

flyaway

Anyone know of anywhere do would do a trade on d old alloys for a new set?

Esel

You could try posting an ad on our sister site, adverts.ie This would probably be the best category Motor Parts / Accessories FS.

vectra

1999 I put a set of 17's on My car.
running 205/40/17's
What a horrible drive it turned out to be

My current car has 205/45/16's
Brings back memories.
No comfort zone at all except for motorway driving.

Anan1

Anan1 wrote: »

It depends on the width of the tyres, the 40 and 45 figures are the sidewall height as a percentage of the tyre width.

That is the most informative thing i've read on boards in weeks..

So a tyre size is made out of inches, milimetres and percentages. Mad.

vectra

Deleted User wrote: »

So a tyre size is made out of inches, milimetres and percentages. Mad.

Nope.
Just Milimeters

225 40 18
am thinking of moving to

225 45 17


225mm wide
40% high = 90mm sidewall

225 wide
45% high =101.25 sidewall.

Difference of approx 10mm .

Esel

^ The tyre size does include an imperial measurement, though....

vectra

esel wrote: »

^ The tyre size does include an imperial measurement, though....

Yes,
But it has nothing to do with profiles etc.

Victor_M

vectra wrote: »

Yes,
But it has nothing to do with profiles etc.

vectra wrote: »

225 40 18

But it's a necessary piece of information required to determine the correct tyre so he is correct it's a mm, % and imperial measurement required to specifically identify a tyre. It's fairly mental all right.

vectra

Victor_M wrote: »

But it's a necessary piece of information required to determine the correct tyre so he is correct it's a mm, % and imperial measurement required to specifically identify a tyre. It's fairly mental all right.

Wheel size in inches has nothing to do with sidewall height which is what give ride comfort or lack of.

Victor_M

vectra wrote: »

Wheel size in inches has nothing to do with sidewall height which is what give ride comfort or lack of.

Understood, but Ads by Google commented on a tyre size being made up for MM, Inches and %'s which is correct. To purchase a new tyre for your car you need to provide the size, diameter in Inches, the width in MM and the tyre wall in % or width, so all 3 values are required.