Tyre Size Question

[MikeKey]

Hi there,

I've just bought a nice set of second hand Mille Miglia HT3s and want to buy some new tyres for them as the ones on the original 17x7 sport wheels are coming to the end of their useful life.

The standard tyres specified by Mitsi are 215/45/17, but quite a few people here seem to recommend a 225/45/17.

If I understand right, if you go for a narrower tyre, (with an appropriate profile to maintain the rolling radius, etc), the tyre will be more stable in corners as it's stretched across the rim and doesn't deform so much.

I would assume, based on that, that going for a 225 instead of a 215 tyre would make the car a bit sloppier in the corners because of this.

My question, then, is this: Is the advantage of physically having more rubber on the road (a wider tyre) better than having a more stable tyre (a narrower tyre)?

Anyone??

Cheers!

Mike

[Nick Mann]

I think you also need to factor in to account the width of the wheel. How wide are the HT3s?

225 is around the maximum acceptable width for a 7" wide wheel, but is really a bit too narrow for a 8" wide wheel. I once saw a table explaining how to best calculate tyre width on wheel width, but I'm blowed if I can find it now!

[bradc]

A 225 wide tyre will fit fine onto an 8" wheel. It will be very slightly stretched, but it isn't much of a problem at all.

I know of a member in NZ running 225's on 8.5" wide wheels, and I'm running 235's on 9.5" wide wheels.

225 may be a bit too wide for a 7" wheel, I'm not actually too sure. I'm running 215/45/17 on my ST-R at the moment on 7" wheels and they go straight up like | | rather than stretched / \ or a bit too wide which would be \ / in saying that though, 225 wide is only 5mm per side wider than 215mm wide tyres, I doubt there could actually be that much difference!

[CANDEE]

Ive had 225's on both sets of my 8" wide rims and they are only a little bit stretched on them and i find that my car slides easier with them... /pan Most people put 225's on 7" wide so you should be fine. :)

There is an article on MMC.org.nz that explains the wider tyres vs narrower tyres and the contact patch is exactly the same. The narrower tyre is deeper, and visa versa for the wider tyre... If that makes sense. :)

[MikeKey]

How wide are the HT3s?

They're 7" wide.

I found the article mentioned by CANDEE on mmc.org.nz and, by chance, the original on Car Bibles which can be found here: http://www.carbibles.com/tyre_bible_pg2.html

As CANDEE says, increasing the tyre width from a 215 to a 225 will do nothing to alter the amount of rubber in contact with the road, i.e., grip, it simply alters the shape of the contact patch.

From the article: "A rim that is too narrow in relation to the tyre width will allow the tyre to distort excessively sideways under fast cornering. On the other hand, unduly wide rims on an ordinary car tend to give rather a harsh ride because the sidewalls have not got enough curvature to make them flex over bumps and potholes."

There are some really good calculators on there which I've used to work out the following:

Tyre ~~~ Ideal Rim width ~~~ Change in rolling radius from stock 215/45
205/45 ~~~ 6.86" (7.0") ~~~ -1.44%
205/50 ~~~ 5.65" (5.5") ~~~ +1.84%
215/45 ~~~ 7.19" (7.0") ~~~ +0.00%
215/50 ~~~ 5.93" (6.0") ~~~ +3.44%
225/45 ~~~ 7.53" (7.5") ~~~ +1.44%
225/50 ~~~ 6.20" (6.0") ~~~ +5.04%

With all that in mind, I think I'll go for 205/45s.

First, there's very little difference in rolling radius. Second, ride quality won't suffer as, if anything, I'm increasing the sidewall height by a tiny amount. Third, I'm changing from a slight \ / to a slight / \ which has to reduce cornering deformation to at least some degree.

225/50s throw the rolling radius out too much, and 225/45s are just needlessly wide and will only give me more corner deformation.

Sound reasonable? I see there are other people who run 205/45s, does anyone have any comments on the difference in feel/performance if you've tried other sizes too?

Thanks for all your help guys, cheers!

Mike

[MikeKey]

Here's a short story about the wheels I bought, while I'm here...

My dad saw a notice at work about a guy wanting to sell some Mille Miglia wheels for £200 that would fit a Galant so he passed it on to me.

Went round in my dad's motor to take a look and, after chatting for a while, he asked about the reg number and it turned out he was the previous owner!

The wheels had only been on the car for a couple of months when he was grudgingly forced to sell it, at which point he swapped the wheels back for the old ones and left the new ones in his garage.

Anyway, because they were going back to their rightful place and they were only taking up space in his garage, he gave them to me for £100 instead!

Result :afro:

[Nick Mann]

I can't argue with your logic except for one detail. 205/45 will have a smaller sidewall than 215/45. The 45 profile is a percentage of the width of the tyre.

It always makes me laugh - the three dimension measurements on most tyres are inches, millimeters and percentage!

[MikeKey]

I can't argue with your logic except for one detail. 205/45 will have a smaller sidewall than 215/45. The 45 profile is a percentage of the width of the tyre.

Ah hah! Well spotted that man! The 1.44% reduction in rolling radius should probably have clued me into that /pan

Oh well, it was late... :inquisiti

Right, I'm off to mytyres.co.uk to see what they have. I'm torn between the Toyo Proxes T1-Rs, Falken ZE 512s and Federal SS-595s. Reckon it'll be the Proxes but we'll see!

Thanks all for the advice :)

[valmes]

Just a short note - stock tire size on Galant/Legnum is 205/55/R16 and 225/50/R16

[bradc]

I put up a little excel calculator if anyone wants to type away at it.

[MikeKey]

Just a short note - stock tire size on Galant/Legnum is 205/55/R16 and 225/50/R16

That depends very much on the Galant/Legnum in question! ;)

[valmes]

That depends very much on the Galant/Legnum in question! ;)

How? Never heard of any Galant/Legnums with 17's from the Factory...

[Rambaud]

How? Never heard of any Galant/Legnums with 17's from the Factory...

But stock on my GDI is 15" - either 205 x 60 x 15 or 195 x 60 x 15, although one of them must be a mistake.

[bradc]

some even came with 14's. Some UK spec cars came with 17x7 wheels with 215/45/17 tyres standard.

[White Lightning]

I am running 225/45/17 tyres on 17x7" wheels ... I have not noticed any issues with handling that I would relate to tyre deformation.

[Johnny_Cashed]

yeah the UK elegance/sport galants came with the 17" 215/45/R17 tyre fitment

[bradc]

Wayne - interesting, can you please take some pics of the wheels showing the sidewall and whether it looks like this ( at the bottom or / or |


Thanks!

[Beastlee]

Sorry to bring this back up but I'm interested on the 225/45/17 being too wide for an 8.0 x 17" rim. I am looking at some Dotz Shurikens and can only get them in a 5x114.3 ET36 8.0x17" fitment so I was looking to go for the 225/45/17 tyre as they are a common size and therefore better value for money.
Is there likely to be issues for me using the above combination?

[bradc]

EVO's come with 235/45/17 tyres on 17x8" wheels, so you don't need to worry about 225 being too wide.

Our production class race cars over here run 225/45/17 semi slicks on the stock 17x8" wheels, and they seem to do ok

[CANDEE]

As brad says you will be fine :) I think my sliding issue on the leggie was due to crap tyres... /rally

[Beastlee]

Thanks guys, now all I need now is to make a final decision on the new F1 Assymetrcal or Vredestein Ultrac Sessantas in XL 94Y guise. Both are going to set me back about £70 delivered each.

[CANDEE]

Thats not a bad price Lee :) Thats the quivelent price for my old crap 17" tyres were..

[ANTHONY]

so whats the best size on an evo 7 wheel?

[bradc]

225/45/17 is closest to the stock radius on our cars, but 235/45/17 gives you a little more tread and is the stock size for evo's

[ANTHONY]

225/45/17 is closest to the stock radius on our cars, but 235/45/17 gives you a little more tread and is the stock size for evo's will it affect the speedo

[bradc]

225/45/17 is the same as stock, so it will be the same as your current stock setup, which is about 97kmh actual when 100kmh is showing on the speedo. 235/45/17 is slightly bigger, so will be around 99kmh actual when at 100kmh on the speedo.

[ANTHONY]

cheers brad:happy: