Technical Tyre Questions...

[Sponge Bob]

Apologies if this has been covered - I've had a little search on the forum / net and need some advice regarding the technicalities of different tyres...

How do you determine which width tyre will go on your alloy? Is it simply a matter of test

I appreciate that a wider tyre will have more contact with the road surface, therefore it will be grippier, but how does the tyre wall size alter the logistics of the vehicle? Does it just make everything more stable by having less distance between the road and the solid alloy?

Also, is it best to get the largest size (circumference way) tyre possible, but without having too larger tyre wall size (I presume large tyre walls would be pretty weak on hard cornering)

Also how do the front and rear size of overall wheel change things? Is it best for them to be the same, or are large rear wheels better for certain things... I see that drag vehicles have huge rear tyres and tiny front ones?

Cheers people!!

[John]

Tyre outside diameter has to be about the same as standard to keep speedometer accurate. It can be recalibrated mind you if you really want something big.

Width fitting - always seems a bit random to me TBH, if someone has a good answer to that I'd be interested as well.

A wider tyre doesn't have a bigger contact patch unless you reduce your tyre pressure - the size of the contact patch is entirely down to tyre pressure. However a wider tyre will have a wider and shorter contact patch.

Being wider allows the dynamic loading to remain within the tyre's contact patch when going around a corner, which keeps the whole of the tyre width in contact with the road. If the dynamic load goes outside the tyre width then the inside of the tyre will lift and the tyre will roll over onto its sidewall. In practice the tyre would lose grip before this happens. All of which means a wider tyre will let you go around corners quicker (in the dry at least!).

Bigger tyres at the back gives more grip at the back, so if the car has a tendency to oversteer then putting wider back tyres will help to cancel this out.

The shorter sidewall reduces its flexibility, which will allow a more efficient transfer of lateral loading (from cornering forces) to & from the road to the wheel.

[Driftin_AW]

if you want a bit of reading, have a look at the article from racecar engineering I posted here:
http://twobrutal.co.uk/showthread.php?t=1231

:)

[djdna2000]

Look at Malcolm's interesting article if you want to work it out, if that makes your head hurt then have a look on the Toyo site as it lists all suitable rim sizes for every tyre they make :)

[Sponge Bob]

Nice one!! Cheers guys... just have to wait another week till I get paid now... bah

So what size tyres would go on a 15" J6 or is it 6J wheel... and what is the standard Mk1 tyre/alloy size? Is it 14" with 195/55 tyre??

[Sooty]

On the mk3 fronts (6" wide), I have 195/50/15. About as wide as is recommended.

Standard mk1 tyre is 185/55/14.

[Sponge Bob]

So if an alloy could cope with, say 205 for example - would you have to compensate for the tire width seen as it's a percentage ratio and go 205/50/15 for example - or 210/45/15 etc etc

[djdna2000]

Yes, but instead of guessing have a look at www.toyo.co.uk and it will tell you.

[dread]

have a gander at this 2http://www.dragtimes.com/1994-Toyota-MR2-Tires-225-50R15-t9773.html

[adamh]

heh sponge.. check out this link for tyre sizing, you can match the exact rolling radius of origonal etc etc.. using different size alloys, it then gives you the correct aspect ratio and tells you if there is any error on the speedo.

mk1 is 185/60/14 !

http://www.twobrutal.co.uk/showthread.php?t=285

[Sponge Bob]

have a gander at this 2http://www.dragtimes.com/1994-Toyota-MR2-Tires-225-50R15-t9773.html

Tis a 1994 Mk2 in the above link mate...!! and unfortunately that website doesn't seem to cover the Mk1... cheers anyway though

[Driftin_AW]

for tyre width vs rim width, generally the range of tyre widths can be found by:
minimum: rim width (in inches) * 25 = tyre width (in mm)
ie 8" * 25 = 200mm (or realistically 205)
maximum: rim width * 30 = tyre width
ie 8" * 30 = 240mm (or realistically 245)

now that's a pretty generalised rule of thumb, you can go outside those ranges, and also the profile size partially dictates the amount of flexibility you have, ie a shorter sidewall wont stretch as easily as a tall one.

[Sponge Bob]

Awesome - cheers for the help..!! I'll see what I can cram on the rear wheels then.

So would there be a benefit in deliberately putting smaller width tyres on the front wheels - even though they could obviouisly take the same as the rear - or would it just be better to leave the biggest maximum tyre on all 4 alloys??

[lodgeman]

from what i have read the biggest you can fit under the front arches with lowered suspension, without any arch changes is 215 but you can fit larger on the rear. 225 is what i have on the rear/ 215 front. as for clearance ? i dont know as i have'nt driven on the road yet! pauls going to have that privelidge first!!:)

[Driftin_AW]

having smaller on the front also tends to make steering a bit easier too!
As I said, the above is a rough guide, I have 245s on a pair of 7.5" wide rims which is a mega squeeze!

[Sponge Bob]

So would 195 at the front and 225 at the back run quite nicely... if so I think I'll give that a shot, or would it be better to go 215 at the front??? or even 185??

Gah i'm so confused :(

[MegatronUK]

It's exactly the same as what I run - 195/45x16 and 225/40x16. Works nice.

[Sponge Bob]

That's settled then... 195 and 225's... :)

[Peebs]

That would be nice I think Ash, trouble is with "WIDE" tyres is they "tramline" (follow weird road surfaces) and low profiles, well they are good for the track, but as a road tyre ? Neh! Because the walls are shorter and harder, you will get less "feedback" from the road and you get VERY little warning when they lare about to lose grip, thats baaad. I agree big wheels look nicer, but they're cack for handling. It's all about what YOU want I suppose...

[Sponge Bob]

Well I do have cat like reactions... but i'd prefer to not push my luck!! When you say big - I'm only on 15" which should leave lots of tyre? I have to say, prior to creating this thread I had zero knowledge of them whatsoever, so it's a bit of a tough call - having to base initial experiences on people's suggestions and then learn as I go...!

[Peebs]

You'll be fine on 15's matey, but believe me, tramlining is 'orrid down the lanes. I would say don't go over 215 front, 225 rear