Correct size tyres for fronts?

[Daston]

Hey guys,

Got a local tyre place to order some Toyos in for me. Went to get them fitted 235/40/18 front and 255/35/18 rear. However my bridgstones are currently 235/35/18 on the fronts and the tyre place wasnt sure that 40 profile of the toyos were the correct size and so didnt want to fit them without checking with Toyo UK.

So was I correct with what I ordered? Or are the bridgstones I have fitted the correct profile?

[drivingfroggy]

I've got the same size Toyos. The guy in Quickfit said they were correct. There's some ratio they go by apparently

[S6 Devil]

http://pistonheads.com/gassing/topic.asp?h=0&f...

[rens914]

with 235/40 in front and 255/35 on back you will have higher tyres on front
the correct size should be
225/40
check here
http://www.buggyboys.be/nl/tech_tellerafwijking.ht...
rens

[drivingfroggy]

[quote=rens914]with 235/40 in front and 255/35 on back you will have higher tyres on front
the correct size should be
225/40


At the risk of being argumentative. How do 225/40 make the tyres any lower than 235/40? They have the exact same profile. They are just narrower.

[Daston]

drivingfroggy said:

rens914 said:

with 235/40 in front and 255/35 on back you will have higher tyres on front
the correct size should be
225/40


At the risk of being argumentative. How do 225/40 make the tyres any lower than 235/40? They have the exact same profile. They are just narrower.

Its to do with the rolling radius.

Just talked to a TVR Indi and they said all the cars they have in are fitted with 235/40/18's.

[12Esc]

drivingfroggy said:

At the risk of being argumentative. How do 225/40 make the tyres any lower than 235/40? They have the exact same profile. They are just narrower.

40 is not the absolute height, but the height as a percentage of the width. 40% of 235 is less then 40% of 240...

[NCE 61]

Should be 225/40 to give the correct rolling radius, had this size on my MK1 and I believe this was the size TVR recommended on the standard Tuscan, later Tuscan S models had 255/35 which is closer to the rolling radius of a 225/40, see http://www.miata.net/garage/tirecalc.html

[The Surveyor]

NCE 61 said:

Should be 225/40 to give the correct rolling radius, had this size on my MK1 and I believe this was the size TVR recommended on the standard Tuscan, later Tuscan S models had 255/35 which is closer to the rolling radius of a 225/40, see http://www.miata.net/garage/tirecalc.html

Why does the rolling radius matter on the front wheels? At the rear yes, where this impacts on speedo reading and drive ratios, but what difference could it possibly make at the front? The 225's look far to streached over the rim and offer no rim protection. My Tuscan has the 235/40's on the front and they are just fine.

Paul

[NCE 61]

The Surveyor said:

NCE 61 said:

Should be 225/40 to give the correct rolling radius, had this size on my MK1 and I believe this was the size TVR recommended on the standard Tuscan, later Tuscan S models had 255/35 which is closer to the rolling radius of a 225/40, see http://www.miata.net/garage/tirecalc.html

Why does the rolling radius matter on the front wheels? At the rear yes, where this impacts on speedo reading and drive ratios, but what difference could it possibly make at the front? The 225's look far to streached over the rim and offer no rim protection. My Tuscan has the 235/40's on the front and they are just fine.

Paul

You are correct rolling radius does not matter I was just checking the difference between the 255/35's & 225/40's and that stayed in my mind for some reason. Cant recall 225/40's looking stretched on the rims although the original 225/35's did.

[drivingfroggy]

As far as I can tell, the difference between the two profile sizes we are talking about is 4mm. Would this make any real difference in real life driving?

[Daston]

Got 235/40 in the end.

As to being a difference not sure about the driving but just by looking at them the 40 profile is less streched. I am hoping it will reduce some of the bump steer I have had with the lower profile.

[Steve Devaney]

I have the same set-up as you (mine are Goodyear Assym's)
What pressure did they inflate them to? Mine are at 28psi all round as confirmed by TVR Power.

I ask as everyone seems to run theirs at different psi readings.

[glow worm]

The Surveyor said:

NCE 61 said:

Should be 225/40 to give the correct rolling radius, had this size on my MK1 and I believe this was the size TVR recommended on the standard Tuscan, later Tuscan S models had 255/35 which is closer to the rolling radius of a 225/40, see http://www.miata.net/garage/tirecalc.html

Why does the rolling radius matter on the front wheels? At the rear yes, where this impacts on speedo reading and drive ratios, but what difference could it possibly make at the front? The 225's look far to streached over the rim and offer no rim protection. My Tuscan has the 235/40's on the front and they are just fine.

Paul

Paul, I don't think 225s give any less protection..I've got to 225s on the front and they look the same as my old 255s...I think more depends on the manufacturer, and the side wall construction..In my case both are Goodyear F1s...be it that the 255s are German and the 225s Chinesse

[The Surveyor]

glow worm said:

The Surveyor said:

NCE 61 said:

Should be 225/40 to give the correct rolling radius, had this size on my MK1 and I believe this was the size TVR recommended on the standard Tuscan, later Tuscan S models had 255/35 which is closer to the rolling radius of a 225/40, see http://www.miata.net/garage/tirecalc.html

Why does the rolling radius matter on the front wheels? At the rear yes, where this impacts on speedo reading and drive ratios, but what difference could it possibly make at the front? The 225's look far to streached over the rim and offer no rim protection. My Tuscan has the 235/40's on the front and they are just fine.

Paul

Paul, I don't think 225s give any less protection..I've got to 225s on the front and they look the same as my old 255s...I think more depends on the manufacturer, and the side wall construction..In my case both are Goodyear F1s...be it that the 255s are German and the 225s Chinesse

Just recal how streached the tyres look on the front of Tamora / T350's which run the narrow tyres. I think they ran the Toyo tyres from new so maybe it is down to the manufacturer.

Paul

[Daston]

Steve Devaney said:

I have the same set-up as you (mine are Goodyear Assym's)
What pressure did they inflate them to? Mine are at 28psi all round as confirmed by TVR Power.

I ask as everyone seems to run theirs at different psi readings.

Have them at 26 rear and 28 front

[rens914]

drivingfroggy said:

As far as I can tell, the difference between the two profile sizes we are talking about is 4mm. Would this make any real difference in real life driving?

it's not a big difference
but
why would you mount bigger wheels in front than on the back-end ?????
and
if you watch closely you can see it
next to that, 225/40 is better to beat the tramlining
if you want to have them wider, take the S set-up = 255/35/18 all around
255/35/18 = 63,57 cm's in height and 199,71 rolling radius
225/40/18 = 63,72 cm's in height and 200,18 rolling radius
235/40/18 = 64,52 cm's in height and 202,70 rolling radius
235/35/18 = 62,17 cm's in height and 195,31 rolling radius
the fact that somebody out there always fits 235/40 in front doesnt mean he's right and you don't have to follow him. (if he yumps of a cliff are you going to follow ?)

it sounds to me that you english really have an tyre issue
rens

Edited by rens914 on Thursday 6th May 10:26

[glow worm]

More importantly 225/40s (front) is how the suspension designer, designed a MK2 'S' with Billies/Eibach springs.