[dailydriversti]

Originally Posted by La Mer

meaning a 225/45/17 will not have the same overall diameter as a 245/45/17......make sure the diameters are the same.

[T3h_Clap]

it would make more sense to put wider tires in the front due to the fact that understeer is bad.

plus the only time the wider rear tires will be a benefit is mid corner, and then your front tires will have less potential grip then the rears. therefore potentially decreasing oversteer tendancies.

I say go all the way around same size so you can still rotate your tires.

no point in doing wider rears.

[smurfm3]

Originally Posted by jph

you probably want to rethink your sizing.
make sure that both front and rear tires have the SAME outside diameter. you don't want to break any diffs.

225/45R17 and 245/40R17 are pretty closely matched, i think you can get away with it.

are you planning to run different wheel sized also, or just different tire sized on the same wheels ?

ps: if it was me, i'd just put 245/40/R17 on all four corners, instead of just in the back. wait a second... i did


J.

Running 225/45R17 and 245/40R17 together will wreck your differentials.

However, 225/45R17 and 255/40R17 are extremely closely matched (.2% difference), whereas 245/40R17 has a 2% shorter diameter.

You have to look at the RPM specs on the tire you're buying. Different manufacturers and models have diameter figures that can be off even over 1% comparing from tire to tire. An example of this is the T1-R versus the RE070. The T1-R in 225/45R17 does 825 revolutions per mile whereas the RE070 does 843. That's enough to cause some serious harm to your car. This is why you can't mix and match tires of different models and sizes without making sure the diameter is equal. Sizes between manufacturers are often not equal.

I would like to try 255/40R17 on the front and 225/45R17 on the rear. I am guessing the added front grip of this combination will shift the balance of the car toward oversteer. This would make the car harder to drive (since it would be more likely to spin), but it would more easily rotate.

[jph]

Originally Posted by smurfm3

Running 225/45R17 and 245/40R17 together will wreck your differentials.

However, 225/45R17 and 255/40R17 are extremely closely matched (.2% difference), whereas 245/40R17 has a 2% shorter diameter.

<s>i beg to differ.</s>

EDIT: nevermind... it looks like i based my calculations on a typo

ps: IIRC SOA wants all tires to be within 2% of each other. so 225/45R17 and 245/40R17 should be within spec.
but you're right, a 255/40R17 would be a better match


J.

[Mykl]

I think your car is going to understeer badly, even with those suspension upgrades.

[T3h_Clap]

Am I missing something?

if the diameters are equal, how is the circumference different?

ok, this is a very tire dependent issue it appears.

the AD07 in 25.3" has 820 revs per mile 235/40 18 and 265/35 18 which makes sense, due to the fact that they have the same diameter.

how a tire of 25" can some how turn 100 more times than another tire at 25" boggles me.

now if the 25" diameter was measured before it was mounted on the wheel, then mounted on the wheel and the tire is "stretched" on the measured rim then ran for a mile and recorded it would indeed be a smaller diamter than if the tire wasn't stretched.

tell me I'm missing something obvious and this has just been a long day.

[T3h_Clap]

the fact of a tire being "pinched" or stretched to the point of significantly changing the overall diameter could push an otherwise "mathmatically sound" un mounted tire combo past the 2 or 3% difference range.

maybe it has been a long day....

[dailydriversti]

Originally Posted by T3h_Clap

tell me I'm missing something obvious and this has just been a long day.

Your missing something obvious and it has just been a long day. <hell i don't know>

[T3h_Clap]

Originally Posted by dailydriversti

Your missing something obvious and it has just been a long day. <hell i don't know>

haha

<twenty eight PM's later>

<haha this isht doesn't work if you use numbers>

[T3h_Clap]

Originally Posted by jph

<s>i beg to differ.</s>

EDIT: nevermind... it looks like i based my calculations on a typo

ps: IIRC SOA wants all tires to be within 2% of each other. so 225/45R17 and 245/40R17 should be within spec.
but you're right, a 255/40R17 would be a better match


J.

your #s were pulled right off tire rack.

I checked, your #s were what they say they are.

I knew i shoulda quoted you!

this topic is still on the table!! why the hell?! are they different Revs per mile?

[jph]

Originally Posted by T3h_Clap

your #s were pulled right off tire rack.

yes. there must be something wrong with the numbers they have for the ps2 in 255/40r17 on tirerack.
when i check different brands or types, they all showed 225/45r17 and 255/40r17 to be almost the same. it can't be that for this one particular tire (that i happened to pick for my example! ) it's any different must be a typo on the tirerack site.

sorry for the confusion, i removed all my speculation


J.

[T3h_Clap]

a tire stated to be 255 doesn't have to really be 255 on a given wheel width.

I'm truely interested in this, this needs to be added to my "t3h_spreadsheet"

[smurfm3]

Originally Posted by jph

<s>i beg to differ.</s>

EDIT: nevermind... it looks like i based my calculations on a typo

ps: IIRC SOA wants all tires to be within 2% of each other. so 225/45R17 and 245/40R17 should be within spec.
but you're right, a 255/40R17 would be a better match


J.

If you ran the 245/40R17 as front tires, they would still wear more rapidly than the 225/45R17's in the back. This means that the difference in diameter would become larger through the life of the tires.

Then again, this idea of different front and rear tire sizes is probably something that 99.98% of us will not try. It is very difficult to get right and the benefits of a setup like this are questionable. You can increase the amount of front grip using suspension changes without taking away your ability to rotate your tires.

[T3h_Clap]

agreed, rotating race tires is good on the budget.

[1FSTSTI]

whoever decides to put larger wheels in the back on a awd car should get 5 to the face