diff. profiles for front & rear tyres

lal · Post by **lal** » Tue Mar 30, 2004 5:40 pm

can someone let me know the effect (if any) by having different profile tyres for front and rear? does it result in an even more inaccurate speedo reading?? or is this the correct size setting for these width?

One of our members has 235/40/R18 on the front and 265/35/R18 rear.
just wanted to know if this is because the rear tyre is so wide.. that you have to compensate??? or should it have been 265/40 to match the front profile?

thanks all.

ruchi · Post by **ruchi** » Tue Mar 30, 2004 5:57 pm

Different profiles front to back won't have an effect on the accuracy of the speedo. What will, is if the over-all rolling circumference of the front tyres is larger than standard.

This person has gone for "fats at the back", giving the car a meaner look through the user of wider tyres at the rear.

Aside from the more aggressive look, having a wider tyre also means that there is greater contact with the road. For a rear wheel drive car, the concept of "fats at the back" can be quite benefitial, but for a front wheel drive car it can be quite detrimental.

From a technical point of view, with a front wheel drive car, you would be better off having "fats on the front", but asthetically this might look kind of strange.

lal · Post by **lal** » Tue Mar 30, 2004 6:12 pm

kewl... I understand what you mean...
in that case.. does anyone have a guideline as to what the maximum width should be fitted on the FTO?
If 265's has been fitted, then I guess any larger and you'd be pushing it

...
but taking into account the sanity side of things... is 235's the max for front and back?

to fit 265's at the rear, would a camber kit need to be fitted? ro can it fit on a stock FTO?

FTO338 · Post by **FTO338** » Tue Mar 30, 2004 6:20 pm

ruchi wrote: For a rear wheel drive car, the concept of "fats at the back" can be quite benefitial, but for a front wheel drive car it can be quite detrimental.

Lol

It also add unnecessary weight to the cars, so its very detrimental.

Adriano · Post by **Adriano** » Tue Mar 30, 2004 6:26 pm

I had narrower tyres back then, then changed to 235s all round... the difference was quite noticeable... the wider ones being heavier to steer, and harder to manouvre.. i guess obviously due to more road contact...
i think its better to have a narrower pair at the front....

D-TRAIN · Post by **D-TRAIN** » Tue Mar 30, 2004 6:38 pm

Dang....265 at the rear is pretty wide.

I have 17 X 8 with 215/45 at the rears and thought I was cutting it pretty fine!

But I guess it'll also depend on what offset your rims are.

ruchi · Post by **ruchi** » Tue Mar 30, 2004 7:05 pm

Adriano wrote:i think its better to have a narrower pair at the front....

In a RWD car yes, in a FWD car no.

Fats at the back work for RWD cars as it provides a greater contact area to get the power to the road, and keeps the front wheels lighter and easier for steering. In a FWD car where both the power and steering are done via the front wheels you are better off having either the same diameter tyres front and rear or "fats at the front" otherwise you can have control issues.

The wheels on a car will pull / push the vehicle in what ever direction they are pointed, so when you corner, the front wheels pull the front of your car in the direction you wish to go but the rear wheels, which don't turn, try to push the car straight ahead. Having wider tyres at the rear will lead to an increase in both oversteer and understeer, depending upon the rate of turn, as the extra grip from the rear tyres will increase the force on the back of the car to continue in the direction it was heading even though the front of the car is trying to turn and head in a different direction.

Having the same tyre widths front and back on a FWD car keeps these forces in balance. Putting "fats on the front" in a FWD car will sway these forces to the front wheels giving them more grip and control when turning. But as mentioned above, the steering wheel will be a little harder to turn with wider tyres on the front.

Post by **smorison** » Tue Mar 30, 2004 7:32 pm

* the wider the tyre the harder it is to turn in and change direction.

* the wider the tyre the wider BUT narrower the patch of rubber that touches the road.

* the lower the profile the harder it is to stop quickly

just some points

aL · Post by aL » Tue Mar 30, 2004 7:55 pm

Its common knowledge to have wider tyres where grip is required(eg. wider in the front for FWD, wider in the rear for RWD).

But I always wondered about the benefits of going as wide a tyre you can fit as possible. When a wider tyre is fitted, the same weight of a car is spread out over a bigger area therefore less force down on surface area??

If there is less force down on surface area would that not mean less grip with the road???

Post by **smorison** » Tue Mar 30, 2004 8:00 pm

aL wrote: If there is less force down on surface area would that not mean less grip with the road???

i have found 225's to be more problematic in wet weather i.e. they aquaplane a lot faster than 205's

aL · Post by aL » Tue Mar 30, 2004 8:51 pm

hi stephen, its andre!

205 are too narrow for me to get traction in the dry. Even with 225 in the front the wheels spin if I move off too quickly.
225 almost rub the guards on full lock

I wonder how some fto owners can fit 245 in the front?
If I could fit 245, I prob could launch the fto much harder and would most likely get a flat 13s.

GPXXX · Post by **GPXXX** » Tue Mar 30, 2004 8:58 pm

aL wrote:hi stephen, its andre!

205 are too narrow for me to get traction in the dry. Even with 225 in the front the wheels spin if I move off too quickly.
225 almost rub the guards on full lock
I wonder how some fto owners can fit 245 in the front?
If I could fit 245, I prob could launch the fto much harder and would most likely get a flat 13s.

i don't want to sound like a sceptic but you'll be lucky to get mid 14s with 245-wide tyres in NA tune...

depending on the wheel offset, 225 should turn at full lock without any probs. but i agree with you, the wider your front tyres, the more grip you will have (but more chance of aquaplaning in the wet too).

aL · Post by aL » Tue Mar 30, 2004 9:10 pm

Ive got a little blower under e hood

GPXXX · Post by **GPXXX** » Tue Mar 30, 2004 10:11 pm

aL wrote: Ive got a little blower under e hood

ahhh, now that makes perfect sense... so tell us a bit more about this setup that you got, hehe... tell! tell! tell!

Post by **smorison** » Tue Mar 30, 2004 11:16 pm

hey andre

where have you been hiding the last 12 months?!?!?!?!?

i hear your selling your car... that sucks!

make sure it goes to a loving owner!

we have a dyno day coming up next month bring it along

Blaze · Post by **Blaze** » Tue Mar 30, 2004 11:21 pm

GPXXX wrote:
aL wrote: Ive got a little blower under e hood
ahhh, now that makes perfect sense... so tell us a bit more about this setup that you got, hehe... tell! tell! tell!

aL has got turbo engine. Was on sale a while ago. (Check out the thread)
Come on aL, we want to know more...
Opss, this could lead to "out of topic"

aL · Post by aL » Tue Mar 30, 2004 11:55 pm

Stephen, Ive been out of the country for the past 7 months dats why u havent seen me around.

Yes Im still selling it, unwillingly, as I might have to leave again, for good.
But if Im staying

I will be chasing 12.5s in the 6 mths or so...........but till then, one step at a time.

ruchi · Post by **ruchi** » Tue Mar 30, 2004 11:58 pm

start a new topic as there's some good info here for people wondering about tyre sizes. Keeping the topics clean and seperate makes it easier to find the info you're after

(I'll admit that I'm guilty of going off topic 'though

)

ruchi · Post by **ruchi** » Wed Mar 31, 2004 12:23 am

aL wrote:When a wider tyre is fitted, the same weight of a car is spread out over a bigger area therefore less force down on surface area??

If there is less force down on surface area would that not mean less grip with the road???

The short answer is that a wider profile tyre will give you better grip in the dry as there is a larger patch of tyre in contact with the road, but in the wet, as Steve has said, the tyre will be more prone to aquaplaning for the very reasons you mentioned above (there is less weight per inch as the weight of the car is distributed over a greater area).

smorison wrote:* the wider the tyre the wider BUT narrower the patch of rubber that touches the road.

* the lower the profile the harder it is to stop quickly

Genuine question (not sh*t stirring): you sure about that first point? If I read it correctly you're saying that the contact patch will be wider (left to right) but will be narrower (front to back). I agree with the wider (left to right) but question the narrower (front to back) as if the circumference of the new tyre is the same as the old tyre, the angles remain the same and therefore so too should the contact patch front to back. Perhaps I've misunderstood what you've said?

Again genuine question (not sh*t stirring): I assume with the second point you're refering to the unsprung weight and inertia, if not, ignore what I say

If so, then it should only be harder to stop if the weight of the new tyre & wheel package is heavier than the old one, but if in upgrading the tyre you went for a much lighter rim and the overall weight of the tyre & wheel combo decreased then the stopping power should improve. Again, have I misinterpretted what you said?

payaya · Post by **payaya** » Sat Apr 03, 2004 9:10 pm

i had 235/40/17's on the front 255/40/17s on the back!

I bought my wheels second hard so i didnt choose the tyres.

The profile the of back tyres where noticabaly higher because of the 40% of the 255. no problems with rubbing, but the front rubbed against the inner wheel guard when fully locked.