Fitting wider front tyres on a rwd car

[mattikake]

Just after some thoughts. I have a mk3 mr2 and it really needs some more manly wheels (I was thinking along the lines of some nice 17" Azev A' or C's).

The thing is, the front tyres are 185's and the rears 205's. If I put 205's on the front - same size wheel all round - how much is this going to disturb the handling of the car?

I'm thinking it's going to be a bit more rear-endy and a bit more vague on turn-in, as a result of increased grip and intertia at the front and it not matching the weight distribution particularly on accelerating, but I guess I'm looking to the experts or the experienced.

Ta!

[RobCrezz]

I guess it will make the car more prone to oversteer as the front will have more grip that before. If you put 205s on the front, i would put 225s on the back.

[mattikake]

How much do you think it would affect oversteer? Massively or only noticable on a racetrack by racing drivers?

I'm thinking of the cost for the wheels to get two different sizes in one order, and the extra cost in tyres that I will burn out. If I go for the same size all round I can swap fronts to back as wear increases.

[GreenV8S]

Wider tyres on the front will mean that the contact patch is shorter and wider. The tyre will be more sensitive to camber changes and you may find you get more tramlining and kickback. For the sort of small change you're considering I wouldn't expect either of these effects to be dramatic, but they will probably be noticeable. Shortening the contact patch also reduces the tyres self-aligning torque and means the self-aligning torque doesn't change as much as the tyre approaches the limit. So the steering may feel lighter but also give you less steering feedback. You will also find that the tyre produces more lateral grip but the grip peaks at smaller slip angles (steering feels more direct) but then falls off more rapidly as the slip angle exceeds the optimum (tyre seems to 'break away' more abruptly).

So: more tramlining and kickback; more ultimate grip; feels more direct for small steering inputs; less feedback as it starts to slide; breaks away more abruptly.

[mattikake]

Excellent reply. Just what I was after... assuming to be correct. Seems believable to me. You think I could get the geometry set to compromise?

As for feedback when sliding starts to happen, in this weather I've been relying on feedback a lot, but that's more of the feel for the rear, not the front. From what I have noticed it doesn't really understeer at all unless you got flying into a corner way too fast. Approach it properly and build up speed to the exit and it only tends to oversteer, sometimes correctable with the steering, sometimes by feathering the throttle. (nice!) Can't say I'd want to lose that feel.

At the same time, it you're beeing silly, the back will break away fast putting you into a fishtail (that so far has only been to step out and to snap back the other way once before under control again).

If grip is increased at the front, even though the front will experience a more violent loss of traction, I'm expecting this to also have an effect on the rear as well? - I guess I'm asking if it will be more prone to faster oversteer or more prone to the same type of progressive oversteer than understeer?

btw, what's your background in car handling? Do you race?

Edited by mattikake on Thursday 7th February 08:28

[ChrisS1]

do not put the same width tyres on all round.
by all means put wider tyres on but keep the staggered width between front and back.

[custardtart]

RobCrezz said:

I guess it will make the car more prone to oversteer as the front will have more grip that before. If you put 205s on the front, i would put 225s on the back.

Expect handling characteristics as per Green V8S said but worth thinking about the following.

Is it a road car? How often do you currently exceed the grip levels when cornering (as opposed to accelerating out of t-junctions)?

If the answer is, not alot, then you won't notice the differnces that much, if the answer is that you drive on the limit everywhere then you will!

[900T-R]

custardtart said:

If the answer is, not alot, then you won't notice the differnces that much, if the answer is that you drive on the limit everywhere then you will!

Problem is that on a lightish RWD car the grip will vary far more between conditions than driving, say, a middleweight FWD saloon - which means most of us have been 'surprised' at some point of another that the limits of grip have been exceeded while not going all that quickly. The MK2 MR2 doesn't have the friendliest of reputations in that regard to start with, so I would most definitely favour feel and progression above outright grip and looks.

[edit - ah, it's a MK3, sorry. Basics still apply - it's still quite mid-engined... ]

at least that's the ethos I'm kind of following with the TVR

Edited by 900T-R on Thursday 7th February 14:47