View Full Version : wider tyres simple answer required.

10th May 2004, 15:45
Hi all,

I got lost in the theory of this and dont want any answers to the tune of, you want less grip so that you can feel the tires breakaway more progressively.

Having learned something from a few damian harty threads, the general consensus seems to be that to a point, wider tires do not give you a larger contact patch they just change its shape, particularly making it wider and shorter thus better for cornering and not so good for straight line dragging.

I kind of get lost when taking a simple model and attempting to fit it into real life.

what I am after is a simple answer with reasons to the following question.

I have the choice of fitting 235 40 17s and 255 40 17s of the same make (both F1 GSD3s), which should I go for?

10th May 2004, 16:14
whats the cost of each tyre?

And personally not them tyres in my personal preference but thats not the question in hand.


10th May 2004, 16:42
interesting you say that, not heard a bad report yet, trying to get re070, price difference is about £5per tire so doesnt bear thinking about.

10th May 2004, 16:43
Some simple corrections...

Bigger tyre DO have more grip.

The reason is often overlooked, bigger sections means that for the same load a lower tyre pressure can do the same work, thereby enhancing grip...

pretend numbers just to illustrate this...

235/40... @32lbs has a contact patch of 'x' sqaure cms.

265/35 [similar tyre wall height] @30lbs has a contact patch of 1.1'x'

The contact patch shape of each will be very similar and so you may only get enhanced grip without any other losses, most drivers will not realise that you can lower pressures to gain more grip.

The 'trick' is to match the different tyre load rates to allow for a full contact patch...

To do this you must go up the load scale as you widen the tyre and decrease its pressure...

so 235/40 might be a 90 W you would have to go to a 265/35 92/93 W or 91/92 Y to get the thing right.

Much overlooked!

10th May 2004, 16:55
good post Mr Bird.

Also, when running in the wet with wide tyres, it can help to increase base presure as that opens up the water chanels and gives more grip.

I would make the choice based on tyres available, for example you can Get SO2 PP's new still in some sizes.

António Correia Jr
10th May 2004, 17:05

Not sure about the best width for you, but I've moved from S03 215/40/17 to 235/40/17 (GoodyearGSD3) upon my conversion to the 22B kit.

The car handles very well with my current power, though I'm keen on trying the S03 in this width since I found the Goodyears sidewalls a bit soft.

One other point that may be overlooked is the tyre weight smile.gif How does 235 compare to 255?

10th May 2004, 17:13
is there likely to be a choice at 255 40 17?

and is the affect on handling purely a function of relative tire pressures, in that is it ok to drop the tire pressure without detrimentally increasing steering weight etc?

I also remember you saying something about a theoretical perect side wall height. What is this and where does it come from?

10th May 2004, 17:17

can't get S02s. thats two complaints about the gsd3s now, both new to me.

I do have the option of the RE070s which are supposed to be amazing, but I am concerned about their wet weather ability.

Availability may be tough since they are a japanese bridgestone tire that come standard on the nsx type r.

am going to try though.

Iain mentions something about load ratings, but my post above wasnt very clear.

What I meant was, do you ever get the choice of a tire in two load ratings, surely it is up to the manufacturer to spec a model of tire and there isn't any variation at that size.

Can anyone help me find a link which might specify load ratings of various sizes of gsd3s?

10th May 2004, 17:19
Strange as it seems the bigger the tyre the lighter it could well be!

The plain fact is that the more 'common' the size then the greater the likelyhood of improvement in materials filter into the market.

Very low profiles will be heavier... anything blow 90mm sidewall height will be quite heavy.

10th May 2004, 17:25
Add sidewall height and this becomes a whole subject in itself...

There are 'bands' in tyre sidewall design, the best height remains somewhere between 100mm to 110mm, these are still best on track, they are always the best on give and take British roads.

Some of the very latest materials make the choice a little better and the 90mm to 100mm band is catching up fast.

For Macpherson type susp. the lower profile [90/100mm SW] is also more readily accomodated than multilink stuff.

10th May 2004, 17:37
Can't comment on the technical reasoning, but can confirm that Impreza's with much wider tyres than me also corner quicker than me on track..... It's hateful.