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MG MGF Technical - Confused Wheels,Tyres

Hello Boys!.

I asked on a previous thread about new wheels, tyres for my F.
Have seen some sexy 17" alloys with 40s tyres, which i believe will fit, without catching or rubbing, and will not need to alter suspension ( or was i told Wrong?.).

My F has standard 15" wheels on now, but front and rear are different sizes?, Front 185 55, rear 205 50.

Will the new wheels( if i get them) have to have different size tyres, like the old?, or were the old tyres Wrong??????.

Confused of Cheshire
Mark

Mark, 17"s fit on the F :o) - have a look at Mike Satur's website for confirmation of this (http://www.mikesatur.co.uk/). Best still, they fit without need for modification of bodywork etc.

You can use the same tyre width all round: MG even did this themselves when MGFs were first brought out on 16"s - in this case using (as I still use) 215/45 R16s.

A narrower front tyre is a "good idea" because it improves steering response, and reduces tram lining.

HTH
Rob Bell

Mark

On the Cd that I gave you at the weekend is the Owners handbook. This details all oem wheel and tyre combinations. MGR fitted 15" and 16" with various combinations of widths. At no time did they fit 17" so there is no MGR recommended tyre data.

Your 185/205 combo are correct for standard 15" wheels.

Beware about getting new wheels until you have considered the posibility of brake upgrades. Some calipers will only fit under certain wheels.

Rob Bell's site may be a good starting point for a shed load of usefull info, as well as Paul Lathwell's

http://www.mgf.ultimatemg.com/

http://www.dotcomoff.co.uk/
JohnP

this bbs is getting spooky.

When I started typing Rob hadn't replyed.

I guess he's a bit like me, types, does something else and then remembers to send.
JohnP

Thanks Rob, John.

Your telling me what i want to hear!!. :)

Now where does she keep her credit card?.

Mark.

Ps , Nice to meet you by the way John, and thanks again for CD.
Mark

>> this bbs is getting spooky. <<

Tell me about it... it's always seems to be you, me and Will posting the same or similar reply within 30 seconds!!! ROFL
Rob Bell

Guess you're on about my wheels! They have the same size front and back, 205s. In case you didn't know, available from http://www.mgfcentre.com . They're also perfectly suited to take the bigger brakes if you want them later.

all the best,
Andy
Andy

The choice of front to rear width wheels changes handling the wider running smaller slip angles, and the steering respose should be better with a wide wheel as shorter contact patch.

Paul
Paul

Paul, I don't think that is true: slip angles would accumilate faster with a narrower tyre - meaning that grip is generated faster with initial steering movement.

Wider tyres have a larger contact patch; slower generation of slip angles, and therefore ultimately greater grip... but initial 'bite' is much slower into a corner.
Rob Bell

As far as I know you will also need spacers to fit 17" wheels, which will also increase the stresses on the wheel bearings.
J Reinhardt

Not necessarily James - assuming that you can find a wheel with the correct PCD and offset.

If the wheels you are looking at have a 100mm PCD rather than 95.25mm, then you have to use a PCD adapter from Mike Satur. The adapter is also - effectively - a 14mm spacer: this needs to be borne in mind when specifying the wheel from a supplier. Mike will have much more information on this if you call him.
Rob Bell

Rob,

Contach patch size is a product of tyre pressure and car weight.

A wide tyre contact patch is difficult to twist hence lower slip angles but reacts quickly.

A narrow tyre allows wider slip angles but because of length of contact patch gives more warning of the limit.

A wider tyre has more rubber and can dissipate heat better than narrow.

Paul
Paul

>> A wide tyre contact patch is difficult to twist hence lower slip angles but reacts quickly. <<

What do you mean by "reacts quickly" Paul?
Rob Bell

My Friend Dan has a set for sale,email him if interested, Team Dynamics Pro Race 1'S 20/40/17 on toyo proxes t1's the front passenger one has a kerb mark avoiding a woman in a focus but he's open to offers, they have had under 8 mths use,and colour is black,Those at NorthWeald Track Day in Jan may remember them on his silver F, Dave

danb_mgf@yahoo.co.uk
DC Morris T6 DCM

Rob,

There is less sideways distortion between the front and back of the contact patch.

If you take a F1 car you notice how quickly they change direction, not surprisingly they run very low slip angles on that width of tyre.

Paul
Paul

My 17" wheels are now available as a direct fit, without the need for spacers. I'll leave it to the others to debate the handling characteristics!

Andy

Andy

I think that the situation is more complex than that? Or have I got the wrong end of the stick?

As you know, for a tyre to actually generate significant grip, it needs to generate a slip angle. A narrow tyre will develop a greater slip angle faster (contact patch distortion, as you mention) - which means that it will generate greater grip sooner than a wider tyre. However, while a wider tyre will develop its angle of slip slower - it also means it is capable of greater mechanical grip simply because it takes longer to exceed the optimal slip angle whereafter the tyre starts to slide.

Ergo, the narrower tyre develops grip faster, but yields adhesion sooner, whilst the 'slower reacting' wide tyre has more ultimate grip... Therefore, I'd have thought, a narrow tyre will give you superior initial steering response.

The F1 example isn't that helpful, as clearly a F1 car has geometry designed specifically for the wide tyres...
Rob Bell

Hi Rob,

F1 ref was to illustrate my use of word "quickly"

The wide tyre has a shorter contact patch so the back of contact Patch has to follow the front in a shorter space at a lower slip angle.

A greater slip angle and you are not travelling in the direction of the steering input.

If looking at ultimate grip the shorter contact patch means more of contact patch reaches maximum grip and starts to slide at same time.

Paul




Paul

But the contact patch need not be shorter on a wider wheel Paul.
Rob Bell

Rob,

You can reduce tyre pressure, and have a larger contact patch, this spreads load, will run a higher slip angle and more flex and heat.

Paul
Paul

This thread was discussed between 15/09/2004 and 17/09/2004

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