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#41
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Peter Bell > wrote:
> In message > > Glenn Richards > wrote: > > > That's not a road I want to start going down. If I can fit the next size > > up tyres on the existing rims, for another 10-15ukp per tyre it'll give > > a small but worthwhile improvement. > > I guess that the question which must be asked is - what improvement do > you expect to achieve? > > Altering the width of a tyre does *not* achieve more rubber on the road, > it merely alters the shape of the 'footprint' - unless you are reducing > the inflation pressure, but you could do that with your existing tyres. > > The actual area of tyre in contact with the road is a simple > relationship - > > contact area = (weight carried by wheel)/(inflation pressure) I'm obviously being a bit thick here, but could you please explain how a, for example, a 185/60 tyre will put the same area of rubber down as a 220/45? -- Steve H 'You're not a real petrolhead unless you've owned an Alfa Romeo' http://www.italiancar.co.uk - Honda VFR800 - MZ ETZ300 VW Golf GL Cabrio - Alfa 75 TS - VW Passat 1.8T 20V SE - COSOC KOTL BoTAFOT #87 - BoTAFOF #18 - MRO # - UKRMSBC #7 - Apostle #2 - YTC # |
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#42
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The formula in a prior post will give you the contact area but makes no
reference to its shape or the tire's friction force. If your tire load remains constant (the same car) a wider tire will have "wider" shape which leads to greater lateral resistance to shift due to its shape alone. The following equation is perhaps more accurate: (friction force = (coeff of fric) x (summation of tire forces (Fx, Fy, Fz) If you want to go around curves faster on dry pavement then a wider tire is the way to go. You should be aware, however, that widening the tires will lower the velocity at which flotation on wet or snowy surfaces occurs. There is also the factor of changing the stress on wheel bearings by the alteration of the "effective" offset. The change of one size wider and one size lower profile will probably have a small effect on bearing stress. More importantly is to make sure that the proposed lower profile will not allow the tire sidewall to contact and suspension or brake component as it flexes, jounces or rebounds. There is limited information on this due to the relative rarity of Audis in the US. Thirty two years ago when I began racing it was much easier as there was always someone else that had tried a combination before and, by trial and error, the acceptable sizes became known. If you wanted to exceed those conventions we would alter suspension components. Changing the shackles on leaf springs or "taking a torch" to coil springs were very common ways to effect the suspension. We knew that this would alter the driving characteristics but.... well... we were young and stupid, and didn't care. But then... I wasn't a middle aged man driving a $45K vehicle either. For what it is worth I have seriously considered going up one size and down one width for my next set of tires... In my case I would replace 215-55-16 with 235-50-16. The speedometer error introduced would be approximately +0.2% "SteveH" > wrote in message ... > Peter Bell > wrote: > >> In message > >> Glenn Richards > wrote: >> >> > That's not a road I want to start going down. If I can fit the next >> > size >> > up tyres on the existing rims, for another 10-15ukp per tyre it'll give >> > a small but worthwhile improvement. >> >> I guess that the question which must be asked is - what improvement do >> you expect to achieve? >> >> Altering the width of a tyre does *not* achieve more rubber on the road, >> it merely alters the shape of the 'footprint' - unless you are reducing >> the inflation pressure, but you could do that with your existing tyres. >> >> The actual area of tyre in contact with the road is a simple >> relationship - >> >> contact area = (weight carried by wheel)/(inflation pressure) > > I'm obviously being a bit thick here, but could you please explain how > a, for example, a 185/60 tyre will put the same area of rubber down as a > 220/45? > > -- > Steve H 'You're not a real petrolhead unless you've owned an Alfa Romeo' > http://www.italiancar.co.uk - Honda VFR800 - MZ ETZ300 > VW Golf GL Cabrio - Alfa 75 TS - VW Passat 1.8T 20V SE - COSOC KOTL > BoTAFOT #87 - BoTAFOF #18 - MRO # - UKRMSBC #7 - Apostle #2 - YTC # |
#43
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"BillyRay" > wrote in message .. . > > There is limited information on this due to the > relative rarity of Audis in the US. > Where in the US do you live? At least 1/3 of the vehicles in the parking lot of the company where I work are Audis. It is certainly the single most popular marque around here... dk |
#44
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#45
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Mid West US.
The keyword is relative. If you stop at Tires-R-Us and ask what sizes of tires you can safely fit in the wheel wells of a Ford or GM car you will easily get an answer.... not so for an Audi. (at least in this area) What kind of company do you work for and where is it located? "Dan Koren" > wrote in message ... > > > "BillyRay" > wrote in message > .. . >> >> There is limited information on this due to the >> relative rarity of Audis in the US. >> > > > Where in the US do you live? > > At least 1/3 of the vehicles in the parking lot of the > company where I work are Audis. It is certainly the > single most popular marque around here... > > > > dk > > |
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