from a memorable thread, here's the thoughts of my friend racing engineer (from Italy), with which I agree with 100%
""Hi Minel,
not so much time for this issue.
Let's remind the three reasons why larger tyres offer better traction:
1) Less tyre deformation, given the lower specific force tranferred between tyre and the asphalt (higher contact area with the same weigh => lower forces to be transferred). Please remember that the equation T = gc*N holds true only for non-deforming materials, while rubber is an elastomer.... Please, remember to your friends that not only static driving has to be taken into account, and that accelerating and mostly breaking will definitely change the weight trasferred to each tyre, and easily put in trouble your tyre. Almost doubling the weight trasnferred to front tyres under braking (for instance), could easily cause serious tyre deformation on small tyres, while will result in zero to little deformation in a larger tyre. This is important to assure that the correct contact area is constantly at work.
2) Better statistical traction, given that the wider covered area allows you to reach some (potential) areas of the asphalt in which the friction coefficient may be better, and then reduces the probability of breaking traction. Just like playng the lottery: the higher the number of tickets you buy, the higher the probability to win. This factor is very important: if you consider a static driving situation, so when little or no tyre deformation is occurring, by using larger tyres you modify your contact pattern from this:
*** ^ driving direction
*** |
*** |
*** |
*** |
to this:
***** ^ driving direction
***** |
***** |
This, I repeat, in static situations, when the inflate pressure holds the same, and larger tyres simply modify the contact pattern. Given such change in that shape, you are more likely to find better grip situations, because you are "scanning" a wider area to look for traction. Please think upon this, you'll realise how important this statistical effect.
3) Last but not least, better tyre construction, since the larger the tyre, the more performing, higly expensive the piece of equipment you are being endowed. Please don't forget that tyres are made by companies, and companies have marketing and customers segmentation policies. You get what you pay for: larger tyres = more expensive, better engineered and constructed. This is a very important point. People think that 225/45 R17 and 245/40 R17 are the same tyre, just different size. FALSE: the construction is different, and if you go further up with the size, also the compounds is modified.
The second tyre in fact is intended to be more performing, and is designed for that. I know this because I've worked for an automotive manufacturer.
Of these three factors, 2 and 3 are always at work when you drive, while factor 1 comes into play only when you are braking/cornering (or accelerating, if you have a +++hp car) and then you load the tyre with a very higher load if compared to static situations.
This is true for dry conditions, and this is true for wet road, as you can easily understand. So no way in which on a wet road smaller tyres can give you better traction performances. Think for instance to wet/ winter tyres for cars: are they smaller, or are they just the same size, with different compound and different design? If reducing the size of the tyre could help traction on wet roads, why tyre manufacturers are not doing that? They could save money also, since smaller tyres are less expensive, both in materials and manufacturing costs, and increase profits!
Think to F1 intermediate tyres, whicy are used for from mid to wed conditions: are they smaller? C'mon, don't waste time on that....
All of this becomes false only when you shift from "wet" conditions to "flooded" conditions, and then the real enemy becomes aquaplaning. In that situation, the larger the tyre, the more easily it will become a "surf board", and as speed rises, you'll start doing surfing, instead of driving
That's why in rallies and other competitions on mud and snow (have you ever seen motobikes' races on ice?), they use very very small (spined) tyres, because in this way the lower contact area allows the tyres to penetrate into the water / mud even at high speed. Of course, the lower surface decreases traction performances, but at least you have some traction, since you are not flying on water / mud / snow, but you are touching the ground.
But who cares about this???
Have you ever experienced real aquaplaning? I have, and from then on, at least as far as I'm at the wheel, when I see the road conditions turning into potential acquaplaning, I slow down, and not start arguing about my tyres size. I'm not a professional driver, and moreover my car is tuned for dry road (wheels, suspensions, boost gain pattern, everything is tuned for dry).
Eventually, even F1 rain tyres are not much smaller than slick, just highly sculpted in order to drive out the largest possible quantity of water.
That's why I strongly suggest not to get involved in this kind of discussion which are really a waste of time. Discussing about cars and mechanincs, in my opinion, is good as far as it helps you understand something useful for your driving experience. I saw your forum, 9 page discussion for this is.... unbelievable.
Hence:
1) If someone thinks that smaller tyre will give him better traction on dry or wet conditions, leave him to his (probably bad) fate;
2) If someone thinks he should use smaller tyres so as to have less chance for aquaplaning, I'd rather suggest him to slow down when it starts raining hard, and keep larger tyres for all the rest;
3) ...and save your precious time to work and earn your TT upgrade
All my best,
Miraglio"
