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Subject says it all, really. Is there some technical reason (i.e. aside from the bling-bling factor) that people want/install the combination of larger-than-OEM-diameter wheels and lower-than-OEM-sidewall-height tires?
Actually it's because tires with short sidewalls are designed to have significantly stiffer and thicker sidewalls. It's not the fact that they are shorter but the fact that because they are shorter they HAVE to be stiffer to prevent rim damage etc...Foxpaw said:I've heard that low profile tires supposedly give better performance on cornering because there less sidewall to flex.
You are talking about Formula cars and Nascar etc... their rules force them to use a specific rim diameter. If you look at powerful race cars based on street cars you will see wide low profile tires like WRC rally cars set up for tarmac stages, and british touring car racing on tracks.logic would dictate that high performance racing cars would have low profile tires when in fact they have much "higher profile" tires.
The best example of this is on drag racing tires with ultra soft sidewalls, but these tires are not designed for turning!"Higher profile" tires are able to deform more, which allows you to get more traction, which is arguably a good thing.
My experience instructing at a skid pad has taught me that me that sidewall construction is a HUGE variable that determines how much a sidewall will flex. A common tire size that many cars have is 205/55R16. Tires in this size come in all flavours including : extreme condition soft winter tires, all season touring (comfort) tires, ultra high performance summer tires and Race compound tires. A skid pad is used to determine the minimum tire pressure required to prevent the tire from flexing onto it's sidewall in a maximum grip turn. The tires of the same size and profile but of different sidewall construction require a minimum pressure of anywhere between 35 psi to 55 psi to prevent flexing when driving the skid pad at about 50 km/hr.b1shmu63 said:The amount of "flexing" will change depending on the presure, the surface area, and the rigidity of the sidewalls. In most cases the sidewalls are too flexible to add significantly to the equation.
When one upgrades to a larger rim with a lower profile tire it has the same outer diameter but it is wider. The contact patch is the surface area of the tire that makes contact with the road. The size of the contact patch is only determined by the weight on the tire and the air pressure in the tire. Going to a wider tire does not increase the contact patch surface area, it only changes the shape of the contact patch. With a wider tire the contact patch is wider so there is less flex in the tire. For example think of tire with zero flex, it would be made of something like steel. The contact patch would be a line not a patch. With something soft like a balloon when you push it against the ground you will see that a flat contact patch appears and gets bigger as you push down harder on the balloon.The problem with a low sidewall height is that the amount of "flex" takes place over a shorter distance. This will case heat buildup to increase at an exponential rate over a linearly decreased area. This means that a low profile tire will get much hotter due to "flex" and will waste significantly more energy.
What about the tires on a dragster? They have very "high profile" tires, but I don't believe that there are any controls on rim size in top fuel classes.Guillermo said:You are talking about Formula cars and Nascar etc... their rules force them to use a specific rim diameter. If you look at powerful race cars based on street cars you will see wide low profile tires like WRC rally cars set up for tarmac stages, and british touring car racing on tracks.
Right, but they only go straight.Foxpaw said:What about the tires on a dragster? They have very "high profile" tires, but I don't believe that there are any controls on rim size in top fuel classes.Guillermo said:You are talking about Formula cars and Nascar etc... their rules force them to use a specific rim diameter. If you look at powerful race cars based on street cars you will see wide low profile tires like WRC rally cars set up for tarmac stages, and british touring car racing on tracks.
Yes, but only when turning. The tread width will be the same on all tires '165' the difference in 'contact patch' (the part of the tire that touches to pavement) will become evident when latteral forces are applied to the side of the tire (side wall 'flex'). Driving in a straight line the tire width will vary little, but turning a corner will cause the 'contact patch' to become smaller. A 165 tire with short side wall will have very little lateral flex, but a 165 tire with tall side wall will have a lot of flex.I am no race expert but are you refering to the fact that a 165/65/R14 tire have less tread width than a 165/60/R15 and that this one has less tread width than a 165/50/R16 ... 165/45/17 ...
With a solid rubber over a solid rim the contact patch will be tiny therefore have little grip. And the tires are also a significant contributor to the total suspension system in cars. Also tires need to maintain a decent contact patch while driving over road irregularities like small stones.Foxpaw said:Hrmm.. So, if low profile tires are better because they prevent flexing, why don't we just have solid tires instead of ones filled with air?
I should append this, sidewall flex is 'bad' in terms of Road Racing, and not so much a concern for normal commuting....but this should explain side wall flex and why its considered 'bad'.