Car Tyres Info

darich

Chippy_Minton wrote: »

Well the basic Range Rover as a 255/55R19 tyre same profile as you Focus. At almost 65k would you call that bottom end?

I'd call it a different size.
55% of 255 is different from 55% of 205.

Rallydriver

:rolleyes: Clarkson and Top Gear have alot to answer for.


Maybe "Extreme tramlining" is a new form of motorsport.

Eric_Pisch

Mark_Hewitt wrote: »

I know it's mostly down to the regulations, but look at the tyres on a Formula 1 car.

most race cars and especially F1 cars design the tyre, its movement etc to be part of the suspension. Tyre pressures can then be used to "soften or harden" the ride to shave of the odd 1/10th of a second.

F1 would be on lower profile tyres if allowed, but they have been regulation locked for a very long time on 13" (i think) rims. Which is probably more down to keeping the look of a F1 car.

Track and off road cars also need very different setups and requirements for tyres.

Many sports car models such as M3, R32 (maybe VXR) etc are actually designed for a specific tyre. The suspensions rebound rate is set with the "bounce" of a specific tyre taken into account so changing the tyre can change the handling characteristics of the car. If you plod along like a grandad at the speed limits then you will probably never notice but if you do track days it becomes noticeable.

Whilst there is some truth in the "fashion" statement with regard to ultra low profile tyres there are also good reasons for them becoming far more common. Tyre technology has improved massively over the last 30 years, beyond comprehension, Evo mag tested tyres a couple of years back and the top tyres stopped in half the distance of some of the cheapest brands in the wet (which is gob smacking difference). This new technology has allowed for ever lower profile tyres to be "mass" produced.

And I am afraid they do make a difference, the smaller tyre wall has alot less movement, when you steer with less movement the steering responds faster and the handling feels crisper. More over for the car manufacturers the smaller tyre wall moves alot less when travelling in a straight line, this means it gets less hot which means its safer when travelling at high speed. Of course not so relevant if you don't go over 70 but in Germany or on a track day it becomes very relevant.

The cost of this is a harder ride, more noise and a higher risk of pot hole damage.

Given that there is such a huge difference between cheap tyres and "designer" brands I personally would never go for the bargain bucket tyres. The 4 tyres and the brakes are all that keep you and your loved ones alive in an emergency. If you have a performance car then IMO I would stick to the top names, If its a family car I personally wouldn't go below the middle of the field price wise.

tomstickland

Like most things, it's a compromise between various requirements. High profile tyres suffer from excessive wall flex.
Low profiles have a diminished ability to absorb potholes and the ability to deal with anything over than flat, smooth surfaces. So when you are driving along a road with a bump in it the low profile tyre will skip over it whilst a more compliant tyre will stay in contact with it.

I've got a particular stretch of B road near me which is ideal for testing suspension set ups.

Premier_2

darich wrote: »

So why to top end cars all have lower profile tyres than lower end ones?
A typical ford focus tyres size might be something like 205x55x16
A focus RS tyres is something like 215x35x19.
3series BMW typically is 205x55x16
M3 BMW is more along the lines of 235x35x19

Why is that?

The above are essentially the same cars but one is a base model while the other is a performance version.

Is it purely because the ford and bmw motor engineers are simply boy racers at heart and think it looks good or is it because the higher performance car will corner/brake/accelerate/respond better with the lower profile tyres??

A car starts out being created by a stylist/designer. It is based primarily on artistic goals, some of which is driven by market research (what the punter wants/expects/will be attracted by)

The engineering team have to give functional feasibilty to the design before being handed over to them.

Now whilst I know that chassis/vehicle dynamics engineers have rejected some of the ultra low profile styles in the past because they know they will not be able to achieve the necessary functional/engineering attributes e.g. ride, durability (of the wheel), etc, I've never known the engineering team to reject the normal profile tyre on the basis of handling, steering or braking attributes.

Many of the BMW & Ford engineers are probably boy racers at heart, but they are limited to the constraints given to them by the stylists/designers unless there is good engineering reason to reject them at the styling stage.

Without wishing to upset any stylists/designers, but I'm sure I will with this last comment, I do think much of what they come up with is just the lastest fad; vanity if you will. It's what they believe the customer will be attracted by.

Rallydriver

Eric_Pisch wrote: »

And I am afraid they do make a difference, the smaller tyre wall has alot less movement, when you steer with less movement the steering responds faster and the handling feels crisper. More over for the car manufacturers the smaller tyre wall moves alot less when travelling in a straight line, this means it gets less hot which means its safer when travelling at high speed. Of course not so relevant if you don't go over 70 but in Germany or on a track day it becomes very relevant.

The cost of this is a harder ride, more noise and a higher risk of pot hole damage.

While I agree with everything you say there taken in isolation, you'll never be driving on any UK road so perfectly surfaced as to bring out the advantages of such low profile tyres. While you may find the odd recently surfaced roundabout or stretch of road, the vast majority of our roads are uneven, potholed, broken, rough, rutted and covered in markings, studs and repairs. Everytime a sufaces changes during hard cornering you lose a bit of contact patch, very low profiles can't flex to follow these changes as effectively, this is when cars start to feel skittish in corners.

I'm not just talking from theory here either, experience backs up that very low profile tyres even of the very latest design combined with the latest suspension designs don't cope well once you're off the well maintained M-way and trunk road networks.

Tarmac rallying is probably the closest form of motorsport to driving on normal roads and probably the most extreme driving on those roads, look at the tyre choices there (they aren't limited by regs) and you won't see a little "rubber band" profile anywhere.

Like everything, there is an optimal point of compromise for a given situation and "rubber bands" are not optimised for general UK driving.

Its also rubbish that most people who buy a "sporty" car will feel any difference to the steering response from a slight reduction in tyre profile. Given the "sports" models in a range will usually be given a range of adjustments against a run of the mill model; quicker steering rack, harder bushes, different suspension geometry etc. etc. Closer to the truth is that the car companies marketing people and the motoring press (who are paid for in the most part by car companies advertising) have manged to persuade the car buying public that they need and will notice all these things, therefore allowing the car makers to sell more profitable models.

Looking at the calculations, the OP's profile is actually pretty reasonable (around 100mm). The ultra low ones I can't see the point of are the ones down under about 90mm.

darich

Rallydriver wrote: »

well maintained M-way and trunk road networks..

Where do you live???:D

Incidentally what you said in your post was what I've been saying all along - lower profile tyres are more responsive and used on high performance cars for that reason.
I realise that the trade off is harsher ride, stiffer suspension and the loss of the odd filling but that's the trade off.
Earlier in the thread you said "theres absolutely no advantage from having them" but you now agree there is but with compromise.
I agree that the trade off price gets higher as the road surface gets and that's why the car manufacturer's don't go to extremes but the principle is still true.

Rallydriver

darich wrote: »

I realise that the trade off is harsher ride, stiffer suspension and the loss of the odd filling but that's the trade off.
Earlier in the thread you said "theres absolutely no advantage from having them" but you now agree there is but with compromise.
I agree that the trade off price gets higher as the road surface gets and that's why the car manufacturer's don't go to extremes but the principle is still true.

I'm only talking about ultra low profiles though, hence I quantified what it would be in terms of actual mm of sidewall that I consider too low. Once you go beyond a level (under 90mm) you get to the point where the profile starts to become a disadvantage because other traits become an issue is what I'm saying. Plus there are other factors in chassis design which play a far greater role.

Its also a complete irrelevance really, 99% of drivers wouldn't notice the advantages you cite between the same car on reasonably low profile tyres and one on bigger wheels with ultra low profiles.

web_ferret

Got 4 x Michelin Energy fitted to my car 2 weeks ago (bargain 20% off at costco).
BUT my average MPG has gone down!

On my Continental Sport Contact 2s, I was averaging around 52mpg, I'm now getting 48 mpg. I got 25k miles out of these from new.
Costco underinflated the tyres but this was resolved when I got home and re-checked the nut and pressures (good job I did).

But why am I using more fuel???

Omega_1

Cannot answer your question - sorry. I exchanged this car with the identical model to the other with the only difference of this having a 6 speed auto box against an auto 5 speed on the other - get considerably less mpg on the new car now ! Am still in a quandry over my tyres though !