100 replies to this topic

[Grim]

Hi,

I'm a newbie to this forum, so please go easy on me. but hopefully i'll help put your minds at ease on this topic, or even enlighten a few of you.

Although I don't actually drive a VX220, i actually work within the technical dept of Bridgestone UK.

You should have no problem getting the correct spec tyre for the front on the VX220, as this is the only tyre we make in that size.

In the rear size however, we make different spec tyres for different cars as OE.

For example, we make the RE040BZ for the VX220 and the Lotus Elise. While both have the same load/speed rating, the actual spec of the tyres are different, to suit the handling characteristics of each car. fitting the incorrect spec of tyre may affect the handling characteristics of the car.

To identify the spec of the VX220 fitment, the easiest way is to check the DOT code.

Front – 175/55 R17 RE040 BZ 81W (to identify this tyre check the DOT code for the CAD)

Rear - 225/45R17 RE040 BZ 90W (to identify this tyre check the DOT code and ensure the letters CFE are present)

for example EJ H8 CFE 2004

The Lotus spec tyres will be marked with DCK.

I hope this helps.

Ian

[Foxy]

The Lotus spec tyres will be marked with DCK.

Is this a wind-up?

Seriouly though, good of you to take the time to post

In what way is the lotus spec different?

Also, what's your view of fitting F1's on the rear with std BS on the front?

We need more threads like this

Indeed

It's not as good as "Can I fit a sub in the boot?"

[Grim]

The Lotus spec tyres will be marked with DCK.

Is this a wind-up?

Seriouly though, good of you to take the time to post

In what way is the lotus spec different?

Also, what's your view of fitting F1's on the rear with std BS on the front?

Nope, not a wind up.

Although the VX220 and the Elise are similar cars, they do have different handling characteristics. When car manufacturers are designing a car, they sometimes like to have tyres that complement the handling of the car.

As for mixing tyres on a car, we'd never recommend mixing patterns or brands and like most tyre manufacturers, would always recommend fitting matching sets of tyres.

Edited by Foxy, 06 September 2006 - 02:36 PM.

[jazzyjeff]

Er...because the Yanks are the most car safety obsessed nation in the world? Therefore they should know a little about tyre safety!

Is that because they have a culture to sue for millions for anything? or the fact they have a fair number of idiots, just look at the president

Both!

JJ

[Foxy]

The Lotus spec tyres will be marked with DCK.

Is this a wind-up?

Nope, not a wind up.

I was referring to the DiCK mark!

[doberman]

The Lotus spec tyres will be marked with DCK.

Is this a wind-up?

Seriouly though, good of you to take the time to post

In what way is the lotus spec different?

Also, what's your view of fitting F1's on the rear with std BS on the front?

Nope, not a wind up.

Although the VX220 and the Elise are similar cars, they do have different handling characteristics. When car manufacturers are designing a car, they sometimes like to have tyres that complement the handling of the car.

As for mixing tyres on a car, we'd never recommend mixing patterns or brands and like most tyre manufacturers, would always recommend fitting matching sets of tyres.

Sorry to step in again, but what tyre manufacturer is going to recommend fitting someone elses tyres to the other end of the car? The important thing is to have matched tyres on the same axle. The VX220 is designed to understeer. Fitting grippier tyres to the rear will reduce the tendancy to oversteer, but will have no effect on the point when the front tyres let go. That said, you can control understeer by putting on the power and spinning the back out, so perhaps you are better with the Bridgestones in this respect. I can only repeat that fitting F1's to the rear has made no appreciable difference to the handling of my car.

[ShinyAndy]

I can only repeat that fitting F1's to the rear has made no appreciable difference to the handling of my car.

..and yet myself and others have commented that it destroyed the handling and balance of the car and would NEVER do it again yet alone recommend anyone else does it

[doberman]

I can only repeat that fitting F1's to the rear has made no appreciable difference to the handling of my car.

..and yet myself and others have commented that it destroyed the handling and balance of the car and would NEVER do it again yet alone recommend anyone else does it

I suppose that my time with a Formula 3 team makes me question why something happens, rather than just state that it does happen. I don't doubt what you say, but I really can't understand why a grippier tyre would destroy the handling and balance; it didn't happen when I fitted F1's.

It is clear that we have had different experiences, so it is probably best to advise others to stick with the standard tyres.

[LazyDonkey]

At the risk of sticking my oar in when i know hee haw about the specifics of tyre construction (not that it stopped others ) the issue with the goodyears isn't simply about more grip than the BS it's also about the sidewall stiffness and how progressively it gives up grip etc ect. IF the tyre has a softer sidewall than the BS then the car COULD feel more bouncy, handle the bumps / imperfections less well etc which is what could "destroy" the handling *. Likewise if it is less progressive than the BS then the same thing could have been said. FWIW i've left my hands in the hands of knockhill instructors, walshy and countless mates etc and no-one has climbed out going "cracking car but the rear could do wth more grip" So for road work i'm in the "if it aint broke" camp * No idea if this is the case

Edited by LazyDonkey, 06 September 2006 - 04:21 PM.

[i need nos]

I can only repeat that fitting F1's to the rear has made no appreciable difference to the handling of my car.

..and yet myself and others have commented that it destroyed the handling and balance of the car and would NEVER do it again yet alone recommend anyone else does it

I suppose that my time with a Formula 3 team makes me question why something happens, rather than just state that it does happen. I don't doubt what you say, but I really can't understand why a grippier tyre would destroy the handling and balance; it didn't happen when I fitted F1's.

It is clear that we have had different experiences, so it is probably best to advise others to stick with the standard tyres.

just stick to the bridgestones and dont believe us when were giving you our opinions, were not bloody forcing u to change them just commenting on how well they grip, and for your info the f1s have stiffend reinforced tyre walls.. case closed..

Edited by i need nos, 06 September 2006 - 05:52 PM.

[walkes]

Front – 175/55 R17 RE040 BZ 81W (to identify this tyre check the DOT code for the CAD)
Rear - 225/45R17 RE040 BZ 90W (to identify this tyre check the DOT code and ensure the letters CFE are present)

Ian
could you give clarification of what the codes actually mean and what makes them different?

I have yet too find anything that actually gives them any useful information, even to the point of e-mail the US Dept. Of Transport. Some help that was

They appear to be random code rather than anything to do with acual tyre rubber compound or shell construction. This appears to be another way to ask for more money for the same product. The treadwear and Traction ratings are the same as the Audit TT tyre IIRC, obviously this is a heavier car, and the side wall is slightly stiffer.

PS can't you make a track day tyre for both standard fit and Exige size wheels

[Pidgeon]

I suppose that my time with a Formula 3 team makes me question why something happens, rather than just state that it does happen. I don't doubt what you say, but I really can't understand why a grippier tyre would destroy the handling and balance; it didn't happen when I fitted F1's.

F3 or not, how do you explain the FACT, that if the rear grip increases an otherwise neutral handling car will turn into an understeering car? If either of you could satisfactorily explain why you do not experience this issue, I would have more respect for your opinion.

[doberman]

I suppose that my time with a Formula 3 team makes me question why something happens, rather than just state that it does happen. I don't doubt what you say, but I really can't understand why a grippier tyre would destroy the handling and balance; it didn't happen when I fitted F1's.

F3 or not, how do you explain the FACT, that if the rear grip increases an otherwise neutral handling car will turn into an understeering car? If either of you could satisfactorily explain why you do not experience this issue, I would have more respect for your opinion.

I had hoped that there would be an end to this, but hay ho I will try to keep it simple. A car understeers because the front tyres lose their grip and the car ceases to turn in and tries to go straight ahead. Grippy tyres at the back won't normally cause the fronts to let go of their grip sooner, so they should have no effect on the onset or severity of understeer. (See my earlier note about controling understeer with power).
I'm really not trying to be clever, it's just a matter of physics.

[ShinyAndy]

Can you try the non simple version because you're only talking about turn in grip from what I can tell in which rear grip is pretty unimportant (simply speaking) Imagine I've already turned in and I'm applying power.. Suddenly my nicely balanced loaded up car with neutral handling turns into a understeering monster as the rear tyre grip overpowers the front grip, so I compensate by applying less throttle which then gives me lift off oversteer and puts me in the ditch. Far better to have balance and a sense of knowing whats going on Having driven a fair amount of mid engined rear wheel drive cars both on track and on the road I have only ever experienced that putting grippier tyres on the rear does nothing other than screw up the nicely balanced handling that this type of car are blessed with

[walkes]

Well said that man.... Have got to agree with Shiny and Partridge on this one. More grip on the rear will produce a car that understeers. I would have thought someone who has driven an F3 car would have known this. Saying that Doberman you did not say you were the driver... Just to throw another one into the thread hijacking What about Pilot Sport Cups 205/55/16 235/45/17 ....

Edited by walkes, 07 September 2006 - 01:25 PM.

[doberman]

Can you try the non simple version because you're only talking about turn in grip from what I can tell in which rear grip is pretty unimportant (simply speaking)

Imagine I've already turned in and I'm applying power..

Suddenly my nicely balanced loaded up car with neutral handling turns into a understeering monster as the rear tyre grip overpowers the front grip, so I compensate by applying less throttle which then gives me lift off oversteer and puts me in the ditch. Far better to have balance and a sense of knowing whats going on

Having driven a fair amount of mid engined rear wheel drive cars both on track and on the road I have only ever experienced that putting grippier tyres on the rear does nothing other than screw up the nicely balanced handling that this type of car are blessed with

The VX220 is not a finely balanced car. Vauxhall have deliberately introduced understeer. Faced with understeer you can either ease off on the power and the car will turn in or, if you are up to it, you can apply power and force the car into the turn with contolled oversteer. It is obvious that a lot of owners can't control their cars properly, just look at all the crashed one's on Ebay! I doubt they all fitted F1's.
I was a mechanic working as a volunteer in an F3 team some years ago. I specialised in handling. Given time and patience we could set a car up so that it had balanced steering, but it is a specialist job and all sorts of factors like changing weight distribution affect the balance. I think it is a bit optimistic to assume that VX's leave the factory with perfectly balanced steering, though it is pretty good. I don't find that my car understeers any sooner with F1's and when it does understeer I apply power induced oversteer and balance the car with the throttle. I believe that F1's are as good on the VX as the originals and I will fit them again because I have found them to be hard wearing and good looking tyres.

You are all entitled to your opinions and I have already said that anyone who is unsure should fit Bridgestones. Feel free to have another pop if yiou like.

[Foxy]

I think it is a bit optimistic to assume that VX's leave the factory with perfectly balanced steering

I think it is a bit optimistic to assume that VX's leave the factory with perfect anything!

I will fit them again because I have found them to be hard wearing and good looking tyres.

...you were doing so well

[2-20]

... I don't find that my car understeers any sooner with F1's and when it does understeer I apply power induced oversteer and balance the car with the throttle.

I agree with you, your car does not understeer sooner with stickier rear tyres.. the limit of the front tyres has not changed .
However power induced oversteer is more difficult to create with stickier rears and and if you don't reach the limit of adhesion, you will only amplify your oversteer.
Control of the car i more difficult.

[doberman]

... I don't find that my car understeers any sooner with F1's and when it does understeer I apply power induced oversteer and balance the car with the throttle.

I agree with you, your car does not understeer sooner with stickier rear tyres.. the limit of the front tyres has not changed .
However power induced oversteer is more difficult to create with stickier rears and and if you don't reach the limit of adhesion, you will only amplify your oversteer.
Control of the car i more difficult.

Thanks, most drivers find it hard to control power induced oversteer whatever type of tyres are fitted.
I am not convinced the F1's are stickier and I suspect it comes down to personal choice in the end. In my Formula 3 days I remember all too well that a perfectly set up car for one driver was declared a pig to handle by another. It all depends on your driving style.

[Pidgeon]

I agree with you, your car does not understeer sooner with stickier rear tyres..

I do not recall anyone stating the car would understeer sooner.

Let us get down to basics. As the cornering force increases, the slip angles of the front and rear tyres increase. For any tyre, we can plot a graph of cornering force against slip angle. The graph will be a curve that will peak and then fall away.

Imagine a car driving in a circle. As the speed increases, the slip angles will increase, reach their optimum level - then pass that level. If the tyres are matched front and rear, the cornering force at which the slip angles peak should be similar - and most importantly, the rate at which cornering force falls away at greater slip angles should be similar.

If we replace the rear tyres with some capable of producing more cornering force - to coin a phrase 'they have more grip', when the original front tyres have exceeded their peak cornering force, the rears will not have - the car understeers as the front slides when the rear does not. That understeer will not have occurred sooner, it will occur at the same cornering force as when the four tyres are matched, the difference being the rear now does not move.

Something else I do not understand about your post. Apart from in a low gear on wet roads, power induced oversteer is not possible to induce in my standard VXT. The application of power will usually cause the front of the car to move away from the apex as you transfer weight to the rear. If the car is already in an understeer condition, power will exacerbate the understeer and simply push the front further from the apex. What happens with yours?