Fitting wider tyres to 15 inch wheels

[larryb]

It is looking like I will be getting the Chassis sorted on my V8s (see other thread) - so the set of refurbished OZ 8 Spoke wheels will be used after all.

I have been struggling to get any new bridgestones and it is looking like I will probably go for 205/55/ZR15 Dunlop SP9000's.

However, some clever chap (at local TVR dealer) suggested that I may be able to fit wider tyres (say 215 or 225) with a differing profile and this would (a) not affect rolling circumference and (b) may give me more choices of tyres to consider?

I assume they can adjust out any height difference when they fit my new sparkly Gaz adjustable suspension.

So.....has anybody fitted wider than (205) standard tyres successfully to an 'S'? Is there a risk they rub on the arches?

Cheers

Larry

[foxy600]

I noticed you mentioned 205/55, when I bought my S2 this was the size of tyre that was fitted, when I replaced them I fitted 205/60, as I was told this was the size they were all fitted with originally. The 60 size is better as it helps with ground clearance. I fitted Dunlop Sport Sp01's and am very pleased with them.

[GreenV8S]

Tyres need to be the right width for the rim. If you go too wide or too narrow it causes the contact patch to distort under side load which leads to various handling and tyre wear problems. You can certainly stretch very wide or narrow tyres on the rim, and as long as they stay on and don't foul the bodywork you could say they'll fit. But the tyres are a critical part of the car's suspension, and getting tyres that work properly is far harder than getting tyres that will fit.

For road tyres in this sort of size range the rule of thumb I use is that the tread should be within the range from 3/4" narrower than the rim to 1/4" wider than the rim.

Converting a standard 7" rim to mm this gives you a range from 155mm to 180mm.

The nominal width of road tyres are conventionally measured at the widest point of the sidewall on the recommended rim width. Typically this works out about 25mm wider than the tread. Adding this to the rim width gives a nominal width between 180mm and 205m. This is the range that will work best. You can go wider or narrower if you like, but the further you go the less well they'll work. In the past TVR have supplied 215 and even 225 tyres on these rims, and they are obviously tolerable and won't kill you, but I reckon they're wider than optimum.

PS don't try to use ride height changes to compensate for changes in tyre diameter, changing the ride height impacts static and roll induced camber and is another way to screw up the handling.

>> Edited by GreenV8S on Sunday 27th November 13:16

[larryb]

Hi Guys

Foxy - I currently have 205/60's on a set of cross spoke split rims. I would like to put new tyres (z rated) on my refurbed Oz 8 spokes as it does not seems worth swapping part worn tyres over. In the 205/60 size I can only find a very limited selection of tyres - none that I feel happy with. However in the 205/55 size there is slightly more selection and the SP9000's are currently favourite.

GreenV8s - I note your comments. 205mm is the optimum? I had assumed that the difference in ride height between 55/60's could be compensated by adjusting the height of the suspension slightly............currently with tired rear suspension my exhaust does bottom out slightly. I guess new shocks and springs will help, but if I drop to 55 profile that will not?

Surely there must be lot's of 'S' owners running on 55 profile tyres?

Larry

[larryb]

Have just looked on Blackcircles for the next size up to 205mm?

They are offering a 215/60 Z rated version of Dunlop SP9000.

GreenV8S - is 10mm (ie. 215) going to make much of a difference?

Cheers

Larry

[Paul V]

I would say a 215/60 is going to be a bit tall, as the 60 refers to the ratio for width to height so 215/55 would be more like what you would need for an S series. As said don’t want to go to wide as will end up with a distorted contact patch, years ago Goodyear had a optimum wheel rim guide for their tyres, might be worth doing a internet search to see if it’s still available.

[foxy600]

I had no problem finding 205/60 tyres, just did a search and found these:

www.camskill.co.uk/products.php?plid=m4b0s412p0
www.johnsonstyres.com/acatalog/FULDA.html

[larryb]

Ooops - I have been a div!

I had thought that the profile ie. 55/60 was height of tyre wall in mm?

[larryb]

Foxy - I want to get Z rated tyres as these were original fitment to V8S's.

I can find lot's of 205/60's in V rating etc. but very few in Z rating?

Cheers

Larry

[Paul V]

If you go to www.mytyres.co.uk they have a list of about 10 tyres which are W rated in a 205/60 R15, they deliver to your door and can then get them fitted at a local tyre centre, I ordered my Griff tyres from them and got prompt delivery and an absolute bargain due to what I expect was them messing up their prices lol.

[JR]

larryb said:

I will probably go for 205/55/ZR15 Dunlop SP9000's.

IMHO this is your best option. The suspension can be set up to cater for the less than 10mm height difference (10mm assumes no tyre wall flex) and it is your only option to give you state of the art UHP rubber in a Z rating.

[profstoff]

JR said:

larryb said: I will probably go for 205/55/ZR15 Dunlop SP9000's. IMHO this is your best option. The suspension can be set up to cater for the less than 10mm height difference (10mm assumes no tyre wall flex) and it is your only option to give you state of the art UHP rubber in a Z rating.

Remember that going down in profile ratio will affect the calibration of your speedo due to the smaller rolling circumference. the bible has more information on this.
I have just bought new Bridgestones (albeit V rated for an S3) from etyres. It might be worth giving them a bell.
If you adjust your ride height on the spring platforms, remember to get the alignment checked afterwards.

[larryb]

Profstoff

I have also been told that the lower profile will mean that I will have greater acceleration, and less top-end. Do you know what the effect on the speedo is - will it under read?

What size Bridgestones did you go for?

I am having new shocks and springs fitted (supplied courtesy of Bugsy ) and a 4 wheel alignment. I hope to get the new tyres on the rims and the whole suspension can then be setup for the new tyres

Cheers

Larry

[V8Smith]

I would think the bridgestones were 205/60x15 standard size for the S, RE720 probably and these are fine Larry you dont NEED Z rated tyres. I run the same size RE720's on the fronts with 245/45x16 on the rear. The grip compared to before is fantastic, W rating is sufficient. The one thing I would say about fitting wider tyres on the fronts, as I am contemplating 215 or 225's if I move to 16" fronts is that with no power steering at parking speeds it will be very heavy! Like Pete said though putting too wide tyres on rims can alter the handling, but to be honesy you probably wonr notice it unless you drive on the track on the limit as Pete does. I have 245 tyres which in theory are slightly too wide I am told (will check one of these days). Like I said in normal driving they grip like never before and its much easier to control although harder to get the back end to give way, so in turn safer maybe?

Larry you can use this tool to check how the new tyre size will affect the speedo. There is another better one but cant seem to find it, will post later if I get chance.

www.tyresave.co.uk/tyresize.html

Heres the better one I found it www.miata.net/garage/tirecalcold.html

Hope that helps?

Mike

>> Edited by V8Smith on Friday 2nd December 08:59

[profstoff]

larryb said:

Profstoff What size Bridgestones did you go for? I am having new shocks and springs fitted (supplied courtesy of Bugsy ) and a 4 wheel alignment. I hope to get the new tyres on the rims and the whole suspension can then be setup for the new tyres Cheers Larry

Mike's right, I got 205/60 as they are the standard tyre, Bridgestone RE720's. I've got 205/55 S02's on the front and IMO the /60s look better as there is bnot so much gap to the wheel arch. The difference in aceleration and the speedo error are due to the difference in gearing. i can't remember what the effect on the speedo is but I know it's covered in the bible. I'll look it up tonight when I get home. When you get the alignment done, make sure they know about TVR's. I cna recommend Austec in Crawley, they did a spot-on job on mine.
I can recommend etyres, they'll come to you, even on a Saturday, and they phoned me to let me know what time they were coming.

[foxy600]

Are Z rated tyres really needed? The S isn't a Pagani Zonda after all??