Tyre Stretch - Impact On Performance?

[Dr T]

Does a mild stretch like a 205/40 on a 8J rim have any positive or negative effect on performance? I remember reading somewhere that a mild stretch has the effect of stiffening the sidewalls so you get less flex, essentially my understanding is that this would mean better grip up to a point but less time to recover it when it does let go.

Only ask as my intention was always to make my car better to drive not look at, unfortunately Natedogg has shown me the dark side of e39 wheel fitment and i'm now the proud owner of a set of 17inch 8J 5 series badboys (the clubsport looking split rims) with an offset of 20 , it's going to look epic but willl running 205/40 up front have any effect on performance good or bad? Rears will have 215/45 I think which i'm already running so that'll be fine.

[DJ Syxx]

Personally I think you will be fine, its not a mad stretch, if it were 195 tyres I'd have cause for concern.

[scrimja]

Less rubber to road contact means less grip. If you like to pose then you'll probably be ok. If you like to actually drive your car properly, be careful. Especially in the wet!

[mit]

Also when you stretch the tyres you're effectively pre-loading the tyre walls, and the tyres don't actually fit the wheels properly.

Here's the law on it (taken from a post on another forum):

1.Regarding wheel width, they must not protrude more than 30mm beyond the wheel arches. (Council Directive 78/549/EEC)

2.Regarding the fitting of the tyre "Each tyre fitted to the vehicle shall be of a nominal size appropriate to the wheel to which it is fitted." Sec16(4 The Motor Vehicles (Approval) Regulations 2001'. The fact that the fit was outside manufacturers recommendations should be very persuasive to convince a court that the tyre was not fitted in a manner suitable to qualify it as 'approved'.

3.Section 40A RTA 1988 states "A person is guilty of an offence if he uses, or causes or permits another to use, a motor vehicle or trailer on a road when...the condition of the motor vehicle...or of its accessories or equipment...is such that the use of the motor vehicle or trailer involves a danger of injury to any person." Evidence to support this offence would include measurements of your wheel and tyre, and statements from the manufacturer or a tyre expert, indicating the potential risk of fitting outside their recommended parameters, namely, overheating, grip loss, unpredictable performance and behaviour etc etc.

4.If your vehicle was involved in a collision, especially one involving injury, where the cause led to the loss of control of your vehicle, dangerous driving may be considered, especially strengthened by Sec 2A(2) where "A person is also to be regarded as driving dangerously for the purposes of section 1 and 2 above if it would be obvious to a competent and careful driver that driving the vehicle in its current state would be dangerous."

[Mike-]

I'll be fitting the same, but 225s on a 9J at the rear. Check tyrestretch.com for ideas, 205 on an 8J isn't too bad.

Don't think I'd run stretched if I drove properly though, but I just pimp about in 5th.

[pj1985]

Dr T- 205/40/17 on an 8J rim isnt even a stretch if you run Falken fk452s as its in the range of fitting for that tyre.

Mike- If you are talking about an 18 or 19 inch rim then again the falken fk452 is fine for a 9J rim. Cant see one listed for 17 inch in 225/40 by falken but other manufacturers will probably have similar limits to their recommended fittings so you can check to see if its officially classed as stretch or not.

[silky]

you will ben fine on those matey. Used to run 205/40 stretched on 8j's on my golf and i never had a single issue on grip and they look sooooooo much better!........195/40 on 8's look better but you do start to notice a difference in handling.

[Natedogg]

i run 195/40x17's on my 8's and there fine - there hadly stretched. now a 185/35 would be stretched (watch this space)

205/40 on any 8 is not a stretch - not even a little bit!!

i run 205/40x17 on my 9's and thats about right - grip wet or dry and look spot on.

people who claim stretch is unsafe have never run stretched tyres. probably never will. i've been doing it for 10 yrs and never had a problem.

just make sure you check and maintain tyre pressures (which you should do any way on any car) andyou won't have an issue.

[pj1985]

people who claim stretch is unsafe have never run stretched tyres. probably never will. i've been doing it for 10 yrs and never had a problem.

just make sure you check and maintain tyre pressures (which you should do any way on any car) andyou won't have an issue.

Quite a general comment there which i dont particularly agree with. I have run stretched tyres for years aswell but there is a limit for me to when it becomes unsafe. Any stretch iv seen mentioned on here is never anything that would be dangerous imo however some of the stuff i have seen elsewhere goes past the limit of safe to me. For example a tyre going down because the pressure in it has got to low and its slipped off the bead is not safe for a daily road car or on anything thats going to be pushed hard. This generally wont be the case on 99% of cars running stretch though.

[Natedogg]

i see your point - sticking a 195 on a 10j just because is show car stuff only.

but my 205 on a 9 only needed 35psi to put it on. it deffo relative. i've done madder things and non-stretched, but i check pressure weekly regardless of tyre and wheel setups - even on my birds standard 106 - so have never had a problem.

if you don't check your pressures your a dimlow i reckon - whether the car is stock, modified or running any kind of stretch.

[pj1985]

Agree with you on most of that like I said. Its not just about the amount of pressure needed imo though its about how much it can drop from what it should be run at aswell. If it took 35psi to seal and your running it at 38psi then thats not safe imo as those few psi are easily lost even if you do check your tyre pressures regularly.

[simonlpearce]

All i would like to add is make sure you keep on top of your tyre pressures!

[Natedogg]

it popped on to the bead at 35psi - it doesn't take that to hold it there.

i run 35 rear, 32 front in the tyres stretched which isn't much above standard.

if i deflate the tyre and remove it from the rim the side wall stays 'stretched' shape.

when chris tried to fit he tyres on his LM's he had 135psi at one point and it still wouldn't seal due to the rim design.

[McTreacle]

Hiya,

I've just fitted my BBS Lm 18' reps. Unfortunately they're not staggered or 19's (i'm saving for a wedding and mrs will kill me!!!) and got them off ebay. The actual alloy wheels are 235 or 8.5j.The offset is 37. The tyres on the front are 225/40/18 and stretched and the rears are 255/35/18 and quite bulky. i've got a 1999 coupe se with Eibach sportlines and i'm getting a lot of rubbing when i go over lumpy bumpy roads, its ok on the flat smooth roads.

What i want to know is, what size tyre should i put on the rear or can rubbing be something that can be lived with, or can it shred your tyres???

cheers

[scrimja]

235's should sort it on the rear or an arch roll.

[McTreacle]

235's should sort it on the rear or an arch roll.

Thanks for the quick reply scrimja.

So should i go 235/35/18? or 235/40/18?

Would 225/40/18 on the rear look pants....it does make the dish look a little bit deeper with a slight stretch?

I really dont fancy arch roll...i'm skint.

[Daz 330 Cs]

235/35/18 Dude & should be all gravy

40 profile will be too high for the rear arches

[McTreacle]

cheers fellas.

[Jorge-]

Just found this,

Stretching tyres is safe, within limits. Here's something I posted on Porka:

Here's a few guidelines from TUV/tyre manufacturers

175/50-13 Max 6-13

195/45-13 Max 8-13 with minimum 36 psi pressure on 8-13

185/50-14 max 7-14

195/45-14 and 195/40-14 Max 8-14

205/45-14 Max 8,5-14

215/40-14 Max 9-14

225/40-14 Max 9-14 (except Toyo's who can be fitted to 10-14)

255/35-14 Max 10,5-14

195/45-15 Max 8-15 (bridgstone B530 is allowed on 8,5-15)

215/40-15 Max 9-15

215/45-15 Max 9-15

215/40-16 Max 9-16

215/35-16 Dunlop max 8,5-16 (used to be allowed on 9-16, but approval has been withdrawn, not sure about Conti)

205/40-17 Max 8,5-17

165/35-17 Max 6,5-17

185/35-17 Max 7-17 (see reifenfreigabe page 2)

Here's a few from Falken, maxium wheel width in () with reifenfreigabe

This did not come from any one website, but from years of traveling on German VW/Polo forums, reading TUV-approval papers, 8 years in the business and other sources.

Going back to the point of 'tell your insurance company you are using tyres over manufacturers limits' (yes I know I am over the limits), but most people would have run a 215/40 on a 17x9. Which is infact completely within the manufacturers limits.

Lifted from E38.

http://www.edition38.com/forums/index.php?showtopic=121542

Goes on to say a lot more, about the realistic problems of stretching, although my main point on this was the manufacturer TUV approval stuff.

[n1k_ns]

I must admit, I would be slightly concerned that in the event of a blowout on the motorway or whatever, (which from what I've read is a greater concern with stretched tyres), when the insurance assessor came to inspect the damaged car, they would notice the stretch and find some way of wangling out of paying. Especially on a total loss, They almost certainly would.

(This is coming from someone who's already had two insurance companies refuse to pay out for not declaring modifications )

[Gaz]

I'm with Nik. If you're running something outside of manufacturers spec, you should definitely be informing your insurance. Even running stretched tyres inside the recomendations, I'd keep that sheet you've posted above close to hand for when the insurers start getting funny about it.

[n1k_ns]

LMAO -

I just did a bit of searching for info on insurance vs. tyre stretch and read this brilliant suggestion on the Lupo forum (should you crash with stretched tyres fitted):

Posted Today, 02:22 AM

Say the stretch was incurred during the accident, or slash the tires so they wouldn't know. Say it was excess debris.

Yep... Great idea that, see where that gets you!

[Gaz]

Say the stretch was incurred during the accident?? How would that work then Mr Lupo driver!

Insurer: "So Mr Lupo, we noticed your tyres were too small for the alloys you were using"

Lupo Driver: "Naaaah mate, the crash must have made my tyres shrink"

[Jorge-]

Duh, didn't you know that happens.

Lol.

I wasn't trying to start a debate or start a for and against stretched tyres, just wanted to show that manufacturers have tested tyres with a stretch and they have been approved to run at what you would expect to be over their limits.

I'm 2kool2krash anyway.

[Aidan316i]

235/35/19 on on 9.5J's FTW!