Different Tyre Profile Front and Rear

[Mr_will]

I currently have 195/50/15's on civic vti-r rims, on my da9.

They should be 195/55/15's, and thats ideally what I would like to have on.

One of my rear tyres has an air bubble in it, and I'm reluctant to leave it on the car in case it blows out.

I'm thinking of replacing both rear tyres with new ones, in 55 profile, even though they both have very good tread left.

My question is, will having 50 profile on one end, and 55 profile on the other, cause me any huge problems? I am planning to do it for 5000-10000kms (the life of the existing 50 profile tyres)

[arron]

Haha..

I've done that by accident after changing back to my street tyres after a trackday..

The only thing I notcied was that the car would constantly pull to one direction.. Besides that the only thing that would get affected would be your diff working overtime...

Haha.. 10,000km is quite a lot dude.. just get the same profiles.. Felt like crap having the tyres different sizes

[Mr_will]

Haha..

I've done that by accident after changing back to my street tyres after a trackday..

The only thing I notcied was that the car would constantly pull to one direction.. Besides that the only thing that would get affected would be your diff working overtime...

Haha.. 10,000km is quite a lot dude.. just get the same profiles.. Felt like crap having the tyres different sizes

well its not going to be different left and right - only front and back, if you get me.

the whole reason i dont want 50 profile is that

a) its the wrong rolling diameter compared to stock

b) the ride is uncomfortable

c) the handling is actually better on 55's

[T-onedc2]

Seeing as the speedo takes the reading from the front drivetrain it'd be more of a problem already as stock is 55 profile, changing the rear won't be a problem, might just look funny for a while, bit higher at the back.

[lenz]

just change all of them and sell the 50 profile tyres

[vinnY]

i think they'll be fine
i was running 195/50/15 and 205/50/15 for months without trouble
i'm actually running 195/55 and 195/50 right now without any troubles either

[JohnL]

the whole reason i dont want 50 profile is that

b) the ride is uncomfortable

c) the handling is actually better on 55's

Something for those running on huge rims and rubber bands to take careful note of...

[vinnY]

^ wow never seen such a short reply from you johnl ;)

on another note i remember having been told by a bridgestone tyre centre that the 195/50 *should* handle better than the 55 profile variant
have they been misinformed or just trying to sell their product as usual?

still trying to scrub in my new tyres, done about 500k's are they're getting there :) adrenalin's ftw

[JohnL]

^ wow never seen such a short reply from you johnl ;)

Do I detect a faint tone of disappointment, or relief?!


on another note i remember having been told by a bridgestone tyre centre that the 195/50 *should* handle better than the 55 profile variant
have they been misinformed or just trying to sell their product as usual?


IMO, all else being equal, then probably right some of the time and not right some of the time (in the 50 vs 55 size, which aren't extreme sizes, then probably correct more often than not...). It depends on what tyres are being compared to what tyres on what rim size on what car with what suspension set up. Pieces of string are rarely exactly the same length.

In any case I wasn't meaning a specific comparison between generic or particular 50 and 55 profile tyres, rather just an in principle comment on the very common misconception of 'the lower the profile the better', whereas the reality is that a more conservative aspect ratio is nearly always the better performer (often substantially so).

Looking at what racing tyres are available in what sizes is an intersting exercise, there seem very few in a 45 profile or less, most seem to be in the 50 to 55 sizes, and a fair few in 60 and even some in 70 profile...

People running rubber bands over massive rims should be aware that to many more knowledgable car enthusuaists they are figures of either quiet ridicule, faint scorn, or even mild pity. This goes double if their car is also scraping it's belly along the road...

[vinnY]

i've just become accustomed to reading a statement and explanation in your posts ;)

shouldn't have been so vague in my post.. i meant 195/50/15 vs 195/55/15
they seemed to justify it saying that there'd be less sidewall flex
i personally do prefer the handling on the 50 profiles at the expensive of the car actually being a little lower and scraping everything off the road(yet to work out why my suspension is so low?!)
could probably just be a placebo effect having the 50's already worn in while the 55's are pretty new at this point

[nd55]

> I'm thinking of replacing both rear tyres with new ones, in 55 profile,

With the proviso of running identical size on an axle (front or back) it'll be fine.

Like others on the thread I've had to compromise tyre choice following accidents.

I'd probably further qualify that by recommending placing lower spec tyres on the front so that it lowers the chance of un-expected over-steer.

But that doesn't sound like it's the case here. 195/50 and 195/55 is a very small difference.

Not like the 175/65R14 OEM steel rims and light 205/50R16 wheels I had to run for too long.

Finding a single forged rim in the right size for a reasonable price is impossible.

Nick.

PS.
> they are figures of either quiet ridicule, faint scorn, or even mild pity

you talking about me???? he, he.

[JohnL]

shouldn't have been so vague in my post.. i meant 195/50/15 vs 195/55/15 they seemed to justify it saying that there'd be less sidewall flex

All else being equal, the shorter the sidewall height the less sidewall flex and the more immediate the steering and handling response, which is a good thing in itself. However, because the shorter sidewall will be vertically stiffer the tyre will be more sensitive to correct camber angles and to changes in the road surface topography (including bumps, dips, ruts and road camber).

The tread needs to be consistantly presented to the road surface as 'flatly' as possible to maximise moment to moment contact patch size and thus provide consistant grip over less than perfectly smooth surfaces, and vertical sidewall compliance assists in this (i.e. assists in allowing the tread to more faithfully follow the contours of the irregular road surface).

If the sidewall is too stiff then grip may tend to be erratic as the contact patch (in effect) abruptly changes size as it passes over road irregularities and changes in road camber. Of course these affects exist all the time with any tyre on almost any road (perfectly smooth is rare even on race tracks), how well the tyre deals with it is a matter of degree.

On car X on road Y a 50 AR tyre may well handle better than a 55 AR tyre, but on road Z (or with car W) the 55 AR tyre may be superior, keeping in mind that 'handling' is a combination of response and grip (consistancy as well as degree and front / rear balance, and the progressiveness of any changes in degree of grip and grip balance).

Just saying that 50 AR will handle better than a 55 AR tyre is an easy statement to make, but rather simplistic and possibly only correct within certain parameters. At any rate, the more extreme the AR of a given tyre may be, the more likely that the parameters within which it will work well will be very narrow, and the more drastically it's performance will drop away when outside those parameters...


i personally do prefer the handling on the 50 profiles at the expensive of the car actually being a little lower and scraping everything off the road(yet to work out why my suspension is so low?!)
could probably just be a placebo effect having the 50's already worn in while the 55's are pretty new at this point

It may depend on what you're interpreting as 'better' handling. Most likely you like the sharper steering and handling response you may be getting from the lower AR tyres, and the roads you're driving on are OK for those tyres (i.e. not too rough). At any rate I'm not sure there would be a great deal of difference between the 50 and the 55 AR tyres, not like the difference between say a 55 and a 65...

Personally I like a very responsive set up and outright grip isn't such a big deal for me as I'm not racing the car, however, consistancy of grip is very important on a road car.

New tyres working less well than somewhat worn tyres isn't a placebo affect. New tyres do suffer from a relative lack of response due to the height of the new tread blocks being higher and the rubber blocks therefore 'squirming' around more under load. When tyres are brand new they also don't grip well due to the mould release agent that takes at least a few K's to scrub off.

Old tyres with little tread left may well grip poorly compared with new tyres (though often have very nice steering response due to the tread blocks not squirming much), but this is most likely to be due to the rubber having aged and hardened. If you were to take the new tyre and scrubbed the tread blocks down then they would be much better than the old worn tyre and the new tyre with stock tread depth, at least in the dry...