tyre size

[Mike-]

how does different tyre size effect performance

ive got 195/60/15 on my ae101 trueno and found out today im meant to hav 195/55/15 i know it effects speed somehow but cant remember.

does it increase acceleration and lessen top speed or the other way round when going from big to small tyres.

also what size tyres do u guys run on ae101s

any help appreciated

[Willdat?]

The affect it has is kinda complicated...basically the change that you're talking about will increase the gearing of the car, so you 'should' be more economical on a long trip, acceleration will probably be decreased it's all a bit academic anyway because the 'indicated speed' also changes...to illustrate my Datsun 1200 could do an indicated 100mph on the original 155 SR 12s, when I upsized to 185 60 14s the indicated top speed dropped to 93mph, to the best of my knowledge this upsize basically removed the optimism that the speedo had from factory...nottoo sure if you get my answer...I'm a little on the rambling side...

[solberg Fan]

Smaller tyres=more acceleration and vice verca. But a small change like that wont be notcable, unless your the man...

[2fas4u]

add to that sizes like 195 or 205 or 225 affects your grip on the road. with a rwd like the SW20, i have 205 in the front and 225 in the rear. i think the extra grip gives me better push off.

[Caveman]

ae101's run 195/55/15 at the front and 195/60/15 at the rear factory. Unless your running after market mags use these tyre sizes.

Cars use the widest tyres that'll fit. On a FWD its usless having wide tyres on the back and they won't fit on the front due to the small turning radius.

There is very little benifit using smaller tyres over bigger tyres. Smaller tyres allow the engine to turn them easier however the tyre has to displace more to cover the same distance as the larger diameter tyre so very little if any benifit is attained.

[andrew]

AE101s either come with 195/55/15s all round or 185/60/14s for the lower spec'ed models.

I wouldn't run anything wider than 195s on the factory 15x6" rims. You will get some tramlining with 205s on a 6" wide rim.

Also bear in mind, tyres grip the road by having have weight pushing the contact patch onto the road. The larger the contact patch, the more area the weight has to be spread over and therefore there is less weight pushing the contact patch onto the road; wider tyres only improve grip up to a point. In the wet, a contact patch too big for the car will result in a lot of aquaplaning.

[JT]

AE101s either come with 195/55/15s all round or 185/60/14s for the lower spec'ed models.

I wouldn't run anything wider than 195s on the factory 15x6" rims. You will get some tramlining with 205s on a 6" wide rim.

Also bear in mind, tyres grip the road by having have weight pushing the contact patch onto the road. The larger the contact patch, the more area the weight has to be spread over and therefore there is less weight pushing the contact patch onto the road; wider tyres only improve grip up to a point. In the wet, a contact patch too big for the car will result in a lot of aquaplaning.

If you keep the pressure in the tires the same, it doesn't matter what width tires you have, the contact area will always be the same. The advantage of a wider tire is the shape is more of a rectange so when cornering less of the tire comes off the road, breaking is improved due to better heat distribution and normally you run a lower profile so the sidewall has less flex.

[andrew]

If you keep the pressure in the tires the same, it doesn't matter what width tires you have, the contact area will always be the same.

I believe this would depend on the amount of camber and whether we are talking about cornering on the limit of not.
Also, if you compare 195 vs. 205 wide tyres on 6" rims (everything else being equal), the 205 is likely to be a bit balloon'ish (IME anyway). The sidewall will react differently under hard cornering and consequently affect the contact patch.

I think we can agree though, that for a given amount of weight in general a wider tyre will provide more lateral grip only up to a point ? And that tyres vs wheel sizes etc is a complex subject

[2fas4u]

very complex

[JT]

I believe this would depend on the amount of camber and whether we are talking about cornering on the limit of not.
Also, if you compare 195 vs. 205 wide tyres on 6" rims (everything else being equal), the 205 is likely to be a bit balloon'ish (IME anyway). The sidewall will react differently under hard cornering and consequently affect the contact patch.

I think we can agree though, that for a given amount of weight in general a wider tyre will provide more lateral grip only up to a point ? And that tyres vs wheel sizes etc is a complex subject

I think the area will still be the same regardless of camber; area=weight/pressure and weight and pressure are the same which means it will just have a more trapezium shape than rectangle. Yes, I'll argee with you on the other points.

The original post was what would happen if he went from 195/60/15 to 195/55/15. The answer is, you will notice (or not) a small increase in acceleration and your geared top speed will be lower (not that a standard 20V will reach it's geared top speed)