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Discussion Starter · #1 · (Edited)
Ok abit of tyre maths :D

My tyres on my Evo are 235/45/R17

The 45 number is the ratio of the height of the tyre sidewall, (section height), expressed as a percentage of the width. It is known as the aspect ratio. In this case, 45% of 235mm is 105.75mm - the section height.

So i am wondering if it would be better to get 235/40/R17 from now on instead, as 40% of 235mm is 94mm thus a smaller sectional height and lower profile which should aid in handling. Are there any disadvantages to this on my car? Is there a limit on how low to go? Obviously it depends on the availablity of tyre sizes aswell.

Also, just as a thought what would happen if you had 40's on the back and 45's on the front, would it completly unsettle the car or plant it better on the road when cornering as the front is pushing more load onto the back tyres surely? bare in mind im not going to to attempt it im just curious as to the effects. :confused: :D

Cheers

Jono
 

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Lower profile tyres have less movement in them and can give less warning that they are about to give. Also the suspension etc is all designed around 45 profile tyres. TBH 45 is low enough, I personally wouldn't go to 40. Most people only drop profile size when they increase the size of their alloys in order to keep the overall radius the same as before.
 

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Discussion Starter · #3 ·
Ahh!! didnt think about the tyres letting go mate ;) Interesting :cool: Will stick with my current setup then Aidy :)
 

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Go for 235/40

235/40 is a much better choice for the sporty road going and occasional track going driver. Less flex in the sidewalls, better acceleration.
Few negatives to consider:
lower high speed, wrong speedometer reading, limit on rim width (235/40 will fit on 8.0-9.5 while 235/45 will fit 7.5-9.0)
 

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My E4 was on 205 50 16 I changed for 215 40 17 and its much much better in every way. While agreeing with Aidy to a point I think 235 40 s would be ok (better) as you have lots of width (as she said to me last night :D )
 
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