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More power maybe doesn't require wider and bigger tyres and wheels?


Berg

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So, after looking at the dyno leaderboard I started wondering- with 300kw or so, do AWD owners not need to get wider wheels, since power is planted through all 4 wheels?

 

Seems like a reasonable thought to me, but just thought I'd ask. 17" wheels by 7 or 7.5 used to be pretty big back in the 90's, but now I see that every 100hp car and their owner's mobility scooter has at least 18" with wide 8.5" or more tyres. (Fashion!)

 

Every shop I've gone to (except my trusty local) has tried to sell me on 19x9.5 wheels, but I reckon it's just bling :-/

 

Opinions?

 

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The diameter of your rim means precisely three fifths of nothing in terms of getting power down (ok it means a little bit around sidewall flex but that's more of a 1000hp problem)

The width of your tyre does.

 

With 268kw, if I apply the jandle at anything below about 80kph it will break all 4 tyres loose. That's with reasonable quality 235/45/R17 on a 17x8 rim.

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Thanks boon, that's what I was wondering. I guess the better way to use the extra power would be semi slicks on the track. I guess AWD only gets us so far before the power becomes less usable. 

 

I'll ask a rally driver with tarmac experience and see what they say as well.

 

 

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I have a lot to do with this. Massive misconceptions about more width means more grip. It's all wrong. If you double width of tyre you half the pounds per square inch of pressure. So equal grip. Only 2 things change that. A 1/2 width tyre will wear out twice a fast. So manufacturers usually use a softer compound on wider tyres to get more grip. 

 

Obviously if you are spinning a wheel a wider tyre will overheat slower and offer more grip longer. 

 

We run 225 wide semi slick tyres for drag racing on 350wkw. Traction only breaks off the line but we keep snapping front axles. Road duty traction is ok from 3rd gear up unless car upset. Remember bigger diameter tyres will usually have better corner grip but smaller diameter usually has more acceleration and braking grip as tyre can deform to the road imperfections. 

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1 hour ago, gotasuby said:

I have a lot to do with this. Massive misconceptions about more width means more grip. It's all wrong. If you double width of tyre you half the pounds per square inch of pressure. So equal grip. Only 2 things change that. A 1/2 width tyre will wear out twice a fast. So manufacturers usually use a softer compound on wider tyres to get more grip. 

 

 

This is a high-school level simplification of calculating mechanical grip; if it was the case nobody in big $$ drag racing would bother tubbing the chassis etc, they would just run ridiculously soft compound 215's and change them every run.

There are obviously times where width won't do anything for you, i.e. ice/snow rally where you want maximum pressure to drive your studded tyres into the surface, but on tarmac more contact patch definitely equals more grip, all other factors remaining the same (compound etc)

 

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Great replies, I'll be reading up about those theories. 

 

So much disinformation in forums on this topic that it's great to hear from people who have either experience or put in the time to understand the main factors and how they might affect their ride.

 

I'll post a link to any literature I find worthwhile. 

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interesting read as well, i do notice in the wet on my standard 17s if i boot of the line the car steps out on boost on 1st and 2nd but with the 18s i don't have any problems with traction at all, the 17s have RE0020s on them so they are decent tires as well, but it could have to do with other factors as well i guess....

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17 minutes ago, dmacnz said:

Subarus running 240 slicks are beating Porsche cup cars with 290+ slicks..... Albeit the Subarus I'm referring too have much more power!

 

The cup car drivers you speak of must be fairly new/inexperienced or taking easy surely??? Back in the days of the NZ Porsche GT3 Championship the older cup cars (996-997) were doing lap times around NZ tracks that most Subarus would struggle to match these days (there are 3 Subaru circuit cars I know of that lapped close to those times - all 3 had VERY good drivers, and yes, more HP than a cup car).

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2 hours ago, 4G63B8 said:

i do notice in the wet on my standard 17s if i boot of the line the car steps out on boost on 1st and 2nd but with the 18s i don't have any problems with traction at all ...

The 18s+tyres don't happen to have a larger OD than the 17s+tyres do they?

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2 hours ago, Joker said:

too many variables & unknowns & yea contact patch "should" be the same / similar 17" vs 18"

 

edit : 18"s could be heavier too.... 'providing' more mass / grip unsprung weight

 

false    xD....it doesn't matter how much grip you have if the tyres not touching the road..

 

I should read slower...

Edited by pedro
factually incorrect
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