Wider tyres for 16" rear rims
Discussion
Anyone know if you can get wider (but maintaining same rolling radius / diameter) width tyre on a rear Chim / Griff 500 7.5x16" 500 rim. I know the Tuscan have 255 instead of 245 but would the rolling radius / diameter me the same if this could be obtained in 16 instead of 18".
And no I don't want bigger wheels (have 16" front) - it is a Q car but any more traction with my bonkers engine will be welcome, if not I'll just have to drive sideways every where!
And no I don't want bigger wheels (have 16" front) - it is a Q car but any more traction with my bonkers engine will be welcome, if not I'll just have to drive sideways every where!
www.dunloptyres.co.uk/site/tyres/car/searchResults/patterns/SP9000/
Ooh well worth a try - sideways it is then..........
Ooh well worth a try - sideways it is then..........
If you're sticking with the 7.5" rim then the optimum size is roughly 225mm, anything wider than that starts to compromise the shape of the contact patch in cornering. The factory fit 245 is arguably too wide, and going even wider is probably not a smart move unless you fit wider rims.
jellison said:
I'll stay with what I have - 400+ft/lb and going skinner is not the plan.
Only saw the pic's of your Blown V8 (NICE) after I had left VW - nice - may go that route some day - then I will need taller and wider rims!
Pictures where?
Hasn't been on the rollers yet but I would guess bhp in the low 300s and torque somewhere between 350 and 400. The power gains are relatively modest and could easily have been achieved by a normally aspirated engine. But the NA engine would have a limited life, be relatively cammy, high oil consumption and generally high maintenance. And when the expensive bits wear out and break you've lost your investment. What's nice about this conversion is that it uses a fairly standard base engine and the expensive bits won't wear out. When the 4.6 blows up I can drop in another one and get exactly the same performance good for another 100k miles for a couple of grand. But apart from anything else I wanted to do for the hell of it.
You've already got way more power than I have so I can see why you'd need more traction especially if you add a supercharger
on the other hand isn't the main attraction to have more power than grip? 
GreenV8S said:
If you're sticking with the 7.5" rim then the optimum size is roughly 225mm, anything wider than that starts to compromise the shape of the contact patch in cornering. The factory fit 245 is arguably too wide, and going even wider is probably not a smart move unless you fit wider rims.
Yes, that's the problem and it's why a few people have switched to 9" rims at the rear. Originally the Griffs had 205f/225r so no problem. A 265/40/17 on a 9.5" rim may suit you.
I'll stay with what I have (as I have grown to like them - and invested a stack in immaculate rears for the front). I used to driving side ways anyway. TR has 250bhp through 205 all round. The New SP9000's on th front are great so get a new set of std 245 rears.
Maybe go bigger if I blow it!
Maybe go bigger if I blow it!
I think this emphasis on tyre width is a bit of a red herring. Wider tyres do not directly equate to more grip.
If you fit wider tyres that changes the shape of the contact patch, making it shorter and wider. The contact patch area doesn't change unless you change the tyre pressure. Making the contact patch shorter and wider reduces changes the variation in shear forces throughout the tread, allowing more of the tyre to reach maximum grip at the same time in cornering. This means you have slightly more cornering grip at the limit, and it peaks at lower slip angles, but it drops off more rapidly when you exceed the slip angle for maximum grip. You also get less self-aligning torque so less feeback through the wheel.
Having gone for a wider tyre with less deflection you can afford to run the tyre slightly softer, increasing the contact patch area slightly. Running the tyre softer increases the coefficient of friction slightly. These are all very small effects though. 50% wider tyre might mean you can afford to run 20% bigger contact patch area, equating to perhaps 5% higher coefficient of friction. Choosing decent tyres and getting the suspension set up right will make far more difference than this.
>> Edited by GreenV8S on Wednesday 23 February 13:42
If you fit wider tyres that changes the shape of the contact patch, making it shorter and wider. The contact patch area doesn't change unless you change the tyre pressure. Making the contact patch shorter and wider reduces changes the variation in shear forces throughout the tread, allowing more of the tyre to reach maximum grip at the same time in cornering. This means you have slightly more cornering grip at the limit, and it peaks at lower slip angles, but it drops off more rapidly when you exceed the slip angle for maximum grip. You also get less self-aligning torque so less feeback through the wheel.
Having gone for a wider tyre with less deflection you can afford to run the tyre slightly softer, increasing the contact patch area slightly. Running the tyre softer increases the coefficient of friction slightly. These are all very small effects though. 50% wider tyre might mean you can afford to run 20% bigger contact patch area, equating to perhaps 5% higher coefficient of friction. Choosing decent tyres and getting the suspension set up right will make far more difference than this.
>> Edited by GreenV8S on Wednesday 23 February 13:42
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