Author Topic: 4x4 Wheels and Tyres  (Read 1765 times)

Cunning Plan

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4x4 Wheels and Tyres
« on: May 08, 2008, 07:38:54 am »
What is the deal with 4x4 wheel and tyres, I know that you can NOT run a different tread or wheel to the other wheels as it will wreck the box / mesh.  So all 4 wheels and tyres need to be the same.....

If you have a truck with 16" wheels with 245/70R16 tyres and the manufacturer offers 18" wheels with 255/60R18 tyres, obviously it has all been worked out so that the speedo wont be out and the tranny can cope with it all just fine.

Am I right in thinking I can have ANY sort of wheel on the truck as long as they are all the same for the tranny to cope with and they arent bigger than the combined 18" with 255 tyres (as then the speedo will be reading slower than what you are actually doing)


1968 VW T2 Bay Bus (currently being restored and upgraded)
1999 Jeep Cherokee XJ (modern classic daily driver)

Roadkill

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4x4 Wheels and Tyres
« Reply #1 on: May 08, 2008, 08:02:12 am »
I would've thought, within reason, that the trans will cope with a larger dia wheel/tyre combo.

It basically means higher top speed, but slower acceleration.

The problem, as you pointed out, is the difference in rolling circumference hence difference in speedo read out.

When in doubt I go to the wheel and tyre bible.

About quarter of the way down on page two gives you what you need.

http://www.carbibles.com/tyre_bible.html

Cunning Plan

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« Reply #2 on: May 08, 2008, 08:47:52 am »
Quoting: Roadkill
About quarter of the way down on page two gives you what you need.

\" target=\"_blank\" rel=\"nofollow\">http://www.carbibles.com/tyre_bible.html


Awesome website, I didnt know there was soo much to tyres!!!!!!  
1968 VW T2 Bay Bus (currently being restored and upgraded)
1999 Jeep Cherokee XJ (modern classic daily driver)

Cunning Plan

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« Reply #3 on: May 08, 2008, 09:13:33 am »
Thanks RK Just read through all of the wheel and tyre section..

Liking the javascript calculator that works it all out for you on page 2..  Cant believe I didnt know about that site

1968 VW T2 Bay Bus (currently being restored and upgraded)
1999 Jeep Cherokee XJ (modern classic daily driver)

Roadkill

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4x4 Wheels and Tyres
« Reply #4 on: May 08, 2008, 09:25:27 am »
No problem.

F Body

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« Reply #5 on: May 08, 2008, 11:51:33 am »
Put four new wider tyres onto the Panda the other week so I thought I'd provide a 1,000 mile update :

The original tyres were Continental Eco Contact 15 x 165 and just sort of 30k they were below the legal limit. Interestingly for a front wheel drive car, it was the rear's that wore out first on the edges
I rotated them several times front to back, but they were still the same.
The wet weather grip on the original low rolling resistance tyres was very poor with masses of under steer

Continental don't do a wider size and Khumo don't do 15" , so I fitted middle of the range Hankook 15 x 175 tyres

Wet weather grip is now vastly improved with at least 50% less under steer and dry grip is now good enough to lift the inside rear wheel when Management is progressing around high speed corners  

How ever there are two minus points, the tyres seem more noisy on concrete surfaces and the fuel consumption has dropped by about 5 mpg.
It was averaging 52 mpg around town, now it's 47 / 48 mpg and at 75mph it's dropped from around 66/67 mpg to 62/63 mpg

It'll be interesting to see how they wear compared to the Conti's, with the Conti's cost £67 each and the Hankooks just under £25 each

art b

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« Reply #6 on: May 08, 2008, 12:13:24 pm »
30k miles on a set of tyres is pretty good...
This forum needs, ''YOU'' posting,Not just reading ! :moon:

Roadkill

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« Reply #7 on: May 08, 2008, 01:16:38 pm »
Quoting: F Body
Wet weather grip is now vastly improved


That will be the compound - nothing to do with the tyre width - wider tyres in the wet will result in relatively less grip.

F Body

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« Reply #8 on: May 08, 2008, 03:29:50 pm »
Quoting: Roadkill
wider tyres in the wet will result in relatively less grip.


Agreed the compound will be different, but surely a wider tyre gives a greater contact area and so increases grip providing the water clearance properties are similar  

Roadkill

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« Reply #9 on: May 08, 2008, 04:18:16 pm »
Quoting: F Body
but surely a wider tyre gives a greater contact area and so increases grip providing the water clearance properties are similar


No.

That works in the dry.  But in wet you're relying more on friction (grip) caused by pressure.  Basically the weight of your car spread over the area put down by the tyres produces pressure and grips the road.

Pressure = weight / area

The smaller the area (same weight), the more friction will be produced.

If you increase the area (same weight) you're merely spreading the same load out, hence reducing effective grip.


Roadkill

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« Reply #10 on: May 08, 2008, 04:21:54 pm »
It's also worth mentioning that fatter tyres, even in the dry, do not necessarily produce more grip either.

It only distorts the patch on the ground produced by the tyres from a square-ish shape (with O.K front and side grip capabilities) to a more rectangular (letterbox) shape with excellent front grip, but lousy side gripping ablities.

F Body

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« Reply #11 on: May 08, 2008, 07:06:19 pm »
Quoting: Roadkill
Pressure = weight / area

The smaller the area (same weight), the more friction will be produced.



It's at times like this I wish I wasn't so thick

So there is probably some weird formula, so clever people can work out the optimum size

Cunning Plan

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« Reply #12 on: May 08, 2008, 07:18:18 pm »
Quoting: F Body
So there is probably some weird formula, so clever people can work out the optimum size


There is!  Its on page 2 of RKs site..  
1968 VW T2 Bay Bus (currently being restored and upgraded)
1999 Jeep Cherokee XJ (modern classic daily driver)

F Body

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« Reply #13 on: May 08, 2008, 07:27:46 pm »
Quoting: Cunning Plan
There is! Its on page 2 of RKs site..


So there is

Quoting: F Body
So there is probably some weird formula


"The area of your contact patch is going to be roughly 375 / 2.11 = 177.7cm² (weight divided by pressure)
Let's say your standard tyres are 185/65R14 - a good middle-ground, factory-fit tyre. That means the tread width is 18.5cm side to side. So your contact patch with all these variables is going to be about 177.7cm² / 18.5, which is 9.8cm. Your contact patch is a rectangle 18.5cm across the width of the tyre by 9.8cm front-to-back where it sits 'flat' on the road.
Still with me?"

"Overall, the area of your contact patch has remained more or less the same. But by putting wider tyres on, the shape of the contact patch has changed"

I think I'll just stick with :

"do wide tyres give me better grip ?
Fat tyres just look good. In fact they look stonkingly good"

Amen

art b

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« Reply #14 on: May 11, 2008, 10:21:31 am »
i would have though wider tyres, give better grip on fast cornering...
This forum needs, ''YOU'' posting,Not just reading ! :moon:

Roadkill

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« Reply #15 on: May 11, 2008, 04:15:32 pm »
Quoting: art b
i would have though wider tyres, give better grip on fast cornering...


Nope - not necessarily - it's all to do with the shape and size of your footprint.

philoldsmobile

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« Reply #16 on: May 11, 2008, 05:07:09 pm »
Quoting: Roadkill
That will be the compound - nothing to do with the tyre width - wider tyres in the wet will result in relatively less grip.



yup.. when i used to race RC saloon cars,  we used to run front (narrow) wheels all round in wet weather, as they provide more pressure on the contact patch, and cut throught the water better.

philoldsmobile

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« Reply #17 on: May 11, 2008, 05:07:51 pm »
Quoting: art b
i would have though wider tyres, give better grip on fast cornering...



many many sierra cosworth owners thought the same thing......

Rob

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« Reply #18 on: May 11, 2008, 05:27:22 pm »
Quoting: F Body
It's at times like this I wish I wasn't so thick


Don't do yourself down Mart..... Not all of us think of you in that way