Tyre Sizes - What's the deal

Post by **slobbo** » 07 Jan 2007, 22:13

I've been trying to work out what effect changing the size of my tyres will be. I found a spreadsheet which allows you to enter the tyre sizes and it gives you the given speed at various engine speeds.

The values below are for fourth gear in a syncro with 1.9TD. The first is using 235/75/15 and the second 215/70/15.

From what I have been told the 215/70s should give me a higher cruising speed but this spreadsheet doesn't seem to agree. What am I missing.

Gear Fourth Fourth
Ratio 0.85 0.85
RPM
0 0 0.00
500 9.31 8.65
1000 18.61 17.31
1500 27.92 25.96
2000 37.23 34.61
2500 46.53 43.27
3000 55.84 51.92
3200 59.56 55.38
3500 65.15 60.57
4000 74.45 69.23
4200 78.18 72.69
4500 83.76 77.88
5000 93.07 86.53
5200 96.79 90.00
5500 102.38 95.19
6000 111.68 103.84
6500 120.99 112.49
7000 130.3 121.15

The spreadsheet can be found below.
http://www.xmission.com/pub/users/a/acp ... earsxl.xls

Post by **sixsprings** » 07 Jan 2007, 22:23

slobbo wrote:The first is using 235/75/15 and the second 215/70/15.

From what I have been told the 215/70s should give me a higher cruising speed but this spreadsheet doesn't seem to agree. What am I missing.

you've been told wrong, and the spreadsheet is right.

235/75/15 will have a larger circumference, and therefore will give you higher gears than 215/70/15, by 7.62%

you don't need a spreadsheet.....
http://tyresave.co.uk/tyresiz2.html

Post by **slobbo** » 07 Jan 2007, 22:42

Ahhhhh - I was hoping to improve the top end cruising using different tyres. Will changing from MT to AT's make a difference then?

I don't want to make an expensive mistake.

Post by **andysimpson** » 07 Jan 2007, 23:51

slobbo wrote:Ahhhhh - I was hoping to improve the top end cruising using different tyres. Will changing from MT to AT's make a difference then?

I don't want to make an expensive mistake.

It will be just a reduction in tyre noise.

Post by **sixsprings** » 08 Jan 2007, 21:47

andysimpson wrote:
slobbo wrote:Ahhhhh - I was hoping to improve the top end cruising using different tyres. Will changing from MT to AT's make a difference then?

I don't want to make an expensive mistake.

It will be just a reduction in tyre noise.

and traction in mud

Post by **slobbo** » 08 Jan 2007, 22:03

Ok I am thinking of BFG 215/75/15 MT - Who knows the cheapest place to get them?

Or any other tyre choices available? I want the Mud Terrain tread.

Post by **Hacksawbob** » 08 Jan 2007, 22:55

Colway MTs or Machos are common choices

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Tyre Sizes - What's the deal

Tyre Sizes - What's the deal

Re: Tyre Sizes - What's the deal