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Old 02-04-2009   #16
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Re: Tyre size

I have it all sorted with him now as his main concern was the insurance wouldnt cover them but after speaking to them they have said its fine and noted it on my policy. The speedo still over reads but not by much more than with my previous tyres as i drove to work with my sat nav this morning to give me an idea of if it was that much further out.
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Old 02-04-2009   #17
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Re: Tyre size

The speedo should read 3,45% more,but it's ok because by default it reads about 8% less so now you are closer to the real speed.
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Old 02-04-2009   #18
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Re: Tyre size

Wrong way round mate, it will read slightly slower: So when your speedo reads 70mph, you're actually travelling at 67.67 mph
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Old 02-04-2009   #19
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Re: Tyre size

Maybe I didn't make it clear...

The speedo by default reads about 6-8% less (don't remember exactly)
The change of the tires gives 3,45% more reading than the original.

So the diffrence now is smaller.The speedo is closer to the real speed.
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Old 02-04-2009   #20
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Re: Tyre size

No i know what your saying but if the speedo is 8% out already then i put a tyre on that is 3% out compared to the standard tyre that makes it so the total the speedo is out by is 11%
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Old 02-04-2009   #21
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Re: Tyre size

Quote Originally Posted by punto_matt View Post
No i know what your saying but if the speedo is 8% out already then i put a tyre on that is 3% out compared to the standard tyre that makes it so the total the speedo is out by is 11%
No,no...

By default speedo reads minus 6-8%

Change of the tyre diameter you have gives plus 3,45% than the standard ones.

So now the speedo should read -6+3,45= -2,55% to -8+3,45= -4,55%
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Last edited by ReaperX; 02-04-2009 at 16:40.
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Old 02-04-2009   #22
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Re: Tyre size

He's saying that the speedo is by default -8% {slower} and your tyres give you +3% {faster}, which would make your new speed -5%.

So you are closer to the true speed, than before.
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Old 02-04-2009   #23
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Re: Tyre size

Yeah i know what hes trying to say.
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Old 02-04-2009   #24
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Re: Tyre size

you gone through a set of tyres already lol how many miles you done?

see much improvement handling wise with the smaller sidewall?
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Old 02-04-2009   #25
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Re: Tyre size

Apologies Matt – ignore my comments on indicated speed (#15) …

ERROR
Quote Originally Posted by Caravadossi View Post
Inside the book:Also initially (I think) your indicated speed will still over-read your actual - although the calc. suggests otherwise (by 2mph or so), I’d argue that’s not enough to take-up all the over-read tolerance. But then as treadwear progresses, you’ll be moving towards where indicated speed = actual speed. How close you’ll be to the (illegal) actual speed being greater than indicated will need a harder look at the numbers.
… a little over-excited there as in my case I considered stepping-up to a larger RR & thus taking-up the over-read tolerance & moving more towards the (illegal) speedo under-read. When in contrast you’ve moved (the opposite way) to a smaller RR & thus increased the speedo over-read – but as you’ve tested, your thinking is straight (despite confusing comments) & it’s not worth fretting over.

Apologies if I’ve added to any confusion. I think I’m right (?) in saying that a step-up in RR bring’s one closer to where indicated speed = actual (or true) speed - & a step-down in RR will increase the speedo over-read & thus widen the gap between indicated speed & actual (or true) speed.

I’d find it interesting to know, from those with SatNav kit indicating mph – what their SatNav mph reading is against the indicated speedo mph, & what tyre size they’re running.
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Old 02-04-2009   #26
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Re: Tyre size

what tyre you running now matt
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Old 02-04-2009   #27
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Re: Tyre size

Quote Originally Posted by grande bolt View Post
what tyre you running now matt
205/40/17
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Old 02-04-2009   #28
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Re: Tyre size

Quote Originally Posted by Tris Harris View Post
you gone through a set of tyres already lol how many miles you done?

see much improvement handling wise with the smaller sidewall?
12k Fronts were down to indicators on 8k so i swapped them onto the back to get some more mileage out of them

Only been up and down the motorway with them so far, will take them out for a proper test tomorrow though. They screech like hell when launching quickly though lol


Quote Originally Posted by Caravadossi View Post
Apologies Matt – ignore my comments on indicated speed (#15) …

ERROR


… a little over-excited there as in my case I considered stepping-up to a larger RR & thus taking-up the over-read tolerance & moving more towards the (illegal) speedo under-read. When in contrast you’ve moved (the opposite way) to a smaller RR & thus increased the speedo over-read – but as you’ve tested, your thinking is straight (despite confusing comments) & it’s not worth fretting over.

Apologies if I’ve added to any confusion. I think I’m right (?) in saying that a step-up in RR bring’s one closer to where indicated speed = actual (or true) speed - & a step-down in RR will increase the speedo over-read & thus widen the gap between indicated speed & actual (or true) speed.

I’d find it interesting to know, from those with SatNav kit indicating mph – what their SatNav mph reading is against the indicated speedo mph, & what tyre size they’re running.
Nah no confusion mate My sat nav used to say when i was doing 70 i would be doing about 67/68 and now its down to 65/66 when at 70. Its no big deal i will just sit at a clock speed of 75 when on the motorway as i should be around 70 then

Quote Originally Posted by grande bolt View Post
what tyre you running now matt

205/40/17 Toyo T1R's
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Old 02-04-2009   #29
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Re: Tyre size

what they like
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Old 02-04-2009   #30
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Re: Tyre size

Road noise seems to be down a bit, personally the ride hasnt got any rougher and the tread depth is massive compared to the potenza's so should get more than 8k out the front 2 lol
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