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New Discs and Wheels... now for some questions!
https://ausmini.com/forums/viewtopic.php?f=5&t=932		 Page 1 of 1
Author:  redfive [ Wed Jun 23, 2004 3:13 pm ]
Post subject:  New Discs and Wheels... now for some questions!
I just got some new wheels and 8.4 inch discs on my mini yesterday, and I have a few questions, but first, some pics...

What a beast!
Image

Old vs New
Image

From behind
Image

Now, as you can see, there's not a lot of clearance in between the wheel and the arch.
I've noticed that the left side of the car is a lot lower than the right side of the car, can this be fixed by just playing with the hydro stuff?

What size are the original mini wheels? I'm trying to figure out how far out my speedo is now :).

My discs are currently rubbing on the pads slightly at all times, I am assuming they were set up like this so that they can settle a bit, but they are getting quite warm driving around. I'm taking it back on Saturday for a checkup, but I'm wonder if it doesn't improve pretty quickly if I should adjust them myself.

Sorry if pics take a little while to load!
Author:  thommo09 [ Wed Jun 23, 2004 3:23 pm ]
Post subject: 
you got these from brickworx over the weekend did you? :)

may i ask how much he charged you?

umm..discs shouldn't need to be adjusted, they're supposed to be self adjusting
-original wheel size is 10"

sorry but i can't help on the hydro...i wouldn't know where to start with that stuff

-jimmy
Author:  min13k [ Wed Jun 23, 2004 5:40 pm ]
Post subject: 
just a few pumps of hydro fluid or let some out of the other side
makka
Author:  leyland74 [ Thu Jun 24, 2004 11:02 am ]
Post subject: 
By original wheel size he's talking about the tires. We can't remember if they are 145/70-10's, 145/75-10, 135/70-10 or 135/75-10.

I think they're 145/70-10's but not sure.

Oh and he doesn't have a hydro pump. So I guess it means letting some out.

BTW is the hydro got a seperate front and rear or left and right. So if it's front and rear you'd be able to make the front lower than the rear but not with the second one.
Author:  Gordie [ Thu Jun 24, 2004 12:09 pm ]
Post subject: 
you can get 135's?
i thought you could only get 145, and 165's for the road?
and yeah they look like 145/70/10's to me
if you still have the old wheels it's written on the side wall of the tyre.
they look good by the way :D
Author:  bnicho [ Thu Jun 24, 2004 1:00 pm ]
Post subject: 
Original tyre size was crossplies for this model. :)

145R10 is the closest available these days in radials. I beloeve they are actually 145/80 R10, not 70. The alternative 10" size is 165/70 R10.

Briefly the first number (eg: 165) is the width of the tyre, the second number (eg: 70) is the sidewall height as a percentage of the width. This is called the aspect ratio. So 165 x .7 = 115.5 mm tyre sidewall. The aspect ratio is not specified for 80 series tyres. So 145 R10 is 145 x .8 = 116mm sidewall or bugger-all different from a 156/70 R10. To find out the rolling damater you muliply sidewall height by two, then add the rim daimater (10 x 25.4 = 254mm). So a 145 R10 tyres has a rolling diameter of 116 x 2 + 254 = 486mm.

Your new tyres are probably

145/70 R12: 101.5 x 2 + 304.8 = 507.8

or 165/60R12 : 99 x 2 + 304.8 = 502.8

So your speedo will underread by 4%ish (read lower 4% lower than before at the same road speed.

You can compare the difference the new tyres will make to your speedo at this site:

http://www.skipspeedracing.com/misc/CalcSpeed/
Author:  leyland74 [ Thu Jun 24, 2004 1:52 pm ]
Post subject: 
Yes, exactly.

His 12's are 145/70/12 so I was telling him his speedo will be out quite a bit and he should get lower profile tyres as this will reduce the rolling diameter.

According to miata (http://www.miata.net/garage/tirecalc.html) the difference is more like 11.1% so his speedo will tell him 60 kph ( it's actually in miles but you know what I mean) when he's going 66.6 kph.

Probably worse since the speedo is in mph so he's probably going a bit fast anyhow, and if he's in a 80 zone the he'd be doing 88.8. All ticketable.
Author:  Anto [ Thu Jun 24, 2004 2:15 pm ]
Post subject: 
I find it much more reliable to read my speed from the tacho. You see I have one of those original Smiths 'generalised' speedos, where I could at any moment be doing anything from 10mph to 90mph. From what I can tell it bears no relation to the actual speed of the car (where do they take the speed readings from? The rear left overrider?). Wouldn't matter anyway as the speedo is technically for a 3.6 diff and I have a 3.4.

What's more, if you change wheel size or diff ratio, you simply have to change your calculations, you don't need a new tacho :wink:

Anto.
Author:  redfive [ Thu Jun 24, 2004 3:12 pm ]
Post subject:  Tyre Sizes again
Tire Size Comparison

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
1. 145/80-10 4.6in 9.6in 19.1in 60.1in 1054 0.0%
2. 145/70-12 4.0in 10.0in 20.0in 62.8in 1009 4.5%
3. 165/60-12 3.9in 9.9in 19.8in 62.2in 1019 3.5%

This info is from http://www.miata.net/garage/tirecalc.html.

1. Stock tyres (I think). They don't have the profile written on them, I checked last night.
2. Current tyres - with my current tyres my speedo is reading 4.5% high, so when I'm doing 37 miles an hour according to the speedo, i'm actually doing closer to 39. There's a good chance the speedo is out by more than that anyways :).
3. Tyres I want - with the tyres I will get next (Yoko A032R's :)), it will be even less out, so thats a bonus.

Thanks for the help people. Everything will get messed up if I get a new diff anyway!
Author:  bnicho [ Thu Jun 24, 2004 5:55 pm ]
Post subject: 
I have a 3.44 Cooper S speedo and 3.65 gearing at the moment, so I run off the tacho and ignore the speedo. When my new gearbox is in I will have a 3.44 diff again.

But tachos can be inaccurate. My mate's XY GT factory tacho was found to be 500 rpm optimistic at 5000 rpm!! :shock:
Author:  bnicho [ Thu Jun 24, 2004 5:58 pm ]
Post subject: 
Miata Net site does not calculate 10" rims (for me anyway). So where are you getting your figures of 11%??
Author:  Anto [ Thu Jun 24, 2004 7:50 pm ]
Post subject: 
bnicho wrote:
But tachos can be inaccurate. My mate's XY GT factory tacho was found to be 500 rpm optimistic at 5000 rpm!! :shock:


I have this strange feeling my tacho is out the other way - you know, the one that gets me speeding fines and when I think I'm redlining I'm actually a few hundred rpm past..... It's a Super Cheap tacho so 'nuff said :wink:
Author:  redfive [ Thu Jun 24, 2004 8:41 pm ]
Post subject: 
Use the bit down the bottom Bnicho, you can fill it in yourself there.

I did: stock size: 145/80-10
Then to compare: 145/70-12, 165/60-12
Author:  grouse_bogun [ Fri Jun 25, 2004 8:40 am ]
Post subject: 
I certainly don't want to be nosey, so tell me to P-off if you like, but how much did the discs set you back?

I would like to know for future reference if I decide to rob a bank and have money to burn. PM me if you like.

Cheers.
Author:  leyland74 [ Fri Jun 25, 2004 2:36 pm ]
Post subject: 
redfive wrote:
Use the bit down the bottom Bnicho, you can fill it in yourself there.

I did: stock size: 145/80-10
Then to compare: 145/70-12, 165/60-12


I too scrolled down to the manual editing version but assumed standard was 145/70-10 and compared to 145/70-12 the difference here is 11.1%.

Results:
Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
145/70-10 4.0in 9.0in 18.0in 56.5in 1121 0.0%
145/70-12 4.0in 10.0in 20.0in 62.8in 1009 11.1%


:)
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