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Author Topic: Wheels, diffs & speedos  (Read 646 times)

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Wheels, diffs & speedos
« on: 16 May 2012, 05:47:00 pm »
I was trying to work out which speedo I would need to give an accurate(ish) reading with 3.54 diffs and 7.50 tyres. I'm sure there was something before, but I can't find it anywhere.  Anyway I ended up writing this formula,  if it's wrong please let me know as I ain't no mathematician but it's how I'm understanding it!

(5280/((W x Pi)/12)) x (D/2.2) = TPM

Where:

W = wheel diameter

D = Diff

TPM = Turns per Mile (Markings on speedo)

So therefore:

(5280/((31 x Pi)/12)) x (3.54/2.2) = 1049

Which I reverse engineered from another formula here

Or am I just making **** up to keep myself occupied?
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Re: Wheels, diffs & speedos
« Reply #1 on: 16 May 2012, 06:01:03 pm »
Don't you have work to do or some sprogs that need a beasting! ::)
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Re: Wheels, diffs & speedos
« Reply #2 on: 16 May 2012, 06:03:27 pm »
Quote from: Mrs Stuey on 16 May 2012, 06:01:03 pm
Don't you have work to do or some sprogs that need a beasting! ::)

Cheers for that golden nugget of advice,  you're on the forum so the chores best be done!
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Re: Wheels, diffs & speedos
« Reply #3 on: 16 May 2012, 06:05:52 pm »
TPM? Shouldn't that be Turns Per Mile?

Slap me if I'm wrong!

Mr.P

Ps. You're not Your!

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Re: Wheels, diffs & speedos
« Reply #4 on: 16 May 2012, 06:09:43 pm »
Quote from: Mr.Pickles on 16 May 2012, 06:05:52 pm
TPM? Shouldn't that be Turns Per Mile?

Slap me if I'm wrong!

Mr.P

Ps. You're not Your!

Runs for cover!

Don't know what you're talking about,  are you going mad?
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Re: Wheels, diffs & speedos
« Reply #5 on: 16 May 2012, 06:19:08 pm »


Cheers for that golden nugget of advice,  you're on the forum so the chores best be done!
[/quote]

Hmmm that's brave talk, good job you are at the other end of the country! :blahblah
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Re: Wheels, diffs & speedos
« Reply #6 on: 16 May 2012, 06:20:47 pm »
Quote from: stuey on 16 May 2012, 06:09:43 pm
Quote from: Mr.Pickles on 16 May 2012, 06:05:52 pm
TPM? Shouldn't that be Turns Per Mile?

Slap me if I'm wrong!

Mr.P

Ps. You're not Your!

Runs for cover!

Don't know what you're talking about,  are you going mad?

I'm well known for my lack of sanity!  :confused:

Mr.P
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"Pickles" The 109 Breaking Down Truck. 1963
"Sandy" 88 squiggy top project. 1960
OLLR Road Maggot Society member. (Classic Chapter)

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Re: Wheels, diffs & speedos
« Reply #7 on: 16 May 2012, 06:34:39 pm »
Quote from: Mrs Stuey on 16 May 2012, 06:19:08 pm


Quote
Cheers for that golden nugget of advice,  you're on the forum so the chores best be done!

Hmmm that's brave talk, good job you are at the other end of the country! :blahblah
You wouldn't be chompsing off if I wasn't!
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Re: Wheels, diffs & speedos
« Reply #8 on: 16 May 2012, 06:46:16 pm »
Pretty sure that corroborates what FenTiger has said - 1050.

Saying that, I have something similar in the dormobile and it is way out
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Re: Wheels, diffs & speedos
« Reply #9 on: 16 May 2012, 10:55:52 pm »
Quote from: AlexB on 16 May 2012, 06:46:16 pm
Pretty sure that corroborates what FenTiger has said - 1050.

Saying that, I have something similar in the dormobile and it is way out

OK Alex,  I'm sure I've got a 1080 or so in the Lightweight and it only slightly under reads,  so it kind of matches up to a certain extent ??
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Re: Wheels, diffs & speedos
« Reply #10 on: 17 May 2012, 06:16:19 am »
Or you could just use a smart phone, a lump of blutac and an app that tells you your speed.
I've given up looking for speedos that have the right tpm, the last one from eblag was stated as lwb so I asked the question about its tpm number and was told it was ex mil refurb but with a swb dial.
I was suckered, it wasn't and its still out, and now it bounces up and down when ever I hit fifty.
Might lay out and get one for my growing collection rebuilt by a reputable company.
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Re: Wheels, diffs & speedos
« Reply #11 on: 17 May 2012, 09:04:30 am »
We fitted a bike speedo to Patrick's Carawagon.

It's fairly easy to do, and being small, is quite discreet stuck to the dash near the steering wheel.

The sensor is fitted to a short piece of strip steel fixed behind a swivel housing bolt, and the magnet is a high power one just stuck to the inside of the wheel rim.

Seems to work quite well, though it sometimes misses a pulse so flickers down to half speed for a second.
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Re: Wheels, diffs & speedos
« Reply #12 on: 03 June 2012, 06:37:32 pm »
Quote from: Mrs Stuey on 16 May 2012, 06:01:03 pm
Don't you have work to do or some sprogs that need a beasting! ::)

Are you an instructor @ the royal corps are you Stuey?
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Re: Wheels, diffs & speedos
« Reply #13 on: 03 June 2012, 07:37:58 pm »
Quote from: ant2f159 on 03 June 2012, 06:37:32 pm
Quote from: Mrs Stuey on 16 May 2012, 06:01:03 pm
Don't you have work to do or some sprogs that need a beasting! ::)

Are you an instructor @ the royal corps are you Stuey?


I'm a light bulb tester and fitter during the day and in my spare time I train dolphins  :smile1
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Re: Wheels, diffs & speedos
« Reply #14 on: 03 June 2012, 08:39:43 pm »
What you need is the speedometer out of a Triumph Stag. That's what I'm told my speedo is out of and it's 1120tpm. It's near enough anyway. I paid £10 for it at Huddersfield automjumble a few years ago.

As you can see, it fits a Land Rover dash perfectly.
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