Phil B's XB coupe

[Phil B]

Went to the drive in last night! Awesome night with the Mrs.

[Phil B]

Ordered new rims and tyres! Should look much better with new boots.

How do I work out what size speedo gear I'll need? The new tyres will be quite different size wise so I figure I'll need a different one.

[NeillNZ]

Originally Posted by Phil B

Ordered new rims and tyres! Should look much better with new boots.

How do I work out what size speedo gear I'll need? The new tyres will be quite different size wise so I figure I'll need a different one.

Can the tyre shop tell you the specification for the rolling circumference? Failing that, what size are the rear tyres and what is your diff ratio?

There are calculators online, but no hard to do yourself:

Your stock tyres were perhaps 205-70-14, which have a rolling diameter of 642mm and circumference of 2018mm.

So they need to rotate 1000/2.018 = 495.53 times for every kilometre, or 4**** times to travel 100km. 4**** times / 60 minutes = 825.9 rpm, that is your wheel speed.

If your diff ratio is 2.92 then the engine rpm will be 825.9 x 2.92 = 2412rpm. That is of course the engine speed in top gear 1:1.

Now suppose your new tyres are 245-50-15 which has a circumference of 1.966m, with the same engine rpm and diff ratio your speed will now be 97.4km/hr, less speed for the same rpm because the tyre circumference is smaller.

In this example the change is not very significant especially when you take in account tyre wear and speedo inaccuracy.

*EDIT, for some reason the forum thinks I'm swearing when I type forty nine thousand, five hundred and fifty five.

[Phil B]

Originally Posted by NeillNZ

Can the tyre shop tell you the specification for the rolling circumference? Failing that, what size are the rear tyres and what is your diff ratio?

I'll have more of a difference than your example, but thanks for that, it really helped me crunch some numbers.

My speedo is pretty much right on now with my 265/50R14s.
My new tyres will be 295/50r15.
Diff ratio is 2.92
Gearbox is a Single Rail

I used an online calculator to work out this:
New tyres will have 174.05mm more circumference than the old.
Old tyres give 1497.7 turns/km out the back of the gearbox.
New tyres give 1375 turns/km out the back of the gearbox.


My question now is: how does this relate to number of teeth on the speedo gear?

[Bearman]

Do you have an I-phone or smartphone? Just download a speedometer app and compare that to your speedo to learn what it reads compared to your actual road speed.

My speedo is currently not working so with this app I know by my tachometer what my speed is,

[Phil B]

Originally Posted by Bearman

Do you have an I-phone or smartphone? Just download a speedometer app and compare that to your speedo to learn what it reads compared to your actual road speed.

My speedo is currently not working so with this app I know by my tachometer what my speed is,

I could, but I really would like it working because the coupe is my daily driver. So I figure for a bit of mucking around, its worth it.

[darkside]

my speedo is in mph so I use an app called digi hub,works a treat and even gives u heads up display on yur windscreen in various colours ,makes me feel like some sorta tek whiz type genious...doc

[Phil B]

On a slightly different note, how much is a fair price to sell my old wheels and tyres for?
2x 14x7 Chrome 12 slotters with 235/60R14s with lots of tread. And 2x 14x8 with 265x50s with a fair amount of tread but they're ageing. Chrome is very good still.

[NeillNZ]

I have made up a mini spreadsheet to work out what you might expect. I will be doing something similar in my XC as I want to retain the original speedo.

For this example I have kept the tyre size the same but changed the speedo drive gear to one of the 6 available from GT Ford Performance for the BW box. I have based it on a stock 205-70-14 tyre with a circumference of 2018mm. I have increased the engine rpm to make the speedo read 100km/hr then calculated the actual speed and error.

I wonder if your old 265-50-14s are close to the stock circumference, since you reckon your speedo reads about right.

So if we know the circumference of your new tyres we can plug that into the spreadsheet and see what happens with all the 6 different speedo drives.

The circumference can be calculated but the actual manufacturers spec will be more accurate I reckon.



*edit* I have also had to make an assumption about the stock drive gear. The calculations are based on the ratio between 2.92 and what is available. Possibly the stock gear is a theoretical 2.75, which will throw the calcs out a bit. Hope that makes sense!

[Phil B]

Originally Posted by NeillNZ

I have made up a mini spreadsheet to work out what you might expect. I will be doing something similar in my XC as I want to retain the original speedo.

For this example I have kept the tyre size the same but changed the speedo drive gear to one of the 6 available from GT Ford Performance for the BW box. I have based it on a stock 205-70-14 tyre with a circumference of 2018mm. I have increased the engine rpm to make the speedo read 100km/hr then calculated the actual speed and error.

I wonder if your old 265-50-14s are close to the stock circumference, since you reckon your speedo reads about right.

So if we know the circumference of your new tyres we can plug that into the spreadsheet and see what happens with all the 6 different speedo drives.

*edit* I have also had to make an assumption about the stock drive gear. The calculations are based on the ratio between 2.92 and what is available. Possibly the stock gear is a theoretical 2.75, which will throw the calcs out a bit. Hope that makes sense!

Thanks for that, that sure helps! My old tyres are close to the stock size, they are 1950mm circumference.
My new ones should be 2124mm, giving a wheel speed of 785rpm@100km/h.
So that's close to a 2.75 ratio gear.

What do you mean by the last part?

[NeillNZ]

I have slotted your tyre dimensions into the spreadsheet:



This is all theoretical of course but that said I reckon you should get the 2.75:1 gear and try it. Better to have your speedo over-read a bit than under-read. Typically they under-read by a few ks at 100km/hr anyway. Do yuo have a smart phone with GPS or a sat-nav you can use to verify it?

I'm not sure how hard it would be to swap the gear on your gearbox. I know on my C4 it was a pretty easy job as the gear is on the end of the speedo cable where it goes into the transmission.

Perhaps undo your speedo cable and see what it's like and note the colour of the gear that is on there now.

I wish I could be more help, but I don't have any real-world experience with doing this. It's something that I'm looking at doing on my car.

Oh yeah, ignore that last part in my post about the ratios. The maths dosn't require us to know the ratio that is in there right now as it is all relative. Bit of a brain fart on my part.

[NeillNZ]

Here are a couple of photos of the speedo cable from my C4:

[Phil B]

Had a look this arvo, mine is pinkish

[Phil B]

How do you lubricate the speedo cable? Is there one end you take off then pull the cable out from the housing? Also what do you use to lube it with? Grease, oil or something else?

[Phil B]

Originally Posted by NeillNZ

I have slotted your tyre dimensions into the spreadsheet:

Perhaps undo your speedo cable and see what it's like and note the colour of the gear that is on there now.

Do you have the teeth counts that relate to the different ratios? I pulled mine out again to double check and I have 19 teeth.

[NeillNZ]

Originally Posted by Phil B

Do you have the teeth counts that relate to the different ratios? I pulled mine out again to double check and I have 19 teeth.

No don't have the teeth count. Looking online there are some suppliers that give the teeth count for their "generic Ford" speedo gears, but I cannot be sure they will fit the Borg Warner boxes.

May have to call GT Ford Performance and get them to check. They don't give the teeth count on their website.

[Phil B]

First scrape :(
Found a wooden fence while turning out of the super tight work car park.

[Phil B]

Any tips for trouble shooting the horn? I only get a very faint noise when i press or release the switch. When the switch is pressed I get 11.8v at the horn. Is this to low for it to work? Have 22 ohms resistance in the earth, that might be it, ill check that first

[Phil B]

Was the earth, lots of paint between the horn and the body. All good now

[Phil B]

Had the fuel pickup out last night to adjust it to get more than 40L useable. Filled up at the servo this morning, had fuel ****ing out everywhere. Go home, defuel, get the seal sitting right, refuel, check no leaks, have shower to was petrol off, go to work. The joys hey!

[Phil B]

Anyone recommend a good place in Cairns for work on my coupe? Service, carb tune, exhaust welding and roadworthy.

[Phil B]

It's all happening:
New wheels and tyres are here, will go on this arvo.
Getting a service, idler arm bush, steering arm joint, front shocks and rear gearbox seal later this week.
Then roadworthy and rego with the QLD plates.
Will drive like a new car! Sure not looking forward to seeing the bank balance after this though...

[Phil B]

I just noticed this morning that I have coolant leaking from the hole in the bottom of my water pump. Does this mean the water pump is stuffed? Had a seal go or something?

[Phil B]

Ok it's stuffed, any recommendations for a new one? Brand and iron or alloy?

[BGBLOK]

Clevo mate???.. not Windsor.. ?

[greenjgs]

Originally Posted by Phil B

Ok it's stuffed, any recommendations for a new one? Brand and iron or alloy?

Hi Phil

On a street car the standard replacement Alloy pump will be fine, Bursons etc have them for around $170.00 or you could go for an Edelbrock for a little under $300 if my memory serves correctly. I have a near new pump if you want it for $100 It did about 10 laps of Sandown before I replaced it with a NASCAR pump. Send me a PM if you want it and I can send it up.

Cheers Graeme

[Phil B]

Originally Posted by greenjgs

Hi Phil

On a street car the standard replacement Alloy pump will be fine, Bursons etc have them for around $170.00 or you could go for an Edelbrock for a little under $300 if my memory serves correctly. I have a near new pump if you want it for $100 It did about 10 laps of Sandown before I replaced it with a NASCAR pump. Send me a PM if you want it and I can send it up.

Cheers Graeme

Thanks for the offer but I got one off eBay and put it on last night. The old pump didn't look too bad for a 37 year old water pump! Nothing wrong it apart from the seal.

[Phil B]

Coupe is currently in a shop getting front shocks, a few steering bushes, rear gearbox seal and points kit for the distributor.

So here's a few pics from the water pump change:
Not too bad for a 37 year old pump!


Shiny new pump looks out of place in the engine bay


And the rest of the engine bay, much better since the paint job but still pretty ordinary

[BGBLOK]

These cars ( our Aussie Fords) always look nicer with the engine bay the same colur as the external paint hey??...

[Phil B]

Originally Posted by BGBLOK

These cars ( our Aussie Fords) always look nicer with the engine bay the same colur as the external paint hey??...

Yeah it would have been nice but my budget and timeframe weren't stretching that far unfortunately. So black it is, which is a huge improvement over the very dirty pale yellow it was