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Mar 23, 2007 13:26:55 GMT
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When i finaly get round to winning some wheels on the bay (as opposed to being outbid) i will be getting some 15's for my 5 GT. The problem lies thus, at present i have 13's so by putting 15's on how much will it mess up my speedo reading. With Beetles and the like it's easy enough to get them re-calibrated due to their simple opperation, but my 5 has an electric type board on the speedo. Therefore is it possible, or will i have to put up with being a few mph out? Make up for lack of retro content  |
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OAP drifta Volvo 340,Williams power
1960 Beetle twin 40's 1776cc
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Speedo calibration QBenzBoy
@benzboy
Club Retro Rides Member 7
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Mar 23, 2007 13:58:43 GMT
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It depends what size tyres you're going to put on the 15's. If they're low enough profile to keep the same rolling radius you'll be OK. A good online tyre calculator will be able to tell you how much your speedo will be out once you dial in your old and new tyre / wheel combos. I'm not on my own computer ATM so I don't have any links to a good tyre calc.  |
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archieboy
Posted a lot
Volvo Amazon 2 door
Posts: 1,168
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Mar 23, 2007 14:01:15 GMT
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Mar 23, 2007 14:19:42 GMT
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Cheers guys  |
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OAP drifta Volvo 340,Williams power
1960 Beetle twin 40's 1776cc
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Mar 23, 2007 14:24:38 GMT
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speedograph in Nottingham will recalibrate and refurbish your speedo for you if necessary.
What I do when I have a car or change bits is go out to a local speed monitoring route, they have those signs that say "SLOW DOWN xx MPH" or "THANK YOU xx MPH" and I cruise though at 30 on my speedo to see what speed that actually is... then I cruise through to try get 30 on their sign and see what that says on my speedo.
Not perfect but it gives you an idea how far out your speedo is.
In the Mazda I can do 34 on the speedo and it says "30 thank you"
in the Oldsmoblie it says "30 Thank You" when the speedo says like 25 MPH.
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1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1994 Ford Fiesta
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Mar 23, 2007 14:27:32 GMT
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You'll probably find the speedo was never really accurate in the first place - they usually read up to 10% over actual road speed (i.e. when you're travelling at 100mph, your speedo could read anything from 100mph to 110mph).
Hence, swapping wheels for something bigger, for the same revs you'll be going faster. So now, instead of doing 100mph when your speedo reads 110, you might be doing 105. It depends on the aspect ratio of the tyres you're going to use. Best way to measure it is to get a GPS Satnav device as these almost always have a true speed indicator - I know TomTom definately does. Cruise at 30mph, 40mph, 50mph etc and get your passenger to note the actual speed. If it's still less than your speedo indicates, you don't need to do anything.
The only problem will arise when your speedo was bang on accurate in the first place, which is unlikely but possible. Our Mondeo must have been perfect, as when I changed to 17" wheels I introduced a 6% difference according to that rolling radius calculator. I've tried it with the GPS method and an indicated 70mph is 76-77mph true speed, meaning I have to trundle through speed cameras just in case. It could however be the dodgy 'lockwood' coloured dials that the car has, which may not be marked out correctly.
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Never trust a man
Who names himself Trevor.
Or one day you might find
He's not a real drug dealer.
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Mar 23, 2007 14:49:29 GMT
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Em's old Celica was almost 100% accurate on the speedo. Theres a way of checkin gyour speed at 70 on the motorway usoing the roadside markerts but I'm damned if I can remember it at the moment.
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Last Edit: Mar 23, 2007 14:50:07 GMT by akku
1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1994 Ford Fiesta
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Mar 23, 2007 14:59:43 GMT
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Some good ideas there. Will have to find one of those signs that says "slow down please" I've never seen the one that says "thankyou" |
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OAP drifta Volvo 340,Williams power
1960 Beetle twin 40's 1776cc
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Kris
Posted a lot
Posts: 1,631
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Mar 23, 2007 15:41:36 GMT
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Em's old Celica was almost 100% accurate on the speedo. Theres a way of checkin gyour speed at 70 on the motorway usoing the roadside markerts but I'm damned if I can remember it at the moment. The markers are 300ft apart, Ill try and work it out  |
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Mar 23, 2007 16:12:28 GMT
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From memory. Renault 5 GT turbos ran a 195/55r13 tyre originally, Though most poeople changed 'em to 185/60s because they are a more common size. so ideally you'll want 195/45s. Edit: i can't type for sh it.  |
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Last Edit: Mar 23, 2007 16:14:18 GMT by Jack
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Mar 23, 2007 17:07:02 GMT
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Look for the painted squares in the road (dead centre of carriageway). They're police calibration marks and they're in pairs, exactly 1 mile apart.
There were some up the road from me (the road that goes from the A610 up towards Ravenshead, Larch Farm if you're local!) and they even had signposts next to them saying "Measured mile start" and "measured mile end". If you drive at 60mph constantly between them it should take a minute. Any less and your speedo reads slow, takes longer and it reads fast. Get the time it takes and you can work out the 'wrongness' of it.
More often found on motorways though.
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Never trust a man
Who names himself Trevor.
Or one day you might find
He's not a real drug dealer.
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