From: Kristian Jonsson
Date: Sun, 1 Nov 1998 12:45:49 +0100
Subject: [imps] Re: tyres
There has been a lot of tire talk over the years, 12 or 13 inch, standard or wide rims.
The Imp front suspension is, as we all know, not really designed for wide wheels. In reality the car doesn´t seems to need that much rubber in the front. But the rear it is an different matter. Have you noticed how silly the Imp looks with its narrow rear track. The rear wheels are disappering inside the body.
In other words: Wider rear wheels with positive offset to make the Imp look decent.
Kristian Jonsson
Sweden
Date: Sun, 01 Nov 1998 17:30:56 -0100
From: rienk steenhuis
Subject: [imps] Re: tyres
Hello Kristian >The Imp front suspension is not really designed for wide wheels.
No it wasn't. But if you have a copy of Tim Millingtons book with the red coupe SRK996F on the front cover then you'll note it would easily cope with a tyre one foot wide.
Rienk
From: Ewins, Paul
Date: Mon, 2 Nov 1998 09:08:00 +1100
Subject: [imps] Wheel Size
Although I can't claim any professional expertise, wheel & tyre combinations is something I have thought about a lot.
The important bit is the Overall Diameter (OD) which is usually on the tyre manufacturer's charts. To work this out from the size designation i.e.
155/80-12 use the formula:
width x aspect ratio x 2 + rim height,
i.e 155 x 0.8 x 2 + 12 x 25.4
= 248 + 304.8 = 552.8
Width by aspect ratio gives you tyre height, but there is bit of tyre above the rim and below the rim so you need to multiply by 2 to get the OD.
As far as I can tell a 155SR12 is a 155/80-12.
185/60 - 13 is the same OD
165/65 - 13 and 215/50-13 are almost the same (545mm OD)
175/60 - 13 is a liitle smaller (540mm OD)
185/55 - 14 is a little taller (559mm)
195/50 - 15 is a little taller again (576mm)
The actual gearing difference of any of these is minimal. Even the 195/50-15 is just 4% taller which equates to an extra 4mph at 100mph. As most speedos read under anyway this is not going to cause too many problems.
The sizes I quoted are all fairly common and will fit on 5.5" or 6" rims (even the 215/50's will fit on 6" rims, although 7" rims are recommended)
I plan to go to 13" rims as soon as possible (funds being the deciding factor) simply because the only 12" tyres I can find are cheap and nasty wheras 13" gives me a variety of race and road rubber.
If you are racing then Formula Ford front slicks are about the right size and may be available second hand quite cheaply. There will be a lot of guys who use them for one race and then ditch them even though there is a lot of life left - just not the ultimate in grip anymore.
Locally, (i.e. Australia) Dunlop do both 175/60-13 and 185/60-13 in a Formula-R which is a road legal race tyre - heaps of grip - and Falken do a 185/60-13 road tyre that is also very good and around 25% cheaper. It is fairly unlikely that you would gain anything by going to a wider tyre, assuming that you could fit it under the guards anyway. Generally I would say that you are much better off buying a really good narrow tyre than an average wide tyre.
As for rims, well personally I think that minilite style wheels look right on most 60's cars and they are usally fairly cheap and available in a wide range of sizes. Modern FWD rims aren't going to be much use unless perhaps you have done a disc brake conversion and need a different off-set to get the wheels back under the guards.
Paul Ewins
From: Nickcleak@aol.com
Date: Sun, 1 Nov 1998 18:09:30 EST
Subject: [imps] Re: Wheel Size
> The important bit is the Overall Diameter (OD)
Maybe it would be more accurate to use the figures below , they are the revs per mile of different tyre sizes .
and there is a noticable difference on gearing between the higher and lower sizes , I borrowed some 165 x 13 wheels in 1974 to try on my Imp and they allowed me to pull 128 mph down a long motorway hill !155 x 12 966 155/70 x 12 1013 155 x 13 920 155/70 x 13 974 165/70 x 13 933 165/65 x 13 969 165/60 x 13 1006 175/60 x 13 983 185/60 x 13 960 175/50 x 13 1060 165/60 x 12 1060 165/70 x 12 980 175/70 x 12 960Nick ...
From: Ewins, Paul
Date: Mon, 2 Nov 1998 11:05:00 +1100
Subject: [imps] Re: Wheel Size
> a noticable difference on gearing between the higher and lower sizes
Well, yeah, the lower sizes are normally fitted to minis, so you would expect that. :-) But why would you want to fit smaller tyres to a road car?
Either way though, if you divide the figure for your proposed tyre by the figure for your current tyre you get the change in gearing because the maths all boils down to the difference in overall diameter. Now if you had a different 4th gear ratio or diff ratio then you can really start to play around with the overall gearing, otherwise you are very much limited to what will fit under the guards. Even at 100mph there is only a few hundred RPM difference between the 195/50-15s and the 155/80-12s
Paul
From: Gary Henderson
Date: Mon, 2 Nov 1998 15:45:26 +1300
Subject: [imps] Re: Wheel Size
Hi Paul
In working out the relative gearing, the published figures are definitely the way to go. The effective rolling radius at road speed is greater than the distance of the hub-centre from the ground when stationary, but less than adding 2x the section to the nominal diameter. (The centrifugal force throws the tread out to nearer a circle.)
For my penny's worth on relative merits of tyres for a standard road car, my old ones (Firestone S-211 - a rough style-equivalent to the old Michelin ZX) were great on corners and good in other areas, but a bit noisy - they gave a 'beat-note' effect against the engine sound. (A bit like a twin-engine plane with the engines not synced.) The present ones are a modern 'square-look' Firestone; much quieter (no beat-note), excellent braking wet or dry, but PATHETIC cornering.
Cheers
GaryH
From: Kristian Jonsson
Date: Mon, 2 Nov 1998 07:29:39 +0100
Subject: [imps] Re: tyres
> then you'll note it would easily cope
> with a tyre one foot wide.
Yes I have the book, and yes, I have noticed the red IMP SRK996F and it looks super, but sometimes you have to compromise.
Kristian
From: Dave Edge
Date: Mon, 02 Nov 1998 05:33:52 PST
Subject: [imps] Re: tyres
Dear all,
Can I put my limited experience of tyres to you all. Experience is limited because I have never had to replace my tyres. I have Fulda 155x12x70 tyres on my slightly lowered coupe. There is no loss of grip in the wet. In the dry they will turn the most unbelievable corners because of their 2 ply sidewalls which give them their strength over other similar tyres with single ply sidewalls. I drive my Stiletto as hard as it is possible on occasions and have never felt them slip unless pushed (ie, turning the wheels further when already on the limit - its all fun with an imp).
I have recently seen an advert for Yokohama 12 inch tyres but can't remember where. I presume they still stock them. I agree with Tim, the lack of weight in an imp means you are better off on the roads with a more flexible sidewall of a 12" wheel. I can imagine that 13 would be a bit too skittish.
Fuldas are Goodyears badge engineered and as such appear to last. I have done 10,000 miles and they still have between 5 and 6 mm of tread on them.
BTW, has anyone tried an imp in the snow. I had the opportunity last winter when I went to university one day it had snowed about 4 inches and everyone stayed at home apart from me. The carparks at UWE consist of about 10 basketball courts. No one around - oh well lets have some fun. That experience convinced me there is nothing unrecoverable about an imp in a spin.
Dave
Date: Mon, 02 Nov 1998 16:19:17 +0100
From: Bert Clewits
Subject: [imps] Re: tyres
> Yes I have the book, and yes, I have noticed the red IMP SRK996F
> and it looks super,
Not anymore though, it's now sitting very sadly in a garage in Sykehouse
Time to get it back on the road Jack !
Bert
From: TMo5018257@aol.com
Date: Mon, 2 Nov 1998 10:25:26 EST
Subject: [imps] Re: tyres
Dave,
> advert for 12 inch Yokahamas
Yokies are unfortunately only available in a 60 profile - basically for a 12inch wheeled M*n*. Therefore not particularly useful to a road Imp... but that said David Llewlyn has been using these tyres on his sprint car with great effect.
Cheers,
Tim
From: Nickcleak@aol.com
Date: Mon, 2 Nov 1998 14:08:56 EST
Subject: [imps] Re: tyres
> BTW, has anyone tried an imp in the snow. [...]
> That experience convinced me there is nothing unrecoverable about
> an imp in a spin.
Yes , of course , an Imp is the next best thing to a Land Rover in the snow ...
Never have i been beaten in the snow in My Imp in 27 years , even in 1982 when it was 6 ft deep. and - 20 C ( yes minus 20 ! )
On a number of occasions i have been the only car up the local hills besides Landrovers . ! I remember clearly climbing a certain hill making steady progress right to the top and there were a group of farmers and stranded motorists cheering as i reached the top ! There were a lot of FWD and RWD front engine cars trying but they were just slithering into the gutter and getting nowhere , obviously technique helps , but so does the incredible traction of the IMP . The steering suffers a little , but it makes it .
I have been putting 3 times the power through the back wheels and still the traction remains in dry and wet ....
Nick ...
From: Nickcleak@aol.com
Date: Mon, 2 Nov 1998 15:10:10 EST
Subject: [imps] Re: Wheel Size
> the 195/50-15s and the 155/80-12s
I'd be interested in the rev / mile figure of those two sizes ..
nick ....
Date: Mon, 02 Nov 1998 20:55:01 -0100
From: rienk steenhuis
Subject: [imps] Re: tyres
Hello Kristian
> but sometimes you have to compromise
Very true, but the compromise isn't allways what you expect it to be. The imp front suspension is actually very good in roll as far as camber change is concerned. But riding over bumps or braking hard will change the camber considerably. In these cases the tyres will need flexible sidewalls or contact with the road is reduced.
I think the imp front suspension was invented by a man called Ballamy in 1933. Defenitely no wide profiles in those days.
Rienk
From: Gary Henderson
Date: Tue, 3 Nov 1998 09:50:34 +1300
Subject: [imps] Re: tyres
Hi Dave
I came home late one night in our usually temperate clime, to find it snowing quite heavily. Both the Imp & the Avenger contained inhibitor only, not antifreeze, so I decided to take each of them for a bit of a drive, to warm things up a bit & prevent any risk of freezing.
The Avenger was really struggling to get up the hill & hung out all the way even on slow corners. The Imp just drove almost 100% normal. Both were on Firestone S-211 tyres in good condition.
Only one proper end to keep an engine...
Cheers
GaryH
Date: Thu, 05 Nov 1998 09:13:25 +1000
From: Mike & Tich Marsh
Subject: [imps] Re: More wheels and tyres
The box shaped Viva of the early seventies (Opel Kadett in many markets including South Africa) had wheels which were interchangeable for Imps, so must have been 4". In fact, in S Africa, they were about the only practical reason you could get decent size wheels and tyres for an Imp.
Mike
From: Paul Williams
Date: Thu, 5 Nov 1998 01:59:18 -0000
Subject: [imps] Re: More wheels and tyres
Dear Graham,
> what Vauxhalls were fitted with Rostyles and were they 4" or 100mm.
The Vauxhalls we're interested in are the "sporting" versions of the HB and HC Vivas, including Magnum and SL90 (4in PCD). Any Rostyles you come across that you can guarantee came from these cars are OK. Beware of similar whells from later Vauxhalls (Chevette etc.) as these are metric.
> If I go home and measure them, am I going for
> the centre of the stud to the centre of the opposite stud?
Yes, although you'll get a more accurate measurement if you take your measurement from the inside edge of one hole, across the centre to the outside edge of the opposite one as it takes the guesswork out of finding the exact centre of the hole. Make sure that you check the stud holes for signs of cracking or overtightening and also that whatever wheel nuts you use match the taper around the holes.
Regards,
Paul
From: Nickcleak@aol.com
Date: Thu, 5 Nov 1998 16:48:11 EST
Subject: [imps] Re: More wheels and tyres
In other words the genuine British Vauxhalls pre Chevette were imperial and when they were taken over by GM OPEL they were no longer Vauxhalls but re-badged metric OPELs ..
nick ...
From: Ewins, Paul
Date: Fri, 6 Nov 1998 09:22:00 +1100
Subject: [imps] Metric vs Imperial wheels and tyres
A similar story in Australia. The only compatible donor car appears to be an early Holden Torana, which of course started life as a Vauxhall Viva. The rebadged Vivas even carried the HB/HC designation while the later four cylinder LC/LJs appear to be the only ones to retain the 12" four stud wheels - the sixes had five stud wheels. Unfortunately these had bland steel wheels with blander hubcaps so there is not much point using them. Their disc brakes would appear to be a different matter though.
Paul Ewins
From: Gary Henderson
Date: Fri, 6 Nov 1998 12:20:37 +1300
Subject: [imps] Re: Metric vs Imperial wheels and tyres
The late Viva 1800s were sold here with something like Rostyles. Don't know what size.
GaryH
From: Nickcleak@aol.com
Date: Mon, 2 Nov 1998 16:58:58 EST
Subject: [imps] Re: tyres
> Only one proper end to keep an engine...
I agree 200 % :)
The Volvo 850 Turbo is a superb car but the engine is at the wrong end!
Nick ..
From: Kristian Jonsson
Date: Tue, 3 Nov 1998 06:22:46 +0100
Subject: [imps] Re: tyres
> it's now sitting very sadly in a garage in Sykehouse
How do you know that ??
K
Kristian
From: Graham Miller
Date: Tue, 3 Nov 1998 10:19:26 -0000
Subject: [imps] More wheels and tyres
Following all the discussion (much of it over my head!!!) about PCD and offset and wheel and tyre size, would Rostyle wheels be any good. I've a set of five that came from a Chevette (I think one of the souped up ones - a scary thought!) Anyway they've got Vauxhall badges, so I assume they'll be imperial instead of metric, but what about everything else.
They're 13" with 185/60 tyres. It did have ordinary Chevette wheels on it, but it has never driven more than a couple of miles so I couldn't comment on any problems. The reason for choosing them was that the 12" rims were rusted so badly that we needed something cheap and affordable to replace them. BTW 185/60 are used on Fiesta XR2's so there'll always be a wide choice of rubber available...
Graham
From: TMo5018257@aol.com
Date: Tue, 3 Nov 1998 05:28:03 EST
Subject: [imps] Re: More wheels and tyres
Graham,
RE: your Vauxhall Chevette Rostyles......
Be careful, Chevettes had a PCD of 100mm which is close (but no cigar) to the Imp's 4 inch pattern. Vivas had a 4 inch PCD and some of the late ones had Rostyles fitted, so they could be from there in which case they'll be fine.
I believe from memory (from an article in Impressions) that you need to use a 1 inch spacer to push the wheels out so that the centre-lines are in the same place as Imp wheels. Anyone else know for sure?
Cheers,
Tim Morgan
From: Graham Miller
Date: Tue, 3 Nov 1998 10:28:11 -0000
Subject: [imps] Re: More wheels and tyres
I forgot to ask... what is PCD?
Graham
From: TMo5018257@aol.com
Date: Tue, 3 Nov 1998 05:40:02 EST
Subject: [imps] Re: More wheels and tyres
Graham
> what is a PCD
I can't remember exactly what it stands for but it is basically the distance between the centres of the wheel studs at diagonals.
Tim
From: Gary and Carol Henderson
Date: Wed, 4 Nov 1998 00:19:21 +-1300
Subject: [imps] Re: More wheels and tyres
Hi Tim, Graham
Pitch Circle Diameter. The stud centres are evenly displaced around the Pitch Circle.
GaryH
From: Jon Day
Date: Tue, 3 Nov 1998 22:02:54 -0000
Subject: [imps] Re: tyres
>>>the red IMP SRK996F and it looks super,
>>it's now sitting very sadly in a garage in Sykehouse
I've witnessed it there too, Its looking a bit sad.
Jon Day
From: Ewins, Paul
Date: Wed, 4 Nov 1998 09:52:00 +1100
Subject: [imps] Re: Wheel Size
>> Even at 100mph there is only a few hundred RPM
>> difference between the 195/50-15s and the 155/80-12s
>I'd be interested in the rev / mile figure of those two sizes ..
I can't remember offhand what the Imp diff ratio is, I think it's 4.27:1 or 4.13:1 so let's start with those.
With a 4.27:1 ratio 155/80-12 (OD of 553mm) should be 15.19 mph per 1000 rpm, so at 100 mph you are doing 6584 rpm or at 8000 rpm you are doing 122 mph 195/50-15 (OD of 576mm) should be 15.83 mph per 1000 rpm, so at 100 mph you are doing 6319 rpm or at 8000 rpm you are doing 127 mph
With a 4.13:1 ratio 155/80-12 should be 15.68 mph per 1000 rpm, so at 100 mph you are doing 6378 rpm or at 8000 rpm you are doing 125 mph 195/50-15 should be 16.34 mph per 1000 rpm, so at 100 mph you are doing 6122 rpm or at 8000 rpm you are doing 131 mph
The small difference is what you would expect given the very small difference in OD between the two wheels. The big question is whether a 195 tyre is going to fit under the guards width-wise...
Paul
Date: Wed, 04 Nov 1998 17:09:03 +0000
From: Roger W.Swift
Subject: [imps] Re: More wheels and tyres
> what is a PCD
Try Pitch circle diameter - The diameter of the circle joining the centre of each bolt or bolt hole.
BUT - a word of warning - There is very little difference between 4" used on the IMP and 100mm used on many later wheels and it is DANGEROUS to use the wrong ones. So measure very carefully!
From: Graham Miller
Date: Wed, 4 Nov 1998 17:12:24 -0000
Subject: [imps] Re: More wheels and tyres
Any Vauxhall experts out there, what Vauxhalls were fitted with Rostyles and were they 4" or 100mm. If I go home and measure them, am I going for the centre of the stud to the centre of the opposite stud?
Graham
From: TMo5018257@aol.com
Date: Wed, 4 Nov 1998 12:33:18 EST
Subject: [imps] Re: More wheels and tyres
Graham,
>Vauxhalls with Rostyles - 4inch or 100mm PCD
Vivas had Rostyles with 4inch PCDs
BUT
Chevettes (Shove-its?) also had Rostyles but with 100mm PCD.
Confused? You will be......
The only way is to measure them. A good alloy wheel / tyre shop may be able to help.
Cheers,
Tim
From: Kristian Jonsson
Date: Wed, 11 Nov 1998 14:55:44 +0100
Subject: [imps] Re: tyres
When I was looking closer to this tyre list I noticed that 155x13 has a smaller radius then 155x12 and 175/70x12 smaller then 155/70x12
This seems to be upside down??
Kristian Jonsson
From: CKirkw00d@aol.com
Date: Wed, 11 Nov 1998 11:13:26 EST
Subject: [imps] Re: tyres
Kristian,
you are reading the chart incorrectly. The figures are revolutions of the wheel per mile. So if the figure is smaller then the wheel diameter must be greater so has less distance to travel to achieve the mile.
I have still to visit the post office for a postage price for the blower.
I work night shift this week but will get on to it soon.
On the subject of heads and warping etc. The later the head the better is my motto, with the sport being the best due to the most 'meat' and generally only the highest tuned engines suffer from warping unless the engine hasn't been built properly or else general neglect during everyday use has occurred.
Colin K.
From: Roger Hawes
Date: Tue, 24 Nov 1998 21:50:12 -0000
Subject: [imps] Nice Wheels
Hello everyone who reads this,
I have seen a lovely set of alloy wheels for sale in a magazine, and I want to buy the biggest and fattest set possible (to impress my mates), but I don't want to jeopardise on performance and safety. I also would like a set of lowish profile tyres to match.
Bearing in mind that I can't understand writing with too many silly little numbers in it, would anyone care to suggest what dimensions of wheel, and dimensions/make of tyre I should purchase (plus approximate prices?). (NB. I drive a stiletto).
Thanks for the advice,
John
Bristol.
From: Nickcleak@aol.com
Date: Tue, 24 Nov 1998 17:31:49 EST
Subject: [imps] Re: Nice Wheels
Revolution 6 x 13 for rear with special 1" extra outset 5.5 x 13 for front
Yokohama AVS 175/60 x 13 tyres
can't beat it !
Nick
From: Roger Hawes
Date: Wed, 25 Nov 1998 19:40:55 -0000
Subject: [imps] Re: Nice Wheels
I didn't think you would be able to resist!
Thanks for the advice, and am I to presume that you own these very wheels?
Is so, where did you get it all from, and what does 1" extra outset mean?
John
From: Nickcleak@aol.com
Date: Thu, 26 Nov 1998 13:43:19 EST
Subject: [imps] Re: Nice Wheels
> where did you get it all from, and what does 1" extra outset mean?
Demon Tweeks were very helpful , they seemed to know the Imp's requirements ,
The rear wheels are set out an extra inch , so they give 2" extra rear track, this helps with stability and make the width at the rear the same as at the front .
In effect the wheels are the same as the front but have a cast-in 1" spacer...
Nick ...