Wheels/ Tyres

From: Graham Miller
Date: Fri, 30 Oct 1998 10:01:04 -0000
Subject: [imps] Re: Shocks

As far as I remember the profile is the height of the tyre expressed as a percentage of tyre width. So the standard profile 135 tyres would be 135mm high. 12 inches is about 300mm, so the overall wheel diameter would be about 435mm. I worked out that 185 60 13's would be OK, so there's about 325mm of wheel and 111mm of rubber which makes about 436, so not much difference in rolling radius. With 165 50 14's, you'd have 350mm of wheel, and 82.5mm of rubber which makes 432.5, so you could probably get away with it. It was years since I played around with this stuff, so please correct me if necessary...

Graham


From: Dave Edge
Date: Fri, 30 Oct 1998 03:28:18 PST
Subject: [imps] Re: Shocks

I suppose a simple way to prove it is to go into a tyre garage and find out the ODs of a stack of tyres and make a note of those that would fit into the arches. The largest OD I assume would be OK is a 155x12x76 tyre (One of which John and Roger Hawes have on their car - I think) What would the OD be for this tyre as it probably is the maximum.

Dave


From: Paul Williams
Date: Fri, 30 Oct 1998 11:30:49 -0000
Subject: [imps] Re: Shocks

The standard size ratio between the tyre width and its height (aspect ratio) is 82% eg: a 155x12 would be 155mm tread width by 127.1mm (155x0.82) sidewall height.

A 185/60 x 13 would have an overall diameter of 522mm (20.5in) compared with a standard 155 x 12, which would be 554mm (21.8in).

Using 185/60's would effect your gearing in that the speedo would overread and, more importantly, the engine would be using higher revs for a given road speed.

Two questions arise:

1/ Can you fit these tyres under your wheelarches without a) falling foul of the law by having the tyres protrude from the car body; or b) making body mods; or c) losing steering range due to contact with the inner wings?

2/ Are you willing to screw the guts out of your engine?


From: Gary and Carol Henderson
Date: Sat, 31 Oct 1998 01:16:57 +-1300 Subject: [imps] Re: Shocks

Hi Graham & co

I think 'standard' profile radials are in fact 80% H/W ratio. 100% is strictly cross-ply country and not recent at that.

'Paint-profiles' are all very well for damping/handling, but are instant history if you clip a rock on the road. I have to laugh at 4WD RVs coming with 60-series tyres!


Cheers

GaryH


From: Gary and Carol Henderson
Date: Sat, 31 Oct 1998 01:28:01 +-1300
Subject: [imps] Re: Shocks

Hi again Dave

Better, the manufacturers usually specify a nominal rolling radius for each type. (This I found when checking out tyre sizes for the L300 4WD.) For example, my standard tyres would be 215x15" (on 6JJ rims); the fatter 235/75x15" have a nominal rolling radius specÚd at only 1 mm greater; in practice the effective gearing is virtually unchanged. They stand bonnet-high alongside the Imp - more adapted to the recent heavy rains here!

Cheers

GaryH.


From: Nickcleak@aol.com
Date: Fri, 30 Oct 1998 09:46:51 EST
Subject: [imps] Re: Shocks

> 'Paint-profiles' are all very well for damping/handling, but are instant
> history if you clip a rock on the road.

indeed , not to mention wheel damage too , i get a lot of bent rims with cars running on 225 / 45 x 17 wheels , it doesn't help when they are running at 25 psi either , even a slight pot hole will ruin a wheel and tyre . no one seems to check their tyre pressures these days !
nick


From: Nickcleak@aol.com
Date: Fri, 30 Oct 1998 09:46:50 EST
Subject: [imps] tyres

> find out the ODs of a stack of tyres
> The largest OD I assume would be OK is a 155x12x76 tyre

the magic figure you need is rev/s per mile here are some examples :
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             960
so a 185/60 x 13 is just about the same rolling radius as a standard 155 x 12

nick ...


From: CKirkw00d@aol.com
Date: Fri, 30 Oct 1998 15:07:24 EST
Subject: [imps] Re: Shocks

My tuppence worth, changing wheel size to 13" is worth it for the simple reason of having a greater choice of rubber. I have recently purchased a new set of minilite style wheels from Midland Wheel Centre giving details of the type of car, i.e. IMP not mini. They provided me with the correct PCD, don't ask, and of the correct bolt hole diameter. I have 6" running 195x60 at the front and 7" with 205x55 at the back. Midland have all the correct offsets and my wheels don't foul metal or stick out past the arches. If the balance of metal inside and outside is right then there will be no extra bearing wear.
With the Spax set soft it handles superbly. Lotus realised that with a good chassis and suspension set up soft proved the best handling on general roads, different on tarmac circuits maybe.
I'm not sure 100% but I think the Nikki was a Jap trying to copy Weber 28/36's. So I feel that the Weber will fit your manifold.


From: TMo5018257@aol.com
Date: Fri, 30 Oct 1998 10:04:24 EST
Subject: [imps] Re: Shocks

So much has been written about the various merits or otherwise of different sizes of tyres. I'll put my two-pennyworth in thus:

a) Do not use ultra-low profile tyres (rubber bands?), as these have a square shouldered design that just does not work with the Imp's free moving suspension. On hard cornering, the tyre simply runs out of tread.

b) Going to 13inch and above.....well, the choice is yours but why? Yes, the arches get filled out etc, but an Imp looks 'overwheeled' and begins to look like a Tonka Toy. Imps handle fine on the road with 155*12 tyres (on the track may be a different thing), but good correct design tyres are a far better bet than low profiles.

c) Getting the correct wheels for 13inch+ - bear in mind insets & offsets when considering going up a size. The vast majority of modern alloys are for Front Wheel Drive cars, and although the stud patterns may fit, they are not right for the car (unless you enjoy changing wheel bearings regularly).

I'm not an expert on tyre sizes, but of the Imps I have driven that have astonished me in terms of levels of adhesion vs feel vs stability vs grin factor....the best have always been on 12inch rims.

Cheers,
Tim Morgan


From: Nickcleak@aol.com
Date: Fri, 30 Oct 1998 17:40:24 EST
Subject: [imps] tyres/wheels

> Do not use ultra-low profile tyres

yes , and if you are cornering and run over a rut it can throw you ...

> Going to 13inch and above... Why?

why ? because of the much greater range of tyres available .
we are rather limited now with 12 " sizes and rubber compound , although i had some 165/60 x 12 tyres on my clan ...
Bearing in mind that the overall diameter is mainly the same with 12" and 13" rims , and there is another factor
... 13" rims leave more room for larger brakes ....

If you try Yokohama AVS 175/60 x 13 tyres you will wonder how you managed with 155 x 12 tyres , this applies just as much to normal everyday driving as well as track driving ....
they hold the road in the wet better than the best 12" tyres do in the dry ...

> The vast majority of modern alloys are for Front Wheel Drive cars

i don't think you will find a FWD rim with a 4½" PCD ... they are mostly 100 mm PCD
i have special revoloution wheels on the rear with an extra 1" outset , this is in effect like having a built in 1 " spacer , the feeling of stability with the 2 " greater rear track is a great improvment ...

> levels of adhesion vs feel vs stability vs grin factor...

please try the yokohama tyres !

Nick ....



From: Nickcleak@aol.com
Date: Fri, 30 Oct 1998 09:46:47 EST
Subject: [imps] tyres

> As far as I remember the profile is the height of the tyre expressed as
> a percentage of tyre width.

The standard say 185 x 14 tyre ie unmarked aspect ratio is 82%

the width of the tread seems to bear little resemblance to the marked width ..
ie a 175/50 x 13 is actually a 195 !

nick ...


Date: Sat, 31 Oct 1998 20:01:37 +1000
From: Darcy Maddock
Subject: [imps] Re: tyres/wheels

> please try the yokohama tyres !

Yes Nick, last year I attended a ten day rally in New Zealand and Brian Bradshaw kindly lent me his Sunbeam Imp. 13" wheels fitted with Yokohamas. They were half smooth with dimples and half tread across the surface. We traveled at speeds above 90mph for most of the event and I have never felt so safe. In heavy rain and in dry the car never put a foot (tyre) wrong. If a corner advisory road sign said 70kmh we were quite confident in taking it at 70mph and if no warning sign was up, 90+ was not even a worry. Only once did a problem arise as I entered a unsigned corner I realised that an item laying in the grass was the sign that should have been standing. We were well into the corner when I hit the brakes very hard (racing style stab) and back on to the throttle and the Imp just followed the corner around. Magic tyres and magic car. Rosemary was behind us in a near standard Imp Sport at the same velocity and said a little later that she thought we were gone but our antics were just enough warning to enable her to get around.
I run Pirellis here in Queensland 13"x6" but they are not a patch on those Yokes.
Unfortunately they are illegal here but I have heard that the road laws are going to be made standard around Australia next year and I may be able to use them. I will be first in line.


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