Wadders
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| posted on 18/2/06 at 08:08 PM |
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13" wheel weight
For anyone interested, i finally got round to weighing one of my new, (very second hand) 13" X 8" revolution Split rims, and if the wifes
digital bathroom scales are to be trusted they weigh in at a very respectable 4.5kg. The 15" cast wheel and tyre which i'm changing from
weigh in at 16.5kg, so should be quite a good saving, i'm hoping for 16-20kg overall. To give an idea of the age, when i took the tyres off,
one of the outer rims had £21.75 inc vat written on, current price is about £70, should look ok once they are refurbed tho.
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birt
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| posted on 18/2/06 at 09:46 PM |
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I must say it is nice to see somebody moving from big wheels to small wheels for a change.
I am baffled by the amount of people who insist on running 15", 16" and even 17" wheels on their kit cars. A weight saving on
wheels and tyres is a lot more important than improving a cars power to weight ratio. Unsprung mass has a significant influence on handling
performance and more importantly for our cars, sprung to unsprung mass ratio. Our cars are extremely light and therefore the spring rates are
relatively low and hence will struggle to react the inertia of a large unsprung mass resulting in excessive contact patch force variation and hence
less ultimate lateral grip. Therefore keeping the unsprung mass of a kit car as low as possible is very important. I personally think big wheels
and tyres on a kit car look silly even before thinking how much they must weigh.
Good man Wadders... I am also running a set of lightweight 13's
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zilspeed
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| posted on 18/2/06 at 10:56 PM |
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I've been preaching this Gospel for a loooong time.
Glad to hear someone else in agreement.
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speed8
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| posted on 18/2/06 at 11:58 PM |
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Planning on 13's myself. They just look so good on small sports cars.
I prefer rubber to bling.
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zilspeed
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| posted on 19/2/06 at 09:34 AM |
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quote:
Originally posted by speed8
Planning on 13's myself. They just look so good on small sports cars.
I prefer rubber to bling.
They give the best results as well. Of all the events I go to, none of the fastest guys have anything other than 13" wheels and tyres. Some of
the really seriously quick guys are not far off single seater times as well.
Our national sprint champion in his megabusa - wheel size ?...
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smart51
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| posted on 19/2/06 at 12:18 PM |
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My choice was either to find a 3.14 diff or have 15" wheels. 3.14s are hard to find and are expensive. I guess I could have split the
difference and got a 3.38 diff and 14" rims but that too would be expensive.
Lighter weight is better, it's just a matter of how much cash you want to spend.
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birt
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| posted on 19/2/06 at 02:35 PM |
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It is a fair point, Sierra diff ratios are not kind to us BEC people. I don't know what the R1 gearing is but my Kwak is on 13's and a
3.38 diff and theoretical top speed is over 125mph.
I accept that a 3.38 means paying for a diff rebuild (assuming you want an LSD) and that bigger wheels is a cheaper option.
It all depends on what and how you use your car I suppose but for the vast majority of time 125mph is ample and I would prefer that my car handles
better for the remaining 99% of the time.
It is worth noting that the rolling radius of a 185/60/14 tyre is less than 3.5mm bigger than a 185/65/13 tyre (like mine).
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smart51
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| posted on 19/2/06 at 04:48 PM |
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I suppose the other option would be 205/82/13 or something like that
Having driven my car a bit now, I think I would prefer it to be a bit faster. 0-60 in 4 seconds sounds good but I find myself with the throttle fully
open too often. I would love to shed a few 10s of kilos from the car but from here on that would cost £s and hours.
If I were building again, I'd go for an open diff, 13" wheels and solid discs at the front rather than vented. I'd also get MNR to
weld me a thin wall road car chassis. 70kg weight saving would give about 12% more acceleration. That on its own isn't enough to make me want
to rebuild though.
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JoelP
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| posted on 19/2/06 at 07:04 PM |
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quote:
Originally posted by Wadders
For anyone interested, i finally got round to weighing one of my new, (very second hand) 13" X 8" revolution Split rims, and if the wifes
digital bathroom scales are to be trusted they weigh in at a very respectable 4.5kg.
stuart taylor do some magnesium one piece alloys in 7x13", for £200 per corner. They weigh 3kgs apparently. To date thats the lightest i
found.
[Edited on 19/2/06 by JoelP]
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chriscook
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| posted on 19/2/06 at 07:26 PM |
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13s here too 
Its not how big they are its what you do with them
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locost_bryan
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| posted on 20/2/06 at 03:33 AM |
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What's the weight of a standard Escort/Cortina steel wheel?
Bryan Miller
Auckland NZ
Bruce McLaren - "Where's my F1 car?"
John Cooper - "In that rack of tubes, son"
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v8kid
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| posted on 21/2/06 at 12:16 PM |
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Trouble is trying to find road legal tyres wide enough in 13" rims. Manufacturers are producing wide tyres for the bling bling brigade in
17" & 18" rims so we are forced to follow suit.
Anyone know where I can get sticky road legal tyres for 10" wide rims?
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oliwb
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| posted on 21/2/06 at 12:26 PM |
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Got some 15x7's for road use (slightly more speed bump friendly) and some 13's were kindly donated to me for track use....I like the look
of the 15's though they fill the wheel arches really nicely as you can see from my photo archive without being too bling-bling and in your face!
Cheers Oli.
If your not living life on the edge you're taking up too much room!
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Wadders
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| posted on 21/2/06 at 12:28 PM |
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Yoko AO32r's are still available from George Polley in 215 section, not sure if they would stretch over 10" rims though.
205's will fit on an 8.5" so it may be possible, Polleys will advise you.
Originally posted by v8kid
Trouble is trying to find road legal tyres wide enough in 13" rims. Manufacturers are producing wide tyres for the bling bling brigade in
17" & 18" rims so we are forced to follow suit.
Anyone know where I can get sticky road legal tyres for 10" wide rims?
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ned
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| posted on 21/2/06 at 01:17 PM |
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I'm going to be running 14" initially as its the smallest size that's guaranteed to fit over my sierra rear brakes without fettling
the handbrake mechanism.
The same problem applies, I can only find upto 195 width tyres in a suitable profile for my rims, Idealy I want 205 for the back and then my current
rims would look a bit on the narrow side 
Ned.
beware, I've got yellow skin
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britishtrident
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| posted on 21/2/06 at 04:13 PM |
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quote:
Originally posted by locost_bryan
What's the weight of a standard Escort/Cortina steel wheel?
Back in my Imp days the days a 8x13 Revolution wheel fitted with a 7.2-20x13 Goodyear G50 racing tyre weighed less than half what a Hillman
Hunter 4.5jx13" wheel with 155x13 tyre weighed.
The 8 inch wide Revolution wheel complete with tyre weighed less than the 4.5x13 steel wheel without a tyre.
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DIY Si
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| posted on 22/2/06 at 01:26 AM |
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If you wnat seriusly sticky rubber, demon tweeks (no, i'm not a fan) sell, for a huge price some wide 13" tyres. Up to and
including225/45/r13. If you step up to 15" rims you can have 335 /35/r15. Only prob being they're £170 and £236 a corner
Made by Michelin incidentally.
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birt
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| posted on 22/2/06 at 07:38 AM |
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Ned, why would you want to go for 205's at the rear?
I would have thought the big twin cam, 4-pot car engined cars (such as an XE) would suffer more of an understeer problem due to the relativly large
chunk of mass out front and relatively stiff front springs.
Also worth remembering that the contact patch area is a function of the normal load on the tyre and the tyre presure. A wider tyre has the potential
to offer more grip since the contact patch becomes wider (but shorter) and hence sees a more even presure distribution across the patch. However, get
the pressures wrong and you get crowning of the patch and you can easilly end up with less available grip.
What you do get with a wider tyre is smaller tyre slip angles which means you will get a smaller body slip angle for the same lateral force and
therefore less yaw acceleration during transient manouvres. To the driver, this can feel like the car is handling better and has a sharper
response.
It is a wrong Preconception that if you stick 10% wider tyres on, you get a 10% increase in contach patch area and a 10% increase in grip.
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ned
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| posted on 22/2/06 at 09:16 AM |
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birt,
at the moment I have 185/60's on 14" rims both front and rear. I'm thinking that 220bhp could do with a little more width at the
back or i'll be a bit short of traction...
Ned.
beware, I've got yellow skin
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britishtrident
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| posted on 22/2/06 at 12:27 PM |
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Bigger at the rear is a good idea --- a lot of builders have felt the brown trouser effects of snap oversteer when flooring the throttle.
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britishtrident
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| posted on 22/2/06 at 12:41 PM |
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quote:
Originally posted by birt
It is a wrong Preconception that if you stick 10% wider tyres on, you get a 10% increase in contach patch area and a 10% increase in grip.
Surprisingly the SVA weights I have seen show most Locost tend to be slightly tail heavy -- It depends a lot on the build but keeping the download per
unit area of the tyre contact patch the same is a good idea to work from
If the rear is 25 kg heavier than the front then 185 section on the front and 205 on rear makes sense.
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birt
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| posted on 22/2/06 at 01:54 PM |
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I was attempting to make the point (but probably not very well) that contact patch area does not directly increase with tyre width. It increases with
a decrease in tyre pressure which may be achieveable with a wider tyre.
However, there are much more complicated reasons why a wider tyre has the potential to offer more grip such as contact patch pressure distribution,
contact patch aspect ratio and hence local deformation, and tyre cornering stiffness.
The comment about heavier at the rear means bigger tyres maybe true but not for the reasons you are suggesting.. If you were 25Kg heavier at the rear
then your contact patch area would be greater at the rear regardless of the width of the tyre.
I am not saying wider tyres at the rear are wrong, just that there is a lot of confussion as to why and when they should be used and an incorrect
assumption that if you stick on bigger tyres, your car will handle better and have more traction.
My comments to Ned regarding weight distribution was more aimed at roll stiffness gradient, yaw inertia and chassis balance as opposed to tyre normal
loading.
As with most of these things, it is best to give things a whirl on the track and find what set-up works best for your car and your style of driving...
More Track Days!!
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britishtrident
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| posted on 22/2/06 at 08:20 PM |
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The old dictum was the mass of air in the tyre carries the load --- not to be taken too far but the greater the tyre volume the lower the tyre
pressure.
One of the problems is that wide tyres tend to be optimised for heavy cars, many have concave treads ie the crown of the tyre is depressed in the
centre.
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zilspeed
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| posted on 23/2/06 at 12:13 AM |
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All of this is precisely why an infra red thermometer is a good idea for optimising tyre pressures.
One of these jobs with the laser sight on it.
I've seen lots of people with these at the speed events.
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