What Tyres?

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What Tyres?

Postby Leedy » Thu Feb 21, 2013 10:51 pm

Hi Guys. I have tried to search the forum for the answer but there are so many contradicting answers? So, My question is....
WHAT SIZE TYRES SHOULD I USE ON MY ROAD CAR?
I HAVE 9" Revolution wheels for the rear and 6" Revolutions for the Front. They are 13" diameter.
It doesnt matter what make. I just need to know what size i.e 205-45-13 0r 175-70-13 etc etc.
Any advice would be greatly appreciated. Thanks
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Re: What Tyres?

Postby oli » Fri Feb 22, 2013 10:36 am

It's not rocket science! Just find an online tyre size calculator, and put in the figures for standard wheels (155/80/12) and see what the rolling radius comes out at. Then all you need to do is use the calculator to find tyres that give the same (or very close) rolling radius for your 13's. Simples.
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Re: What Tyres?

Postby james » Fri Feb 22, 2013 10:55 am

The widest 13" tyre availabe that isn't an expensive trackday tyre is a 205/60R13. It's massive, and will still be stretched on a 9" wheel.
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Re: What Tyres?

Postby Dogsbody » Fri Feb 22, 2013 3:45 pm

It will be interesting to see if you can turn the wheel without fouling the inner or outer wings.
I had 175-70-12 on 6" banded steels on the Stiletto 20 odd years ago, couldn't put them in the front as they fouled.

I have 215-40-17's on 7" wheels on my Puma and thats the correct tyre for the rim size.
The garage will sweat trying to get 205's on a 9" rim :wink:
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Re: What Tyres?

Postby The Nun » Fri Feb 22, 2013 3:54 pm

Dogsbody wrote:It will be interesting to see if you can turn the wheel without fouling the inner or outer wings.
:wink:


The wheel will probably turn without any problems but whether it fouls the arches when steering is another question. :wink:
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Re: What Tyres?

Postby james » Fri Feb 22, 2013 4:30 pm

205/60R13 have been put on the back of an Imp - and they turned - but they'd be far too big for the front.

On the 6" fronts you'd be ok with a 175 or 185/60R13. Both have been fitted without issues - it just comes down to the offset of the wheel.
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Re: What Tyres?

Postby Rod » Fri Feb 22, 2013 11:53 pm

Without wishing to seem disparaging the question I have to ask is why? :? Is there any point in running such wheel/tyre sizes on a roadgoing Imp? :roll:

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Re: What Tyres?

Postby Mike Hanna » Sat Feb 23, 2013 12:14 am

Hi all. I feel I must comment on this trend of fitting wide wheels on the rear of Imps before someone gets seriously hurt. The Imp has about 66% of its weight on the rear, even more will transfer to the outside rear wheel when cornering. The further out the wheel is from the hub the greater the leverage will be on the hub/ suspension arm. The end result is the hub housing rips off the arm! As all these arms are now between 37 and 50 years old they can be seriously weakened by rust and fatigue (Even Sport ones are not strong enough). I have recently been modifying arms for race and rally cars which involves getting them sand blasted and believe me when I say some of the original welding is shoddy to say the least! SO BEWARE and keep safe. Regards. Mike
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Re: What Tyres?

Postby Dogsbody » Sat Feb 23, 2013 7:52 am

Another thing to consider with big tyres is the weight exerted by the car over the tyres foot print.
My Puma tips the scales at roughly 1.5 X the weigh of a Imp.
It has 215-40-17 tyres all round, good quality rubber. No Budgets on a Ford Racing Puma.
The dry handling is amazing, but in the wet there is not enough weight on the tyres to keep everything planted.
Think roller skate on ice.
Of the 500 FRP's built by Tickford, less than 300 still survive :shock: I bet at least 100 of the missing went through the hedge backwards in the wet :lol:
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Re: What Tyres?

Postby Lotus-e-Clan » Sat Feb 23, 2013 9:59 am

The tyres and suspension work together. If you have a stiff, low-roll set up for racing on fat tyres then the weight transfer to the outer gripping wheel is reduced so you will have less cornering grip than with a more compliant suspension setting... and that will probably only show-up dramatically when the road has less grip (wet).

The std Clan on skinny 155 tyres with 1+inch spacers as shown in this period photo. With spacers, there is potentially more strain on the rear hubs compared to a normal Imp but there is less weight at the rear than an Imp for the suspension and hubs carriers to cope with. The soft std Clan suspension settings means it transfers quite a lot of it's weight onto the outer gripping tyres - so via specific suspension settings the Lotus guys got as much grip as possible out of the skinny tyres and consequently the Clans wet grip was applauded by contemporary road testers.

Note there is not a lot of "inboard" rubber over the hub.....
Image

...compared to the Clan with 205/50/13 on 8 inch rims and a 25 mm offset (no spacers). These bring more rubber inboard (over the hub) as well as outboard compared to std. Strain on the rear hubs is certainly no more than the std Clan with spacers and I believe it is probably less going by the dramatic reduction in rear bearing wear over the 6 years since fitting these wider wheels and tyres. So pay attention to rear wheel OFFSET:
Image

.. initial suspension settings gave plenty of roll even on uprated rear springs (Imp) ... I had plenty of rear grip but relatively low front end grip which resulted in too much understeer. :shock:
Image

....and here is an old pro demonstrating that proper weight transfer front AND rear gives good turn-in 8) ... note his calm and content expression ... very much in control ..almost bored infact :lol:
Image


.... a very light car on wide rear rubber albeit a soft trackday compound (AVON CR500 205/55/13 rear 175/55/13 front) . The suspension settings are set-up to work with the low weight and available grip from the tyres. 8)
Image
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Re: What Tyres?

Postby Dogsbody » Sat Feb 23, 2013 1:01 pm

This dosen't look much at first glance as the car is almost flat.
But look at the angle of the air freshener hanging from the mirror and the front tyre exposing the rim where its under stress.
Standard suspension as it left the factory.
Image
The LSD sorts out understeer :wink:
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Re: What Tyres?

Postby Colin Valentine » Sat Feb 23, 2013 2:04 pm

Quote from Lotus-e-clan
"The tyres and suspension work together.
If you have a stiff, low-roll set up for racing on fat tyres then the weight transfer to the outer gripping wheel is reduced so you will have less cornering grip than with a more compliant suspension setting... and that will probably only show-up dramatically when the road has less grip (wet)."

I have to disagree with Lotus-e-clan man's analysis on this.
I think he's got the explanation wrong.
A stiff, low-roll set -up will give MORE weight transfer, NOT less.
Hence the move to wide low profile tyres, for better grip on the outer tyre.
Especially on Race Cars.
It works superbly on smooth dry tarmac where there is plenty of grip.
But when grip levels are reduced, as on a wet track.
Then a softer set-up with narrow tyres, as per the original Clan will be much better.
Public roads are also a problem.
Surface camber changes can mean that only a part of the wide tyre is in contact with the road surface.
The grip from a wide tyre can change from mega to near zero in an instant, due to road camber changes.
If you don't believe me come to a Car Trial.
Wet grass is just as good as a Skid Pan.
Stiff cars on wide tyres just don't work, but soft suspension and narrow tyres do.
My Saxo with soft suspension and narrow tyres will easily outclimb powerful cars with wide tyres.
I'd also advise against Negative camber at the front of an Imp for road use.
This tends to cause unstable handling characteristic, and make the steering very heavy.
The car will have initial understeer, which becomes almost terminal.
Then if the car rolls a bit, the front finds some grip and the car can suddenly snap into terminal oversteer.
The car is just horrible to drive.
Bin there, done that, learned most of the lessons......................
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Re: What Tyres?

Postby Dave ' Linwood ' Lane » Sat Feb 23, 2013 2:11 pm

Colin Valentine wrote:I'd also advise against Negative camber at the front of an Imp for road use.
This tends to cause unstable handling characteristic, and make the steering very heavy.
The car will have initial understeer, which becomes almost terminal.
Then if the car rolls a bit, the front finds some grip and the car can suddenly snap into terminal oversteer.
The car is just horrible to drive.
Bin there, done that, learned most of the lessons......................
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Agree on the rest Colin but not this bit , too much negative on the front is horrible but no more than 1 1/2 degrees negative on the front improves things no end providing you havnt got Carlos Fandango sized tyres on the front :lol: , ive finally got the Singer to handle really well like this , putting genuine van shocks on the back stiffended the arse up a bit and it now feel grippy , and very drivable .
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Re: What Tyres?

Postby Duk » Sat Feb 23, 2013 2:19 pm

I'll keep quiet about front camber and low profile tyres with wide rear wheels :lol:
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Re: What Tyres?

Postby Lotus-e-Clan » Sat Feb 23, 2013 4:10 pm

Point taken Colin about the lack of clarity of the explanation. But the message remains the same ... the suspension and tyres work together and a softer set-up is better in the wet.

I think one needs to differentiate between the speed of weight transfer and total weight transfer.

Weight transfer is more progressive and less instant with a softer set up as the initial spring compression is absorbing the pressure from the weight transfer. But as the softer springs compress further and the car rolls more to the gripping side then more of the cars weight is transferred to the tyre. Put another way the stiffer setup is much faster at transferring weight to the gripping tyres and you can change direction much quicker. But I maintain that ultimately, with the stiffer low-roll set-up, the full potential weight transfer to the gripping tyres is limited compared to a softer setup. So with a stiff set-up the limit of grip is reached more quickly - a softer set-up is slower to transfer but can ultimately transfer more pressure on the gripping side.

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Re: What Tyres?

Postby Leedy » Sun Feb 24, 2013 6:13 pm

Hi all. And thanks for all the comments. I have been messing with imps since way back in the late 70's. I actually had one of the fastest imps back in the late 80's and it was shown at several shows. Before sadly selling it to a motor sport dealer and it being shipped out to Japan. I DO know all about the dangers of wide wheels and hubs. I DO know all about the negative camber. stiffer springs etc etc etc. As its been over 15 years since building an imp. I couldnt remember what tyres I had on my old car. So. I simply asked the question about WHAT TYRES? I really didnt need a lecture about why I should fit these to a road car or about some guys ford Puma? So to all the comments from the genuine people who actually did give great advice. Thank you. To all the other people who commented. Please get off your soap box! I can now see why lots of people dont post on here. Its because they get a lecture from people who dont really have a clue!!!! Rant over
Thanks OLI, JAMES and COLIN
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Re: What Tyres?

Postby bungi » Sun Feb 24, 2013 6:19 pm

i ran 175/50/13 front and 175/60/13 rear and had no issuse
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Re: What Tyres?

Postby johnh875 » Mon Feb 25, 2013 12:21 am

Leedy I don't think the general point "why so wide" was out of line as you hadn't pointed out your experience in the first post and plenty of 'new' Impers ask the same question. The Imp is such a different proposition from most cars in terms of weight distribution and camber change that these things bear explaining. That discussion did subsequently expand/wander, but it is the internet and that happens!

As a starting point for finding out what size/make tyres are available to begin with you could try tirerack.com as they have a fairly comprehensive listing. They are in the US so may not have much interest in 13" sizes any more, so if you can find an experienced tyre seller locally who might have some knowledge of what obscure sizes can still be had (ie outside of 205/60R13), that may prove more fruitful! I dare say there is not much call for wide 13" rubber any more, for example is 175/70R12 available any more?
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Re: What Tyres?

Postby Rod » Mon Feb 25, 2013 12:31 pm

Leedy, I'm sorry if my post was one that offended you, however I still cannot for the life of me understand why you would wish to go so wide for minimal gain and numerous complications simply for road use. Leaving aside the points already mentioned here and simply looking at the practicalities have you really considered the complications involved in running different sizes front to back? OK people do but life's too short in my opinion for the ensuing hassles. My own experience was long ago but I can tell you that 175/70 12 Goodyear Ultragrips on 5j x 12 wheels will foul on the inside of the wheel arch on full lock. Again we're going back to the early '70's but the sweetest handling Imp I ever knew was running Avon Wide Safety Cross Plies on 5J x 12 wheels. Time has moved on and there will be some better alternative these days but for day to day use on modern roads I doubt 6" wheels on the front and 9" on the back is it.

Sorry if this upsets you but rest in the knowledge that you almosr certainly know better.
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Re: What Tyres?

Postby Dave ' Linwood ' Lane » Mon Feb 25, 2013 12:56 pm

Most tyres catch the inner arch on the front , passengers side normally :shock: , the shell was designed for crossplys which are mega skinny , 6 x 13 with 175 / 60 / 13s and possibly 185 / 60 / 13s will go fine on the front with the correct offset
No point in anything bigger front or rear
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Re: What Tyres?

Postby Duk » Mon Feb 25, 2013 1:01 pm

A 205/60/13 on a 9" is no more stretched than a 195/45/13 on an 8" rim which I use with no problems whatsoever and handle great. The 205 is also 35mm taller so gearing will be better.
If you go for this size it can be nankangs or falkens, I have the nankang tyre but in 165/55 size on a 7" and have never let me down and handle great, this particular model is known to cope with stretch well
http://www.camskill.co.uk/m73b0s375p0/C ... _205_60R13
Image
205/60 on a 9"
Image
Front can be 175/60/13 and will 18mm shorter height wise than the rear but when on the car I'd think they would look very similar to the rear as they wont be 'ballooning' like 185/60's do.
http://www.camskill.co.uk/m73b0s373p0/C ... _175_60R13
Image

Suppose it depends if you care about a bit of stretch
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Re: What Tyres?

Postby Leedy » Mon Feb 25, 2013 7:45 pm

Thanks DUK. Thats just the info I was after. To the other impers. I didnt mean to sound un greatful. But some times (I read other posts on here) People just give so much advice and get carried away. Just to help with future posts. The imp I am in the process of building has a rawlson fron and rear body kit. Its all been strengthened and welded where required. The inner and outtrer arches have all been cut away and the camber angles have been altered on the king pin carrier and on the rear cross member. It will be running discs front and rear with a fly off handbrake. It is going to be a road car but also able to drive to the track and give it large and show these kids how the old uns can do it. The Imp. Not me lol. I have a lot of work still to do and I will, once its getting nearer to being finished put a few pics up.
Once again. thanks for the help. Leedy
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Re: What Tyres?

Postby Colin Valentine » Tue Mar 26, 2013 7:57 pm

I'd be interested to know how you do the rear discs.
I do the Fiesta Front Disc Kits, and occasionally get asked for rear discs.
But I have never figured out a good way to do rear discs.
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