Narrower tyres on 16" wheel rims

[paul jacobs]

Given that the general feeling about 16" wheels is that the front tyres are too wide, causing tramlining and other unwanted side effects, has anybody tried fitting 185 or 195 section tyres to the fronts only, leaving the 205/45/16 on the rear?

 

On the face of it, this seems to be a perfectly plausable route to take. Obviously it then prohibits using the fronts at the rear, but that isn't such a big deal, keep a std 205 as spare, then it can be used on any axle.

 

As a by the by, I have been using 205/ 50 / 16 tyres recently and find that the speedo is now accurate to within 1% and I have no other unwanted side effects, but I still wonder if narrower fronts on the 7" rims would work.

[EFA]

PAul,

 

Tyre width is not the problem with the 16" wheels.

 

There are however 2 problems associated with 16" HPC wheels:

 

The angle the wishbones have to be set to and the effect on roll steer through roll centre geometry is one problem (i.e the -ve camber reduces as the roll increases - in tighter corners this means significantly less grip)

 

Other problem is the type of tyres available in 205/45/16 - this is a tyre size for heavier cars - a Seven cannot get these tyres up to temp and keep them anywhere near warm - in reality off the track and on the road a Seven even has difficulty keeping ACB10's in A33 compound warm, and this is why people hate them - the cool running performance is abysmal! Of course A33 works well on track, but the loading on tyres should be much greater (unless you are a complete headcase!!)

 

Try ruiing the 16" rims with Toyo T-1S or Kumho V700 - these are about the softest street legal rubber you can get in this rim size.

 

In a Seven - and particularly anything with a heavy decent engine in it wink.gif - will have better turn in on wider rubber. Tramlining on radials will be down to a poor bump steer setup, or again the geometry working outside of its normal design (read 13" wheels) range.

 

Fat Arn

Visit the K2 RUM siteid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

[Dartmoor7]

I am currently running Bridgestone S02s on the front of my 1.4SS

and while I haven't been as impressed with them as some people, they have reduced the tramlining a bit. This may be because while they are nominally a 205 width tyre, the actual width of the contact patch is definitely less than the previous tyres.

As you know Paul, the stickiness is not the problem as A032s are available in 205/50x16.

There may be a problem fitting a narrower tyre because of the 7" width of the wheel.

 

Jerry Parker

L7SVN

1.4 Supersport

 

Edited by - l7svn on 27 May 2002 12:53:57

 

Edited by - l7svn on 27 May 2002 12:55:52

[Mike Bees]

I run on 205/50x15 fronts, and have found as Arnie states that if you run a reasonably low (or should that be 'normal') ride height at the front then the geometry goes all to pot (it's even worse at the back...). The steering fights and twitches like a mad thing on non-smooth surfaces. Raise the front a bit so that the lower wishbones are at least parallel with the ground and the problem all but disappears.

 

Mike

[STEVE GILBERT]

Also reduce the tramlining effect significantly by going to 0,20 mins Toe In. I did this yesterday and compared to my track set up 30mins toe out the road manners are vastly improved on the 16 inch wheels with pilots I use on the road (I use 13 on track)

If nothing else try it as it costs nowt(ish)

 

Steve

[paul jacobs]

OK Arnie, good point about retaining working temps. so the smaller the tyre the more it "works" which is a GOOd thing, the geomety is a whole different kettle of fish of course.

 

I've always had great difficulty in finding the best setup, it is just so much trial and error. When you are using a car with known setup it is much easier, but don't forget that I'm now running a 21, which has "narrow" wishbones, but a wider engine compartment, effectively giving me "wide" track, but I've got a heavy thumbsdown.gif but reliable teeth.gif Vauxhall engine, and to cap it all, Caterham in their wisdom used different suspension pickup and roll centres from the standard chassis, with the result that all 21's roll a lot when cornering, unless unacceptabley hard springs are used. I am now running 450lbs on the front and 200 at the rear for example, whilst the factory 21 GTO fitted with a featherweight K engine, uses 600 lbs on the front. OK I grant you that, according to Caterham the 21 chassis is 4 times stiffer [no rude jokes there, those at the back!wink.gif so can make these harder springs work better, but it is still far to hard for road use.

 

I've also noticed that the steering is substantially heavier at all speeds with 205s on, not really surprising I suppose, but there again would 195's help this too?

 

Yes Steve, toe in would help a lot, but you then lose the turn in advantage, so it's always swings and roundabouts, and it's the roundabouts where you need good turn in [sorry couldn't help myself].

 

Edited by - Paul Jacobs on 27 May 2002 20:11:48

[EFA]

Paul,

 

You eliminate roll by using springs which prevent the front end dipping under braking and the rest of the stiffening should come from an ARB.

 

450lb springs on the front will make the car very skittish - ther eis no compliance in the system if you use 16" ultra low profiles - nothing to absorb small high frequency bumps.

 

Fat Arn

Visit the K2 RUM siteid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

 

Edited by - fat arnie on 27 May 2002 20:34:01

[paul jacobs]

Exactly Arnie, which is why I find that a 50 section seems to work well, using the compliance of the sidewall to ride the smaller irregularities in road surface. But I still can't help wondering if narrow front tyres but using the same 7" rim size would feel better, give lighter steering at slow speeds but not give massive understeer on higher speed corners, because of the smaller amount of rubber on the contact patch?

 

Bear in mind the extra weight I'm carrying, the car weighs in at around 740kgs, in roadgoing trim with 6 gallons of fuel etc, and IMO is not skittish at all, quite the opposite infact, it feels very planted, same in the wet, perhaps even better then, which indicates that it is still a little too soft for serious track work.

[STEVE GILBERT]

Shame you wont try a little more toe in, after all, given the basic flaws that have been described it seems like at best you will only ever get a compromise, and the one you say you want to reduce is tramlining. What about playing with the front tyre pressures, how has this affected the way she drives?

 

[paul jacobs]

Well, actually Steve, on my heavier (Vx engined)biggrin.gif 21 I don't actually get tramlining, but I understand that this is a problem on Sevens. My main complaint is the abominably heavey steering at parking speed. I tried a set of 14" 185/60 tyres and wheels a couple of years ago, and the reduced steering effort was a revelation, but I can't use such small rims now because of the larger front discs that I've fitted, 15" wheels will just fit, but frankly there seems little difference with those, using 195's than the standard 16s, and I really need the extra ground clearance.