Lotus Elan

Tire Report

PostPost by: Rob_LaMoreaux » Mon Jul 12, 2004 3:05 am

Keith,

Why did you choose the Sumitomo HTR T4s?

I just looked at their specs and the treadwear rating of 560 would eliminate them from my list of tires in a heartbeat.

I hate the 155R13 Michelin MX4s I have on my steel rims since they have almost no grip and their treadwear rating is only 420, although I will say that with 23psi front and 26psi rear they seem to let go predictably and safe if early. The ride though is quite nice.

When I looked up 165/70R13 at Tirerack they listed the yokohama Y379 with a treadwear rating of 180 which would handle much better. I wish I had found those Y379s 4 years ago when I got the MX4s.

For trackdays and autocrossing I have 175/60R13 Yokohama A032Rs on Panasport 13x5s which work pretty good unless I screw up the entry to a corner in which case they tend to understeer. Hopefully they wear out this year so I can get the soft compound version of the A032R, or the Kumho Ecsta V700 if I get the time to put the adjustable spring perches on so I can fit them. The Kumhos have a section width of 7.5" where the Yokohamas are only 6.9" wide, and thus on my S4 they have about 3/16" of clearance on either side. I will say that both the V700s and the A032rs are a bit too square shouldered for everyday on the street since the ride is a bit harsher than I like, but those Y379s look perfect. If only I had the cash available at the moment (getting married next spring).

Rob
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PostPost by: type26owner » Mon Jul 12, 2004 11:16 am

Rob,
You're right these tires are marginal. I just consider it a real technical challenge to get them to perform well at the edge. With such a narrow wheelbase and the CG like it is stock I perfer having tires which tend not to try and bite in and roll the car if the driver makes a boo boo and gets it sideways to much. I don't want to be terrified or sorry by the putting on to much bite. That's not my idea of having fun. What is fun though is being able to keep up with the Elans with the wide sticky tires on the track. I was able to do that last time. :D

If you dig deeper in the available literature you'll find that comparing tires between brands by the treadwear rating value is impossible. There is no standardization what so ever. The numbering system is random (remove random and insert arbitrary instead) and unique to each manufacturers' perception. Between the different tire types that a single manufacturer markets it's useful a little. Stick with comparing all the other type ratings. They are directly comparable and are based on a uniform standard.

The reason I'm forced to use these tires is the clearance to the fiberglass on the rear is nearly zero now using the 4.5J steel wheels on my S2. I won't flare it and cross over that line.
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-Keith
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PostPost by: Rob_LaMoreaux » Mon Jul 12, 2004 11:55 am

While I agree comparing treadwear between manufacturers is difficult since they use different locations for the test, the actual test is the same across manufacturers so, while your HTR T4s may be just as hard as the Michelin MX4s I have which have a treadwear rating of 420, the Yokohama Y379 with a treadwear of 180 is much much softer than the HTR T4 at 560, and they are both listed as having a section width of 6.5"

Since you said you had adjustable perches and such I wasn't sure which body and how much clearance you had. I can understand the clearance problem, especially since I had my front fender slightly damaged at the LOG autocross in wisconsin a couple years ago, with the stock size 155R13s..

Glad to hear you got them to work decent.
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PostPost by: type26owner » Wed Jul 14, 2004 7:48 pm

Rob,
The Yokohama's specs are the reason I didn't even consider them. It has only a 'B' traction rating which normally means they have horribly low grip. They are also a full inch undersize then the tire size the car was designed to run. Which screws up my topend speed since I've got the 3.9 diff. They are only pressure rated for 35psi. Just try cornering in your Elan at over 100 mph with only 35psi in these tall skinny tires and see what happens. I don't want to test my new rollhoop first time out on the race track. My best guess is those tires would be dangerous for track use. I already have first-hand knowledge that the BT70 Bridgerocks are dangerous. That's why I made that decision. Looks like I made a wise one, so far. I'll file an update after the trackday.

Have removed my comments about treadwear after reviewing the info again. Found I have a flawed memory again, doh. <_<
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-Keith
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PostPost by: TonyC » Thu Jul 15, 2004 11:44 am

<!--QuoteBegin-type26owner+Jul 14 2004, 07:48 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (type26owner @ Jul 14 2004, 07:48 PM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin--> ...Just try cornering in your Elan at over 100 mph with only 35psi in these tall skinny tires and see what happens..... [/quote]
Please explain what might happen. I've followed this thread and I'm having a very difficult time understanding your requirement to run such incredibly high presures?
Over 35psi ? 40 psi? 55psi (!)?
All to stop sidewall flex?
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PostPost by: type26owner » Thu Jul 15, 2004 2:00 pm

TonyC,
With similar sized Michelin's fitted and only 35 psi inflation all around at Laguna Seca the car had a wicked high speed instability while cornering or braking. In a corner it would yaw rapidly. The frequency was about one hertz and either end of the car would slide out by 6 to 12 inches at each oscillation. That's with the driver doing his best to dampen the yawing via the steering wheel. If no correction was applied entering a turn it was pretty much a randon process whether the car would go off from understeering or oversteering. It was almost impossible to keep it under control from the yawing while doing threshold braking in a straight line also. It was the worst handling car I'd ever driven and I nearly parked it for the day after the first session.

I had zero prior experience trying to tune the handling on a car with tall skinny tire on narrow wheels. Anyway the solution to cure these condition turned out to be run the tire pressures way up. I had the rears inflated 23psi over the maximum rating. I took a real chance a tire would not fail at high speed. Drove the rest of that day with <span style='color:red'> lots of fear</span> . The Sumitomo's 51psi maximum pressure rating was number one reason I picked them. I'm going to be a couple of seconds slower per lap then the guys with the sticky, wider, shorter stuff. Big deal, it's still a blast of fun.

BTW, if you think I'm crazy running the pressures this high may I suggest you read what Carroll Smith has to say about it in Engineer To Win. I concur absolutely.
Regards,
-Keith
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PostPost by: TonyC » Thu Jul 15, 2004 3:37 pm

Keith, I realy do you think you have chased yourself up a blind alley here and I'm wondering who advised such high presures.
As I understand it, at high sped turn in you get rapid body roll that results in roll oversteer. As you run through the corner the car changes state from over to understeer in rapid succession with you sawing at the wheel. If you try to maintain a line it will either carry on roll oversteering and drop you off the track, or will develop understeer and drop you off the track. (Is this is alway at the same speed, same throttle opening, is this with the throttle being open or closed)

Also, when braking heavily the car is unstable, trying to pitch left or right.

Part of the problem will be the presure, 35 is high and you will have a reduced contact patch and a tyre fighting the road surface. The main crux of the problem though appears to be a spring/damper issue. (And perhaps a few geometry issues as well)
The pitching under heavy braking sounds like the car is not controling the front/rear weight transference very well - resulting in the instability.
The high speed corner problems again sound similar - especially if it is pitching into body roll very suddenly. The under/oversteer chnages again sound like the car is not managing its weight effectivly, but may also be due to large geometry changes in roll. IE, rear toeout increasing in roll.

The 55psi rating on the tyre is it's maximum inflation level, when warm. I shudder to think how high a presure the tyre is reaching when warm if the cold presure is 55psi. You realy are risking a blowout. It may seem that increasing the tyre presure is helping but I think it is masking the real problem, and by keeping these high presures you running the risk of an accident. I woudl go back to lower presures (maybe a few psi above factory) and look again at the handling of the car and start by looking at tyre compound and spring/dampers/geometry.
Even 35psi cold is too much. If I am at a track day and want to do some drifting I increase my rear tyres to 30-40psi becuase it reduces the grip so much you can drift all day. This is a trick used by drifters on many cars.

I don't race Elans, but have run a road elan+2 for many years. I have raced for a number of years with a much modified MGB, going through a variety of suspension setup and tyre types and have never come across a need for cold presures so high.
It is very presumptious of me to suggest these things without having seen or experienced the car I know, so please don't take offence, I jut believe there is something else wrong and the tyre presures are the wrong route to go.

Tony
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PostPost by: type26owner » Fri Jul 16, 2004 12:29 pm

Tony,
You've got different events and info that I tried to accurately describe all garbled up incorrectly. Undoubtably my writing skills are lacking somewhat and the cause...

The Sumitomo HTR T4's are a passenger grade radial tire rated for mud and snow not a racing tire. At 35 psi they handle and sound like they are going to break the bead and deflate on the rears when pushed hard. There is no way I'd run less pressure cause it ain't safe. Maybe it would be okay for autocrossing but not for the high speed stuff the way I drive.

If Carroll Smith and Fred Puhn credentials aren't good enough to sway you then I'm going to fail also. Have you read their books lately? Your advice would help me understand the physics and actually convince me you're correct if you could please cite a reference in one of the suspension tuning books and then explain to me why it would apply to my situation. That's the best and ONLY way to sway an engineering savvy person.

I have all my handling problems resolved at this juncture and I'm ready for the track. Regards,
-Keith
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PostPost by: steveww » Fri Jul 16, 2004 2:33 pm

Using M&S tyres on the track is certainly a novel approach. Not sure your tyre choice was the right place to start. I know getting any sort of performance tyre in 155x80x13 is pretty much impossible but I am sure there are better tyres available than a M&S tyre, good for rallies though.

My S4 Elan is currently running on Uniroyal rallye 680. Again these are T rated passenger car tyres and not exactly sticky. They are mounted on 5x13 minilites. The suspension set up is pretty standard. Standard anti-roll (sway) bar. Standard rear springs/dampers and rotoflex. New adjustable Gaz front dampers/springs. Will be upgrading to adjustable Gaz and UJs on the back this winter. The spring rates are pretty soft as the car is mainly used on the road. For track work I will adjust the damper bump rate.

So far I have used the high pressures from the workshop manual of 24F 29R and so far so good. Braking stability is fine. Pushing through a corner I get mild understeer going in which I can push through in to oversteer which is easily balanced with throttle/steering. Keep the power on through the corner in a nice drift and out on to the straight no problem. I find the Elan's handling excellent, neutral and easy to control, a lot easier than my old Porsche which was VERY tricky on the limit (managed a 1080 spin at Silverstone). My testing was done at Bedford Autodrome on the West circuit. I have held an MSA National A license for many years and raced various types of cars from saloons to single seaters.

I must say I am with Tony C on this one. The instability you are reporting sounds shocking and I would take a back to basics approach to the whole set up.
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PostPost by: type26owner » Fri Jul 16, 2004 3:02 pm

Steve,
I drove my Elan for several years on the road before doing so the first time at the Laguna Seca racetrack. Thought it was track ready and was shocked to discover that it had this wicked handling problem the first time out. Driving on the road is no way near the same as on the track. Until you get it going at 10/10s at the maximum velocity you CAN"T evaluate the true handling.

Would it help here any if I quoted what Carroll smith and Fred Puhn have to say about the pressures to run with tall skinny tires? It's totally counter-intuitive but the physics involved are valid.

Here's something off-the-wall. I spoke recently to some un-named persons who have influence with some of the Asian tire companies. I pleaded for them to reintroduce a performance tire for us. They're going to be expensive but just maybe we might get lucky in a year or two... Apparently some of the companies are looking for niche markets as small as 50k pounds of tires as a single lot and are willing to produce just one lot per year. Okay if this happens everyone NEEDS to help create a demand to keep it self-sustaining.
Regards,
-Keith
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PostPost by: steveww » Fri Jul 16, 2004 4:56 pm

Keith,

I did my testing on the West Circuit at Bedford Autodrome. This being a racing circuit I can assure you the testing was at 9/10 did not go to 10/10 as I did not want to break anything. i.e way beyond the type of driving I do on the road. As I said I was pretty happy with the handling/performance, the brakes also did not fade which is always a plus :)

I am sure with some sticky tyres and harder springs/dampers more grip could be found and the lap times reduced but I want to keep my fillings in place when I drive on the roads ;) From previous experience it would be a fair bet to say that with these tweeks the handling would become more twitchy. The trick is to find the maximum grip you can drive and have the car set up so that you are happy with it. There is no point being able to pull 3g latterally if when it goes you can not recover it and you spin. Better to have 1.5g and be able to control the spin, as you are not going to push to the limit if there are dire consequences from exceeding that limit.

Each to their own - an old friend of mine who I have raced against for many years likes his cars really pointy i.e. no understeer at all and a loose tail, works for him as he has finished in front of me many times. However I can not get any near his lap times with his set up. Personally I don't mind a bit of understeer if it makes the car less twitchy. With this set up I have finished in front of him many times as well. :D
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PostPost by: type26owner » Fri Jul 16, 2004 7:43 pm

Hey Steve,
My ideal setup is one which is the suspension's reaction force range is appropriately matched to the applied ones. This can give a fairly neutral handling response which I perfer but it also goes beyond that requirement in an often overlooked way. If I get it adjusted correctly it will tend to self correct itself out of a condition when I've driven outside of the traction circle. When it's wrong it will tend to amplify the problem. Setting it up so it dampens is the trick.

I have a test procedure to perturb the car to tune it properly to get it close without needing track time. I'm not going to reveal it here because on a car with a poorly tuned suspension (the stock one) it's an extremely dangerous maneuver. My present setup has passed that test with flying colors. It makes the car extremely easy to drive at the limit.
Regards,
-Keith
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PostPost by: TonyC » Mon Jul 19, 2004 11:56 am

M&S tyres for the track. That is a singluarly perculiar choice. :)

I am familar with the work of Carrol Smith. in fact I had a quick look at Tune to Win over the weekend but the chapters on tyre presues only really spoke about the usual things of using the temprature across the tyre face to select presures, etc. Although he does discuss going as low as 18psi (obviously these are soft race tyres). I have read other peoples work and a few years ago used to regularly discuss handling matters with a chap who worked as a tyre testing and suspension 'sorter'. Your tyres are tall and skinny, but not that tall and skinny. Wonder what presuers they use in a 1930's ERA?
Anyway, none of the references I could find suggested very high presuers. It's intriguing though and I will probably get a copy of engineer to win to see what is described.

Just out of interest, have you tried sourcing any crossply tyres, I'm pretty sure the speciallst suppliers would find a tyre in the right size, the stiff sidewall might be what you are looking for. I'm pretty sure Dunlop (the UK based motorsport company - not the French (?) road tyre company) could help.
In fact, a UK based company called Colway do make a road going 'sports' tyre in a 155/70x13. These are tyres desgined for tarmac road rallying and will come in a reasonably soft compound. I've used their molded slicks in the past and they were quite good (but not as good as those from yokohama or dunlop). They are used by a number of historic road rally competitors (Used to do this a few years back in a Mk2 cortina and TR4)

If you are happy with your handling now, then fair enough. But you've got to love a bit of debate. It's what gets the old brain a-thinking :)

Tony

<edit> Just seen that you are using 165/70x13. That means you could use the Dunlop D83J which will be signifcantly faster around the track. it opens up a number of other Colway options as well.
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PostPost by: rgh0 » Mon Jul 19, 2004 12:41 pm

Tony

M+S tyres on the track are not that unusual. I used to use a Pirrelli 155 / 80 x 13 M+S tyre for track work, great in the rain and good when buffed down in the dry. I stopped doing this about 15 year ago when I moved on to play with slicks and formula ford fronts and finally moved to sticky road legal race compound tyres when these started to become available.

Keith

However I must agree with Tony that I think something else is going wrong if you need 50 psi tyre pressures to achieve stable handling. 35 to 40 PSI max would be the pressure range I would expect for a 165 /70 x 13 road tyre. I feel that the result of you going above this pressure is making the car stable but reducing the ultimate cornering force available.

The rear outside tyre of an Elan adopts a positive camber with respect the road due to body roll as the the Chapman strut suspension design has minimal camber change with respect the body on bump. The fronts maintain a negative camber due to the unequal wishbone design which has increasing negaive camber on bump that counteracts the body roll. Excessive body roll on turn in can lead to the rear oversteer you experienced due to this, especially if the tyre design has stiff sidewalls and a square corner that the tyre can ride up on causing the tread to loose road contact. I suspect the high pressures you are running are just making this process more stable and easier to control.

If you are braking as you turn in and are trying to ride the traction circle as per Carroll Smith you also will get rear toe out due to brake loads distorting the bushes which will also contribute to oversteer. My cornering stability on turn in at high speeds improved significantly when I replaced the inner rear rubber bushes with poly type bushes that dont distort under load.

All of this stuff is good theory and discussion but ultimately you need to look at tyre wear patterns, pressure rise and tread temperatures based on actual track testing to determine if your tyres are working right.

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PostPost by: type26owner » Mon Jul 19, 2004 3:25 pm

Love to debate these issues with you guys. This is the fun part of this forum. Tony, my apologies, it was Tune To Win I was refering to earlier. You do understand why I'm super cautious about taking advice from persons I don't know.....the input is welcomed though. For me this is where the real fun of Lotus ownership and operation is achieved. :D

There is another possible explanation for the handling issues I'm experiencing though. Are the Chapman struts prone to jacking when set to the standard ride height? This seems pretty far fetched to me but I've been wrong before.

Come to think of it my 62 Corvette had the same handling problem almost exactly. Just it would do this instability crap at 70 mph. It was possible to perturb the car so it would wiggle the rear end at an increasing amplitude so on the fourth or so slide it would spin out while going straight down the road. The only tires available for it had a similiar ratio of wheel width to section width to aspect ratio. I could not buy tires with a high enough pressure rating to cure it. Was able to buy steel rally wheels which were 6 inches wide and braze on the lugs to fit the beautiful hubcaps. That extra inch of wheel width cured the problem. Spoke to 61 owner just three weeks ago and he had to do the exact same modification. They handle like trucks (lorries) anyway but having a straight line instabilty really sucks. Stock Elans should not duplicate this behavior but do.

I'll do so more homework on this subject and see if I can find anything more.

I suspect the high pressures you are running are just making this process more stable and easier to control.

Rohan, yep and it's reducing the amount of torsional distortion known as the slip angle so the stored energy is less. I suspect that abundant energy when released is wiggling the rear around so I don't have much of a steady state condition. There's no way of applying any sort of damper except with the pressure.

Luckily for me I'm still got a reasonable amount of coeffient of friction with these pressures. Found the fronts are okay at 40psi. Might be able to lower them some more. Don't really anticipate having the tires heat up much with the pressures this high. There apparently is a correlation between lower pressures causing higher temps. Got a new digital pressure guage, temperature gauge and a 12v air pump to bring along for tuning.
Regards,
-Keith
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