Lotus Elan

Tire Report

PostPost by: type26owner » Sun Jun 20, 2004 3:18 pm

Sumitomo uses a different marking system then most other manufacturers. They designate the the light side of the tire with a yellow circle and the radially stiffest point with a red dot. I made the mistake of trusting the installers to know this stuff because they're in that business. Guess how my tires were installed. :angry: In spite of this setback the steering wheel shimmy appears to be now zero on a smooth roadway for the first time. This happened because I shaved them true so there is no radial runout and had them balanced using my homebuilt lugcentric fixture. Lesson learned is the conical center pocket and hole on the steel wheels is okay for clamping purposes but sucks as an alignment feature.

These tires are rated for 51psi. Inflated them to that value to get the first data point for the finding the best pressure to maximize the grip and still have it handle at high speed without terrifying the driver. First impression is 51psi is too much pressure and the slip angle is greatly reduced. Best guess these tires are going to perform well at around 40psi but I won't know for sure until I get it out on the racetrack. Really looking forward to getting in some laps for only the second time (first time was several years ago at Laguna Seca) with my Elan at Thunderhill. :D

I think these tires are going to perform rather well. I found at least six other tire brands which had performance tires which might fit the stock wheels but most were lesser known asian brands. However many of those had a better 'H' speed rating and might be even better performing then the Sumitomo's.
-Keith
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PostPost by: Fred Talmadge » Sun Jun 20, 2004 4:31 pm

Exactly what type and size of tire did you get?
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PostPost by: type26owner » Mon Jun 21, 2004 12:01 am

Hey Fred,
That info was included on the Topic Description. It's the Sumitomo HTR T4 165/70R13.
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-Keith
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PostPost by: steveww » Mon Jun 21, 2004 9:21 am

For those of us in the UK:

Uniroyal Rallye 680 155x80x13 T
Falken FK-07U 165x70x13 or 175x70x13 H

I have had good reports on the above tyres by a number of people.
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PostPost by: type26owner » Mon Jun 21, 2004 7:44 pm

40psi in the rears is frightening. My car handles just like a Jordan now! It won't change direction quickly at high speed without going into a bigtime oversteering slide. Clearly it's still got way to much sidewall flex at 40psi. Definitely going up in pressure on the rears. :angry: Not so sure these tires are going to be okay for the racetrack.

I could be buying some of those off brands tires searching for grip and handling yet.
-Keith
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PostPost by: rgh0 » Tue Jun 22, 2004 8:44 am

Keith

You definitely have a problem with this setup if 40 psi is to low a pressure. I have never used this and given the weight of an Elan you should not need to.

I have progressively dropped pressures as I have gone to lower profile tyres over the years and always found that the same pressure front to ear within about 1 pound best.

eg
Track use pressures over the years have been
around 36 psi for 155 x 80 michelin XAS ( on 4.5 inch wheels)
around 33 psi for 165 x 70 bridgestones ( on 4.5 inch wheels)
around 30 psi for 175 x60 hoosiers or yokohamas ( on 5.5 inch wheels)


I suspect the 4.5 inch stock wheel is to narrow for this particular 165 x 70 tyre your using and its rolling on the rim. The alternative is that the tyres are sticky and you need to do some work on stiffening the suspension in roll, I have seen and experienced this problem with excessive oversteer on Elans with standard suspensions running sticky tyres even when they had wider and more suitable wheels. A guy rolled his Elan at a track day in Sydney just recently and looking at the photos I suspect this was the problem.

Rohan
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PostPost by: type26owner » Tue Jun 22, 2004 2:00 pm

Hi Rohan
Though I removed a good deal of the top layer truing the tires perhaps the grip will improve with some more wear. I'm okay while threshhold braking. It's just the rate of body roll when intiating a turn at speed which is the problem now. I have to do the weight transfer very slowly or it snaps the rears loose into a wicked slide. Recovery is not all that certain. Not at all fun to drive it this way. Like I stated it's as skidish as the Jordan F1 cars appear to be now. Since I own a tire truer now I suppose shaving most of the tread off is an option too.

I'm just applying the higher pressures for survival's sake. Coming to terms with reality it appears that I may need new wheels to fit lower profile tires with 'AA' traction ratings. Looks like 14", 5.5 to 6" wide and with an appropriate offset to clear the glasswork is required. I don't have to obey any vintage racing requirements so anything is possible. The real unknown is how wide a section width can one fit without bodywork flares but with the upgraded smaller diameter spring kits I have installed on the struts. Searching the web it doesn't look promising to find this size combination in an alloy wheel. Prepared to cut the centers out of new steel 4.5J wheels and weld then into donor 14" rims of the right width to get there though. That's the only way I can achieve the necessary offset to resolve clearance issues and have better choices for tires. All the while trying to maintain the 23" tire OD to not completely screw up the gearing. BTW, I've got the DB semi-competion coil over springs already on the car.

Please elaborate on how to cure the oversteer. I've got the extra rubber stop cushions installed on the rear struts as per your suggestion to reduce body roll. The roll has been cut in half it appears. The new tires and the rubber cushions are the only changes I've made on the car since the last track outing. The NLA Michelin MX4 155R13 I ran then had to be inflated to 50psi on three corners and the left rear I sat over had to have 55psi. It handled like a dream and was very easy to go extremely quickly. If I could just get it back to that point I'd be pleased. Not many cars were passing me at the end of the day and when they did it was on the straightaways under acceleration. Have not installed a stiffer front swaybar yet, it's still stock. Was waiting to see if it was absolutely necessary.

These tires don't heat up much with normal driving. Going to try scrubbing them until they do and see if building up the temp helps any.

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-Keith
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PostPost by: steveww » Tue Jun 22, 2004 6:10 pm

AFAIK you have to be a bit careful width how wide on the tread you go as the Lotus suspension was not designed to keep wide flat tyres flat on the ground as the suspension moves.

Most people recommend a stiffer anti-roll (sway) bar for track use.

Do you have fully adjustable suspension - spring platforms and dampers. If so you might want to try softening up the front and hardening the rear. This should reduce the roll oversteer.

I have been having clearance issues with 13" minilite wheels on my S4. The minilite only has 95mm backspace instead of 103mm, that 8mm makes all the difference. Due to the thicker material of the alloy minilite greater backspace would cause the wheel to hit the suspension. I was considering going to 14" which would solve those clearance issues and allow for greater backspace. Using a 14" wheel works out as 185x60x14 for the same gearing but I think 185 is far too wide with out body mods. 175x65x14 would be a better bet as well as 165x70x14
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PostPost by: type26owner » Wed Jun 23, 2004 1:45 am

Rohan,
I lied. Forgot I now have Col Croucher CV axles installed and have lost any roll stiffness contribution from the donuts.

Steve,
Been doing my homework and have a ray of hope that the oversteer can be tuned away using these tires and wheels. Seems I've unbalanced the Tire Lateral Load Transfer Distribution (TLLTD) and now have to much of a transit weight loading the outside rears on an abrupt turn-in. Carroll Smith and others sources recommend stiffening the front in roll and therefore inducing more understeer. This also diagonally loads the inside rear tire which helps reduces the oversteer. Maybe competition rated fronts springs are now also required.

There's a good possibility the extra rubber cushions on the rear struts are to long and that is exasperating this condition. Can shorten them in situ so tuning them is no big deal. Looks like morphing an adjustable piggybacked stiffener onto the swaybar is worthwhile and now required.

Noticed while scrubbing the Sumitomo's that at the same pressure I used to run on the Michelin's that these new tires have more flex in the sidewalls. Maybe I just need to exercise them more to stretch out the belts. 50psi in the rears has helped allot. Could even need more pressure in the rears only to reduce the sidewall flex. Rears are now showing feathering wear on the shoulders at 50psi.

Tried to contact Dave Bean to plead for help but he was out of the office. Will annoy him tomorrow. :)
Regards,
-Keith
p.s. This is a major distraction from my main focus of understanding the physics of Webers and applying corrective measures. :rolleyes:
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PostPost by: rgh0 » Wed Jun 23, 2004 9:24 am

Keith


I would approach the suspension tuning in the following stages until you get the rear under control to your taste. This assumes you are satisfied that tyre roll on the rims is not a major contributor. These steps are what I have progressively done on my car over the years to control the sort of snap oversteer on turn in you describe as I have moved to progressively stickier tyres.


1. A BIG front roll bar 23 to 25 mm This may be enough depending on your tastes in combination with the rear bump stop mods and standard springs. You need to fabricate new drop links to hold the bar. The DB competition roll bar is 25mm ( 1 inch). I would skip the DB fast road 19mm ( .750 inch bar) step


2. Stiffer front springs about 110 to 120 lb / in in combination with the stiffer front bar and rear bump stop mods. Plus 2 front springs are this rate and sagged plus 2 springs give the right ride height and are cheap !. This should cure any oversteer and is a nice combination for road use with modern sticky tyres


3. Stiffer rear springs to about 110 to 120 lb /in and stiffer again front springs around 150 to 160 lb/in. This third step is really starting to get a too stiff for routine road use but it will improve stability a step further especially in high speed sweeping corners and will enable you to give europas, sevens and elises a run for their money in most circumstances. This is the DB recommended competiton setup and where I have evolved to also.

4. Going beyond step 3 to 250 lb/in fronts and 150 lb/ in rears is what TTR recommends for racing but I ( and some others) feel this is too stiff especially in the wet and on tracks that are not dead smooth. Need to have a properly stiffened 26R style chassis ( or spyder) otherwise chassis flex will be getting significant at these springs rates also I feel

good luck
Rohan
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PostPost by: type26owner » Wed Jun 23, 2004 7:29 pm

Thanks Rohan for the info. Dave Bean basically confirmed what you've recommended. According to Dave on most Elans when any suspension related changes are done they're prone to oversteer. I bought a 1" front swaybar to try first and increase the load on the outside front to induce it to understeer. He also said to valve the Spax dampers up to a harder setting on all four corners. Though they don't have any affect when cornering on the jounce of the outside wheels it does help by slowing down the roll rate because the inside suspension extends in rebound travel and the dampers will slow that extension process down. The trick to reducing the nasty oversteer is to redistribute the corner weights with primarily the front swaybar and slow down the roll rate around the roll centers with the dampers so the outside rear is not overloaded beyond it's traction limit.

Can you apex the turns and run over the curbs with the inside wheels without lifting the front outside tire enough to cause lots of understeer with the 1" swaybar?

Best news is I discovered this morning that the tire pressure guage which lives in the glovebox and I've been using all along indicates 7 psi higher then what it should. An actual 55 psi pressure in the rears has cured the sidewall flexing issue. Oversteer level has been reduced from frightening to just annoying now. :)

Regards,
-Keith
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PostPost by: rgh0 » Thu Jun 24, 2004 11:34 am

Keith

With the 1" front bar no major understeer problems except if you get a corner badly wrong with entry speed.

eg
If go in to slow for a tight corner and get on the power to early you can get understeer or if go in to fast and turn in to late can break away the front end first.

In general if you get the speed into the corner right you can balance the car nicely on the throttle once you turn in. In many corners you can lift the front inside wheel ofF the ground without any detrimental affect on the handling.

Rohan
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PostPost by: type26owner » Thu Jun 24, 2004 1:57 pm

Oh Good. It's no fun if the curbs and presumably the rumble strips also have to be avoided. Much more fun to plow right over them.

Been reading up on suspension tuning again and am completely confused whether the dampers should be made harder or softer to slow down the transient loads causing my oversteer problem. Forgotten what a complex subject this really is. Hoping I won't have to struggle to much to get my car to handle back to neutral. Found this website which explains the process in some detail but realized I would need a man-week of rereading the articles over and over again to come up to speed so I could apply this info at the track. Performance driving and suspension tuning is not for the ignorant. <_<
<a href='http://www.smithees-racetech.com.au/' target='_blank'>http://www.smithees-racetech.com.au/</a>

Regards,
-Keith
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PostPost by: steveww » Thu Jun 24, 2004 3:17 pm

As a general rule of thumb....

Soft front - hard rear = oversteer
Hard front - soft rear = understeer

If your dampers are adjustable then firming up the bump setting will slow the rate of roll down. However if the dampers are too firm then running the curbs is out and if the track is not totally smooth then the car will bounce from crest to crest.

Different drivers like different set ups. Personally I like a bit of understeer leading in to oversteer. A friend of mine likes his cars really pointy with no understeer and a loose tail.

I think what might be happening with you is that the springs are compressing at the rear and sitting it on the bumpstops giving you a too hard rear end. As you have dropped the donuts you might want to go to firmer rear springs to compensate for the lack of donuts. However you might be able to dial this out in the dampers?

To set up my cars for the track I go along to a track day with an open pitlane and tweek settings all day. Take a notebook and keep a log as it is very easy to get lost in all the settings. Find a set up that suits you and one that you can drive.

Have fun B)
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PostPost by: type26owner » Wed Jul 07, 2004 3:08 pm

Looks like the tailend wiggling issues I'm having are dominated by the torsional windup associated with the very large slip angle of these tires. These tires have so much sidewall flex below 50 psi on the 4.5" wide wheels that they make excellent springs. When I turn in quickly they will do a big lateral deflection and then release the energy just as quickly when the level is changed. My only option is to up the pressure until the grip is reduced via reducing the slip angle along with the contact patch area to get away from this troublesome super-elastic behavoir. So I've ended up applying bicycle tire pressures. Also looks like I need different pressures on all four corners but I'm still tuning. Luckily it's made the car fast, stable and neutral. Since I don't have lots of power to cause any oversteer problem coming off the corners and can't squirt down the straights it's all about conserving speed through the twisty bits like a Formula Vee does. Plus it makes for a rookie driver taking it to the perimeter of the traction circle a blast of fun and safe. I'm ready for the trackday now.
-Keith
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