The Lotus Cars Community banner

1 - 20 of 25 Posts

·
Registered
Joined
·
1,938 Posts
Discussion Starter #1
OK, as is the case with many of you, I'm sure, my future Elise purchase is a topic of idle conversation at work (about 5-6 other guys in my company know I have a deposit down, and are either cheering me on and waiting patiently for rides, or are telling me I'm nuts).

Anyhow, we had a group looking at the latest high-res pics lately, and one guy dismissed/dissed the car's wheel dimensions, and tire/fender gap. His basic argument was, "If it's such a bad-ass performance car, then why doesn't it have 19-inch wheels, and why isn't it slammed to the pavement."

We can all take some pretty good guesses at what *THIS* guy drives, right? :)

Anyhow, in respect to the wheels, I explained the concepts of unsprung weight and rolling resistance, and pretty much shut him down. But other than explaining that ridiculously lowered cars hurt ride quality, I was at a loss to explain why lowering a car too far can be bad for pure speed and cornering. I know there's a reason why some of the ridiculously lowered coil-over jobs we see on "import tuners" are actually counter-productive, performance-wise, but I couldn't articulate it.

So: Why *shouldn't* high-performance cars be lowered as far down as possible, assuming ride quality is inconsequential? What determines a point of diminishing returns? What determines a point of *negative* returns?

Or am I basically wrong?
 

·
Forum Founder
Joined
·
29,083 Posts
In some ways, they or he is correct. Lower is better. Lower CoG is good.

The Elise is pretty low and that tire/fender gap is not that big. The tire will come close under suspension loading to touching the inside of the wheel well up front.


To make it lower, would cause some problems. The suspension of the car works to do a number of things such as absorb bumps and handle transitions and weight shifts. That requires some compliance in the suspension. If a race car didn't need that, they they could dump the springs, struts, etc. If you lower a car too much, you also have to increase the spring rates to keep the car from bottoming out on the bump stops. Hitting the bump stops is not a good thing for handling.

Making the springs/struts too stiff, removing compliance, is not a good thing either because the tires will lose their ability to maintain grip. When you setup a race car and are checking to see if the struts are too stiff, it's when the car "skitters" on cornering. The tire makes intermittent contact with the road surface.

Why would someone think that larger rims are better rims? Larger rims (everything else being the same) are heavier and are more resistant to the application of torque. That is another compromise area. Most upsizing of rims is for style and looks.


The more I learn about suspension, the more I find I don't know. It's very complicated stuff. But we do know that cars can be too stiff. Cars can be too low. Wheels can be too big.
 

·
Registered
Joined
·
1,938 Posts
Discussion Starter #3
Randy Chase said:
Making the springs/struts too stiff, removing compliance, is not a good thing either because the tires will lose their ability to maintain grip. When you setup a race car and are checking to see if the struts are too stiff, it's when the car "skitters" on cornering. The tire makes intermittent contact with the road surface.
Well, that is one of the arguments I was searching for. I knew intuitively that certain coil-over set-ups, while technically feasible (i.e., not hitting bump stops), might still be ill-advised.


But we do know that cars can be too stiff. Cars can be too low. Wheels can be too big. [/B]
That was what I was trying to explain. But his basic argument is: If it can be physically executed, and if it's what race cars do, then it must be good.
 

·
Forum Founder
Joined
·
29,083 Posts
A lot of race cars do what they do, because they have rules and limits.

Look at SCCA Solo cars that are allowed any wheel size (Street Prepared for example) and see what the fastest cars all do. They run 13" rims.
 

·
Forum Founder
Joined
·
29,083 Posts
A lot of race cars do what they do, because they have rules and limits.

Look at SCCA Solo cars that are allowed any wheel size (Street Prepared for example) and see what the fastest cars all do. They run 13" rims.

For my self, when I try to conceptualize why or how something like this works, I take it to an extreme. If you had rims that were 48" in diameter, would the car be even faster? One effect is that a larger rim actually raises the car.
 

·
Registered
Joined
·
1,315 Posts
The basic problem with these discussions is that in the end, people are usually talking about a "streetable" car. So considering ALL the driving situations that make a street car useable means a significant compromise of performance. IMHO there are lots of items people buy for "performance" that have the opposite effect. Wheels are a good example. Lotus have put together 2 great packages, standard and LSS, trust that they have made the best choice!
As for the nay sayers, who cares, just don't give them a ride when you get your Elise :D The faces of the others will tell the truth.
Personally, I smile inside when someone starts with "what's the top speed?" and "how much hp does it have?" You know they they don't have a clue....
 

·
Registered
Joined
·
1,579 Posts
This might not add much to what Randy and adamant ("Medicated until delivery" :D ) already said, but maybe a different spin on it will help your convincing effort. I think there are two questions here.

Why isn't the Elise lower? As adamant pointed out, it's a street car. Even if Lotus makes fewer compromises than most manufacturers, it still needs reasonable ride quality (suspension travel), and a certain amount of ground clearance. Otherwise they couldn't sell 2500 of them a year. If they built it as a race car, it would be lower, and stiffer.

Why can lowering a car have negative effects on handling? The suspension was designed with a certain ride height in mind. When you lower it, you change the suspension geometry. That moves the roll centers, changes camber curves, can introduce bump steer, etc. Many street cars profit from moderate lowering. But the "slammed" approach if for looks, not performance.
 

·
Registered
Joined
·
1,352 Posts
Found this on the web......

Keep in mind that a larger diameter wheel will serve to essentially lower the final drive ratio of your transmission. In other words, the larger the wheel, the less revolutions it will make compared to a smaller diameter rim. The effects of this phenomenon are far reaching, impacting many of your vehicle’s operating systems.
A positive consequence of choosing a larger diameter wheel is that your tires will last longer (unless you’re doing burnouts). Caution, since tires come in different compounds, this point is only valid when comparing tires of similar composition. Your car’s speedometer will also be effected by using a wheel/tire combination that is larger than the stock diameter. The common result of this phenomenon is a speeding ticket. The reason for this is that the speedometer is tricked into thinking that your car is going slower than it actually is (since there are less tire revolutions per mile). A positive effect of changing to a larger diameter set-up is that your wheel bearings may last longer, however you will be putting more stress on your transmission. It’s much easier to turn a small wheel than it is to turn a larger, heavier wheel. That also explains why there will be a reduction in torque when you use a larger wheel/tire combination. The good news is that although you may not be quicker off the line, you will be able to hold first and second gear longer before having to shift.
 

·
Registered
Joined
·
5,222 Posts
Nice explaination Randy!

If I may I'd like to add a few other points...

1. To expand on one of Randy's points. Suspension is ALL about compromises. In most circumstances softer well-controlled/designed suspension (to a point - there is too soft, like a Caddy ride) will give you better mechanical grip. Today's race cars run on billard table smooth tracks with LOTS of aero download. Aero download = big stiff springs to hold the car off the tarmac. Lotus learned this lesson a half century ago - the Lotus Mark III had softer suspension than its competition (that were going stiffer), but soundly beat them.

2. Most tire experts today will tell you that with today's current technology the best performance compromise (there's that word again) is an 18" wheel with about a 45 aspect ratio. The compromise is between grip, handling & ride. I suggest getting a copy of Haney's book "The Racing & High Performance Tire" http://insideracingtechnology.com. Basically, super short stiff sidewall don't allow enough compliance to keep a proper/stable contact patch unless you can control the contact patch with suspension (typically means stiffer suspension).

3. Race cars of today are incredibly sensitive to tire pressure (1/2 lb increments can be felt). Most of the mechanical grip is tuned with tire pressure because the suspensions are so stiff to carry the aero loading. Street cars have little or no aero loading and rely pretty much 100% on mechanical grip. So, any correlation between race set-up & street set-up are pretty silly (unless you drive routinely on the street at 100mph and run a full ground effects package on your street car).

I have the utmost respect for a Racing Team's Engineers because they have to optimize a package that is full of compromises. I agree with Randy, the more you learn about suspensions and tires, the more "stupid" you feel. Doesn't mean we stop learning, it motivates you to keep learning.

Kiyoshi
 

·
Registered
Joined
·
592 Posts
Tire and wheel sizes have been increasing for a couple of related issues. The wheel diameter has been increasing to allow larger brakes. This is a result of most "sports cars" weighing about 3,000 lbs. The Elise is not hampered by this penalty. The engineers for the S1 Elise wanted small wheels, but they were increased by 1" by the marketing department, and this is Lotus! You can imagine how wheel/tires are decided by the large manufacturers :mad:

As for ride height, I expect the Elise to already be low enough to cause minor issues that would not be allowed by a major manufacturer. I expect steep driveways and speed bumps to already challenge the car. And I can assure you the suspension is quite stiff (on the Euro 111S I drove). About equal to my E36 M3.

As to khamai's reference to tire engineers stating 18" wheels with 45% aspect ratio as being the best compromise, I cannot believe this applies to the Elise. This is likely based on the current definition of a performance car. The M3, 911, Corvette, 360 etc are all up in the 3,000 lb range and this may be the optimal set up for them. They all likely have brakes that require at least a 17" wheel. I agree on the aspect ratio, as this provides for low slip angles. However as the tires get narrower, 45% aspect ratio may result in too short a sidewall to protect the rim. The front tires on the Elise are only 55% aspect ratio, all the previously mentioned cars have tires well over 200 mm wide.

My philosophy is you want the smallest wheel that fits over the brakes and the softest suspension possible. Load transfer is proportional to stiffnes and the goal is to minimize load transfer. Start with as soft a suspension as possible to minimize bottoming and then add stiffness to control tire kinematics. So the stiffness is required to try and keep the tire in proper contact with the road. The reason a F1 car is so stiff is to absorb the incredible aero load. And even then, they seek to soften the roll stiffness while maintaining vertical stiffness. The 3rd spring/shock on a modern F1 car is designed to increase vertical stiffness without increasing roll stiffness.
 

·
Registered
Joined
·
592 Posts
Oh, by the way. The Lotus is an acquired taste that is appreciated by people who understand and agree with its philosphy and goals. Let them think what they want, you will know :D They can still like their cars. When I put Fiske wheels on my E36 M3, Fiske asked what size I wanted - I said 17" and they said good. They can fit 18", but they said 17" is better. As too lowering cars, I have not lowered my M3, but nothing wrong with a moderate lowering using a coil over set up. It does help the handling, but it does have drawbacks for everyday use.
 

·
Registered
Joined
·
1,938 Posts
Discussion Starter #12
Just to put the original issue in perspective, it was as much a discussion of why his lowered Honda (motivated by aesthetic concerns) is ill-advised as it was a discussion of the Elise. I was trying to explain to him that installing an aftermarket suspension willy-nilly, without *really* knowing how the car's geometry will react, is ill-advised. But he returned with the lower center of gravity argument, and... and thus my original questions.

Speaking of the Elise suspension, does anyone have any thoughts on the durability of its major wear/tear parts: shocks, bushings, etc? Will the sheer lightness and relatively low torque of the car give these parts greater longevity? Does anyone know what the rest-of-world Elise owners report about suspension life?
 

·
Registered
Joined
·
6,293 Posts
I would think that another problem with putting a very big and heavy wheel on a car would be that the brakes would have to work much harder to stop that big heavy wheel spinning.

Patrick
2005 Elise going Dub;)
 

·
Registered
Joined
·
5,158 Posts
For reference, F1 cars run somethingl like 15" rims. Most of the compliance that is built into the cars comes from tire deflection. You can actually see the tire deforming sometimes and it's very cool to see it under a slow replay. There comes a point where the car is too stiff and can no longer keep the tires on the ground. F1 cars tend to run softer around Monza so they can jump the curbs. :) I realize F1 isn't so relevant to street cars, but it's fun to make the comparison.

From the Sands Museum (http://www.sandsmuseum.com) interview with Nick Adams:

I asked about the size of the wheels and the profile of the tires. He chuckled and admitted the style was more towards very low profile tires, what I call rubber bands. He might have preferred to put 13-inch rims on the car and suggested, along with the tire manufacturers, that 50 and 45 profile tires are about as low as you want to go for performance. In the United States, the road infrastructure is very poor, with joins and potholes pounding the suspension. The lower profile tires transmit much of the shock loading into the suspension. The lower the tire, the more weight needed to handle the loads in the wheels and tires. High profile tires do not maintain tread stability. The best compromise with lightweight and good tread control is with 50 series tires. Even though the engineers have communicated this to the style department, the stylists still draw their cars with rubber band tires.
 

·
Registered
Joined
·
1,938 Posts
Discussion Starter #15
Just to put the original issue in perspective, it was as much a discussion of why his lowered Honda (motivated by aesthetic concerns) is ill-advised as it was a discussion of the Elise. I was trying to explain to him that installing an aftermarket suspension willy-nilly, without *really* knowing how the car's geometry will react, is ill-advised. But he returned with the lower center of gravity argument, and... and thus my original questions.

Speaking of the Elise suspension, does anyone have any thoughts on the durability of its major wear/tear parts: shocks, bushings, etc? Will the sheer lightness and relatively low torque of the car give these parts greater longevity? Does anyone know what the rest-of-world Elise owners report about suspension life?
 

·
Registered
Joined
·
1,063 Posts
JonM3Coupe said:
Speaking of the Elise suspension, does anyone have any thoughts on the durability of its major wear/tear parts: shocks, bushings, etc?
The bits that tend to wear out quickly on the Elise suspension-wise (and must probably be considered 'consumables') are:

- Balljoints (esp. lower balljoints)
- Track rod ends
- Wheel bearings (S1 at least.. S2 not much data yet)
- Wishbone/A-arm bushings

How hard the car is used has quite an impact on the rate these wear out (except perhaps the wishbone bushes)

Some people go through balljoints every 15 to 30k miles as they are put under much more stress then they would encounter in a 'normal' (McPherson style) suspension. They now also have to cope with a vertical load instead of only a side-to-side load.

Track rod ends (esp. at the back) can get 'loose' after some time and this is accelerated when using 'sticky' tires like (semi)slicks.

It's very advisable to replace the factory rear track rods (which have normal balljoints on the ends) to motorsport track rods using spherical bearings on the end and special brackets to attach them in 'double shear' (both top and bottom allow load bearing) to the hub carrier and the subframe.

The factory track rod balljoint bolts are known to bend/break with hard use, so keep an eye on them.

Wheel bearings can be troublesome if people don't run the proper offset wheels.

Wishbone bushes suffer more from rubber degradation over time. These can be replaced by solid bushes made from stuff like nylatron.

This doesn't even impact ride quality much (does 'sharpen' it up though..) as they are only used as pivot/hinge points for the wishbones and are not used under compression of flex like seen in other suspension setups. So the 'hardness' of the bushes plays little effect in the ride quality. These will of course allow more noise/vibration from the suspension to reach the chassis.. that is noticable, but for most people still quite acceptable.

Shock absorbers are usually OK for quite some time, especially since Lotus went to Bilstein from the S2 onwards, but as this is a sports car you'd probably replace them way before they start to show physical problems like leaks as their performance will already have degraded and you'll feel that when driving the car for a while or when getting into a 'fresh' one.

Aftermarket shocks usually need a re-build every 2 years, so I presonally put the 'lifespan' of the standard shocks at the same level.

Bye, Arno.
 

·
Registered
Joined
·
648 Posts
arno,

have you replace the track rods at the rear? have you had problems with them and R compound tyres? I know this was a problem with S1s but not seen any issues with S2s. If you have replaced them or know of someone who has, where do you get them from? they are different to the S1s yes?
 

·
Registered
Joined
·
148 Posts
Interesting post!

When I used to do a lot of track days, every once in a while someone would show up with a slammed, highly modified import. Usually sporting 19+" wheels and ultra low suspension. Some would leave the track experience pissed off and not understanding why they get beat by old 1970's cars with 14" wheels. Others would listen to people and have a greater appreciation for proper setup and suspension. Those guys would usually come back with a little different setup!

Slammed is not always the answer. The whole idea of proper suspension is always a compromise of several factors. I won't repeat what was said above because its pretty damn thorough. Suffice it to say that if ultra low ride height and stiff springs was the answer, Slam your car to the ground, replace your shocks with a steel bar and see how it handles! The whole point of suspension is to keep the tire firmly planted on the ground. Suspension needs room to work hence ride height!

Personally, I like sidewall flex. I run 50 or 60 aspect tires on my race car. I also run full soft on my rear shocks. Oh yeah... on 14" wheels! I seem to get more bite out of a tire with some sidewall. Its amazing that people equate looks to performance.

Jose Soriano
 

·
Registered
Joined
·
637 Posts
ex-M3 said:
Tire and wheel sizes have been increasing for a couple of related issues. The wheel diameter has been increasing to allow larger brakes. This is a result of most "sports cars" weighing about 3,000 lbs. The Elise is not hampered by this penalty. The engineers for the S1 Elise wanted small wheels, but they were increased by 1" by the marketing department, and this is Lotus! You can imagine how wheel/tires are decided by the large manufacturers :mad:
Actually that was on the S1 (according to the Jeremy Walton book).

The engineers who did the chassis calculated that 14" front and rear wheels was the best engineering setup for the elise. Of course, styling has a lot to do with selling the car so they ended up putting 15" front and 16" rear wheels on. You guys are getting 16" front and 17" rear wheels. Notice the trend? Lotus are crazy about unsprung weight (one of the reasons they mount shocks upside down compared to everyone else). Marketing must be having a field day.

What I'd like is an S1 with a toyota engine and some work paid to keeping the thing light, eg polycarb windows, light wheels and so on. The main X factor the elise has is it's layout/weight. I'd hate to see that diluted over time but it's what has been happening.

Craigy

ps. Bling Bling chromed wheels. With spinners. Horrific.
 
1 - 20 of 25 Posts
Top