Tire Selection Is Where The Rubber Meets The Road!

Changing tires is something we must contemplate at some point.  Sportscars generally require this sooner than later.  Care must be taken or you can ruin the beautiful handling of your Lotus.  Tire selection is a very complex issue and not one that can be fully addressed in a short article.  Since your tire is what holds your car to the road, I thought it would be a good issue to discuss.

Lotus ride & handling engineers work closely with tire manufacturers to develop the tires found on their cars.  The Elise with a Sport pack came with Yokohama AO48 tires.  They are a special tire compound (LTS) developed by Yokohoma for Lotus.  Car manufacturers buy thousands of tires so tire manufacturers are often willing to create special tires for the OEs.  This allows those crafty OE engineers to ‘fine-tune’ their cars. 

The Elise came with two different suspensions: Standard and Sport that demanded different tires.  The Standard (there is no such thing as the ‘Touring’ suspension) suspension featured narrower front wheels with 175 front and 225 rear Yokohama AD07 tires.  The Sport packaged cars came with more aggressively tuned dampers with wider(front) forged wheels and stickier Yoko A048 r-compound tires in a 195 front and 225 rear.  These sizes and tires work as intended and few alternatives exist that deliver the same overall performance. So does this mean we should only use factory approved tires?  No, you can veer from their spec tire but you need to go in with your eyes wide open. 

What are the key areas that must be considered during tire selection?  Here is an abbreviated list - in no particular order:

1.      Size

2.      Compound

3.      Brand/model

4.      Vehicle weight

5.      Availability

 

Tire size is something that many people immediately begin experimenting with.  Often times, a tire is available in a multitude of sizes and car owners believe they might try wider tires to create more grip.  This can work, but many times, it may deliver the opposite effect as the tires don’t get into their operating temperature range due to the low weight of our cars. 

Lotus are light weight, which narrows (pun intended) our tire options.  Lighter cars demand softer compound tires.  What works well on a 3300lb Corvette/BMW/Porsche will be hard as a rock on a Lotus.  You may have noticed that our street tires are considered track tires by those heavy weight sportscars.  So your favorite aggressive street tire on your last GT3 may not work on your new Exige.  Of course, if you can go with even softer tires, wider widths are possible but the only tires that are softer tend to be non-street friendly tires.

OE tire size is usually dictated by weight distribution of a car.  Since modern Lotus are mid-engine cars, they have more weight in the rear which means wider tires are needed in the rear and narrower in the front.  On a car, like a BMW or Miata, with 50/50 weight distribution, you will often see owners running the same tires front to rear.  This will not work on our Lotus with 40/60 weight balance.   Note the Elise/Exige have 195/225 tire size split or a 175/225.

grripp.jpg

The rabbit hole of tire knowledge sucks you in deeper when you start to consider tire temperatures.  Tires are designed to operate in a certain temperature range.  You have heard about accidents that occurred due to ‘cold’ tires.  Tires gain temperature due to friction as they are driven.  It is critical that they get within their operating range to work effectively.  If they are outside of this range, poor results can be expected.  Wider tires may not be able to achieve the temps required if all other variables, like car weight, remain the same.  The net result is a tire that grips even less than a narrower tire. 

How about going with smaller rims and larger side wall tires?  I introduced this idea ten years ago in an attempt to improve our compliance and grip on rough canyon roads.  Our Lotus friends in Japan showed me the way.  The 15”/16” rims work nicely in this environment but introduces several other issues that we can discuss in another article.  Most of you want to stick with stock sized rims and need tires that are suitable. 

Tire Grip Graph.jpg

The graph above shows the lateral force curves generated by two different tires.  Both tires show a linear response initially and as the slip angle increases the lateral forces generated drop off.  The arrows define an area that is at the edge of grip or control for Tire A.  This is actually where the best race drivers operate their cars whilst dazzling us with their superior car control.  This curve is different for each tire size, compound, etc.  When you change the tire in your car, you need to be aware that you will be changing where your car will begin to lose grip.  So if your new tire can not generate enough heat, the curve will certainly be worse than stock.  If you choose a harder compound to get more life, the same result can ensue.  This is especially true with the front tires on a modern Lotus since they support less weight and are the ones that do all the turning!

So what’s a poor Lotus owner, with worn out tires supposed to do?  Here are my suggestions based on some assumptions that you:

1.      Enjoy driving your car aggressively and occasionally at the limit

2.      Want tires that fit within your wheel wells

3.      Are not a part of ‘Stance Nation’

4.      Have stock sized rims

5.      Drive on the street

My recommendations:

1.      Buy stock sizes

2.      Buy factory recommended brands

3.      Never split tire types – front to rear

4.      Consider competitive brands in stock sizes and compounds

  • I am a big fan of the new Toyo R888R and the older R888 in 195/225 sizes

5.      Call your local or not local Lotus Specialist and pick their brain for advice.

6.      Get your tires mounted/balanced correctly or you will really hate those tires!